Abstract
Single-photon frequency conversion for quantum interface plays an important role in quantum communications and networks, which is crucial for the realization of quantum memory, faithful entanglement swapping and quantum teleportation. In this talk, I will present our recent experiments about single-photon frequency conversion based on quadratic nonlinear processes. Firstly, we demonstrated spectrum compression of broadband single photons at the telecom wavelength to the near-visible window. A positively chirped single-photon-level laser pulse and a negatively chirped classical one are converted to a narrowband single-photon pulse, with a spectrum compression factor of 58, through sum-frequency generation (SFG), marking a critical step towards coherent photonic interface. Secondly, we demonstrated the nonlinear interaction between two chirped broadband single-photon-level coherent states. A high SFG efficiency of 1.06 × 10−7 is realized, which may be utilized to achieve heralding entanglement at a distance. Finally, we theoretically introduced and experimentally demonstrated single-photon frequency conversion in the telecom band, enabling switching of single photons between dense wavelength-division multiplexing channels. Using cascaded quasi-phase matched sum/difference frequency generation, the signal photon of a photon pair from spontaneous down-conversion is precisely shifted to identically match its counterpart, i.e. idler photon, in frequency to manifest a clear non-classical dip in the Hong-Ou-Mandel interference. Moreover, quantum entanglement between the photon pair is maintained after the frequency conversion. Our researches have realized three significant quantum interfaces via single-photon frequency conversion, which hold great promise for the development of quantum communications and networks.
Highlights
In recent years, nonlinear quantum optics has developed rapidly, such as quantum communication [1], quantum computation [2], quantum memory [3], quantum network [4], and so on
We report single-photon frequency conversion in a telecommunication band based on cascaded quadratic nonlinearity, i.e., sum frequency generation (SFG) and difference frequency generation (DFG), in a Periodically polarized lithium niobate (PPLN) waveguide
We have experimentally demonstrated that the spectrum of singlephoton-level laser pulse was compressed by a factor of 58 in a PPLN waveguide chip, where a chirped single-photon-level laser pulse and an antichirped laser pulse by fiber Bragg gratings are used to achieve a pulse with new frequency through SFG
Summary
Nonlinear quantum optics has developed rapidly, such as quantum communication [1], quantum computation [2], quantum memory [3], quantum network [4], and so on. Any node in a quantum network has the capability of quantum communication, quantum memory, quantum entanglement swapping, and generation of single photon sources. We utilized PPLN waveguide chip to realize several kinds of different functions of single-photon frequency conversion for coherent quantum interface. We report single-photon frequency conversion in a telecommunication band based on cascaded quadratic nonlinearity, i.e., SFG and difference frequency generation (DFG), in a PPLN waveguide. It shows that the frequency of single photons can be precisely converted to a DFG with continuous adjustability in a wide telecommunication band and their quantum characteristics are protected after the single-photon frequency conversion [7]
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