Einstein is well known for his rejection of quantum mechanics in the form it emerged from the work of Heisenberg, Born and Schrodinger in 1926. Much less appreciated are the many seminal contributions he made to quantum theory prior to his final scientific verdict: that the theory was at best incomplete. His many key conceptual innovations leading to the emergence of modern quantum theory place him as arguably its central figure . In this talk I will focus on his introduction of the idea of quanta of light in 1905, the beginning of the photon concept in physics. Einstein recognized these quanta as “fundamental waves”, i.e. entities with wave-like properties which do not require a supporting medium, and he connected them closely with his argument for energy-mass equivalence. He spent much of his research effort between 1908 and 1911 on a failed attempt to generalize Maxwell’s wave equation to include light quanta, but in 1909 he was able to derive rigorously a fluctuation formula for blackbody radiation which implied wave-particle duality. His 1916-17 works on the quantum theory of radiation derived the Planck blackbody formula by means of the detailed balance condition and introduced the concepts of spontaneous and stimulated emission, while also strengthening the argument for considering light quanta to be “real” and not a heuristic construct. The observation of the Compton effect in 1923-1925 finally led to general acceptance of this idea, and soon afterwards they acquired the label “photons”. In modern physics photons are one of the fundamental force-carrying bosons in the Standard Model. Modern research in quantum optics, and more recently in circuit quantum electrodynamics, has enabled us for the first time to completely control the states of one or a few photons, and create arbitrary non-classical states in their Hilbert space. Because of this new level of control, few-photon states of microwave cavities are becoming leading candidates for quantum information storage and processing, due to the possibility of efficient error detection and correction . I will review both the history described above and some highlights of these very recent developments in this talk.  “Einstein and the Quantum: The Quest of the Valiant Swabian”, A. Douglas Stone, Princeton University Press (2013).  Extending the lifetime of a quantum bit with error correction in superconducting circuits, N. Ofek, R.J. Schoelkopf et al. Nature , 536, 441–445 (2016).
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Professor Stone’s current research is in optical physics and photonics, focusing on laser physics and microcavity optics, optical phenomena in complex and disordered systems, wave chaos and random matrix theory, non-hermitian effects and gain/loss engineering. He also has an active interest in quantum measurement and quantum computing. Trained as a condensed matter theorist, his earlier research was in the field of Anderson localization and quantum transport phenomena in disordered media, mesoscopic fluctuations of electronic conduction, non-linear dynamics, and quantum chaos.
His major contributions to optical physics include the introduction of ray and wave chaos concepts for the description of deformed microcavities and lasers, the development of Steady-state Ab initio Laser Theory (SALT) for describing novel microlasers, including random and chaotic cavity lasers, the discovery of Coherent Perfect Absorption or time-reversed lasing, the discovery of long-range correlations in the scattering properties of disordered systems (all topics in collaboration with various colleagues).
Professor Stone was one of the first condensed matter theorists to emphasize the novel properties of mesoscopic systems which are much larger than the atomic scale, but differ in their behavior from bulk solids. Prominent among these are phase coherence and related sample-specific fluctuations in all physical properties. Together with Patrick Lee he showed that the fluctuations of mesoscopic conductance are universal, with a variance depending only on the fundamental unit of conductance, e2/h, an effect which can be explained by the spectral rigidity of random matrices. Mesoscopic fluctuations have a direct connection to the field of quantum chaos which has applications in nuclear, atomic, condensed matter and optical physics, and Stone has applied concepts from quantum chaos theory to explain fluctuations in semiconductor quantum wires and quantum dots.