286 research outputs found
Iterative maximum-likelihood reconstruction in quantum homodyne tomography
I propose an iterative expectation maximization algorithm for reconstructing
a quantum optical ensemble from a set of balanced homodyne measurements
performed on an optical state. The algorithm applies directly to the acquired
data, bypassing the intermediate step of calculating marginal distributions.
The advantages of the new method are made manifest by comparing it with the
traditional inverse Radon transformation technique
Maximum likelihood estimation of photon number distribution from homodyne statistics
We present a method for reconstructing the photon number distribution from
the homodyne statistics based on maximization of the likelihood function
derived from the exact statistical description of a homodyne experiment. This
method incorporates in a natural way the physical constraints on the
reconstructed quantities, and the compensation for the nonunit detection
efficiency.Comment: 3 pages REVTeX. Final version, to appear in Phys. Rev. A as a Brief
Repor
Experimental demonstration of entanglement-enhanced classical communication over a quantum channel with correlated noise
We present an experiment demonstrating entanglement-enhanced classical
communication capacity of a quantum channel with correlated noise. The channel
is modelled by a fiber optic link exhibiting random birefringence that
fluctuates on a time scale much longer than the temporal separation between
consecutive uses of the channel. In this setting, introducing entanglement
between two photons travelling down the fiber allows one to encode reliably up
to one bit of information into their joint polarization degree of freedom. When
no quantum correlations between two separate uses of the channel are allowed,
this capacity is reduced by a factor of more than three. We demonstrated this
effect using a fiber-coupled source of entagled photon pairs based on
spontaneous parametric down-conversion, and a linear-optics Bell state
measurement.Comment: 4 pages, 2 figures, REVTe
Subwavelength fractional Talbot effect in layered heterostructures of composite metamaterials
We demonstrate that under certain conditions, fractional Talbot revivals can
occur in heterostructures of composite metamaterials, such as multilayer
positive and negative index media, metallodielectric stacks, and
one-dimensional dielectric photonic crystals. Most importantly, without using
the paraxial approximation we obtain Talbot images for the feature sizes of
transverse patterns smaller than the illumination wavelength. A general
expression for the Talbot distance in such structures is derived, and the
conditions favorable for observing Talbot effects in layered heterostructures
is discussed.Comment: To be published in Phys. Rev.
The accuracy of a 2D and 3D dendritic tip scaling parameter in predicting the columnar to equiaxed transition (CET)
The dendrite tip kinetics model accuracy relies on the reliability of the stability constant used, which is usually experimentally determined for 3D situations and applied to 2D models. The paper reports authors` attempts to cure the situation by deriving 2D dendritic tip scaling parameter for aluminium-based alloy: Al-4wt%Cu. The obtained parameter is then incorporated into the KGT dendritic growth model in order to compare it with the original 3D KGT counterpart and to derive two-dimensional and three-dimensional versions of the modified Hunt’s analytical model for the columnar-to-equiaxed transition (CET). The conclusions drawn from the above analysis are further confirmed through numerical calculations of the two cases of Al-4wt%Cu metallic alloy solidification using the front tracking technique. Results, including the porous zone-under-cooled liquid front position, the calculated solutal under-cooling and a new predictor of the relative tendency to form an equiaxed zone, are shown, compared and discussed two numerical cases. The necessity to calculate sufficiently precise values of the tip scaling parameter in 2D and 3D is stressed
The Role of the Dendritic Growth Models Dimensionality in Predicting the Columnar to Equiaxed Transition (CET)
The dendrite tip kinetics model accuracy relies on the reliability of the stability constant used, which is usually experimentally determined for 3D situations and applied to 2D models. The paper reports authors` attempts to cure the situation by deriving 2D dendritic tip scaling parameter for aluminium-based alloy: Al-4wt%Cu. The obtained parameter is then incorporated into the KGT dendritic growth model in order to compare it with the original 3D KGT counterpart and to derive two-dimensional and three-dimensional versions of the modified Hunt’s analytical model for the columnar-to-equiaxed transition (CET). The conclusions drawn from the above analysis are further confirmed through numerical calculations of the two cases of Al-4wt%Cu metallic alloy solidification using the front tracking technique. Results, including the porous zone-under-cooled liquid front position, the calculated solutal under-cooling, the average temperature gradient at a front of the dendrite tip envelope and a new predictor of the relative tendency to form an equiaxed zone, are shown, compared and discussed for two numerical cases. The necessity to calculate sufficiently precise values of the tip scaling parameter in 2D and 3D is stressed
Exploiting entanglement in communication channels with correlated noise
We develop a model for a noisy communication channel in which the noise
affecting consecutive transmissions is correlated. This model is motivated by
fluctuating birefringence of fiber optic links. We analyze the role of
entanglement of the input states in optimizing the classical capacity of such a
channel. Assuming a general form of an ensemble for two consecutive
transmissions, we derive tight bounds on the classical channel capacity
depending on whether the input states used for communication are separable or
entangled across different temporal slots. This result demonstrates that by an
appropriate choice, the channel capacity may be notably enhanced by exploiting
entanglement.Comment: 9 pages, 5 figure
Quantum homodyne tomography with a priori constraints
I present a novel algorithm for reconstructing the Wigner function from
homodyne statistics. The proposed method, based on maximum-likelihood
estimation, is capable of compensating for detection losses in a numerically
stable way.Comment: 4 pages, REVTeX, 2 figure
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