125 research outputs found
Optimal waveform estimation for classical and quantum systems via time-symmetric smoothing. II. Applications to atomic magnetometry and Hardy's paradox
The quantum smoothing theory [Tsang, Phys. Rev. Lett. 102, 250403 (2009);
Phys. Rev. A, in press (e-print arXiv:0906.4133)] is extended to account for
discrete jumps in the classical random process to be estimated, discrete
variables in the quantum system, such as spin, angular momentum, and photon
number, and Poissonian measurements, such as photon counting. The extended
theory is used to model atomic magnetometers and study Hardy's paradox in phase
space. In the phase-space picture of Hardy's proposed experiment, the
negativity of the predictive Wigner distribution is identified as the culprit
of the disagreement between classical reasoning and quantum mechanics.Comment: 11 pages, 3 figure
Quantum metrology with open dynamical systems
This paper studies quantum limits to dynamical sensors in the presence of
decoherence. A modified purification approach is used to obtain tighter quantum
detection and estimation error bounds for optical phase sensing and
optomechanical force sensing. When optical loss is present, these bounds are
found to obey shot-noise scalings for arbitrary quantum states of light under
certain realistic conditions, thus ruling out the possibility of asymptotic
Heisenberg error scalings with respect to the average photon flux under those
conditions. The proposed bounds are expected to be approachable using current
quantum optics technology.Comment: v1: submitted to ISIT 2013, v2: updated with new results on detection
bounds, v3: minor update, submitted, v4: accepted by New J. Phy
Testing quantum mechanics: a statistical approach
As experiments continue to push the quantum-classical boundary using
increasingly complex dynamical systems, the interpretation of experimental data
becomes more and more challenging: when the observations are noisy, indirect,
and limited, how can we be sure that we are observing quantum behavior? This
tutorial highlights some of the difficulties in such experimental tests of
quantum mechanics, using optomechanics as the central example, and discusses
how the issues can be resolved using techniques from statistics and insights
from quantum information theory.Comment: v1: 2 pages; v2: invited tutorial for Quantum Measurements and
Quantum Metrology, substantial expansion of v1, 19 pages; v3: accepted; v4:
corrected some errors, publishe
Quantum Imaging beyond the Diffraction Limit by Optical Centroid Measurements
I propose a quantum imaging method that can beat the Rayleigh-Abbe
diffraction limit and achieve de Broglie resolution without requiring a
multiphoton absorber as the detector. Using the same non-classical states of
light as those for quantum lithography, the proposed method requires only
intensity measurements, followed by image post-processing, to produce the same
complex image patterns as those in quantum lithography. The method is expected
to be experimentally realizable using current technology.Comment: 4 pages, 2 figures; v2: accepted by PRL, see also the accompanying
Viewpoint commentary by Anisimov and Dowling [Physics 2, 52 (2009),
http://physics.aps.org/articles/v2/52
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