1
00:00:00,050 --> 00:00:01,770
The following
content is provided

2
00:00:01,770 --> 00:00:04,000
under a Creative
Commons license.

3
00:00:04,000 --> 00:00:06,860
Your support will help MIT
OpenCourseWare continue

4
00:00:06,860 --> 00:00:10,720
to offer high quality
educational resources for free.

5
00:00:10,720 --> 00:00:13,320
To make a donation or
view additional materials

6
00:00:13,320 --> 00:00:17,200
from 100s of MIT courses,
visit MIT OpenCourseWare

7
00:00:17,200 --> 00:00:17,825
at ocw.mit.edu.

8
00:00:26,196 --> 00:00:29,855
PROFESSOR: Welcome
to a new teaching,

9
00:00:29,855 --> 00:00:32,872
new lecturing of 8.421.

10
00:00:32,872 --> 00:00:38,680
8.421 is an advanced course in
atomic physics-- graduate level

11
00:00:38,680 --> 00:00:40,430
course.

12
00:00:40,430 --> 00:00:46,230
8.421 is part of a new semester
sequence in atomic physics.

13
00:00:50,100 --> 00:00:54,550
Actually, 8.421 is taken
first in this sequence

14
00:00:54,550 --> 00:00:58,960
because we start with more basic
things about light and atoms.

15
00:00:58,960 --> 00:01:01,280
But the cost is
designed in such a way

16
00:01:01,280 --> 00:01:06,480
that you can start
with 8.422 or 8.421.

17
00:01:06,480 --> 00:01:10,225
So just to get an idea, who
has already taken 8.422?

18
00:01:10,225 --> 00:01:12,670
Should be about half the class.

19
00:01:12,670 --> 00:01:13,790
OK, great.

20
00:01:13,790 --> 00:01:17,700
So yes, you're not
repeating anything.

21
00:01:17,700 --> 00:01:22,570
And maybe for those of you
it's a little bit anticlimactic

22
00:01:22,570 --> 00:01:23,990
because you had all the fun.

23
00:01:23,990 --> 00:01:26,260
You saw all the
great things which

24
00:01:26,260 --> 00:01:28,510
can be done with
two level systems.

25
00:01:28,510 --> 00:01:30,415
And now in this
course we sit down

26
00:01:30,415 --> 00:01:33,920
and I explain to you what
are those two levels.

27
00:01:33,920 --> 00:01:36,170
What happens to those two
levels in magnetic field

28
00:01:36,170 --> 00:01:37,350
and electric fields?

29
00:01:37,350 --> 00:01:40,540
How are what they modified by
the lens shift and all of that?

30
00:01:40,540 --> 00:01:42,790
But you see how the two
things are connected.

31
00:01:45,360 --> 00:01:48,940
I talk about some course
formalities in a few moments.

32
00:01:48,940 --> 00:01:56,070
But let me first point
out that you're interested

33
00:01:56,070 --> 00:02:00,240
or you're doing research in
atomic physics at a really

34
00:02:00,240 --> 00:02:02,860
exciting time.

35
00:02:02,860 --> 00:02:08,060
AMO science is booming
and is rapidly advancing.

36
00:02:15,440 --> 00:02:21,430
And a lot of it is really
do to, well, of course,

37
00:02:21,430 --> 00:02:24,260
new insight, new ideas,
new breakthrough,

38
00:02:24,260 --> 00:02:27,420
but also combined
with technology.

39
00:02:27,420 --> 00:02:31,235
We have seen over the
last couple of decades

40
00:02:31,235 --> 00:02:34,500
a major development
in light sources.

41
00:02:38,858 --> 00:02:43,510
If I remember what lasers
I have used in my PH.D.

42
00:02:43,510 --> 00:02:47,700
And what lasers you were using,
well, there's a big difference.

43
00:02:47,700 --> 00:02:50,940
Big difference in performance
but also big difference

44
00:02:50,940 --> 00:02:53,360
in reliability and convenience.

45
00:02:53,360 --> 00:02:59,060
But just a few systems which
didn't exist a few decades ago.

46
00:02:59,060 --> 00:03:03,080
The Ti:sapphire laser, which
has really become the workhorse

47
00:03:03,080 --> 00:03:06,710
of generating lots and lots of
power in the infrared domain.

48
00:03:06,710 --> 00:03:08,090
But then it can
also be frequency

49
00:03:08,090 --> 00:03:09,722
doubled to the visible.

50
00:03:13,410 --> 00:03:15,760
When I was a [INAUDIBLE]
in the early '90s,

51
00:03:15,760 --> 00:03:20,920
people just starting to use
diode lasers in atomic physics.

52
00:03:20,920 --> 00:03:24,880
Here you are 20 years later.

53
00:03:24,880 --> 00:03:27,680
We see you much more
solid state lasers.

54
00:03:27,680 --> 00:03:31,610
And I would say even in
the last 5 to 10 years

55
00:03:31,610 --> 00:03:34,330
there has been another,
well, revolution

56
00:03:34,330 --> 00:03:38,160
is too strong a word but
another major advance by having

57
00:03:38,160 --> 00:03:44,590
extremely high power fiber
lasers, which are covering

58
00:03:44,590 --> 00:03:47,460
more and more of
the spectral range.

59
00:03:51,200 --> 00:03:59,710
So those advanced lasers
empower in the spectral range.

60
00:03:59,710 --> 00:04:08,480
We have seen major advances
in shaping short pulses.

61
00:04:08,480 --> 00:04:11,550
I remember when I was a student
how femtosecond lasers were

62
00:04:11,550 --> 00:04:14,450
that the latest--
well, they're required.

63
00:04:14,450 --> 00:04:18,700
The [INAUDIBLE] and femtosecond
pulses could only be produced

64
00:04:18,700 --> 00:04:21,990
in a few laboratories in
the world with a discovery

65
00:04:21,990 --> 00:04:25,940
of the Ti:sapphire laser
in Kerr lens mode locking.

66
00:04:25,940 --> 00:04:29,930
This has now become standard and
is even commercially available.

67
00:04:29,930 --> 00:04:33,650
But researchers have pushed
on attosecond policies

68
00:04:33,650 --> 00:04:37,480
are now the frontier
of the field.

69
00:04:37,480 --> 00:04:47,970
Well, if you have very short
pulses that also opens up

70
00:04:47,970 --> 00:04:51,120
the possibility to go
to very high intensity,

71
00:04:51,120 --> 00:04:55,060
you don't need so
much energy per pulse.

72
00:04:55,060 --> 00:04:57,170
You just, if the
pulse is very short,

73
00:04:57,170 --> 00:05:02,620
you reach a very high intensity,
which is the range of terawatt.

74
00:05:02,620 --> 00:05:05,850
And it is now pretty standard
if you focus the short pulse

75
00:05:05,850 --> 00:05:06,515
laser.

76
00:05:06,515 --> 00:05:08,960
In the focus of the
short pulse laser,

77
00:05:08,960 --> 00:05:12,140
you create electric
field strengths,

78
00:05:12,140 --> 00:05:15,780
which are stronger than the
electric field in an atom.

79
00:05:15,780 --> 00:05:18,790
So therefore, the
dominant electric field

80
00:05:18,790 --> 00:05:20,110
is the one of the laser.

81
00:05:20,110 --> 00:05:23,660
And then you may add
[INAUDIBLE] on whatever scheme

82
00:05:23,660 --> 00:05:30,040
the field between the electons
or the electron and the proton.

83
00:05:30,040 --> 00:05:35,050
So this is the
generational flight.

84
00:05:35,050 --> 00:05:39,540
But light also
wants to be control.

85
00:05:39,540 --> 00:05:42,625
And this is done
by using cavities.

86
00:05:42,625 --> 00:05:44,820
A single photon
would just fly by.

87
00:05:44,820 --> 00:05:48,300
But If you want a photo to
really intimately interact

88
00:05:48,300 --> 00:05:50,040
with a atom-- maybe
get it absorbed,

89
00:05:50,040 --> 00:05:52,100
immediate absorbed, immediate.

90
00:05:52,100 --> 00:05:55,690
If you really want to have the
photon as a [INAUDIBLE] state

91
00:05:55,690 --> 00:05:57,750
and not just as
something which flies by,

92
00:05:57,750 --> 00:06:01,770
you need cavities,
resonators, and we have really

93
00:06:01,770 --> 00:06:05,350
seen peak advances in
superconducting cavities

94
00:06:05,350 --> 00:06:09,320
as super codings in
the optical regime.

95
00:06:09,320 --> 00:06:19,852
And cavity QED in the optical
and the microwave domain

96
00:06:19,852 --> 00:06:23,000
have led to major
advances in the series

97
00:06:23,000 --> 00:06:27,100
of spectacular
experiment performed now

98
00:06:27,100 --> 00:06:28,830
with single photons.

99
00:06:28,830 --> 00:06:32,200
So the single
photon is no longer

100
00:06:32,200 --> 00:06:37,395
an idealized concept for
the description of life atom

101
00:06:37,395 --> 00:06:38,220
interaction.

102
00:06:38,220 --> 00:06:41,070
It has been a reality.

103
00:06:41,070 --> 00:06:44,770
And single photon control
has advances quickly.

104
00:06:48,060 --> 00:06:54,180
Well you can make major
advances in terms of light.

105
00:06:54,180 --> 00:06:56,320
Find new lasers, shorter
policies, higher intensity

106
00:06:56,320 --> 00:06:58,260
policies, and things like this.

107
00:06:58,260 --> 00:07:01,450
But the other part of atomic
physics-- one is light,

108
00:07:01,450 --> 00:07:05,960
the other one are the atoms-- we
haven't invented new atoms yet.

109
00:07:05,960 --> 00:07:09,320
We still got stuck with
the same periodic table.

110
00:07:09,320 --> 00:07:19,060
But we have modified the way
how we can prepare and control

111
00:07:19,060 --> 00:07:22,140
atomic samples.

112
00:07:22,140 --> 00:07:25,310
A big revolution
in the '90s or '80s

113
00:07:25,310 --> 00:07:30,245
has been the cooling of
atoms that now microkelvin,

114
00:07:30,245 --> 00:07:33,550
nanokelvin, and with
evaporative cooling,

115
00:07:33,550 --> 00:07:38,620
even picokelvin regime
had become possible.

116
00:07:38,620 --> 00:07:44,830
In terms of atomic
samplers, this

117
00:07:44,830 --> 00:07:50,160
was an evolution which
took place during my time

118
00:07:50,160 --> 00:07:51,760
as a researcher.

119
00:07:51,760 --> 00:07:55,296
Atoms always mean you're the
sample of individual atoms.

120
00:07:55,296 --> 00:07:56,670
Sometimes you
started interaction

121
00:07:56,670 --> 00:07:58,680
when two atoms are colliding.

122
00:07:58,680 --> 00:08:00,790
But atomic physics
was really the physics

123
00:08:00,790 --> 00:08:03,150
of senior particles
or two particles

124
00:08:03,150 --> 00:08:06,770
interacting, colliding,
or forming a molecule.

125
00:08:06,770 --> 00:08:12,170
But the moment we reach for
cooling nanokelvin temperature,

126
00:08:12,170 --> 00:08:17,170
atoms move so slowly that
they feel out each other.

127
00:08:17,170 --> 00:08:19,200
And that means suddenly
we have a system

128
00:08:19,200 --> 00:08:22,170
to do many-body physics.

129
00:08:22,170 --> 00:08:31,930
So the event of quantum
degenerate gases

130
00:08:31,930 --> 00:08:36,535
and many developments after that
with optical lattices and lots

131
00:08:36,535 --> 00:08:39,600
of bells and
whistles really meant

132
00:08:39,600 --> 00:08:44,090
that-- and this dramatic--
that atomic physics

133
00:08:44,090 --> 00:08:47,220
has made the transition
from single and two particle

134
00:08:47,220 --> 00:08:49,633
physics to many body physics.

135
00:08:54,040 --> 00:08:56,670
And for several research
groups in this end

136
00:08:56,670 --> 00:08:58,480
of what are called
atoms, this is,

137
00:08:58,480 --> 00:09:01,130
of course, an
important point here.

138
00:09:05,280 --> 00:09:12,170
Well, somewhat related to
that but more generally,

139
00:09:12,170 --> 00:09:17,270
the precision and
preparation and manipulation

140
00:09:17,270 --> 00:09:24,350
which atomic physics has
reached with quantum systems

141
00:09:24,350 --> 00:09:27,920
puts now atomic physics
in a leading position

142
00:09:27,920 --> 00:09:33,820
at the forefront of exploring
new aspects of Hilbert space.

143
00:09:33,820 --> 00:09:36,520
One can say that
Hilbert space is vast.

144
00:09:36,520 --> 00:09:39,630
But what is realized,
this simple quantum system

145
00:09:39,630 --> 00:09:42,420
is only a tiny little
corner of Hilbert space.

146
00:09:42,420 --> 00:09:44,670
And atomic physics,
if I want to define it

147
00:09:44,670 --> 00:09:46,780
in the most abstract
way, the goal

148
00:09:46,780 --> 00:09:49,370
is to master Hilbert space.

149
00:09:49,370 --> 00:09:54,570
And that means we
want to harness

150
00:09:54,570 --> 00:09:57,980
parts of Hilbert space,
which are characterized

151
00:09:57,980 --> 00:10:01,010
by quantum entanglement.

152
00:10:01,010 --> 00:10:03,320
Maybe single forms
between two particles

153
00:10:03,320 --> 00:10:06,460
but also between many particles.

154
00:10:06,460 --> 00:10:11,220
And of course, this is it
to a whole new frontier

155
00:10:11,220 --> 00:10:14,135
in quantum computation and
quantum information processing.

156
00:10:21,070 --> 00:10:28,270
So this sort of should show
you how technology, new ideas,

157
00:10:28,270 --> 00:10:31,510
control, and manipulation
is suddenly opening up

158
00:10:31,510 --> 00:10:34,070
whole new scientific directions.

159
00:10:34,070 --> 00:10:38,750
And just to add something
more recent to the list,

160
00:10:38,750 --> 00:10:41,080
we have now a major
research direction

161
00:10:41,080 --> 00:10:46,440
in AMO physics dealing
with cold molecules.

162
00:10:46,440 --> 00:10:52,290
And they're even prospects
of rewritting chapters

163
00:10:52,290 --> 00:10:54,010
of chemistry.

164
00:10:54,010 --> 00:10:56,540
What happens when
you do chemistry

165
00:10:56,540 --> 00:11:00,640
but not in the ordinary way
but at nanokelvin temperature?

166
00:11:00,640 --> 00:11:03,310
Or what happens when
you do chemistry

167
00:11:03,310 --> 00:11:07,140
where you have coherent
control in such a way

168
00:11:07,140 --> 00:11:13,280
that maybe the molecules
before and after the reaction

169
00:11:13,280 --> 00:11:17,620
are in a cool and
superposition state.

170
00:11:17,620 --> 00:11:22,020
So in that sense, the
conclusion of that introduction

171
00:11:22,020 --> 00:11:27,480
is atomic physics
has been successful

172
00:11:27,480 --> 00:11:31,605
because it continues
to redefine itself.

173
00:11:38,940 --> 00:11:41,880
And to prove the case, I
can say when I predict,

174
00:11:41,880 --> 00:11:44,461
when I try to
predict-- I didn't even

175
00:11:44,461 --> 00:11:45,960
try because I know
it wouldn't work.

176
00:11:45,960 --> 00:11:47,800
But if I tried to
predict 10 years ago what

177
00:11:47,800 --> 00:11:51,730
would be the hot topics of
today, I would have failed.

178
00:11:51,730 --> 00:11:57,950
What happens is just
breakthroughs and discoveries.

179
00:11:57,950 --> 00:12:00,750
And usually they happen in areas
where they are not predicted.

180
00:12:08,160 --> 00:12:12,660
As another angle,
atomic physics has

181
00:12:12,660 --> 00:12:17,880
seen more than its usual
share of Nobel prizes

182
00:12:17,880 --> 00:12:20,290
in the last two decades.

183
00:12:24,080 --> 00:12:26,440
Maybe the price in
1989 for ion trapping

184
00:12:26,440 --> 00:12:28,792
in Ramsey spectroscopy.

185
00:12:28,792 --> 00:12:32,420
Ramsey spectroscopy is used for
the generation of atomic clock.

186
00:12:32,420 --> 00:12:34,920
Iron trapping is a
basic building block.

187
00:12:34,920 --> 00:12:37,380
This was sort of givenof
some of the technology.

188
00:12:37,380 --> 00:12:41,090
But this was the only prize in
the long list I'm writing down

189
00:12:41,090 --> 00:12:43,990
now which was given for
something which was maybe

190
00:12:43,990 --> 00:12:45,500
invented a few decades ago.

191
00:12:45,500 --> 00:12:48,990
A lot of Nobel prizes are given
decades after the discovery.

192
00:12:48,990 --> 00:12:51,030
But all the more recent
Nobel Prize and this

193
00:12:51,030 --> 00:12:54,130
speaks for the
vitality of the field,

194
00:12:54,130 --> 00:12:57,600
we awarded for
developments which had just

195
00:12:57,600 --> 00:13:01,270
happened in the decade
before the prize.

196
00:13:01,270 --> 00:13:08,790
Whether it was laser cooling
just invented in the '80s.

197
00:13:08,790 --> 00:13:11,970
Whether it was Bose
Einstein condensation

198
00:13:11,970 --> 00:13:18,030
observed for six years
before the 2005 prize

199
00:13:18,030 --> 00:13:22,440
on precision spectroscopy with
lasers and frequency comb.

200
00:13:22,440 --> 00:13:26,460
This was also a development that
happened just a few years ago.

201
00:13:26,460 --> 00:13:31,790
And the most recent recognition
for Serge Haroche and Dave

202
00:13:31,790 --> 00:13:34,640
Wineland is about
the manipulation

203
00:13:34,640 --> 00:13:36,490
of individual quantum system.

204
00:13:36,490 --> 00:13:38,890
And this is where the
highlights of this

205
00:13:38,890 --> 00:13:46,320
were accomplished just
a few years, lets say,

206
00:13:46,320 --> 00:13:47,810
over the last five or 10 years.

207
00:14:10,571 --> 00:14:11,070
OK.

208
00:14:16,330 --> 00:14:19,120
Just sort of to make
a general case here,

209
00:14:19,120 --> 00:14:24,020
I continue to be amazed
how interesting ad

210
00:14:24,020 --> 00:14:29,470
rich the physics of
simple systems are.

211
00:14:29,470 --> 00:14:36,330
I actually expect that there
maybe even two Nobel Prizes

212
00:14:36,330 --> 00:14:40,390
in the near future
for, pretty much,

213
00:14:40,390 --> 00:14:42,340
understanding the
Schrodinger equation.

214
00:14:42,340 --> 00:14:46,520
You would say this has been
done in the old days of quantum

215
00:14:46,520 --> 00:14:48,280
mechanics in the '20s and '30s.

216
00:14:48,280 --> 00:14:50,700
And of course, lots of
people have been recognized.

217
00:14:50,700 --> 00:14:56,030
But there are two aspects
of the Schrodinger equation,

218
00:14:56,030 --> 00:14:58,390
which hadn't been
understood or which

219
00:14:58,390 --> 00:15:00,430
have been understood
only recently.

220
00:15:00,430 --> 00:15:02,850
One is the aspect of
entanglement and error

221
00:15:02,850 --> 00:15:04,300
correction.

222
00:15:04,300 --> 00:15:06,560
Nobody until 10 or
20 years-- nobody

223
00:15:06,560 --> 00:15:08,810
until [INAUDIBLE]
and collaborators

224
00:15:08,810 --> 00:15:10,790
introduced error
correction would

225
00:15:10,790 --> 00:15:14,190
have thought that the quantum
system can [INAUDIBLE] here,

226
00:15:14,190 --> 00:15:15,710
but you can
reestablish coherence

227
00:15:15,710 --> 00:15:19,230
by what is called quantum
error corrections.

228
00:15:19,230 --> 00:15:24,650
[INAUDIBLE] properties of the
simplest wording or equation

229
00:15:24,650 --> 00:15:26,330
for just a few--
well, [INAUDIBLE]

230
00:15:26,330 --> 00:15:30,030
it's for a few particles--
which we are not known

231
00:15:30,030 --> 00:15:33,420
or even the expert in the
field would have fled and said,

232
00:15:33,420 --> 00:15:35,150
no, this is not possible.

233
00:15:35,150 --> 00:15:39,130
And another aspect of actually
single particle quantum

234
00:15:39,130 --> 00:15:43,340
physics, which has been fully
appreciated only recently

235
00:15:43,340 --> 00:15:46,730
is the question of [INAUDIBLE]
phase and topological phase.

236
00:15:46,730 --> 00:15:49,500
All the [INAUDIBLE] in
quantum metaphysics,

237
00:15:49,500 --> 00:15:52,780
which is also spilling over
to atomic physics of quantum

238
00:15:52,780 --> 00:15:54,730
[INAUDIBLE]
topologically insulate

239
00:15:54,730 --> 00:15:59,730
as an [INAUDIBLE] means that
there are non-trivial phases--

240
00:15:59,730 --> 00:16:05,612
non-trivial symmetries in the
single particle Schrodinger

241
00:16:05,612 --> 00:16:07,070
equation.

242
00:16:07,070 --> 00:16:09,630
So it's just that
as a case in point

243
00:16:09,630 --> 00:16:12,300
that the single particle
Schrodinger equation a lot

244
00:16:12,300 --> 00:16:14,380
of people thought in
the '40s and '50s.

245
00:16:14,380 --> 00:16:14,880
That's it.

246
00:16:14,880 --> 00:16:16,800
There is nothing
else to do research.

247
00:16:16,800 --> 00:16:20,580
And now we when whole
new fields emerging

248
00:16:20,580 --> 00:16:25,610
exploiting new aspects of
the Schrodinger equation.

249
00:16:25,610 --> 00:16:27,640
Will there be something
else of the same caliber

250
00:16:27,640 --> 00:16:28,510
to be discovered?

251
00:16:31,340 --> 00:16:33,940
20 years ago, people
would've said no.

252
00:16:33,940 --> 00:16:37,287
And I just gave you two examples
of major new insight, which

253
00:16:37,287 --> 00:16:39,370
is has really changed our
understanding of quantum

254
00:16:39,370 --> 00:16:39,869
physics.

255
00:16:44,640 --> 00:16:48,930
A few years ago, I served
on a National Academy

256
00:16:48,930 --> 00:16:56,170
of Science committee trying to
do the impossible to predict

257
00:16:56,170 --> 00:16:58,660
the future of the field.

258
00:16:58,660 --> 00:17:00,575
But sometimes the National
Academy of Science

259
00:17:00,575 --> 00:17:05,450
is asked to give advice and try
to provide the best [INAUDIBLE]

260
00:17:05,450 --> 00:17:08,250
impossible but is exciting.

261
00:17:08,250 --> 00:17:11,130
Of course, we didn't
predict the future.

262
00:17:11,130 --> 00:17:14,910
But at least to the
extent possible,

263
00:17:14,910 --> 00:17:19,650
we summarized what are
the frontier areas where

264
00:17:19,650 --> 00:17:22,400
we see rapid
development and where

265
00:17:22,400 --> 00:17:27,310
it would be worth
investing further.

266
00:17:27,310 --> 00:17:31,260
And you will actually see that
a number of those frontier areas

267
00:17:31,260 --> 00:17:33,070
are where your research happens.

268
00:17:37,420 --> 00:17:42,370
One is the traditional area
of precision measurements.

269
00:17:42,370 --> 00:17:44,170
As long as atomic
physics exists,

270
00:17:44,170 --> 00:17:47,452
one of the specialty
of atomic physics is we

271
00:17:47,452 --> 00:17:50,200
can emphasize
measurements, atomic locks,

272
00:17:50,200 --> 00:17:53,430
and precision measurements of
fundamental concepts and all

273
00:17:53,430 --> 00:17:54,590
that.

274
00:17:54,590 --> 00:17:58,970
And that continues
until the present day.

275
00:17:58,970 --> 00:18:02,040
It was just two weeks ago
that there was a new nature

276
00:18:02,040 --> 00:18:06,640
paper on the really major
advance in atomic clocks.

277
00:18:06,640 --> 00:18:10,000
Strontium neutral atom clock
has reached the precision

278
00:18:10,000 --> 00:18:12,839
of 6 times 10 to the minus 18.

279
00:18:12,839 --> 00:18:13,380
It's amazing.

280
00:18:13,380 --> 00:18:15,010
We'll talk more about it.

281
00:18:15,010 --> 00:18:18,290
You really have to carefully
understand and measure

282
00:18:18,290 --> 00:18:21,830
small changes in the black-body
radiation because just

283
00:18:21,830 --> 00:18:24,844
the black-body radiation
creates frequency shifts, which

284
00:18:24,844 --> 00:18:26,385
would interfere with
their precision.

285
00:18:26,385 --> 00:18:29,280
An amazing accomplishment
for the field.

286
00:18:29,280 --> 00:18:33,100
So precision
measurements continue

287
00:18:33,100 --> 00:18:36,180
to be an important frontier.

288
00:18:36,180 --> 00:18:39,370
Of course, is there's always
the aspect of metrology,

289
00:18:39,370 --> 00:18:41,580
determine time frequency,
and other things

290
00:18:41,580 --> 00:18:43,500
with higher and higher accuracy.

291
00:18:43,500 --> 00:18:45,960
But there are also applications.

292
00:18:45,960 --> 00:18:50,560
Just one example is
making atomically.

293
00:18:50,560 --> 00:18:52,620
Atomic physics methods
can be now used

294
00:18:52,620 --> 00:18:55,075
if you open at home
in an environment you

295
00:18:55,075 --> 00:18:57,290
can measure the magnetic field.

296
00:18:57,290 --> 00:19:01,430
So people are now talking
by using atoms or artificial

297
00:19:01,430 --> 00:19:05,170
atoms in the form of AV senders
to measure the magnetic field,

298
00:19:05,170 --> 00:19:07,320
biological sounds, and all that.

299
00:19:07,320 --> 00:19:10,540
So measurement is
fundamental aspects

300
00:19:10,540 --> 00:19:12,430
but is also applied aspects.

301
00:19:15,352 --> 00:19:17,690
Well, other frontiers
are, of course,

302
00:19:17,690 --> 00:19:20,230
you can use support ultra cold.

303
00:19:23,000 --> 00:19:26,820
We've talked about
high intensity lasers.

304
00:19:26,820 --> 00:19:27,605
Ultra intense.

305
00:19:32,800 --> 00:19:35,270
Ultra short.

306
00:19:35,270 --> 00:19:38,280
Atomic physics is
more and more getting

307
00:19:38,280 --> 00:19:42,840
involved with nano materials.

308
00:19:42,840 --> 00:19:46,480
Materials with blue properties.

309
00:19:46,480 --> 00:19:51,190
Maybe materials with negative
index of the refrection,

310
00:19:51,190 --> 00:19:55,400
metamaterials or, in general
or plus [INAUDIBLE] materials.

311
00:19:55,400 --> 00:19:59,790
Nano materials can help
to shed light and explore

312
00:19:59,790 --> 00:20:03,560
new aspects of how light
interacts with matter.

313
00:20:03,560 --> 00:20:06,100
And of course,
the major frontier

314
00:20:06,100 --> 00:20:08,565
is the frontier of
quantum information.

315
00:20:14,640 --> 00:20:21,100
So given all this
excitement, you

316
00:20:21,100 --> 00:20:27,880
have many reasons to want
to learn more about it.

317
00:20:27,880 --> 00:20:32,974
And this course is definitely
a good starting point.

318
00:20:32,974 --> 00:20:34,390
Let me maybe tell
you a little bit

319
00:20:34,390 --> 00:20:39,370
what is the philosophy behind
the cost and what you will get.

320
00:20:39,370 --> 00:20:41,500
That means, of course,
at the same time

321
00:20:41,500 --> 00:20:44,650
what you will not get.

322
00:20:44,650 --> 00:20:50,100
This course is meant as an
systematic, basic introduction

323
00:20:50,100 --> 00:20:51,200
into AMO physics.

324
00:21:04,150 --> 00:21:06,780
It should really lead
the basic foundation

325
00:21:06,780 --> 00:21:10,630
that when you talk about
atoms to talk about light

326
00:21:10,630 --> 00:21:13,780
you are really an expert and you
can talk about it at the most

327
00:21:13,780 --> 00:21:15,190
profound level.

328
00:21:15,190 --> 00:21:18,250
So it's important here, and
this is the goal of this course,

329
00:21:18,250 --> 00:21:21,860
to provide enough knowledge
and enough foundation for that.

330
00:21:21,860 --> 00:21:24,240
So it's not a cause
where I just try

331
00:21:24,240 --> 00:21:25,740
to sample highlights
of the field

332
00:21:25,740 --> 00:21:28,770
and provide you with a
semi understanding of all

333
00:21:28,770 --> 00:21:30,330
this wonderful phenomena.

334
00:21:30,330 --> 00:21:34,570
I rather try to focus on
selective basic things

335
00:21:34,570 --> 00:21:39,220
but then also exciting things
but rather explain them

336
00:21:39,220 --> 00:21:42,240
thoroughly and teach you by
example than teaching you

337
00:21:42,240 --> 00:21:43,230
the big overview.

338
00:21:46,070 --> 00:21:48,830
The course, if I
want to characterize,

339
00:21:48,830 --> 00:21:57,480
is I would say it is
a conservative course.

340
00:21:57,480 --> 00:22:03,680
It's also, r in this
sense, traditional.

341
00:22:03,680 --> 00:22:06,860
One reason for that is MIT.

342
00:22:06,860 --> 00:22:09,170
The tradition we have at MIT.

343
00:22:09,170 --> 00:22:12,470
At MIT we have this
several generations

344
00:22:12,470 --> 00:22:17,270
of atomic physicists who
have shaped the field.

345
00:22:17,270 --> 00:22:22,710
And I learned atomic
physics as a postdoc

346
00:22:22,710 --> 00:22:25,160
from Dave Pritchard, who was
a graduate student of Dan

347
00:22:25,160 --> 00:22:26,700
Kleppner.

348
00:22:26,700 --> 00:22:29,130
Dan Kleppner was a graduate
student from Norman Ramsey.

349
00:22:31,890 --> 00:22:36,170
And Norman Ramsay was
a postdoc with I Rabi.

350
00:22:36,170 --> 00:22:39,560
And Rabi resonance
is this reciprocating

351
00:22:39,560 --> 00:22:40,790
of atomic physics.

352
00:22:40,790 --> 00:22:43,370
The resonance is sort
of what we will also

353
00:22:43,370 --> 00:22:46,400
focus on today and
in the first week.

354
00:22:46,400 --> 00:22:48,710
This is, sort of, the
most important concept

355
00:22:48,710 --> 00:22:50,920
in atomic physics
to really understand

356
00:22:50,920 --> 00:22:55,340
the nature of resonances
and all its implication.

357
00:22:55,340 --> 00:22:59,900
So I should say late in
my life-- I was already

358
00:22:59,900 --> 00:23:02,200
passed 30-- when I took
the first atomic physics

359
00:23:02,200 --> 00:23:04,315
class in my life, I took
it from Dave Pritchard.

360
00:23:04,315 --> 00:23:06,150
And I was really,
sort of, amazed

361
00:23:06,150 --> 00:23:11,070
about the course, which
had the traditional topics

362
00:23:11,070 --> 00:23:12,880
but provided a lot of insight.

363
00:23:12,880 --> 00:23:14,920
You can teach
traditional physics

364
00:23:14,920 --> 00:23:19,240
from the perspective of somebody
who does research today.

365
00:23:19,240 --> 00:23:21,890
So I want to give
you all connections.

366
00:23:21,890 --> 00:23:24,130
But at the same
time, I like a lot

367
00:23:24,130 --> 00:23:26,200
about the traditional approach.

368
00:23:26,200 --> 00:23:28,950
And some of it can be traced
back to Norman Ramsey.

369
00:23:31,490 --> 00:23:33,770
So eventually, over
the last years,

370
00:23:33,770 --> 00:23:37,910
I was the main person who has
shaped that on atomic physics

371
00:23:37,910 --> 00:23:42,360
course when I expanded it from
one semester to two semesters.

372
00:23:42,360 --> 00:23:45,470
But when I created
a lot of new topics,

373
00:23:45,470 --> 00:23:49,110
I always looked through Dan's
and Dave's notes and made

374
00:23:49,110 --> 00:23:54,090
sure the best of what they
taught, the best ideas they put

375
00:23:54,090 --> 00:23:57,670
the course, they still
survive until the present day.

376
00:23:57,670 --> 00:24:00,275
So this course is a
development and continuation

377
00:24:00,275 --> 00:24:03,260
of a longstanding tradition.

378
00:24:03,260 --> 00:24:05,760
I should say I
have been immensely

379
00:24:05,760 --> 00:24:09,010
enjoyed to co-teach the
course on a couple of occasion

380
00:24:09,010 --> 00:24:11,500
with Vladan Vuletic
and Ike Chuang.

381
00:24:11,500 --> 00:24:13,600
And Ike has made
major contribution

382
00:24:13,600 --> 00:24:16,640
to the second part of
the course and Vladan

383
00:24:16,640 --> 00:24:19,580
especially to what
we will be discussing

384
00:24:19,580 --> 00:24:23,150
in the next few weeks.

385
00:24:23,150 --> 00:24:33,070
So what I think is unusual-- you
won't find it in many textbooks

386
00:24:33,070 --> 00:24:39,120
is that we start
out by discussing

387
00:24:39,120 --> 00:24:43,570
the phenomenon of resonance
of the harmonic oscillator.

388
00:24:43,570 --> 00:24:49,080
And we will emphasize for
a while the classical part

389
00:24:49,080 --> 00:24:54,375
but then also, of course, go to
the quantum mechanical aspects

390
00:24:54,375 --> 00:24:55,870
of resonance.

391
00:24:55,870 --> 00:25:00,850
Now I have to say this balance
between classical and quantum

392
00:25:00,850 --> 00:25:04,130
mechanics is something
I will emphasize

393
00:25:04,130 --> 00:25:06,220
again and again in the course.

394
00:25:06,220 --> 00:25:10,350
I can guarantee you in this
course I will sometimes ask you

395
00:25:10,350 --> 00:25:14,330
interesting question, which
challenge your intuition.

396
00:25:14,330 --> 00:25:17,950
And you will most
likely recognize

397
00:25:17,950 --> 00:25:23,590
that often when your intuition
goes completely wrong

398
00:25:23,590 --> 00:25:26,680
it happens because
you believe too much

399
00:25:26,680 --> 00:25:30,250
or you over-interpret one
aspect of quantum physics.

400
00:25:30,250 --> 00:25:33,520
If I then tell you, but wait a
moment, now think classically.

401
00:25:33,520 --> 00:25:35,530
Push the classical
concept further.

402
00:25:35,530 --> 00:25:39,580
Regard the electron and the
atom as an harmonic oscillator.

403
00:25:39,580 --> 00:25:43,230
Regard light scattering
as the effect

404
00:25:43,230 --> 00:25:45,810
not of a quantum mechanical
atom but of a driven harmonic

405
00:25:45,810 --> 00:25:46,730
oscillator.

406
00:25:46,730 --> 00:25:50,610
Suddenly, a lot of things which
come out of quantum mechanics

407
00:25:50,610 --> 00:25:52,590
make much more sense.

408
00:25:52,590 --> 00:25:56,750
So I've often seen when I had
a conflict in my understanding.

409
00:25:56,750 --> 00:26:01,520
And it's a semi-classical and
quantum mechanical explanation,

410
00:26:01,520 --> 00:26:06,560
I've learned to trust much more
the semi-classical explanation.

411
00:26:06,560 --> 00:26:09,930
So that's why I feel it's
important to understand

412
00:26:09,930 --> 00:26:11,700
the classical aspects.

413
00:26:11,700 --> 00:26:13,770
And usually I would
also say understand

414
00:26:13,770 --> 00:26:18,760
the means to really
understand it's limits.

415
00:26:18,760 --> 00:26:22,300
And often I feel you can
understand the phenomenon only

416
00:26:22,300 --> 00:26:25,400
when you have a quantum
aspect, a classical aspect,

417
00:26:25,400 --> 00:26:29,450
and we know exactly where they
overlap and where they differ.

418
00:26:29,450 --> 00:26:33,910
So to see even quantum
mechanical objects occasionally

419
00:26:33,910 --> 00:26:38,810
from the classical perspective
provides additional insight.

420
00:26:38,810 --> 00:26:41,940
So therefore, I would
emphasize classical aspects.

421
00:26:41,940 --> 00:26:44,375
And for instance, it
may come for many of who

422
00:26:44,375 --> 00:26:47,840
as a surprise and you
will see that next week

423
00:26:47,840 --> 00:26:53,901
that some aspects like the
generalized Rabi frequency,

424
00:26:53,901 --> 00:26:56,150
which you all or many of you
have seen for a two level

425
00:26:56,150 --> 00:26:58,330
system.

426
00:26:58,330 --> 00:27:01,590
We find it in
classical resonance.

427
00:27:01,590 --> 00:27:06,970
Just the classic equation
of motion of a gyroscope

428
00:27:06,970 --> 00:27:09,150
has a generalized
Rabi frequency.

429
00:27:09,150 --> 00:27:11,960
And I do feel that
it is absolutely

430
00:27:11,960 --> 00:27:15,200
important for the understanding
of concepts that you know

431
00:27:15,200 --> 00:27:16,696
where do the concepts emerge?

432
00:27:16,696 --> 00:27:17,320
Where are they?

433
00:27:17,320 --> 00:27:21,610
Are they already there in
classical physics and survive

434
00:27:21,610 --> 00:27:23,100
in quantum physics?

435
00:27:23,100 --> 00:27:28,450
Or is it something new,
which is genuinely quantum.

436
00:27:28,450 --> 00:27:31,900
So yes, I will teach a little
bit more classical physics

437
00:27:31,900 --> 00:27:33,620
than in the standard
[INAUDIBLE] course.

438
00:27:33,620 --> 00:27:39,310
But because I've seen within
my own research experience

439
00:27:39,310 --> 00:27:42,680
that it's healthy to shape
the intuition for the fuller

440
00:27:42,680 --> 00:27:45,716
understanding of the
systems we're dealing with.

441
00:27:49,330 --> 00:27:55,300
So residence is an
overarching theme here.

442
00:27:55,300 --> 00:27:59,580
But then we have to
introduce our main players.

443
00:27:59,580 --> 00:28:01,860
The atoms come to stage.

444
00:28:01,860 --> 00:28:09,480
And we want to understand
the electronic structure,

445
00:28:09,480 --> 00:28:11,980
the fine structure, the
hyperfine structure,

446
00:28:11,980 --> 00:28:14,220
you're going to
understand what happens in

447
00:28:14,220 --> 00:28:18,210
magnetic, electric, and
electromagnetic light fields.

448
00:28:22,380 --> 00:28:26,090
We want to understand
in a deep way

449
00:28:26,090 --> 00:28:29,013
how do atoms interact
with radiation.

450
00:28:33,520 --> 00:28:34,779
This also leads us.

451
00:28:34,779 --> 00:28:35,820
There's a big difference.

452
00:28:35,820 --> 00:28:38,403
You would say, well, what's the
difference when atoms interact

453
00:28:38,403 --> 00:28:41,080
with microwave and atoms
interact with light.

454
00:28:41,080 --> 00:28:45,640
Well light or at high
frequency spontaneous emission

455
00:28:45,640 --> 00:28:46,660
becomes important.

456
00:28:46,660 --> 00:28:49,020
And then you have an
open quantum system.

457
00:28:49,020 --> 00:28:51,460
You have an [INAUDIBLE],
which couples automatically

458
00:28:51,460 --> 00:28:52,920
to many, many states.

459
00:28:52,920 --> 00:28:56,740
So that's why radiation
is different from just

460
00:28:56,740 --> 00:29:00,140
electric and magnetic fields
because of the presence of all

461
00:29:00,140 --> 00:29:03,590
the vacuum modes, and
we'll talk a lot about it.

462
00:29:08,390 --> 00:29:11,210
There's one special aspect
about the cost, which

463
00:29:11,210 --> 00:29:15,020
I don't think I've seen in
textbooks in the same way.

464
00:29:15,020 --> 00:29:19,170
We are singling out
in a rather long unit

465
00:29:19,170 --> 00:29:23,120
the aspect of line shape.

466
00:29:23,120 --> 00:29:25,255
OK, we talk a lot about
an atom as a resonance.

467
00:29:25,255 --> 00:29:27,730
But when you measure
the resonance,

468
00:29:27,730 --> 00:29:29,330
there is a line shape.

469
00:29:29,330 --> 00:29:32,680
And I found it
extremely insightful

470
00:29:32,680 --> 00:29:35,680
when I first saw Dave Pritchard
doing it in his atomic physics

471
00:29:35,680 --> 00:29:39,500
course to just talk
about all aspects which

472
00:29:39,500 --> 00:29:44,550
modify a resonance from a data
function from a stick diagram

473
00:29:44,550 --> 00:29:46,640
into a real shape.

474
00:29:46,640 --> 00:29:47,770
It can be doppled up water.

475
00:29:47,770 --> 00:29:49,470
It can be finite
lifetime broadening.

476
00:29:49,470 --> 00:29:52,476
It can be inhomogenous field.

477
00:29:52,476 --> 00:29:54,225
But there are lots of
interesting effects.

478
00:29:54,225 --> 00:29:57,250
And By discussing
them all together

479
00:29:57,250 --> 00:30:00,240
you gain major insight.

480
00:30:00,240 --> 00:30:07,810
So we discuss how photon recoil,
how the velocity of atoms

481
00:30:07,810 --> 00:30:09,950
effect the line shape.

482
00:30:09,950 --> 00:30:13,500
And if you think you've
understood everything,

483
00:30:13,500 --> 00:30:20,265
I will talk to you about in a
very counter intunitive aspect

484
00:30:20,265 --> 00:30:24,460
of line shapes named
Dicke narrowing.

485
00:30:24,460 --> 00:30:26,990
If you put atoms
in the environment,

486
00:30:26,990 --> 00:30:28,880
you would say they collide.

487
00:30:28,880 --> 00:30:31,270
This should lead to
collision and broadening.

488
00:30:31,270 --> 00:30:35,330
But there is one aspect where
collisions lead to narrowing.

489
00:30:35,330 --> 00:30:38,390
And that's sort of a highlight
of this chapter which really

490
00:30:38,390 --> 00:30:41,070
sort of shows you
how actually all

491
00:30:41,070 --> 00:30:45,215
of those broadening mechanisms
are somehow connected.

492
00:30:49,100 --> 00:30:57,840
Finally, and this puts us more
towards the end of the course,

493
00:30:57,840 --> 00:31:03,060
we want to understand what
happens when atoms interact not

494
00:31:03,060 --> 00:31:06,840
just with one photon
but several photons.

495
00:31:06,840 --> 00:31:11,470
And then we talk about
multiple photon processes.

496
00:31:11,470 --> 00:31:13,810
I should actually
say that I'm also

497
00:31:13,810 --> 00:31:17,070
emphasizing the multi
photon process a lot.

498
00:31:17,070 --> 00:31:19,070
I mean, often we just
simply do a transition

499
00:31:19,070 --> 00:31:20,450
between two levels.

500
00:31:20,450 --> 00:31:23,450
And there is a operator that can
be single photon or two photon

501
00:31:23,450 --> 00:31:25,930
operator, yes.

502
00:31:25,930 --> 00:31:29,560
But to understand the multi
photon aspect is important.

503
00:31:29,560 --> 00:31:33,750
And maybe to just give
you one aspect of it,

504
00:31:33,750 --> 00:31:36,330
when you think you do
one photon physics,

505
00:31:36,330 --> 00:31:38,610
often, you do two
photon physics.

506
00:31:38,610 --> 00:31:42,210
A lot of people think atoms
can absorb the photon.

507
00:31:42,210 --> 00:31:43,890
I've never seen
in my life an atom

508
00:31:43,890 --> 00:31:45,480
which has absorbed a photon.

509
00:31:45,480 --> 00:31:47,530
The photon is
immediately readmitted.

510
00:31:47,530 --> 00:31:49,170
It's a scattering event.

511
00:31:49,170 --> 00:31:53,020
An atom cannot absorb the photon
for good because the lifetime

512
00:31:53,020 --> 00:31:55,020
of the excited state is short.

513
00:31:55,020 --> 00:31:59,910
So when you think absorption
is a single photon event,

514
00:31:59,910 --> 00:32:01,830
there is a limitation
where, yes, you're

515
00:32:01,830 --> 00:32:03,850
allowed to think about it.

516
00:32:03,850 --> 00:32:07,340
But if you get confused
and it will confuse you,

517
00:32:07,340 --> 00:32:10,420
then you need the fact that
every absorption process

518
00:32:10,420 --> 00:32:12,415
is actually a two
photon process.

519
00:32:12,415 --> 00:32:14,080
Photon in and photon out.

520
00:32:14,080 --> 00:32:17,840
And sometimes by remembering
that it's not single photons,

521
00:32:17,840 --> 00:32:20,280
there are always two
photons involved,

522
00:32:20,280 --> 00:32:23,826
it helps you to avoid some
pitfalls of the similar photon

523
00:32:23,826 --> 00:32:25,490
picture.

524
00:32:25,490 --> 00:32:27,680
So therefore, multi photon, yes.

525
00:32:27,680 --> 00:32:30,510
It's not just high intensity
to photo transitions

526
00:32:30,510 --> 00:32:31,970
and atomic and such.

527
00:32:31,970 --> 00:32:34,630
It's also about the
deeper understanding.

528
00:32:34,630 --> 00:32:36,880
How does the single photon
interact with atoms?

529
00:32:40,770 --> 00:32:45,140
And finally, there
is something which

530
00:32:45,140 --> 00:32:47,740
has fascinated many physicists.

531
00:32:47,740 --> 00:32:50,440
The question about coherence.

532
00:32:50,440 --> 00:32:55,380
And coherence is as
fascinating as it is diverse

533
00:32:55,380 --> 00:33:00,260
because coherence can
have as many aspects

534
00:33:00,260 --> 00:33:05,140
and has many implications.

535
00:33:05,140 --> 00:33:10,040
And I also like a lot in
this traditional MIT cause

536
00:33:10,040 --> 00:33:13,384
that coherence is sort of
singled out as a chapter.

537
00:33:13,384 --> 00:33:15,550
And now I'll tell you about
all the different phases

538
00:33:15,550 --> 00:33:18,180
of coherence in
this chapter and not

539
00:33:18,180 --> 00:33:21,790
scattered throughout
the whole course.

540
00:33:21,790 --> 00:33:23,560
We have coherence
in single atoms.

541
00:33:26,390 --> 00:33:29,030
The simplest one is the
coherent superposition

542
00:33:29,030 --> 00:33:35,980
of two level, which is so
simple that it's almost boring.

543
00:33:35,980 --> 00:33:38,850
But there is an
enormous richness

544
00:33:38,850 --> 00:33:42,060
when we put in a third letter.

545
00:33:42,060 --> 00:33:43,900
About 20 years ago,
an understanding

546
00:33:43,900 --> 00:33:46,540
of three level
physics has really

547
00:33:46,540 --> 00:33:49,410
created a new
frontier in the field.

548
00:33:49,410 --> 00:33:51,090
Let me just tell you buzz words.

549
00:33:51,090 --> 00:33:52,510
Lasing without inversion.

550
00:33:52,510 --> 00:33:55,250
Electromagnetically
induced resonance.

551
00:33:55,250 --> 00:33:59,660
Those concepts happen due to
coherence between three levels.

552
00:33:59,660 --> 00:34:04,310
And we'll talk about that
towards the end of the course.

553
00:34:04,310 --> 00:34:10,080
Well we have coherence within
an atom between two different

554
00:34:10,080 --> 00:34:12,550
or three different
energy levels.

555
00:34:12,550 --> 00:34:17,350
But we can have also
coherence between the atoms.

556
00:34:17,350 --> 00:34:22,810
And at that point, the atoms
interact not individually.

557
00:34:22,810 --> 00:34:26,130
They act collectively.

558
00:34:26,130 --> 00:34:28,790
And of course,
coherence between atoms

559
00:34:28,790 --> 00:34:31,172
can be the coherence
of many atoms

560
00:34:31,172 --> 00:34:32,630
in a Bose-Einstein
condensate where

561
00:34:32,630 --> 00:34:36,560
they form one big matter wage.

562
00:34:36,560 --> 00:34:38,944
But it can also
be the coherence.

563
00:34:38,944 --> 00:34:41,560
The atoms are not
coherent because they've

564
00:34:41,560 --> 00:34:43,590
formed the Bose-Einstein
condensate.

565
00:34:43,590 --> 00:34:48,300
But they interact in a
coherent way with light.

566
00:34:48,300 --> 00:34:53,120
So there's only one aspect
where the atoms act coherently.

567
00:34:53,120 --> 00:34:54,960
They may be in different
quantum states.

568
00:34:54,960 --> 00:34:59,120
But the interaction with the
light is absolutely identical.

569
00:34:59,120 --> 00:35:01,380
And when it then comes
to optical properties

570
00:35:01,380 --> 00:35:04,940
of the system, the
light doesn't care

571
00:35:04,940 --> 00:35:06,650
if the atoms are different.

572
00:35:06,650 --> 00:35:10,220
The light only cares if
whether the atoms interact

573
00:35:10,220 --> 00:35:12,661
with the light in an
absolute identical way.

574
00:35:12,661 --> 00:35:14,160
And then you have
certain symmetries

575
00:35:14,160 --> 00:35:16,500
of the light atomic reaction.

576
00:35:16,500 --> 00:35:19,310
And these coherence
between many atoms

577
00:35:19,310 --> 00:35:25,800
in the interaction
with light needs to-- I

578
00:35:25,800 --> 00:35:27,270
just give you the passwords.

579
00:35:27,270 --> 00:35:32,570
It's responsible for
the process of phase

580
00:35:32,570 --> 00:35:35,300
matching when you have a crystal
and frequency-doubled laser

581
00:35:35,300 --> 00:35:39,460
light you want all the atoms
to interact coherently.

582
00:35:39,460 --> 00:35:51,040
And it is also important for the
phenomenon of super radiance.

583
00:35:51,040 --> 00:35:52,840
I found this
subject of coherence

584
00:35:52,840 --> 00:35:54,900
particularly fascinating.

585
00:35:54,900 --> 00:35:58,790
I should say it was the
subject of coherence where

586
00:35:58,790 --> 00:36:05,762
some maybe 10 years ago, I was
in a long lasting controversy

587
00:36:05,762 --> 00:36:08,286
with some colleagues
in my field.

588
00:36:08,286 --> 00:36:09,910
You know, they're
people like Phillips.

589
00:36:09,910 --> 00:36:12,076
When I met him, he's one
of the smartest [INAUDIBLE]

590
00:36:12,076 --> 00:36:14,310
atomic physicist and
one of the fastest ones.

591
00:36:14,310 --> 00:36:16,590
And ideas just fly
back and forth.

592
00:36:16,590 --> 00:36:19,030
And there was only
one example where

593
00:36:19,030 --> 00:36:22,430
we disagreed over a
long period of time

594
00:36:22,430 --> 00:36:24,510
where he had good,
intuitive arguments,

595
00:36:24,510 --> 00:36:27,210
I had good intuitive arguments,
and we couldn't agree.

596
00:36:27,210 --> 00:36:30,560
And this was related
to the question when

597
00:36:30,560 --> 00:36:34,891
it came to warm
atom amplification.

598
00:36:34,891 --> 00:36:37,800
You know, some coherent
process, whether it

599
00:36:37,800 --> 00:36:40,900
is really necessary to a
Bose-Einstein condensate

600
00:36:40,900 --> 00:36:45,500
or whether you can get away
with less, which is more

601
00:36:45,500 --> 00:36:48,040
the simple radiant way
where the atoms are

602
00:36:48,040 --> 00:36:54,970
different on different states
but they have an identical way

603
00:36:54,970 --> 00:36:56,738
to interact with light.

604
00:36:56,738 --> 00:37:00,300
And in the end, I could prove
that certain aspect which

605
00:37:00,300 --> 00:37:02,420
all people thought
in the field were

606
00:37:02,420 --> 00:37:06,635
due to the coherent nature
of atoms where sort of they

607
00:37:06,635 --> 00:37:08,840
were due to the fact
that these atoms can

608
00:37:08,840 --> 00:37:10,680
be regarded as an atom laser.

609
00:37:10,680 --> 00:37:16,310
It was just some form of
super radiance in disguise.

610
00:37:16,310 --> 00:37:20,250
So anyway, you will notice
some of my own interest

611
00:37:20,250 --> 00:37:22,600
in the chapter of
coherence when I teach it.

612
00:37:22,600 --> 00:37:25,870
So it's something which
is this phase matching

613
00:37:25,870 --> 00:37:28,540
and super radiance is
the physics of the '50s.

614
00:37:28,540 --> 00:37:31,720
But a deeper
understanding of it really

615
00:37:31,720 --> 00:37:34,830
developed when we had
Bose-Einstein condensate

616
00:37:34,830 --> 00:37:36,970
and could put some of
those ideas to the test.

617
00:37:41,770 --> 00:37:45,940
So lets what you expect.

618
00:37:45,940 --> 00:37:49,330
Let's an overview
over the topics.

619
00:37:49,330 --> 00:37:52,490
The course will
have 26 lectures.

620
00:37:52,490 --> 00:37:55,390
And these are the
topics we cover.

621
00:37:58,090 --> 00:38:01,750
Do you have any questions
about the two levels

622
00:38:01,750 --> 00:38:03,540
in the structure of the course?

623
00:38:07,240 --> 00:38:11,070
There is something I'm
going to say about homework.

624
00:38:11,070 --> 00:38:15,230
This semester Ike Chuang
has teamed up with me.

625
00:38:15,230 --> 00:38:18,250
And as many of you
know, Ike is one

626
00:38:18,250 --> 00:38:22,340
of the real drivers
of MITx, edX,

627
00:38:22,340 --> 00:38:24,950
and digital learning at MIT.

628
00:38:24,950 --> 00:38:30,150
So he is now teaming
up with me and trying

629
00:38:30,150 --> 00:38:35,330
to put some of the
pieces online that you

630
00:38:35,330 --> 00:38:38,950
can have conceptional questions
where you can work on.

631
00:38:38,950 --> 00:38:40,650
And you will et
immediate feedback

632
00:38:40,650 --> 00:38:43,160
whether you're on the
right track or not.

633
00:38:43,160 --> 00:38:44,815
So this is a new
element, which we

634
00:38:44,815 --> 00:38:47,220
ant to introduce to the course.

635
00:38:47,220 --> 00:38:49,020
I still think there
are certain problems

636
00:38:49,020 --> 00:38:52,120
you have to just sit down
with a white piece of paper

637
00:38:52,120 --> 00:38:53,640
not knowing what
to write and start

638
00:38:53,640 --> 00:38:54,940
scribbling some creations.

639
00:38:54,940 --> 00:38:57,210
So we'll have
conventional problems.

640
00:38:57,210 --> 00:39:00,640
But you also want to
experiment to what degree

641
00:39:00,640 --> 00:39:04,305
is it possible to use
elements of new technology

642
00:39:04,305 --> 00:39:07,690
of digital learning
for a course like that.

643
00:39:07,690 --> 00:39:10,240
I actually have
to say I regard it

644
00:39:10,240 --> 00:39:15,290
as a really very interesting
and Paul promising experiment

645
00:39:15,290 --> 00:39:19,060
to have some aspects of
teaching and learning

646
00:39:19,060 --> 00:39:20,650
in a graduate course.

647
00:39:20,650 --> 00:39:23,270
When MIT does MITx
and, you know,

648
00:39:23,270 --> 00:39:26,470
broadcasting education
to the whole world,

649
00:39:26,470 --> 00:39:29,810
it's much easier
to think about what

650
00:39:29,810 --> 00:39:32,610
to do when you have
a basic introduction

651
00:39:32,610 --> 00:39:34,760
to classical physics
into circuit design.

652
00:39:34,760 --> 00:39:37,370
There is, sort of, a
standard curriculum.

653
00:39:37,370 --> 00:39:39,740
A lot of questions are simple.

654
00:39:39,740 --> 00:39:42,440
It's pretty
straightforward how you

655
00:39:42,440 --> 00:39:46,280
can have simple questions as
multiple choice questions.

656
00:39:46,280 --> 00:39:48,000
But this is different.

657
00:39:48,000 --> 00:39:50,240
This is really a graduate
course in atomic physics.

658
00:39:50,240 --> 00:39:54,710
It's about deep and
profound understanding

659
00:39:54,710 --> 00:39:56,880
of complicated and
complex physics.

660
00:39:56,880 --> 00:40:00,840
I'm not sure to what
extent those complexity can

661
00:40:00,840 --> 00:40:03,300
be broken into smaller
elements, which

662
00:40:03,300 --> 00:40:05,190
can be put up as multiple
choice questions.

663
00:40:05,190 --> 00:40:06,650
Probably not.

664
00:40:06,650 --> 00:40:10,010
But on the other hand,
since MIT will never

665
00:40:10,010 --> 00:40:12,570
reach millions of people
with a graduate course

666
00:40:12,570 --> 00:40:14,590
in atomic physics,
the whole interest

667
00:40:14,590 --> 00:40:18,950
of going to the whole world
and reaching the whole world

668
00:40:18,950 --> 00:40:19,510
is absent.

669
00:40:19,510 --> 00:40:24,470
And for me, I just want to
introduce this technology

670
00:40:24,470 --> 00:40:29,440
to increase the residential
experience for you students.

671
00:40:29,440 --> 00:40:31,010
So for instance,
videotaping, I'm

672
00:40:31,010 --> 00:40:32,920
not sure if these
videotapes will ever

673
00:40:32,920 --> 00:40:36,460
be shown to a worldwide audience
before we make them available.

674
00:40:36,460 --> 00:40:39,590
But the primary audience
maybe people like you

675
00:40:39,590 --> 00:40:42,080
who have a conflict
in attending a class

676
00:40:42,080 --> 00:40:45,850
and you want to check what
was presenting in class.

677
00:40:45,850 --> 00:40:49,480
I also have the idea that
this would be in the future.

678
00:40:49,480 --> 00:40:51,600
Once we have the
videotapes, maybe I

679
00:40:51,600 --> 00:40:55,160
can tell you look at the
video recording of the class.

680
00:40:55,160 --> 00:40:57,730
And instead of having
a lecture, we'll

681
00:40:57,730 --> 00:41:00,320
just have a
classroom discussion.

682
00:41:00,320 --> 00:41:02,740
So these are aspects
I want to experiment.

683
00:41:02,740 --> 00:41:06,410
But it's sort of exciting to see
how can new technology be used

684
00:41:06,410 --> 00:41:10,110
for a course, which is very,
very different from all

685
00:41:10,110 --> 00:41:14,252
the other courses, which
have been put online at MIT.

686
00:41:17,210 --> 00:41:22,340
Well then, as expected,
we have some 20 minutes

687
00:41:22,340 --> 00:41:41,712
to start with our first
topic, which is resonance.

688
00:41:47,520 --> 00:41:57,040
And resonance is
what describes what

689
00:41:57,040 --> 00:41:59,890
is relevant for
two level systems.

690
00:41:59,890 --> 00:42:03,560
And also, and we
will touch upon this,

691
00:42:03,560 --> 00:42:08,878
resonances are the way hope
precision measurements are

692
00:42:08,878 --> 00:42:09,378
made.

693
00:42:12,240 --> 00:42:16,955
So what is a resonance?

694
00:42:20,540 --> 00:42:26,450
Well, we can first look at
the classical resonance.

695
00:42:26,450 --> 00:42:38,670
Well a resonance is something
where we have some variable

696
00:42:38,670 --> 00:42:44,540
and it varies periodically.

697
00:42:44,540 --> 00:42:53,670
So in other words, yes,
there is a variable,

698
00:42:53,670 --> 00:42:54,780
which an be anything.

699
00:42:54,780 --> 00:42:57,900
It can be the population
of quantum state.

700
00:42:57,900 --> 00:42:59,370
It can be an electric field.

701
00:42:59,370 --> 00:43:01,900
It can be the
position of an atom.

702
00:43:01,900 --> 00:43:03,790
It can be anything
you can think about

703
00:43:03,790 --> 00:43:05,930
and anything you can measure.

704
00:43:05,930 --> 00:43:14,250
And if this variable
the varies periodically,

705
00:43:14,250 --> 00:43:16,710
you have a resonance.

706
00:43:16,710 --> 00:43:19,840
Of course, the periodic
variation usually

707
00:43:19,840 --> 00:43:22,900
requires that you
drive the system.

708
00:43:22,900 --> 00:43:26,350
So you first drive it.

709
00:43:26,350 --> 00:43:27,740
And then the system oscillates.

710
00:43:31,030 --> 00:43:41,930
And this means now that when
you drive the system-- so this

711
00:43:41,930 --> 00:43:43,590
maybe a free oscillation.

712
00:43:43,590 --> 00:43:50,505
But now you drive the system
with a variable frequency.

713
00:43:53,500 --> 00:43:59,760
And what you then observe
is you observe a peak.

714
00:43:59,760 --> 00:44:02,950
So the phenomenon
of resonance is

715
00:44:02,950 --> 00:44:05,770
that you have something
which can periodically vary.

716
00:44:05,770 --> 00:44:15,580
And when you drive it,
you see peaked response

717
00:44:15,580 --> 00:44:18,895
when driven with a
variable frequency.

718
00:44:29,300 --> 00:44:30,780
Yep, this is pretty basic.

719
00:44:30,780 --> 00:44:33,560
And I don't want to
dwell much more about it.

720
00:44:33,560 --> 00:44:39,040
But I can tell you we are
interested in atomic physics

721
00:44:39,040 --> 00:44:43,150
in every single possible
aspect of this resonance.

722
00:44:43,150 --> 00:44:44,310
The shape of the curve.

723
00:44:44,310 --> 00:44:46,020
How we can modify it.

724
00:44:46,020 --> 00:44:47,730
What happens when
we tie it strongly?

725
00:44:47,730 --> 00:44:49,550
When we tie it weakly?

726
00:44:49,550 --> 00:44:56,390
I mean, resonance is really the
language we talk atoms with.

727
00:44:56,390 --> 00:44:59,870
So but here I just want to give
a lighthearted introduction.

728
00:45:02,450 --> 00:45:04,880
The first thing we want
to add to the phenomenon

729
00:45:04,880 --> 00:45:07,540
that there is a resonance
at a certain frequency

730
00:45:07,540 --> 00:45:11,650
is finite damping
that would mean,

731
00:45:11,650 --> 00:45:15,140
after the system is
driven, the oscillation

732
00:45:15,140 --> 00:45:17,595
does not last for an
infinite amount of time.

733
00:45:22,280 --> 00:45:27,340
And that implies that
when we drive the system

734
00:45:27,340 --> 00:45:33,150
and look at the response
as a function of frequency,

735
00:45:33,150 --> 00:45:35,716
it's there is a finite
[INAUDIBLE] delta

736
00:45:35,716 --> 00:45:37,020
f for the driven system.

737
00:45:43,060 --> 00:45:52,410
And as we will see in many ways,
the damping time in delta f

738
00:45:52,410 --> 00:45:55,420
are related by
Fourier transform.

739
00:46:04,910 --> 00:46:09,940
And we usually
characterize oscillators

740
00:46:09,940 --> 00:46:11,900
by the sharpness
of the resonance.

741
00:46:15,540 --> 00:46:18,690
And the sharpness
of the resonance

742
00:46:18,690 --> 00:46:22,905
is a ratio of the beats of the
resonance and the frequency

743
00:46:22,905 --> 00:46:24,650
or the inverse of it.

744
00:46:24,650 --> 00:46:28,720
So if you have an oscillator,
the kilohertz and the resonance

745
00:46:28,720 --> 00:46:30,560
is one hertz wide.

746
00:46:30,560 --> 00:46:35,990
We see the resonance has a Q--
a quality factor of 1,000--

747
00:46:35,990 --> 00:46:39,420
and that means you
can observe a thousand

748
00:46:39,420 --> 00:46:42,180
oscillations before the
oscillation decays away.

749
00:46:51,770 --> 00:46:55,165
So what is special about
atomic physics here?

750
00:46:55,165 --> 00:46:58,244
Why do I emphasize it
in the introduction

751
00:46:58,244 --> 00:46:59,410
of an atomic physics course?

752
00:47:04,613 --> 00:47:08,504
Well, the system is
that in atomic physics

753
00:47:08,504 --> 00:47:11,830
we often have exquisitely
isolated system.

754
00:47:11,830 --> 00:47:15,060
An atom [INAUDIBLE]
vacuum chamber or systems,

755
00:47:15,060 --> 00:47:19,180
which are prepared with all of
the tools and the precision,

756
00:47:19,180 --> 00:47:22,600
which we have developed over
decades in atomic physics.

757
00:47:22,600 --> 00:47:25,520
And therefore, the result
is that in atomic physics

758
00:47:25,520 --> 00:47:32,270
our oscillators
are characterized

759
00:47:32,270 --> 00:47:40,490
by an extremely high
quality factor Q.

760
00:47:40,490 --> 00:47:44,130
And let me give you an example.

761
00:47:44,130 --> 00:47:57,720
If we look at an
optical excitation,

762
00:47:57,720 --> 00:48:05,860
the-- maybe let me point
out it's something you all

763
00:48:05,860 --> 00:48:08,980
should try when you take
a class in atomic physics

764
00:48:08,980 --> 00:48:11,550
and even more so when you do
research in atomic physics

765
00:48:11,550 --> 00:48:16,870
that you have a few numbers
in your mind which match.

766
00:48:16,870 --> 00:48:21,150
So you know, every single
person in this room

767
00:48:21,150 --> 00:48:23,840
should know what is
the frequency of light.

768
00:48:23,840 --> 00:48:30,090
How many hertz is-- what is
the frequency of a laser?

769
00:48:30,090 --> 00:48:32,930
The number I usually
use for those estimates

770
00:48:32,930 --> 00:48:35,976
is 10 to 15 hertz.

771
00:48:35,976 --> 00:48:39,371
Who knows what wavelengths this
laser-- 10 to the 15 hertz--

772
00:48:39,371 --> 00:48:39,870
is?

773
00:48:44,960 --> 00:48:47,760
Well I view some visible light.

774
00:48:47,760 --> 00:48:50,780
But the speed of light
is 3 times 10 to the 10.

775
00:48:50,780 --> 00:48:54,040
So therefore, if I just use
the power 10 to the 15 hertz,

776
00:48:54,040 --> 00:48:57,340
it has to be 300 [INAUDIBLE].

777
00:48:57,340 --> 00:49:00,300
OK, so never forget that
for the rest of your life.

778
00:49:00,300 --> 00:49:04,630
300 nanometer is
10 to the 15 hertz.

779
00:49:04,630 --> 00:49:07,630
That means that most
of us who are working

780
00:49:07,630 --> 00:49:10,965
with rubidium, lithium, and
sodium, which is 600 nanometer

781
00:49:10,965 --> 00:49:14,760
or 800 nanometer, the
frequency is more 5 times

782
00:49:14,760 --> 00:49:17,990
10 to the 14 or 3
times 10 to the 14.

783
00:49:17,990 --> 00:49:20,780
But just as a ballpark
number, 10 to the 15 hertz

784
00:49:20,780 --> 00:49:21,900
is 300 nanometer.

785
00:49:24,750 --> 00:49:29,140
OK, so if we have an
optical excitation

786
00:49:29,140 --> 00:49:32,990
and many atoms have
that, what is the Q?

787
00:49:32,990 --> 00:49:37,718
What is the quality
factor of this resonance?

788
00:49:37,718 --> 00:49:44,100
Well when you stabilize
you laser to a vapor cell

789
00:49:44,100 --> 00:49:46,310
and you look at the
resonance, then you

790
00:49:46,310 --> 00:49:49,730
observe in a vapor cell that you
have room temperature Doppler

791
00:49:49,730 --> 00:49:53,820
broadening-- we'll talk about
Doppler broadening later

792
00:49:53,820 --> 00:49:58,710
in this course-- that
usually corresponds

793
00:49:58,710 --> 00:50:03,920
to a frequency on the
order of a gigahertz.

794
00:50:03,920 --> 00:50:15,670
And that means that your quality
factor is on the order of 10

795
00:50:15,670 --> 00:50:20,070
to the 6-- a million.

796
00:50:20,070 --> 00:50:20,920
That's pretty good.

797
00:50:20,920 --> 00:50:22,030
A million oscillation.

798
00:50:22,030 --> 00:50:24,760
That's a very pure oscillator.

799
00:50:24,760 --> 00:50:32,322
But of course, you can do much
better if you do Doppler free

800
00:50:32,322 --> 00:50:32,863
spectroscopy.

801
00:50:35,666 --> 00:50:37,040
Either by having
the atomic beam,

802
00:50:37,040 --> 00:50:39,550
which is intersected
at the right angle.

803
00:50:39,550 --> 00:50:42,820
Or even better, put the
atoms in an optical lattice.

804
00:50:42,820 --> 00:50:45,680
And this is what people are now
doing with the optical lattice

805
00:50:45,680 --> 00:50:49,840
clocks that they put an
atom in optical lattice

806
00:50:49,840 --> 00:50:52,090
where the Doppler broadening
is completely eliminated.

807
00:50:54,660 --> 00:51:03,690
If you take a metastable
level, the lifetime

808
00:51:03,690 --> 00:51:07,330
of the exciting state
is, maybe, one second.

809
00:51:07,330 --> 00:51:14,270
And strontium and other atoms
have those metastable labels.

810
00:51:14,270 --> 00:51:18,290
Then you can actually
get aligned with,

811
00:51:18,290 --> 00:51:20,680
which is one hertz.

812
00:51:20,680 --> 00:51:24,710
And the Q factor is on
the order of 10 to the 15.

813
00:51:27,330 --> 00:51:32,610
I will show you a graphic
example of such an experiment

814
00:51:32,610 --> 00:51:36,830
in one hertz line widths
of an optical transition

815
00:51:36,830 --> 00:51:41,600
for an optical clock experiment
in the next class on Monday

816
00:51:41,600 --> 00:51:43,560
when I want to discuss
other aspects of it.

817
00:51:43,560 --> 00:51:48,150
But this is one of the
worlds best oscillator

818
00:51:48,150 --> 00:51:49,200
you can imagine.

819
00:51:49,200 --> 00:51:50,282
10 to the 15.

820
00:51:50,282 --> 00:51:52,106
It's a mind boggling number.

821
00:51:55,880 --> 00:52:00,970
Well it's clear why
clocks have gone atomic.

822
00:52:00,970 --> 00:52:05,710
Mechanical systems
are actually not bad

823
00:52:05,710 --> 00:52:08,300
but, of course,
not nearly as good.

824
00:52:08,300 --> 00:52:16,690
If you take quartz
oscillator, well you

825
00:52:16,690 --> 00:52:23,030
can build pretty good clocks
out of quartz oscillators.

826
00:52:23,030 --> 00:52:25,540
You have quality
factors which vary

827
00:52:25,540 --> 00:52:28,010
between a few thousands
and a million.

828
00:52:30,630 --> 00:52:33,840
The best values are
reached at low temperature.

829
00:52:37,780 --> 00:52:46,800
And actually, even in the
event of atomic clocks,

830
00:52:46,800 --> 00:52:50,280
quartz oscillators or
sapphire oscillators still

831
00:52:50,280 --> 00:52:56,480
play a roll because you
need, sort of, fly wheels.

832
00:52:56,480 --> 00:52:58,070
In atomic clock
you may interrogate

833
00:52:58,070 --> 00:53:01,960
only every Ramsey spectroscopy.

834
00:53:01,960 --> 00:53:05,605
You know, every tens of
seconds you get a signal.

835
00:53:05,605 --> 00:53:08,230
And in between you
need a fly wheel.

836
00:53:08,230 --> 00:53:11,500
And then clocks, which have a
very high signal to noise ratio

837
00:53:11,500 --> 00:53:13,535
but not the [INAUDIBLE]
help you to interpolate

838
00:53:13,535 --> 00:53:14,410
between measurements.

839
00:53:18,010 --> 00:53:22,320
We see actually a renaissance
of mechanical systems

840
00:53:22,320 --> 00:53:25,530
in the form of
micro-mechanical oscillators.

841
00:53:30,040 --> 00:53:33,100
It was only achieved in
the last 2 or 3 years

842
00:53:33,100 --> 00:53:35,420
that micro mechanical
oscillators could

843
00:53:35,420 --> 00:53:37,910
be cool to the
actual ground state.

844
00:53:37,910 --> 00:53:41,300
And there's a lot of
interest of coupling

845
00:53:41,300 --> 00:53:43,890
the emotion of the
mechanical oscillator

846
00:53:43,890 --> 00:53:47,400
to an atomic oscillator because
they have different properties

847
00:53:47,400 --> 00:53:52,040
and for parental computation
and other explorations

848
00:53:52,040 --> 00:53:55,320
of Hilbert space you want to
have different oscillators.

849
00:53:55,320 --> 00:53:59,177
And, you know, combine the
best of the properties.

850
00:53:59,177 --> 00:54:00,885
So therefore, there
is a real renaissance

851
00:54:00,885 --> 00:54:03,480
in mechanical oscillators.

852
00:54:03,480 --> 00:54:06,740
And those micro-mechanical
mechanical oscillators

853
00:54:06,740 --> 00:54:10,780
have often quality
factors of 10 to the 5.

854
00:54:19,910 --> 00:54:33,678
Here, I want to show you a
picture of a fairly nice one.

855
00:54:38,620 --> 00:54:44,080
Yeah, this is a micro
fabricated device.

856
00:54:44,080 --> 00:54:47,080
It looks like a little mushroom.

857
00:54:47,080 --> 00:54:54,150
And what happens is this
mushroom type structure

858
00:54:54,150 --> 00:54:58,220
can confine light, which
travels around the parameter

859
00:54:58,220 --> 00:55:01,770
as a so-called
whispering gallery mode.

860
00:55:01,770 --> 00:55:04,250
It's similar to an
acoustic mode, which

861
00:55:04,250 --> 00:55:08,130
can travel in the dome
of a big cathedral.

862
00:55:08,130 --> 00:55:10,490
That's how it was discovered.

863
00:55:10,490 --> 00:55:12,220
It's an amazing effect.

864
00:55:12,220 --> 00:55:14,360
I wish somebody would
demonstrate it to me.

865
00:55:14,360 --> 00:55:16,276
But if you go to one of
the ancient cathedrals

866
00:55:16,276 --> 00:55:20,520
and you're in a dome, somebody
can talk in one direction,

867
00:55:20,520 --> 00:55:22,950
the sound can travel
around, and you can hear it.

868
00:55:22,950 --> 00:55:25,300
There's a guided
special mode, which

869
00:55:25,300 --> 00:55:28,740
can travel around the
parameter of the dome.

870
00:55:28,740 --> 00:55:30,840
And here in the
microscopic domain,

871
00:55:30,840 --> 00:55:36,490
it's light, which is confined
in such and resonated.

872
00:55:50,140 --> 00:55:56,540
So this is resonator for
whispering gallery mode.

873
00:55:56,540 --> 00:56:02,860
And that can have a Q on
the order of a billion.

874
00:56:24,800 --> 00:56:27,500
So the idea here
is that you have

875
00:56:27,500 --> 00:56:30,760
either one of those
mushrooms or a glass sphere

876
00:56:30,760 --> 00:56:35,740
and the light can,
sort of, travel around.

877
00:56:35,740 --> 00:56:44,040
And this is the
characteristics of this mode.

878
00:56:44,040 --> 00:56:47,680
Well you can go from
a tiny glass sphere

879
00:56:47,680 --> 00:56:49,730
to astronomical dimensions.

880
00:56:58,150 --> 00:57:00,440
And you also find oscillators.

881
00:57:00,440 --> 00:57:06,080
And the Q of those
oscillators is not really bad.

882
00:57:06,080 --> 00:57:10,000
How good is the Q of the
rotation of the earth?

883
00:57:14,210 --> 00:57:17,510
It fulfills all of
our requirements

884
00:57:17,510 --> 00:57:19,970
for resonance and oscillator.

885
00:57:19,970 --> 00:57:21,220
It's a [INAUDIBLE] phenomenon.

886
00:57:26,530 --> 00:57:31,580
The Earth rotates around
the sun once a year.

887
00:57:31,580 --> 00:57:34,690
And the question is
how stable is it.

888
00:57:34,690 --> 00:57:38,765
Well the number is 10 to the 7.

889
00:57:38,765 --> 00:57:40,600
It has a Q of 10 to the 7.

890
00:57:40,600 --> 00:57:45,629
So the precision of the
rotation of the earth

891
00:57:45,629 --> 00:57:47,170
is better than one
part in a million.

892
00:57:50,200 --> 00:57:53,510
You can also look at the
rotation of neutron star.

893
00:57:53,510 --> 00:57:57,230
If those neutron stars
emit flashes of X-rays,

894
00:57:57,230 --> 00:58:01,080
these are pulses, and you can
measure the rotation of neutron

895
00:58:01,080 --> 00:58:04,980
stars, those neutron stars
have a quality factor of 10

896
00:58:04,980 --> 00:58:05,934
to the 10.

897
00:58:14,520 --> 00:58:21,063
And of course, [INAUDIBLE]
says, if a resonance has

898
00:58:21,063 --> 00:58:25,190
a high quality factor, it can
be used for quality research.

899
00:58:25,190 --> 00:58:27,750
Then everywhere the line
is the more sensitive

900
00:58:27,750 --> 00:58:30,750
you are to tiny little changes.

901
00:58:30,750 --> 00:58:33,450
And you probably know that
this pulsar with a Q of 10

902
00:58:33,450 --> 00:58:40,440
to the 10, well, has been
used for the first, also

903
00:58:40,440 --> 00:58:44,170
indirect, observation
of computation waves.

904
00:58:44,170 --> 00:58:48,192
The pulsar rotates with
a very precise frequency.

905
00:58:48,192 --> 00:58:50,400
And you can measure it with
one part of 10 to the 10.

906
00:58:50,400 --> 00:58:53,430
And people have seen
that, over the years,

907
00:58:53,430 --> 00:58:57,680
the frequency of
rotation became smaller.

908
00:58:57,680 --> 00:58:59,400
And you can figure
out that it becomes

909
00:58:59,400 --> 00:59:02,670
smaller by just one
part in 10 to the 10

910
00:59:02,670 --> 00:59:04,500
because you're at this position.

911
00:59:04,500 --> 00:59:07,960
And what happens is when the
pulsar rotates-- when a neutron

912
00:59:07,960 --> 00:59:11,650
star rotates-- it emits
gravitational waves.

913
00:59:11,650 --> 00:59:14,040
And the gravitational
wave is energy,

914
00:59:14,040 --> 00:59:17,120
which is taking away from the
kinetic energy of the rotation.

915
00:59:17,120 --> 00:59:19,510
And therefore, the
pulses slows down.

916
00:59:19,510 --> 00:59:23,540
So having an oscillator
with such a high Q

917
00:59:23,540 --> 00:59:28,240
has an allowed researchers
to find a small effect

918
00:59:28,240 --> 00:59:31,089
in the damping of this
oscillator, which in this case

919
00:59:31,089 --> 00:59:32,130
were gravitational waves.

920
00:59:35,030 --> 00:59:36,530
Of course, the story
I will tell you

921
00:59:36,530 --> 00:59:40,047
is about very small changes
of atomic oscillators,

922
00:59:40,047 --> 00:59:41,880
which led to the discovery
of the Lamb shift

923
00:59:41,880 --> 00:59:44,280
and to quantum electrodynamics.

924
00:59:44,280 --> 00:59:45,650
But the story is the same.

925
00:59:45,650 --> 00:59:49,638
A high quality oscillator
is the tool for discovery.

926
00:59:54,000 --> 00:59:58,000
OK, so we've talked
about resonances.

927
01:00:00,850 --> 01:00:03,540
Of course, there are
resonances which are useful

928
01:00:03,540 --> 01:00:06,650
and others which
are less useful.

929
01:00:06,650 --> 01:00:13,150
By useful we mean
they're reproducible.

930
01:00:13,150 --> 01:00:16,520
We can really make a measurement
and trust it and repeat and do

931
01:00:16,520 --> 01:00:17,630
it again.

932
01:00:17,630 --> 01:00:20,300
And that's not enough
for being useful.

933
01:00:20,300 --> 01:00:23,680
You also want to learn
something about it.

934
01:00:23,680 --> 01:00:28,230
So usually, we got
resonances as useful

935
01:00:28,230 --> 01:00:38,250
when they are connected
by a theory to something

936
01:00:38,250 --> 01:00:39,870
we are interested in.

937
01:00:39,870 --> 01:00:49,450
It can either be
fundamentally constance

938
01:00:49,450 --> 01:00:54,318
or let me say other
parameters of interest.

939
01:00:58,900 --> 01:01:02,420
If you want to measure the
magnetic field with very

940
01:01:02,420 --> 01:01:04,970
high precision and you
look at atomic resonance,

941
01:01:04,970 --> 01:01:08,220
it's only useful when you
[INAUDIBLE], which tells you

942
01:01:08,220 --> 01:01:10,970
how the shift or the
broadening of the resonance

943
01:01:10,970 --> 01:01:14,970
is related to magnetic fields.

944
01:01:14,970 --> 01:01:19,460
And this is, again, a
specialty of AMO physics.

945
01:01:19,460 --> 01:01:22,090
We have plenty of
resonances, which

946
01:01:22,090 --> 01:01:24,260
are useful by those standards.

947
01:01:29,560 --> 01:01:35,010
And if you compare to
astrophysical oscillators,

948
01:01:35,010 --> 01:01:44,430
or quartz oscillators, or
fabricated oscillators,

949
01:01:44,430 --> 01:01:49,130
in atomic physics, we
have the great advantage

950
01:01:49,130 --> 01:01:52,210
that atoms are identical.

951
01:01:52,210 --> 01:01:56,170
We know when you measure the
concision atomic hydrogen

952
01:01:56,170 --> 01:01:59,030
in Japan and Europe and
in the United States,

953
01:01:59,030 --> 01:02:02,390
the venue has to be the same.

954
01:02:02,390 --> 01:02:04,620
For other oscillators,
you often don't note It.

955
01:02:09,610 --> 01:02:13,060
So the showcase
of atomic physics

956
01:02:13,060 --> 01:02:33,650
is the Rydberg constant,
which is the best known--

957
01:02:33,650 --> 01:02:37,300
the most accurately known--
constant in all of physics.

958
01:02:37,300 --> 01:02:40,750
And the reason is because
it can be directly measured

959
01:02:40,750 --> 01:02:43,830
by performing spectroscopy
and hydrogen with highly

960
01:02:43,830 --> 01:02:44,580
stabilized lasers.

961
01:02:54,870 --> 01:03:00,790
OK, of course, the question is
who's interested in all those

962
01:03:00,790 --> 01:03:01,820
[INAUDIBLE]?

963
01:03:01,820 --> 01:03:04,811
Why do you want to spend
all of your PhD or half

964
01:03:04,811 --> 01:03:09,930
of your life measuring the
Rydberg constant to, maybe,

965
01:03:09,930 --> 01:03:12,510
10 times more precision?

966
01:03:12,510 --> 01:03:13,760
Well it depends.

967
01:03:13,760 --> 01:03:18,640
It's maybe not
something for everybody.

968
01:03:18,640 --> 01:03:21,610
But there are some
connoisseurs who

969
01:03:21,610 --> 01:03:25,800
think that every
digit has provided

970
01:03:25,800 --> 01:03:28,120
new inside into nature.

971
01:03:28,120 --> 01:03:31,360
And let me just give
you one example.

972
01:03:31,360 --> 01:03:34,700
If you measure the Rydberg
constant very precisely,

973
01:03:34,700 --> 01:03:36,900
you can now-- and
this has become

974
01:03:36,900 --> 01:03:40,170
the frontier of our
field-- ask the question,

975
01:03:40,170 --> 01:03:44,340
is their change with time
a fundamental constance?

976
01:03:47,090 --> 01:03:51,460
So when you measure the
Rydberg constant today with 10

977
01:03:51,460 --> 01:03:54,150
to the minus 15 precision
and measure it again

978
01:03:54,150 --> 01:03:57,890
in a year, who is
guaranteeing to you that you

979
01:03:57,890 --> 01:04:00,450
will measure the same value.

980
01:04:00,450 --> 01:04:02,700
So with the precision
which I've just

981
01:04:02,700 --> 01:04:05,660
given to you in this measurement
of the Rydberg constant,

982
01:04:05,660 --> 01:04:09,690
people are now able to
say whether the Rydberg

983
01:04:09,690 --> 01:04:15,370
constant has changed 10
to the minus 15 per year.

984
01:04:15,370 --> 01:04:20,710
Of course of know, the
age of the universe

985
01:04:20,710 --> 01:04:26,010
is 14 billion years.

986
01:04:26,010 --> 01:04:28,490
That's about 10 to the 10 years.

987
01:04:28,490 --> 01:04:32,510
So even the worst case is
that if you would go back

988
01:04:32,510 --> 01:04:35,460
to the beginning of the universe
and the Rydberg constant would

989
01:04:35,460 --> 01:04:37,230
change to 10 the
minus 15 per year,

990
01:04:37,230 --> 01:04:39,800
it would've changed
by 10 to the minus 5

991
01:04:39,800 --> 01:04:42,090
over the age of the universe.

992
01:04:42,090 --> 01:04:45,920
But this would be climatic
because the connection shows

993
01:04:45,920 --> 01:04:48,620
that life would
not have developed.

994
01:04:48,620 --> 01:04:52,020
The whole organic chemistry
would have been different

995
01:04:52,020 --> 01:04:54,950
if some fundamental
constant of nature

996
01:04:54,950 --> 01:04:59,310
had been different by one part
in 10 to the minus 6, 7, or 8.

997
01:04:59,310 --> 01:05:02,060
So you have extremely
stringent limits

998
01:05:02,060 --> 01:05:04,160
how much fundamental
constant could

999
01:05:04,160 --> 01:05:06,820
have changed through
the evolution of life

1000
01:05:06,820 --> 01:05:09,150
because life would
not have been the same

1001
01:05:09,150 --> 01:05:12,970
if fundamental
constant had changed.

1002
01:05:12,970 --> 01:05:15,350
The question, of
course, is should

1003
01:05:15,350 --> 01:05:17,055
those fundamental
constant change.

1004
01:05:17,055 --> 01:05:18,920
Well the answer
is we don't know.

1005
01:05:18,920 --> 01:05:23,410
But there is a whole research
area in string theory

1006
01:05:23,410 --> 01:05:27,710
where they say that our
universe is, sort of, just

1007
01:05:27,710 --> 01:05:32,180
one of many possible minima
in a multi-dimensional space.

1008
01:05:32,180 --> 01:05:34,770
And it's actually dynamic
minima [INAUDIBLE]

1009
01:05:34,770 --> 01:05:36,510
changes the function of time.

1010
01:05:36,510 --> 01:05:38,880
So there are people who
wouldn't be surprised

1011
01:05:38,880 --> 01:05:42,200
if the world is not
the same in the future

1012
01:05:42,200 --> 01:05:46,240
as it is right now
because the universe

1013
01:05:46,240 --> 01:05:50,250
or whatever defines fundamental
constants is changing

1014
01:05:50,250 --> 01:05:52,940
as a function of time.

1015
01:05:52,940 --> 01:05:56,260
So the question is will
it be during your lifetime

1016
01:05:56,260 --> 01:05:57,870
or will it even
be during, maybe,

1017
01:05:57,870 --> 01:06:01,050
your PH.D when one
researcher says you know

1018
01:06:01,050 --> 01:06:01,935
have an [INAUDIBLE].

1019
01:06:01,935 --> 01:06:07,040
And we find out that, yes, we
measure fundamental constant

1020
01:06:07,040 --> 01:06:09,060
using the most
accurate atomic clock.

1021
01:06:09,060 --> 01:06:11,150
And a year later, you
have measured something

1022
01:06:11,150 --> 01:06:15,910
that's just a tiny bit but
significantly different.

1023
01:06:15,910 --> 01:06:18,650
The second aspect why you
should always measure things

1024
01:06:18,650 --> 01:06:20,984
as accurately as
possible and this

1025
01:06:20,984 --> 01:06:22,650
is, sort of the,
tradition of our field.

1026
01:06:22,650 --> 01:06:25,000
If you can measure
something very accurately,

1027
01:06:25,000 --> 01:06:28,430
do it because, yes,
there maybe surprising.

1028
01:06:32,130 --> 01:06:36,180
And for instance, when people
looked at the Zeeman shift

1029
01:06:36,180 --> 01:06:40,690
with higher
precision, they found

1030
01:06:40,690 --> 01:06:42,610
where we talk about
when we talk about atoms

1031
01:06:42,610 --> 01:06:44,620
in the magnetic field
when people looked

1032
01:06:44,620 --> 01:06:50,070
at the anomalies Zeeman
effect, the discovery of that

1033
01:06:50,070 --> 01:06:51,990
is what nobody expected.

1034
01:06:51,990 --> 01:06:55,480
That particles
electron has a spin.

1035
01:06:55,480 --> 01:07:00,520
Or when people saw a tiny
shift in the spectrum

1036
01:07:00,520 --> 01:07:04,950
of atomic hydrogen, it was
1,000 megahertz splitting.

1037
01:07:04,950 --> 01:07:06,497
It was the Lamb shift.

1038
01:07:06,497 --> 01:07:08,580
This was the discovery of
quantum electrodynamics.

1039
01:07:21,680 --> 01:07:31,180
And we know that precision
always becomes a tool.

1040
01:07:31,180 --> 01:07:35,590
A tool to control atomic systems
control quantum mechanics

1041
01:07:35,590 --> 01:07:36,916
with more precision.

1042
01:07:36,916 --> 01:07:38,790
For instance, if you
can completely, sort of,

1043
01:07:38,790 --> 01:07:41,425
hyperfine structure,
you can prepare atoms

1044
01:07:41,425 --> 01:07:42,633
in a certain hyperfine state.

1045
01:07:42,633 --> 01:07:44,904
If you don't have the
resolution, you can't do that.

1046
01:07:53,770 --> 01:07:59,800
OK so we're now going to talk.

1047
01:07:59,800 --> 01:08:01,110
Go back to the resonance.

1048
01:08:11,370 --> 01:08:16,406
When we look at
typical resonance,

1049
01:08:16,406 --> 01:08:18,385
we have a frequency omega.

1050
01:08:18,385 --> 01:08:20,711
A resonance frequency omega 0.

1051
01:08:23,800 --> 01:08:27,350
And we measure line
with delta omega.

1052
01:08:27,350 --> 01:08:32,380
In many cases, we will
discuss in great detail

1053
01:08:32,380 --> 01:08:35,369
the line shape is a Lorentzian.

1054
01:08:35,369 --> 01:08:41,350
And the Lorentzian is the
imaginary part of the 1 over 6

1055
01:08:41,350 --> 01:08:42,990
function.

1056
01:08:42,990 --> 01:08:46,510
Omega 0 minus omega.

1057
01:08:46,510 --> 01:08:49,120
And then there is
this parameter gamma.

1058
01:08:56,540 --> 01:09:00,220
Gamma, which appears
in the Lorentzian,

1059
01:09:00,220 --> 01:09:05,319
is identical to the full
width at half maximum.

1060
01:09:05,319 --> 01:09:10,304
And the Q factor of a Lorentzian
is omega 0 over gamma.

1061
01:09:17,750 --> 01:09:25,170
Let me finish a few more minutes
with a short note about-- we've

1062
01:09:25,170 --> 01:09:26,770
talked about resonances.

1063
01:09:26,770 --> 01:09:29,220
I've talked about now the
two important parameters.

1064
01:09:29,220 --> 01:09:33,859
The resonance frequency and the
full widths at half maximum.

1065
01:09:33,859 --> 01:09:35,790
How do we measure those?

1066
01:09:35,790 --> 01:09:41,644
And there is actually
sometimes a confusion.

1067
01:09:47,020 --> 01:09:49,340
The more systematic
approach is you

1068
01:09:49,340 --> 01:09:52,130
should measure all
those frequency and line

1069
01:09:52,130 --> 01:10:02,170
width in angular
frequency units, which

1070
01:10:02,170 --> 01:10:07,570
are technically
radian per second.

1071
01:10:07,570 --> 01:10:10,050
2 pi per second.

1072
01:10:10,050 --> 01:10:13,230
But since radian
has more dimension,

1073
01:10:13,230 --> 01:10:17,870
you sometimes say we measure
it in inverse seconds.

1074
01:10:20,410 --> 01:10:25,340
So this is the measurement
angular frequencies.

1075
01:10:25,340 --> 01:10:29,760
And this is different from
the unit of frequencies.

1076
01:10:33,630 --> 01:10:37,730
When we have a frequency, which
is an angular frequency divided

1077
01:10:37,730 --> 01:10:47,090
by 2 pi, frequencies are
usually measured in hertz.

1078
01:10:47,090 --> 01:10:52,530
The problem is that a hertz is
always also 1 over a second.

1079
01:10:52,530 --> 01:10:55,480
And this is where
the confusion comes.

1080
01:10:55,480 --> 01:11:01,990
So then you just point out how
you can avoid the confusion.

1081
01:11:01,990 --> 01:11:06,280
You may right an angular
frequency or maybe a 0.

1082
01:11:06,280 --> 01:11:09,800
It is 2 pie times 1 megahertz.

1083
01:11:09,800 --> 01:11:13,940
Then you exactly
know what it is.

1084
01:11:13,940 --> 01:11:21,180
Of course, this is nothing
else than six times 6.28 times

1085
01:11:21,180 --> 01:11:26,322
10 to the 6 second
to the minus 1.

1086
01:11:26,322 --> 01:11:37,310
But you should never
say that omega 0 is

1087
01:11:37,310 --> 01:11:42,720
6.8 times 10 to the 6
hertz because then people

1088
01:11:42,720 --> 01:11:45,010
don't really know
and you get confused

1089
01:11:45,010 --> 01:11:47,980
and you confuse other
people if you really

1090
01:11:47,980 --> 01:11:51,100
mean that this has a
frequency of 6 times

1091
01:11:51,100 --> 01:11:54,430
into the 6 hertz on
angular frequency.

1092
01:11:54,430 --> 01:11:58,370
So just be clean in your
thinking and your homework

1093
01:11:58,370 --> 01:12:00,390
and all that that
a frequency when

1094
01:12:00,390 --> 01:12:03,160
you mean angular frequency
is 1 over second,

1095
01:12:03,160 --> 01:12:06,570
when you mean it as a
frequency, it's hertz,

1096
01:12:06,570 --> 01:12:09,390
and this is often the
clearest form to say,

1097
01:12:09,390 --> 01:12:13,380
yes, I know where to put the two
pie and I put it in explicitly.

1098
01:12:13,380 --> 01:12:19,000
So we often in our papers
report frequencies like that.

1099
01:12:19,000 --> 01:12:36,424
Finally, there is the
question about gamma.

1100
01:12:40,360 --> 01:12:43,750
So what are the units for gamma?

1101
01:12:43,750 --> 01:12:48,830
Well if you look at the
exponential which decays,

1102
01:12:48,830 --> 01:12:51,320
it has e to the minus i omega t.

1103
01:12:51,320 --> 01:12:56,230
And then it has the
imaginary part, gamma t.

1104
01:12:56,230 --> 01:12:59,620
So gamma is really
a temporal decay.

1105
01:12:59,620 --> 01:13:02,120
And there is no question
about frequency and angular

1106
01:13:02,120 --> 01:13:02,620
frequency.

1107
01:13:02,620 --> 01:13:03,850
It's not a frequency.

1108
01:13:03,850 --> 01:13:05,100
It's not an angular frequency.

1109
01:13:05,100 --> 01:13:07,640
It's a decay of it.

1110
01:13:07,640 --> 01:13:15,930
So for instance, if gamma
is 10 to the 4 per second,

1111
01:13:15,930 --> 01:13:21,390
you should never say gamma
is 10 to the 4 hertz.

1112
01:13:21,390 --> 01:13:24,030
Or you should also
never say gamma

1113
01:13:24,030 --> 01:13:31,790
is 2 pi times 1.66 kilohertz.

1114
01:13:31,790 --> 01:13:34,840
That just doesn't
make any sense.

1115
01:13:34,840 --> 01:13:37,496
Gamma is really
at a damping rate.

1116
01:13:37,496 --> 01:13:38,412
AUDIENCE: [INAUDIBLE].

1117
01:13:38,412 --> 01:13:39,472
PROFESSOR: Yes?

1118
01:13:39,472 --> 01:13:40,430
I need one more minute.

1119
01:13:40,430 --> 01:13:40,971
AUDIENCE: OK.

1120
01:13:40,971 --> 01:13:45,280
PROFESSOR: And is there
for an inverse time.

1121
01:13:45,280 --> 01:13:50,710
The damping time
associated with this camera

1122
01:13:50,710 --> 01:13:56,070
is simply the inverse of it and
in the case chosen its hundred

1123
01:13:56,070 --> 01:13:57,760
microsecond.

1124
01:13:57,760 --> 01:14:01,490
So just keep that in mind.

1125
01:14:01,490 --> 01:14:02,490
Time is over.

1126
01:14:02,490 --> 01:14:04,835
Any questions?

1127
01:14:04,835 --> 01:14:06,110
OK, great.

1128
01:14:06,110 --> 01:14:11,010
We meet again same place,
same time, on Monday.