8,822 research outputs found
On local invariants of pure three-qubit states
We study invariants of three-qubit states under local unitary
transformations, i.e. functions on the space of entanglement types, which is
known to have dimension 6. We show that there is no set of six independent
polynomial invariants of degree less than or equal to 6, and find such a set
with maximum degree 8. We describe an intrinsic definition of a canonical state
on each orbit, and discuss the (non-polynomial) invariants associated with it.Comment: LateX, 13 pages. Minor typoes corrected. Published versio
Alternative model of the Antonov problem
Astrophysical systems will never be in a real Thermodynamic equilibrium: they
undergo an evaporation process due to the fact that the gravity is not able to
confine the particles. Ordinarily, this difficulty is overcome by enclosing the
system in a rigid container which avoids the evaporation. We proposed an
energetic prescription which is able to confine the particles, leading in this
way to an alternative version of the Antonov isothermal model which unifies the
well-known isothermal and polytropic profiles. Besides of the main features of
the isothermal sphere model: the existence of the gravitational collapse and
the energetic region with a negative specific heat, this alternative model has
the advantage that the system size naturally appears as a consequence of the
particles evaporation.Comment: RevTex4, 9 pages, 10 figures, Version Submitted to PR
Global entanglement in multiparticle systems
We define a polynomial measure of multiparticle entanglement which is
scalable, i.e., which applies to any number of spin-1/2 particles. By
evaluating it for three particle states, for eigenstates of the one dimensional
Heisenberg antiferromagnet and on quantum error correcting code subspaces, we
illustrate the extent to which it quantifies global entanglement. We also apply
it to track the evolution of entanglement during a quantum computation.Comment: 9 pages, plain TeX, 1 PostScript figure included with epsf.tex
(ignore the under/overfull \vbox error messages); for related work see
http://math.ucsd.edu/~dmeyer/research.html or
http://www.math.ucsd.edu/~nwallach
Three-qubit pure-state canonical forms
In this paper we analyze the canonical forms into which any pure three-qubit
state can be cast. The minimal forms, i.e. the ones with the minimal number of
product states built from local bases, are also presented and lead to a
complete classification of pure three-qubit states. This classification is
related to the values of the polynomial invariants under local unitary
transformations by a one-to-one correspondence.Comment: REVTEX, 9 pages, 1 figur
Thermodynamic entropy of a many body energy eigenstate
It is argued that a typical many body energy eigenstate has a well defined
thermodynamic entropy and that individual eigenstates possess thermodynamic
characteristics analogous to those of generic isolated systems. We examine
large systems with eigenstate energies equivalent to finite temperatures. When
quasi-static evolution of a system is adiabatic (in the quantum mechanical
sense), two coupled subsystems can transfer heat from one subsystem to another
yet remain in an energy eigenstate. To explicitly construct the entropy from
the wave function, degrees of freedom are divided into two unequal parts. It is
argued that the entanglement entropy between these two subsystems is the
thermodynamic entropy per degree of freedom for the smaller subsystem. This is
done by tracing over the larger subsystem to obtain a density matrix, and
calculating the diagonal and off-diagonal contributions to the entanglement
entropy.Comment: 18 page
Local symmetry properties of pure 3-qubit states
Entanglement types of pure states of 3 qubits are classified by means of
their stabilisers in the group of local unitary operations. It is shown that
the stabiliser is generically discrete, and that a larger stabiliser indicates
a stationary value for some local invariant. We describe all the exceptional
states with enlarged stabilisers.Comment: 32 pages, 5 encapsulated PostScript files for 3 figures. Published
version, with minor correction
Accessing the dynamics of large many-particle systems using Stochastic Series Expansion
The Stochastic Series Expansion method (SSE) is a Quantum Monte Carlo (QMC)
technique working directly in the imaginary time continuum and thus avoiding
"Trotter discretization" errors. Using a non-local "operator-loop update" it
allows treating large quantum mechanical systems of many thousand sites. In
this paper we first give a comprehensive review on SSE and present benchmark
calculations of SSE's scaling behavior with system size and inverse
temperature, and compare it to the loop algorithm, whose scaling is known to be
one of the best of all QMC methods. Finally we introduce a new and efficient
algorithm to measure Green's functions and thus dynamical properties within
SSE.Comment: 11 RevTeX pages including 7 figures and 5 table
Properties of Entanglement Monotones for Three-Qubit Pure States
Various parameterizations for the orbits under local unitary transformations
of three-qubit pure states are analyzed. The interconvertibility, symmetry
properties, parameter ranges, calculability and behavior under measurement are
looked at. It is shown that the entanglement monotones of any multipartite pure
state uniquely determine the orbit of that state under local unitary
transformations. It follows that there must be an entanglement monotone for
three-qubit pure states which depends on the Kempe invariant defined in [Phys.
Rev. A 60, 910 (1999)]. A form for such an entanglement monotone is proposed. A
theorem is proved that significantly reduces the number of entanglement
monotones that must be looked at to find the maximal probability of
transforming one multipartite state to another.Comment: 14 pages, REVTe
Classification of multi-qubit mixed states: separability and distillability properties
We give a complete, hierarchic classification for arbitrary multi-qubit mixed
states based on the separability properties of certain partitions. We introduce
a family of N-qubit states to which any arbitrary state can be depolarized.
This family can be viewed as the generalization of Werner states to multi-qubit
systems. We fully classify those states with respect to their separability and
distillability properties. This provides sufficient conditions for
nonseparability and distillability for arbitrary states.Comment: 12 pages, 2 figure
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