ICTS Big Questions: A Journey into the Quantum Universe with Subir Sachdev - Free Educational videos for Students in K-12 | Lumos Learning

ICTS Big Questions: A Journey into the Quantum Universe with Subir Sachdev - Free Educational videos for Students in k-12


ICTS Big Questions: A Journey into the Quantum Universe with Subir Sachdev - By International Centre for Theoretical Sciences



Transcript
00:08 and hello everyone and welcome . Good , good evening
00:14 . Good afternoon , Good morning . Uh , to
00:17 every uh , to all of you who could join
00:19 us today . Uh , we're meeting at a rather
00:22 terrible time in India , as you know , and
00:26 uh , I think many of us have been very
00:29 stressed about situation , the well being of our family
00:35 members , friends and have been tragedies everywhere . It's
00:39 , it's a , it's a kind of a really
00:42 unfortunate period we are going through , but , but
00:46 I thought that we should nevertheless free ourselves on ,
00:51 rather not be chained to this uh , to this
00:54 depressing uh , situation that's unfolding around us , but
01:01 perhaps take our mind for a little while , at
01:04 least to something more eternal and more uh , um
01:09 , which will live long past all of us .
01:12 Uh , so , uh , so this is why
01:15 we have today's big questions , cities and uh ,
01:22 it's a great pleasure to welcome process to be such
01:26 thing uh from from Harvard to , to to this
01:32 episode , as you know , we we started this
01:36 last year during the lockdown and this is uh a
01:39 bit so we really sort of completing the first year
01:42 of uh this and we have really ventured into many
01:48 different domains uh starting from cosmology , the very big
01:53 and so on and and also the very small ,
01:55 the particle physics Fatima then into the world of the
01:59 mind with uh with Syria uh last time into the
02:05 mathematical universe with uh with Angel . Uh today ,
02:11 it's a number , very fascinating universe that should be
02:14 able to take us into uh which is the quantum
02:18 universe . Let me just share my slides one minute
02:22 . I just have a little bit of uh this
02:25 thing where where is it ? Okay , yeah ,
02:29 okay , so so severe is uh so we'll we'll
02:34 really have a session and so we will hopefully disentangle
02:37 quantum mechanics for us by entangling us into it .
02:42 Uh but uh severe is the hurtle smith professor of
02:47 physics at Harvard . He has is really a pioneering
02:51 physicist and uh numerous recognitions and uh I just wanted
02:57 to pick out the direct medal which cites his pioneering
03:00 contributions to many areas of theoretical condensed matter physics and
03:04 then goes on to list uh really impressive list of
03:10 contributions . The largest on saga price of the american
03:14 uh Physical society is the fellow of the National Academy
03:17 of Sciences and so on and it goes on .
03:21 Uh He has again been a pillar of support for
03:26 I . C . T . S . Uh through
03:28 uh by being part of our international advisory board for
03:33 a very long time , has been helping us in
03:37 as we grow our faculty in different areas , especially
03:42 in condensed matter physics . Um Some beers work has
03:45 been pioneering . It's it's very I think amongst contemporary
03:51 theoretical physicists it's very unusual to have someone like severe
03:55 because uh in any era of specialization where people sort
04:01 of find their nation sort of uh focus on that
04:05 superior has has enormous breath . And this has uh
04:12 we have seen this repeatedly uh in some ways it's
04:17 uh he has brought ideas from string theory from the
04:21 physics of black holes to bear on questions in strongly
04:25 interacting systems , strongly interacting materials and I'm sure you'll
04:31 hear about that from him today . But he has
04:33 also gone the flow has gone the other way .
04:37 So one of the models which is currently very influential
04:40 in string theory for understanding the physics of black holes
04:44 and features like quantum chaos and so on , is
04:47 a model proposed by uh severe that such a week
04:51 I have model which uh has uh has been a
04:57 very uh very uh important model in that it is
05:02 solvable and it's you're able to actually see many features
05:06 which are otherwise normally , which would be out of
05:10 reach uh , to uh , to a sort of
05:13 analytical understanding . And so this has influenced things of
05:17 course , in condensed matter physics , but as I
05:19 said , the ideas have flown the other way .
05:22 So it's very unique to have someone who's sort of
05:25 taken ideas from string theory to subject at first very
05:29 far removed , like condensed matter physics and vice versa
05:33 , head in the flow in the other direction as
05:37 well . So , uh , so this this is
05:40 part of the reason why I think Siberia is uh
05:43 and at the heart of a lot of this is
05:45 the is the phenomenon of quantum entanglement uh which he
05:51 will take us through today . And uh , so
05:54 , uh , but before , before I hand over
05:58 to severe , uh , I just want to mention
06:02 of course uh CTS fundraising thanks to all who could
06:07 contribute to our annual fundraising and you can continue to
06:11 help uh as we build our I . C .
06:14 T . S . Endowment . And a very important
06:17 way in which you can help our efforts . Especially
06:19 now with these with this lockdown is to connect us
06:24 , connect me with potential supporters and val vicious anywhere
06:28 across the world and of course spread the word amongst
06:31 your circles uh for people who might want to be
06:35 engaged with I . C . T . S .
06:36 Uh So thank you again for all your support and
06:40 for showing up at such a critical moment . But
06:44 I hope you will find it uh nevertheless accelerating .
06:48 So uh so the pilot onto the pilot service for
06:53 the journey ? Yeah . Okay . I hope you
06:57 can hear me and see my screen and see the
07:01 yellow green circle . That's all right rajesh . Yes
07:04 . Yes . Okay . Well thank you very much
07:07 strategies for that . Very , very kind introduction .
07:11 Uh , I must say I should also say a
07:14 few words about the incredible work that you rajesh and
07:19 also spent a warrior have been doing . And uh
07:23 , uh , not only doing high quality physics ,
07:26 uh , in India , but also at the same
07:28 time building this incredible institution CTS , which I I
07:32 love to visit partly because it's it's the town that
07:36 I went to school in Bangalore . Uh , and
07:41 I hope the situation in Bangla is going to improve
07:43 soon . And uh , I look forward to my
07:45 next visit to see you . Okay . So ,
07:50 so I'm really flattered to be asked to talk on
07:52 big questions . That's not the way I approach my
07:55 research . Normally I just think about some tiny little
07:58 question and then maybe later on it has something back
08:01 in some other question . But so I started ,
08:04 you know , thinking about how to phrase how to
08:07 present some of the things I've been working on ,
08:10 some big context . So I'm going to go really
08:12 big inspired by rajesh . So forgive the , you
08:16 know , the reach . But anyway , I think
08:17 it be found anywhere to connect this up too ,
08:20 other big questions in the history of physics . So
08:24 let me begin , uh , by , by Newton
08:27 . So we've all heard of uh , in high
08:29 school and the Newton's laws of motion . Well ,
08:32 they were probably not due to him . I think
08:35 most of them are understood before what we learned in
08:37 high school . But what was really new to Newton
08:40 was something uh , also something more remarkable . What
08:46 do you show for the first time that the same
08:48 laws of motion apply to the planets on planetary scales
08:54 , which is about a trillion meters . That's the
08:57 , roughly the size of the solar system . Uh
09:00 , as they applied , you know , two apples
09:02 falling on earth exactly the same laws . The laws
09:07 were exactly the same . You could by computing the
09:09 motion of the planets , uh , then reduce how
09:13 fast an approval for . And this was really a
09:16 very big thing . It was really the first time
09:18 that , that , you know , people understood that
09:23 what's happening in the heavens , it's also what's happening
09:25 on the Earth . It's the same , it's the
09:26 same laws . Uh , and so newton scan ,
09:30 very vast distance scale , from Julian meters , uh
09:35 , to about a meter . And of course ,
09:38 and everything in between . And as far as people
09:41 learned over the next 200 years , everything worked perfectly
09:45 . So , in some sense , Newton has ,
09:47 some people thought , you know , that was the
09:49 end of physics . What else is there to do
09:52 ? Of course , that's not true at all .
09:54 Uh and you can say the physics in the ,
09:57 you know , the 20th century and the 21st century
10:00 is about extending the reach of this range , or
10:05 to even larger scales and smaller scales . And and
10:10 that's kind of what I'm gonna try to do today
10:12 , just quickly . Uh so let's keep going to
10:15 even smaller and smaller scales from an apple to a
10:19 dust particle to even smaller scales , uh , grains
10:25 of pollen . People could see that things worked exactly
10:28 the same . Newton's laws were still okay Up until
10:32 around the early 1900s , when people started to understand
10:37 that in fact , mutants didn't apply at a scale
10:41 , which is around 10 to 3 to minus 10
10:44 m , 1/10 of a nanometer , uh , which
10:48 is the size of a hydrogen . And so in
10:50 a hydrogen atom , you have an electron uh in
10:55 in the right to food picture going around like a
10:58 planet around the nucleus , which is positively charged proton
11:03 . Um And initially people started to apply newton's laws
11:06 of motion to this electron also , but it became
11:10 very clear , especially , you know , from observations
11:15 that I won't have time to go through , that
11:17 this simply did not work . Uh So there was
11:20 just again , a plethora of observations started with the
11:23 so called black , black black body spectrum and various
11:27 measures of spectra of atoms and so on and so
11:31 forth . Uh And then uh you would say there
11:34 was a big event , almost as big as Newton's
11:37 discovery of the universal law of gravitation , Which was
11:42 the discovery of the quantum theory uh by shorting and
11:45 Heisenberg in 1925 . So there was a new theory
11:49 which could describe perfectly uh we know today not just
11:53 the structure of a single heritage and item , but
11:55 partisan molecules , you know big molecules D . N
11:59 . A . And so on . So and even
12:02 big crystal and solids as we talk about nature .
12:06 So and this theory initially seemed like a small deviation
12:10 some correction to nutrients framework . But soon it became
12:14 clear that it was something much more radical . Introduced
12:18 a whole new idea into physics and into our theory
12:21 of the universe that didn't exist at all in the
12:25 new Newtonian formulation . And this is the idea of
12:29 the principle of superposition . So I'm sure most of
12:33 you've heard about the famous cat which is both dead
12:36 and alive . That's of course just uh you know
12:40 nobody's ever achieved that uh would be very very difficult
12:44 to have such a proposition of a life can that
12:47 cat ? But it just makes the basic point which
12:51 can be achieved in uh in much smaller objects ,
12:54 is that you could have a physical system which is
12:57 in two distinct states , for example , an electron
13:01 , uh , you know , at one position and
13:03 in a different position , you could make a state
13:07 of the electron , which is in fact in both
13:10 states at the same time . So you can superimpose
13:13 , you can take two distinct physical states and make
13:17 another state , which is the sum or difference of
13:19 them are actually more any linear combination and add and
13:23 subtract states . So that's really the if you when
13:26 you when you dig down into what's going on in
13:28 the quantum theory , it took a few years to
13:31 appreciate this . That's really what the heart of everything
13:36 , the principle of superposition . Uh So once people
13:41 understood this , you can now ask the converse question
13:44 . Now , we've gone on to very small scales
13:45 and you've discovered this principle . Uh no , let's
13:49 go back up and scale things up , not just
13:52 up to a cat all the way to the solar
13:55 system and even beyond it , is this still apply
14:00 ? Uh So the short answer is there , as
14:02 far as we know today , the answer is yes
14:04 . And I'll try to give you some flavor of
14:07 the type of questions people have been addressing uh to
14:10 to to go from the small to the large now
14:13 . Um All right , so let's just take that
14:17 one step at a time . So here I'm going
14:19 to take two electrons , not one electron . Uh
14:22 So the very simple picture of a hydrogen atom is
14:25 an electron that's orbiting around uh the item , but
14:28 it also spin on spins on its own axis .
14:31 Uh And it turns out the spin is a very
14:35 simple object corner mechanically . Uh So quickly summarize by
14:40 saying that the electron can only spin clockwise or anti
14:44 clockwise . So there's two possible states of the spin
14:46 of the electron , let's say the alphabet represented spinning
14:50 anti clockwise counterclockwise and the down arrow representing spinning clockwise
14:57 . Okay , so now let's take two electrons ,
15:00 as you'll find in the hydrogen molecules with these two
15:02 protons and two electrons . A very simple description uh
15:08 of the state of every hydrogen molecule that's out there
15:13 is this particular state . Uh And this state is
15:17 a superposition now again for in principle of to physically
15:20 distinct states . And the state on the left uh
15:24 is an electron that spending the first electron on the
15:27 left adam is fitting . That's a counterclockwise and the
15:31 electron on the right items spinning clockwise . But there
15:35 is another distinct state . But the electron on the
15:38 left adam is spinning clockwise and the one on the
15:41 right edge and spinning counterclockwise . So these are two
15:44 distinct states . And you know , in principle ,
15:46 if I could do a clever enough experiment , I
15:49 could go in and measure which direction is this electron
15:52 spinning . Uh And you know , I could either
15:56 see a clockwise or counterclockwise electron . But the actual
16:00 state of the electron is the superposition of these two
16:04 distinct states . It's really in both at the time
16:07 and until you look at it , you don't know
16:10 which one is it ? It's really involved . Uh
16:13 Okay , so but you do have something strange emerging
16:17 here , which is the start of what we call
16:19 entanglement . If you measure this electron and you find
16:23 that it's that is up or counterclockwise , then the
16:28 other one necessarily is clockwise . So there is a
16:35 perfect correlation between the orientations , but you can't tell
16:39 which one of which one is up and which one
16:41 is done , but you're sure that one is up
16:43 , the other star . And it's only the act
16:45 of measurement that determines which is which . Alright ,
16:49 so that's you know , now the same idea of
16:51 superposition already started trying to starting a song . Very
16:55 , very strange in for a single molecule . But
17:00 this is no question that this is what happens .
17:03 Ah So the world corn of entanglement is a modern
17:07 world . I'm not sure exactly what it entered our
17:10 lexicon , but this paper were Einstein , Podolski and
17:13 Rosen . I don't think they use it in this
17:15 paper either , but they put their they really pointed
17:19 out the essence and the mystery of entanglement . So
17:23 one way to state their argument is , imagine you
17:26 have this uh hydrogen molecule and you do a very
17:30 clever experiment where you separate the two atoms and their
17:35 electrons without disturbing them without disturbing the spin in particular
17:39 . That's very hard to do . But imagine you
17:41 could do it in principle , you can do that
17:44 . And this particular adam put the , you know
17:46 , with me in boston and principal and the other
17:48 one would be in Bangalore . Ah The corner mechanics
17:52 would say that they're still entangled , that they're still
17:56 correlated . Uh And nobody knows whether the electron and
18:00 electron in Bangalore Is up and the one in Boston
18:04 is down or vice versa . In fact , it's
18:06 not even determined . It it's only the act of
18:10 measurement which will because of the way you perturb the
18:13 system . This is kind of like the uncertainty principle
18:16 in action that will determine which is open , which
18:19 is down . So it could be this way or
18:22 that way we don't know , they're still entangled .
18:25 Uh And it's only the measurement of an electron which
18:28 determines the state of the other electron . So this
18:33 is something that in fact E . P . R
18:35 . Found unacceptable . And they pretty much said in
18:38 the title of the paper , something is wrong with
18:40 . Quantum mechanics are incomplete . Is a precise where
18:43 they use this can't possibly be the case . Uh
18:47 The theory is bizarre and it seemed like you know
18:53 , something was traveling instantaneously from boston to Bangor .
18:57 Okay , so the answer is this is in fact
19:00 what happens uh Nothing is traveling instantaneously . The concept
19:05 we have to then accept is that the entanglement or
19:09 the concept of a quantum state is not a local
19:11 concept and the state is not neither in boston northern
19:15 dangle or it's it's really in both places . Uh
19:18 That's really one of the radical ideas that comes out
19:22 of quantum mechanics . Um Okay So now today of
19:26 course there's almost 1935 . Like this is an article
19:30 in New York Times , uh talking about an experiment
19:34 number two electrons , but two photons to be uh
19:38 little lumps of light , 1.3 kilometers apart where they
19:42 did indeed say this , this this does happen .
19:44 And that I think uh now , five years later
19:48 there's much even longer scales . Much better experiments showing
19:52 what people say , spooky action . Einstein called spooky
19:56 action . But again , uh that's a pocket .
19:59 So I don't think you ever use those words ,
20:00 but anyway , All right , so that's then a
20:06 description of entanglement . Uh just two particles in this
20:12 . Even in this experiment , we're talking about two
20:13 particles on the very small scale . So let me
20:18 know , change gears completely and go back . Actually
20:23 , strictly speaking , very , very heavy . We
20:25 were talking about single electrons , let's go to very
20:28 , very heavy objects black holes . So , a
20:34 black hole , it's it's so heavy that is full
20:38 of gravitation , is so strong that if some adam
20:41 inside the black hole emitted a being of light ,
20:44 the light would start to escape the black hole ,
20:47 but then would be pulled back and would never be
20:49 able to go . Uh So there's a horizon beyond
20:54 which uh no , like whatever ever escaped from the
20:58 inside of a black hole , because the gravity of
21:00 photo gravity is so strong , okay . Um and
21:05 and this the existence of black holes and many of
21:08 the properties was really came about from Einstein's theory of
21:11 general relativity , 1918 . Uh and that's before the
21:17 invention of the quantum theory in 1925 . Uh And
21:21 and , you know , it was also , it's
21:23 an amazing theory , but one thing to keep in
21:26 mind , it is not as radical departure from Newton's
21:29 equations as the core . In theory , it can
21:32 be viewed as some kind of correction uh to Newton's
21:35 equations , when things move really fast near the velocity
21:39 of light . Uh it's really the same Newtonian framework
21:43 except you have to uh you know , okay ,
21:46 you have to think about curvature of space time ,
21:50 but still within the its evolution , natural evolutionary mutant
21:54 . It's not a radical departure like Volunteer was .
21:58 Uh so in particular , Einstein's theory would give you
22:01 this radius of horizon for a mass , M .
22:04 G is Newton's constant and see as the velocity of
22:06 light . This is the only equation I really use
22:10 uh if you plug in here , earth mass ,
22:13 you get a radius of nine millimeters . So that's
22:16 how dense you have to make things you predict the
22:18 whole Earth and squeeze it down to nine millimeters for
22:21 the earth to become a black hole . uh so
22:24 this was thought to be completely ridiculous uh in the
22:27 1920s and 30s and much later , but today we
22:31 know there's lots and lots of black holes out there
22:34 . So now they're going really big . Uh this
22:36 is a picture that actually my wife Lucia pointed out
22:39 to me in the popular press recently Showing 25,000 miracles
22:45 , supermassive black holes . Uh These are black holes
22:48 are a million to a billion times the mass of
22:51 our sun . And each one of these dots represents
22:55 a supermassive black hole at the center of its own
22:59 galaxy . So we can't see the galaxy in this
23:01 particular view because of the frequency at which they're looking
23:05 at it . Uh And each black hole is about
23:09 10 times larger than a son . Uh and it's
23:12 at the center of its own galaxy . In fact
23:14 , it's almost as bright as the rest of the
23:16 galaxy , and including our own galaxy has such a
23:18 huge black hole at the center of it . All
23:23 right , so , now I've told you about the
23:24 Newtonian Einstein theory of black holes and how they're out
23:28 there . And everything in these and similar observations agrees
23:33 with the predictions of Einstein's theory , but Phyllis being
23:37 Phyllis is they don't stop with just uh you know
23:40 , what's what's possible , They've got what's been done
23:43 the time to think of what could be possible .
23:45 So , so we developed this theory of the very
23:47 small the quantum theory . Uh and so like Newton
23:51 , they're going to try to scale it up all
23:53 the way to black holes . And as is there
23:56 any effect of the quantum theory on black holes ,
23:59 Is it going to change anything ? Um And this
24:02 step was really first taken by Stephen Hawking in a
24:06 sense , that was his most important contribution . Uh
24:10 and one way to understand what he did , although
24:12 he didn't phrase it in these terms , is to
24:14 take again take a pair of entangled electrons and imagine
24:19 that somehow you can separate them , we're putting one
24:23 inside a black hole and the other outside of that
24:26 . Then the quantum theory would say that they're still
24:29 they're still entangled . There's no uh just because you're
24:33 , one is inside and outside the black hole ,
24:35 it doesn't matter as long as you didn't disturb the
24:37 spin , they're still intact uh and vice versa .
24:43 So , so that's again very bizarre . And one
24:46 of the consequences of this was that black holes turned
24:51 out , okay , this I've already said this quantum
24:54 entanglement between the inside and the outside of black hole
24:57 and a consequence of this entanglement um is that black
25:01 holes actually have a temperature ? Uh They're not just
25:06 disquiet isn't uh body out of it , nothing can
25:09 ever escape . They're ready very , very slowly and
25:13 very low temperature , uh you know , light and
25:17 energy and small particles ah and what hawking computed not
25:23 buy this argument with some related argument that what the
25:28 temperature of every black holders and we call it ,
25:30 of course , the hugging temperature . Well from the
25:33 entanglement point of view , you can understand this in
25:36 the following manner . Say I'm outside the black hole
25:39 and I have uh this electron with me . Uh
25:45 you know , it's entangled with the other electron which
25:47 is inside the black hole , but there's no possible
25:51 way I can never figure out over any conceivable time
25:54 uh until the black totally evaporates when we're not going
25:58 to wait that long . What's happening to this one
26:00 ? So that black , that other electron is just
26:04 totally gone . It's beyond the horizon , It's inside
26:08 the horizon . So for me , this electron is
26:11 really not entangled with anybody . Uh it's totally random
26:15 and randomness , you know , is the essence of
26:17 temperature and entropy . That's how things become hard and
26:21 become random . So this electron seems like a hard
26:23 electron to me . And that's roughly how you can
26:27 understand the existence of black hole . All right ,
26:32 so this is one of the I think uh this
26:35 is hawking is really greatest discovery um that the corn
26:39 um theory from the very , very small applied to
26:42 the very , very big does have some consequences ,
26:45 although in this case the consequences so far are so
26:47 weak that there hasn't been any experiment detecting this consequence
26:51 . But who knows in the future it could well
26:53 be . Uh All right . So now I want
26:57 to uh you know , try to connect the small
27:00 and the big with this entanglement a bit bit more
27:04 so Hawking had of course a very brilliant advance ,
27:06 but it was short of a complete theory . Many
27:10 questions it opened up as many questions uh as it
27:14 answered . Uh you couldn't really tell , you know
27:17 exactly how information will be preserved as a black hole
27:20 started radiating away and evaporating uh and what happened when
27:25 it became really small . So there are many many
27:27 complicated questions Hawking's theory raised , which I think the
27:34 community has been a lot of progress on . But
27:35 it's still , I would say there's still many ,
27:37 many open questions uh starting , you know , even
27:41 though there's an enormous amount of work since how things
27:44 work . Uh and part of the reason is so
27:47 difficult is that having a complete theory of a black
27:51 hole of entanglement on the scale of a black hole
27:55 is that we have to consider not just to particle
27:57 entanglement , as I'm stanford all skin rosen talked about
28:01 , but multi particle entangled but entanglement for essentially infinite
28:05 number of particles , all of the particles making up
28:08 a black hole . We have to figure out some
28:10 general theory of how they entangled with each other and
28:14 there's really no such plate theory . Uh But this
28:21 problem of multi particle entanglement for over in the last
28:25 , I would say 20 years or so , over
28:26 30 years and started to appear in other branches of
28:29 physics , which are closer to branches that I work
28:32 on . Many of you may heard about kind of
28:35 computers and in some ways that is what point of
28:38 the building is . It's the way it's a way
28:41 of controlling the entanglement of many particles . Computer scientific
28:45 , all 10 cubits . Uh in a way that
28:47 you could prepare something useful . But controlling entanglement is
28:51 extremely hard because you have to really separate those degrees
28:55 of freedom from everything around them from the environment .
28:59 Uh And and that's really , you know , the
29:01 challenge that the whole thing is facing , whether they'll
29:04 be able to overcome that and uh they're making small
29:09 steps towards that direction . But I would say a
29:11 long way from having some useful calling computer at this
29:15 morning . Ah And finally another place where multi particle
29:20 entanglement appears is in the study of certain materials .
29:25 Sometimes we call them corner materials . These are crystals
29:29 with multiple elements which were on their own display phases
29:33 with multi electron and time when you just make the
29:35 crystal in the lab and the electrons turned out to
29:38 be entangled in some complicated way . Uh And then
29:42 you can study their properties and this is , this
29:45 is usually the world that I live in . So
29:48 here is a very famous example . It's made up
29:51 of these elementary tune barium copper oxide . Uh Here's
29:55 a picture of little pieces of the crystal is the
29:58 structure of the various atoms that repeat themselves in this
30:02 configuration to form a crystal like that . And it's
30:05 what's called a high temperature superconductor . Uh what you
30:10 mean by that is you could take this little uh
30:13 little palette of peroxide uh and different in liquid nitrogen
30:19 . That's what's been done here to this talent here
30:22 and it's placed over a bunch of magnets . Uh
30:25 And then yes , I hope you can see the
30:27 movie . The rest of there's this uh superconducting magnet
30:31 floating over the honoring magnets . Uh and of course
30:37 it fell down because it's got hot once it gets
30:40 above about 100 Kelvin . Uh then then it no
30:44 longer super conducts . All right . So trying to
30:48 does this behavior was discovered around 1987 1988 , just
30:53 when I was starting my career as a physicist .
30:55 Uh , and I've been thinking about such materials ever
30:58 since . Uh , they show what we call the
31:01 phase diagram . This is here on the horizontal axis
31:05 , change the density of electrons in the crystal by
31:08 some clinical means . You're raising the temperature and here's
31:12 the superconductor that I just showed you . But most
31:16 interesting is some regime here that people call the strange
31:19 metal . Strange . Well , because it's strange and
31:23 our current understanding and this strange metal is actually a
31:26 phase where there's complicated multi particle entanglement really at many
31:32 , essentially all scales , uh , in the crystal
31:36 . And that's why the metal behaves in such a
31:38 bizarre way . Okay , so , uh , so
31:43 that's uh , you know , the domain that I
31:46 mentioned here earlier of Corner Materials , where that's an
31:50 actual material which displays faces . A multi electronic entanglement
31:55 . So they are black holes . This Corner computers
31:58 , maybe someday with controlled entanglement here , we can't
32:01 control it , it does what it wants to do
32:03 . And we're trying to figure out what it's doing
32:05 in the corner materials . So , let me just
32:09 finish by mentioning uh the s like a model that
32:15 is frequently mentioned the beginning . Uh So , this
32:18 is a , you know , a model that I
32:22 cooked up in 1993 . Uh just trying to find
32:27 some model of multi particle entanglement from which you could
32:30 say something definite . So , it was really born
32:34 of desperation . I was trying to understand the the
32:38 strange metal phase and is still working on that .
32:41 Uh So we wanted to find some simple , simplest
32:45 model , but you can make some progress . Uh
32:49 and it turns out we're still discovering many features of
32:53 the ceasefire came out through uh and it has some
32:56 very interesting structure of entanglement , uh which is ,
32:59 in a sense , scaling variant uh and allows you
33:02 to go from a very small to the very big
33:05 . Uh so has a scaling variant diagnosed structure ,
33:09 electrons entangled really , mostly speaking at all distance and
33:13 time scales . And understanding how that happens in this
33:16 model has led to new insights on the physics of
33:20 strange metals . Uh and as Rogers also mentioned uh
33:24 these days and understanding the structure of black holes .
33:27 Okay , so , so what is the heart of
33:31 this uh disability for this simple model to describe such
33:36 very different systems , apart from the fact that it
33:38 involves entanglement ? Well , if you in the original
33:43 variables that you wrote in town , uh it's very
33:47 much motivated by what's happening in that crystal , how
33:51 the electrons are moving around . We try to make
33:53 a model of how the electrons moving around and got
33:55 a strange matter , but over the years , inspired
34:00 in particular by many developments in string theory , uh
34:05 the concept of duality has played an important role .
34:08 So you can take a new dual set of variables
34:12 . Uh so these are describing the same system ,
34:14 but in a very different way . And these dual
34:18 sort of variables in fact end up obeying equations which
34:22 are very similar . The equations of Einstein's , the
34:26 combination of Einstein's theory of general activity and for the
34:30 mechanics , and this has led to insights on a
34:33 certain class of black holes . Okay , so let
34:39 me just uh fortunately it turns out I can describe
34:42 it as like a model just in a few pictures
34:45 . It's really that simple . And so I'll close
34:48 with that , show you a picture of it .
34:50 Uh so what you do is you take a bunch
34:52 of positions uh placed randomly and then you put in
35:00 occupy some fraction of them with electrons . So here
35:03 each cripple dark represents an electron . I'm ignoring it
35:07 spin . So it just let me just imagine the
35:09 spins are all up . Um and you put a
35:13 hole bunch of them on these traps and now you
35:17 want the electrons to move around because of the uncertainty
35:21 principle . Uh they want to hop to other places
35:24 just naturally from corner mechanics . That's what you call
35:28 tunneling from one side to the other . Um So
35:32 the electrons , you want them to turn all around
35:34 now , if you just let them turn around as
35:37 they as they wish , Uh then you get a
35:42 metal . So that's been , you know , understood
35:43 for 50 years or even longer . Uh if you
35:46 take a bunch of random positions and allowed uh electrons
35:50 to move around , you get a metal , which
35:52 is not what we want to understand . We understand
35:55 metals extremely well . So what you have to do
35:59 is something just put a little twist , put a
36:01 little restrictions on how they can move . And the
36:04 restriction is that they move in pairs . That's it
36:08 . So , for example , this pair of electrons
36:10 can tunnel uh from here from these two sides to
36:16 these two sides . Now , the electrons are identical
36:20 particles . So you can't distinguish quantum mechanically between this
36:24 tunneling and this tunnel . It could be that this
36:27 one went here and that one went there . They
36:29 really both happened at the same time , effectively .
36:33 And so you can see that what this process leads
36:36 is an entanglement . It generates entanglement even though initially
36:40 it wasn't there . Uh huh . So these two
36:43 can hop around . And and that particular hopping happens
36:48 at some some rate , which depends on exactly the
36:51 environment you put these electrons in , uh and so
36:56 on . So you pick any two sides and you
36:57 allow them to pop that way . And for each
37:02 one of these pig processes , you attach a number
37:06 number roughly tells you often that particular event is going
37:11 to happen and these two let's move here to there
37:14 and in a real crystal , these processes happen .
37:17 And it's a very complicated process to figure out what
37:20 that number is that you're attached to each process .
37:23 Yeah , So our idea , it's ridiculous how simple
37:28 it was . It was to say , okay ,
37:30 I don't know what's happening . So to each of
37:33 these processes , just attach a random number , an
37:37 independent random number for every process . So everything that
37:40 can happen is allowed to happen and how often it
37:43 happens is ranked uh huh Amazingly . that gave really
37:48 the first sub model that you could work out completely
37:52 and understand now in great detail the structure of the
37:56 many particle entanglement . Once you allowed these amputees each
38:01 of these processes to have a random number associated .
38:05 Okay , uh so the pair there and each of
38:08 this entanglement is happening with the random aptitude is the
38:12 technical word that we use uh quantum mechanically . Okay
38:17 . Uh I think that's it . So , so
38:21 that's that's what the s like a model . It
38:23 is . It's really has entangled . I got all
38:25 the distances in all times and that allows you to
38:29 describe things that are in a little crystal all the
38:33 way up to black holes . And we're really learning
38:38 a lot these days by connecting the very small to
38:41 the very big , not only by the s like
38:44 a model , but also many other models , including
38:48 , and in particular , this duality that I mentioned
38:50 is something radishes . Uh It's a very brilliant contributions
38:54 recently , more in the context of string theory .
38:57 The duality between these two different ways of looking at
39:00 intact . So thank you Roger . Mhm Thanks a
39:05 lot severe for that , taking us through this vast
39:09 landscape in uh and giving us a glimpse of uh
39:14 one of the things that I think most strikes me
39:17 about these developments that you've been pioneering is the interconnectedness
39:22 of ideas and theoretical physics . How you cannot really
39:27 kind of put firewalls . So to say between different
39:30 areas , ideas , you have to let the ideas
39:34 move around in idea space and they find new homes
39:39 , they find new , remarkable ways . And and
39:42 each time you get these sort of when you view
39:45 things like when you start viewing black holes in terms
39:48 of strange metals , that's just completely mind blowing .
39:51 I mean that you can do that . I mean
39:54 they seem like completely pulls apart but that's I think
39:58 the remarkable thing about physics . Uh So uh so
40:04 please ask your questions about , you can ask on
40:09 the chat , you can unmute yourself and uh you
40:14 can ask , put up your hand and ask to
40:17 be in muted uh etcetera . So , so uh
40:23 let's uh and feel free to talk about , ask
40:28 about anything . As they say that you were afraid
40:31 to ask anything about quantum mechanics , that you were
40:34 always uh that you were very uh mystified by .
40:40 So as you can see the this structure of quantum
40:44 entanglement is is at the heart of a lot of
40:48 things . I think even some of these new materials
40:51 that should be mentioned that uh these are things that
40:55 are likely to sort of appear in our lifetime ,
40:58 uh things around us . I'm sure they are going
41:03 to revolutionized technology in the future . So there's a
41:09 question from sign they've about is the duality uh also
41:14 related to the small dissenters duality conjecture from string theory
41:19 . Uh Oh , yes , of course . Yeah
41:22 . So there's there's a duality in string theory is
41:25 sometimes called the dsc F . T duality , uh
41:28 which is , I think it's much more than a
41:31 conjecture today , especially different . Some of the work
41:34 by Rajesh recently , uh it's essentially proven that there's
41:39 a duality between uh uh well , what are called
41:43 informal field theories , So informal field theories are not
41:47 quite strange metals , they're similar , but there is
41:51 another form of matter that's not , doesn't occur in
41:54 the real , in the natural world that easily uh
41:57 with , with long range entanglement . So , Cook
42:01 . And so that's a duality between informal field theory
42:04 and black holes . The duality between the , so
42:08 I came out on black holes is a cousin of
42:10 that . Uh it doesn't have a formal field here
42:13 on one side . I'm exactly the same type and
42:18 yeah , okay . Uh it's in fact it's much
42:21 simpler version of it because it's essentially proven without doubt
42:26 by starting from either side . Uh and uh okay
42:31 , because yeah , the two are similar so now
42:37 , but I , you know , I will say
42:39 in that , although I was able to describe the
42:44 S . Y . K model in a few pictures
42:46 , you have to take a whole year of string
42:49 theory to understand informal field leaders . So it is
42:53 a lot lot simpler . So Roger Banerjee asked how
42:59 do two electrons decide to entangle uh in some sense
43:03 ? Uh uh when when how do they get entangled
43:08 or ? Yeah . Right . So , uh I
43:13 think so , these pictures that I showed were kind
43:17 of misleading . So let me share again . Ah
43:22 , I mean that's the best we can do .
43:24 Right . So I was uh , so you have
43:29 these electrons and I was sort of pretending that things
43:33 are evolving in time , but these electrons sit here
43:36 and then two of them move and the two of
43:38 the others move and so on . But really they're
43:43 all happening at the same time . So the time
43:45 evolution and the slides is totally fake . Uh there
43:51 there's a certain attitude for any pair of electrons to
43:54 entangle . So it's a number that you assigned at
43:58 some point . It depends on how far apart they
44:00 are . How , you know , what's the nature
44:03 of the interaction between them ? There's some electrical forces
44:06 that you have to worry about . So once ,
44:08 you know , all those forces , there's a certain
44:10 rate at which they were attacked . And that's true
44:14 for any pair of electrons in the set . And
44:17 what makes this uh you know , quantum problem is
44:19 all of that is happening at the same time .
44:21 It's not as if they're in , these two are
44:24 entangled and the other two are entangling . That's a
44:27 really a newtonian point of view , if you wish
44:30 , if that was the problem because all that very
44:32 easily you could just take write down some kind of
44:35 Markov chain and and just write down some probability distribution
44:39 of the electrons . That is not what happens .
44:42 They really all entangling together at the same time .
44:45 That's what makes multi particle entanglement really complicated . I
44:53 hope I answered that question . Shashi you body .
44:59 Uh by the way , I should mention to you
45:02 severe . Uh Shashi Central and I were all classmates
45:05 in the same year in Physics . Uh Center for
45:11 many of the I T . K . People on
45:13 the skull uh S . PhD but severe . So
45:16 uh uh can actually , well that was a very
45:21 distinguished I thi K class . Uh She asked why
45:27 is it so hard to achieve artificial entanglement in quantum
45:31 computers while easy to find it in natural systems like
45:35 eitC materials ? Uh Well it's because yeah , entanglement
45:44 is always hard to achieve if you want to achieve
45:47 a certain type of the time . So in the
45:50 high dc materials we're just they achieve some sort of
45:54 entanglement which depends on all kinds of details of their
45:57 structure . And we're just trying to figure it out
46:00 , we're trying to measure what's there if you wanted
46:02 to change it and control it to something that we
46:04 want that's extremely hard and that's really what we want
46:08 to do in upon a computer . You know ,
46:10 you know , it just studying the entire movement that
46:13 happens to be there . Uh , you want to
46:15 make your own entanglement in a way that does something
46:18 useful for you , uh , in the sense of
46:20 computing something . And to do that , you really
46:23 have to take each each electron and control its entanglement
46:29 very precisely . Uh , and so , you know
46:33 , people have all kinds of ingenious ideas and what
46:35 to do that almost certainly going to make errors .
46:38 So you have to have quite America correction . And
46:42 the current status of things . Is that Even for
46:45 a single electron , No 1s , I made a
46:49 fully what's called a fault tolerant a bit actually ,
46:54 you know , they could correct its own entanglement by
46:57 by by some error correction method . So that's a
47:00 very , very challenging problem . But okay , people
47:03 have all kinds of creative ideas and how that will
47:06 move forward . I mean , my my own view
47:08 is that , you know , it's sort of like
47:10 going to the moon . It's it's a very nice
47:12 goal to go to have , you know , people's
47:15 colonies on the moon or something like that . But
47:17 along the way , we're going to discover all kinds
47:19 of amazing things and useful things . And I'm sure
47:23 that's what's going to happen on a computer is nobody
47:25 knows what they're actually going to be useful for .
47:28 I doubt they're going to be useful for , you
47:30 know , fact arising big numbers , which is sort
47:32 of like going to the moon . Uh , but
47:36 there are many other things are going to mars ,
47:38 I should say . Yeah , Okay , that's a
47:42 personal point of view . Many , many of my
47:44 closest friends in my department to disagree with me ,
47:47 but okay , okay , jesse muted . Uh ,
47:55 yeah . On the subject of entanglement , uh ,
47:58 wife , uh , says you've piqued our curiosity .
48:03 Do you have an explanation of what results an entangled
48:06 state , meaning ? What's an observation that causes the
48:10 cat to choose whether it's alive or dead ? I
48:13 guess the wave function collapse . Does that that's still
48:19 the mysterious issue that ? Well , I mean ,
48:22 so the cat and it depends what you mean by
48:24 the cat . The cat itself , you know ,
48:26 just the air molecules . So the cat is breathing
48:29 . Uh , as a cat breeds the air molecules
48:32 , those air molecules are entangling with the cat .
48:35 Uh , so that , in a sense that in
48:38 a sense , will break , you know , so
48:41 if you try to make a superposition of life and
48:43 death cab , you have to get rid of all
48:45 the air and that will kill the cat . Anyway
48:47 , so you really have to totally isolated . Uh
48:52 , and so that , you know , that's just
48:54 a picture that people like to make . I think
48:57 people have made what they call cat states of maybe
49:01 100 electrons in a very controlled environment in a very
49:05 cold system Where there is essentially no air , nothing
49:10 is an ultra high vacuum uh and under certain conditions
49:14 and you can make a cat states , but you
49:16 know , 700 electrons where all electrons are up and
49:21 the dead cat is all electrons are dull . So
49:24 that's what people call a cat steak . Uh But
49:29 you know , I I I still wanted to show
49:31 the picture because then everybody knows what I'm trying to
49:34 say . Uh huh . But I guess the question
49:38 of the collapse of the wave function is still whatever
49:42 was 100 years ago . Right . I mean ,
49:45 that's not something we have . Uh even , Well
49:49 , I would say , I think one view is
49:51 that the collapse of the very function itself is entanglement
49:54 . So when I look at something yeah , my
49:57 brain , I have been entangled with what I'm looking
49:59 at and and since I've entangled with what I'm looking
50:02 at , I'm going to see what I'm entangled with
50:05 , which is one of those things . But this
50:07 raises the philosophical question more about the other me ,
50:10 which saw the other part of the State . Well
50:11 , I don't know what to do about that because
50:14 that's not something that I'm observing , you know ,
50:18 that gets us into many worlds and so on .
50:20 Right by the way , there's a very interesting graphic
50:23 comic . I was recommending to Seville's wife last time
50:27 we met , I think it's called totally Random and
50:31 it's by I think Geoffrey bob and his uh and
50:36 I think his wife who was the illustrator . But
50:38 it's a graphic novel , you can find it on
50:40 amazon and it explores many of these ideas in a
50:44 very fun way meant for non technical uh audience .
50:49 So Vineet Gupta as quantum entanglement can be used to
50:54 teleport particles . Is this something that can be used
50:58 to transmit information across long distances ? Uh I guess
51:02 it's not more about quantum and I love that ,
51:06 correct . So you can the quantum teleportation uh you
51:10 know what uh telephoning actual matter uh for the for
51:15 the second part of the question is the correct way
51:17 to say uh you're really sending part of information .
51:21 So if you have a court of state here ,
51:23 you know , if I have an electron sitting here
51:26 and it's in some superposition state is both up and
51:29 down and I don't know exactly what kind of state
51:33 had said , and if I look at it um
51:36 I will uh I will see it either up or
51:40 down and I'll destroy the state just by the act
51:42 of looking at it . But what I can do
51:45 by a very clever protocol without that , I can
51:48 take my electron in a certain state . And it's
51:51 important that I don't know what state it's in .
51:53 I can still send it to from here to Bangalore
51:56 in principle . So that the person uh in Bangalore
52:01 has the same state . The electron in Bangalore has
52:04 the same state that I had here . No electron
52:07 has moved . I could send the information by a
52:09 beam of light or so . Well actually not even
52:11 been back . What requires is that , you know
52:16 , you take this pair , the CpR pair that
52:19 I showed you and you know , so I have
52:22 to go to Bangla or you have to create an
52:24 if you are a pair then I have to come
52:26 back to boston carrying my half of our affair .
52:29 And the person in Bangladesh has the other half .
52:32 So we met for a while . We share this
52:35 if you are there and then I can bring in
52:38 another electron over here and send the information on this
52:41 electron without knowing exactly what states and all the way
52:45 to bang law . And I can be confident that
52:47 Roger stone has the same state that I had before
52:50 in his electron over there . That's what teleportation is
52:54 about . Uh it's not magic . You have to
52:58 have some contacts in the past where you share entanglement
53:03 and then you can use that in the future to
53:05 send one of information . Yeah , yeah . That's
53:08 why it doesn't violate relativity as unit was uh wondering
53:13 . Yeah . Uh so uh annan Rajaram and asked
53:16 once a pair of electrons are entangled , do they
53:19 remain entangled forever ? Or is there a probability that
53:23 they disentangle ? Uh huh . Uh great question .
53:29 Yes , they they can disentangle . I mean you
53:33 have to bring in some other electrons uh and with
53:36 the right sort of interaction , you can disentangle them
53:38 and transfer the entitlement to the other one . Quantum
53:41 teleportation does something like that . Yeah . Yeah .
53:47 Uh this uh from Youtube , there's a question by
53:51 Pierre Luc are different . Strange mental states are always
53:56 distinguishable by scattering experiments . Well , that's a great
54:03 question . Uh I think I would say we're still
54:09 in the process of classifying the different possibilities for strange
54:12 metals . There are many different materials that show strength
54:15 metals . There are similar and different uh to each
54:18 other , but some of the details of different the
54:20 temperature range of which exist and their response to various
54:25 spectral probes is different . Uh And they are curious
54:31 for many of them , although that's still , you
54:33 know , subject of active research . Uh And those
54:38 are also , you know , the theories are similar
54:41 to each other and similar in some ways to get
54:43 us like a model also . Uh But we still
54:46 don't have a full , you know what I would
54:48 say , a definitive classification of strange metals . And
54:51 and and you know , the full taxonomy of this
54:53 , these are the five different kinds and uh this
54:57 is what you'll find this material and that you'll find
54:59 other material . Uh My hope is to reach that
55:02 maybe someday . Uh That's been the goal of my
55:06 research for a while . Yeah . So uh is
55:12 there a there's a question what there's a question probably
55:16 that needs maybe some uh clarification what forces involved in
55:22 quantum entanglement ? Yeah , I guess that's there's no
55:25 real force . Yeah . But uh yeah , I
55:29 mean , I would say it's sort of like ,
55:31 let's go back Newton's laws . So Newton's laws have
55:34 kind of two components . Uh one is force equals
55:38 mass times acceleration . And the other is that the
55:43 force of gravity is G . M . One M
55:46 two Harar square . So the forces gravity uh what
55:49 we call the Kinnah Matic part , which is ethical
55:53 that made it applies to any force ethical , then
55:55 they would apply to gravitational forces . Electrical forces in
55:59 principle also the strong and weak forces , if you
56:02 could find them in the right to jane . Um
56:05 So there's the actual force of many different forces in
56:09 the strange metals that I deal with . It's mostly
56:11 almost all electrical forces . Uh But then there is
56:16 a kin dramatic part which tells you how does the
56:19 position and momentum of the particle respond to a certain
56:22 force ? Uh And and that's what quantum mechanics tells
56:28 us . It's independent of what particular force using it
56:32 . It's a statement of the evolution of the quantum
56:34 state for any any force . And I what was
56:40 the precise question ? I think I forgot . I
56:43 think I answered the question . Yeah . So that's
56:49 a sort of a general question from again hurts .
56:54 Do you find yourself making connections of drawing analogy between
56:58 phenomena and physics with other areas of life such as
57:03 philosophy , art or human behavior ? A great question
57:09 . I try to avoid that . You know ,
57:12 I think I think I leave the philosophy that the
57:15 philosophers and uh you know , you could say we
57:20 have very narrow point of view . I mean the
57:22 people who make connections between the duality and the concept
57:26 of duality in religion and philosophy . I uh there
57:31 may be I know at some level , but I
57:34 know that Mhm . It's hard to phrase the connection
57:38 in scientific terms , which will actually influence some of
57:42 the things I was thinking about my work . Uh
57:46 But uh yeah , I guess what I would say
57:51 is that uh huh the reality of quantum theory uh
57:56 if you want a more philosophical point of view ,
57:59 uh so you know , and these black holes ,
58:02 the , you know , the supermassive black holes ,
58:04 Galaxies and the electrons and uh it's so incredible and
58:10 so unbelievable that even the most fantastic stories of origin
58:14 and religion don't come to the actual close to the
58:16 truth . It's much more fantastic than anybody even humans
58:20 ever imagined . Uh All the stories of creation are
58:26 just a weak imitation of the actual reality . Okay
58:33 , that sounds really just I'm going to get Yeah
58:37 , but I mean , narrowing things a bit in
58:41 across different areas of physics . Uh I mean ,
58:45 how do you find yourself sort of uh thinking about
58:49 something like black holes which was so far away from
58:53 your original uh interest ? How do you find yourself
59:00 thinking about uh making these connections ? Or is that
59:06 sort of organic ? Or is it uh is it
59:09 something you kind of uh when you're when you're hearing
59:12 talks from other areas do you make ? Yeah ,
59:16 try to make the connections . Uh Yeah , I
59:22 mean I guess it uh taking back to my own
59:26 uh progress on some of these topics , I mean
59:29 in almost all cases I've been just focused on a
59:32 very narrow what seems like a very narrow question .
59:34 Uh But I you know , try to really understand
59:38 it well and not accept the easy answer and you
59:43 write a paper and then move on to something else
59:45 . You really want to dive into the depth of
59:48 it and start wow trying to make progress and then
59:53 and while you're working this question you kind of be
59:58 open to what else is going on . You know
59:59 , go to lots of seminars in different fields and
60:02 just been listening . Uh and then you know ,
60:05 where the conference is talking to people and then every
60:07 now and then suddenly somebody will say something that will
60:10 legal connection . That's typically the way it's happened for
60:14 me . It's not that I'm sitting in my chair
60:16 and trying to think big thoughts . Usually you're ,
60:18 you're trying to think those little thoughts and and hopefully
60:21 some connection gets made someday . Yeah . Okay .
60:26 Yeah . So an androgen ramen uh what is your
60:30 prediction for ? How long before we see the first
60:33 practical applications of quantum computing ? Will it be in
60:36 our lifetimes ? I would say , you know ,
60:40 define practical uh you know , uh I would say
60:47 within a day , All right , I have a
60:49 lot of friends in this field and you know what
60:51 I say , they'll get upset at me , but
60:54 I got to say what I want . I would
60:56 say now , lifetime maybe . Uh you know ,
61:01 we'll understand more about the structure of matter and structure
61:04 of complicated quantum mechanics uh in in the kind of
61:08 materials I was telling you about are more complicated molecules
61:13 that are important in chemical reactions . Uh so ,
61:17 so there's a , you know , you know ,
61:22 sort of , you know , ordinary computers , classical
61:25 computers that I have found it very , very difficult
61:27 to factories large numbers . And that's one of the
61:30 problems that we hope one of computers that solve .
61:32 But there are other problems that are very , very
61:34 difficult for ordinary computers . And this is like computing
61:37 for McCain's computing the effects of quantum entanglement on physical
61:42 properties of a certain crystal or of a certain set
61:45 certain big molecules . We can't compute it very accurately
61:49 by an ordinary computer because it's uh it's impossibly hard
61:54 uh for reasons I won't go into , but quantum
61:58 computers can simulate some of this . Uh and I
62:03 think so , these quantum simulation task as they fall
62:06 , that's looking , you know , very reachable in
62:09 the neutral in the near term Minnick , you know
62:13 , in the lifetime . I have left as a
62:14 researcher , I think there will be real progress there
62:19 and there's already quite a bit of exciting work in
62:21 that direction even in the last few months . Uh
62:26 and will that have some practical impact ? But ,
62:29 you know , it's hard to tell . I I
62:31 think I think eventually it will . I mean ,
62:33 if you go back and look at , you know
62:36 , of course , the big story we always like
62:38 to tell the development of transistor and the laser and
62:40 how it launched the electronic revolution that all came from
62:44 advances in quantum physics and understanding uh behavior at corner
62:50 behavior of electrons in materials . And I think there's
62:52 a but you're likely another frontier in that direction that
62:57 could well open up . So so I wouldn't worry
63:02 about , you know , R . S . A
63:05 . Being uh suddenly not not safe . I'm not
63:09 worried about that in my lifetime . But I think
63:11 there could be many other benefits of quantum computing .
63:16 I mean , do you have I mean there are
63:19 many different kinds of approaches people take to building quantum
63:23 computers using superconducting cubits . Or maybe even uh then
63:28 there of course there are the ideas of using topological
63:31 lee protected states . Uh So do you think that
63:35 some of the I mean in some sense , progress
63:38 in understanding uh So do you think like this technologically
63:43 protected states they seem attractive on paper that uh that
63:47 you are kind of protecting that entanglement that you talked
63:50 about in some very rigid paul anthropology ? Do you
63:55 think something like that could eventually materialised ? I think
63:59 so far people are struggling if I'm not mistaken uh
64:03 to realize something like that . Yeah . So so
64:08 my okay . Uh my own view is that the
64:12 topological way of doing things is really the only way
64:17 that will eventually succeed if at all . I think
64:20 the people trying to apology which is the Microsoft group
64:23 uh then what they seem to be much further behind
64:27 right now from google or intel or any of the
64:31 other people using other methods . But the other methods
64:35 , uh you know , they they really are what
64:39 I would say is doing corn and computer science rather
64:42 than one of physics . They're trying to take ideas
64:45 from computer science and how you correct errors and implementing
64:48 them in a series of gate operations . And yeah
64:52 , once you have a whole bunch of sequences of
64:55 data operations , I'm skeptical that the corn and computer
64:58 science model of the real world is actually going to
65:00 work . Once you get a very large number of
65:02 it's okay . That that's a minority point of view
65:05 , I should say . But that's my opinion .
65:07 Uh , there are a few friends of mine who
65:09 would agree with me , I think I would say
65:11 . Uh , but topological way of doing things in
65:16 some ways what they're doing when we're saying it is
65:18 they're putting the corn um , error correction right in
65:21 the hardware . It's a hardware level born american action
65:25 rather than a software level hardware direction . So they're
65:28 really actually carefully studying the entanglement of what actually makes
65:33 a bit rather than taking some gate model that may
65:36 not reflect reality , what actually makes it get .
65:39 They have a they have a theory of what makes
65:41 a bit and then from that theory and their understanding
65:44 of it , you can argued and on the very
65:48 general connect uh huh conditions that they should be parliamentary
65:52 corrections possible . And I mean those arguments I find
65:55 very persuasive , but on the other hand , implementing
65:58 error correction at the hardware level is extremely difficult and
66:01 Microsoft has huge effort trying to do that . We
66:05 still haven't , as I said , no one's fully
66:08 calling America even a single bit , but I would
66:11 say once that's achieved by Microsoft or whoever does it
66:14 , then the road to building an actual point computer
66:17 before easier in the topological direction . That's my view
66:23 . Yeah , just uh for for me also just
66:26 has a total outsider , it seemed like a robust
66:29 way to sort of go about . Uh but but
66:35 I always got the feeling that it's a bit of
66:37 the underdog right now , that yeah , but usually
66:40 it's the underdog that Yeah , yeah , but but
66:46 you know , with the superconducting cubits and the iron
66:50 traps , you can , you can , you know
66:51 , you can make a few Cubans and have them
66:53 do fun things and it looks great . Uh and
66:55 now they're going up with 50 bits , but they're
66:57 very quickly , they're not doing computing . What they're
67:00 doing is quantum simulation . Really ? That's what they're
67:03 all doing right now . Uh Yeah , okay .
67:10 I don't like to say I told you so ,
67:11 but I told you so . So Jp Jenna wants
67:19 to know the distance across which quantum entangled phenomena can
67:25 be realized . Uh For instance , other activities on
67:29 earth can be controlled from a distant galaxy , I
67:31 guess in some science fiction is the thing . But
67:34 I guess the science question is how is there are
67:38 there limits to the distances across which quantum entanglement can
67:42 be realized ? Uh No , as far as we
67:46 know , they're orange . I mean you can have
67:48 particles on two sides of a black hole or even
67:50 two sides of a galaxy be entangled with each other
67:52 in principle . But you know about somebody from a
67:55 different galaxy controlling us . There is mm you know
68:01 , unless we we interacted with that galaxy at some
68:06 time deep dark in the past and shared some mutual
68:10 entanglement and that entanglement didn't get destroyed by other preservations
68:15 . Uh there's no way for them to control us
68:18 . I mean they it's not some you know uh
68:23 like star trek or um teleportation from here to that
68:27 . Uh there has to have been some interacts in
68:30 the past which was coherently preserved until today for uh
68:35 for quantum entangled . To be useful for something like
68:38 teleportation . Oh yeah , yeah . I think there's
68:44 one science fiction novel I read that sort of tries
68:47 to take this . I mean , it tries to
68:50 bring it in a little more scientifically like this ,
68:53 I think by creating that initial contact and then having
68:58 this other galaxy kind of try to control things on
69:02 earth by the science fiction chinese science fiction writer Session
69:06 lou I think the three body problem uh and it's
69:09 uh equals but anyhow , but that's I think science
69:14 fiction . Um There's another question from Pierre Luc it
69:18 says , are there not already consequences of having gone
69:22 from a classical to a quantum formulation of information theory
69:27 , presumably meaning just that ? Yeah , the rules
69:33 are very different for quantum information and the limits of
69:38 uh quantum information . So are there consequences in uh
69:45 leaving aside quantum computing , I guess ? Uh the
69:48 transmission of information . Right ? Uh Sorry , I
69:53 understand . Excuse me . You are there limits to
69:56 I think it's our the question is are there not
70:01 already consequences of having gone from a classical to a
70:06 quantum formulation of information theory ? I mean , uh
70:10 is that I think that's uh if I can sort
70:14 of read between the lines that uh are there drastic
70:18 consequences ? Are their radical sort of changes uh in
70:23 doing that ? Well , I want the classical information
70:28 theory of Shannon uh is pretty much still valid .
70:31 And uh I think the flow is in more the
70:35 other way people taking ideas from classical information theory and
70:39 helping understand corner of entanglement using classes using information theory
70:45 . And so there's been a huge explosion of working
70:48 using quantum information uh not just for transmission of information
70:54 , but also for even asking questions like what happens
70:58 uh when a black hole evaporates , you know ,
71:01 so the kind of thought , you know , I
71:04 suppose you had a black hole and it started radiating
71:07 like Hawking said and eventually started evaporated . And then
71:10 I gave you a different black hole , which only
71:12 differed by Somebody threw 1 , 1 particle into it
71:18 . So these are almost identical black holes , but
71:20 there initial state is slightly different . Could you ?
71:24 By looking at what's coming out , the information that's
71:26 coming out from the radiation tell , uh , which
71:30 black hole had that extra particle thrown in ? Uh
71:34 , So that's one of the deep questions that string
71:37 theorists and others have been sorting out these days .
71:39 And the answer is yes , you can , but
71:41 it's extremely difficult , but at least in principle you
71:43 can . And I think ideas from classical information theory
71:47 have really played an important role in understanding questions of
71:50 this type , correct me if I'm wrong , graduates
71:53 graduates know more about on the nose . So ,
72:01 uh , papa has a very interesting question . Does
72:05 the Big Bang imply that everything was entangled in the
72:09 past ? And of course , she says she as
72:12 a non scientist , it's sort of a , uh
72:15 , general question on her . But , but I
72:17 think it's an interesting question , but uh , uh
72:22 , I mean there's questions of inflation , right ?
72:24 So if you didn't have inflation than people who are
72:26 not causally connected at some point , I think there's
72:29 still , uh , I believe there's the visible universe
72:34 , which is the time it takes for light to
72:36 travel , uh , From the Big Bang ? Take
72:40 the time from now to the Big Bang , which
72:42 is 13.6 billion years and you go out 13.6 billion
72:46 years in space , you still , that's our visible
72:50 universe . Who knows what's beyond that ? And in
72:53 principle , I think we could be entangled with anything
72:55 in the visible universe . Yes . Yeah . I
72:58 mean , I guess there's a question of uh ,
73:01 like you said earlier about Newton's laws , that's the
73:03 time evolution . But then there's the initial state and
73:06 we still are I mean , there are hypothesis of
73:10 what the initial state was . I mean , there
73:12 are some natural initial states you could consider so called
73:16 bunch Davies vacuum and all the for inflation , which
73:21 would mean that there and and as Super said ,
73:24 there's a horizon uh due to the inflation . So
73:29 things in some sense , just like the black hole
73:31 horizon are sort of entangled across that horizon . And
73:35 us as well . So there is a certain sense
73:38 and there's a certain sense in which the spacetime expand
73:43 , inflationary spacetime has a temperature like the black hole
73:46 as the temperature . So in some ways , yeah
73:50 . But but it's , we still don't know whether
73:52 that's really the case or not . I mean this
73:54 are uh these are just ideas about what the initial
73:58 vacuum was like and uh we still don't have a
74:02 theory which tells us uh uh this thing . Uh
74:08 So yeah , but but it's a very valid very
74:11 very interesting question . Uh So uh I shook why
74:16 she asked , I wonder if there's a radical impact
74:19 on causality due to quantum mechanics . We still seem
74:23 to cling to the view that the cosmos is just
74:25 deterministic and principal given sufficient computational ability . Uh That's
74:35 a very good question . Uh um So the equations
74:39 of quantum mechanics are deterministic despite the uncertainty principle uh
74:46 in the sense that and there is no violation of
74:49 causality in the sense that if you knew the corn
74:51 um state At time T0 , then equating the quantum
74:57 mechanics in principle fully determine the corner state in the
75:01 future . Where , in a sense , the uncertainty
75:04 comes in is that it's impossible to know the phone
75:07 um state if I give you a little electron in
75:09 a box and tell you here's your electron . And
75:11 I tell you predict his future . Well your 1st
75:16 1st choice . Well , let me look at the
75:19 electron to figure out the state right now and then
75:22 I'll predict the future . But but just by the
75:24 act of looking at it , you will destroy the
75:25 electron . On the other hand , if I give
75:28 you an electron , I told you it's in this
75:30 state , I just tell you it's in this state
75:33 and then knowing that you can predict the future of
75:35 the electron . But you have to believe me that
75:38 I told you the truth . There's no way of
75:39 confirming I told you the truth . Okay , so
75:42 that's a very simple way of putting it . Uh
75:45 equations are deterministic , but but there are certain unknowable
75:51 aspect opponent theory that you can't uh fully determined unknown
75:55 state . That's where the uncertainty comes in in a
75:58 sense . Uh but causality uh and determinism are really
76:05 not are still present . It's just harder to implement
76:09 them . Uh huh . So let me just like
76:16 I think we should close very soon . It's quite
76:20 late for uh people . And in fact I have
76:24 to go get my second vaccine . And uh close
76:29 . I just wanted a last work where distinct thought
76:32 from you severe about Uh you mentioned in the last
76:36 30 years or so , 2030 years is when the
76:39 idea of quantum entanglement in the understanding of various phases
76:43 of matter and materials has really kind of uh come
76:48 center stage . Uh and so uh do you see
76:54 radical new developments in in kind of producing new materials
77:01 or kind of seeing amazing new phenomenon uh coming over
77:06 the horizon ? It is it something that you feel
77:10 is ? Uh I mean I I if I knew
77:15 what was coming on the horizon I do working on
77:17 . Okay , I would know . Uh So it's
77:20 hard to predict , but you can look at the
77:22 recent past and see all the sequence of incredible discoveries
77:26 uh And they don't seem to be you know ,
77:30 slowing down in any way . In the past couple
77:33 of years . It was twisted by their graphene ,
77:35 There's different compounds showing spin liquid behavior or quite .
77:41 Uh And then now very recently I've been involved in
77:44 some work by Michelle locals group at Harvard and realizing
77:49 a spin liquid using cold atoms and lasers I think
77:52 should grow at actually and I . C . D
77:54 . S . But an important role in that .
77:57 Uh So yeah I think there's you know , I
78:04 would agree with you that uh there's a lot happening
78:08 on the corner frontier in physics all the way from
78:12 materials in the lab to new understanding of very deep
78:16 understanding of going information here , black holes and amazing
78:19 thing is that they are connected in some way .
78:23 Uh So yeah , no I get the sense that
78:27 it's like a tip of an iceberg that one is
78:30 sort of uncovering and so of course much of the
78:33 iceberg room incident . But hopefully it's going to come
78:36 into view in in the in the coming years and
78:40 it's probably an exciting time for young people to be
78:43 getting into the field asking questions about uh this .
78:49 Uh So we just take uh last question from Rather
78:55 Banerjee about what happens to the entangled electron when we
79:01 observe the state of its path . Uh So presumably
79:06 when ? Yeah yeah so that's it will change .
79:13 That's really what E . P . R . Were
79:16 objecting to that . You know if I have a
79:20 pair of entangled electrons and one is the british in
79:22 one of the beef , I just looked at his
79:26 electron . Then my electron will change to a particular
79:29 state that's determined by the consequences of radishes . I
79:33 shouldn't say determined by that's connected to our correlated to