8,184 research outputs found
Classification of Symmetry-Protected Phases for Interacting Fermions in Two Dimensions
Recently, it has been shown that two-dimensional bosonic symmetry-protected
topological(SPT) phases with on-site unitary symmetry can be completely
classified by the group cohomology class . Later, group
super-cohomology class was proposed as a partial classification for SPT phases
of interacting fermions. In this work, we revisit this problem based on the
mathematical framework of -extension of unitary braided tensor
category(UBTC) theory. We first reproduce the partial classifications given by
group super-cohomology, then we show that with an additional structure, a complete classification of SPT phases for
two-dimensional interacting fermion systems for a total symmetry group
can be achieved. We also discuss the classification of
interacting fermionic SPT phases protected by time-reversal symmetry.Comment: references added; published versio
Enhanced mechanical strength and ductility of metal-repaired defective carbon nanotubes : a density functional study
Author name used in this publication: G. P. Zheng2007-2008 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe
Continuous-variable controlled-Z gate using an atomic ensemble
The continuous-variable controlled-Z gate is a canonical two-mode gate for
universal continuous-variable quantum computation. It is considered as one of
the most fundamental continuous-variable quantum gates. Here we present a
scheme for realizing continuous-variable controlled-Z gate between two optical
beams using an atomic ensemble. The gate is performed by simply sending the two
beams propagating in two orthogonal directions twice through a spin-squeezed
atomic medium. Its fidelity can run up to one if the input atomic state is
infinitely squeezed. Considering the noise effects due to atomic decoherence
and light losses, we show that the observed fidelities of the scheme are still
quite high within presently available techniques.Comment: 7 pages, 3 figures, to appear in Physical Review
Extrinsic and Intrinsic Nonlinear Hall Effects across Berry-Dipole Transitions
Three-dimensional Hopf insulators are a class of topological phases beyond
the tenfold-way classification. The critical point separating two
rotation-invariant Hopf insulator phases with distinct Hopf invariants is quite
different from the usual Dirac-type or Weyl-type critical points and uniquely
characterized by a quantized Berry dipole. Close to such Berry-dipole
transitions, we find that the extrinsic and intrinsic nonlinear Hall
conductivity tensors in the weakly doped regime are characterized by two
universal functions of the ratio between doping level and bulk energy gap, and
are directly proportional to the change in Hopf invariant across the
transition. Our work suggests that the nonlinear Hall effects display a
general-sense quantized behavior across Berry-dipole transitions, establishing
a correspondence between nonlinear Hall effects and Hopf invariant.Comment: 6 page
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