2022 · Aspect, Clauser & Zeilinger: Entanglement Proved
In 1935, Einstein and two colleagues argued quantum mechanics must be incomplete: it predicted that two particles could be entangled — linked so that measuring one instantly determines the other, no matter how far apart. Einstein called it "spooky action at a distance" and insisted some hidden, sensible explanation must exist. For thirty years, it was philosophy. Then John Bell (1964) devised a test: if hidden explanations were right, certain measurement correlations could never exceed a limit. Quantum mechanics said they could.
Three experimentalists, working decades apart, settled it. John Clauser performed the first Bell test in 1972 (with Stuart Freedman), when the topic was so unfashionable colleagues warned it could ruin his career. Alain Aspect in 1982 closed the biggest loophole, switching his detectors while the photons were in flight so no signal could sneak between them. Anton Zeilinger took entanglement into the wild: quantum teleportation (1997), entanglement swapping, and distributing entanglement over 144 kilometres between Canary Islands.
Every experiment violated Bell's limit. Einstein's hidden variables lost; entanglement is real. The trio shared the 2022 Nobel Prize in Physics "for experiments with entangled photons, establishing the violation of Bell inequalities and pioneering quantum information science" — the first Nobel Prize awarded for quantum information itself.
Go deeper — the math & the rigor
The workhorse of these experiments is the Bell state — two photons whose polarizations are perfectly correlated yet individually random:
\[|\Phi^+\rangle = \frac{|00\rangle + |11\rangle}{\sqrt{2}}\]
Bell's theorem, in the CHSH form used in the labs, says any locally realistic hidden-variable theory must satisfy \(|S| \le 2\) for a certain combination \(S\) of measurement correlations. Quantum mechanics predicts up to \(|S| = 2\sqrt{2} \approx 2.83\) — and the experiments agree with quantum mechanics, decisively. No local hidden variables can reproduce the observed correlations: the universe is, at bottom, nonlocal.
Why this prize matters for quantum computing: entanglement is the resource that makes quantum computing quantum — it is what lets \(n\) qubits explore \(2^n\) amplitudes together, the fuel of every quantum speedup in your syllabus. Beyond computing, Bell tests enable device-independent quantum key distribution: cryptographic security certified by the violation itself, with no need to trust the devices. Aspect, Clauser, and Zeilinger turned a philosophical argument into the foundation of quantum technology.
Key takeaways
- Einstein's 1935 EPR argument claimed entanglement implied quantum mechanics was incomplete; Bell (1964) made it testable.
- Clauser (1972) ran the first Bell test; Aspect (1982) closed the communication loophole; Zeilinger pioneered teleportation and long-distance entanglement.
- Every test violated Bell's inequality — local hidden variables are ruled out.
- They shared the 2022 Nobel Prize for entangled-photon experiments and pioneering quantum information science.
- Entanglement is the resource behind quantum speedup and enables device-independent quantum cryptography.
Check your understanding
Q1.What did the Bell tests of Clauser, Aspect, and Zeilinger prove?
Measured correlations exceed Bell's limit (|S| ≤ 2) up to 2√2, matching quantum predictions and ruling out Einstein's local hidden variables.
Q2.For what were Aspect, Clauser, and Zeilinger awarded the 2022 Nobel Prize?
That is the official 2022 motivation — the first Nobel Prize given for quantum information science itself.
Q3.Why is entanglement central to quantum computing?
Entanglement creates the exponentially large joint state space that quantum algorithms exploit; without it, qubits are just independent classical bits.
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