Ultrafast QND measurements based on diamond-shape artificial atom

TL;DR

This paper introduces a high-fidelity, ultrafast QND measurement scheme for a diamond-shaped artificial atom in circuit QED, leveraging a novel coupling design to achieve rapid, accurate quantum state readout.

Contribution

It presents a new diamond-shaped artificial atom design enabling fast, high-fidelity QND measurements without Purcell limitations in circuit QED.

Findings

Achieves QND measurement fidelity of 99.9%.

Measurement times are on the order of tens of nanoseconds.

Utilizes state-of-the-art Josephson parametric amplifiers.

Abstract

We propose a Quantum Non Demolition (QND) read-out scheme for a superconducting artificial atom coupled to a resonator in a circuit QED architecture, for which we estimate a very high measurement fidelity without Purcell effect limitations. The device consists of two transmons coupled by a large inductance, giving rise to a diamond-shape artificial atom with a logical qubit and an ancilla qubit interacting through a cross-Kerr like term. The ancilla is strongly coupled to a transmission line resonator. Depending on the qubit state, the ancilla is resonantly or dispersively coupled to the resonator, leading to a large contrast in the transmitted microwave signal amplitude. This original method can be implemented with state of the art Josephson parametric amplifier, leading to QND measurements in a few tens of nanoseconds with fidelity as large as 99.9 %.