1,696 research outputs found
Adaptive tracking of a time-varying field with a quantum sensor
Sensors based on single spins can enable magnetic field detection with very
high sensitivity and spatial resolution. Previous work has concentrated on
sensing of a constant magnetic field or a periodic signal. Here, we instead
investigate the problem of estimating a field with non-periodic variation
described by a Wiener process. We propose and study, by numerical simulations,
an adaptive tracking protocol based on Bayesian estimation. The tracking
protocol updates the probability distribution for the magnetic field, based on
measurement outcomes, and adapts the choice of sensing time and phase in real
time. By taking the statistical properties of the signal into account, our
protocol strongly reduces the required measurement time. This leads to a
reduction of the error in the estimation of a time-varying signal by up to a
factor 4 compared to protocols that do not take this information into account.Comment: 10 pages, 6 figure
Loss-resistant unambiguous phase measurement
Entangled multi-photon states have the potential to provide improved
measurement accuracy, but are sensitive to photon loss. It is possible to
calculate ideal loss-resistant states that maximize the Fisher information, but
it is unclear how these could be experimentally generated. Here we propose a
set of states that can be obtained by processing the output from parametric
down-conversion. Although these states are not optimal, they provide
performance very close to that of optimal states for a range of parameters.
Moreover, we show how to use sequences of such states in order to obtain an
unambiguous phase measurement that beats the standard quantum limit. We
consider the optimization of parameters in order to minimize the final phase
variance, and find that the optimum parameters are different from those that
maximize the Fisher information.Comment: 8 pages, 7 figures, comments are welcom
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