The effect of spectator qubit on CR gate performance

Superconducting qubits have emerged to become a promising platform for quantum computing [1]. In a superconducting circuit, many qubits are coupled electronically to one another [2]. A cross-resonance (CR) gate is a particularly important two-qubit gate, which enables operation of CNOT in these superconducting circuits. In CR gate, two qubits, the so-called control and target, are coupled and the control qubit is driven at frequency of the target qubit [3,4]. In this process, the control and target qubits are open to other qubits on the chip, the so-called spectator qubits . We study the entropy flow from one spectator qubit to another spectator qubit via the control and target qubits.

[1] J. Clarke, F. Wilhelm, Superconducting quantum bits, Nature 453, 1031–1042 (2008)

[2] Xuexin Xu, M.H. Ansari, ZZ freedom in two qubit gates, Phys. Rev. Applied 15, 064074 (2021), arXiv:2009.00485

[3] Jaseung Ku, Xuexin Xu, Markus Brink, David C. McKay, Jared B. Hertzberg, Mohammad H. Ansari, B.L.T. Plourde, Suppression of Unwanted ZZ Interactions in a Hybrid Two-Qubit System, Phys. Rev. Lett. 125, 200504 (2020), arXiv:2003.02775

[4] Xuexin Xu, M. Ansari, Parasitic-Free Gate: An Error-Protected Cross-Resonance Switch in Weakly Tunable Architectures, Phys. Rev. Applied 19, 024057, arXiv:2212.05519