Hybrid Predictive Quantum Feedback: Extending Qubit Lifetimes Beyond the Wiseman-Milburn Limit

TL;DR

This paper introduces a hybrid quantum feedback method combining an ancilla qubit and a predictive algorithm to extend qubit lifetimes beyond traditional limits, demonstrating significant improvements through simulations.

Contribution

The authors develop a modular hybrid feedback scheme with ancilla-assisted quantum coherence and predictive control, surpassing the Wiseman-Milburn limit in qubit lifetime extension.

Findings

Numerical simulations show 3-4 times longer T1 times compared to W--M limit.

The hybrid method improves population retention and energy stability.

The approach is compatible with existing hardware and can be integrated into current feedback loops.

Abstract

Amplitude damping fundamentally limits qubit lifetimes by irreversibly leaking energy and information into the environment. Standard Wiseman--Milburn feedback offers only modest improvement because it acts on a single measured quadrature and its corrective drive is degraded by loop delay. We introduce a compact hybrid upgrade with two components: (i) a coherently coupled \emph{ancilla} qubit that receives the homodyne current and feeds back \emph{quantum-coherently} on the system, recovering information from \emph{both} field quadratures and intentionally engineered to decay much faster than the system; and (ii) a lightweight supervised predictor that forecasts the near-future homodyne current, phase-aligning the correction to overcome hardware latency. A Lindblad treatment yields closed-form effective decay rates: the ancilla suppresses the emission channel by a cooperativity factor, while the predictor further suppresses the residual decay in proportion to forecast quality. Using IBM-scale parameters (baseline \(T_1 = 50~\mu\mathrm{s}\)), numerical simulations surpass the W--M limit, achieving \(\sim 3\!-\!4\times\) longer \(T_1\) together with improved population retention and integrated energy. The method is modular and hardware-compatible: ancilla coupling and supervised prediction can be added to existing W--M loops to convert leaked information into a precise, time-advanced corrective drive. We also include a detailed, student-friendly derivation of the effective rates for both ancilla-assisted and prediction-enhanced feedback, making the impact of each design element analytically transparent.