Uncollapsing of a quantum state in a superconducting phase qubit

TL;DR

This paper demonstrates the uncollapsing of a quantum state in a superconducting qubit through a sequence of partial measurements and rotations, achieving over 70% fidelity in state recovery.

Contribution

It introduces a method to probabilistically reverse partial measurements in superconducting qubits, advancing quantum control techniques.

Findings

State recovery fidelity exceeds 70% for partial-collapse strength below 0.6

The uncollapsing process effectively cancels the information extracted by the initial measurement

Quantum process tomography confirms the success of the uncollapsing procedure

Abstract

We demonstrate in a superconducting qubit the conditional recovery ("uncollapsing") of a quantum state after a partial-collapse measurement. A weak measurement extracts information and results in a non-unitary transformation of the qubit state. However, by adding a rotation and a second partial measurement with the same strength, we erase the extracted information, effectively canceling the effect of both measurements. The fidelity of the state recovery is measured using quantum process tomography and found to be above 70% for partial-collapse strength less than 0.6.