Two-step frequency conversion for connecting distant quantum memories by transmission through an optical fiber

Abstract

Long-distance quantum communication requires entanglement between distant quantum memories. For the purpose, photon transmission is necessary to connect the distant memories.Here, for the first time, we develop a two-step frequency conversion process (from a visible wavelength to a telecommunication wavelength and back) involving the use of independent two-frequency conversion media where target quantum memories are nitrogen-vacancy centers in diamonds (with an emission/absorption wavelength of 637.2 nm), and experimentally characterize the performance of this process acting on light from an attenuated CW laser. A total conversion efficiency of approximately 7% is achieved. The noise generated in the frequency conversion processes is measured, and the signal-to-noise ratio is estimated for a single photon signal emitted by an NV center. The developed frequency conversion system has future applications via transmission through long optical fiber channel at a telecommunication wavelength for quantum repeater network.

Two-photon comb with wavelength conversion and 20-km distribution for quantum communication

“…The WC-TPC has two important parameters: noise floor level and signalto-noise ratio (SNR). The noise floor level is influenced by many factors, including the presence of a residual laser, which can induce other nonlinear processes such as SPDC and Raman scattering 36,37 , dark counts in the detector, and stray light (related results are presented in Supplementary Note 5).…”

“…The noise floor level is influenced by many factors, including the presence of a residual laser, which can induce other nonlinear processes such as SPDC and Raman scattering [36] [37], dark counts in the detector, and stray light (related results are presented in the Supplementary note 5). Two-photon correlation was characterized by the normalized second-order signal-idler correlation coefficient g 𝑠,𝑖…”

“…In previous studies, cavity-enhanced spontaneous parametric down conversion (SPDC) photon sources were demonstrated for many applications 20 ; for example, demonstrating theoretical/ proof-of-principle models [21][22][23][24][25][26] , highly bright single modes [27][28][29][30][31] , and narrow linewidths [32][33][34][35] . On the other hand, for compatibility between telecom and QM absorption line, wavelength conversion (WC) is demonstrated using a laser 36,37 and single photons 38,39 for application to nitrogen-vacancy centers, rare-earth-doped crystals, quantum dots, and rubidium gas, among others. Wavelength conversion still has difficulty about conversion efficiency and noise photon to realize photonic interface.…”

Compact frequency-stabilized pump laser for wavelength conversion in long-distance quantum communication

“…The observed beam profile is sufficient for obtaining a highefficiency coupling to a wavelength conversion medium, such as a waveguide-type periodically poled lithium niobate (PPLN). In a previous work by several authors of the present study [19], the maximum wavelength conversion between 637.2 nm and a telecommunication wavelength was achieved with a pump power of about 500 mW where another laser with a slightly different wavelength (1071 nm) was used. However, we also demonstrated the same wavelength conversion process with the present laser and achieved a maximum conversion efficiency up to 35 % with a pump laser power of about 300 mW.…”

Spectral noise in frequency conversion from the visible to the telecommunication C-band

“…This is due to non-phase-matched broadband spontaneous parametric down conversion (SPDC) of the pump laser [14]. This noise contribution scales linearly with the pump power, as observed and verified in numerous experiments [11,12,14,17]. Yet, recent experiments have shown that the noise can be suppressed to acceptable levels by strong filtering around the target wavelength [5,[10][11][12][13].…”