Abstract
Reducing the time necessary for experimental measurements allows more data to be obtained, which in turn leads to a more sensitive result. A roughly twofold speedup in differentiating between two charge states of a point defect in diamond is demonstrated, which could substantially facilitate the detection of small magnetic fields.
Highlights
Efficient discrimination of quantum states is important for, e.g., fast qubit readout [1,2,3,4], rapid feedback and steering [5,6,7], preparation of nonclassical states of light [5,8,9,10], and nanoscale magnetometry [11,12]
We show that for two common readout schemes, the speedup is bounded by 4 and 2, respectively, in the limit of high single-shot readout fidelity
Given sufficient information about the statistics and dynamics of a physical readout apparatus, it is possible to speed up a readout through a real-time adaptive decision rule [1,2,3,4,5,6,10]
Summary
Efficient discrimination of quantum states is important for, e.g., fast qubit readout [1,2,3,4], rapid feedback and steering [5,6,7], preparation of nonclassical states of light [5,8,9,10], and nanoscale magnetometry [11,12]. Implementing an adaptive decision rule requires the ability to update a stochastically varying measure of confidence in the state, typically a likelihood function, in real time. We formulate the adaptive decision for a two-state readout in terms of a first-passage time problem We use this formalism to theoretically establish the maximum achievable speedups for several physical readout models. To experimentally study the achievable speedup, we implement an adaptive decision rule for a readout that discriminates between two charge states of a single NV center in diamond [12,20]. We propose a simple readout, based on the discrimination of two distinct decay channels, for which the speedup becomes unbounded as the fidelity is increased Such a readout could be realized in either atomic or quantum-dot systems.
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