On-demand quantum state transfer and entanglement between remote microwave cavity memories

Coupling isolated quantum systems through propagating photons is a central theme in quantum science ^1,2 , with the potential for groundbreaking applications such as distributed, fault-tolerant quantum computing ^3-5 . To date, photons have been used widely to realize high-fidelity remote entanglement ^6-12 and state transfer ^13-15 by compensating for inefficiency with conditioning, a fundamentally probabilistic strategy that places limits on the rate of communication. In contrast, here we experimentally realize a long-standing proposal for deterministic, direct quantum state transfer ¹⁶ . Using efficient, parametrically controlled emission and absorption of microwave photons, we show on-demand, high-fidelity state transfer and entanglement between two isolated superconducting cavity quantum memories. The transfer rate is faster than the rate of photon loss in either memory, an essential requirement for complex networks. By transferring states in a multiphoton encoding, we further show that the use of cavity memories and state-independent transfer creates the striking opportunity to deterministically mitigate transmission loss with quantum error correction. Our results establish a compelling approach for deterministic quantum communication across networks, and will enable modular scaling of superconducting quantum circuits.