1,106 research outputs found
Multipartite entanglement in 2 x 2 x n quantum systems
We classify multipartite entangled states in the 2 x 2 x n (n >= 4) quantum
system, for example the 4-qubit system distributed over 3 parties, under local
filtering operations. We show that there exist nine essentially different
classes of states, and they give rise to a five-graded partially ordered
structure, including the celebrated Greenberger-Horne-Zeilinger (GHZ) and W
classes of 3 qubits. In particular, all 2 x 2 x n-states can be
deterministically prepared from one maximally entangled state, and some
applications like entanglement swapping are discussed.Comment: 9 pages, 3 eps figure
Asymptotic entanglement capacity of the Ising and anisotropic Heisenberg interactions
We compute the asymptotic entanglement capacity of the Ising interaction ZZ,
the anisotropic Heisenberg interaction XX + YY, and more generally, any
two-qubit Hamiltonian with canonical form K = a XX + b YY. We also describe an
entanglement assisted classical communication protocol using the Hamiltonian K
with rate equal to the asymptotic entanglement capacity.Comment: 5 pages, 1 figure; minor corrections, conjecture adde
Normal forms and entanglement measures for multipartite quantum states
A general mathematical framework is presented to describe local equivalence
classes of multipartite quantum states under the action of local unitary and
local filtering operations. This yields multipartite generalizations of the
singular value decomposition. The analysis naturally leads to the introduction
of entanglement measures quantifying the multipartite entanglement (as
generalizations of the concurrence and the 3-tangle), and the optimal local
filtering operations maximizing these entanglement monotones are obtained.
Moreover a natural extension of the definition of GHZ-states to e.g. systems is obtained.Comment: Proof of uniqueness of normal form adde
A bipartite class of entanglement monotones for N-qubit pure states
We construct a class of algebraic invariants for N-qubit pure states based on
bipartite decompositions of the system.
We show that they are entanglement monotones, and that they differ from the
well know linear entropies of the sub-systems. They therefore capture new
information on the non-local properties of multipartite systems.Comment: 6 page
Genralized Robustness of Entanglement
The robustness of entanglement results of Vidal and Tarrach considered the
problem whereby an entangled state is mixed with a separable state so that the
overall state becomes non-entangled. In general it is known that there are also
cases when entangled states are mixed with other entangled states and where the
sum is separable. In this paper, we treat the more general case where entangled
states can be mixed with any states so that the resulting mixture is
unentangled. It is found that entangled pure states for this generalized case
have the same robustness as the restricted case of Vidal and Tarrach.Comment: Final version. Editorial changes and references added to independent
wor
Quantum entanglement theory in the presence of superselection rules
Superselection rules severly constrain the operations which can be
implemented on a distributed quantum system. While the restriction to local
operations and classical communication gives rise to entanglement as a nonlocal
resource, particle number conservation additionally confines the possible
operations and should give rise to a new resource. In [Phys. Rev. Lett. 92,
087904 (2004), quant-ph/0310124] we showed that this resource can be quantified
by a single additional number, the superselection induced variance (SiV)
without changing the concept of entanglement. In this paper, we give the
results on pure states in greater detail; additionally, we provide a discussion
of mixed state nonlocality with superselection rules where we consider both
formation and distillation. Finally, we demonstrate that SiV is indeed a
resource, i.e., that it captures how well a state can be used to overcome the
restrictions imposed by the superselection rule.Comment: 16 pages, 5 figure
A new family of matrix product states with Dzyaloshinski-Moriya interactions
We define a new family of matrix product states which are exact ground states
of spin 1/2 Hamiltonians on one dimensional lattices. This class of
Hamiltonians contain both Heisenberg and Dzyaloshinskii-Moriya interactions but
at specified and not arbitrary couplings. We also compute in closed forms the
one and two-point functions and the explicit form of the ground state. The
degeneracy structure of the ground state is also discussed.Comment: 15 pages, 1 figur
Charge qubit entanglement in double quantum dots
We study entanglement of charge qubits in a vertical tunnel-coupled double
quantum dot containing two interacting electrons. Exact diagonalization is used
to compute the negativity characterizing entanglement. We find that
entanglement can be efficiently generated and controlled by sidegate voltages,
and describe how it can be detected. For large enough tunnel coupling, the
negativity shows a pronounced maximum at an intermediate interaction strength
within the Wigner molecule regime.Comment: revised version of the manuscript, as published in EPL, 7 pages, 4
figure
Amino acid metabolism conflicts with protein diversity
The twenty protein coding amino acids are found in proteomes with different
relative abundances. The most abundant amino acid, leucine, is nearly an order
of magnitude more prevalent than the least abundant amino acid, cysteine. Amino
acid metabolic costs differ similarly, constraining their incorporation into
proteins. On the other hand, sequence diversity is necessary for protein
folding, function and evolution. Here we present a simple model for a
cost-diversity trade-off postulating that natural proteomes minimize amino acid
metabolic flux while maximizing sequence entropy. The model explains the
relative abundances of amino acids across a diverse set of proteomes. We found
that the data is remarkably well explained when the cost function accounts for
amino acid chemical decay. More than one hundred proteomes reach comparable
solutions to the trade-off by different combinations of cost and diversity.
Quantifying the interplay between proteome size and entropy shows that
proteomes can get optimally large and diverse
Classification of qubit entanglement: SL(2,C) versus SU(2) invariance
The role of SU(2) invariants for the classification of multiparty
entanglement is discussed and exemplified for the Kempe invariant I_5 of pure
three-qubit states. It is found to being an independent invariant only in
presence of both W-type entanglement and threetangle. In this case, constant
I_5 admits for a wide range of both threetangle and concurrences. Furthermore,
the present analysis indicates that an SL^3 orbit of states with equal tangles
but continuously varying I_5 must exist. This means that I_5 provides no
information on the entanglement in the system in addition to that contained in
the tangles (concurrences and threetangle) themselves. Together with the
numerical evidence that I_5 is an entanglement monotone this implies that SU(2)
invariance or the monotone property are too weak requirements for the
characterization and quantification of entanglement for systems of three
qubits, and that SL(2,C) invariance is required. This conclusion can be
extended to general multipartite systems (including higher local dimension)
because the entanglement classes of three-qubit systems appear as subclasses.Comment: 9 pages, 10 figures, revtex
- …