Suppressed crosstalk between two-junction superconducting qubits with mode-selective coupling.

Abstract

Fixed-frequency qubits can suffer from always-on interactions that inhibit independent control. While this problem can be alleviated with the use of flux-tunable buses, this introduces other challenges such as sensitivity to flux noise. Here, we describe a superconducting architecture using qubits that comprise of two capacitively-shunted Josephson junctions connected in series. Historically known as tunable coupling qubits, such two-junction qubits support two modes with distinct frequencies and different spatial symmetries. By selectively coupling only one type of modes and using the other as our qubit basis, we greatly suppress crosstalk between the data modes while permitting all-microwave two-qubit gates.