State tomography of capacitively shunted phase qubits with high fidelity

TL;DR

This paper presents a new superconducting qubit design that reduces decoherence sources and achieves high-fidelity quantum state tomography with single-shot measurements.

Contribution

The authors introduce a novel qubit architecture separating the capacitor from the Josephson junction, significantly reducing TLS coupling and enabling high-fidelity, single-shot quantum state tomography.

Findings

Reduced TLS coupling by an order of magnitude.

Achieved measurement fidelity of 90%.

First demonstration of quantum state tomography with superconducting qubits.

Abstract

We introduce a new design concept for superconducting quantum bits (qubits) in which we explicitly separate the capacitive element from the Josephson tunnel junction for improved qubit performance. The number of two-level systems (TLS) that couple to the qubit is thereby reduced by an order of magnitude and the measurement fidelity improves to 90%. This improved design enables the first demonstration of quantum state tomography with superconducting qubits using single shot measurements.