Spurious microwave crosstalk in floating superconducting circuits

TL;DR

This paper identifies a previously overlooked spurious crosstalk channel in floating superconducting qubits caused by free modes, which can limit qubit performance, and offers insights for circuit design improvements.

Contribution

It reveals the origin of microwave crosstalk in floating transmon qubits due to free modes and analyzes how geometric layouts influence this effect.

Findings

Spurious crosstalk channel exists even without stray coupling.

Free modes supported by floating structure cause crosstalk.

Design strategies can mitigate this crosstalk.

Abstract

Crosstalk is a major concern in the implementation of large-scale quantum computation since it can degrade the performance of qubit addressing and cause gate errors. Finding the origin of crosstalk and separating contributions from different channels are essential prerequisites for figuring out crosstalk mitigation schemes. Here, by performing circuit analysis of two coupled floating transmon qubits, we demonstrate that, even if the stray coupling, e.g., between a qubit and the drive line of its nearby qubit, is absent, microwave crosstalk between qubits can still exist due to the presence of a spurious crosstalk channel. This channel arises from free modes, which are supported by the floating structure of transmon qubits, i.e., the two superconducting islands of each qubit with no galvanic connection to the ground. For various geometric layouts of floating transmon qubits, we give the contributions of microwave crosstalk from the spurious channel and show that this channel can become a performance-limiting factor in qubit addressing. This research could provide guidance for suppressing microwave crosstalk between floating superconducting qubits through the design of qubit circuits.