1,177 research outputs found
Inseparability of Quantum Parameters
In this work, we show that 'splitting of quantum information' [6] is an
impossible task from three different but consistent principles of unitarity of
Quantum Mechanics, no-signalling condition and non increase of entanglement
under Local Operation and Classical Communication.Comment: 9 pages, Presented in Quantum Computing Back Action in IIT Kanpur
(2006). Accepted in International Journal of Theoretical Physic
Self Replication and Signalling
It is known that if one could clone an arbitrary quantum state one could send
signal faster than the speed of light. However it remains interesting to see
that if one can perfectly self replicate an arbitrary quantum state, does it
violate the no signalling principle? Here we see that perfect self replication
would also lead to superluminal signalling.Comment: Modified version of quant-ph/0510221, Accepted in International
Journal of Theoretical Physic
Entrapment of magnetic micro-crystals for on-chip electron spin resonance studies
On-chip Electron Spin Resonance (ESR) of magnetic molecules requires the
ability to precisely position nanosized samples in antinodes of the
electro-magnetic field for maximal magnetic interaction. A method is developed
to entrap micro-crystals containing spins in a well defined location on a
substrate's surface. Traditional cavity ESR measurements are then performed on
a mesoscopic crystal at 34 GHz. Polycrystalline diluted Cr spins were
entrapped as well and measured while approaching the lower limit of the ESR
sensitivity. This method suggests the feasibility of on-chip ESR measurements
at dilution refrigerator temperatures by enabling the positioning of samples
atop an on-chip superconducting cavity.Comment: to appear in Journal of Applied Physic
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
Purification of Mixed State with Closed Timelike Curve is not Possible
In ordinary quantum theory any mixed state can be purified in an enlarged
Hilbert space by bringing an ancillary system. The purified state does not
depend on the state of any extraneous system with which the mixed state is
going to interact and on the physical interaction. Here, we prove that it is
not possible to purify a mixed state that traverses a closed time like curve
(CTC) and allowed to interact in a consistent way with a causality-respecting
(CR) quantum system in the same manner. Thus, in general for arbitrary
interactions between CR and CTC systems there is no universal 'Church of the
larger Hilbert space' for mixed states with CTC. This shows that in quantum
theory with CTCs there can exist 'proper' and 'improper' mixtures.Comment: Latex2e, No Figs, 4 + pages, An error corrected, Results unchange
Coherent manipulation of electron spins up to ambient temperatures in Cr(S=1/2) doped KNbO
We report coherent spin manipulation on Cr (\emph{S} = 1/2, \emph{I} =
0) doped KNbO, which constitutes a dilute two-level model relevant for
use as a spin qubit. Rabi oscillations are observed for the first time in a
spin system based on transition metal oxides up to room temperature. At liquid
helium temperature the phase coherence relaxation time \emph{} reaches
s and, with a Rabi frequency of 20 MHz, yields a single qubit
figure of merit \emph{} of about 500. This shows that a diluted ensemble
of Cr (\emph{S} = 1/2) doped KNbO is a potential candidate for
solid-state quantum information processing.Comment: 4 page
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
Quantum Dissension: Generalizing Quantum Discord for Three-Qubit States
We introduce the notion of quantum dissension for a three-qubit system as a
measure of quantum correlations. We use three equivalent expressions of
three-variable mutual information. Their differences can be zero classically
but not so in quantum domain. It generalizes the notion of quantum discord to a
multipartite system. There can be multiple definitions of the dissension
depending on the nature of projective measurements done on the subsystems. As
an illustration, we explore the consequences of these multiple definitions and
compare them for three-qubit pure and mixed GHZ and W states. We find that
unlike discord, dissension can be negative. This is because measurement on a
subsystem may enhance the correlations in the rest of the system. This approach
can pave a way to generalize the notion of quantum correlations in the
multiparticle setting.Comment: 9 pages 6 figures typo fixed and some arguments adde
Baryon and lepton number transport in electroweak phase transition
We consider the baryon number generation by charge transport mechanism in the
electroweak phase transition taking properly into account thermal fluxes
through the wall separating true and false vacuum in the spatial space. We show
that the diffusion from the true vacuum to the false one has a large
diminishing effect on the baryon number unless the wall velocity is near to,
but less than, the speed of sound in the medium and the ratio between the
collision rate and wall thickness is about 0.3. The maximum net baryon density
generated is , where is the entropy
density of the Universe. If the wall proceeds as a detonation, no baryon number
is produced.Comment: 13 pages + 2 figures available on request, HU-TFT-94-15, TURKU-FL-P1
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