Japan Team Demonstrates World-Record 10-Channel Link for Networking Quantum Computers

A research group at the University of Osaka, led by Professor Yamamoto Takashi, has demonstrated a 10-channel multiplexed quantum photonic interface, a world record the team says is a key technology for optically connecting multiple quantum computers together. The work was done in collaboration with Japan's National Institute of Information and Communications Technology (NICT) and Hamamatsu Photonics K.K., and was published in the journal Optica.

Neutral-atom quantum computers, which use individual atoms as quantum bits or qubits, are expected to work with arrays of roughly 10,000 atoms, but a fault-tolerant universal quantum computer is expected to need more than 1 million qubits for error correction. One promising route to that scale is interconnecting multiple quantum processors by distributing entangled photons between them, which requires a multiplexed interface capable of linking many qubits in parallel. Previous approaches relied on parallel optical fibers and were limited to only a few channels, in part because of insufficient integration density and wide spacing between atoms.

The Osaka team built an optical system using an integrated waveguide array and demonstrated parallel photon delivery and detection from a neutral-atom array. Photons emitted from 10 atoms, spaced at micrometer-scale intervals, were coupled into 10 parallel channels of a 32-channel waveguide array, transmitted through optical fibers and detected in parallel using a multi-channel superconducting nanostrip photon detector system, built for the experiment by NICT and Hamamatsu Photonics. The experiment confirmed negligible crosstalk between channels and correlations between the atoms' quantum states and the polarization of the emitted photons, supporting the interface's potential for linking many atom-photon pairs at once. The approach is expected to be scalable to around 100 parallel channels.

"Through research and development spanning from neutral-atom arrays to superconducting nanostrip photon detector systems, we have achieved the first demonstration of a multiplexed optical interface," said Yamamoto. He said the team will next work to scale up the multiplexing and connect neutral-atom quantum computers, as part of Japan's JST Moonshot Research and Development Program, which targets a fault-tolerant universal quantum computer by 2050.