Stabilizing two-qubit entanglement with dynamically decoupled active feedback


We propose and analyze a protocol for stabilizing a maximally entangled state of two noninteracting qubits using active state-dependent feedback from a continuous two-qubit half-parity measurement in coordination with a concurrent, non-commuting dynamical decoupling drive. We demonstrate the surprising result that such a drive be simultaneous with the measurement and feedback, and can also be part of the feedback protocol itself. We show that robust stabilization with near-unit fidelity can be achieved even in the presence of realistic nonidealities, such as time delay in the feedback loop, imperfect state-tracking, inefficient measurements, and dephasing from 1/f-distributed qubit-frequency noise. We mitigate feedback-delay error by introducing a forward-state-estimation strategy in the feedback controller that tracks the effects of control signals already in transit.

Justin Dressel
Justin Dressel
Associate Professor of Physics

Researches quantum information, computation, and foundations.