Rapid Ballistic Readout for Flux Qubits

TL;DR

This paper introduces a novel magnetic flux detector based on ballistic fluxon motion in a Josephson transmission line, optimized for quantum measurements with potential for advanced quantum control.

Contribution

It proposes a new flux detection method using ballistic fluxons in a Josephson transmission line, with detailed analysis of detector characteristics and quantum measurement capabilities.

Findings

Calculated detector characteristics of the Josephson transmission line.

Derived equations for conditional evolution of the measured system.

Showed potential for implementing quantum measurement strategies with fluxon control.

Abstract

We suggest a new type of the magnetic flux detector which can be optimized with respect to the measurement back-action, e.g. for the situation of quantum measurements. The detector is based on manipulation of ballistic motion of individual fluxons in a Josephson transmission line (JTL), with the output information contained in either probabilities of fluxon transmission/reflection, or time delay associated with the fluxon propagation through the JTL. We calculate the detector characteristics of the JTL and derive equations for conditional evolution of the measured system both in the transmission/reflection and the time-delay regimes. Combination of the quantum-limited detection with control over individual fluxons should make the JTL detector suitable for implementation of non-trivial quantum measurement strategies, including conditional measurements and feedback control schemes.