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arXiv:1310.6227 · Journal of the Optical Society of America B

Frequency-entanglement preparation based on the coherent manipulation of frequency nondegenerate energy-time entangled state

Qiang Zhou, Shuai Dong, Wei Zhang, Lixing You, Yuhao He, Weijun Zhang, Yidong Huang, Jiangde Peng

Published Jul 8, 2014• 12 citations
arXivHTMLPDF

Abstract

In this paper, a scheme for frequency-entanglement preparation is proposed and demonstrated based on the coherent manipulation of the frequency nondegenerate energy-time entangled state through an unbalanced Mach–Zehnder interferometer (UMZI). The principle of the coherent manipulation process is analyzed theoretically and demonstrated by experiments of nonclassical two-photon interference under different phase differences between the two arms in the UMZI, showing a fringe visibility of (96.9±1.0)%. The frequency-entangled two-photon state can be prepared under a proper phase difference, which is demonstrated by an experiment of spatial quantum beating with a fitting visibility of (99.0±0.8)%. The proposed scheme provides a simple and general way to prepare frequency-entangled states from the frequency nondegenerate energy-time entangled state, which can be easily realized through setups based on fiber optics.

DOI
10.1364/josab.31.001801

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In this paper, a scheme for frequency-entanglement preparation is proposed and demonstrated based on the coherent manipulation of the frequency nondegenerate energy-time entangled state through an unbalanced Mach–Zehnder interferometer (UMZI). The principle of the coherent manipulation process is analyzed theoretically and demonstrated by experiments of nonclassical two-photon interference under different phase differences between the two arms in the UMZI, showing a fringe visibility of (96.9±1.0)%. The frequency-entangled two-photon state can be prepared under a proper phase difference, which is demonstrated by an experiment of spatial quantum beating with a fitting visibility of (99.0±0.8)%. The proposed scheme provides a simple and general way to prepare frequency-entangled states from the frequency nondegenerate energy-time entangled state, which can be easily realized through setups based on fiber optics.
Optical interferometers are extensively used in fundamental physics studies, gravitational wave detection, quantum metrology, topological photonics, and quantum information processing. Fiber-based interferometers are compact, mechanically robust, and cheap, and thus are ubiquitously deployed. However, the optical phase in fiber interferometers is sensitive to ambient perturbation, resulting in compromised phase-sensing precision. Therefore, phase control, shifting, and stabilization of fiber interferometers are essential. Methods to create stable interference patterns and to lock a fiber interferometer at arbitrary phase have been shown, which however are sophisticated, bulky, and delicate, preventing wider application in harsh environments outside laboratories or in space. Here we demonstrate an innovative method for arbitrary-phase locking of fiber unbalanced Mach-Zehnder interferometers. Compared with existing methods, our method is much simpler. We showcase the preparation and characterization of a narrow-band, energy-time-entangled photon state generated in integrated nonlinear microresonators, where two-photon interference visibility reaches 0.993(6). Our method constitutes a critical building block for photonic quantum networks, and is useful to emerging single-photon interference in curved space-time that facilitates exploration of the interface of quantum mechanics and general relativity.
We propose a simple scheme using an unbalanced Mach-Zehnder interferometer to directly measure the entangled beams with correlation of amplitude quadratures and anticorrelation of phase quadratures. In the experiment, we use two fibers with lengths of 2 and 50 m to construct the interferometer. The correlation variances of amplitude difference and phase sum of the entangled beams from a nondegenerate optical parametric amplifier are simultaneously measured to be 1.79 and 1.62 dB below the shot noise limit, respectively. Such a simple and convenient method has potential applications in quantum measurements.
The quantum entanglement of amplitude and phase quadratures between two intense optical beams with a total intensity of 22 mW and a frequency difference of 1 nm, which are produced from an optical parametric oscillator operating above threshold, is experimentally demonstrated with two sets of unbalanced Mach-Zehnder interferometers. The measured quantum correlations of intensity and phase are in reasonable agreement with the results calculated based on a semiclassical analysis of the noise characteristics given by Fabre et al. [J. Phys. (France) 50, 1209 (1989)].
The dependence of the quantum correlation of twin beams generated from a non-degenerate optical parametric oscillator on the analysis frequency was theoretically studied with semi-classical method. It was pointed out that the quantum entanglement is higher at lower analysis frequency. By means of a pair of unbalanced fiber Mach-Zehnder interferometers，the correlation noise spectrum of the intensity-difference and the phase-sum of twin beams with non-degenerate frequencies and total power of 20mW were experimentally measured，which were 3.1 and 1.3dB below the corresponding shot noise limit at 2MHz，respectively. The experimental results are in agreement with the theoretical predictions.
In this paper, a generation scheme for telecom band hyper-entanglement is proposed and demonstrated based on the vector spontaneous four wave mixing (SFWM) processes in optical fibers. Two kinds of two-photon states are generated, one is hyper-entangled in the degree of freedoms (DOFs) of energy-time and polarization, the other is hyper-entangled in DOFs of energy-time and discrete-frequency. Experiments of Franson-type interference, two-photon interference under non-orthogonal polarization bases and spatial quantum beating are realized to demonstrate the entanglement in energy-time, polarization and frequency, respectively. This scheme provides a simple way to realize telecom band hyper-entanglement, which has potential for large geographic-scale applications of quantum communication and quantum information over optical fibers.
Discrete frequency-bin entanglement is an essential resource for applications in quantum information processing. In this Letter, we propose and demonstrate a scheme to generate discrete frequency-bin entanglement with a single piece of periodically poled lithium niobate waveguide in a modified Sagnac interferometer. Correlated two-photon states in both directions of the Sagnac interferometer are generated through cascaded second-order optical nonlinear processes. A relative phase difference between the two states is introduced by changing the polarization state of pump light, thus manipulating the two-photon state at the output of the Sagnac interferometer. The generated two-photon state is sent into a fiber polarization splitter, and then a pure discrete frequency-bin entangled two-photon state is obtained by setting the pump light. The frequency entanglement property is measured by a spatial quantum beating with a visibility of 96.0±6.1%. The density matrix is further obtained with a fidelity of 98.0±3.0% to the ideal state. Our demonstration provides a promising method for the generation of pure discrete frequency-bin entanglement at the telecom band, which is desired in quantum photonics.