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16th Congress of the International Commission for Optics: Optics as a Key to High Technology

Non-classical properties of superposition states in phase-sensitive reservoirs and phase-sensitive amplifiers

M. S. Kim

Published Jul 26, 1993• 0 citations
Publisher

Abstract

We investigate the influence of phase-sensitive reservoirs (attenuators) and phase-sensitive amplifiers on quantum-mechanical superposition (Schrodinger cat) states of light. In particular, we study how the quantum coherence emerging as a consequence of quantum interference between two coherent state is decaying under the influence of the environment.

DOI
10.1117/12.2308450

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We investigate the influence of phase-sensitive reservoirs (attenuators) and phase-sensitive amplifiers on quantum-mechanical superposition (Schrodinger cat) states of light. In particular, we study how the quantum coherence emerging as a consequence of quantum interference between two coherent state is decaying under the influence of the environment.
We study phase properties of quantum mechanical superposition states decaying into phase-sensitive reservoirs. We show that the Wigner phase quasiprobability distribution reflects the quantum interference effects very well while the Pegg–Barnett and the Husimi phase probability distributions are quite insensitive with respect to the character of the quantum interference between component states. We study in detail phase properties of the even coherent state which decays into the thermal and the squeezed reservoirs. In thermal reservoirs the phase of the superposition state becomes randomized under the influence of thermal fluctuations. The higher the number of thermal photons the faster the randomization process is. On the other hand we show that depending on the relative phase between the superposition state and the phase-sensitive reservoir the process of phase randomization can be either enhanced or completely suppressed.
Any quantum-mechanical system is not isolated. It interacts with its environment (for instance, it interacts with reservoirs). It is known that the decay rate of quantum coherences in phase-sensitive (squeezed) reservoirs can be significantly modified compared to the decay rate in ordinary (phase- insensitive) thermal reservoirs. Depending on phases of the quantum system (field mode) and the squeezed reservoir the decay rate of the quantum coherence can be either enhanced or significantly suppressed. In this paper we study in which way the phase properties of an even coherent state 1 (CS) are changed under the influence of reservoirs.
We examine the nonclassical property of a Schr\"odinger cat state, i.e., a superposition of two coherent states, when it is amplified by either a phase-sensitive or a phase-insensitive amplifier. In both cases the corresponding P representation remains nonpositive in some area of the complex plane, for any amplification factor. The contribution to the P function from these areas decreases exponentially with an amplification factor. With a phase-sensitive amplifier the onset of decay can be postponed to a larger amplification factor. Thus the nonclassical nature of the field can be preserved under a wide range of conditions, in spite of the noise introduced in the amplification process. \textcopyright{} 1996 The American Physical Society.
We study statistical properties of quantum superposition states (Schr\"odinger-cat states) amplified by phase-sensitive (squeezed) amplifiers. We show that the phase-sensitive amplifier with a properly chosen phase can preserve quantum coherences and nonclassical behavior of the Schr\"odinger-cat-state input even for a gain factor G larger than 2. In particular, we show that for an even coherent state (CS) phase-sensitive amplifiers can preserve squeezing for G>2 but simultaneously in the process of amplification the noise added by the amplifier leads to a rapid increase of fluctuations in the photon number. Because of the finite maximum degree of squeezing obtainable for the even CS the maximum gain factor Gm{\mathit{G}}_{\mathit{m}}Gm​ for which squeezing can still be observed in the output state is finite. The phase-sensitive amplifier with a properly chosen phase can also reduce fluctuations in the photon number of the initial even CS. Nevertheless, one cannot amplify the initial even CS with super-Poissonian photon statistics into the state with sub-Poissonian photon statistics.
Strong laser-atom interactions can produce highly non-classical states of light by using the process of high-harmonic generation in atoms. When the high-harmonic generation is present, the quantum state of the fundamental mode following the interaction is known as the Schrödinger cat state, which is a superposition of the laser's initial coherent state and the coherent state with a smaller amplitude that results from its interaction with atoms. Here, we demonstrate that new light states with significantly different Wigner function distributions can be produced by combining two separate Schrödinger cat states. Through the engineering of Schrödinger cat states' parameters, we are able to produce Wigner functions that exhibit high sensitivity in relation to the system parameter. Our research paves the way for the creation of non-classical light by superposing Schrödinger cat states with application in such as quantum sensing.