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Physica Scripta

Enhancing quantum illumination effects using kerr and cross-kerr media in electro-opto-mechanical transducer

M R Ghafarzadeh, Mohammad Kazem Tavassoly

Published Oct 1, 2025• 0 citations

Abstract

Abstract Recently in [Phys. Rev. Lett. 114, 080503 (2015)] an electro-opto-mechanical converter has been used to evaluate microwave-optical entanglement, applicable in the quantum illumination techniques at microwave frequencies. Choosing this frequency domain is due to the fact that, microwaves have generally a more suitable spectral region for target detection than light waves. In this paper we aim to investigate the effect of nonlinear Kerr and cross-Kerr media on the microwave-optical entanglement degree in an electro-opto-mechanical transducer. We evaluate some key measures of the system, i.e., entanglement metrics, logarithmic negativity, coherent information and quantum discord. Our analysis demonstrates that, adding Kerr and cross-Kerr terms to the Hamiltonian of the electro-opto-mechanical system increases the entanglement metric, logarithmic negativity and quantum discord by approximately 3 to 4 times and the coherent information increases slightly, whenever the system possesses strong optical-mechanical coupling, low optical dissipation or both conditions. Conversely, when the system possesses weak optical-mechanical coupling, high optical dissipation or both conditions, it leads to weakening/death of all above-considered criteria. The constructive effect of Kerr media on the above quantumness signs makes the system more beneficial for quantum illumination purposes, which is an important factor in the quantum information science and technologies.

DOI: 10.1088/1402-4896/ae0ed0

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In this study, the main focus is laid on the design of an optoelectronic converter as a part of the quantum radar to enhance the entanglement between retained and returned modes at high temperatures. The electro-opto-mechanical converter has been widely studied, and the results showed that the operation at high temperature is so crucial to generate and preserve the entanglement between modes. The main problem arises because the mechanical part operating at a low frequency leads to a large number of thermally excited photons, and eventually, the entanglement between modes becomes lost. To solve the problem, we replace the mechanical part with the optoelectronic components. The optical cavity is coupled to the microwave cavity in the newly designed system through a Varactor diode excited by a photodetector. As the main goal, to improve the entanglement sustainability, the effect of the coupling factor of the microwave cavity to photodetector is investigated. The results show that the mentioned factor creates some degrees of freedom to enhance the entanglement at high temperatures compared to the electro-opto-mechanical converter. At some specific values of the coupling factor, the retained and returned fields remained completely entangled up to 5.5 K and partially entangled around 50 K.

Quantum illumination is a quantum optical sensing technique, which employs an entangled source to detect low-reflectivity object immersed in a bright thermal background. Hybrid cavity-optomagnonics system promises to work as quantum illumination because a yttrium iron garnet (YIG) sphere can couple to microwave field and optical field. In this paper, we propose a scheme to enhance the entanglement between the output fields of the microwave and optical cavities by considering the intrinsic Kerr nonlinearity of the YIG. We investigate the difference between intrinsic Kerr nonlinearity and optomagnonical parametric-type coupling on improving entanglement. Our result show that the large value optomagnonical parametric-type coupling does not mean the large entanglement, nevertheless, the large value of Kerr nonlinearity does monotonously improve the entanglement for our group of parameters. Consequently, under feasible parameters of current experiment, the signal-to-noise ratio and probability of detection error can be improved after considering the magnon Kerr nonlinearity.

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.

A quantum transducer converts an input signal to an output probe at a distant frequency band while maintaining the quantum information with high fidelity, which is crucial for quantum networking and distributed quantum sensing and computing. In terms of microwave–optical quantum transduction, the state-of-the-art quantum transducers suffer low transduction efficiency from weak nonlinear coupling, wherein increasing pump power to enhance efficiency inevitably leads to thermal noise from heating. Moreover, we reveal that the efficiency-bandwidth product of a cavity electro-optical or electro-optomechanical transducer is fundamentally limited by pump power and nonlinear coupling coefficient, irrespective of cavity engineering efforts. To overcome this fundamental limit, we propose to noiselessly boost the transduction efficiency by consuming intraband entanglement (e.g., microwave–microwave or optical–optical entanglement in the case of microwave–optical transduction). Via a squeezer–coupler–antisqueezer sandwich structure, the protocol enhances the transduction efficiency to unity in the ideal lossless case, given an arbitrarily weak pump and nonlinear coupling. In practical cavity systems, our entanglement-assisted protocol surpasses the non-assisted fundamental limit of the efficiency-bandwidth product and reduces the threshold cooperativity for positive quantum capacity by a factor proportional to two-mode squeezing gain. Given a fixed cooperativity, our approach increases the broadband quantum capacity by orders of magnitude. The entanglement-assisted advantage is robust to ancilla loss and cavity detuning.