10,257 research outputs found
Quantum filtering for multiple measurements driven by fields in single-photon states
In this paper, we derive the stochastic master equations for quantum systems
driven by a single-photon input state which is contaminated by quantum vacuum
noise. To improve estimation performance, quantum filters based on
multiple-channel measurements are designed. Two cases, namely diffusive plus
Poissonian measurements and two diffusive measurements, are considered.Comment: 8 pages, 6 figures, submitted for publication. Comments are welcome
Non-Markovian quantum trajectories for spectral detection
We present a formulation of non-Markovian quantum trajectories for open
systems from a measurement theory perspective. In our treatment there are three
distinct ways in which non-Markovian behavior can arise; a mode dependent
coupling between bath (reservoir) and system, a dispersive bath, and by
spectral detection of the output into the bath. In the first two cases the
non-Markovian behavior is intrinsic to the interaction, in the third case the
non-Markovian behavior arises from the method of detection. We focus in detail
on the trajectories which simulate real-time spectral detection of the light
emitted from a localized system. In this case, the non-Markovian behavior
arises from the uncertainty in the time of emission of particles that are later
detected. The results of computer simulations of the spectral detection of the
spontaneous emission from a strongly driven two-level atom are presented
Detecting itinerant single microwave photons
Single photon detectors are fundamental tools of investigation in quantum
optics and play a central role in measurement theory and quantum informatics.
Photodetectors based on different technologies exist at optical frequencies and
much effort is currently being spent on pushing their efficiencies to meet the
demands coming from the quantum computing and quantum communication proposals.
In the microwave regime however, a single photon detector has remained elusive
although several theoretical proposals have been put forth. In this article, we
review these recent proposals, especially focusing on non-destructive detectors
of propagating microwave photons. These detection schemes using superconducting
artificial atoms can reach detection efficiencies of 90\% with existing
technologies and are ripe for experimental investigations.Comment: 11 pages, 8 figure
Quantum nondemolition detection of a propagating microwave photon
The ability to nondestructively detect the presence of a single, traveling
photon has been a long-standing goal in optics, with applications in quantum
information and measurement. Realising such a detector is complicated by the
fact that photon-photon interactions are typically very weak. At microwave
frequencies, very strong effective photon-photon interactions in a waveguide
have recently been demonstrated. Here we show how this type of interaction can
be used to realize a quantum nondemolition measurement of a single propagating
microwave photon. The scheme we propose uses a chain of solid-state 3-level
systems (transmons), cascaded through circulators which suppress photon
backscattering. Our theoretical analysis shows that microwave-photon detection
with fidelity around 90% can be realized with existing technologies
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