High-resolution spectroscopy of single photons using a virtually imaged phased-array and a single-photon avalanche diode array for frequency-multiplexed quantum communications.

Quantum internet is emerging as a next-generation infrastructure that enables a range of applications. One of the major challenges in quantum communication is overcoming transmission loss and limited communication speed, especially over long distances. Frequency-multiplexed quantum repeaters have been proposed as a solution, utilizing multiple frequency modes in a single communication channel to enhance both speed and efficiency. A critical requirement for frequency-multiplexed quantum repeaters is high-resolution frequency-mode measurement. In our research, we investigate the use of a virtually imaged phased-array (VIPA) for high-resolution frequency separation, combined with a single-photon avalanche diode (SPAD) array for precise frequency-mode detection. VIPA can spatially separate closely spaced frequency modes, a key advantage in the context of quantum repeaters, where higher resolution is essential for managing multiple modes. This study demonstrates the proof of concept for the integration of VIPA and SPAD array, providing a pathway toward efficient, high-speed, frequency-multiplexed quantum communication, specifically tailored for long-distance quantum repeater networks.