43,430 research outputs found
Quantum tunneling through planar p-n junctions in HgTe quantum wells
We demonstrate that a p-n junction created electrically in HgTe quantum wells
with inverted band-structure exhibits interesting intraband and interband
tunneling processes. We find a perfect intraband transmission for electrons
injected perpendicularly to the interface of the p-n junction. The opacity and
transparency of electrons through the p-n junction can be tuned by changing the
incidence angle, the Fermi energy and the strength of the Rashba spin-orbit
interaction. The occurrence of a conductance plateau due to the formation of
topological edge states in a quasi-one-dimensional p-n junction can be switched
on and off by tuning the gate voltage. The spin orientation can be
substantially rotated when the samples exhibit a moderately strong Rashba
spin-orbit interaction.Comment: 4 pages, 4 figure
Metal-insulator transition in a multilayer system with a strong magnetic field
We study the Anderson localization in a weakly coupled multilayer system with
a strong magnetic field perpendicular to the layers. The phase diagram of 1/3
flux quanta per plaquette is obtained. The phase diagram shows that a
three-dimensional quantum Hall effect phase exists for a weak on-site disorder.
For intermediate disorder, the system has insulating and normal metallic phases
separated by a mobility edge. At an even larger disorder, all states are
localized and the system is an insulator. The critical exponent of the
localization length is found to be .Comment: Latex file, 3 figure
Continuous-Variable Quantum State Transfer with Partially Disembodied Transport
We propose a new protocol of implementing continuous-variable quantum state
transfer using partially disembodied transport. This protocol may improve the
fidelity at the expense of the introduction of a semi-quantum channel between
the parties, in comparison with quantum teleportation using the same strength
of entanglement. Depending on the amount of information destroyed in the
measurement, this protocol may be regarded as a teleportation protocol
(complete destruction of input state), or as a cloning protocol
(partial destruction), or as a direct transmission (no destruction). This
scheme can be straightforwardly implemented with the experimentally accessible
setup at present.Comment: 4 pages, to appear in Phys. Rev. Let
Tensor product representation of topological ordered phase: necessary symmetry conditions
The tensor product representation of quantum states leads to a promising
variational approach to study quantum phase and quantum phase transitions,
especially topological ordered phases which are impossible to handle with
conventional methods due to their long range entanglement. However, an
important issue arises when we use tensor product states (TPS) as variational
states to find the ground state of a Hamiltonian: can arbitrary variations in
the tensors that represent ground state of a Hamiltonian be induced by local
perturbations to the Hamiltonian? Starting from a tensor product state which is
the exact ground state of a Hamiltonian with topological order,
we show that, surprisingly, not all variations of the tensors correspond to the
variation of the ground state caused by local perturbations of the Hamiltonian.
Even in the absence of any symmetry requirement of the perturbed Hamiltonian,
one necessary condition for the variations of the tensors to be physical is
that they respect certain symmetry. We support this claim by
calculating explicitly the change in topological entanglement entropy with
different variations in the tensors. This finding will provide important
guidance to numerical variational study of topological phase and phase
transitions. It is also a crucial step in using TPS to study universal
properties of a quantum phase and its topological order.Comment: 10 pages, 6 figure
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