Quarter-wave Resonator Based Tunable Coupler for Xmon Qubits

TL;DR

This paper introduces a tunable coupler for Xmon qubits using a quarter-wave resonator with an asymmetric dc-SQUID, enabling effective qubit coupling control and reduced crosstalk for scalable quantum circuits.

Contribution

It presents a novel design of a tunable coupler based on a quarter-wave resonator with an asymmetric dc-SQUID, improving scalability and reducing noise in quantum circuits.

Findings

Coupler frequency can be effectively tuned via flux bias.

Asymmetry in dc-SQUID reduces coupling to cavity modes.

Design suppresses ZZ crosstalk and minimizes flux noise.

Abstract

We propose a scheme of tunable coupler based on quarter-wave resonator for scalable quantum integrated circuits. The open end of the T-type resonator is capacitively coupled to two Xmon qubits, while another end is an asymmetric dc-SQUID which dominates the inductive energy of coupler resonator. The dc-Current applied through the flux bias line could change the magnetic flux inside the dc-SQUID, so the frequency of coupler resonator can be effectively tuned and the qubit-qubit coupling can be totally switched off. As the increase of junction asymmetry for the dc-SQUID, the coupling of SQUID's effective phase difference and cavity modes become smaller at required working frequency regime of coupler resonator, and this could reduce the descent of the resonator's quality factor. The separation between two cross-capacitor can be larger with help of transverses width of the T-shape resonator, and then the ZZ crosstalk coupling can be effectively suppressed. The asymmetric dc-SQUID is about 5 millimeters away from the Xmon qubits and only needs a small current on the flux bias line, which in principle creates less flux noises to superconducting Xmon qubits.