Kavli Affiliate: Birgitta Whaley
| First 5 Authors: Sacha Greenfield, Leigh Martin, Felix Motzoi, K. Birgitta Whaley, Justin Dressel
| Summary:
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 that such a drive can
be simultaneous with the measurement and feedback, while also playing a key
part in 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, dephasing from $1/f$-distributed
qubit-frequency noise, and relaxation. 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. More generally, the
steady state is globally attractive without the need for ancillas, regardless
of the error state, in contrast to most known feedback and error correction
schemes.
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