Numerical Analysis of the Capacities for Two-Qubit Unitary Operations

We present numerical results on the capacities of two-qubit unitary operations for creating entanglement and increasing the Holevo information of an ensemble. In all cases tested, the maximum values calculated for the capacities based on the Holevo information are close to the capacities based on the entanglement. This indicates that the capacities based on the Holevo information, which are very difficult to calculate, may be estimated from the capacities based upon the entanglement, which are relatively straightforward to calculate.Comment: 9 pages, 10 figure

Phase boundaries in deterministic dense coding

We consider dense coding with partially entangled states on bipartite systems of dimension $d\times d$, studying the conditions under which a given number of messages, $N$, can be deterministically transmitted. It is known that the largest Schmidt coefficient, $\lambda_0$, must obey the bound $\lambda_0\le d/N$, and considerable empirical evidence points to the conclusion that there exist states satisfying $\lambda_0=d/N$ for every $d$ and $N$ except the special cases $N=d+1$ and $N=d^2-1$. We provide additional conditions under which this bound cannot be reached -- that is, when it must be that $\lambda_0<d/N$ -- yielding insight into the shapes of boundaries separating entangled states that allow $N$ messages from those that allow only $N-1$. We also show that these conclusions hold no matter what operations are used for the encoding, and in so doing, identify circumstances under which unitary encoding is strictly better than non-unitary.Comment: 7 pages, 1 figur

Noncommutative spin-1/2 representations

In this letter we apply the methods of our previous paper hep-th/0108045 to noncommutative fermions. We show that the fermions form a spin-1/2 representation of the Lorentz algebra. The covariant splitting of the conformal transformations into a field-dependent part and a \theta-part implies the Seiberg-Witten differential equations for the fermions.Comment: 7 pages, LaTe

Particle production in p-p collisions at sqrt(s) = 17 GeV within the statistical model

A thermal-model analysis of particle production of p-p collisions at sqrt(s) = 17 GeV using the latest available data is presented. The sensitivity of model parameters on data selections and model assumptions is studied. The system-size dependence of thermal parameters and recent differences in the statistical model analysis of p-p collisions at the super proton synchrotron (SPS) are discussed. It is shown that the temperature and strangeness undersaturation factor depend strongly on kaon yields which at present are still not well known experimentally. It is conclude, that within the presently available data at the SPS it is rather unlikely that the temperature in p-p collisions exceeds significantly that expected in central collisions of heavy ions at the same energy.Comment: 6 pages, 3 figures, submitted to Phys. Rev.

Generalized Massive Gravity and Galilean Conformal Algebra in two dimensions

Galilean conformal algebra (GCA) in two dimensions arises as contraction of two copies of the centrally extended Virasoro algebra ($t\rightarrow t, x\rightarrow\epsilon x$ with $\epsilon\rightarrow 0$). The central charges of GCA can be expressed in term of Virasoro central charges. For finite and non-zero GCA central charges, the Virasoro central charges must behave as asymmetric form $O(1)\pm O(\frac{1}{\epsilon})$. We propose that, the bulk description for 2d GCA with asymmetric central charges is given by general massive gravity (GMG) in three dimensions. It can be seen that, if the gravitational Chern-Simons coupling $\frac{1}{\mu}$ behaves as of order O($\frac{1}{\epsilon}$) or ($\mu\rightarrow\epsilon\mu$), the central charges of GMG have the above $\epsilon$ dependence. So, in non-relativistic scaling limit $\mu\rightarrow\epsilon\mu$, we calculated GCA parameters and finite entropy in term of gravity parameters mass and angular momentum of GMG.Comment: 9 page

Rigid invariance as derived from BRS invariance: The abelian Higgs model

Consequences of a symmetry, e.g.\ relations amongst Green functions, are renormalization scheme independently expressed in terms of a rigid Ward identity. The corresponding local version yields information on the respective current. In the case of spontaneous breakdown one has to define the theory via the BRS invariance and thus to construct rigid and current Ward identity non-trivially in accordance with it. We performed this construction to all orders of perturbation theory in the abelian Higgs model as a prelude to the standard model. A technical tool of interest in itself is the use of a doublet of external scalar ``background'' fields. The Callan-Symanzik equation has an interesting form and follows easily once the rigid invariance is established.Comment: 33 pages, Plain Te

Quantum data processing and error correction

This paper investigates properties of noisy quantum information channels. We define a new quantity called {\em coherent information} which measures the amount of quantum information conveyed in the noisy channel. This quantity can never be increased by quantum information processing, and it yields a simple necessary and sufficient condition for the existence of perfect quantum error correction.Comment: LaTeX, 20 page

Twist and teleportation analogy of the black hole final state

Mathematical connection between the quantum teleportation, the most unique feature of quantum information processing, and the black hole final state is studied taking into account the non trivial spacetime geometry. We use the twist operatation for the generalized entanglement measurement and the final state boundary conditions to obtain transfer theorems for the black hole evaporation. This would enable us to put together the universal quantum teleportation and the black hole evaporation in the unified mathematical footing. For a renormalized post selected final state of outgoing Hawking radiation, we found that the measure of mixedness is preserved only in the special case of final-state boundary condition in the micro-canonical form, which resmebles perfect teleportation channel.Comment: version_

Noncommutative Lorentz Symmetry and the Origin of the Seiberg-Witten Map

We show that the noncommutative Yang-Mills field forms an irreducible representation of the (undeformed) Lie algebra of rigid translations, rotations and dilatations. The noncommutative Yang-Mills action is invariant under combined conformal transformations of the Yang-Mills field and of the noncommutativity parameter \theta. The Seiberg-Witten differential equation results from a covariant splitting of the combined conformal transformations and can be computed as the missing piece to complete a covariant conformal transformation to an invariance of the action.Comment: 20 pages, LaTeX. v2: Streamlined proofs and extended discussion of Lorentz transformation

Optimal Time-Reversal of Multi-phase Equatorial States

Even though the time-reversal is unphysical (it corresponds to the complex conjugation of the density matrix), for some restricted set of states it can be achieved unitarily, typically when there is a common de-phasing in a n-level system. However, in the presence of multiple phases (i. e. a different de-phasing for each element of an orthogonal basis occurs) the time reversal is no longer physically possible. In this paper we derive the channel which optimally approaches in fidelity the time-reversal of multi-phase equatorial states in arbitrary (finite) dimension. We show that, in contrast to the customary case of the Universal-NOT on qubits (or the universal conjugation in arbitrary dimension), the optimal phase covariant time-reversal for equatorial states is a nonclassical channel, which cannot be achieved via a measurement/preparation procedure. Unitary realizations of the optimal time-reversal channel are given with minimal ancillary dimension, exploiting the simplex structure of the optimal maps.Comment: 7 pages, minor change