Browsing by Author "Ou, Z. Y."

Now showing 1 - 10 of 33
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    Absolute sensitivity of phase measurement in an SU(1,1) type interferometer
    (OSA, 2018) Du, Wei; Jia, Jun; Chen, J. F.; Ou, Z. Y.; Zhang, Weiping; Physics, School of Science
    Absolute sensitivity is measured for the phase measurement in an SU(1,1) type interferometer, and the results are compared to that of a Mach–Zehnder interferometer operated under the condition of the same intra-interferometer intensity. The interferometer is phase locked to a point with the largest quantum noise cancellation, and a simulated phase modulation is added in one arm of the SU(1,1) interferometer. Both the signal and noise level are estimated at the same frequency range, and we obtained 3 dB improvement in sensitivity for the SU(1,1) interferometer over the Mach–Zehnder interferometer. Our results demonstrate a direct phase estimation and may pave the way for practical applications of a nonlinear interferometer.
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    Accessible precisions for estimating two conjugate parameters using Gaussian probes
    (American Physical Society, 2020-05) Assad, Syed M.; Li, Jiamin; Liu, Yuhong; Zhao, Ningbo; Zhao, Wen; Lam, Ping Koy; Ou, Z. Y.; Li, Xiaoying; Physics, School of Science
    We analyze the precision limits for a simultaneous estimation of a pair of conjugate parameters in a displacement channel using Gaussian probes. Having a set of squeezed states as an initial resource, we compute the Holevo Cramér-Rao bound to investigate the best achievable estimation precisions if only passive linear operations are allowed to be performed on the resource prior to probing the channel. The analysis reveals the optimal measurement scheme and allows us to quantify the best precision for one parameter when the precision of the second conjugate parameter is fixed. To estimate the conjugate parameter pair with equal precision, our analysis shows that the optimal probe is obtained by combining two squeezed states with orthogonal squeezing quadratures on a 50:50 beam splitter. If different importance is attached to each parameter, then the optimal mixing ratio is no longer 50:50. Instead, it follows a simple function of the available squeezing and the relative importance between the two parameters.
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    Approaching single temporal mode operation in twin beams generated by pulse pumped high gain spontaneous four wave mixing
    (OSA, 2016-01) Liu, Nannan; Liu, Yuhong; Guo, Xueshi; Yang, Lei; Li, Xiaoying; Ou, Z. Y.; Department of Physics, School of Science
    By investigating the intensity correlation function, we study the spectral/temporal mode properties of twin beams generated by the pulse-pumped high gain spontaneous four wave mixing (SFWM) in optical fiber from both the theoretical and experimental aspects. The results show that the temporal property depends not only on the phase matching condition and the filters applied in the signal and idler fields, but also on the gain of SFWM. When the gain of SFWM is low, the spectral/temporal mode properties of the twin beams are determined by the phase matching condition and optical filtering and are usually of multi-mode nature, which leads to a value larger than 1 but distinctly smaller than 2 for the normalized intensity correlation function of individual signal/idler beam. However, when the gain of SFWM is very high, we demonstrate the normalized intensity correlation function of individual signal/idler beam approaches to 2, which is a signature of single temporal mode. This is so even if the frequencies of signal and idler fields are highly correlated so that the twin beams have multiple modes in low gain regime. We find that the reason for this behavior is the dominance of the fundamental mode over other higher order modes at high gain. Our investigation is useful for constructing high quality multi-mode squeezed and entangled states by using pulse-pumped spontaneous parametric down-conversion and SFWM.
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    Atom-Light Hybrid Interferometer
    (APS, 2015-07) Chen, Bing; Qiu, Shuying; Guo, Jinxian; Chen, L. Q.; Ou, Z. Y.; Zhang, Weiping; Department of Physics, School of Science
    A new type of hybrid atom-light interferometer is demonstrated with atomic Raman amplification processes replacing the beam splitting elements in a traditional interferometer. This nonconventional interferometer involves correlated optical and atomic waves in the two arms. The correlation between atoms and light developed with the Raman process makes this interferometer different from conventional interferometers with linear beam splitters. It is observed that the high-contrast interference fringes are sensitive to the optical phase via a path change as well as the atomic phase via a magnetic field change. This new atom-light correlated hybrid interferometer is a sensitive probe of the atomic internal state and should find wide applications in precision measurement and quantum control with atoms and photons.
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    Atom-light superposition oscillation and Ramsey-like atom-light interferometer
    (OSA, 2016-07) Qiu, Cheng; Chen, Shuying; Chen, L. Q.; Chen, Bing; Guo, Jinxian; Ou, Z. Y.; Zhang, Weiping; Department of Physics, School of Science
    Coherent wave splitting is crucial in interferometers. Normally, the waves after this splitting are of the same type. But recent progress in interactions between atom and light has led to the coherent conversion of photon to atomic excitation. This makes it possible to split an incoming light wave into a coherent superposition state of atom and light and paves the way for an interferometer made of different types of waves. Here we report on a Rabi-like coherent-superposition oscillation observed between an atom and light in a Raman process. We construct a new kind of hybrid interferometer based on the atom–light coherent superposition state. Interference fringes are observed in both the optical output intensity and atomic output in terms of the atomic spin wave strength when we scan either or both of the optical and atomic phases. Such a hybrid interferometer can be used to interrogate atomic states by optical detection and will find its applications in precision measurement and quantum control of atoms and light.
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    Complete temporal mode analysis in pulse-pumped fiber-optical parametric amplifier for continuous variable entanglement generation
    (The Optical Society, 2015) Guo, Xueshi; Liu, Nannan; Li, Xiaoying; Ou, Z. Y.; Department of Physics, School of Science
    Mode matching plays an important role in measuring the continuous variable entanglement. For the signal and idler twin beams generated by a pulse pumped fiber optical parametric amplifier (FOPA), the spatial mode matching is automatically achieved in single mode fiber, but the temporal mode property is complicated because it is highly sensitive to the dispersion and the gain of the FOPA. We study the temporal mode structure and derive the input-output relation for each temporal mode of signal and idler beams after decomposing the joint spectral function of twin beams with the singular-value decomposition method. We analyze the measurement of the quadrature-amplitude entanglement, and find mode matching between the multi-mode twin beams and the local oscillators of homodyne detection systems is crucial to achieve a high degree of entanglement. The results show that the noise contributed by the temporal modes nonorthogonal to local oscillator may be much larger than the vacuum noise, so the mode mis-match can not be accounted for by merely introducing an effective loss. Our study will be useful for developing a source of high quality continuous variable entanglement by using the FOPA.
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    Direct Temporal Mode Measurement for the Characterization of Temporally Multiplexed High Dimensional Quantum Entanglement in Continuous Variables
    (APS, 2020-05-29) Huo, Nan; Liu, Yuhong; Li, Jiamin; Cui, Liang; Chen, Xin; Palivela, Rithwik; Xie, Tianqi; Li, Xiaoying; Ou, Z. Y.; Physics, School of Science
    Field-orthogonal temporal mode analysis of optical fields has recently been developed for a new framework of quantum information science. However, so far, the exact profiles of the temporal modes are not known, which makes it difficult to achieve mode selection and demultiplexing. Here, we report a novel method that measures directly the exact form of the temporal modes. This, in turn, enables us to make mode-orthogonal homodyne detection with mode-matched local oscillators. We apply the method to a pulse-pumped, specially engineered fiber parametric amplifier and demonstrate temporally multiplexed multidimensional quantum entanglement of continuous variables in telecom wavelength. The temporal mode characterization technique can be generalized to other pulse-excited systems to find their eigenmodes for multiplexing in the temporal domain.
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    Direct temporal mode measurement of photon pairs by stimulated emission
    (American Physical Society, 2020-03) Chen, Xin; Li, Xiaoying; Ou, Z. Y.; Physics, School of Science
    It is known that photon pairs generated from pulse-pumped spontaneous parametric processes can be described by independent temporal modes and form a multitemporal mode entangled state. However, the exact form of the temporal modes is not known even though the joint spectral intensity of photon pairs can be measured by the method of stimulated emission tomography. In this paper, we describe a feedback-iteration method which, combined with the stimulated emission method, can give rise to the exact forms of the independent temporal modes for the temporally entangled photon pairs.
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    Distribution of entangled photon pairs over few-mode fibers
    (Nature Publishing group, 2017-11-12) Cui, Liang; Su, Jie; Li, Xiaoying; Ou, Z. Y.; Physics, School of Science
    Few-mode fibers (FMFs) have been recently employed in classical optical communication to increase the data transmission capacity. Here we explore the capability of employing FMF for long distance quantum communication. We experimentally distribute photon pairs in the forms of time-bin and polarization entanglement over a 1-km-long FMF. We find the time-bin entangled photon pairs maintain their high degree of entanglement, no matter what type of spatial modes they are distributed in. For the polarization entangled photon pairs, however, the degree of entanglement is maintained when photon pairs are distributed in LP 01 mode but significantly declines when photon pairs are distributed in LP 11 mode due to a mode coupling effect in LP 11 mode group. We propose and test a remedy to recover the high degree of entanglement. Our study shows, when FMFs are employed as quantum channels, selection of spatial channels and degrees of freedom of entanglement should be carefully considered.
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    Effects of losses in the hybrid atom-light interferometer
    (OSA, 2016-08) Chen, Zhao-Dan; Yuan, Chun-Hua; Ma, Hong-Mei; Li, Dong; Chen, L. Q.; Ou, Z. Y.; Zhang, Weiping; Department of Physics, School of Science
    Collective atomic excitation can be realized by the Raman scattering. Such a photon-atom interface can form an SU(1,1)-typed atom-light hybrid interferometer, where the atomic Raman amplification processes take the place of the beam splitting elements in a traditional Mach-Zehnder interferometer. We numerically calculate the phase sensitivities and the signal-to-noise ratios (SNRs) of this interferometer with the method of homodyne detection and intensity detection, and give their differences of the optimal phase points to realize the best phase sensitivities and the maximal SNRs from these two detection methods. The difference of the effects of loss of light field and atomic decoherence on measure precision is analyzed.