Stabilizing two-qubit entanglement with dynamically decoupled active feedback

• DOI: 10.1103/physrevapplied.21.024022
• Publication Date: 2024-02-12T15:02:03Z
• Authors: Sacha Greenfield; Leigh Martin; Felix Motzoi; K. Birgitta Whaley; Justin Dressel; Eli M. Levenson-Falk
• Keywords: Dephasing; Decoupling (probability); Feedback loop; Feedback Control

We propose and analyze a protocol for stabilizing maximally entangled state of two noninteracting qubits using active state-dependent feedback from continuous two-qubit half-parity measurement in coordination with concurrent, noncommuting dynamical decoupling drive. demonstrate that such drive can be simultaneous the feedback, while also playing key part itself. show robust stabilization near-unit fidelity achieved even presence realistic nonidealities, as time delay loop, imperfect state-tracking, inefficient measurements, dephasing $1/f$-distributed qubit-frequency noise, relaxation. mitigate feedback-delay error by introducing forward-state-estimation strategy controller tracks effects control signals already transit. More generally, steady is globally attractive without need ancillas, regardless state, contrast to most known error-correction schemes.