IYQ Quantum Milestones

December 15, 2025

To celebrate the International Year of Quantum Science and Technology, Physics Magazine has assembled a special collection tracing the field’s most consequential breakthroughs. Drawing on both classic pieces from our archives and newly commissioned articles, the series highlights the experiments, ideas, and debates that shaped the foundations of quantum mechanics. Together, these milestones offer a concise history of how quantum theory took form and how it continues to evolve.

1905: Einstein and the Photoelectric Effect

In one of his annus mirabilis papers, Einstein explained the photoelectric effect by considering light as a stream of energy quanta—which were later called photons.

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1916: Millikan’s Measurement of Planck’s Constant

The experiment provided further proof of the reality of photons, yet Millikan didn’t accept their existence until later in his career.

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1923: Photons Are Real

Arthur Compton’s results convinced most skeptics that in some experiments, light can act like a stream of particles.

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1927: Electrons Act Like Waves

Davisson and Germer showed that electrons scatter from a crystal the way x rays do, proving that particles of matter can act like waves.

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1928: The Dirac Equation Unifies Quantum Mechanics and Special Relativity

A seminal paper by Paul Dirac, who relied on mathematical intuition, laid the foundation for quantum electrodynamics.

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1935: What’s Wrong with Quantum Mechanics?

Einstein and his coauthors claimed to show that quantum mechanics led to logical contradictions. The objections exposed the theory’s strangest predictions.

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1947: Lamb Shift Verifies New Quantum Concept

The discovery of a small discrepancy in hydrogen’s atomic spectrum came at just the right time to push quantum theory forward.

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1957: Sprouting Parallel Universes

The many-worlds interpretation of quantum mechanics says that a measurement can cause a splitting of reality into separate worlds.

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1959: Ghostly Influence of Magnetic Field

Aharonov and Bohm proposed a scenario in which quantum particles experience electromagnetic effects even though there is no field in their immediate vicinity.

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1964: John Stewart Bell Quietly Rings in New Era of Quantum Theory

In 1964, Bell showed that quantum physics predicts correlations that violate certain inequalities. The work implied that quantum mechanics is not compatible with locality, even if there were “hidden variables” not accounted for in quantum theory.

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1993: Teleportation Is Not Science Fiction

Theorists proposed an idea they called quantum teleportation—a means of transferring the identity of one particle to another over some distance.

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1995: Correcting Quantum Computer Errors

Researchers proposed methods to preserve the integrity of quantum bits—techniques that may become the key to practical quantum computing on a large scale.

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