On October 4, 80-year-old John F. Clauser woke up in his California home to find he had received the Nobel Prize in Physics (opens in a new tab). He received the award at a ceremony in Stockholm, Sweden, on December 10 with Anton Zeilinger and Alain Aspect for their work on quantum entanglement.
It was a moment of celebration for Clauser, whose groundbreaking experiments with particles of light helped prove key elements of Quantum mechanics (opens in a new tab).
“Everyone wants to win a Nobel Prize,” Clauser said. “I am very happy.”
But Clauser’s journey to winning science’s top prize hasn’t always been straightforward.
In the 1960s, Clauser was a graduate student in physics at Columbia University. Luckily, he found an article in the university library that would shape his career and lead him to continue the experimental work that won him the Nobel Prize.
The paper, written by Irish physicist John Stewart Bell and published in the journal Physics in 1964, examined whether or not quantum mechanics provided a complete description of reality. At the heart of the matter was the phenomenon of quantum entanglement.
Quantum entanglement occurs when two or more particles bind together in some way, and regardless of their distance in space, their states remain bound.
For example, imagine particle A flying in one direction and particle B in the other. If the two particles are entangled – meaning they share a common quantum state – a measurement of particle A will immediately determine the outcome of the measurement of particle B. It doesn’t matter if the particles are a few feet away or several years away – light from each other. — their long-distance quantum binding is instantaneous.
This possibility was rejected by Albert Einstein and his colleagues in the 1930s. Instead, they argued that there is an “element of reality” that is not considered in quantum mechanics.
In his 1964 paper, Bell argued that it was possible to test experimentally whether quantum mechanics failed to describe such elements of reality. He referred to these unaccounted items as “hidden variables”.
In particular, Bell had local variables in mind. This means that they only affect the physical installation in their immediate vicinity. As Clauser explained, “If you put things locally in one box and make a measurement in another box far away, the experimental parameter choices made in one box cannot affect the experimental results in the other box, and vice versa.”
Clauser decided to test Bell’s proposal. But when he wanted to experience it, his adviser made him reconsider.
“At the beginning, the most difficult thing was to have the opportunity,” recalls Clauser. “Everyone told me it wasn’t possible, why bother!”
The quantum laboratory
In 1972, Clauser finally had the chance to test Bell’s proposal while working in a postdoctoral position at Lawrence Berkeley National Laboratory in California. He joins the doctoral student Stuart Freedman. Together, they set up a lab full of optical equipment.
“Nobody had done this before,” Clauser said. “We had no money to do anything. We had to build everything from scratch. I got my hands dirty, I was immersed in cutting oil, there was a lot wires and I built a lot of electronics.”
Clauser and Freedman managed to create entangled photons by manipulating calcium atoms. The light particles, or photons, flew through polarizing filters that Clauser and Freedman could rotate relative to each other.
Quantum mechanics predicted that more photons would simultaneously pass the filters than would be the case if photon polarization were determined by local and hidden variables.
Clauser and Freedman’s experiment showed that the predictions of quantum mechanics were correct. “We regard these results as strong evidence against local theories of hidden variables,” they wrote in 1972 in Physical examination letters (opens in a new tab).
A difficult start
Clauser and Freedman’s results were confirmed in other experiments by Alain Aspect and Anton Zeilinger.
“My work was in the 70s, Aspect was in the 80s, Zeilinger was in the 90s,” Clauser said. “We worked sequentially to improve the pitch.”
But the impact of Clauser’s revolutionary experience was not immediately recognized.
“Things were tough,” Clauser recalls. “Everyone said, ‘Nice experiment, but maybe you want to go out and measure numbers and stop wasting time and money and start doing real physics.'”
It took 50 years for Clauser to receive the Nobel Prize for his experimental work. His colleague, Stuart Freedman, died in 2012.
“My associates are long dead,” Clauser said. “My claim to fame is that I’ve lived long enough.”
Asked if he had any advice for young researchers given his own initial difficulty, Clauser said, “If you prove something that everyone thinks is true, and you’re the first to doing it, you probably won’t be recognized for 50 years. That’s the bad news. The good news is that I had a lot of fun doing this job.
Clauser and Freedman’s experiment paved the way for elaborate technologies that use quantum entanglement, such as quantum computers and cryptographic protocols.
When asked if he thought quantum mechanics was a complete theory, Clauser replied, “I suspect there’s a more fundamental theory underneath, but that’s just pure conjecture. I don’t know. not what it is. I also admit that I am totally confused, I have no idea what all of this means.”
John F. Clauser’s quotes have already been published in an interview the author did for the Swedish magazine Forskning och Framsteg.