Generation of non-classical states from an optical parametric oscillator/amplifier and their applications

Abstract

Quantum information and quantum optics are rapidly advancing areas of modern physics. As an important device in quantum optics and quantum information, the optical parametric amplifier/oscillator (OPA/O) has been extensively studied and applied to the generation of non-classical state since the 1980s. This article reviews the progress in the generation of nonclassical state from an OPO/A and application of twin beams in quantum optics and quantum information.Keywords entanglement, optical parametric oscillator, squeezed state, twin beams PACS numbers 42.50.Dv, 03.67.Dd Non-classical states or quantum states are arguably the important resource in the field of quantum information [1, 2] and quantum optics. The most well-known nonclassical state of light is the so-called squeezed state. It is special since its optical noise is redistributed such that its noise is less than the standard quantum noise limit in one quadrature while the fluctuations are larger in the correspondingly orthogonal quadrature. Another nonclassical state is the twin beams state, in which intensity difference fluctuations between them is less than that between two coherent beams. In addition, entanglement, i.e., nonlocal quantum correlation between two or more quantum mechanical objects, is the essential resource in present quantum information and communications technology. Furthermore, it has also been used to verify the foundations of the quantum theory. Thus, the development of techniques to generate these quantum states is of great importance in this field. Lots of efficient methods have been proposed to generate the non-classical state. Among them, two of the most successful systems for squeezed state generation have been the optical parametric oscillator (OPO) and optical parametric amplifier (OPA), both of which have the same underlying the second-order (χ (2) ) nonlinearity. With the χ (2) nonlinearity, the two-photon state from spontaneous parametric down-conversion (SPDC) has served as a test bed for verifying the foundations of the quantum theory, such as the Einstein, Podolsky and Rosen (EPR) paradox [3], and has been exploited as a powerful source for demonstrating quantum information experiments with discrete variable [4]. On the other hand, OPA/O has also developed into one of the most efficient tools to produce entangled states and squeezed state of light for quantum information systems with continuous variable (CV) from the first realization of squeezed state from an OPO at a couple of decades ago.The operation regime for the above device is one in which the OPO is pumped by a harmonic wave (frequency 2 ω ), whose power is close to the threshold power for the onset of parametric oscillation. The input subharmonic waves are usually either vacuum modes or very weak, so that in the amplification process no or very little power is transferred to them from the pump wave (no pump deletion). Basic optical processes of OPO involving the χ (2) nonlinearity are illustrated in Fig. 1. We