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arXiv:1403.1917 · Optics Letters

Generation of 15 μm discrete frequency-entangled two-photon state in polarization-maintaining fibers

Qiang Zhou, Wei Zhang, Chenzhi Yuan, Yidong Huang, Jiangde Peng

Published Mar 27, 2014• 14 citations
arXivHTMLPDF

Abstract

In this Letter, the generation of a 1.5 μm discrete frequency-entangled two-photon state is realized based on a piece of commercial polarization-maintaining fiber (PMF). It is connected with a polarization beam splitter to realize a modified Sagnac fiber loop (MSFL). Correlated two-photon states are generated through a spontaneous four-wave-mixing process along the two propagation directions of the MSFL, and output from the MSFL with orthogonal polarizations. Their quantum interference is realized through a 45° polarization collimation between polarization axes of PMFs inside and outside the MSFL, while their phase difference is controlled by the polarization state of the pump light. The frequency-entangled property of the two-photon state is demonstrated by a spatial quantum beating experiment with a fringe visibility of 98.2±1.3%, without subtracting the accidental coincidence counts. The proposed scheme generates a 1.5 μm discrete frequency-entangled two-photon state in a polarization-maintaining way, which is desired in practical quantum light sources.

DOI
10.1364/ol.39.002109

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In this Letter, the generation of a 1.5 μm discrete frequency-entangled two-photon state is realized based on a piece of commercial polarization-maintaining fiber (PMF). It is connected with a polarization beam splitter to realize a modified Sagnac fiber loop (MSFL). Correlated two-photon states are generated through a spontaneous four-wave-mixing process along the two propagation directions of the MSFL, and output from the MSFL with orthogonal polarizations. Their quantum interference is realized through a 45° polarization collimation between polarization axes of PMFs inside and outside the MSFL, while their phase difference is controlled by the polarization state of the pump light. The frequency-entangled property of the two-photon state is demonstrated by a spatial quantum beating experiment with a fringe visibility of 98.2±1.3%, without subtracting the accidental coincidence counts. The proposed scheme generates a 1.5 μm discrete frequency-entangled two-photon state in a polarization-maintaining way, which is desired in practical quantum light sources.
In this Letter, a linear scheme to generate polarization entanglement at 1.5 μm based on commercial polarization maintained dispersion shifted fiber (PM-DSF) is proposed. The birefringent walk-off effect of the pulsed pump light in the PM-DSF provides an effective way to suppress the vector scattering processes of spontaneous four-wave mixing. A 90 deg offset of fiber polarization axes is introduced at the midpoint of the fiber to realize the quantum superposition of the two correlated photon states generated by the two scalar processes on different fiber polarization axes, leading to polarization entanglement generation. Experiments of the indistinguishable property on single-side and two-photon interference in two nonorthogonal polarization bases are demonstrated. A two-photon interference fringe visibility of 89±3% is achieved without subtracting the background counts, demonstrating its great potential in developing highly a efficient and stable fiber based polarization-entangled quantum light source at the optical communication band.
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.
In this paper, a generation scheme of telecom band frequency-degenerate polarization entangled photon pairs is proposed and demonstrated experimentally. It is based on the vector spontaneous four wave mixing (SFWM) process in a Sagnac fiber loop, in which two frequency-degenerate and polarization orthogonal biphoton states have equal probabilities for generating along the clockwise and counter-clockwise directions. The quantum interference between them at the 50:50 fiber coupler of the fiber loop separates the two frequency-degenerate photons in a pair, leading to the generation of polarization entanglement. The raw fringe visibilities of the two-photon interferences under two non-orthogonal polarization bases are 91% and 90%, respectively. Information can be encoded on the generated photon pairs using the polarization entangled Bell states, which requires the frequency-degenerate property. It is demonstrated by a simplified Bell state measurement with a fringe visibility of 83%.
In this Letter, a linear scheme to generate polarization entanglement at 1.5 um based on commercial polarization maintained dispersion shifted fiber (PM-DSF) is proposed. The birefringent walk-off effect of the pulsed pump light in the PM-DSF provides an effective way to suppress the vector scattering processes of spontaneous four wave mixing. A 90 degree offset of fiber polarization axes is introduced at the midpoint of the fiber to realize the quantum superposition of the two correlated photon states generated by the two scalar processes on different fiber polarization axes, leading to polarization entanglement generation. Experiments of the indistinguishable property on single side and two-photon interference in two non-orthogonal polarization bases are demonstrated. A two photon interference fringe visibility of 89\pm3% is achieved without subtracting the background counts, demonstrating its great potential in developing highly efficient and stable fiber based polarization-entangled quantum light source at optical communication band.
We propose and experimentally demonstrate a generation scheme of telecom-band fiber-based frequency-degenerate polarization-entanglement photon pair source. Basing on the vector spontaneous four wave mixing process in a Sagnac fiber loop along the clockwise and counter-clockwise directions, two frequency-degenerate and polarization orthogonal biphoton states generate and then lead to the polarization entanglement states by the interference at the beamsplitter. The raw fringe visibilities of the two-photon interferences are 97% and 92%, respectively. Information can be encoded on the generated photon pairs using the polarization entangled Bell states. It is demonstrated by a simplified Bell state measurement with a fringe visibility of 83%.
We describe the generation of entangled and hyperentangled photon pairs using a microstructure-fiber Sagnac interferometer, which is formed by a polarizing beam splitter and a highly nonlinear microstructure fiber twisted by 90° from end to end. This interferometer allows two identical four-wave mixing processes to occur on the same fiber principal axis, ensuring perfect spatial and temporal mode matching of the two four-wave mixing outputs on the polarizing beam splitter to create entanglement over the entire four-wave mixing phase-matching spectral range. With an average pump power of 220 μW, we measure a two-photon coincidence rate of 1 kHz with ▵λ = 0.9 nm. Two-photon interference visibilities exceed 91% for polarization-entangled photon pairs generated from this source, and are > 84% for both time-bin and polarization degrees of freedom for hyperentangled photons, all without subtracting accidental coincidences.