249 research outputs found
Polarization state of a biphoton: quantum ternary logic
Polarization state of biphoton light generated via collinear
frequency-degenerate spontaneous parametric down-conversion is considered. A
biphoton is described by a three-component polarization vector, its arbitrary
transformations relating to the SU(3) group. A subset of such transformations,
available with retardation plates, is realized experimentally. In particular,
two independent orthogonally polarized beams of type-I biphotons are
transformed into a beam of type-II biphotons. Polarized biphotons are suggested
as ternary analogs of two-state quantum systems (qubits)
Energy Localization in the Peyrard-Bishop DNA model
We study energy localization on the oscillator-chain proposed by Peyrard and
Bishop to model the DNA. We search numerically for conditions with initial
energy in a small subgroup of consecutive oscillators of a finite chain and
such that the oscillation amplitude is small outside this subgroup for a long
timescale. We use a localization criterion based on the information entropy and
we verify numerically that such localized excitations exist when the nonlinear
dynamics of the subgroup oscillates with a frequency inside the reactive band
of the linear chain. We predict a mimium value for the Morse parameter (the only parameter of our normalized model), in agreement with the
numerical calculations (an estimate for the biological value is ).
For supercritical masses, we use canonical perturbation theory to expand the
frequencies of the subgroup and we calculate an energy threshold in agreement
with the numerical calculations
Limit quantum efficiency for violation of Clauser-Horne Inequality for qutrits
In this paper we present the results of numerical calculations about the
minimal value of detection efficiency for violating the Clauser - Horne
inequality for qutrits. Our results show how the use of non-maximally entangled
states largely improves this limit respect to maximally entangled ones. A
stronger resistance to noise is also found.Comment: Phys. Rev. A in pres
Measurement of qutrits
We proposed the procedure of measuring the unknown state of the three-level
system - the qutrit, which was realized as the arbitrary polarization state of
the single-mode biphoton field. This procedure is accomplished for the set of
the pure states of qutrits; this set is defined by the properties of SU(2)
transformations, that are done by the polarization transformers.Comment: 9 pages, 9 figure
Qutrit state engineering with biphotons
The novel experimental realization of three-level optical quantum systems is
presented. We use the polarization state of biphotons to generate a specific
sequence of states that are used in the extended version of BB84 protocol. We
experimentally verify the orthogonality of the basis states and demonstrate the
ability to easily switch between them. The tomography procedure is employed to
reconstruct the density matrices of generated states.Comment: 5 pages, 4 figures. typos correcte
Multiple Current States of Two Phase-Coupled Superconducting Rings
The states of two phase-coupled superconducting rings have been investigated.
Multiple current states have been revealed in the dependence of the critical
current on the magnetic field. The performed calculations of the critical
currents and energy states in a magnetic field have made it possible to
interpret the experiment as the measurement of energy states into which the
system comes with different probabilities because of the equilibrium and
non-equilibrium noises upon the transition from the resistive state to the
superconducting state during the measurement of the critical currentComment: 5 pages, 5 figure
Comment on ``Dispersion-Independent High-Visibility Quantum Interference ... "
We show in this Comment that the interpretation of experimental data as well
as the theory presented in Atat\"ure et al. [Phys. Rev. Lett. 84, 618 (2000)]
are incorrect and discuss why such a scheme cannot be used to "recover"
high-visibility quantum interference.Comment: Comment on Atat\"ure et al. [Phys. Rev. Lett. 84, 618 (2000)], 2nd
revision, To appear in Phys. Rev. Lett. April, (2001
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