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New Journal of Physics

Feedback-assisted quantum nondemolition measurement in an atom-light-correlated interferometer

Gao-Feng Jiao

Published May 29, 2025• 0 citations
Publisher

Abstract

Abstract Quantum nondemolition (QND) measurement plays an essential role in quantum optics and quantum information. Here, a feedback-assisted atom-light-correlated interferometer (FALCI) is proposed and applied to the QND measurement of photon number, in which the phase of the probe acquires information about the photon number of the signal without perturbing it due to the AC-Stark effect. A beam splitter with adjustable reflectivity is employed as a feedback controller to enhance the performance of QND measurement. The FALCI harnesses interference between quantum-correlated atoms and light to perform the measurement. It is found that the quantum correlation can be enhanced by manipulating the feedback ratio. Furthermore, the QND measurement sensitivity is theoretically studied via homodyne detection. It is demonstrated that the FALCI can achieve the sensitivity enhancement with suitable feedback ratio. For the lossy case, feedback control can mitigate the effect of losses on the sensitivity.

DOI
10.1088/1367-2630/adde7f

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Abstract Quantum nondemolition (QND) measurement plays an essential role in quantum optics and quantum information. Here, a feedback-assisted atom-light-correlated interferometer (FALCI) is proposed and applied to the QND measurement of photon number, in which the phase of the probe acquires information about the photon number of the signal without perturbing it due to the AC-Stark effect. A beam splitter with adjustable reflectivity is employed as a feedback controller to enhance the performance of QND measurement. The FALCI harnesses interference between quantum-correlated atoms and light to perform the measurement. It is found that the quantum correlation can be enhanced by manipulating the feedback ratio. Furthermore, the QND measurement sensitivity is theoretically studied via homodyne detection. It is demonstrated that the FALCI can achieve the sensitivity enhancement with suitable feedback ratio. For the lossy case, feedback control can mitigate the effect of losses on the sensitivity.
Quantum non-demolition (QND) measurement is an important tool in the field of quantum information processing and quantum optics. The atom-light hybrid interferometer is of great interest due to its combination of atomic spin wave and optical wave, which can be utilized for photon number QND measurement via the AC-Stark effect. In this paper, we present an actively correlated atom-light hybrid interferometer where the output is detected with the method of active correlation output readout via a nonlinear Raman process (NRP). Then this interferometer is used for QND measurement of photon number and the signal-to-noise ratio (SNR) is studied. Compared to the traditional SU(2) interferometer, the SNR in a balanced case is improved by a gain factor of ggg of NRP. Furthermore, the performance of QND measurement is analyzed. In the presence of losses, the measurement quality is reduced. We can adjust the gain parameter of the NRP in readout stage to reduce the impact due to losses. Moreover, this scheme is a multiarm interferometer, which has the potential of multiparameter estimation with many important applications in the detection of vector fields, quantum imaging and so on.
When atoms are illuminated by an off-resonant field, the AC Stark effect will lead to phase shifts in atomic states. The phase shifts are proportional to the photon number of the off-resonant illuminating field. By measuring the atomic phase with newly developed atom-light hybrid interferometers, we can achieve quantum non-demolition measurement of the photon number of the optical field. In this paper, we analyze theoretically the performance of this QND measurement scheme by using the QND measurement criteria established by Holland et al [Phys. Rev. A 42, 2995 (1990)]. We find the quality of the QND measurement depends on the phase resolution of the atom-light hybrid interferometers. We apply this QND measurement scheme to a twin-photon state from parametric amplifier to verify the photon correlation in the twin beams. Furthermore, a sequential QND measurement procedure is analyzed for verifying the projection property of quantum measurement and for the quantum information tapping. Finally, we discuss the possibility for single-photon-number-resolving detection via QND measurement.
Nonlinear feedback utilizing nonlinear elements usually provides better performance in preparation and manipulation of quantum states compared to linear feedback using linear elements. In this work, by employing nonlinear feedback, we propose a nonlinear-feedback-assisted interferometer for quantum metrology. We theoretically analyze the phase sensitivity via homodyne detection on both of output ports. It is found that this proposal can realize phase sensitivity enhancement by manipulating the nonlinear feedback strength. Furthermore, the phase sensitivity can saturate the classical and quantum Cramér-Rao bound, respectively. Moreover, we demonstrate that this proposal is superior to the linear-feedback-assisted interferometer.
Quantum non-demolition (QND) measurement is an important tool in the fields of quantum information processing and quantum optics. The atom-light hybrid interferometer is of great interest due to its combination of an atomic spin wave and an optical wave, which can be utilized for photon number QND measurement via the AC-Stark effect. In this paper, we present an SU(1,1)-SU(2)-concatenated atom-light hybrid interferometer, and theoretically study QND measurement of the photon number. Compared to the traditional SU(2) interferometer, the signal-to-noise ratio in a balanced case is improved by a gain factor of the nonlinear Raman process (NRP) in this proposed interferometer. Furthermore, the condition of high-quality QND measurement is analyzed. In the presence of losses, the measurement quality is reduced. We can adjust the gain parameter of the NRP in the readout stage to reduce the impact due to losses. Moreover, this scheme is a multiarm interferometer, which has the potential of multiparameter estimation with many important applications in the detection of vector fields, quantum imaging, and so on.
Abstract The topology of feedback optical parametric amplifier (FOPA) renders a number of significant advantages over the topology of traditional optical parametric amplifier (TOPA) such as a higher degree of quantum correlation, all-phase entanglement enhancement, and the robustness of the losses. Here, we propose a feedback-assisted interferometer based on the topology of FOPA for quantum metrology. We theoretically study the phase sensitivity with the method of homodyne detection and product detection. By manipulating the feedback strength of the FOPA, the phase sensitivity can be further enhanced, and approach the quantum Cramér-Rao bound. Furthermore, we demonstrate that our proposal is superior to the SU(1,1) interferometer based on the topology of TOPA.
Quantum dense metrology (QDM) performs high-precision measurements by a two-mode entangled state created by an optical parametric amplifier (PA), where one mode is a meter beam and the other is a reference beam. In practical applications, the photon losses of meter beam are unavoidable, resulting in a degradation of the sensitivity. Here, we employ coherent feedback that feeds the reference beam back into the PA by a beam splitter to enhance the sensitivity in a lossy environment. The results show that the sensitivity is enhanced significantly by adjusting the splitting ratio of the beam splitter. This method may find its potential applications in QDM. Furthermore, such a strategy that two non-commuting observables are simultaneous measurements could provide a new way to individually control the noise-induced random drift in phase or amplitude of the light field, which would be significant for stabilizing the system and long-term precision measurement.