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Physical Review A

Field-squeeze operators via coherent population trapping

Qingping Hu, Xiangming Hu, Liang Hu, Guanghui Wang

Published Jan 2, 2019• 1 citation
Publisher

Abstract

We present a scheme to generate unitarily two-mode and four-mode field squeezing in optical cavities with the near-resonantly dressed three-level atoms in the $\mathrm{\ensuremath{\Lambda}}$ configuration. The dressing fields open two coherent population trapping (CPT) windows, within which the atoms stay predominantly in the dark state and yield strong nonlinearities for both the dressing fields themselves and the other applied fields. The two-mode squeeze operator is separated from degrees of freedom of atoms in a common CPT window, and the multimode squeeze operator is segregated in different CPT windows. The resulting two-mode and multimode interaction strengths are at least one order higher than in the previous dispersive schemes, where all fields are far off resonant with the atoms. The present near-resonant scheme is robust to spontaneous emission since atoms are nearly trapped in a long-lived superposition state.

DOI
10.1103/physreva.99.013805

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We present a scheme to generate unitarily two-mode and four-mode field squeezing in optical cavities with the near-resonantly dressed three-level atoms in the \ensuremathΛ\mathrm{\ensuremath{\Lambda}}\ensuremathΛ configuration. The dressing fields open two coherent population trapping (CPT) windows, within which the atoms stay predominantly in the dark state and yield strong nonlinearities for both the dressing fields themselves and the other applied fields. The two-mode squeeze operator is separated from degrees of freedom of atoms in a common CPT window, and the multimode squeeze operator is segregated in different CPT windows. The resulting two-mode and multimode interaction strengths are at least one order higher than in the previous dispersive schemes, where all fields are far off resonant with the atoms. The present near-resonant scheme is robust to spontaneous emission since atoms are nearly trapped in a long-lived superposition state.
Spin squeezing has important applications in the field of quantum metrology and quantum information processing. Here we propose that coherent population trapping is well suitable for establishing cavity dissipation mechanism and generating a spin-squeezed state. An ensemble of N double Λ -type atoms is placed inside the two-mode optical cavity, where one Λ subsystem is driven resonantly by two strong control fields to form a dark resonance and the other Λ subsystem is coupled by two cavity vacuum fields and two external fields with large detunings. Due to the dark resonance, the atoms are trapped in a dark state and one has the maximal coherence between the two ground states. Two double off-resonance stimulated Raman scattering interactions are induced between fields and dressed atoms to establish a dissipative quantum dynamical process based on a collective cavity reservoir. As a result, strong stable spin squeezing is generated, which is verified by our numerical and analytical results. Published by the American Physical Society 2024
We study the effects of equal and unequal Rabi frequencies as well as cavity bandwidth on the optimal noise of the output fields from a two-mode optical cavity, which is fed by two coherent fields and encloses a collection of three-level Λ atoms. Each of the output modes is shown to be highly squeezed in the case of smaller symmetrical atomic detunings compared to the spontaneous-emission rates, where the system is in the vicinity of perfect coherent population trapping (CPT). We find that the squeezing on each output mode is larger than that reported by Dantan et al (2006 Phys. Rev. Lett. 97 023605) when adjusting the equal Rabi frequencies. The cavity bandwidth affects, not the degree of squeezing, but the linewidth of the spectral components. In an alternative way, the squeezing of each outgoing mode can be understood as a consequence of the enhanced cross-phase modulation, different from the nonlinear Faraday effect in Dantan's paper (2006 Phys. Rev. Lett. 97 023605). The application of squeezed light is to obtain high-precision measurement, optical communication, and interferometric detection of gravitational radiation.
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We study the nonlinear effect in a three-level atomic system in Λ configuration. As two or more fields are confined within the common electromagnetically induced transparency (EIT) window, they directly disturb EIT dark state at the same time, which leads to the self- and cross-Kerr nonlinear interactions. Our scheme is different from the existed schemes based on three-level or multilevel systems only existing single type of nonlinear interactions. In the common EIT windows, the self- and cross-Kerr nonlinearities are established with suppressed linear absorption and our scheme can be generalized polychromatic Kerr nonlinearity. Because the atoms are almost trapped in the ground states and the atom population becomes unchanged, the scheme is robust to the atomic spontaneous emission. Our scheme is a promising avenue for preparation of squeezing and entanglement .