138 research outputs found
Decoherence Free Subspace and entanglement by interaction with a common squeezed bath
In this work we find explicitly the decoherence free subspace (DFS) for a two
two-level system in a common squeezed vacuum bath. We also find an orthogonal
basis for the DFS composed of a symmetrical and an antisymmetrical (under
particle permutation) entangled state. For any initial symmetrical state, the
master equation has one stationary state which is the symmetrical entangled
decoherence free state. In this way, one can generate entanglement via common
squeezed bath of the two systems. If the initial state does not have a definite
parity, the stationary state depends strongly on the initial conditions of the
system and it has a statistical mixture of states which belong to the DFS. We
also study the effect of the coupling between the two-level systems on the DFS.Comment: 4 pages, 1 figur
Multiparty Quantum Secret Sharing Based on Entanglement Swapping
A multiparty quantum secret sharing (QSS) protocol is proposed by using
swapping quantum entanglement of Bell states. The secret messages are imposed
on Bell states by local unitary operations. The secret messages are split into
several parts and each part is distributed to a party so that no action of a
subset of all the parties but their entire cooperation is able to read out the
secret messages. In addition, the dense coding is used in this protocol to
achieve a high efficiency. The security of the present multiparty QSS against
eavesdropping has been analyzed and confirmed even in a noisy quantum channel.Comment: 5 page
Long-range entanglement generation via frequent measurements
A method is introduced whereby two non-interacting quantum subsystems, that
each interact with a third subsystem, are entangled via repeated projective
measurements of the state of the third subsystem. A variety of physical
examples are presented. The method can be used to establish long range
entanglement between distant parties in one parallel measurement step, thus
obviating the need for entanglement swapping.Comment: 7 pages, incl. 2 figures. v2: added a few small clarifications and a
referenc
Quantum secret sharing between multi-party and multi-party without entanglement
We propose a quantum secret sharing protocol between multi-party ( members
in group 1) and multi-party ( members in group 2) using a sequence of single
photons. These single photons are used directly to encode classical information
in a quantum secret sharing process. In this protocol, all members in group 1
directly encode their respective keys on the states of single photons via
unitary operations, then the last one (the member of group 1) sends
of the resulting qubits to each of group 2. Thus the secret message
shared by all members of group 1 is shared by all members of group 2 in such a
way that no subset of each group is efficient to read the secret message, but
the entire set (not only group 1 but also group 2) is. We also show that it is
unconditionally secure. This protocol is feasible with present-day techniques.Comment: 6 pages, no figur
Large scale prop-fan structural design study. Volume 1: Initial concepts
In recent years, considerable attention has been directed toward improving aircraft fuel consumption. Studies have shown that the inherent efficiency advantage that turboprop propulsion systems have demonstrated at lower cruise speeds may now be extended to the higher speeds of today's turbofan and turbojet-powered aircraft. To achieve this goal, new propeller designs will require features such as thin, high speed airfoils and aerodynamic sweep, features currently found only in wing designs for high speed aircraft. This is Volume 1 of a 2 volume study to establish structural concepts for such advanced propeller blades, to define their structural properties, to identify any new design, analysis, or fabrication techniques which were required, and to determine the structural tradeoffs involved with several blade shapes selected primarily on the basis of aero/acoustic design considerations. The feasibility of fabricating and testing dynamically scaled models of these blades for aeroelastic testing was also established. The preliminary design of a blade suitable for flight use in a testbed advanced turboprop was conducted and is described in Volume 2
Efficient Multi-Party Quantum Secret Sharing Schemes
In this work, we generalize the quantum secret sharing scheme of Hillary,
Bu\v{z}ek and Berthiaume[Phys. Rev. A59, 1829(1999)] into arbitrary
multi-parties. Explicit expressions for the shared secret bit is given. It is
shown that in the Hillery-Bu\v{z}ek-Berthiaume quantum secret sharing scheme
the secret information is shared in the parity of binary strings formed by the
measured outcomes of the participants. In addition, we have increased the
efficiency of the quantum secret sharing scheme by generalizing two techniques
from quantum key distribution. The favored-measuring-basis Quantum secret
sharing scheme is developed from the Lo-Chau-Ardehali technique[H. K. Lo, H. F.
Chau and M. Ardehali, quant-ph/0011056] where all the participants choose their
measuring-basis asymmetrically, and the measuring-basis-encrypted Quantum
secret sharing scheme is developed from the Hwang-Koh-Han technique [W. Y.
Hwang, I. G. Koh and Y. D. Han, Phys. Lett. A244, 489 (1998)] where all
participants choose their measuring-basis according to a control key. Both
schemes are asymptotically 100% in efficiency, hence nearly all the GHZ-states
in a quantum secret sharing process are used to generate shared secret
information.Comment: 7 page
Fluorescence microscopy visualization of halomucin, a secreted 927 kDa protein surrounding Haloquadratum walsbyi cells
At the time of its first publication, halomucin from Haloquadratum walsbyi strain HBSQ001 was the largest archaeal protein known (9159 aa). It has a predicted signal sequence, making it likely to be an extracellular or secreted protein. Best BLAST matches were found to be mammalian mucins that protect tissues to dehydration and chemical stress. It was hypothesized that halomucin participates in protection against desiccation by retaining water in a hull around the halophilic organisms that live at the limits of water activity. We visualized Halo quadratum cells by staining their intracellular polyhydroxybutyrate granules using Nile Blue. Halomucin was stained by immunofluorescence with antibodies generated against synthetic peptides derived from the halomucin amino acid sequence. Polyhydroxybutyrate stained cells were reconstructed in 3D which highlights not only the highly regular square shape but also the extreme flatness of Haloquadratum. Double-staining proves halomucin to be extracellular but to be only loosely associated to cells in agreement with its hypothesized function
The von Neumann Entropy of EPR Spin Correlation for the Relativistic Pairs
Variation of the von Neumann entropy by the Lorentz transformation is
discussed. Taking the spin-singlet state in the center of mass frame, the von
Neumann entropy in the laboratory frame is calculated from the reduced density
matrix obtained by taking the trace over 4-momentum after the Lorentz
transformation. As the model to discuss the EPR spin correlation, it is
supposed that one parent particle splits into a superposition state of various
pair states in various directions. Computing the von Neumann entropy and the
Shannon entropy, we have shown a global behavior of the entropy to see a
relativistic effect. We discuss also the super-relativistic limit,
distinguishability between the two particles of the pair and so on.Comment: 15 pages, 9 figures; changed the title, revised the manuscript, added
reference
Geometric quantum computation using fictitious spin- 1/2 subspaces of strongly dipolar coupled nuclear spins
Geometric phases have been used in NMR, to implement controlled phase shift
gates for quantum information processing, only in weakly coupled systems in
which the individual spins can be identified as qubits. In this work, we
implement controlled phase shift gates in strongly coupled systems, by using
non-adiabatic geometric phases, obtained by evolving the magnetization of
fictitious spin-1/2 subspaces, over a closed loop on the Bloch sphere. The
dynamical phase accumulated during the evolution of the subspaces, is refocused
by a spin echo pulse sequence and by setting the delay of transition selective
pulses such that the evolution under the homonuclear coupling makes a complete
rotation. A detailed theoretical explanation of non-adiabatic geometric
phases in NMR is given, by using single transition operators. Controlled phase
shift gates, two qubit Deutsch-Jozsa algorithm and parity algorithm in a
qubit-qutrit system have been implemented in various strongly dipolar coupled
systems obtained by orienting the molecules in liquid crystal media.Comment: 37 pages, 17 figure
Implementing Shor's algorithm on Josephson Charge Qubits
We investigate the physical implementation of Shor's factorization algorithm
on a Josephson charge qubit register. While we pursue a universal method to
factor a composite integer of any size, the scheme is demonstrated for the
number 21. We consider both the physical and algorithmic requirements for an
optimal implementation when only a small number of qubits is available. These
aspects of quantum computation are usually the topics of separate research
communities; we present a unifying discussion of both of these fundamental
features bridging Shor's algorithm to its physical realization using Josephson
junction qubits. In order to meet the stringent requirements set by a short
decoherence time, we accelerate the algorithm by decomposing the quantum
circuit into tailored two- and three-qubit gates and we find their physical
realizations through numerical optimization.Comment: 12 pages, submitted to Phys. Rev.
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