Control-free control: manipulating a quantum system using only a limited set of measurements

TL;DR

This paper explores how to prepare any quantum state of a qubit solely through specific measurements without using unitary operations, highlighting the role of measurement back-action in quantum control.

Contribution

It introduces protocols for quantum state preparation using limited measurements, emphasizing measurement back-action as a control resource without unitary operations.

Findings

Arbitrary qubit states can be prepared with certain measurement sets.

Measurement back-action can be exploited for quantum control.

Protocols do not require unitary operations for state preparation.

Abstract

We present and discuss different protocols for preparing an arbitrary quantum state of a qubit using only a restricted set of measurements, with no unitary operations at all. We show that an arbitrary state can indeed be prepared, provided that the available measurements satisfy certain requirements. Our results shed light on the role that measurement-induced back-action plays in quantum feedback control and the extent to which this back-action can be exploited in quantum-control protocols.