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

Abstract

Quantum computing and quantum communication, have been greatly developed in recent years and expected to contribute to quantum internet technologies, including cloud quantum computing and unconditionally secure communication. However, long-distance quantum communication is challenging mainly because of optical fiber losses; quantum repeaters are indispensable for fiber-based transmission because unknown quantum states cannot be amplified with certainty. In this study, we demonstrate a versatile entanglement source in the telecom band for fiber-based quantum internet, which has a narrow linewidth of sub-MHz range, entanglement fidelity of more than 95%, and Bell-state generation even with frequency multimode. Furthermore, after a total distribution length of 20-km in fiber, twophoton correlation is observed with an easily identifiable normalized correlation coefficient, despite the limited bandwidth of the wavelength converter. The presented implementation promises an efficient method for entanglement distribution that is compatible with quantum memory and frequency-multiplexed long-distance quantum communication applications.

Single-shot high-resolution identification of discrete frequency modes of single-photon-level optical pulses

“…We also demonstrate a high-resolution FTMMs using AFC, which can be applied to narrow linewidth photons. The demonstrated FTMM is capable of identifying frequency modes in the 100 MHz interval, which is close to the FSR of recent cSPDC two-photon sources [8,17] and the lower limit of frequency interval of AFCs in Pr:YSO.…”

“…In this study, we achieved frequency mode identification at 100 MHz intervals, which is close to the frequency multiplexing limit of AFC in Pr:YSO, a promising quantum memory for quantum repeater. Since the FSR of a cSPDC source with high coupling to quantum memory has been demonstrated to be about 100 MHz [8,17], this spectroscopic system not only achieves the upper limit of discrete-mode spectral resolution with Pr:YSO, but also shows promising results for improving the quantum entanglement generation rate.…”

“…Therefore, in the case of frequency-multiplexed quantum repeater using AFCs in Pr:YSO, the upper limit of the entanglement distribution rate can be increased by making the frequency-mode interval as narrow as possible. As a frequency-multiplexed photon pair source, cavity-enhanced spontaneous parametric down-conversion (cSPDC) [15][16][17], which is also used in Ref. [8], would be promising.…”

Low SWaP miniaturized fiber coupled external cavity diode laser (ECDL) with high optical isolation as plug and play solution

“…[12] In quantum applications, PDH stabilized single frequency lasers are used to generate coherent states of light, which are essential for many quantum computing and communication protocols. [13] They are also used in quantum sensing and metrology to measure small changes in the properties of materials or systems, and can be used to improve the accuracy and sensitivity of quantum sensors. [14] A PDH frequency stabilization scheme was applied to the proposed miniaturized ECDL.…”

Cavity-enhanced two-photon source emitting narrow linewidth telecommunication wavelength photons for improved quantum memory-coupling efficiency enabling long-distance quantum communications

“…To generate a narrow linewidth entangled photon pair, spontaneous parametric down conversion (SPDC) inside a cavity can be utilized. [9][10][11][12][13] Recently, quantum-entangled photon pairs with linewidths of less than a few megahertz have been successfully generated by nearly-degenerate SPDC at telecommunication wavelengths. 13) In contrast, nearlydegenerate photon pairs exhibit a wide cluster width (?100 GHz).…”