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Demonstration of channel-selective quantum frequency conversion

Toshiki Kobayashi, Tomoaki Arizono, Masahiro Yabuno, Shigehito Miki, Tsuyoshi Kodama, Hideki Shimoi, Takashi Yamamoto, Rikizo Ikuta

Published Jan 1, 2025• 0 citations
Publisher

Abstract

We report a channel-selective quantum frequency conversion (QFC) from a 780-nm single photon to telecom wavelength channels around 1540 nm by selecting one of multiple frequencies of pump light.
DOI
10.1364/cleo_fs.2025.ff106_8

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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.
Interconnecting heterogeneous quantum systems is an important step toward realizing the quantum internet. We propose a quantum network hub that interfaces local quantum devices with dense wavelength-division multiplexing (DWDM) networks in the telecom band via quantum frequency conversion (QFC) with frequency-channel selectivity. We show that standard periodically poled lithium niobate waveguides used for QFC exhibit a dispersion sweet spot, for example around the 780 nm band, enabling wide tunability of the pump wavelength while maintaining phase matching. Experimentally, we demonstrate the network hub by implementing a channel-selective and polarization-insensitive QFC from 780 nm to telecom wavelengths around 1540 nm. We achieve a pump tuning range of 2 THz and successfully distribute polarization-encoded single photons into 16 frequency channels on the ITU-T DWDM grid with 25 GHz channel spacing, while preserving the quantum information. These results position the QFC-based hub as a versatile backbone for connecting a wide range of quantum devices, spanning both photonic and matter-based systems, across frequency-multiplexed telecom networks.
Dense wavelength division multiplexing (DWDM) is a key technology for realizing high-capacity and flexible quantum communication networks. To enable the emerging quantum internet, quantum frequency conversion is also essential for bridging different quantum systems over optical fiber networks. In this work, aiming at a frequency-multiplexed quantum internet, we present a channel-selective quantum frequency conversion (CS-QFC) based on difference frequency generation in a PPLN waveguide, which has been widely used in conventional QFC experiments. The CS-QFC converts a frequency of a photon at a single frequency to any frequency in the DWDM channels by dynamically selecting one of the pump lights. In the experiment, we demonstrated the CS-QFC from 780 nm to around 1540 nm employing one of the pump lights around 1580 nm detuned with a spacing of 25 GHz. From the experiment using the laser light, we showed that the output-frequency tunability of our CS-QFC reaches 2.5 THz, which corresponds to the ability to establish a 100-ch DWDM dynamic link from a single quantum system. Using photon pairs, we performed an experiment in which photons were routed into seven of the DWDM channels. As a result, photons were converted to the channels corresponding to the pump frequencies, while keeping the nonclassical cross-correlation functions, and no crosstalk to the other channels was observed.
Quantum frequency conversion (QFC) which converts the frequencies of photons while preserving the quantum state is an essential technology for realizing the quantum internet and quantum interconnect. For the QFC based on the frequency downconversion from visible to the telecom wavelengths around 1500 nm, it is widely known that noise photons produced by the strong pump light used for QFC contaminate the frequency-converted photon, which degrades the quality of the quantum property of the photon after QFC. In conventional QFC experiments, noise photons are removed using external narrowband frequency filter systems. In contrast, in this study, we implement a compact QFC device integrating the cavity structure only for the converted mode. While the cavity structure can enhance not only the desired QFC efficiency but also the noise photon generation rate, we show that the cavity-enhanced QFC followed by a relatively wide bandpass filter achieves the signal-to-noise ratio comparable to the QFCs with external narrowband filters. We experimentally demonstrate the cavity-enhanced QFC using a single photon at 780 nm to 1540 nm, in which the non-classical photon statistics is clearly observed after QFC.
We study multiplexed quantum frequency conversion (m-QFC) on a single waveguide, where a single pump beam simultaneously converts multiple signal beams at distinct wavelengths. Using a three-peak periodically poled lithium niobate (PPLN) waveguide, we demonstrate the multiplexed upconversion in the telecom band with internal efficiencies up to 73.6%. Tested with a multichannel photon-pair source, the quantum correlation is preserved well after the conversion, with coincidence-to-accidental ratio reaching 767. These results highlight a viable device approach to multiplexed quantum key distribution, quantum sensing, and quantum computing.
We demonstrate efficient (>30%) quantum frequency conversion of visible single photons (711 nm) emitted by a quantum dot to a telecom wavelength (1313 nm). Analysis of the first- and second-order coherence before and after wavelength conversion clearly proves that pivotal properties, such as the coherence time and photon antibunching, are fully conserved during the frequency translation process. Our findings underline the great potential of single photon sources on demand in combination with quantum frequency conversion as a promising technique that may pave the way for a number of new applications in quantum technology.