24 research outputs found
Quantum Walk on a Line with Two Entangled Particles
We introduce the concept of a quantum walk with two particles and study it
for the case of a discrete time walk on a line. A quantum walk with more than
one particle may contain entanglement, thus offering a resource unavailable in
the classical scenario and which can present interesting advantages. In this
work, we show how the entanglement and the relative phase between the states
describing the coin degree of freedom of each particle will influence the
evolution of the quantum walk. In particular, the probability to find at least
one particle in a certain position after steps of the walk, as well as the
average distance between the two particles, can be larger or smaller than the
case of two unentangled particles, depending on the initial conditions we
choose. This resource can then be tuned according to our needs, in particular
to enhance a given application (algorithmic or other) based on a quantum walk.
Experimental implementations are briefly discussed
Spin-Space Entanglement Transfer and Quantum Statistics
Both the topics of entanglement and particle statistics have aroused enormous
research interest since the advent of quantum mechanics. Using two pairs of
entangled particles we show that indistinguishability enforces a transfer of
entanglement from the internal to the spatial degrees of freedom without any
interaction between these degrees of freedom. Moreover, sub-ensembles selected
by local measurements of the path will in general have different amounts of
entanglement in the internal degrees of freedom depending on the statistics
(either fermionic or bosonic) of the particles involved.Comment: 5 figures. Various changes for clarification and references adde
Optimal State Discrimination Using Particle Statistics
We present an application of particle statistics to the problem of optimal
ambiguous discrimination of quantum states. The states to be discriminated are
encoded in the internal degrees of freedom of identical particles, and we use
the bunching and antibunching of the external degrees of freedom to
discriminate between various internal states. We show that we can achieve the
optimal single-shot discrimination probability using only the effects of
particle statistics. We discuss interesting applications of our method to
detecting entanglement and purifying mixed states. Our scheme can easily be
implemented with the current technology
Ground state fidelity and quantum phase transitions in free Fermi systems
We compute the fidelity between the ground states of general quadratic
fermionic hamiltonians and analyze its connections with quantum phase
transitions. Each of these systems is characterized by a real
matrix whose polar decomposition, into a non-negative and a unitary
, contains all the relevant ground state (GS) information. The boundaries
between different regions in the GS phase diagram are given by the points of,
possibly asymptotic, singularity of . This latter in turn implies a
critical drop of the fidelity function. We present general results as well as
their exemplification by a model of fermions on a totally connected graph.Comment: 4 pages, 2 figure
Generation and Distribution of Quantum Oblivious Keys for Secure Multiparty Computation
The oblivious transfer primitive is sufficient to implement secure multiparty
computation. However, secure multiparty computation based only on classical
cryptography is severely limited by the security and efficiency of the
oblivious transfer implementation. We present a method to efficiently and
securely generate and distribute oblivious keys by exchanging qubits and by
performing commitments using classical hash functions. With the presented
hybrid approach, quantum and classical, we obtain a practical and high-speed
oblivious transfer protocol, secure even against quantum computer attacks. The
oblivious distributed keys allow implementing a fast and secure oblivious
transfer protocol, which can pave the way for the widespread of applications
based on secure multiparty computation.Comment: 11 pages, 5 figure
Fermionic entanglement in itinerant systems
We study pairwise quantum entanglement in systems of fermions itinerant in a
lattice from a second-quantized perspective. Entanglement in the
grand-canonical ensemble is studied, both for energy eigenstates and for the
thermal state. Relations between entanglement and superconducting correlations
are discussed in a BCS-like model and for -pair superconductivity.Comment: 8 Pages LaTeX, 5 Figures included. Presentation improved, results and
references adde
Entanglement-assisted orientation in space
We demonstrate that quantum entanglement can help separated individuals in making decisions if their goal is to find each other in the absence of any communication between them. We derive a Bell-like inequality that the efficiency of every classical solution for our problem has to obey, and demonstrate its violation by the quantum efficiency. This proves that no classical strategy can be more efficient than the quantum one. © 2006 World Scientific Publishing Company