Quantum Communication with Microwave Photons

Sharing information coherently between physically separated chips in a netwrok of quantum computers could be an essential element for realizing a viable quantum information processing system. A direct, deterministic quantum channel may be advantageous both for larger scale fault-tolerant or non-error-corrected quantum processors realizing universal quantum computation or solving noisy intermediate-scale quantum (NISQ) problems. We implement a deterministic state transfer and entanglement protocol between individually packaged chips connected by coaxial lines [1]. Individual chips may serve as universal nodes capable of sending, receiving, storing, and processing quantum information. Our protocol is based on an all-microwave process, which entangles or transfers the state of a superconducting qubit with a time-symmetric itinerant single photon. We transfer qubit states at rates of 50 kHz, absorb photons at the receiving node with a probability of 98 %, achieve a transfer process fidelity of 80 %, prepare on demand remote entanglement with a fidelity of 79 % and show that time bin encoding can be used to further improve these metrics.

[1] P. Kurpiers et al., Nature 558, 264-267 (2018)