28 research outputs found
Ancilla models for quantum operations: For what unitaries does the ancilla state have to be physical?
Any evolution described by a completely positive trace-preserving linear map
can be imagined as arising from the interaction of the evolving system with an
initially uncorrelated ancilla. The interaction is given by a joint unitary
operator, acting on the system and the ancilla. Here we study the properties
such a unitary operator must have in order to force the choice of a physical-
that is, positive-state for the ancilla if the end result is to be a
physical-that is, completely positive-evolution of the system.Comment: Quantum Information Processing, (2012
Multiplicativity of completely bounded p-norms implies a new additivity result
We prove additivity of the minimal conditional entropy associated with a
quantum channel Phi, represented by a completely positive (CP),
trace-preserving map, when the infimum of S(gamma_{12}) - S(gamma_1) is
restricted to states of the form gamma_{12} = (I \ot Phi)(| psi >< psi |). We
show that this follows from multiplicativity of the completely bounded norm of
Phi considered as a map from L_1 -> L_p for L_p spaces defined by the Schatten
p-norm on matrices; we also give an independent proof based on entropy
inequalities. Several related multiplicativity results are discussed and
proved. In particular, we show that both the usual L_1 -> L_p norm of a CP map
and the corresponding completely bounded norm are achieved for positive
semi-definite matrices. Physical interpretations are considered, and a new
proof of strong subadditivity is presented.Comment: Final version for Commun. Math. Physics. Section 5.2 of previous
version deleted in view of the results in quant-ph/0601071 Other changes
mino
Electron Cooling Experiments in CSR
The six species heavy ion beam was accumulated with the help of electron
cooling in the main ring of Cooler Storage Ring of Heavy Ion Research Facility
in Lanzhou(HIRFL-CSR), the ion beam accumulation dependence on the parameters
of cooler was investigated experimentally. The 400MeV/u 12C6+ and 200MeV/u
129Xe54+ was stored and cooled in the experimental ring CSRe, the cooling force
was measured in different condition.Comment: 5 pages 11 figure
Relations for certain symmetric norms and anti-norms before and after partial trace
Changes of some unitarily invariant norms and anti-norms under the operation
of partial trace are examined. The norms considered form a two-parametric
family, including both the Ky Fan and Schatten norms as particular cases. The
obtained results concern operators acting on the tensor product of two
finite-dimensional Hilbert spaces. For any such operator, we obtain upper
bounds on norms of its partial trace in terms of the corresponding
dimensionality and norms of this operator. Similar inequalities, but in the
opposite direction, are obtained for certain anti-norms of positive matrices.
Through the Stinespring representation, the results are put in the context of
trace-preserving completely positive maps. We also derive inequalities between
the unified entropies of a composite quantum system and one of its subsystems,
where traced-out dimensionality is involved as well.Comment: 11 pages, no figures. A typo error in Eq. (5.15) is corrected. Minor
improvements. J. Stat. Phys. (in press
Many body physics from a quantum information perspective
The quantum information approach to many body physics has been very
successful in giving new insight and novel numerical methods. In these lecture
notes we take a vertical view of the subject, starting from general concepts
and at each step delving into applications or consequences of a particular
topic. We first review some general quantum information concepts like
entanglement and entanglement measures, which leads us to entanglement area
laws. We then continue with one of the most famous examples of area-law abiding
states: matrix product states, and tensor product states in general. Of these,
we choose one example (classical superposition states) to introduce recent
developments on a novel quantum many body approach: quantum kinetic Ising
models. We conclude with a brief outlook of the field.Comment: Lectures from the Les Houches School on "Modern theories of
correlated electron systems". Improved version new references adde
Finite-time destruction of entanglement and non-locality by environmental influences
Entanglement and non-locality are non-classical global characteristics of
quantum states important to the foundations of quantum mechanics. Recent
investigations have shown that environmental noise, even when it is entirely
local in influence, can destroy both of these properties in finite time despite
giving rise to full quantum state decoherence only in the infinite time limit.
These investigations, which have been carried out in a range of theoretical and
experimental situations, are reviewed here.Comment: 27 pages, 6 figures, review article to appear in Foundations of
Physic
When are quantum systems operationally independent?
We propose some formulations of the notion of "operational independence" of two subsystems S1,S2 of a larger quantum system S and clarify their relation to other independence concepts in the literature. In addition, we indicate why the operational independence of quantum subsystems holds quite generally, both in nonrelativistic and relativistic quantum theory