Quantum Optics

Several topics of current interest in quantum optics, such as electron optics vs photon optics, squeezed states of light, cavity quantum electrodynamics, and quantum nondemolition measurements are reviewed.Electron optics and photon opitics are essentially identical in single particle interference effects. However, when two entangled particles are involved in the interferometry, the fermionic character of electrons and bosonic character of photons produce remarkably different results. The suppression of partition noise due to dissipation in fermionic (electron) systems is in sharp contrast to the enhancement of partition noise due to dissipation in bosonic (photon) systems.Electromagnetic waves, with the noise on one quadrature amplitude reduced to below the quantum noise of a coherent state and the noise on the other quadrature amplitude enhanced to above it, are called squeezed states of light. Such nonclassical states of light have been studied extensively for the last decade because of their potential applications to various precision measurements. Generation of number-phase squeezed states by constant current driven semiconductor lasers is emphasized in this article. The extension of this technique to mesoscopic systems for regulated single photon generation is also described.Spontaneous emission of an atom is either enhanced or suppressed by modifying a vacuum field fluctuation by a cavity wall. In a high-Q cavity, spontaneous emission is made even a reversible process. Such a technique of manipulating spontaneous emission is called cavity quantum electrodynamics. A new class of optical microcavity is making possible the exploration of cavity quantum electrodynamic phenomena in condensed matter systems. Control of spontaneous emission in a semiconductor quantum well microcavity and its application to a low-threshold microlaser are emphasized in this article.Quantum nondemolition measurements are the repeated measurements of an observable without changing the free evolution of the observable. The measurement back action is confined to the conjugate observable of the measured observable and the Heisenberg uncertainty principle is still satisfied. This new measurement scheme can improve the measurement sensitivity of a quantum object and has recently been demonstrated.