Single-shot qubit readout in circuit Quantum Electrodynamics

TL;DR

This paper demonstrates a new transmon qubit readout method using a Josephson Bifurcation Amplifier in circuit QED, enabling fast, high-fidelity single-shot measurements without extra qubit relaxation.

Contribution

The work introduces a novel readout technique for transmon qubits using a Josephson Bifurcation Amplifier, achieving high-fidelity single-shot discrimination.

Findings

Achieved Rabi oscillations with 94% visibility

Demonstrated dephasing and relaxation times >0.5 μs

Readout does not induce additional qubit relaxation

Abstract

The future development of quantum information using superconducting circuits requires Josephson qubits [1] with long coherence times combined to a high-fidelity readout. Major progress in the control of coherence has recently been achieved using circuit quantum electrodynamics (cQED) architectures [2, 3], where the qubit is embedded in a coplanar waveguide resonator (CPWR) which both provides a well controlled electromagnetic environment and serves as qubit readout. In particular a new qubit design, the transmon, yields reproducibly long coherence times [4, 5]. However, a high-fidelity single-shot readout of the transmon, highly desirable for running simple quantum algorithms or measur- ing quantum correlations in multi-qubit experiments, is still lacking. In this work, we demonstrate a new transmon circuit where the CPWR is turned into a sample-and-hold detector, namely a Josephson Bifurcation Amplifer (JBA) [6, 7], which allows both fast measurement and single-shot discrimination of the qubit states. We report Rabi oscillations with a high visibility of 94% together with dephasing and relaxation times longer than 0:5 \mu\s. By performing two subsequent measurements, we also demonstrate that this new readout does not induce extra qubit relaxation.