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Conference on Lasers and Electro-Optics

Telecom Narrow Bandwidth Two-photon Source with High Fidelity Polarization Entanglement

Kazuya Niizeki, Daisuke Yoshida, Ming-Yang Zheng, Xiu-Ping Xie, Kotaro Okamura, Nobuyuki Takei, Tomoyuki Horikiri

Published May 5, 2019• 0 citations
Publisher

Abstract

We demonstrate two-photon sources for long-distance quantum communication. The highest spectral brightness $3.94\times 10^{5}\mathrm{pairs}/(\mathrm{s} \mathrm{ MHz} \mathrm{mW})$ , the narrowest linewidth in telecom of 1.06 MHz and entanglement fidelity of91.8% are shown. © 2019 The Author(s)

DOI
10.23919/cleo.2019.8749696

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We demonstrate two-photon sources for long-distance quantum communication. The highest spectral brightness 3.94×105pairs/(sMHzmW)3.94\times 10^{5}\mathrm{pairs}/(\mathrm{s} \mathrm{ MHz} \mathrm{mW})3.94×105pairs/(sMHzmW) , the narrowest linewidth in telecom of 1.06 MHz and entanglement fidelity of91.8% are shown. © 2019 The Author(s)
We demonstrate an ultrabright narrow-band two-photon source at the 1.5 µm telecom wavelength for long-distance quantum communication. By utilizing a bow-tie cavity, we obtain a cavity enhancement factor of 4.06 × 10 4 . Our measurement of the second-order correlation function G (2) (τ) reveals that the linewidth of 2.4 MHz has been hitherto unachieved in the 1.5 µm telecom band. This two-photon source is useful for obtaining a high absorption probability close to unity by quantum memories set inside quantum repeater nodes. Furthermore, to the best of our knowledge, the observed spectral brightness of 3.94 × 10 5 pairs/(s·MHz·mW) is also the highest reported over all wavelengths.
A high-quality narrowband polarization-entangled source in the telecom band is preferred to avoid frequency dispersion for long-distance transmission in optical fibers and to efficiently couple with telecom-band quantum memories. Here, we report narrowband, telecom-band, polarization-entangled photon pair generation based on the superposition of single-longitudinal-mode photon pairs from two monolithic nonlinear crystal cavities in a passively stable interferometer based on beam displacers. The photon pairs generated from the cavities exhibit a high coincidence to accidental coincidence ratio of 20 000 and a bandwidth below 500 MHz. Two-photon polarization interference, Bell inequality, and quantum state tomography are performed to indicate the high quality of the entangled source. The current configuration demonstrates greater stability than traditional free space cavity-enhanced polarization-entangled state generation, which is promising for quantum communication applications.
Quantum computing and quantum communication, have been greatly developed in recent years and expected to contribute to quantum internet technologies, including cloud quantum computing and unconditionally secure communication. However, long-distance quantum communication is challenging mainly because of optical fiber losses; quantum repeaters are indispensable for fiber-based transmission because unknown quantum states cannot be amplified with certainty. In this study, we demonstrate a versatile entanglement source in the telecom band for fiber-based quantum internet, which has a narrow linewidth of sub-MHz range, entanglement fidelity of more than 95%, and Bell-state generation even with frequency multimode. Furthermore, after a total distribution length of 20-km in fiber, two-photon correlation is observed with an easily identifiable normalized correlation coefficient, despite the limited bandwidth of the wavelength converter. The presented implementation promises an efficient method for entanglement distribution that is compatible with quantum memory and frequency-multiplexed long-distance quantum communication applications. Quantum technologies have seen a remarkable development in recent years and are expected to contribute to quantum internet technologies. The authors present an experimental implementation over commercial telecom fibres of a two-photon comb source for quantum communications with long coherence times and narrow bandwidth, which is used in a 20 km distribution experiment to show the presence of remote two-photon correlations.
We report the realization of a new polarization entangled photon-pair source based on a titanium-indiffused waveguide integrated on periodically poled lithium niobate pumped by a CW laser at 655 nm. The paired photons are emitted at the telecom wavelength of 1310 nm within a bandwidth of 0.7 nm. The quantum properties of the pairs are measured using a two-photon coalescence experiment showing a visibility of 85%. The evaluated source brightness, on the order of 10(5) pairs s(-1)GHz(-1)mW(-1), associated with its compactness and reliability, demonstrates the source's high potential for long-distance quantum communication.