Undoing a weak quantum measurement of a solid-state qubit

TL;DR

This paper proposes an experiment to reverse a weak measurement on a solid-state qubit, restoring its initial state with a success probability that depends on measurement strength, illustrating a form of quantum erasure.

Contribution

It introduces a feasible method to undo weak quantum measurements in solid-state qubits, demonstrating the concept experimentally and analyzing success probabilities.

Findings

Success probability decreases with measurement strength.

Full state restoration is possible for weak measurements.

The process acts as a quantum eraser.

Abstract

We propose an experiment which demonstrates the undoing of a weak continuous measurement of a solid-state qubit, so that any unknown initial state is fully restored. The undoing procedure has only a finite probability of success because of the non-unitary nature of quantum measurement, though it is accompanied by a clear experimental indication of whether or not the undoing has been successful. The probability of success decreases with increasing strength of the measurement, reaching zero for a traditional projective measurement. Measurement undoing (``quantum un-demolition'') may be interpreted as a kind of a quantum eraser, in which the information obtained from the first measurement is erased by the second measurement, which is an essential part of the undoing procedure. The experiment can be realized using quantum dot (charge) or superconducting (phase) qubits.