Fighting Decoherence by Feedback-controlled Dissipation

Abstract

Repeated closed-loop control operations acting as piecewise-constant Liouville superoperators conditioned on the outcomes of regularly performed measurements may effectively be described by a fixed-point iteration for the density matrix. Even when all Liouville superoperators point to the completely mixed state, feedback of the measurement result may lead to a pure state, which can be interpreted as selective dampening of undesired states. Using a microscopic model, we exemplify this for a single qubit, which can be purified in an arbitrary single-qubit state by tuning the measurement direction and two qubits that may be purified towards a Bell state by applying a special continuous two-local measurement. The method does not require precise knowledge of decoherence channels and works for large reservoir temperatures provided measurement, processing, and control can be implemented in a continuous fashion.

to appear in PRA

References in corpus (4)

• Quantum States and Phases in Driven Open Quantum Systems with Cold Atoms
• Preservation of Positivity by Dynamical Coarse-Graining
• Systematic Perturbation Theory for Dynamical Coarse-Graining
• Charge Qubit Purification by an Electronic Feedback Loop

Cited by in corpus (2)

• Reverse quantum state engineering using electronic feedback loops
• Feedback-charging a metallic island