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Optics Express

Production of degenerate polarization entangled photon pairs in the telecom-band from a pump enhanced parametric downconversion process

Peter James Thomas, Christopher J. Chunnilall, David J. M. Stothard, D. A. Walsh, Malcolm H. Dunn

Published Dec 3, 2010• 10 citations
Publisher

Abstract

The design and implementation of a novel source of degenerate polarization entangled photon pairs in the telecom band, based on a cavity enhanced parametric downconversion process, is presented. Two of the four maximally entangled Bell states are produced; the remaining two are obtainable by the addition of a half wave plate into the setup. The coincident photon detection rate in the A/D basis between two detectors at the output of the device revealed the production of highly entangled states, resulting in quantum interference visibilities of 0.971 ± 0.041 (ϕ = 0 state) and 0.932 ± 0.036 (ϕ = π state) respectively. The entangled states were found to break the Clauser-Horne-Shimony-Holt (CHSH) Bell inequality by around 6 standard deviations. From the measured coincidence counting rates and the optical system losses, an entangled photon pair production rate of 8.9 × 10(4) s(-1) mW(-1) pump was estimated.

DOI
10.1364/oe.18.026600

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arXiv:quant-ph/0402191•Physical Review Letters•Feb 9, 2005•454 citations
The design and implementation of a novel source of degenerate polarization entangled photon pairs in the telecom band, based on a cavity enhanced parametric downconversion process, is presented. Two of the four maximally entangled Bell states are produced; the remaining two are obtainable by the addition of a half wave plate into the setup. The coincident photon detection rate in the A/D basis between two detectors at the output of the device revealed the production of highly entangled states, resulting in quantum interference visibilities of 0.971 ± 0.041 (ϕ = 0 state) and 0.932 ± 0.036 (ϕ = π state) respectively. The entangled states were found to break the Clauser-Horne-Shimony-Holt (CHSH) Bell inequality by around 6 standard deviations. From the measured coincidence counting rates and the optical system losses, an entangled photon pair production rate of 8.9 × 10(4) s(-1) mW(-1) pump was estimated.
In this paper we report a polarization-entangled photon-pair source in a 1.5-μm band which can generate arbitrary entangled states including four maximum entangled states (Bell states) by using cascaded optical second nonlinearities (second-harmonic generation and the following spontaneous parametric down conversion) in a periodically poled LiNbO(3) (PPLN) ridge-waveguide device. Exchange among the Bell states was achieved by using an optical phase bias compensator (OPBC) in a Sagnac loop interferometer and a half-wave plate outside the loop for polarization conversion. Quantitative evaluation was made on the performance of the photon-pair source through the experiments of two-photon interferences, quantum state tomography, and test of violation of Bell inequality. We observed high visibilities of 96%, fidelities of 97%, and 2.71 of the S parameter in inequality of Clauser, Horne, Shimony, and Holt (CHSH). The experimental values, including peak coincidence counts in the two-photon interference (approximately 170 counts per second), remained almost unchanged in despite of the exchange among the Bell states. They were also in good agreement with the theoretical assumption from the mean number of the photon-pairs under the test (0.04 per pulse). More detailed experimental studies on the dependence of the mean number of the photon-pairs revealed that the quantum states were well understood as the Werner state.
Correlated photon pairs generated through spontaneous parametric downconversion have become a key resource for research into enhanced optical measurement and quantum optical information processing. A pump-enhanced χ(2) source of correlated photons in the telecom band is presented. An investigation of the pair photon coincidence detection rate measured from the source, together with the evaluation of system losses, indicated a single spatial fibre-optic mode pair production rate of 6.12 × 104 s−1 mW−1 pump power, an order of magnitude greater than was measured without enhancement. A Hong-Ou-Mandel interference experiment confirmed that the enhancement did not have any adverse effect on the spatial and frequency indistinguishability of the emitted pairs. The source comprises a symmetric and linear enhancement cavity for the pump, making it particularly suitable for generating polarisation entangled photon pairs without the need for compensating crystals 1 Thomas, PJ, Chunnilall, CJ, Stothard, DJM, Walsh, DA and Dunn, MH. 2010. Opt. Express, 18: 26600–26612. [Crossref], [PubMed], [Web of Science ®] , [Google Scholar].
The authors present an efficient source of high purity polarization-entangled photon pairs in the standard 1550nm telecommunication band using a type-II degenerate parametric downconversion process. They first measured the spatial intensity distributions of the downconverted light to verify the beamlike, collinear, and noncollinear generations at the 1550nm wavelength. All four Bell states could easily be generated by selecting the intersection of two downconverted light cones in the noncollinear phase matching. They observed two-photon fringe visibilities of up to 98±3% and violations of Bell’s inequality by up to nine standard deviations when the accidental coincidences were subtracted.
We report a source of polarization-entangled photon pairs in the 1550-nm telecommunication band, which is based on non-collinear spontaneous parametric down-conversion in a periodically poled lithium niobate crystal pumped by picosecond pulses. This source is realized utilizing a polarization-based Sagnac interferometer employing a type-0 non-collinear quasi-phase-matching configuration. Polarization entanglement is verified through measurement of the polarization-correlation interference fringes with visibility >96% and by testing the experimental violation of the Clauser-Horne-Shimony-Holt (CHSH) form of Bell's inequality. The CHSH-Bell parameter S is found to be 2.72 ± 0.04, with 18 standard deviations from the statistical uncertainty.
Bell states are fundamental resources in quantum optics, underpinning a range of applications in quantum computation and communication. However, many experimental sources focus on generating a single Bell state, limiting their utility for protocols that require the full set of maximally entangled states. In this work, we present a polarization-entangled photon-pair source based on spontaneous parametric down-conversion in a periodically poled potassium titanyl phosphate crystal integrated into a Sagnac loop interferometer. Our source initially generates one Bell state, which is then transformed into the complete set of Bell states through the application of phase and bit flips using phase plates. We characterize the entanglement quality of all generated states via two-photon interference measurements, quantum state tomography, and evaluation of the Bell parameter. Our results show spectral brightness of 0.15 kHz/mW/nm with interference visibilities of ∼98% (H/V basis) and ∼96% (A/D basis) and state fidelity of ∼0.97 across all Bell states, with all states demonstrating a clear violation of the Clauser–Horne–Shimony–Holt inequality (S≥2.6). This approach offers a practical solution for obtaining all four Bell states with high efficiency from a single source, which could facilitate more versatile implementations in quantum information processing.
We present a fiber-based source of polarization-entangled photons that is well suited for quantum communication applications in the 1550 nm band of standard fiber-optic telecommunications. Polarization entanglement is created by pumping a nonlinear-fiber Sagnac interferometer with two time-delayed orthogonally polarized pump pulses and subsequently removing the time distinguishability by passing the parametrically scattered signal and idler photon pairs through a piece of birefringent fiber. Coincidence detection of the signal and idler photons yields biphoton interference with visibility greater than 90%, while no interference is observed in direct detection of either signal or idler photons. All four Bell states can be prepared with our setup and we demonstrate violations of the Clauser-Horne-Shimony-Holt form of Bell's inequality by up to 10 standard deviations of measurement uncertainty.