Hello and welcome to this series on physics and philosophy from the University of Oxford.
And bang! He disappeared. And a puff of smoke.
The ability of genies to appear and disappear at will is a familiar idea in much of children's literature.
The concept of teleportation has sparked our imagination and has often been explored in science fiction.
But could we really transport ourselves instantaneously from one point in space to another?
The possibility of teleportation is just one of the mind boggling phenomena that results from the theory of quantum mechanics.
An exploration into the microscopic behaviour of the universe.
Quantum theory has provided us with many surprising and unexpected results.
How far into the realm of science fiction is modern science taking us?
I am Ankita an urban. And I am speaking to Professor VLATKO Vedral, Professor of Quantum Information Science and Fellow at Wolfson College, Oxford.
Professor Vedral has written a number of books on quantum theory, including the popular science book Decoding Reality, published in 2010.
In this, he discusses the idea of the universe being made of quantum information and describes some of the surprising results.
Quantum mechanics provides us with. These have consequences in fields such as quantum computing, quantum cryptography and perhaps even teleportation.
This interview was recorded via Skype, so the sound quality is lower than previous podcasts.
The advent of quantum mechanics in the 20th century marked a huge turning point and one in physics.
What was it about this new theory that made it so revolutionary?
I think the most revolutionary aspect probably was, first of all, to break away from causality of classical physics in classical physics,
which is basically any physics before quantum physics and certainly includes Newtonian mechanics, but it also includes electromagnetic phenomena.
Basically, anything at that time was causal in the sense that if you control your initial conditions,
if you make your experiment and you make exactly the same preparation of your experiment,
then you should always expect the same kind of outcome of your of your experiment.
If you can control your system initially perfectly well, then you can say exactly deterministically what's going to happen in the future.
And the first thing that quantum mechanics really violated is exactly this, that if you you know,
if you control your experiment with hundred percent accuracy and efficiency,
you still cannot predict what's going to happen in any individual experiment.
And this was a big surprise. In fact, Einstein really disliked very strongly this feature of quantum mechanics.
He kept saying, God doesn't play dice, and I can't believe that God would construct this kind of random universe in some sense.
So this was a big really break away from classical physics. And the second thing, and interestingly enough, Einstein also complained about this a lot.
He called this spooky action that the distance was nonlocality of quantum mechanics.
The fact that it looks as though you can make a measurement on one part of
the universe but affect something that's very far away from where you acted.
And I think these two features are the key features of quantum mechanics.
So the fundamental randomness and and the possibility of having correlations between events that are very far from from one another.
So the results that it provides seem quite counterintuitive to me.
So as you said, Einstein was a famous critic. Could you please tell us about a little bit about the EPR paradox that he postulated as a.
Yes, as a criticism?
Yes, I think that was that was really a revolutionary paper in many ways, and especially from our perspective now that we really understand that,
that we can even base some of our technology on on these ideas, in fact.
But but they. So EPR paper was really meant as a criticism of quantum mechanics.
And it was in particular criticism of the uncertainty principle,
which is also at the root of this randomness is very much linked to the randomness that I mentioned.
Basically, Uncertainty Principle says that if we know one property of our system really well, like a position of an object,
then we have really no information about another property like the momentum or velocity of of this object.
And, and this is not so in, in stark contrast with Newtonian mechanics, with classical mechanics,
where you can basically measure any property of any system with any accuracy.
And this is independent of any of the measurements that you make.
So you can certainly make the position and velocity measurement of a classical object to any desired accuracy.
So I haven't had a problem with that.
And his colleagues, Podolsky and Rosen, who wrote this paper together with him, and basically what they said is they said,
imagine if we have these two quantum objects which are so highly entangled that their properties behave in perfect synchrony.
So if I if I measure position of one of them, then I can immediately tell what the position of the other one is.
And if I measure velocity of one of them, then I can immediately tell what the velocity of the other one is because they are perfectly correlated.
They have all the properties perfectly correlated. And then Einstein said, Look,
this can actually allow us to violate the uncertainty principle because I can measure a
position on one of the particles and thereby learn about the other particle's position.
And then I can measure momentum on the other particles, the speed on the other particle, if you like.
And this should allow me to have the position and the momentum measured to any desired accuracy.
And big seems to go beyond the uncertainty principle.
So it's a little bit funny the argument because he was using one property of quantum mechanics to invalidate another property of quantum mechanics.
So he was using entanglement, which we know is also a genuine quantum property to somehow go beyond beyond the uncertainty principle.
And it was the revolutionary idea because somehow he really identified exactly what where the.
About quantum mechanics. And it took at least another another 30 years before that was really formalised into into an inequality by John Bell.
And you could even test to what degree quantum mechanics is with you know, you can quantify this weirdness.
And in fact, now, like I said, we can even use it for technology.
So it's advanced quite a bit from from that time. So could you please explain the idea of entanglement a bit more?
You mentioned that if the particles are entangled, you can look at one and see what's happening with the other.
How does that work? How can that happen?
I don't think we really have an explanation for that because it's so non-local that we can't really tell a story in the usual spacetime way.
So, you know, we can't just say we did something here and then something changed and so on.
We are forced to speak in terms of in terms of measurement outcomes on on these separated systems.
In a way, I think it's one way of understanding what this tells us about reality.
And in in the physics jargon, we would say that that entanglement holds out the possibility of hidden variables.
So basically, people like Einstein also, you know, people who like to speak to the kind of classical picture of the world they would like to
say that any property of any physical system exists independently of our measurements.
It's just that we need to make a measurement to find out for our sense of what this property really is.
But quantum mechanics tells us something different. It tells us that the property itself is not determined before you make that measurement,
and it's not really independent of of you making the measurement.
So it's not like the particle already has a position and it has a certain velocity such that we don't know it.
What quantum mechanics says is that even nature itself, you know, even God, if you like,
that metaphorical language doesn't really know the position and the velocity of the particle.
So it's completely non determined.
And I think this is really this big break away from causality and it tells us that properties don't really exist independent of making measurements.
And I think this was also the thing to Einstein, because we like to think of the world as an objective world,
which exists independently of us and independently of what we decide to do with it.
But but it seems that everything we do in quantum mechanics indicates other ways that that our engagement is crucial,
and we cannot really do anything without it.
And so what are the some of the applications of entanglement is, for example, superfast quantum computing is that possibility?
I think that that's actually what's exciting about it. And again,
that's I think that's what's really beautiful about physics that you have this really
fundamental mystery and we are still arguing in the physics community how to,
you know, how do we really understand entanglement? And there are all sorts of people offering all sorts of different interpretations and so on.
But in spite of the fact that we haven't quite understood all the implications of that, we actually see how to use it technologically.
And I think the two big applications or maybe three in fact, are one of them is certainly superfast computing.
And I think what's interesting is not that we could just solve certain problems faster and more efficiently.
I think what's interesting to physicists as well is that we can simulate other physical systems more effectively.
So in physics, you know, we want to understand more and more complex, and that usually requires much more computational power.
And in fact, if you really want to properly simulate even a small number of atoms,
I think conventional computers are already lost because they require more memory and power than than is available.
But but if you go and use quantum systems to simulate other quantum systems,
then of course that becomes much more efficient, in fact, exponentially more efficient.
And I think I'm really excited by that prospect.
So people use a handful of atoms now to simulate all sorts of transport properties in complex systems, even biological systems.
Now we have we have an idea how to simulate complex biological systems with quantum computers.
And I think I think there would be a big revolution actually in that direction.
The third thing I wanted to mention is quantum cryptography, which which I think is really exciting.
It's already out there in the market. I think you can buy quantum encryption if you really have enough.
It's probably too expensive, but if you have enough money, you can buy it.
And the idea is that if you really want something that's much more secure than anything classically available,
then it seems that encoding information into quantum systems and manipulating it with quantum
systems is actually gives you a higher degree of security than anything in classical physics.
So if you want to send maybe a message that.
Not too long, but you want to really guarantee that no one else can break this message between you and the receiver.
Then you should really be using quantum mechanical systems for that.
And it's again exactly a consequence of the indeterminacy.
You know, the uncertainty principle basically protects you to some degree against any eavesdropping.
And this is probably you know, this is the biggest breakthrough, I would say, in technology kind of thing.
And what about the idea of teleportation? I know that's been linked to entanglement.
Is that too much into science fiction or is that actually a possibility?
I think, you know, it's been demonstrated on simple systems.
It's a good question because the time when when this really becomes exciting is if we can teleport ourselves from A to B,
you know, I travel a lot, for example, between Oxford and Singapore.
And I think sometimes you really think, you know, wouldn't it be nice to just be teleported instantaneously, more or less at the speed of light,
if you like, which is more or less instantaneous as far as we are concerned, between between Oxford and Singapore.
But so far we've only been able to do this with very small objects, with particles of light, with photons, with a few atoms.
But we haven't been able to go beyond that, and we certainly haven't been able to do it across large distances.
You know, you can teleport an object from one side of your laboratory to another, which is maybe ten metres across.
But what we'd really like to do is teleport things much further away and teleport a larger objects than just a few items.
And I think this really is at the moment, I would say, you know, the right word.
You know, it's still science fiction, although we see nothing wrong with it.
So I think most of us are optimistic that one day this will be a real possibility.
This might take a long time. That sounds very exciting, but thank you so much for your time.
I know that you're.