Realization of a binary-outcome projection measurement of a three-level superconducting quantum system

TL;DR

This paper demonstrates a high-fidelity binary-outcome measurement method for a three-level superconducting quantum system, enabling non-demolition detection of leakage errors and exploration of quantum contextuality.

Contribution

It introduces a novel dispersive readout scheme with identical cavity frequency shifts for excited states, achieving 94.3% fidelity in projective measurements.

Findings

Achieved 94.3% fidelity in binary-outcome measurements.

Enabled quantum non-demolition detection of leakage errors.

Facilitated exploration of measurement contextuality in superconducting circuits.

Abstract

Binary-outcome measurements allow to determine whether a multi-level quantum system is in a certain state while preserving quantum coherence between all orthogonal states. In this paper, we explore different regimes of the dispersive readout of a three-level superconducting quantum system coupled to a microwave cavity in order to implement binary-outcome measurements. By designing identical cavity frequency shifts for the first and second excited states of the system, we realize strong projective binary-outcome measurements onto its ground state with a fidelity of $94.3\%$. Complemented with standard microwave control and low-noise parametric amplification, this scheme enables the quantum non-demolition detection of leakage errors and can be used to create sets of compatible measurements to reveal the contextual nature of superconducting circuits.