Bell inequalities and the 2022 Nobel Prize in Physics

Short answer: The 2022 Nobel Prize in Physics went to Alain Aspect, John Clauser and Anton Zeilinger for experiments with entangled photons that established the violation of Bell inequalities. Bell's inequality says that if hidden variables explain the correlations between entangled particles, those correlations cannot exceed a certain value, while quantum mechanics predicts a stronger correlation. The Royal Swedish Academy of Sciences says the results cleared the way for new technology based on quantum information.

The Core Scientific Achievement

The Royal Swedish Academy of Sciences awarded the 2022 Nobel Prize in Physics to Alain Aspect, John F. Clauser, and Anton Zeilinger. The official citation states the prize was given "for experiments with entangled photons, establishing the violation of Bell inequalities and pioneering quantum information science." The committee says each laureate conducted groundbreaking experiments using entangled quantum states. In these states, two particles behave like a single unit even when they are separated. What happens to one particle in an entangled pair determines what happens to the other, even if they are far apart. The committee says these results have cleared the way for new technology based upon quantum information.

The Role of Hidden Variables

For a long time, the central question in physics was whether the correlation between entangled particles was caused by hidden variables. These hidden variables were described as instructions that tell the particles which result they should give in an experiment. In the 1960s, John Stewart Bell developed a mathematical inequality named after him. This inequality states that if there are hidden variables, the correlation between the results of a large number of measurements will never exceed a certain value. However, quantum mechanics predicts that a certain type of experiment will violate Bell’s inequality. This violation results in a stronger correlation than would otherwise be possible under the hidden variable hypothesis.

Experimental Validation by the Laureates

John Clauser developed John Bell’s ideas, leading to a practical experiment. When he took the measurements, they supported quantum mechanics by confirming the predicted violations. Alain Aspect and Anton Zeilinger also conducted experiments using entangled quantum states. Their work, alongside Clauser’s, established the violation of Bell inequalities. The prize citation describes this work as pioneering quantum information science. The committee says Clauser's measurements supported quantum mechanics by confirming the predicted violations.

Implications for Quantum Technology

The committee says the "ineffable effects of quantum mechanics are starting to find applications." There is now a large field of research that includes quantum computers, quantum networks, and secure quantum encrypted communication. One key factor in this development is how quantum mechanics allows two or more particles to exist in an entangled state. The prize committee noted that the laureates' results have cleared the way for new technology based upon quantum information. These are described as fields of research, not as deployed systems. The focus remains on the foundational experiments that enabled these research directions.

FAQ

Who won the 2022 Nobel Prize in Physics?

Alain Aspect, John Clauser and Anton Zeilinger, according to the Royal Swedish Academy of Sciences.

What was the prize for?

"For experiments with entangled photons, establishing the violation of Bell inequalities and pioneering quantum information science."

What is a Bell inequality?

Developed by John Stewart Bell in the 1960s. It says that if hidden variables exist, the correlation between the results of a large number of measurements will never exceed a certain value. Quantum mechanics predicts that a certain type of experiment will violate it.

What is entanglement?

The committee describes an entangled state as one in which two particles behave like a single unit even when separated: what happens to one determines what happens to the other, even far apart.

Does this mean quantum technology is in use?

The committee says there is now a large field of research including quantum computers, quantum networks and secure quantum encrypted communication. This article makes no claim about specific deployed systems.