Andreev qubit readout from dynamic interference supercurrent

TL;DR

This paper proposes a novel, nondestructive method for reading out Andreev qubits using the supercurrent oscillations in a quantum-dot Josephson junction, reducing overhead and avoiding ancilla qubits.

Contribution

It introduces a new approach for Andreev qubit readout based on dynamic interference supercurrent, eliminating the need for ancilla and enabling near nondestructive measurements.

Findings

Supercurrent oscillations can probe Andreev qubits without ancilla.

The method predicts an AC Josephson effect without external voltage.

The approach reduces experimental complexity for quantum computing applications.

Abstract

Nondemolition protocols use ancilla qubits to identify the fragile quantum state of a qubit without destroying its encoded information, thus playing a crucial role in nondestructive quantum measurements particularly relevant for quantum error correction. However, the multitude of ancilla preparations, information transfers, and ancilla measurements in these protocols create an intrinsic overhead for information processing. Here we consider an Andreev qubit defined in a quantum-dot Josephson junction and show that the macroscopic time-dependent oscillatory supercurrent arising from the quantum interference of the many-body eigenstates, can be used to probe the qubit itself-arbitrarily close to the nondestructive limit-under currently available experimental capabilities. This readout of arbitrary superposition states of Andreev qubits avoids ancillae altogether and significantly reduces experimental overhead as no repetitive qubit reinitialization is needed. Our prediction of an AC-like Josephson effect without an applied external voltage, which enables the nondestructive qubit readout, is a unique macroscopic manifestation of the microscopic dynamics of the Andreev quantum state. Our findings should have an unprecedented impact on advancing research and applications involving Andreev dots, thus positioning them as promising qubit contenders for quantum processing and technologies.