Flux qubits in a planar circuit quantum electrodynamics architecture: quantum control and decoherence

TL;DR

This paper demonstrates superconducting flux qubits integrated into a circuit QED setup, achieving high-contrast readout and revealing intrinsic relaxation times and flux noise levels, advancing understanding of decoherence in quantum circuits.

Contribution

It presents experimental results on flux qubits in a planar cQED architecture, including coherence times, flux noise, and insights into decoherence mechanisms, highlighting the platform's potential for quantum studies.

Findings

Maximum dispersive readout contrast of 72%

Energy relaxation times of 7 μs and 20 μs at symmetry point

Flux noise levels around 2.6-2.7 μΦ₀/√Hz at 1 Hz

Abstract

We report experiments on superconducting flux qubits in a circuit quantum electrodynamics (cQED) setup. Two qubits, independently biased and controlled, are coupled to a coplanar waveguide resonator. Dispersive qubit state readout reaches a maximum contrast of $72\,\%$. We find intrinsic energy relaxation times at the symmetry point of $7\,\mu\text{s}$ and $20\,\mu\text{s}$ and levels of flux noise of $2.6\,\mu \Phi_0/\sqrt{\text{Hz}}$ and $2.7\,\mu \Phi_0/\sqrt{\text{Hz}}$ at 1 Hz for the two qubits. We discuss the origin of decoherence in the measured devices. These results demonstrate the potential of cQED as a platform for fundamental investigations of decoherence and quantum dynamics of flux qubits.