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Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)

Photon Pair Generation at 2.080μm by Down-Conversion

Taylor Shields, Robert H. Hadfield, Matteo Clerici, Shashi Prabhakar, Damian Powell, Gregor G. Taylor, D. Morozov, Mehdi Haji Ebrahim, Michael Kues, Lucia Caspani, Corin B. E. Gawith

Published Jun 1, 2019• 1 citation

Abstract

Quantum-optical technologies are transforming communication and metrology by enabling security and sensitivity beyond classical limits. Currently, these technologies are available at visible, near-infrared (NIR) and telecom wavelengths but are strongly underdeveloped at longer wavelengths. There is a growing demand for quantum sources operating in the 2 μm region for various applications. For example, such sources can enable daylight satellite-to-ground based quantum communications by taking advantage of an atmospheric transparency window with reduced solar blackbody radiation compared to telecom wavelengths [1,2,3]. Moreover, squeezed 2 μm sources are expected to have an impact on quantum metrology. For example, in gravitational wave detectors (eg. LIGO), such long wavelengths could reduce the quantum noise and scattering loss from crystalline silicon test masses [4]. Here, we report the generation and characterisation of a photon pair source at 2.080 μm with coincidence-to-accidental ratio (CAR) exceeding 10.

DOI: 10.1109/cleoe-eqec.2019.8872702

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Generation and Detection of Down-converted Photon Pairs at

2.080\ \boldsymbol{\mu} \mathbf{m}

Quantum correlated, highly non-degenerate photons can be used to synthesize disparate quantum nodes and link quantum processing over incompatible wavelengths, thereby constructing heterogeneous quantum systems for otherwise unattainable superior performance. Existing techniques for correlated photons have been concentrated in the visible and near-IR domains, with the photon pairs residing within one micron. Here, we demonstrate direct generation and detection of high-purity photon pairs at room temperature with 3.2 um wavelength spacing, one at 780 nm to match the rubidium D2 line, and the other at 3950 nm that falls in a transparent, low-scattering optical window for free space applications. The pairs are created via spontaneous parametric downconversion in a lithium niobate waveguide with specially designed geometry and periodic poling. The 780 nm photons are measured with a silicon avalanche photodiode, and the 3950 nm photons are measured with an upconversion photon detector using a similar waveguide, which attains 34% internal conversion efficiency. Quantum correlation measurement yields a high coincidence-to-accidental ratio of 54, which indicates the strong correlation with the extremely non-degenerate photon pairs. Our system bridges existing quantum technology to the challenging mid-IR regime, where unprecedented applications are expected in quantum metrology and sensing, quantum communications, medical diagnostics, and so on.

Quantum-enhanced optical systems operating within the 2- to 2.5-μm spectral region have the potential to revolutionize emerging applications in communications, sensing, and metrology. However, to date, sources of entangled photons have been realized mainly in the near-infrared 700- to 1550-nm spectral window. Here, using custom-designed lithium niobate crystals for spontaneous parametric down-conversion and tailored superconducting nanowire single-photon detectors, we demonstrate two-photon interference and polarization-entangled photon pairs at 2090 nm. These results open the 2- to 2.5-μm mid-infrared window for the development of optical quantum technologies such as quantum key distribution in next-generation mid-infrared fiber communication systems and future Earth-to-satellite communications.