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Quantum non-demolition measurement based on an actively correlated atom-light hybrid interferometer

Gao-Feng Jiao, Keye Zhang, Liu-Sha Chen, Chun-Hua Yuan, Weiping Zhang

Published May 29, 2021• 0 citations
OpenAlex

Abstract

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 $g$ 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.

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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.
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.
The atom-light hybrid interferometer recently attracted much attention in the research of precision metrology for its combination of light and atomic spin wave. With the AC Stark effect and proper design, it can be applied in the scheme of quantum non-demolition (QND) measurement of photon numbers. In this work, we apply the QND criteria to the scheme and theoretically derive its explicit formulas with various losses of the atomic-light hybrid interferometer. With the formulas and actual experiment parameters, we estimate and compare the performance of the vapor-atom-based and cold-atom-based hybrid interferometer in the QND measurement, analyze the influences of different kinds of losses, and provide optimized working parameter ranges of the interferometer.
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.
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.
Any amplifier requires coupling to its internal degrees of freedom for energy gain. This coupling introduces extra quantum noise to the output. On the other hand, if the internal degree of the amplifier can be accessed and manipulated, we can manage and even reduce the quantum noise of the amplifier's output. In this Letter, we present an experiment to reduce the quantum noise of a Raman amplifier by preparing the atomic medium in a correlated state with the Stokes light field. We report an observation of quantum noise reduction of more than 3.5 dB in the atomic Raman amplification process. From another perspective, the Raman amplifier at high gain in turn serves as a measurement tool for the quantum correlation between the atom and light. Furthermore, such a scheme, when viewed as a whole, also forms a quantum-entangled atom-light hybrid interferometer that can lead to quantum-enhanced sensors.
Any amplifier requires coupling to its internal degrees of freedom for energy gain. This coupling introduces extra quantum noise to the output. On the other hand, if the internal degree of the amplifier can be accessed and manipulated, we can manage and even reduce the quantum noise of the amplifier's output. In this Letter, we present an experiment to reduce the quantum noise of a Raman amplifier by preparing the atomic medium in a correlated state with the Stokes light field. We report an observation of quantum noise reduction of more than 3.5 dB in the atomic Raman amplification process. From another perspective, the Raman amplifier at high gain in turn serves as a measurement tool for the quantum correlation between the atom and light. Furthermore, such a scheme, when viewed as a whole, also forms a quantum-entangled atom-light hybrid interferometer that can lead to quantum-enhanced sensors.