Maximal adaptive-decision speedups in quantum-state readout

Abstract

The average time $T$ required for high-fidelity readout of quantum states can be significantly reduced via a real-time adaptive decision rule. An adaptive decision rule stops the readout as soon as a desired level of confidence has been achieved, as opposed to setting a fixed readout time $t_f$. The performance of the adaptive decision is characterized by the "adaptive-decision speedup," $t_f/T$. In this work, we reformulate this readout problem in terms of the first-passage time of a particle undergoing stochastic motion. This formalism allows us to theoretically establish the maximum achievable adaptive-decision speedups for several physical two-state readout implementations. We show that for two common readout schemes (the Gaussian latching readout and a readout relying on state-dependent decay), the speedup is bounded by $4$ and $2$, respectively, in the limit of high single-shot readout fidelity. We experimentally study the achievable speedup in a real-world scenario by applying the adaptive decision rule to a readout of the nitrogen-vacancy-center (NV-center) charge state. We find a speedup of $\approx 2$ with our experimental parameters. In addition, we propose a simple readout scheme for which the speedup can, in principle, be increased without bound as the fidelity is increased. Our results should lead to immediate improvements in nanoscale magnetometry based on spin-to-charge conversion of the NV-center spin, and provide a theoretical framework for further optimization of the bandwidth of quantum measurements.

18 pages, 11 figures. This version is close to the published version

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• Repetitive quantum non-demolition measurement and soft decoding of a silicon spin qubit
• Amplified Sensitivity of Nitrogen-Vacancy Spins in Nanodiamonds using All-Optical Charge Readout
• Robust readout of bosonic qubits in the dispersive coupling regime
• Robust and fast post-processing of single-shot spin qubit detection events with a neural network
• Enhancing qubit readout through dissipative sub-Poissonian dynamics
• Dark State Polarizing a Nuclear Spin in the Vicinity of a Nitrogen-Vacancy Center
• Generalized figure of merit for qubit readout
• The EPR Paradox Implies A Minimum Achievable Temperature
• Towards free-response paradigm: a theory on decision-making in spiking neural networks
• Time-adaptive phase estimation
• Spin-qubit readout analysis based on a hidden Markov model
• Real-Time Charge Initialization of Diamond Nitrogen-Vacancy Centers for Enhanced Spin Readout