280 research outputs found
Enhancing qubit readout through dissipative sub-Poissonian dynamics
Single-shot qubit readout typically combines high readout contrast with
long-lived readout signals, leading to large signal-to-noise ratios and high
readout fidelities. In recent years, it has been demonstrated that both readout
contrast and readout signal lifetime, and thus the signal-to-noise ratio, can
be enhanced by forcing the qubit state to transition through intermediate
states. In this work, we demonstrate that the sub-Poissonian relaxation
statistics introduced by intermediate states can reduce the single-shot readout
error rate by orders of magnitude even when there is no increase in
signal-to-noise ratio. These results hold for moderate values of the
signal-to-noise ratio () and a small number of
intermediate states (). The ideas presented here could have
important implications for readout schemes relying on the detection of
transient charge states, such as spin-to-charge conversion schemes for
semiconductor spin qubits and parity-to-charge conversion schemes for
topologically protected Majorana qubits.Comment: 10 pages, 6 figures. Two appendices have been added. This version is
close to the final published versio
Efficient synchronization of structurally adaptive coupled Hindmarsh-Rose neurons
The use of spikes to carry information between brain areas implies complete
or partial synchronization of the neurons involved. The degree of
synchronization reached by two coupled systems and the energy cost of
maintaining their synchronized behaviour is highly dependent on the nature of
the systems. For non-identical systems the maintenance of a synchronized regime
is energetically a costly process. In this work, we study conditions under
which two non-identical electrically coupled neurons can reach an efficient
regime of synchronization at low energy cost. We show that the energy
consumption required to keep the synchronized regime can be spontaneously
reduced if the receiving neuron has adaptive mechanisms able to bring its
biological parameters closer in value to the corresponding ones in the sending
neuron
Maximal adaptive-decision speedups in quantum-state readout
The average time 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 . The
performance of the adaptive decision is characterized by the "adaptive-decision
speedup," . 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 and , 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 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.Comment: 18 pages, 11 figures. This version is close to the published versio
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