In Conversation with Professor Philip Stamp: Superfluid Helium and Quantum Vacuum Tunnelling
In this conversation, I speak with Professor Philip Stamp, Professor of Theoretical Physics at the University of British Columbia and Director of the Pacific Institute of Theoretical Physics.
CiTR 101.9 FM / The Blue Hour
Recorded live on July 7, 2026
You can listen to the episode on CiTR.
The Blue Hour, hosted by Farha Guerrero, airs live every Tuesday at 2 p.m. on CiTR 101.9 FM in Vancouver and at citr.ca.
Professor Philip Stamp is Professor of Theoretical Physics at the University of British Columbia and Director of the Pacific Institute of Theoretical Physics, known as PITP, which he returned to Canada to establish in 2002.
Mostly raised in New Zealand and educated in the United Kingdom, Professor Stamp began his academic life in philosophy and literature before turning to theoretical physics. He has since worked as a physicist in France, Spain, New Zealand, the Netherlands, Japan, Canada, and the United States.
His research explores many aspects of quantum mechanics, including macroscopic quantum phenomena, quantum tunnelling, quantum gravity, and quantum cosmology.
In this episode, we speak about his recent work with collaborators on superfluid helium and quantum vacuum tunnelling. The research uses an ultra-thin film of superfluid helium to examine the Schwinger effect, a famous prediction in quantum electrodynamics in which, under extreme conditions, the quantum vacuum may produce particle–antiparticle pairs.
In Professor Stamp’s work, this idea is approached through vortex and anti-vortex pairs emerging in a quantum liquid. Our conversation turns to the meaning of the quantum vacuum, the difficulty of observing the Schwinger effect directly, the relationship between theory and experiment in physics, and finally, the strange beauty of a universe that is, in Professor Stamp’s words, both magical and real.
Transcript
This selected transcript brings together the parts of the conversation most directly concerned with superfluid helium and quantum vacuum tunnelling.
Farha: Your recent research certainly got a lot of traction last fall. Perhaps before we dig further, you can first define the Schwinger effect—an idea now spanning more than seventy years. More than seventy years after Schwinger’s original prediction, you and your collaborators discovered something quite extraordinary. So why don’t we begin there? What did Julian Schwinger predict in 1951?
Professor Philip Stamp: Let me back up and ask the real question is, what is the vacuum?
We think we know what a vacuum is. It's something that's utterly empty. There's nothing there. In fact, for most of human history that's what people thought. If you look out into the sky, there's something that was noticed a long time ago, which is that it's black, at night.
And this tells you something incredibly important about the universe, not only that it's almost completely empty, but that it has only existed for a finite period of time in its present form, but it really is empty.
The mean density of the universe is one hydrogen atom per 10 cubic meters. That's very empty indeed. The earth's atmosphere is roughly 10 ^ 30 times more dense than that. Space is very big but it's also really empty.
That's why we can see all the way back because light just travels all the way from wherever it was emitted 15 billion years ago to us without being disturbed by anything on the way.
The vacuum seems to be simple, just nothing, emptiness. The first discovery that showed that couldn't be right was that of Einstein. He showed that the vacuum, in fact spacetime, can have all these properties. It can be curved, twisted and so forth and that curvature and that twisting carries energy, huge amounts of energy in fact.
The vacuum is not structureless even though it looks like it. It has all these properties which we describe using ordinary language as stretching and twisting and so forth. These are just words which describe the mathematics.
That was the first notion that the vacuum was not simple. The second was with was the discovery of quantum mechanics and we discovered that the vacuum is something that you can excite that if you kick it hard enough you'll produce particles. But kicking it hard enough means really kicking it hard.
What Schwinger discovered theoretically, it's never been seen, was that if you applied an incredibly strong electric field to the vacuum, it would become unstable and a profusion of particles would appear, and they would just go on without limit. The vacuum would seem to be disgorging without limit these particles which are electrons and positrons.
Now, the reason it's never been seen is because the fields required to do that are just colossal, way beyond our capacity to produce on Earth, but it tells you now that the vacuum is a bit like some featureless sea. You look at it, there seems to be nothing going on. Maybe if there was a bit of wind, you'd see a few waves, but that's it. But it turns out that underneath there's all sorts of things going on. And the only way we can see that is by disturbing it in some way.
The vacuum is not simple. Well, this had never been seen, actually we were thinking about something totally different which was if you have a current flowing through a two-dimensional superfluid, we expected something interesting to happen. And a superfluid is a fluid which has no resistance to flow and has other interesting properties but that's the one that counts here.
If I start a superfluid moving it'll simply go on forever. And I really mean forever if you're at zero temperature until it flows too fast and then all of a sudden these so-called quantized vortices will appear and actually they'll slow the flow.
They'll appear out of nothing and they'll appear in pairs. There'll be one vortex spinning one way with fluid flowing around it, say clockwise, and the other one will be an anti-vortex with fluid going around it anticlockwise. And these will slowly pull apart and they'll be pulled apart by the flow. We worked all of this out.
Farha: So, almost like whirlpools?
Professor Philip Stamp: A vortex is like a little whirlpool. And you have two whirlpools which are spinning oppositely. So, if you pull them apart the total amount of circular flow is not changed because they cancel each other out. But if you go near, if you are near only one of them you see a whirlpool, a vortex.
We predicted theoretically that this could happen at zero temperature by a process called quantum tunnelling, and it was at that point I thought, well, this is interesting. It looks analogous to the Schwinger effect. Here's this magic word analogy that you mentioned at the beginning.
What does analogous to mean? It certainly doesn't mean identical to. The question is how good is the analogy? Is it a fruitful one? Or are you going to find that it breaks down at some point? There have been analogies in physics that have been just wrong.
For example, for centuries people believed that light traveling through empty space was like sound traveling through water. It was something moving in a medium. And so they talked about the ether. The ether was something that people believed in for centuries. And then Einstein came along and said no, there's no such thing. That this analogy is just wrong. And so people can be misled by analogies and get into all sorts of trouble.
That's why I'm suspicious of analogies.
But this analogy turns out to be pretty good. And you mentioned that there was a lot of press about that paper. They all focused on the analogy. That's all they were interested in the science press. The fact that it looked like the Schwinger effect which is a famous effect because Schwinger made this prediction and it was extraordinary that the vacuum was unstable. And he made it at the very beginning of our understanding of quantum electrodynamics which was a huge revolution in physics at the in the middle of the last century.
And so the press climbed onto that and in my view they missed some of what was really interesting about it which was the superfluid part of it which is the real system we're talking about.
I think that it's truth is sacred but so is reality. Analogies are one thing but there is something real that you have to focus on.
Farha: That's, I think, why you use the word truth. Now I'm curious if we can just break this down a little bit because this is a paper that you, as far as I understand you have done the math to predict this. It is still theoretical, but you do believe that this could be an experiment that can actually happen.
And so why don't we break this down? So, in your model, this two-dimensional superfluid helium film serves as an analog of the quantum vacuum as you've explained. If we were to imagine this as an actual experiment, what would it look like?
Professor Philip Stamp: The simplest experiment does not mean it is the easiest to do, but it is the simplest to imagine. You would have some flat piece of say, graphite or something that can be made completely flat and you would have superfluid helium 4 flowing over it.
And then you would look to see what happened as you increase the flow rate and there are ways that you can detect these vortices, these whirlpools. They are very small, but you can detect them in different ways. And you watch to see what happens. And the prediction is that as you reach a certain flow velocity, the vortices or the vortex/anti-vortex pairs will start to be produced and they'll be produced at a very specific rate which is calculated.
And that rate can be varied by varying the flow velocity. But the key point is that this would happen at very low temperatures. So, the only way it can happen is through what's called quantum tunnelling.
It's a completely quantum process. So that's the simple experiment that could be done, except it's a very hard experiment to do. Because observing the vortices is very hard.
There are other ways that one could do it. For example with so-called superconducting films. Superconductors are like superfluids except that it's electrons that are flowing and systems can be made superconducting at a much higher temperature than superfluids. It makes the experiments much easier to do.
It's also much easier to see superconducting vortices because they carry a magnetic field which is easy to see. It might be that the experiment ends up being done on superconducting films.
The way it works, is theorists use what we understand about nature, theoretically to make predictions. And then experiments are done to check it out. And if it all works, everybody goes home happy. If it doesn't work, it might even be better because that means you found that there's something wrong.
Or you can have a situation as occurred with Einstein where he produced a theory which had whose predictions were so shocking that he didn't even believe them himself. And yet they all turned out to be true, then you know, that you've gotten a tiger by the tail and that you've somehow probed very deeply into the truth about nature.
Einstein himself used to talk about this. He was always very modest about what he did. He said I think I've I think I've pulled back a little bit of the veil by which he meant the veil hiding reality. He like the Greek philosophers was in no doubt that what we experience is not reality, that we infer reality but that we don't experience it directly.
And he felt that it was extremely difficult to pull back the veil but with general relativity he did it and he got far more than he bargained for. The ind of theory we're doing is nowhere near at that level. We're we're just using what we understand about superfluids to make predictions about how they would behave in these flowing films and then realize that there's this very interesting analogy with the Schwinger process.
People are never going to be able to see the Schwinger process in a lab, but if the analogy works, they'll be looking at a surrogate system where they can investigate something that ought to be like it. In that case the analogy can be useful if it if it's correct.
Farha: Do you see this experiment in your mind's eye actually being done? Is that what's driving you with your research? How close are is this a possibility?
Professor Philip Stamp: I'm not going to do the experiment.
Farha: Exactly. But who would and where would it take place? And I would imagine, that do would need to have very cold temperatures for it to take place? You've got to create the right environment for it to happen.
Professor Philip Stamp: There are a number of places where I could imagine it being done. One of them is Brisbane, Australia, but there are other places.
And, you never know who's going to look at a paper like this and say, "Oh, that's an experiment I could do." It might be somebody you've never heard of.
In principle, there are lots of labs in the world that could do it but it will be a difficult experiment and you just put your finger on why it will need quite low temperatures.
And also the problem is to see the vortices in the superfluid. It's very hard. That's why I'm saying that maybe it'll be done with superconducting films because then you don't have to go to such low temperatures and it's very much easier to see the vortices. So, it's possible that's how it'll be done and in that case it could be done pretty much anywhere because there are so many places in the world that can do experiments on superconducting films.
One of the reasons for that is that they're important for technology. So, lots of people look at them without any thought of testing anything fundamental. They're just interested in making devices of some sort. That's a huge industry across the world. Who knows who would do an experiment like that.
Farha: And even helium, if you remember, was in the news during the recent Middle East crisis involving Qatar and the Strait of Hormuz. There was concern about making sure that helium could still reach the rest of the world, especially people carrying out this kind of scientific laboratory research.
Professor Philip Stamp: I don't know if you're interested in why that's so important.
Farha: I would love it if you could answer that.
Professor Philip Stamp: Helium for a long time came from two sources. Coal mines, very deep down because the gas was produced by radioactive decay and deep down in the earth had nowhere to go. People for example, in Poland would dig these deep mines and they would find quite a lot of helium and they were sensible enough to capture it and store it. And then of course sell it.
And the other source was the fabrication of nuclear weapons and to a much lesser extent of nuclear reactors. Well, the nuclear weapons source has dried up. And the coal mines, people aren't mining coal so much these days. So, the helium supply in the world is disappearing.
And if you want to go to very low temperatures, you have to have helium. So, it's become more expensive. When I was a graduate student, we used to say that a container of liquid helium 4 cost about as much as an equivalent quantity of beer. But now it's far more expensive than whiskey.
Farha: I'm going to be speaking with someone you may know as well from the Sauder School of Business, Dr. Werner Antweiler. He has a background in energy and trade and so this may even come up.
But let's, let's just go back to the tunnelling again because this is so important and to just to give us a visual.
If I understand correctly, quantum tunnelling is a system that passes through an energy barrier that in ordinary classical physics it should not be able to cross. So can tell us, how we can we imagine what quantum tunnelling looks like?
Professor Philip Stamp: It's always very difficult to describe what quantum tunnelling is because most people don't have in their minds the idea of an energy barrier. It's a scientific concept.
The French have a word for quantum tunnelling. They call it l'effet passe-muraille, which means the going through the wall effect. So, they imagine that something is on one side of a wall and then it appears on the other side having gone through and yet the wall is still there. So, how did it get through? It seems completely counterintuitive.
And yet that's what happens in tunnelling. You have some physical system which is contained which is held back by some force such that it should never be able to get away. Or which is so confined in some region with a potential barrier around it like a wall.
And nevertheless it does. And the reason that can happen in quantum mechanics is because it's not meaningful in quantum mechanics to say that a specific physical system is in a specific state.
This is perhaps the most fundamental thing about quantum mechanics is that any physical system can exist in what's called a superposition of states. In other words, it exists in more than one state at a given time.
You can imagine that normally we talk about tossing a coin and it either produces heads or tails. In quantum mechanics it can be in a superposition of both.
The most dramatic example of this is so-called Schrödinger's cat paradox where you engineer a state in which a cat is simultaneously alive and dead. And Schrödinger who was one of the founders of quantum mechanics used this to show how counterintuitive it was. So, if a system can exist in more than one state at a time it can if oscillate between them or it can pass from one to the other and that's what happens in quantum tunnelling.
Further Reading
For readers interested in Professor Philip Stamp’s work and the ideas discussed in this conversation:
“Vacuum Tunneling of Vortices in Two-Dimensional ⁴He Superfluid Films”, by Michael J. Desrochers, Dominic Marchand, and P. C. E. Stamp, published in the Proceedings of the National Academy of Sciences.