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Journal of Mathematical Physics

Properties of near superposition of two squeezed vacuum states

Anas Othman

Published Aug 1, 2024• 3 citations
Publisher

Abstract

The near superposition of squeezed vacuum states (NSVS) is investigated in this article. The state appears to be a superposition of a squeezed vacuum state (SVS) and a derivative-squeezed vacuum state. We have shown that NSVS is significantly different from any regular superposition of two SVSs. NSVS, like SVS, displays only even photons, but with different distributions. In some cases, NSVS has no vacuum state. NSVS displays sub-Poissonian statistics for small values of the squeezing parameter. NSVS reveals linear and amplitude-squared squeezing, with amplitude-squared squeezing surpassing SVS in most cases. The minimum uncertainty is explored, and a possible method for generating NSVS is explained. We have discovered that NSVS exhibits a similar behavior for all phase differences except when it equals precisely zero. This phenomenon has been identified and could potentially enable more sensitive measurements.

DOI
10.1063/5.0186279

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The near superposition of squeezed vacuum states (NSVS) is investigated in this article. The state appears to be a superposition of a squeezed vacuum state (SVS) and a derivative-squeezed vacuum state. We have shown that NSVS is significantly different from any regular superposition of two SVSs. NSVS, like SVS, displays only even photons, but with different distributions. In some cases, NSVS has no vacuum state. NSVS displays sub-Poissonian statistics for small values of the squeezing parameter. NSVS reveals linear and amplitude-squared squeezing, with amplitude-squared squeezing surpassing SVS in most cases. The minimum uncertainty is explored, and a possible method for generating NSVS is explained. We have discovered that NSVS exhibits a similar behavior for all phase differences except when it equals precisely zero. This phenomenon has been identified and could potentially enable more sensitive measurements.
Abstract Superposition of two coherent states, the Schrodinger’s cat state, can exhibit different nonclassical properties having foundational applications in quantum information processing. We consider the ‘superposition of Schrodinger’s cat state with the vacuum state (SCVS)’ of the optical field. We discuss different witness of nonclassicality properties such as lower- and higher-order squeezing (viz., squeezing, Hong & Mandel’s fourth-order squeezing, amplitude-squared squeezing) and sub-Poissonian photon statistics. Further, we discuss the negativity of the Wigner function of SCVS indicating the nonclassicality of the state under investigation. We find that the vacuum state contribution in SCVS exhibits different nonclassicalities under some conditions stronger where the nonclassicalities exhibited by the state without vacuum state contribution are weaker.
Abstract Recently, photon subtraction from the single-mode squeezed vacuum state (SVS) has been explored as a technique to enhance its squeezing strength (SS). Notably, the enhancement is observed only when an even number of photons is subtracted, and this effect is limited to a specific range of the squeezing parameter r. In this paper, we introduce a novel class of single-mode nonclassical states, termed as qubit superposed SVSs (qSSVSs), via the coherent superposition of a SVS and a single-photon-subtracted SVS. The primary objective of this work is to enhance the SS for any r > 0 through the creation of these superposed states. Our analysis reveals that the qSSVSs not only improve the SS but also exhibit enhanced nonclassical features such as the negativity of Wigner function, single-mode antibunching effect, photon-number distribution, and sub-Poissonian photon statistics. Furthermore, we demonstrate that the qSSVSs provide superior phase sensitivity in a quantum Mach–Zehnder interferometer compared to the original SVS. Importantly, the generation of qSSVSs is feasible using readily available optical devices, including a beam splitter, a photodetector, and an amplitude displacement. These states hold significant potential for practical applications in quantum information science, particularly for tasks such as information encoding and processing in quantum computing systems.
Quadrature variances of a radiation field depend not only on the photon number distribution in the field but also on the relative phases of the photon number probability amplitudes. Two fields with the same photon number distribution can show different degrees of squeezing if photon number states are superposed with different relative phases. It is thus possible, for example, for a radiation field with Poissonian photon statistics to exhibit squeezed quadrature fluctuations. Since different relative superposition phases in general yield different maximum and minimum values of the quadrature variances, measurement of the variances can yield information concerning the relative phases between different number states.
In Section 11.5 we showed that, although the complex amplitude of the electromagnetic field has a well-defined value in any coherent state, yet the real and imaginary (Hermitian and anti-Hermitian) parts of the field fluctuate with equal dispersions. The phenomenon of vacuum fluctuations is a manifestation of this effect, because the vacuum state is an example of a particular coherent state. This behavior is quite different from that of an ordinary, classical field. In a squeezed state, which is even more non-classical, as we shall see, one part of the field fluctuates less and another part fluctuates more than in the vacuum state. In general, a squeezed state is one in which the distribution of canonical variables over the phase space has been distorted or ‘squeezed’ in such a way that the dispersion of one variable is reduced at the cost of an increase in the dispersion of the other variable. In the following we shall examine the properties of squeezed states when the two canonical variables are two quadratures of the electromagnetic field. Although the squeezing terminology is sometimes applied to variables other than the two field quadratures, it is less meaningful in those cases. A number of review articles on squeezing have been published and can be consulted for more details (Walls, 1983; Schumaker, 1986; Loudon and Knight, 1987; Teich and Saleh, 1989, 1990; Kimble, 1992).