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Generation of Enhanced and Robust bipartite optomechanical entanglement via an auxiliary qubit induced quadratic mechanical nonlinearity

Subhadeep Chakraborty, Amarendra K. Sarma

Published Jun 21, 2016• 0 citations
OpenAlex

Abstract

We present a scheme for obtaining steady-state optomechanical entanglement in an optomechanical system, in which the mechanical mirror is perturabatively coupled to an auxiliary qubit. The coupling between the mechanical oscillator and the single qubit results in a quadratic mechanical nonlinear term in the Hamiltonian describing the system. We find that the mechanical nonlinearity not only enhances the degree of optomechanical entanglement but also generate it at a considerably lower optomechanical coupling strength. We observe that the degree of entanglement decreases monotonically with increasing temperature. However, the maximum temperature up to which entanglement persists increase with increasing nonlinear amplitude. Thus, the bipartite entanglement in presence of the mechanical nonlinearity becomes more robust against thermal phonon fluctuations.

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We present a scheme for obtaining steady-state optomechanical entanglement in an optomechanical system, in which the mechanical mirror is perturabatively coupled to an auxiliary qubit. The coupling between the mechanical oscillator and the single qubit results in a quadratic mechanical nonlinear term in the Hamiltonian describing the system. We find that the mechanical nonlinearity not only enhances the degree of optomechanical entanglement but also generate it at a considerably lower optomechanical coupling strength. We observe that the degree of entanglement decreases monotonically with increasing temperature. However, the maximum temperature up to which entanglement persists increase with increasing nonlinear amplitude. Thus, the bipartite entanglement in presence of the mechanical nonlinearity becomes more robust against thermal phonon fluctuations.
In this work, we investigate a theoretical study of the stationary entanglement of an optomechanical system by adding a Kerr medium in the cavity where the mechanical resonator is perturbatively connected to an auxiliary qubit. The degree of entanglement between the cavity field and the mechanical system is measured by using the logarithmic negativity. We show that optomechanical entanglement is decreased by Kerr interaction due to photon blockage enhanced by mirror–qubit coupling, we also show that this enhancement is influenced by the temperature. In addition, we find that, in the presence of the mirror–qubit coupling, entanglement can arise with far weaker optomechanical coupling. The proposed scheme shows that the presence of the mirror–qubit coupling and Kerr medium is an effective control for an optomechanical system.
We theoretically investigate the steady-state bipartite entanglements, mechanical ground-state cooling, and mechanical quadrature squeezing in a hybrid electro-optomechanical system where a moving membrane is linearly coupled to the microwave field mode of an LC circuit, while it simultaneously interacts both linearly and quadratically with the radiation pressure of a single-mode optical cavity. We show that by choosing a suitable sign and amplitude for the quadratic optomechanical coupling (QOC), one can achieve enhanced and thermally robust stationary bipartite entanglement between the subsystems, improved mechanical ground-state cooling, and QQQ-quadrature squeezing of the mechanical mode beyond the 3-dB limit of squeezing. In particular, we find that in the presence of QOC with negative sign and in the resolved sideband regime the bipartite optical-mechanical entanglement can be increased by about 2 orders of magnitude around the temperature of 1 mK, and it can be preserved against thermal noise up to the ambient temperature of 0.1 K. Furthermore, the QOC with positive sign can give rise to the enhancement of the mechanical ground-state cooling by about 1 order of magnitude in the optical and microwave red-detuned regime. We also find that for the positive sign of QOC and near the microwave resonance frequency the squeezing degree of the QQQ quadrature of the mechanical mode can be amplified up to 15 dB. Such a hybrid electro-optomechanical system can serve as a promising platform to engineer an improved entangled source for quantum sensing as well as 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.
In this work, we theoretically study the quantum correlations present in an optomechanical system by invoking an additional cross-Kerr-type coupling between the optical and mechanical modes. Under experimentally achievable conditions, we first show that a significant enhancement of the steady-state entanglement could be achieved at a considerably lower driving power, which is also extremely robust with respect to the system parameters and environmental temperature. We then employ Gaussian quantum discord (QD) as a more genuine measure of the quantumness of the correlation. We find that in the presence of cross-Kerr nonlinearity, QD becomes more robust and survives up to a much higher number of thermal phonons as compared to the optomechanical entanglement.
Entanglement had played a crucial role in developing frontier technologies as a critical resource, for instance, in quantum teleportation and quantum sensing schemes. Notably, thanks to the ability to cool down the vibrational modes of mechanical oscillators to its quantum regime, entanglement between mechanical modes and the production of nonclassical mechanical states have emerged as central resources for quantum technological applications. Thus, proposing deterministic schemes to achieve those tasks is of paramount importance. While the dominant scheme for bipartite mechanical entanglement involves Gaussian optomechanical interactions (linearized regime) to generate two-mode squeezed vacuum states, entangling two-modes exploiting the bare non-Gaussian optomechanical interaction (nonlinear strong single-photon regime) remains less covered. This work proposes an on-demand scheme to engineer phononic non-Gaussian bipartite entanglement in the nonlinear regime by exploiting cavity dissipation. Interestingly, our protocol (operating in the resolved sideband and photon blockade regime) renders the possibility of achieving a high degree of steady-state entanglement. We further show that our deterministic scheme is robust in the presence of decoherence and temperature within state-of-the-art optomechanics, along with the required conditions to obtain non-Gaussianity of the achieved bipartite mechanical steady-state.
Quantum control of phonons has become a focus of attention for developing quantum technologies. Here, we present a proposal to realize phonon blockade in a quadratically coupled optomechanical system, where a strong nonlinear interaction between photons and phonons can be induced by an external field coherently driving the cavity and the effective coupling strength is tunable by adjusting the amplitude of the driving field. This optically induced nonlinearity is different from standard methods for the realization of phonon blockade, where the nonlinearity is achieved by coupling the mechanical system to superconducting qubits. We both analytically and numerically study the phonon statistical properties via the steady-state solution of the second-order correlation function and find phonon blockade can be efficiently realized for a large cooperativity of the system, which is achievable based on the optically enhanced nonlinear coupling and high quality mechanical system.