High-visibility single-shot readout for superconducting qubits in cavities
by
Patrice Bertet(CEA)
→
Europe/Stockholm
FR32
FR32
Description
The biggest challenge for quantum information processing with superconducting circuits is to obtain qubits with long coherence times and a high fidelity readout. Major progress in the control of coherence has recently been achieved with a new circuit design where a transmon qubit is measured by a coplanar waveguide resonator (CPWR), yielding reproducibly long coherence times thanks to the transmon insensitivity to major decoherence sources in superconducting qubits and to the well-controlled electromagnetic environment provided by the CPWR. However, a high-fidelity single-shot readout of the transmon quantum state is still lacking. Indeed, the readout method based on the qubit-state-dependent phase shift of a microwave pulse transmitted through (or reflected by) the resonator, lacks the required signal-to-noise to discriminate the two qubit states in a time shorter than the qubit relaxation time. To overcome this limitation we use instead a sample-and-hold detector that allows fast measurement and single-shot discrimination. This detector is a Josephson Bifurcation Amplifier (JBA), capacitively coupled to the qubit. We report Rabi oscillations with high visibility (94%) together with long coherence times. By performing two successive measurements, we also demonstrate that the readout process does not induce extra qubit relaxation.
