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
79:38	the consequences of not the consequence connected to what right
79:42	eight observed . But for me to actually make sure
79:46	that uh the entanglement was correct , I would have
79:51	to call up radish and say what did you observe
79:53	? And rather should tell me what he observed and
79:55	then I would uh see that was consistent . So
80:00	it's so that it does and that information only travels
80:03	the velocity of light or slower . So uh so
80:07	that's when information gets transmitted . So what you can
80:10	do with entanglement is not you can't send information faster
80:15	instantaneously , but you can send it securely . So
80:18	for example , I mean this is a very they're
80:20	better algorithms for this . But uh you know ,
80:24	suppose I know that radish and I are entangled .
80:27	I have a pair of electrons that entangled like mine
80:29	is up and this is done and vice a person
80:32	. So then we share this in the past .
80:34	And then Rodgers looks at his electron and it's down
80:40	and I look at my electron and it's up .
80:42	So at this point I know that radishes electron is
80:45	dark And No one else knows this . So I
80:49	can call up Roger , I should say if your
80:51	electron was down uh invest in this company . If
80:55	you're electron was up invest in the other company .
80:58	Uh and no one can tell what I told Roger
81:01	, even if they heard what I told him .
81:03	But I , but Rogers will perfectly understand what I
81:06	said because we share this information . So that's the
81:10	, the way you have the best , very simple
81:12	explanation of corn of photography . You can securely send
81:16	information , but it's , that's not any faster .
81:19	Okay . Yeah . You're muted radish . Sorry .
81:27	Uh , so thanks a lot to be for very
81:31	patiently taking so many questions , spending time with us
81:37	. Uh , such a , such a moment .
81:40	I mean , I hope you get your second shop
81:42	very soon . And , uh , yeah , right
81:46	. You've got your second shot already . Oh no
81:48	, I'm still , yeah . I mean , I've
81:51	got mine my first shot about four weeks ago .
81:54	So , uh , hopefully soon get it . There
81:57	are there are issues shortages . Yeah , But let's
82:01	see how it goes . But , uh , anyway
82:03	, everyone on the call . Please stay safe .
82:05	All the best for you and your families and friends
82:09	and everyone . It's a difficult time . But anyway
82:13	, I hope you got a little respite from that
82:15	. This thing here in this marvelous world of quantum
82:19	mechanics and entanglement . So , uh , good night
82:23	, good day and so on to all and by
82:26	, by severe and uh , hopefully soon in India
82:31	when things thinking hopefully things get better . Uh ,
82:34	thank you . All right . Bye bye . Thanks
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