|
| related topics |
| {time, wave, function} |
| {state, states, coherent} |
| {measurement, state, measurements} |
| {phase, path, phys} |
| {photon, photons, single} |
| {light, field, probe} |
| {cos, sin, state} |
| {temperature, thermal, energy} |
| {cavity, atom, atoms} |
| {state, algorithm, problem} |
|
Adaptive Quantum Measurements of a Continuously Varying Phase
D. W. Berry, H. M. Wiseman
abstract: We analyze the problem of quantum-limited estimation of a stochastically
varying phase of a continuous beam (rather than a pulse) of the electromagnetic
field. We consider both non-adaptive and adaptive measurements, and both dyne
detection (using a local oscillator) and interferometric detection. We take the
phase variation to be \dot\phi = \sqrt{\kappa}\xi(t), where \xi(t) is
\delta-correlated Gaussian noise. For a beam of power P, the important
dimensionless parameter is N=P/\hbar\omega\kappa, the number of photons per
coherence time. For the case of dyne detection, both continuous-wave (cw)
coherent beams and cw (broadband) squeezed beams are considered. For a coherent
beam a simple feedback scheme gives good results, with a phase variance \simeq
N^{-1/2}/2. This is \sqrt{2} times smaller than that achievable by nonadaptive
(heterodyne) detection. For a squeezed beam a more accurate feedback scheme
gives a variance scaling as N^{-2/3}, compared to N^{-1/2} for heterodyne
detection. For the case of interferometry only a coherent input into one port
is considered. The locally optimal feedback scheme is identified, and it is
shown to give a variance scaling as N^{-1/2}. It offers a significant
improvement over nonadaptive interferometry only for N of order unity.
- oai_identifier:
- oai:arXiv.org:quant-ph/0111013
- categories:
- quant-ph
- comments:
- 11 pages, 6 figures, journal version
- doi:
- 10.1103/PhysRevA.65.043803
- arxiv_id:
- quant-ph/0111013
- journal_ref:
- Phys. Rev. A 65, 043803 (2002)
- created:
- 2001-11-01
- updated:
- 2002-09-19
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