Appendix F: Key Experiments in Quantum Mechanics

"No amount of experimentation can ever prove me right; a single experiment can prove me wrong." -- Albert Einstein

Quantum mechanics was not born from philosophical speculation or mathematical elegance alone. It was dragged into existence by experiment after stubborn experiment, each one refusing to obey the classical rules that had served physics so well for centuries. This appendix presents a chronological timeline of the pivotal experiments that created, tested, refined, and ultimately vindicated the quantum mechanical description of nature.

For each entry, we provide the date, the experimenters, what was measured, what the result showed, and where the experiment connects to the main text. Cross-references use the notation Ch N.S (Chapter N, Section S).

1900 -- Planck's Blackbody Radiation Formula

Who: Max Planck (Berlin)

What was done: Planck sought a theoretical formula to match the experimentally measured spectrum of thermal radiation emitted by a perfect absorber (a blackbody). The Rayleigh-Jeans law, derived from classical electrodynamics and statistical mechanics, predicted that the energy radiated per unit frequency should grow without bound at high frequencies -- the infamous "ultraviolet catastrophe." Wien's earlier empirical formula worked at high frequencies but failed at low frequencies. Neither classical approach could reproduce the full spectrum.

What it showed: To derive a formula matching the data, Planck was forced to assume that the energy of each oscillator in the cavity walls was restricted to discrete multiples of $h\nu$, where $\nu$ is the frequency and $h = 6.626 \times 10^{-34}$ J$\cdot$s is a new fundamental constant. This was the first appearance of energy quantization in physics. Planck himself regarded it as a mathematical trick ("an act of desperation"), but the formula matched the experimental data perfectly across all frequencies and temperatures.

Significance: Planck's quantization hypothesis marks the conventional birth of quantum mechanics. The constant $h$ (Planck's constant) would prove to be the fundamental scale separating classical from quantum behavior.

Textbook connection: Ch 1.2, Ch 1 code (blackbody_comparison.py), Appendix C ($h$ and $\hbar$).

1905 -- Einstein's Photoelectric Effect

Who: Albert Einstein (Bern), building on experimental observations by Philipp Lenard (1902)

What was done: Lenard had shown that when ultraviolet light strikes a metal surface, electrons are ejected -- but their maximum kinetic energy depends on the frequency of the light, not its intensity. Classical wave theory predicted that brighter light should produce more energetic electrons, regardless of frequency. Einstein proposed that light itself is quantized into discrete packets (later called photons), each carrying energy $E = h\nu$.

What it showed: Einstein's photon hypothesis explained every feature of the photoelectric effect: the existence of a threshold frequency below which no electrons are ejected (because $h\nu < \phi$, the work function), the linear relationship between maximum kinetic energy and frequency ($K_{\max} = h\nu - \phi$), and the proportionality of photocurrent to intensity (more photons, more electrons, but same energy per photon). Robert Millikan confirmed these predictions quantitatively in 1916, despite his own initial skepticism.

Significance: This was the first clear evidence that electromagnetic radiation has particle-like properties. It established wave-particle duality as a fundamental feature of nature, not merely a mathematical convenience. Einstein received the 1921 Nobel Prize for this work.

Textbook connection: Ch 1.3, Ch 1 code (photoelectric_simulation.py), the photon concept pervades Ch 7, 24, 27.

1911 -- Rutherford Scattering

Who: Hans Geiger and Ernest Marsden, directed by Ernest Rutherford (Manchester)

What was done: Alpha particles from a radioactive source were fired at a thin gold foil. Most passed straight through or were deflected only slightly, as expected. But a small fraction -- about 1 in 8,000 -- were deflected through large angles, some bouncing almost straight back. Rutherford famously compared this to firing a cannonball at tissue paper and having it bounce back.

What it showed: The Thomson "plum pudding" model of the atom, in which positive charge was spread uniformly throughout a sphere, could not explain large-angle scattering. Rutherford concluded that the atom's positive charge and virtually all its mass must be concentrated in a tiny nucleus, roughly $10^{-15}$ m across -- about 100,000 times smaller than the atom itself. This raised an immediate crisis: classical electrodynamics predicted that orbiting electrons should continuously radiate energy and spiral into the nucleus within about $10^{-11}$ seconds.

Significance: Rutherford scattering established the nuclear model of the atom and created the stability crisis that the Bohr model (1913) and ultimately quantum mechanics (1926) would resolve.

Textbook connection: Ch 1.5 (atomic structure), Ch 5 (hydrogen atom), Ch 22 (scattering theory -- Rutherford cross section derived quantum mechanically).

1913 -- The Bohr Model and the Franck-Hertz Experiment

Who: Niels Bohr (Copenhagen); James Franck and Gustav Hertz (Berlin, 1914)

What was done: Bohr postulated that electrons in atoms occupy discrete orbits with quantized angular momentum ($L = n\hbar$, $n = 1, 2, 3, \ldots$), and that transitions between orbits produce or absorb photons of specific frequencies. This yielded the correct hydrogen emission spectrum: $E_n = -13.6\,\text{eV}/n^2$. Franck and Hertz independently confirmed energy quantization in atoms by accelerating electrons through mercury vapor and observing that energy was absorbed only in discrete amounts (4.9 eV for mercury's first excitation).

What it showed: Energy levels in atoms are quantized. The Bohr model's quantitative success for hydrogen -- predicting the Rydberg constant from fundamental constants -- was stunning, even though the model would later be superseded by the full Schrodinger treatment. The Franck-Hertz experiment provided direct, model-independent evidence for discrete energy levels.

Significance: The Bohr model was the bridge between classical physics and quantum mechanics. Its successes (hydrogen spectrum) and failures (multi-electron atoms, intensities, fine structure) motivated the search for a complete theory.

Textbook connection: Ch 1.5 (Bohr model), Ch 5 (hydrogen atom solved properly), Ch 17-18 (perturbation theory explains what Bohr could not).

1922 -- The Stern-Gerlach Experiment

Who: Otto Stern and Walther Gerlach (Frankfurt)

What was done: A beam of silver atoms was passed through an inhomogeneous magnetic field. Classically, the magnetic moment of each atom should be oriented randomly, producing a continuous smear on the detector screen. Instead, the beam split into exactly two discrete spots.

What it showed: The component of angular momentum along the field direction is quantized -- it takes only discrete values, not a continuous range. For the silver atom's outer electron (which has orbital angular momentum $l = 0$ in the ground state), the splitting is entirely due to electron spin, a purely quantum mechanical degree of freedom with no classical analogue. The two spots correspond to $m_s = +1/2$ ("spin up") and $m_s = -1/2$ ("spin down").

Significance: The Stern-Gerlach experiment is the single most important demonstration of measurement in quantum mechanics. It shows that measurement does not merely reveal a pre-existing value but forces the system into one of the allowed eigenstates. Sequential Stern-Gerlach experiments (e.g., $z$-filter $\to$ $x$-filter $\to$ $z$-filter) demonstrate that quantum measurements on incompatible observables are fundamentally irreversible.

Textbook connection: Ch 1.7, Ch 6 (measurement postulate), Ch 8 (spin-1/2 as paradigmatic two-state system), Ch 13 (full spin formalism), Ch 28 (measurement problem).

1923 -- Compton Scattering

Who: Arthur Holly Compton (Washington University, St. Louis)

What was done: X-rays were scattered from free electrons in a graphite target. The scattered X-rays had a longer wavelength than the incident X-rays, with the shift depending on the scattering angle according to $\Delta\lambda = \frac{h}{m_e c}(1 - \cos\theta)$. The quantity $\lambda_C = h/(m_e c) = 0.00243$ nm is the Compton wavelength of the electron.

What it showed: The wavelength shift could not be explained by classical wave theory (which predicts no shift). Compton showed that treating the X-ray as a particle (photon) with momentum $p = h/\lambda$ colliding elastically with an electron, and applying conservation of energy and momentum, yielded exactly the observed formula. This was the definitive confirmation that photons carry momentum as well as energy.

Significance: Compton scattering, together with the photoelectric effect, established beyond doubt that electromagnetic radiation has both wave and particle properties. Compton received the 1927 Nobel Prize.

Textbook connection: Ch 1.4, Compton wavelength in Appendix C.

1927 -- Davisson-Germer: Electron Diffraction

Who: Clinton Davisson and Lester Germer (Bell Labs)

What was done: Electrons accelerated through 54 V were directed at a nickel crystal. The scattered electrons showed a clear diffraction pattern, with intensity maxima at angles predicted by the Bragg condition using the de Broglie wavelength $\lambda = h/p$. Independently, George Paget Thomson (Cambridge) observed electron diffraction through thin metal foils.

What it showed: Electrons -- which had always been considered particles -- exhibit wave behavior. The de Broglie hypothesis ($\lambda = h/p$) was quantitatively confirmed. Matter waves are real.

Significance: This completed the wave-particle duality picture: light behaves as particles (photoelectric, Compton), and particles behave as waves (electron diffraction). Davisson and Thomson shared the 1937 Nobel Prize. The irony is rich: J.J. Thomson won the Nobel Prize for showing the electron is a particle; his son G.P. Thomson won it for showing the electron is a wave.

Textbook connection: Ch 1.8 (de Broglie waves), Ch 1 code (de_broglie_wavelengths.py), Ch 3 (wave mechanics made rigorous).

1927 -- The Fifth Solvay Conference

Who: Bohr, Einstein, Heisenberg, Schrodinger, Dirac, Born, Pauli, de Broglie, and 22 others (Brussels)

What was done: This was not a single experiment but the most consequential physics conference in history. Bohr presented the Copenhagen interpretation. Einstein challenged it with a series of ingenious thought experiments designed to show that quantum mechanics was incomplete or inconsistent. Bohr refuted each challenge.

What it showed: The Bohr-Einstein debates crystallized the interpretive questions that remain unresolved today: Is the wave function a complete description of reality? Does measurement create outcomes or merely reveal them? Is quantum randomness fundamental or a sign of hidden variables? These questions would simmer for decades before Bell (1964) showed how to test them experimentally.

Significance: The Solvay Conference established the Copenhagen interpretation as the mainstream view and framed the foundational debates that continue to this day. It also demonstrated that the mathematical formalism of quantum mechanics was not in dispute -- only its interpretation.

Textbook connection: Ch 1.10 (historical context), Ch 24 (EPR and Bell), Ch 28 (measurement problem and interpretations).

1935 -- The Einstein-Podolsky-Rosen (EPR) Paper

Who: Albert Einstein, Boris Podolsky, and Nathan Rosen (Princeton)

What was done: EPR published a thought experiment (not a laboratory experiment) arguing that quantum mechanics is incomplete. They considered two particles that interact and then separate. By measuring the position of particle 1, one can predict the position of particle 2 with certainty; by measuring the momentum of particle 1, one can predict the momentum of particle 2 with certainty. Since the particles are far apart, measurement on particle 1 cannot physically affect particle 2 (locality). Therefore, EPR argued, particle 2 must have definite values of both position and momentum simultaneously -- but quantum mechanics forbids this. Conclusion: quantum mechanics is incomplete.

What it showed: The EPR argument revealed that quantum mechanics, if complete, requires nonlocal correlations -- what Einstein called "spooky action at a distance." The paper did not claim quantum mechanics gives wrong predictions, only that its description of reality must be incomplete, and that "hidden variables" must exist to restore local realism.

Significance: EPR is the founding document of quantum foundations. It would take nearly three decades (Bell, 1964) to show that the question could be resolved experimentally, and nearly five decades (Aspect, 1982) to perform the experiment.

Textbook connection: Ch 24.1-24.3 (EPR argument in full), Ch 11 (tensor products and entanglement formalism), Ch 28 (interpretations).

1952 -- Bohm's Reformulation of EPR with Spin

Who: David Bohm (Sao Paulo)

What was done: Bohm reformulated the EPR thought experiment using a pair of spin-1/2 particles in the singlet state $|\Psi^-\rangle = \frac{1}{\sqrt{2}}(|\uparrow\downarrow\rangle - |\downarrow\uparrow\rangle)$ instead of the continuous position-momentum variables used by EPR. This made the argument conceptually cleaner and experimentally more tractable: measuring the spin of particle 1 along any axis instantly determines the spin of particle 2 along that axis.

What it showed: Bohm's version made the EPR puzzle sharper and more experimentally accessible. It also inspired Bohm to develop his own hidden-variable interpretation (Bohmian mechanics, or pilot-wave theory), demonstrating that hidden-variable theories were not logically impossible, contrary to what some had believed based on von Neumann's flawed no-go theorem.

Significance: Bohm's reformulation was the direct catalyst for Bell's theorem twelve years later. Bell's inequality is formulated entirely in terms of spin measurements on Bohm's version of the EPR state.

Textbook connection: Ch 24.2 (Bohm's version), Ch 13 (spin singlet state), Ch 28.3 (Bohmian mechanics).

1964 -- Bell's Theorem

Who: John Stewart Bell (CERN)

What was done: Bell proved a mathematical theorem: any theory that is both local (no faster-than-light influences) and realistic (particles have definite properties whether or not they are measured) must satisfy certain statistical inequalities -- now called Bell inequalities -- for correlations between measurements on entangled particles. Bell then showed that quantum mechanics violates these inequalities. Therefore, if quantum mechanics is correct, nature cannot be both local and realistic.

What it showed: The EPR debate was not merely philosophical -- it was empirically testable. If Bell's inequality is violated in experiment, then either locality or realism (or both) must be abandoned. This was, as physicist Abner Shimony put it, an instance of "experimental metaphysics."

Significance: Bell's theorem is one of the most profound results in all of physics. It draws a sharp, testable line between the quantum world and any possible classical description. The 2022 Nobel Prize recognized the experimental work it inspired.

Textbook connection: Ch 24.4-24.6 (Bell's theorem derived), Ch 24 code (bell_test_chsh.py), Ch 39 (capstone: Bell test simulator).

1959/1960/1986 -- The Aharonov-Bohm Effect

Who: Yakir Aharonov and David Bohm (1959, theoretical prediction); R.G. Chambers (1960, first observation); Akira Tonomura et al. (1986, definitive electron holography confirmation)

What was done: Aharonov and Bohm predicted that an electron traveling through a region with zero magnetic field can still be affected by a magnetic vector potential $\mathbf{A}$ if it encircles a region where $\mathbf{B} \neq 0$ (e.g., a solenoid). The electron acquires a phase shift $\Delta\phi = (e/\hbar)\oint \mathbf{A} \cdot d\mathbf{l}$ that depends on the enclosed magnetic flux. Chambers observed the effect in 1960, and Tonomura's 1986 experiment using nanofabricated toroids provided the definitive, loophole-free confirmation.

What it showed: The electromagnetic potentials ($\phi$, $\mathbf{A}$) are not merely mathematical conveniences -- they have direct physical significance in quantum mechanics. In classical physics, only the fields $\mathbf{E}$ and $\mathbf{B}$ are measurable; the potentials are gauge-dependent and supposedly unobservable. Quantum mechanics elevates the potentials to fundamental status.

Significance: The Aharonov-Bohm effect is the paradigmatic example of a geometric/topological phase in quantum mechanics. It paved the way for Berry's phase (1984) and the understanding of topological phases of matter.

Textbook connection: Ch 29 (geometric phase), Ch 32 (Berry phase), Ch 36 (topological phases).

1972 -- Freedman-Clauser: First Bell Test

Who: Stuart Freedman and John Clauser (UC Berkeley)

What was done: Freedman and Clauser performed the first experimental test of Bell's inequality using entangled photons produced by atomic cascade emission in calcium atoms. They measured the polarization correlations of photon pairs at various detector angles.

What it showed: Bell's inequality was violated, consistent with quantum mechanical predictions. This was the first experimental evidence against local hidden variable theories. However, the experiment had significant "loopholes": the detectors were not efficient enough (detection loophole), and the measurement settings were chosen in advance rather than randomly during the photons' flight (locality loophole).

Significance: This was the first real-world test of quantum mechanics versus local realism, opening the era of experimental quantum foundations.

Textbook connection: Ch 24.7 (experimental Bell tests), Ch 39 (capstone discusses loopholes).

1982 -- Aspect's Experiments

Who: Alain Aspect, Philippe Grangier, and Gerard Roger (Orsay, France)

What was done: Aspect and collaborators performed a series of increasingly refined Bell test experiments. The critical innovation in the third experiment was the use of fast acousto-optical switches that changed the detector settings while the photons were in flight, closing the locality loophole (the detection loophole remained open). The measurement settings were changed every 10 nanoseconds -- faster than light could travel between the two detectors.

What it showed: Bell's inequality was violated by a large margin (up to 40 standard deviations), in quantitative agreement with quantum mechanics. The fast switching eliminated the possibility that one detector "knew" the setting of the other through any subluminal signal.

Significance: Aspect's experiments were widely regarded as the definitive refutation of local hidden variable theories, though the detection loophole remained. Aspect shared the 2022 Nobel Prize for this work.

Textbook connection: Ch 24.7, Ch 39 (loophole analysis).

1995 -- Bose-Einstein Condensation Achieved

Who: Eric Cornell and Carl Wieman (JILA/University of Colorado); independently Wolfgang Ketterle (MIT)

What was done: Using laser cooling and evaporative cooling techniques, Cornell and Wieman cooled a gas of approximately 2,000 rubidium-87 atoms to about 170 nanokelvin -- less than a millionth of a degree above absolute zero. At this temperature, the de Broglie wavelengths of the atoms overlap, and a macroscopic fraction of the atoms collapses into the same quantum ground state, forming a Bose-Einstein condensate (BEC). Ketterle independently achieved BEC with sodium atoms and demonstrated interference between two condensates.

What it showed: Bose-Einstein condensation, predicted by Bose and Einstein in 1924-1925, is a real macroscopic quantum phenomenon. A BEC is a state of matter in which thousands to millions of atoms share a single quantum wave function, making quantum effects visible at macroscopic scales.

Significance: BEC provided a new platform for studying quantum phenomena: superfluidity, vortices, atom lasers, and quantum simulation. Cornell, Wieman, and Ketterle shared the 2001 Nobel Prize.

Textbook connection: Ch 15 (identical particles, Bose-Einstein statistics), Ch 26 (condensed matter), Ch 34 (second quantization and Fock space).

1998 -- Quantum Error Correction Demonstrated

Who: D. Cory, M. Price, and T. Havel (MIT); independently E. Knill, R. Laflamme, et al. (Los Alamos)

What was done: Using nuclear magnetic resonance (NMR) quantum computing techniques, researchers demonstrated the basic principles of quantum error correction -- encoding a logical qubit into multiple physical qubits and correcting errors without directly measuring (and thereby destroying) the quantum information. These early demonstrations used three-qubit codes to correct single bit-flip errors.

What it showed: Quantum information, despite its extreme fragility, can be protected against errors through cleverly designed encoding schemes. The theoretical frameworks developed by Peter Shor (1995) and Andrew Steane (1996) were shown to be experimentally viable.

Significance: Quantum error correction is the essential ingredient that makes large-scale quantum computing theoretically possible. Without it, decoherence would destroy quantum information far too quickly for useful computation.

Textbook connection: Ch 35 (quantum error correction -- Shor and Steane codes), Ch 33 (decoherence), Ch 40 (capstone: quantum computing).

2001 -- Shor's Algorithm Implemented on 7 Qubits

Who: Lieven Vandersypen, Matthias Steffen, Gregory Breyta, Costantino Yannoni, Mark Sherwood, and Isaac Chuang (IBM Almaden / Stanford)

What was done: Using a 7-qubit NMR quantum computer, the team factored the number 15 into its prime factors (3 and 5) using Shor's quantum factoring algorithm. This was the first experimental demonstration of a quantum algorithm solving a classically significant problem.

What it showed: Shor's algorithm, which Peter Shor had proven in 1994 could factor large numbers exponentially faster than any known classical algorithm, could actually be implemented on real quantum hardware. While factoring 15 is trivial classically, the demonstration proved the principle: quantum algorithms can exploit superposition and entanglement to solve problems in fundamentally new ways.

Significance: This experiment demonstrated that quantum speedup is not just a theoretical possibility but a laboratory reality. The practical implications for cryptography and number theory are enormous, though factoring cryptographically relevant numbers requires millions of error-corrected qubits -- still far beyond current technology.

Textbook connection: Ch 25 (quantum information and algorithms), Ch 40 (capstone: implementing Shor's algorithm on a simulator).

2012 -- Discovery of the Higgs Boson

Who: ATLAS and CMS collaborations at CERN's Large Hadron Collider (approximately 6,000 physicists)

What was done: By colliding protons at center-of-mass energies up to 8 TeV and analyzing the decay products, both the ATLAS and CMS detectors independently observed a new particle with mass approximately 125 GeV/$c^2$, consistent with the Higgs boson predicted by the Standard Model. The discovery was announced on July 4, 2012.

What it showed: The Higgs field -- the mechanism by which fundamental particles acquire mass through spontaneous symmetry breaking -- is real. The Higgs boson is an excitation of this field. Its discovery completed the Standard Model of particle physics, a quantum field theory that describes the electromagnetic, weak, and strong interactions.

Significance: The Higgs discovery is the crowning triumph of quantum field theory (QFT), the relativistic extension of quantum mechanics. It validated fifty years of theoretical development (Higgs, Brout, Englert, Guralnik, Hagen, Kibble, 1964) and the principle that symmetry breaking generates structure. Francois Englert and Peter Higgs shared the 2013 Nobel Prize.

Textbook connection: Ch 32 (nuclear and particle physics), Ch 34 (second quantization), Ch 37 (bridge to QFT).

2015 -- Loophole-Free Bell Tests

Who: B. Hensen et al. (Delft University of Technology); L.K. Shalm et al. (NIST Boulder); M. Giustina et al. (University of Vienna)

What was done: Three independent groups, within months of each other, performed Bell test experiments that simultaneously closed both the locality loophole (measurement settings chosen randomly and space-like separated) and the detection loophole (high-efficiency detectors capturing nearly all events). The Delft experiment used entangled nitrogen-vacancy centers in diamond separated by 1.3 km, with random number generators determining measurement settings. The NIST and Vienna experiments used entangled photons with superconducting nanowire detectors achieving detection efficiencies above 90%.

What it showed: Bell's inequality was violated with high statistical significance in all three experiments, with all major loopholes closed simultaneously. The Delft experiment achieved $p < 0.039$; the NIST experiment achieved $p < 2.3 \times 10^{-7}$.

Significance: These experiments represent the definitive, essentially loophole-free refutation of local hidden variable theories. Nature is not locally realistic. Any viable interpretation of quantum mechanics must either abandon locality, abandon realism, or adopt some other radical departure from classical intuition.

Textbook connection: Ch 24.8 (loophole-free tests), Ch 39 (capstone: detailed loophole analysis).

2019 -- Google's Quantum Supremacy Claim

Who: Frank Arute et al. (Google AI Quantum, Santa Barbara)

What was done: Using a 53-qubit superconducting processor called "Sycamore," Google's team performed a specific random circuit sampling task in approximately 200 seconds. They claimed that the same task would take the world's most powerful classical supercomputer approximately 10,000 years to perform. IBM subsequently challenged this estimate, arguing that with sufficient classical memory and algorithmic optimizations, the task could be completed classically in about 2.5 days.

What it showed: Even under IBM's revised estimate, the quantum processor achieved a speedup of roughly a factor of 1,000 for this specific task. This was the first credible claim that a programmable quantum computer had performed a computation that is infeasible for any existing classical computer -- a milestone called "quantum supremacy" or "quantum advantage."

Significance: Quantum supremacy, while achieved for an artificial task with no immediate practical application, demonstrated that quantum computing has crossed a fundamental threshold: quantum processors can outperform classical ones on at least some tasks. The debate about the precise classical difficulty of the task highlights the subtlety of quantum advantage claims.

Textbook connection: Ch 25 (quantum computing fundamentals), Ch 36 (quantum technologies), Ch 37 (state of the art), Ch 40 (capstone).

2022 -- Nobel Prize for Bell Test Experiments

Who: Alain Aspect (France), John Clauser (USA), and Anton Zeilinger (Austria)

What was done: The Nobel Committee awarded the 2022 Physics Prize "for experiments with entangled photons, establishing the violation of Bell inequalities and pioneering quantum information science." This recognized the full arc from Clauser's first Bell test (1972) through Aspect's loophole-closing experiments (1982) to Zeilinger's quantum teleportation and advanced entanglement experiments (1990s-2010s).

What it showed: The Nobel Prize represented the physics community's definitive acknowledgment that the foundations of quantum mechanics -- entanglement, nonlocality, and their technological implications -- are not merely philosophical curiosities but central pillars of modern physics. The award also recognized that foundational experiments have practical applications: quantum cryptography, quantum teleportation, and quantum computing all descend directly from Bell test experiments.

Significance: For decades, work on quantum foundations was considered somewhat marginal -- interesting philosophy, perhaps, but not "real" physics. The 2022 Nobel Prize reversed this perception entirely, affirming that understanding entanglement and nonlocality is among the most important achievements in the history of physics.

Textbook connection: Ch 24 (entanglement and Bell's theorem), Ch 25 (quantum information science), Ch 39 (capstone: Bell test simulator).

Summary Timeline

This timeline is necessarily selective. Hundreds of other experiments have contributed to our understanding of quantum mechanics, including neutron interferometry, quantum teleportation (Zeilinger et al., 1997), quantum key distribution demonstrations, cavity QED experiments (Haroche and Wineland, 2012 Nobel Prize), and the ongoing development of topological qubits. The experiments listed here were chosen because they mark the clearest turning points in the story this textbook tells.