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arXiv:2307.10956 · EPJ Quantum Technology

Continuous variable entanglement between propagating optical modes using optomechanics

Greeshma Gopinath, Yong Li, Sankar Davuluri

Published Jun 20, 2024• 1 citation
arXivHTMLPDF

Abstract

Abstract In this study, a method for entangling two spatially separated output laser fields from an optomechanical cavity is proposed. In the existing standard methods, entanglement is created by driving the two-mode squeezing part of the linearized optomechanical interaction;, however our method generates entanglement using the quantum back-action nullifying meter technique. As a result, entanglement can be generated outside the blue sideband frequency in both resolved and unresolved sideband regimes. We further show that the system is stable in the entire region where the Duan criterion for inseparability is fulfilled. The effect of thermal noise on the generated entanglement is examined. Finally, we compare this technique with standard methods for entanglement generation using optomechanics.

DOI
10.1140/epjqt/s40507-024-00252-y

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Optomechanical generation of entangled optical beams is usually hindered by thermal noise. We present a theoretical study of low frequency entanglement generation between two optical harmonics emitted from a cavity optomechanical system operating in the resolved-sideband regime. The system comprises three nearly equidistant optical modes in a high-finesse cavity, with the central mode coherently driven. This configuration enables radiation-pressure interactions that generate strong quantum correlations between the two sideband modes. Remarkably, these correlations persist even at large numbers of thermal quanta if one properly engineers the optical cooling rate of the mechanical mode. Our findings demonstrate the feasibility of robust entanglement under ambient conditions, opening new avenues for hybrid quantum technologies based on mechanical interfaces and continuous-variable quantum information processing.
Quantum entanglement is a crucial resource in quantum technologies, enabling advancements in quantum computing, quantum communication, and quantum precision measurement. Here, we propose a method to enhance optomechanical entanglement by introducing an optical Kerr nonlinear medium and a squeezed vacuum reservoir of the optomechanical cavity. By performing the displacement and squeezing transformations, the system can be reduced to a standard linearized optomechanical system with normalized driving detuning and linearized-coupling strength, in which the optical and mechanical modes are, respectively, coupled to an optical vacuum bath and a mechanical heat bath. We focus on the entanglement generation in the single stable regime of the system. By evaluating the steady-state logarithm negativity, we find that the optomechanical entanglement can be enhanced within a wide range of the Kerr constant. In addition, the Kerr nonlinearity can extend the stable region, enabling considerable entanglement generation in the blue-sideband parameter region. We also investigate the dependence of the entanglement generation on the average thermal phonon occupation of the mechanical bath and the optical driving amplitude. It is found that the presence of the Kerr nonlinearity allows the generation of optomechanical entanglement even when the thermal phonon occupation of the mechanical bath is as high as 3000. Our findings will provide valuable insights into enhancing fragile quantum resources in quantum systems.
We consider a dissipative cavity optomechanical system which couples to an auxiliary cavity with a high-quality factor and is driven by an amplitude-modulated laser field. Due to the introduction of the auxiliary cavity, we find that the steady-state mechanical squeezing can be enhanced compared to the case without an auxiliary cavity and the so-called 3 dB limit can also be broken in the resolved-sideband regime. Moreover, the squeezing can also be achieved even in the unresolved-sideband regime. We study the optomechanical entanglement in the presented system. It is found that the enhanced entanglement can be obtained by introducing the auxiliary cavity, and the entanglement can also be generated in the unresolved-sideband regime for appropriate system parameters. Numerical results show that the presented schemes have strong robustness against the thermal noise acting on the mechanical mode.
We study steady-state continuous-variable entanglement in a three-mode optomechanical system consisting of an active optical cavity (gain) coupled to a passive optical cavity (loss) supporting a mechanical mode. For a driving laser which is blue-detuned, we show that coupling between optical and mechanical modes is enhanced in the unbroken-PT\mathcal{PT}PT-symmetry regime. We analyze the stability and this shows that steady-state solutions are more stable in the gain and loss systems. We use these stable solutions to generate distant entanglement between the mechanical mode and the optical field inside the gain cavity. It results in a giant enhancement of entanglement compared to what is generated in the single lossy cavity. This work offers the prospect of exploring quantum state engineering and quantum information in such systems. Furthermore, such entanglement opens up an interesting possibility to study spatially separated quantum objects.
Abstract We propose a protocol how to generate and verify bipartite Gaussian entanglement between two mechanical modes coupled to a single optical cavity, by means of short optical pulses and measurement. Our protocol requires neither the resolved sideband regime, nor low thermal phonon occupancy, and allows the generation and verification of quantum entanglement in less than a mechanical period of motion. Entanglement is generated via effective two-mode mechanical squeezing through conditioning position measurements. We study the robustness of entanglement to experimental deviations in mechanical frequencies and optomechanical coupling rates.
Abstract We investigate the effect of a degenerate optical parametric amplifier (OPA) placed inside an optomechanical cavity on the steady-state entanglement of two cavity modes, which jointly interact with a mechanical resonator. Two cavity modes are, respectively, driven at the red and blue sideband associated with the mechanical resonator, which generates entanglement between them in the limit of resolved sideband. The OPA gives rise to single-mode squeezing of the cavity fields, which results in significant improvement of the two-mode entanglement. It is found that an optimal nonlinear gain of the OPA exists, depending on the system temperatures, which yields the maximum entanglement. The improvement is particularly remarkable for the system at cryogenic temperatures.