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arXiv:2211.08867 · Applied Physics Letters

Quantum entangled Sagnac interferometer

Wen Zhao, Xuan Tang, Xueshi Guo, Xiaoying Li, Z. Y. Ou

Published Feb 6, 2023• 7 citations
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Abstract

A SU(1,1) interferometer (SUI) is a kind of quantum entangled interferometer that uses directly entangled quantum fields for sensing phase change. For rotational sensing, Sagnac geometry is usually adopted. However, because SUI depends on the phase sum of the two arms, traditional Sagnac geometry, when applied to SUI, will result in null signal. In this paper, we modify the traditional Sagnac interferometer by nesting SUIs inside. We show that the rotational signal comes from two parts labeled as “classical” and “quantum,” respectively, and the quantum part, where quantum entangled fields are used for sensing, has the rotational signal enhanced by a factor related to the gain of the SUI.

DOI
10.1063/5.0135084

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A SU(1,1) interferometer (SUI) is a kind of quantum entangled interferometer that uses directly entangled quantum fields for sensing phase change. For rotational sensing, Sagnac geometry is usually adopted. However, because SUI depends on the phase sum of the two arms, traditional Sagnac geometry, when applied to SUI, will result in null signal. In this paper, we modify the traditional Sagnac interferometer by nesting SUIs inside. We show that the rotational signal comes from two parts labeled as “classical” and “quantum,” respectively, and the quantum part, where quantum entangled fields are used for sensing, has the rotational signal enhanced by a factor related to the gain of the SUI.
With the help of quantum entanglement, quantum dense metrology (QDM) is a technique that can make joint estimates of two conjugate quantities such as phase and amplitude modulations of an optical field, with an accuracy beating the standard quantum limit simultaneously. SU(1,1) interferometers (SUIs) can realize QDM with detection loss tolerance but is limited in absolute sensitivity. Here, we present a QDM scheme with a linear or SU(2) interferometer nested inside an SUI. By using a degenerate SUI and controlling the phase angle of the phase-sensitive amplifiers in the SUI, we can achieve the optimum quantum enhancement in the measurement precision of an arbitrary mixture of phase and amplitude modulation.
We present a simple and robust design for a squeezing-enhanced Sagnac interferometer that employs the concept of SU(1,1) interference to significantly surpass the classical sensitivity limit (shot-noise limit - SNL) in rotational sensing. By strategically placing an optical parametric amplifier (OPA) inside the Sagnac loop, light is automatically squeezed in both forward and backward directions of the loop, which enhances the detectability of a small phase. For measuring the squeezed quadrature, we explore two approaches: Direct detection of the output intensity, which is simple, but requires a high-efficiency photo-detector; and parametric homodyne with an additional OPA, which accepts practical detectors with no efficiency limitation, but is technically more complex. Our analysis demonstrates super-classical sensitivity under most realistic conditions of loss and detector inefficiency, thereby leveraging the resources of squeezing and the principles of SU(1,1) interference, while maintaining compatibility with standard Sagnac configurations.
We present a simple and robust design for a squeezing-enhanced Sagnac interferometer that employs the concept of SU(1,1) interference to significantly surpass the classical sensitivity limit (shot-noise limit, SNL) in rotational sensing. By strategically placing an optical parametric amplifier (OPA) inside the Sagnac loop, light is automatically squeezed in both forward and backward directions of the loop, which enhances the detectability of a small phase. For measuring the squeezed quadrature, we explore two approaches: Direct detection of the output intensity, which is simple but requires a high-efficiency photo-detector; and parametric homodyne with an additional OPA, which accepts practical detectors with no efficiency limitation, but is technically more complex. Our analysis demonstrates super-classical sensitivity under most realistic conditions of loss and detector inefficiency, thereby leveraging the resources of squeezing and the principles of SU(1,1) interference, while maintaining compatibility with standard Sagnac configurations.
We present a simple and robust design for a squeezing-enhanced Sagnac interferometer that significantly surpasses the the shot-noise limit of sensitivity in rotational sensing. By strategically placing an optical parametric amplifier (OPA) inside the Sagnac loop, light is automatically squeezed in both forward and backward directions of the loop, which enhances the detectability of a small phase. For measuring the squeezed quadrature, we explore two approaches: parametric homodyne and direct detection. In direct detection, the intensity of the output dark port is measured directly, which is very simple, but necessitates photo-detectors of near-unit efficiency. With parametric homodyne, an additional OPA is placed at the Sagnac output to amplify the quadrature of interest above the classical noise limit, eliminating the need for near-ideal photo-detectors. Our analysis demonstrates super-classical sensitivity under most realistic conditions of loss and detector inefficiency, thereby leveraging leveraging the resources of squeezing and the principles of SU(1,1) interference, while maintaining compatibility with standard Sagnac configurations.
The quantum correlation of light and atomic collective excitation can be used to compose an SU(1,1)-type hybrid light-atom interferometer, where one arm in the optical SU(1,1) interferometer is replaced by the atomic collective excitation. The phase-sensing probes include not only the photon field but also the atomic collective excitation inside the interferometer. For a coherent squeezed state as the phase-sensing field, the phase sensitivity can approach the Heisenberg limit under the optimal conditions. We also study the effects of the loss of light field and the dephasing of atomic excitation on the phase sensitivity. This kind of active SU(1,1) interferometer can also be realized in other systems, such as circuit quantum electrodynamics in microwave systems, which provides a different method for basic measurement using the hybrid interferometers.