Nonclassical light has the potential to provide improvements in signal-to-noise ratio in a variety of applications. This tutorial provides a characterization of nonclassical light, describes its two present manifestations—quadrature-squeezed and number-squeezed (antibunched) light — discusses methods for generating and detecting these two kinds of nonclassical light, and considers potential applications with a critical view as to when nonclassical light might be useful.
Nonclassical light has the potential to provide improvements in signal-to-noise ratio in a variety of applications. This tutorial provides a characterization of nonclassical light, describes its two present manifestations—quadrature-squeezed and number-squeezed (antibunched) light — discusses methods for generating and detecting these two kinds of nonclassical light, and considers potential applications with a critical view as to when nonclassical light might be useful.
In this tutorial article the authors provide a discussion of squeezed states of light from an elementary point of view. An outline of the topics considered is provided in the contents list below. Following the presentation of topics 1-3, which are of a general nature, they discuss two kinds of nonclassical light: quadrature-squeezed light (topics 4-6) and photon-number-squeezed light (topics 7-9). In the last part of the article they provide a listing of early nonclassical light experiments and consider a number of applications (and potential applications) of squeezed light. Finally, they provide a survey of the available general literature.
The generation of nonclassical light has recently received a great deal of attention because three forms of it have now been observed in the laboratory: antibunched light, photon-number-squeezed (or sub-Poisson) light, and quadrature-squeezed light. These characteristics may, but need not, accompany each other in any given light source. Nonclassical light has been produced in experiments using resonance fluorescence, the Franck-Hertz effect, parametric interact ions, and semiconductor light sources. It is likely to be useful in providing new insights in various physical and biological processes, and in applications such as lightwave communications. Some of the characteristics, methods of generation, and expected uses of squeezed light will be addressed.
In 1963 Glauber /Phys. Rev. 130, 2529 and 131, 2766/ published a basic theoretical study that revealed the broad variety of possible photon states. Later on a quantum-statistical analysis showed that states with classical analog (this light Is termed classical light) as well as states without classical analog (so-called nonclassical light) can occur. Following the definition given by Teich, Saleh, and Perina /JOSAB2 (1985) 275) nonclassical light exhibits one or more of the attributes squeezed, antibunched, sub-Poissonian, what is connected with a negative value of the field-fluctuation excess, the bunching excess, or the Poisson excess. These negative values mean quantum fluctuations below the classical standard quantum limits of ideal laser light; thus, nonclassical light may yield an essential improvement of the optical measurement accuracy, in particular of the signal-to-noise ratio. There exists a common property of the three attributes concerning the Glauber-Sudarshan representation P(c ), which is the real weight function belonging to the incoherent mixture (density operators) of Glauber states with different complex amplitudes. In the case of classical light P(oç ) is a positive definite function, whereas nonclassical light requires a nonpositive definite function P(o.), which cannot be interpreted as a proper probability distribution - as it is possible in the case of light with a classical analog /M. Schubert, Ann. d. Phys. 4k (1987) 53/. In addition to its possible important applications nonclassical light yields a deep insight into the quantum nature of the radiation field.
This chapter presents a synopsis on nonclassical light, emphasizes the roles of different quantum amplifiers, and discusses the problem of overcoming the detrimental effect of loss. The generation of two-photon coherent state (TCS) and near-number state (NNS) via nonlinear optical processes are, in some sense, surprisingly similar. This similarity is in addition to that between TCS and number-phase minimum uncertainty states when the nonclassical effects are small. It seems to arise from an underlying intrinsic quantum correlation. Nonclassical light do not propagate well. This is because significant loss, be it radiative, absorption, or otherwise, is often incurred during propagation. Nonclassical light with matching detection leads to significant improvement in signal-to-noise (SNR) ratio. Even in situations where SNR is not the most appropriate performance measure, it is clear that the low noise characteristics of TCS and NNS, or simply their difference from classical states, could be useful.
Recently a number of laboratories have demonstrated the generation of squeezed light, a new kind of light which in some of its aspects exhibits less quantum noise then coherent light. Here a description will be given of how such light is generated and detected. With the successful generation and detection of squeezed light by a number of laboratories1-5 a new degree of control over the quantum statistics of light has been achieved. Light can now be generated which, in some of its aspects, has less quantum noise than coherent light. Such light may find applications in optical communications and in sensitive and precision measurement. Here a description will be given of how squeezed light is generated and detected.6-8 The discussion will be restricted to what is called "quadrature squeezing". The electric field operator for a single mode of the electromagnetic field can be written in the form
We briefly review the ideas that have shaped modern optics and have led to various applications of light ranging from spectroscopy to astrophysics, and street lights to quantum communication. The review is primarily focused on the modern applications of classical light and nonclassical light. Specific attention has been given to the applications of squeezed, antibunched, and entangled states of radiation field. Applications of Fock states (especially single photon states) in the field of quantum communication are also discussed.