Quantum Information Paradox: Real or Fictitious?

One of the outstanding puzzles of theoretical physics is whether quantum information indeed gets lost in the case of Black Hole (BH) evaporation or accretion. Let us recall that Quantum Mechanics (QM) demands an upper limit on the acceleration of a test particle. On the other hand, it is pointed out here that, if a Schwarzschild BH would exist, the acceleration of the test particle would blow up at the event horizon in violation of QM. Thus the concept of an exact BH is in contradiction of QM and quantum gravity (QG). It is also reminded that the mass of a BH actually appears as an INTEGRATION CONSTANT of Einstein equations. And it has been shown that the value of this integration constant is actually zero. Thus even classically, there cannot be finite mass BHs though zero mass BH is allowed. It has been further shown that during continued gravitational collapse, radiation emanating from the contracting object gets trapped within it by the runaway gravitational field. As a consequence, the contracting body attains a quasi-static state where outward trapped radiation pressure gets balanced by inward gravitational pull and the ideal classical BH state is never formed in a finite proper time. In other words, continued gravitational collapse results in an "Eternally Collapsing Object" which is a ball of hot plasma and which is asymptotically approaching the true BH state with M=0 after radiating away its entire mass energy. And if we include QM, this contraction must halt at a radius suggested by highest QM acceleration. In any case no EH is ever formed and in reality, there is no quantum information paradox.Comment: 8 pages in Pramana Style, 6 in Revtex styl

Minimum cbits for remote preperation and measurement of a qubit

We show that a qubit chosen from equatorial or polar great circles on a Bloch spehere can be remotely prepared with one cbit from Alice to Bob if they share one ebit of entanglement. Also we show that any single particle measurement on an arbitrary qubit can be remotely simulated with one ebit of shared entanglement and communication of one cbit.Comment: Latex, 7 pages, minor changes, references adde

Fluctuation, time-correlation function and geometric Phase

We establish a fluctuation-correlation theorem by relating the quantum fluctuations in the generator of the parameter change to the time integral of the quantum correlation function between the projection operator and force operator of the ``fast'' system. By taking a cue from linear response theory we relate the quantum fluctuation in the generator to the generalised susceptibility. Relation between the open-path geometric phase, diagonal elements of the quantum metric tensor and the force-force correlation function is provided and the classical limit of the fluctuation-correlation theorem is also discussed.Comment: Latex, 12 pages, no figures, submitted to J. Phys. A: Math & Ge

Quantum discord and classical correlation can tighten the uncertainty principle in the presence of quantum memory

Uncertainty relations capture the essence of the inevitable randomness associated with the outcomes of two incompatible quantum measurements. Recently, Berta et al. have shown that the lower bound on the uncertainties of the measurement outcomes depends on the correlations between the observed system and an observer who possesses a quantum memory. If the system is maximally entangled with its memory, the outcomes of two incompatible measurements made on the system can be predicted precisely. Here, we obtain a new uncertainty relation that tightens the lower bound of Berta et al., by incorporating an additional term that depends on the quantum discord and the classical correlations of the joint state of the observed system and the quantum memory. We discuss several examples of states for which our new lower bound is tighter than the bound of Berta et al. On the application side, we discuss the relevance of our new inequality for the security of quantum key distribution and show that it can be used to provide bounds on the distillable common randomness and the entanglement of formation of bipartite quantum states.Comment: v1: Latex, 4 and half pages, one fig; v2: 9 pages including 4-page appendix; v3: accepted into Physical Review A with minor change

Origin of negative differential resistance in a strongly coupled single molecule-metal junction device

A new mechanism is proposed to explain the origin of negative differential resistance (NDR) in a strongly coupled single molecule-metal junction. A first-principles quantum transport calculation in a Fe-terpyridine linker molecule sandwiched between a pair of gold electrodes is presented. Upon increasing applied bias, it is found that a new phase in the broken symmetry wavefunction of the molecule emerges from the mixing of occupied and unoccupied molecular orbital. As a consequence, a non-linear change in the coupling between molecule and lead is evolved resulting to NDR. This model can be used to explain NDR in other class of metal-molecule junction device.Comment: Submitted for review on Feb 4, 200

Baryon and Lepton Number Assignment in E6E_6 Models

In $E_6$ models there are new particles whose baryon number is not uniquely assigned. We point out that the baryon and lepton number assignment to these particles can change the baryogenesis scenario significantly. We consider left-right symmetric extension of the standard model in which $(B-L)$ quantum number is gauged. The identification of $(B-L)$ with a generator of $E_6$ is used to define the baryon and lepton numbers for the exotic particles in a way that the electroweak baryon and lepton number anomaly corresponding to the $SU(2)_L$ group vanishes, {\it i.e.}, there is no non-perturbative baryon or lepton number violation during the electroweak phase transition. We study some consequences of the new assignment.Comment: 14 pages, LaTeX file, 1 submitted Figure file(.eps

Unification of SU(2)xU(1) Using a Generalized Covariant Derivative and U(3)

A generalization of the Yang-Mills covariant derivative, that uses both vector and scalar fields and transforms as a 4-vector contracted with Dirac matrices, is used to simplify and unify the Glashow-Weinberg-Salam model. Since SU(3) assigns the wrong hypercharge to the Higgs boson, it is necessary to use a special representation of U(3) to obtain all the correct quantum numbers. A surplus gauge scalar boson emerges in the process, but it uncouples from all other particles.Comment: 12 pages, no figures. To be published in Int. J. Mod. Phys.

Dark matter from SU(4) model

The left-right symmetric Pati-Salam model of the unification of quarks and leptons is based on SU(4) and SU(2)xSU(2) groups. These groups are naturally extended to include the classification of families of quarks and leptons. We assume that the family group (the group which unites the families) is also the SU(4) group. The properties of the 4-th generation of fermions are the same as that of the ordinary-matter fermions in first three generations except for the family charge of the SU(4)_F group: F=(1/3,1/3,1/3,-1), where F=1/3 for fermions of ordinary matter and F=-1 for the 4-th generation. The difference in F does not allow the mixing between ordinary and fourth-generation fermions. Because of the conservation of the F charge, the creation of baryons and leptons in the process of electroweak baryogenesis must be accompanied by the creation of fermions of the 4-th generation. As a result the excess n_B of baryons over antibaryons leads to the excess n_{\nu 4}=N-\bar N=n_B of neutrinos over antineutrinos in the 4-th generation. This massive fourth-generation neutrino may form the non-baryonic dark matter. In principle their mass density n_{\nu 4}m_N in the Universe can give the main contribution to the dark matter, since the lower bound on neutrino mass m_N from the data on decay of the Z-bosons is m_N > m_Z/2. The straightforward prediction of this model leads to the amount of cold dark matter relative to baryons, which is an order of magnitude bigger than allowed by observations. This inconsistency may be avoided by non-conservation of the F-charge.Comment: 9 pages, 2 figures, version accepted in JETP Letters, corrected after referee reports, references are adde

Alternating Spin and Orbital Dimerization in Strong-coupling Two-band Models

We study a one-dimensional Hamiltonian consisting of coupled SU(2) spin and orbital degrees of freedom. Using the density matrix renormalization group, we calculate the phase-diagram and the ground state correlation functions for this model. We find that, in addition to the ferromagnetic and power-law antiferromagnetic phases for spin and orbital degrees of freedom, this model has a gapless line extending from the ferromagnetic phase to the Bethe ansatz solvable SU(4) critical point, and a gapped phase with doubly degenerate ground states which form alternating spin and orbital singlets. The spin-gap and the order parameters are evaluated and the relevance to several recently discovered spin-gap materials is discussed.Comment: 4 pages REVTEX and 4 Postscript figure