60 research outputs found
Quantum dynamics and statistics of two coupled down-conversion processes
In the framework of Heisenberg-Langevin theory the dynamical and statistical
effects arising from the linear interaction of two nondegenerate
down-conversion processes are investigated. Using the strong-pumping
approximation the analytical solution of equations of motion is calculated. The
phenomena reminiscent of Zeno and anti-Zeno effects are examined. The
possibility of phase-controlled and mismatch-controlled switching is
illustrated.Comment: 17 pages, 7 figure
Image processing as state reconstruction in optics
The image reconstruction of partially coherent light is interpreted as the
quantum state reconstruction. The efficient method based on maximum-likelihood
estimation is proposed to acquire information from registered intensity
measurements affected by noise. The connection with totally incoherent image
restoration is pointed out. The feasibility of the method is demonstrated
numerically. Spatial and correlation details significantly smaller than the
diffraction limit are revealed in the reconstructed pattern.Comment: 10 pages, 5 figure
Q fever in Bulgaria and Slovakia.
As a result of dramatic political and economic changes in the beginning of the 1990s, Q-fever epidemiology in Bulgaria has changed. The number of goats almost tripled; contact between goat owners (and their families) and goats, as well as goats and other animals, increased; consumption of raw goat milk and its products increased; and goats replaced cattle and sheep as the main source of human Coxiella burnetii infections. Hundreds of overt, serologically confirmed human cases of acute Q fever have occurred. Chronic forms of Q fever manifesting as endocarditis were also observed. In contrast, in Slovakia, Q fever does not pose a serious public health problem, and the chronic form of infection has not been found either in follow-ups of a Q-fever epidemic connected with goats imported from Bulgaria and other previous Q-fever outbreaks or in a serologic survey. Serologic diagnosis as well as control and prevention of Q fever are discussed
Nondiffracting beams for vortex tomography
We propose a reconstruction of vortex beams based on the implementation of
quadratic transformations in the orbital angular momentum. The information is
encoded in a superposition of Bessel-like nondiffracting beams. The measurement
of the angular probability distribution at different positions allows for the
reconstruction of the Wigner function.Comment: 3 pages. 2 eps figures. To appear in Optics Letter
Entanglement of coherent states and decoherence
A possibility to produce entangled superpositions of strong coherent states
is discussed. A recent proposal by Howell and Yazell [Phys. Rev. A 62, 012102
(2000)] of a device which entangles two strong coherent coherent states is
critically examined. A serious flaw in their design is found. New modified
scheme is proposed and it is shown that it really can generate non-classical
states that can violate Bell inequality. Moreover, a profound analysis of the
effect of losses and decoherence on the degree of entanglement is accomplished.
It reveals the high sensitivity of the device to any disturbances and the
fragility of generated states
Quantum channel of continuous variable teleportation and nonclassicality of quantum states
Noisy teleportation of nonclassical quantum states via a two-mode
squeezed-vacuum state is studied with the completely positive map and the
Glauber-Sudarshan -function. Using the nonclassical depth as a measure of
transmission performance, we compare the teleportation scheme with the direct
transmission through a noisy channel. The noise model is based on the coupling
to the vacuum field. It is shown that the teleportation channel has better
transmission performance than the direct transmission channel in a certain
region. The bounds for such region and for obtaining the nonvanished
nonclassicality of the teleported quantum states are also discussed. Our model
shows a reasonable agreement with the observed teleportation fidelity in the
experiment by Furusawa et al. [Science {\bf 282}, 706 (1998)]. We finally
mention the required conditions for transmitting nonclassical features in real
experiments.Comment: 16 pages, 4 figure
Photostatistics Reconstruction via Loop Detector Signatures
Photon-number resolving detectors are a fundamental building-block of optical
quantum information processing protocols. A loop detector, combined with
appropriate statistical processing, can be used to convert a binary on/off
photon counter into a photon-number-resolving detector. Here we describe the
idea of a signature of photon-counts, which may be used to more robustly
reconstruct the photon number distribution of a quantum state. The methodology
is applied experimentally in a 9-port loop detector operating at a
telecommunications wavelength and compared directly to the approach whereby
only the number of photon-counts is used to reconstruct the input distribution.
The signature approach is shown to be more robust against calibration errors,
exhibit reduced statistical uncertainty, and reduced reliance on a-priori
assumptions about the input state.Comment: 13 pages, 12 figure
Room temperature photon number resolving detector at telecom wavelengths
Large dynamic range room temperature photon number resolving (PNR) detectors
can be very useful for measuring very low light intensities and for analyzing
multiphoton quantum states. In this paper we present a PNR detector based on
the up-conversion (UC) of telecom signal into visible wavelength and on its
detection by a thermoelectrically cooled multi-pixel silicon avalanche
photodiodode (APD), also known as Silicon Photon Multiplier (SiPM). An
efficiency of 4% is attained and the poissonian statistics of input coherent
states is maintained up to approximately 20 simultaneous detections. The
cross-talk effects on the detected signal are estimated in order to properly
calibrate the detector. This scheme can be used at arbitrary wavelengths above
the visible spectral window with appropriate up-conversion
Quantum theory of incompatible observations
Maximum likelihood principle is shown to be the best measure for relating the
experimental data with the predictions of quantum theory.Comment: 3 page
Decoherence, fluctuations and Wigner function in neutron optics
We analyze the coherence properties of neutron wave packets, after they have
interacted with a phase shifter undergoing different kinds of statistical
fluctuations. We give a quantitative (and operational) definition of
decoherence and compare it to the standard deviation of the distribution of the
phase shifts. We find that in some cases the neutron ensemble is more coherent,
even though it has interacted with a wider (i.e. more disordered) distribution
of shifts. This feature is independent of the particular definition of
decoherence: this is shown by proposing and discussing an alternative
definition, based on the Wigner function, that displays a similar behavior. We
briefly discuss the notion of entropy of the shifts and find that, in general,
it does not correspond to that of decoherence of the neutron.Comment: 18 pages, 7 figure
- …