Parasitic RF-SQUIDs in superconducting qubits due to wirebonds

TL;DR

This paper uncovers how wirebonds in superconducting qubits can host parasitic Josephson junctions, forming RF-SQUIDs that interfere with qubit operation and contribute to decoherence, revealing a previously unknown decoherence source.

Contribution

It demonstrates that wirebonds can contain parasitic Josephson junctions forming RF-SQUIDs, which interfere with qubits, a novel insight into decoherence mechanisms in superconducting circuits.

Findings

Parasitic RF-SQUIDs are formed in wirebonds used in superconducting qubits.

These RF-SQUIDs strongly couple to qubits and resonators, affecting their coherence.

Magnetic field sweeps reveal periodic signatures indicating interference effects.

Abstract

Superconducting qubits show great promise to realize practical quantum computers from micro-fabricated integrated circuits. However, their solid-state architecture bears the burden of parasitic modes in qubit materials and the control circuitry which cause decoherence and interfere with qubits. Here, we present evidence that wirebonds, which are used to contact the micro-circuits and to realize chip-to-chip airbridges, may contain parasitic Josephson junctions. In our experiment, such a junction was enclosed in a superconducting loop and so gave rise to the formation an RF-SQUID which interfered with a nearby flux-tunable transmon qubit. Periodic signatures observed in magnetic field sweeps revealed a strong AC-dispersive coupling of the parasitic RF-SQUID to both the qubit and its readout resonator, in addition to the DC-inductive coupling between RF-SQUID and qubit. Our finding sheds light on a previously unknown origin of decoherence due to parasitic Josephson junctions in superconducing circuits.