74 research outputs found
Generalized quantum measurements. Part I: Information properties of soft quantum measurements
A special class of soft quantum measurements as a physical model of the fuzzy
measurements widely used in physics is introduced and its information
properties are studied in detail.Comment: 25 pages, 3 figures, 25 ref
Coherent and compatible information: a basis to information analysis of quantum systems
Relevance of key quantum information measures for analysis of quantum systems
is discussed. It is argued that possible ways of measuring quantum information
are based on compatibility/incompatibility of the quantum states of a quantum
system, resulting in the coherent information and introduced here the
compatible information measures, respectively. A sketch of an information
optimization of a quantum experimental setup is proposed.Comment: 10 pages, 5 figures, submitted to the Procs of 17th Int'l Conf. on
Coherent and Nonlinear Optics (ICONO-2001), June 26-July 1, 2001, Minsk,
Belaru
Physical implementation of entangling quantum measurements
We clarify the microscopic structure of the entangling quantum measurement
superoperators and examine their possible physical realization in a simple
three-qubit model, which implements the entangling quantum measurement with an
arbitrary degree of entanglement.Comment: 6 pages, 2 fihure
Entangling quantum measurement and its properties
We study the mathematical structure of superoperators describing quantum
measurements, including the \emph{entangling measurement}--the generalization
of the standard quantum measurement that results in entanglement between the
measurable system and apparatus. It is shown that the coherent information can
be effectively used for the analysis of such entangling measurements whose
possible applications are discussed as well.Comment: 8 pages, 1 figure; accepted for publication in Phys. Rev.
Coherent information analysis of quantum channels in simple quantum systems
The coherent information concept is used to analyze a variety of simple
quantum systems. Coherent information was calculated for the information decay
in a two-level atom in the presence of an external resonant field, for the
information exchange between two coupled two-level atoms, and for the
information transfer from a two-level atom to another atom and to a photon
field. The coherent information is shown to be equal to zero for all
full-measurement procedures, but it completely retains its original value for
quantum duplication. Transmission of information from one open subsystem to
another one in the entire closed system is analyzed to learn quantum
information about the forbidden atomic transition via a dipole active
transition of the same atom. It is argued that coherent information can be used
effectively to quantify the information channels in physical systems where
quantum coherence plays an important role.Comment: 24 pages, 7 figs; Final versiob after minor changes, title changed;
to be published in Phys. Rev. A, September 200
Entanglement transfer between bipartite systems
The problem of a controlled transfer of an entanglement initially encoded
into two two-level atoms that are successively sent through two single-mode
cavities is investigated. The atoms and the cavity modes form a four qubit
system and we demonstrate under which conditions the initial entanglement
encoded into the atoms can be completely transferred to other pairs of qubits.
We find that in the case of a nonzero detuning between the atomic transition
frequencies and the cavity mode frequencies, no complete transfer of the
initial entanglement is possible to any of the other pairs of qubits. In the
case of exact resonance and equal coupling strengths of the atoms to the cavity
modes, an initial maximally entangled state of the atoms can be completely
transferred to the cavity modes. The complete transfer of the entanglement is
restricted to the cavity modes only with the transfer to the other pairs being
limited to up to 50%. We have found that the complete transfer of an initial
entanglement to other pairs of qubits may take place if the initial state is
not the maximally entangled state and the atoms couple to the cavity modes with
unequal strengths. Depending on the ratio between the coupling strengths, the
optimal entanglement can be created between the atoms and one of the cavity
modes.Comment: 3 figures. Oral talk presented in CEWQO 18, Madrid 201
Analysis of radiatively stable entanglement in a system of two dipole-interacting three-level atoms
We explore the possibilities of creating radiatively stable entangled states
of two three-level dipole-interacting atoms in a configuration by
means of laser biharmonic continuous driving or pulses. We propose three
schemes for generation of entangled states which involve only the lower states
of the system, not vulnerable to radiative decay. Two of them employ
coherent dynamics to achieve entanglement in the system, whereas the third one
uses optical pumping, i.e., an essentially incoherent process.Comment: Replaced with the final version; 14 pages, 6 figures; to appear in
Phys. Rev. A, vol. 61 (2000
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