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Conference on Lasers and Electro-Optics

Frequency down-conversion of non-classical light from visible wavelength to telecom wavelength using difference-frequency generation

Rikizo Ikuta, Tsuyoshi Kitano, Yoshiaki Kusaka, Takashi Yamamoto, Masato Koashi, Nobuyuki Imoto

Published Jan 1, 2011• 0 citations
Publisher

Abstract

We experimentally demonstrate frequency down-conversion of non-classical light by difference-frequency generation. We prepared a heralded single photon at wavelength of 780 nm, which corresponds to a resonant wavelength of a Rb atom for a quantum memory, and then converted the wavelength to a telecommunication wavelength of 1522 nm. The observed second-order correlation g(2)(0) of the converted light is 0.54 ± 0.12, which clearly shows sub-Poissonian photon statistics of light.

DOI
10.1364/cleo_at.2011.jthb18

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We experimentally demonstrate frequency down-conversion of non-classical light by difference-frequency generation. We prepared a heralded single photon at wavelength of 780 nm, which corresponds to a resonant wavelength of a Rb atom for a quantum memory, and then converted the wavelength to a telecommunication wavelength of 1522 nm. The observed second-order correlation g(2)(0) of the converted light is 0.54 ± 0.12, which clearly shows sub-Poissonian photon statistics of light.
In our recent studies, we demonstrated a conversion of a visible photon at 780 nm to a 1522-nm photon by using difference frequency generation. Intensity correlation measurement on the converted light confirmed that the non-classical property of the input single photon is retained over the conversion process. We further performed a conversion of one half of an entangled photon pair and observed a highly entangled photon pair at 780-nm and 1522-nm, which shows that the quantum information is really transferred in the quantum interface.
We experimentally demonstrated the Hong-Ou-Mandel (HOM) interference between two photons after visible-to-telecommunication wavelength conversion. In the experiment, we prepared a heralded single photon by using spontaneous parametric down conversion (SPDC) and the other photon from a weak laser source at 780 nm. We converted the wavelength of both photons to the telecommunication wavelength of 1522 nm by using difference-frequency generation in a periodically poled lithium niobate, and then observed the HOM interference between the photons. The observed visibility is $0.76\ifmmode\pm\else\textpm\fi{}0.12$ which clearly shows the nonclassical interference of the two photons. The high-visibility interference is an important step for fiber-based quantum communications of photons generated from visible-photon emitters.
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In quantum repeater schemes for long distance quantum communication, quantum memories (QMs) play a vital role. For these applications, QMs need to be connected to the fiber optics network. However most QMs operate at wavelengths where the absorption in optical fibers is high. Therefore, their connection to a quantum frequency converter (QFC) to telecom wavelengths is required. In this work we convert an heralded single photon emitted by a rubidium atomic ensemble QM, using a QFC implemented with a non-linear waveguide. The main advantages of this converter setup are its compactness, relative simplicity and wavelength flexibility. We show that after this process the non-classical correlations between the heralding photons and converted heralded photons generated in the QM are preserved. This is the first time that frequency conversion of non-classical light emitted by an atomic QM is performed with a solid state device.
We experimentally demonstrate a high-fidelity visible-to-telecommunication wavelength conversion of a photon by using a solid-state-based difference frequency generation. In the experiment, one half of a picosecond visible entangled photon pair at 780 nm is converted to a 1522-nm photon, resulting in the entangled photon pair between 780 and 1522 nm. Using superconducting single-photon detectors with low dark count rates and small timing jitters, we selectively observed well-defined temporal modes containing the two photons. We achieved a fidelity of $0.93\ifmmode\pm\else\textpm\fi{}0.04$ after the wavelength conversion, indicating that our solid-state-based scheme can be used for faithful frequency down conversion of visible photons emitted from quantum memories composed of various media.
We demonstrate channel-selective frequency up-conversion from telecom wavelengths around 1540 nm for optical fiber communication to visible wavelengths around 780 nm, based on second-order optical nonlinearity in a cavity of the converted modes. In our experiment, we selectively convert a light from any frequency mode within frequency-multiplexed telecom signals to a desired output mode, determined by the cavity resonances. Based on the experimental results of the frequency up-conversion, we derive the signal-to-noise ratio of the process at the single-photon level, and discuss its applicability to channel-selective quantum frequency conversion (CS-QFC) in the context of frequency-multiplexed quantum networks. Finally, we describe specific use cases of the CS-QFC, which show its utility as a reconfigurable switching element in frequency-multiplexed networks, particularly for selectively performing Bell-state measurements between two photons originating from different frequencies.