Quantum state transfer between fixed-frequency qubits using an itinerant microwave photon

Quantum communication between remote chips is vital in developing large-scale superconducting quantum computers. One approach to achieve this is to use itinerant microwave photons on a transmission line. Previous implementations [1-3] relied on tunable circuit elements such as a SQUID to compensate for mismatches of device parameters between the sender and receiver, introducing additional costs for scalability. In this work, we demonstrate quantum state transfer between fixed-frequency transmon qubits on separate chips without using any frequency-tunable circuit element. We leverage a frequency-tunable photon generation and absorption method using a qubit coupled to a broadband resonator under a parametric drive detuned within the resonator bandwidth [4] to enable microwave photon transfer without tuning of the circuit frequencies. Additionally, we optimize the resonator parameters for the photon emission and absorption to ensure robust performance against device parameter variations. We perform quantum process tomography to characterize the transfer process fidelity and discuss the error sources. Our approach eliminates the need for dedicated flux lines to adjust circuit frequencies, improving the hardware efficiency of quantum communication systems.

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

[2] J. Qiu et al., arXiv:2302.08756 (2023)

[3] J. Grebel et al., Phys. Rev. Lett. 132, 047001 (2024)

[4] T. Miyamura, 2024 APS March meeting, M53.00012 (2024).