1,622 research outputs found
Anomalous Phase Shift of Quantum Oscillations in 3D Topological Semimetals
Berry phase physics is closely related to a number of topological states of
matter. Recently discovered topological semimetals are believed to host a
nontrivial Berry phase to induce a phase shift of in the
quantum oscillation ( for hole and for electron carriers). We
theoretically study the Shubnikov-de Haas oscillation of Weyl and Dirac
semimetals, taking into account their topological nature and inter-Landau band
scattering. For a Weyl semimetal with broken time-reversal symmetry, the phase
shift is found to change nonmonotonically and go beyond known values of and . For a Dirac semimetal or paramagnetic Weyl semimetal,
time-reversal symmetry leads to a discrete phase shift of or , as a function of the Fermi energy. Different from the previous works, we
find that the topological band inversion can lead to beating patterns in the
absence of Zeeman splitting. We also find the resistivity peaks should be
assigned integers in the Landau index plot. Our findings may account for recent
experiments in CdAs and should be helpful for exploring the Berry phase
in various 3D systems.Comment: 5 pages, 3 figures, with Supplemental Materia
Theory for high spin systems with orbital degeneracy
High-spin systems with orbital degeneracy are studied in the large spin
limit. In the absence of Hund's coupling, the classical spin model is mapped
onto disconnected orbital systems with spins up and down, respectively. The
ground state of the isotropic model is an orbital valence bond state where each
bond is an orbital singlet with parallel spins, and neighbouring bonds interact
antiferromagnetically. The possible relevance to the transition metal oxides
are discussed.Comment: 4 page, three figures, to appear in Phys. Rev. Let
Entanglement production and decoherence-free subspace of two single-mode cavities embedded in a common environment
A system consisting of two identical single-mode cavities coupled to a common
environment is investigated within the framework of algebraic dynamics. Based
on the left and right representations of the Heisenberg-Weyl algebra, the
algebraic structure of the master equation is explored and exact analytical
solutions of this system are obtained. It is shown that for such a system, the
environment can produce entanglement in contrast to its commonly believed role
of destroying entanglement. In addition, the collective zero-mode eigen
solutions of the system are found to be free of decoherence against the
dissipation of the environment. These decoherence-free states may be useful in
quantum information and quantum computation.Comment: 10 pages, 7 figures, Revtex
Tomography increases key rates of quantum-key-distribution protocols
We construct a practically implementable classical processing for the BB84
protocol and the six-state protocol that fully utilizes the accurate channel
estimation method, which is also known as the quantum tomography. Our proposed
processing yields at least as high key rate as the standard processing by Shor
and Preskill. We show two examples of quantum channels over which the key rate
of our proposed processing is strictly higher than the standard processing. In
the second example, the BB84 protocol with our proposed processing yields a
positive key rate even though the so-called error rate is higher than the 25%
limit.Comment: 13 pages, 1 figure, REVTeX4. To be published in PRA. Version 2 adds
many references, a closed form key rate formula for unital channels, and a
procedure for the maximum likelihood channel estimatio
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