High-efficiency inter-chip links between superconducting qubits through a detachable quantum bus*

Modular architectures are a promising approach for scaling superconducting quantum processors, due to their potential to avoid crosstalk and to scale beyond a single wafer.  One approach for a modular device is to connect modules with a superconducting cable used as a ‘quantum bus’ [1-5], with recent work showing inter-chip gates of up to 99% fidelity [6].  From an engineering perspective, it would be highly desirable to achieve high performance with ‘plug & play’ connections that can be reconfigured at will.  Here, we present a modular hardware scheme for performing gates between superconducting transmon qubits on separated chips through a detachable quantum bus, realized with a superconducting cable.  By inducing a Raman process using parametric drives, we have realized excitation swaps between qubits in around 100 ns and with an estimated efficiency of about 95%.  The quality factor of the cable connection was about 30,000, using NbTi cables.  We also show that for an Al cable connection, quality factors exceeding 200,000 can be realized, bringing sub-percent errors within reach.  This would allow the construction of a reconfigurable network as a means to scale a modular, multi-wafer superconducting quantum computer.

 

[1]. N. Leung et al., Npj Quantum Information 5, no. 1 (February 15, 2019): 1–5.

[2]. Youpeng Zhong et al., Nature 590, no. 7847 (February 2021): 571–75.

[3]. Luke D. Burkhart et al., PRX Quantum 2, no. 3 (August 5, 2021): 030321.

[4]. Yan, H. et al. Phys. Rev. Lett. 128, 080504 (2022).

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

[6]. Niu, J. et al.,  Nat Electron 6, 235–241 (2023)