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arXiv:2308.10850 · Applied Physics Letters

Four-wave mixing with anti-parity-time symmetry in hot 85Rb vapor

Ziqi Niu, Yue Jiang, Jianming Wen, Chuanwei Zhang, Shengwang Du, Irina V. Novikova

Published Jan 22, 2024• 9 citations
arXivHTMLPDF

Abstract

We report an experimental demonstration of anti-parity-time symmetric optical four-wave mixing in thermal rubidium vapor, where the propagation of probe and stokes fields in a double-Λ scheme is governed by a non-Hermitian Hamiltonian. We are particularly interested in studying quantum intensity correlations between the two fields near the exceptional point, taking into account loss and accompanied Langevin noise. Our experimental measurements of classical four-wave mixing gain and the associated two-mode relative-intensity squeezing are in reasonable agreement with the theoretical predictions.

DOI
10.1063/5.0173354

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We report an experimental demonstration of anti-parity-time symmetric optical four-wave mixing in thermal rubidium vapor, where the propagation of probe and stokes fields in a double-Λ scheme is governed by a non-Hermitian Hamiltonian. We are particularly interested in studying quantum intensity correlations between the two fields near the exceptional point, taking into account loss and accompanied Langevin noise. Our experimental measurements of classical four-wave mixing gain and the associated two-mode relative-intensity squeezing are in reasonable agreement with the theoretical predictions.
The goal of the project is to produce a pair of intensity-squeezed light fields using Four-Wave Mixing (FWM) in hot Rubidium vapor. In this process, interaction of atoms with near-resonant strong control optical field results in strong amplification of a weak probe optical field and in generation of a quantum correlated conjugate Stokes optical field. In order to establish the quantum correlation between the Stokes and probe fields, we measured the differential intensity noise between the Stokes and probe fields. If the noise falls below the quantum noise limit, then two-mode intensity squeezing has been achieved, as a first step toward realization of the polarization Bell states. We also examine the conservation of orbital angular momentum (OAM) in the FWM process with OAM-bearing input fields.
We have measured -3.5 dB (-8.1 dB corrected for losses) relative intensity squeezing between probe and conjugate beams generated by stimulated, nondegenerate four-wave mixing in hot rubidium vapor. Unlike early observations of squeezing in atomic vapors based on saturation of a two-level system, our scheme uses a resonant nonlinearity based on ground-state coherences in a three-level system. Since this scheme produces narrowband, squeezed light near an atomic resonance, it is of interest for experiments involving cold atoms or atomic ensembles.
Non-Hermitian optical systems with parity-time (PT) symmetry have recently revealed many intriguing prospects that outperform conservative structures. The previous works are mostly rooted in complex arrangements with controlled gain-loss interplay. Here, we demonstrate anti-PT symmetry inherent in the nonlinear optical interaction based upon forward optical four-wave mixing in a laser-cooled atomic ensemble with negligible linear gain and loss. We observe that the pair of frequency modes undergo a nontrivial anti-PT phase transition between coherent power oscillation and optical parametric amplification in presence of a large phase mismatch.
The goal of the project is to produce a pair of polarization-entangled light fields using four-wave mixing in hot Rb vapor. In this process, interaction of atoms with near-resonant strong control optical field results in strong amplification of a nearly-collinear probe optical field and in generation of a quantum correlated conjugate Stokes optical field. In order to establish the quantum correlation between the Stokes and probe fields, we have adopted a homodyne detection scheme. If the differential noise between the Stokes and probe fields is below the quantum noise limit, then intensity fluctuation entanglement has been achieved, and it is possible to produce the polarization Bell states.
Abstract We study both theoretically and experimentally the generation of quantum correlations in the continuous variable regime by way of four-wave mixing in a hot atomic vapor. Two theoretical approaches have been developed. On one side, we study the four- wave mixing under the "classical" non-linear optics point of view. In such a way we obtain the evolution equation for an ideal linear amplifier in a χ(3) medium. On the other side, we present a microscopic model with 4 levels in the double-Λ configuration to calculate the χ(3) coefficient in a atomic vapor dressed with a laser. This calculation allows us to derive the spectra of intensity noise for interesting parameters. The experimental part of this work describes the demonstration of this effect on the D1 line of rubidium 85. We present a measurement of relative intensity squeezing as high as -9.2dB below the standard quantum limit, and an original regime where quantum correlations have been measured without amplification. These results have broad applications in the field of multimode quantum optics, e.g. quantum imaging or the multimode quantum memories. Keywords quantum fluctuations, squeezing, quantum correlations, atomic vapor, four wave mixing, continuous variable, entanglement.
We experimentally investigate four-wave mixing (FWM) in a diamond interaction scheme using ⁸⁵Rb vapor, and identify the optimal conditions for joint amplification and relative intensity squeezing of two optical fields: one near the ⁸⁵Rb D1 optical transition (λ = 794.6 nm) and the other in the telecom O-band (λ = 1324 nm). We achieved a reduction of relative intensity noise by up to 2.6 ± 0.4 dB compared to the shot noise level, signi- fying the non-classical quantum correlations. The ob- served level of intensity squeezing is primarily limited by the available pump laser power, which constrains the achievable FWM gain. Numerical simulations show good agreement with the experimental results.