17,847 research outputs found
Implementable Quantum Bit-String Commitment Protocol
Quantum bit-string commitment[A.Kent, Phys.Rev.Lett., 90, 237901 (2003)] or
QBSC is a variant of bit commitment (BC). In this paper, we propose a new QBSC
protocol that can be implemented using currently available technology, and
prove its security under the same security criteria as discussed by Kent. QBSC
is a generalization of BC, but has slightly weaker requirements, and our
proposed protocol is not intended to break the no-go theorem of quantum BC.Comment: To appear in Phys. Rev. A., 9 pages, 2 figure
Derivative pricing under the possibility of long memory in the supOU stochastic volatility model
We consider the supOU stochastic volatility model which is able to exhibit
long-range dependence. For this model we give conditions for the discounted
stock price to be a martingale, calculate the characteristic function, give a
strip where it is analytic and discuss the use of Fourier pricing techniques.
Finally, we present a concrete specification with polynomially decaying
autocorrelations and calibrate it to observed market prices of plain vanilla
options
Estimating entanglement of unknown states
The experimental determination of entanglement is a major goal in the quantum
information field. In general the knowledge of the state is required in order
to quantify its entanglement. Here we express a lower bound to the robustness
of entanglement of a state based only on the measurement of the energy
observable and on the calculation of a separability energy. This allows the
estimation of entanglement dismissing the knowledge of the state in question.Comment: 3 pages, 1 figure. Comments welcome. V2: references updated. Accepted
version by Applied Physics Letter
Verifying continuous-variable entanglement in finite spaces
Starting from arbitrary Hilbert spaces, we reduce the problem to verify
entanglement of any bipartite quantum state to finite dimensional subspaces.
Hence, entanglement is a finite dimensional property. A generalization for
multipartite quantum states is also given.Comment: 4 page
Quantum computing of delocalization in small-world networks
We study a quantum small-world network with disorder and show that the system
exhibits a delocalization transition. A quantum algorithm is built up which
simulates the evolution operator of the model in a polynomial number of gates
for exponential number of vertices in the network. The total computational gain
is shown to depend on the parameters of the network and a larger than quadratic
speed-up can be reached.
We also investigate the robustness of the algorithm in presence of
imperfections.Comment: 4 pages, 5 figures, research done at
http://www.quantware.ups-tlse.fr
Experimental approximation of the Jones polynomial with DQC1
We present experimental results approximating the Jones polynomial using 4
qubits in a liquid state nuclear magnetic resonance quantum information
processor. This is the first experimental implementation of a complete problem
for the deterministic quantum computation with one quantum bit model of quantum
computation, which uses a single qubit accompanied by a register of completely
random states. The Jones polynomial is a knot invariant that is important not
only to knot theory, but also to statistical mechanics and quantum field
theory. The implemented algorithm is a modification of the algorithm developed
by Shor and Jordan suitable for implementation in NMR. These experimental
results show that for the restricted case of knots whose braid representations
have four strands and exactly three crossings, identifying distinct knots is
possible 91% of the time.Comment: 5 figures. Version 2 changes: published version, minor errors
corrected, slight changes to improve readabilit
Controlling quantum systems by embedded dynamical decoupling schemes
A dynamical decoupling method is presented which is based on embedding a
deterministic decoupling scheme into a stochastic one. This way it is possible
to combine the advantages of both methods and to increase the suppression of
undesired perturbations of quantum systems significantly even for long
interaction times. As a first application the stabilization of a quantum memory
is discussed which is perturbed by one-and two-qubit interactions
Computation by measurements: a unifying picture
The ability to perform a universal set of quantum operations based solely on
static resources and measurements presents us with a strikingly novel viewpoint
for thinking about quantum computation and its powers. We consider the two
major models for doing quantum computation by measurements that have hitherto
appeared in the literature and show that they are conceptually closely related
by demonstrating a systematic local mapping between them. This way we
effectively unify the two models, showing that they make use of interchangeable
primitives. With the tools developed for this mapping, we then construct more
resource-effective methods for performing computation within both models and
propose schemes for the construction of arbitrary graph states employing
two-qubit measurements alone.Comment: 13 pages, 18 figures, REVTeX
Quantum Computation with Diatomic Bits in Optical Lattices
We propose a scheme for scalable and universal quantum computation using
diatomic bits with conditional dipole-dipole interaction, trapped within an
optical lattice. The qubit states are encoded by the scattering state and the
bound heteronuclear molecular state of two ultracold atoms per site. The
conditional dipole-dipole interaction appears between neighboring bits when
they both occupy the molecular state. The realization of a universal set of
quantum logic gates, which is composed of single-bit operations and a two-bit
controlled-NOT gate, is presented. The readout method is also discussed.Comment: 5 pages, 1 eps figure, accepted for publication in Phys. Rev.
A new method for the measurement of the natural periods of buildings
It is shown that the inertia force obtained by a man moving his body back and forth in synchronism with the natural period of vibration of a large structure is sufficient to build up a measurable amplitude of motion. By recording such structural vibrations versus time, the natural period and damping of several of the lower modes of vibration can be determined. The amplitudes of motion set up in this way are for many structures significantly larger than can be obtained from wind excitation, which has been used in the past for the measurement of the period of the fundamental mode
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