41 research outputs found
Quantum Entanglement of Identical Particles
We consider entanglement in a system of fixed number of identical particles.
Since any operation should be symmetrized over all the identical particles and
there is the precondition that the spatial wave functions overlap, the meaning
of identical-particle entanglement is fundamentally different from that of
distinguishable particles. The identical-particle counterpart of the Schmidt
basis is shown to be the single-particle basis in which the one-particle
reduced density matrix is diagonal. But it does not play a special role in the
issue of entanglement, which depends on the single-particle basis chosen. The
nonfactorization due to (anti)symmetrization is naturally excluded by using the
(anti)symmetrized basis or, equivalently, the particle number representation.
The natural degrees of freedom in quantifying the identical-particle
entanglement in a chosen single-particle basis are occupation numbers of
different single particle basis states. The entanglement between effectively
distinguishable spins is shown to be a special case of the occupation-number
entanglement.Comment: 5 pages, revtex4. A sentence is improve
Ground-State Entanglement in Interacting Bosonic Graphs
We consider a collection of bosonic modes corresponding to the vertices of a
graph Quantum tunneling can occur only along the edges of
and a local self-interaction term is present. Quantum entanglement of one
vertex with respect the rest of the graph is analyzed in the ground-state of
the system as a function of the tunneling amplitude The topology of
plays a major role in determining the tunneling amplitude
which leads to the maximum ground-state entanglement. Whereas in most of the
cases one finds the intuitively expected result we show that it
there exists a family of graphs for which the optimal value of is pushed
down to a finite value. We also show that, for complete graphs, our bi-partite
entanglement provides useful insights in the analysis of the cross-over between
insulating and superfluid ground statesComment: 5 pages (LaTeX) 5 eps figures include
Quantifying Quantum Correlations in Fermionic Systems using Witness Operators
We present a method to quantify quantum correlations in arbitrary systems of
indistinguishable fermions using witness operators. The method associates the
problem of finding the optimal entan- glement witness of a state with a class
of problems known as semidefinite programs (SDPs), which can be solved
efficiently with arbitrary accuracy. Based on these optimal witnesses, we
introduce a measure of quantum correlations which has an interpretation
analogous to the Generalized Robust- ness of entanglement. We also extend the
notion of quantum discord to the case of indistinguishable fermions, and
propose a geometric quantifier, which is compared to our entanglement measure.
Our numerical results show a remarkable equivalence between the proposed
Generalized Robustness and the Schliemann concurrence, which are equal for pure
states. For mixed states, the Schliemann con- currence presents itself as an
upper bound for the Generalized Robustness. The quantum discord is also found
to be an upper bound for the entanglement.Comment: 7 pages, 6 figures, Accepted for publication in Quantum Information
Processin
Bipartite entanglement in systems of identical particles: the partial transposition criterion
We study bipartite entanglement in systems of N identical bosons distributed
in M different modes. For such systems, a definition of separability not
related to any a priori Hilbert space tensor product structure is needed and
can be given in terms of commuting subalgebras of observables. Using this
generalized notion of separability, we classify the states for which partial
transposition turns out to be a necessary and sufficient condition for
entanglement detection.Comment: LaTeX, 22 page
Quantum computing in optical microtraps based on the motional states of neutral atoms
We investigate quantum computation with neutral atoms in optical microtraps
where the qubit is implemented in the motional states of the atoms, i.e., in
the two lowest vibrational states of each trap. The quantum gate operation is
performed by adiabatically approaching two traps and allowing tunneling and
cold collisions to take place. We demonstrate the capability of this scheme to
realize a square-root of swap gate, and address the problem of double
occupation and excitation to other unwanted states. We expand the two-particle
wavefunction in an orthonormal basis and analyze quantum correlations
throughout the whole gate process. Fidelity of the gate operation is evaluated
as a function of the degree of adiabaticity in moving the traps. Simulations
are based on rubidium atoms in state-of-the-art optical microtraps with quantum
gate realizations in the few tens of milliseconds duration range.Comment: 11 pages, 7 figures, for animations of the gate operation, see
http://www.itp.uni-hannover.de/~eckert/na/index.htm
Quantifying Entanglement Production of Quantum Operations
The problem of entanglement produced by an arbitrary operator is formulated
and a related measure of entanglement production is introduced. This measure of
entanglement production satisfies all properties natural for such a
characteristic. A particular case is the entanglement produced by a density
operator or a density matrix. The suggested measure is valid for operations
over pure states as well as over mixed states, for equilibrium as well as
nonequilibrium processes. Systems of arbitrary nature can be treated, described
either by field operators, spin operators, or any other kind of operators,
which is realized by constructing generalized density matrices. The interplay
between entanglement production and phase transitions in statistical systems is
analysed by the examples of Bose-Einstein condensation, superconducting
transition, and magnetic transitions. The relation between the measure of
entanglement production and order indices is analysed.Comment: 20 pages, Revte
Symmetries of a mean-field spin model
NatuurwetenskappeInstituut Vir Teoretiese FisikaPlease help us populate SUNScholar with the post print version of this article. It can be e-mailed to: [email protected]
ENISA: 5G design and architecture of global mobile networks; threats, risks, vulnerabilities; cybersecurity considerations [version 2; peer review: 2 approved, 1 approved with reservations]
Abstract —The literature on 5G design and architecture numbers in the hundreds of thousands, which makes analyzing this vast corpus of technical knowledge impossible within the scope of a single article. A rigorous literature scan has revealed investigations of various specific 5G components, or specific aspects of 5G design, architecture, or security, but none that are comprehensive in scope, encompassing all of the aforementioned categories, or that take into account the associated vulnerabilities, threats and risks to the basic 5G infrastructure. In this sense the 5G framework advocated by The European Union Agency for Cybersecurity (ENISA) in its comprehensive report is singular in relation to the extensive literature associated with the 5G domain and the fragmented character of scientific reporting related to 5G technology. It is the purpose of this article to go beyond the existing literature and examine in depth the details of the ENISA 5G Threat Landscape Report and reveal ENISA’s painstaking efforts to stand out among other leading-edge players in the 5G arena and achieve its strategic aims of integrating cybersecurity considerations with threats, risks, and vulnerabilities into an architecture of 5G right from the start of the design and development process. In formulating such a framework, ENISA has set the stage for standardization of cybersecurity considerations in relation to 5G design and architecture that may be considered a first approximation towards best practice in the field. ENISA’s role in the European Union as a leader in setting the pace of development of 5G networks is acknowledged in EU’s legislation and its directives. Significantly, its strategic direction targets future implementations of 5G networks by vendors, operators, and practitioners. This should equip EU with the necessary resilience to withstand hybrid threat onslaughts on its Pan-European network, a topic to be dealt with in full in a follow-on paper
Dynamical bottlenecks to intramolecular energy flow
4 pages, 4 figuresInternational audienceVibrational energy flows unevenly in molecules, repeatedly going back and forth between trapping and roaming. We identify bottlenecks between diffusive and chaotic behavior, and describe generic mechanisms of these transitions, taking the carbonyl sulphide molecule OCS as a case study. The bottlenecks are found to be lower-dimensional tori; their bifurcations and unstable manifolds govern the transition mechanisms