Nobel prize in physics awarded to pioneers of quantum information

The 2022 Nobel prize in physics has been jointly awarded to Alain Aspect, John F. Clauser and Anton Zeilinger

By Alex Wilkins

Alain Aspect, John F. Clauser and Anton Zeilinger

Niklas Elmehed/Nobel Prize Outreach

The 2022 Nobel prize in physics has been jointly awarded to Alain Aspect, John F. Clauser and Anton Zeilinger for experiments with entangled photons and their work in pioneering quantum information science.

“I’m still kind of shocked, but it’s a very positive shock,” said Zeilinger during a press conference.

All three winners were awarded for their fundamental contributions to work on quantum mechanics, which involved experiments using entangled, or connected, particles of light called photons. These showed that information could be instantly transmitted over infinite distances, known as quantum teleportation.

Each of the winners’ experiments carried out a real-life test of a mathematical theorem first proposed by physicist John Bell in 1964, called Bell’s theorem. This attempts to measure whether quantum mechanics is like the billiard-ball model of Newtonian mechanics, where one thing must follow another at a local scale, or whether particles separated by any amount of space can affect each other.

Bell’s proposal involved measuring the properties of two entangled particles in a system isolated from anything else that could influence the results – such as an observer inadvertently affecting an entangled partner through measurement – to see if they exceed a certain value, creating a mathematical inequality and proving that local effects alone can’t explain quantum mechanics.

In 1972, John F. Clauser and his colleague Stuart J. Freedman were the first to test Bell’s inequality, by measuring the entangled photons that came from collisions of calcium atoms.

Clauser and Freedman’s data appeared to violate Bell’s inequality, the first real-world example to do so, at a high level of statistical accuracy, implying that quantum mechanics really could have non-local effects. However, there were certain loopholes with this experiment, which had many differences from Bell’s original idea.

In 1980, Alain Aspect at the University of Paris-Saclay, France, and his colleagues managed to measure the Bell inequality again, to a much greater degree of precision and with less doubt, by measuring the polarisation (or orientation) of pairs of photons.

The team used a random switching device to decide which photon to measure before they had reached the detectors. This ruled out the chance of an observer having an effect, as some critics had thought might occur in Clauser’s experiment, and many physicists felt that Aspect’s measurements laid to rest the idea that quantum mechanics acted locally.

In 1989, Anton Zeilinger at University of Vienna, Austria, and his colleagues expanded Bell’s inequality beyond just two entangled particles to a state of three or more entangled particles called a GHZ state. This forms a key pillar for many quantum technologies, including quantum computing, which can use GHZ states to make quantum bits, or qubits.

“We wanted to go back and honour the people who laid the ground for what was to become [quantum information science],” said Thors Hans Hansson, a member of the Nobel Committee for Physics, during the press conference.

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