John Clauser's five-decade wait for Nobel Prize was worth it

Data shows that Nobel Prize laureates in physics typically had to wait an average of 20 years before receiving the prestigious honor. For John Clauser, that wait was more than twice as long.

John Clauser talks with the Korea JoongAng Daily at a hotel in Dongdaemun District, eastern Seoul, on June 26. The physicist won the 2022 Nobel Prize 50 years after his groundbreaking research on quantum mechanics. [PARK SANG-MOON]

Data shows that Nobel Prize laureates in physics typically had to wait an average of 20 years before receiving the prestigious honor.

For John Clauser, that wait was more than twice as long. On Oct. 4, 2022, the 80-year-old physicist was named the co-recipient of the Nobel Prize in Physics alongside Alain Aspect and Anton Zeilinger. They were credited with conducting groundbreaking “experiments with entangled photons, establishing the violation of the Bell inequalities and pioneering quantum information science.”

Clauser’s research, which dates back to 1972, confirmed that quantum mechanics was correct and laid the foundation for emerging new applications in cryptography and computing.

The Korea JoongAng Daily sat down with the Nobel laureate last week at a hotel in Dongdaemun District, eastern Seoul, to discuss his award-winning achievements.

Clauser was visiting the country to give special lectures at Quantum Korea 2023, an international conference on quantum information hosted by the Ministry of Science and ICT, and Korea University as part of the Next Intelligence Forum celebrating the school's 120th anniversary in 2025.

This interview has been edited for length and clarity.

Q. Congratulations on your Nobel Prize win. How does it feel?

A. I was totally thrilled of course. Ninety percent of scientists want to win a Nobel Prize and the other 10 percent are liars. It's the highest honor one can get.

Tell us about your award-winning research.

So basically, there was a debate between Niels Bohr and Albert Einstein on the meaning of quantum mechanics and whether or not quantum mechanics was a complete theory. As it turns out, it was never fully resolved. In order to try to understand where the randomness comes from, where the superpositions in quantum mechanics come from, he [Einstein] believed that quantum mechanics was not a complete theory. And he wanted to add additional variables that were not in the theory, called "hidden variables," in order to explain entanglement.

Now, what's entanglement? [Erwin] Schrödinger came up with two equations. The first equation described hydrogen, one electron. The second equation described helium, two electrons. In the second equation, he found that the two electrons were somehow intertwined and entangled, as Schrödinger called it, in a very complicated way, which was not understood, but was necessary in order to explain the spectrum of helium. According to Schrödinger's second equation, when the two electrons are widely separated, they still remain entangled in a very strange and intimate way. So the question then was, is that really correct? If they're intimately inside a helium atom, of course they're going to interact. But if you separate them very far apart, they still interact according to quantum mechanics. This was very disturbing to both Schrödinger and Einstein. And so Schrödinger even proposed that maybe the equation was wrong. Maybe the entanglement of the electrons disappears, but that would change the results of the predictions of the theory. So this became the debate between Bohr and Einstein.

Einstein wanted to add additional variables, and Bohr said no, they're not needed. And any changes to the theory that you can think of would change the predictions. And nobody wanted to admit that the predictions might be wrong. That was just out of the question. And so basically, that persisted up till 1964 when John Bell looked at this theory.

What he discovered was a very surprising result. In fact, it was a pure irony that adding these extra variables to quantum mechanics did exactly the opposite of what Einstein, [Boris] Podolsky, and [Nathan] Rosen had predicted that it would do, that it was totally incompatible and also changed the predictions of quantum mechanics.

Then in 1969, when I was still a graduate student, [Michael] Horne, [Abner] Shimony, [Richard] Holt and I said, well, maybe quantum mechanics is not always perfectly correct. We took Bell's result and we changed it into a form that was actually experimentally testable.

So I ended up doing an experiment with Stuart Freedman in 1972. And I didn't know what I was going to get when I did the experiment. I knew I was going to somehow settle the debate between Bohr and Einstein. But I didn't know ahead of time. And I was betting, frankly, on Einstein. He was one of my great heroes. But I didn't know. Doing the experiment, I found out that Einstein was wrong and Bohr was right.

I had the audacity to actually go out and try and test it. Actually, I did four different experiments back in the early ‘70s. And then my co-Nobel laureates, Alain Aspect from Paris, his work was done in the ‘80s, and Anton Zeilinger started in the late ‘80s and continued on into the ‘90s and 2000s. Things had taken off dramatically since then.

Clauser with the quantum mechanics experiment he and Stuart Freedman used to test Bell‘s theorem at UC Berkley in California, where Clauser was a postdoctoral fellow, on Nov. 7, 1975. [EPA/YONHAP]

You mentioned in a previous article that when you decided to test Bell's proposal, everyone told you it wasn't possible, even your advisor. What motivated you to conduct the experiment anyway?

I realized what was at stake. What was at stake was the whole platform for doing physics. Kind of starting back with Galileo and Newton through Einstein, this is how one would like to have a description of physics covered by differential equations that describes how stuff moves around in the three-dimensional world we live in as a function of time. The theory that Mike Horne and I produced shows that that is impossible. This is kind of the whole basic platform that underlies Einstein's plan of attack of physics. Unfortunately, we have pulled all the legs out from under the table on that one. It was very disappointing. I recognized at the beginning that this was going to be a problem. Mike Horne and I finally worked out all the details of doing this. Nobody else seemed to realize just how much was at stake in doing the experiments. That's kind of what kept me going. Even though everybody else told me I was totally crazy in doing the experiments, that it will ruin my career. Well, it sort of did. I've never been a professor. But I thought it was important.

Various quantum technologies utilizing quantum entanglement are being developed now, such as quantum computers and quantum encryption satellites. What technology do you consider to be the highest priority in terms of national development?

I suspect, frankly, quantum computers are a bit oversold. The number of problems that a normal computer can solve is in the millions or billions. There are only a handful of problems that quantum computers can usefully solve. Quantum encryption was the primary driver of new technology. The financial industry, of course, is very interested in encryption, of being able to send totally encrypted communications of financial matters and the like, as all government agencies are with their secrets. So encrypted communication, even just on your phone, is very important today. So quantum encryption is quite valuable. I would say that that's much more valuable than quantum computing.

In regards to satellite quantum communications, what would be the scale or quantity of entangled particles required for that, and is it possible to maintain entanglement at that scale?

It is possible. The first such satellite was the Chinese Micius satellite which was launched a few years ago. The United States, to my knowledge and according to an article in Optics & Photonics News, doesn’t have any quantum-encrypted satellites. Many other countries have programs to do quantum encryption. To my knowledge, the only [quantum-encrypted] satellite that's actually flying now is the Chinese Micius satellite. I think I've asked my colleagues why there are no American satellites. And the best guess is that there are too many [potential] leaks along the way, too many ways of actually getting it hacked to and from the stations.

What other fields in quantum do you think have the potential of winning the next Nobel Prize?

Good luck! It took me 50 years. I don't know why it took so long. Those Nobel prizes, I guess, have politics involved. I don't make those decisions. I just was happy to have received one. But, okay, in physics, pure physics, the most pressing problem I see is somehow unifying general relativity with quantum mechanics. I think that entanglement is kind of the source of the problem in combining the two.

What research topics do you believe are crucial for the academic community to focus on in order to create breakthroughs in quantum?

No one can tell. Certainly, all of us who are doing the work had no idea that there would be applications. We were just studying pure physics. But it is essential to have a good, strong scientific program of study. Without that, you get nowhere. Now, there are areas of physics being studied that I think are silly, like string theory. But who knows? I cannot predict.

Now that you mention it, hopes are really high for quantum technology after quantum entanglement was proven. Some say that the market size value will be worth over 1 trillion won, or $77 billion, by 2030. Did you expect the market to grow so large 50 years ago?

Absolutely not. This is totally beyond anything I ever would have dreamed of. Back when I was doing the experiments, I didn't know what results I was going to get. I was betting on Einstein, but I didn't know what the result would be. I knew I would get a result and I knew I would settle the debate. Beyond that, I didn't know anything.

Quantum is actually one of Korea's 12 national strategic technologies — technologies that the Korean government seeks to strategically develop. Do you have any thoughts on Korea's quantum research?

I don't know enough about it to answer.

What about America's quantum research?

Certainly, for science, American science has been grossly underfunded ever since Ronald Reagan was president. The science budget as a percent of GDP has been dropping routinely ever since the Reagan administration. Under Republicans, it has dropped. Under Democrats, it tends to hold flat. But the net result is that, over the years, it has sunk to one of the lowest in the world. I'm very disappointed in the state of scientific research in the United States. Moreover, there is a competition between so-called STEM universities and liberal arts. Liberal arts seem to be winning out over STEM. The net result is that science literacy, and in particular mathematics literacy, has declined. I strongly suspect that the Korean population is probably better educated than the American population in general. I don't have any statistics on that, but I wouldn't be surprised.

In the long run, what problems do you think would arise from underfunding in STEM research?

It takes money to do research. The United States became a world leader in World War II, effectively. There was a massive amount of money put into scientific research, aeronautics, radar electronics, physics, and atomic bomb research. Just massive amounts of money were poured in. At the end of the war, scientists walked away with gobs of new technology that they could apply to experimental physics, which just simply did not exist at all prior to the war. It was an overnight change in the state of technology. It all had to do with a massive amount of government funding for the World War II effort.

BY LEE SUNG-EUN [lee.sungeun@joongang.co.kr]