10,923 research outputs found
Digital Quantum Estimation
Quantum Metrology calculates the ultimate precision of all estimation
strategies, measuring what is their root mean-square error (RMSE) and their
Fisher information. Here, instead, we ask how many bits of the parameter we can
recover, namely we derive an information-theoretic quantum metrology. In this
setting we redefine "Heisenberg bound" and "standard quantum limit" (the usual
benchmarks in quantum estimation theory), and show that the former can be
attained only by sequential strategies or parallel strategies that employ
entanglement among probes, whereas parallel-separable strategies are limited by
the latter. We highlight the differences between this setting and the
RMSE-based one.Comment: 5 pages+5 supplementary informatio
Quantum metrology with nonclassical states of atomic ensembles
Quantum technologies exploit entanglement to revolutionize computing,
measurements, and communications. This has stimulated the research in different
areas of physics to engineer and manipulate fragile many-particle entangled
states. Progress has been particularly rapid for atoms. Thanks to the large and
tunable nonlinearities and the well developed techniques for trapping,
controlling and counting, many groundbreaking experiments have demonstrated the
generation of entangled states of trapped ions, cold and ultracold gases of
neutral atoms. Moreover, atoms can couple strongly to external forces and light
fields, which makes them ideal for ultra-precise sensing and time keeping. All
these factors call for generating non-classical atomic states designed for
phase estimation in atomic clocks and atom interferometers, exploiting
many-body entanglement to increase the sensitivity of precision measurements.
The goal of this article is to review and illustrate the theory and the
experiments with atomic ensembles that have demonstrated many-particle
entanglement and quantum-enhanced metrology.Comment: 76 pages, 40 figures, 1 table, 603 references. Some figures bitmapped
at 300 dpi to reduce file siz
Quantum Estimation of Parameters of Classical Spacetimes
We describe a quantum limit to measurement of classical spacetimes.
Specifically, we formulate a quantum Cramer-Rao lower bound for estimating the
single parameter in any one-parameter family of spacetime metrics. We employ
the locally covariant formulation of quantum field theory in curved spacetime,
which allows for a manifestly background-independent derivation. The result is
an uncertainty relation that applies to all globally hyperbolic spacetimes.
Among other examples, we apply our method to detection of gravitational waves
using the electromagnetic field as a probe, as in laser-interferometric
gravitational-wave detectors. Other applications are discussed, from
terrestrial gravimetry to cosmology.Comment: 23 pages. This article supersedes arXiv:1108.522
Quantum Heisenberg Chain with Long-Range Ferromagnetic Interactions at Low Temperature
A modified spin-wave theory is applied to the one-dimensional quantum
Heisenberg model with long-range ferromagnetic interactions. Low-temperature
properties of this model are investigated. The susceptibility and the specific
heat are calculated; the relation between their behaviors and strength of the
long-range interactions is obtained. This model includes both the
Haldane-Shastry model and the nearest-neighbor Heisenberg model; the
corresponding results in this paper are in agreement with the solutions of both
the models. It is shown that there exists an ordering transition in the region
where the model has longer-range interactions than the HS model. The critical
temperature is estimated.Comment: 17 pages(LaTeX REVTeX), 1 figure appended (PostScript), Technical
Report of ISSP A-274
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