1,891 research outputs found
Scalable solid-state quantum computation in decoherence-free subspaces with trapped ions
We propose a decoherence-free subspaces (DFS) scheme to realize scalable
quantum computation with trapped ions. The spin-dependent Coulomb interaction
is exploited, and the universal set of unconventional geometric quantum gates
is achieved in encoded subspaces that are immune from decoherence by collective
dephasing. The scalability of the scheme for the ion array system is
demonstrated, either by an adiabatic way of switching on and off the
interactions, or by a fast gate scheme with comprehensive DFS encoding and
noise decoupling techniques.Comment: 4 pages, 1 figur
Layer-by-layer nucleation mechanism for quantum dot formation in strained heteroepitaxy
2010-2011 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe
Effect of bilayer coupling on tunneling conductance of double-layer high T_c cuprates
Physical effects of bilayer coupling on the tunneling spectroscopy of high
T cuprates are investigated. The bilayer coupling separates the bonding
and antibonding bands and leads to a splitting of the coherence peaks in the
tunneling differential conductance. However, the coherence peak of the bonding
band is strongly suppressed and broadened by the particle-hole asymmetry in the
density of states and finite quasiparticle life-time, and is difficult to
resolve by experiments. This gives a qualitative account why the bilayer
splitting of the coherence peaks was not clearly observed in tunneling
measurements of double-layer high-T oxides.Comment: 4 pages, 3 figures, to be published in PR
Reply to "Comment on 'Fano resonance for Anderson Impurity Systems' "
In a recent Comment, Kolf et al. (cond-mat/0503669) state that our analysis
of the Fano resonance for Anderson impurity systems [Luo et al., Phys. Rev.
Lett 92, 256602 (2004)] is incorrect. Here we want to point out that their
comments are not based on firm physical results and their criticisms are
unjustified and invalid.Comment: 1 page, 1 figure, to appear in PR
The Structure on Invariant Measures of generic diffeomorphisms
Let be an isolated non-trival transitive set of a generic
diffeomorphism f\in\Diff(M). We show that the space of invariant measures
supported on coincides with the space of accumulation measures of
time averages on one orbit. Moreover, the set of points having this property is
residual in (which implies the set of irregular points is also
residual in ). As an application, we show that the non-uniform
hyperbolicity of irregular points in with totally 0 measure
(resp., the non-uniform hyperbolicity of a generic subset in )
determines the uniform hyperbolicity of
Absence of the zero bias peak in vortex tunneling spectra of high temperature superconductors?
The c-axis tunneling matrix of high-Tc superconductors is shown to depend
strongly on the in-plane momentum of electrons and vanish along the four nodal
lines of the d(x^2-y^2)-wave energy gap. This anisotropic tunneling matrix
suppresses completely the contribution of the most extended quasiparticles in
the vortex core to the c-axis tunneling current and leads to a spectrum similar
to that of a nodeless superconductor. Our results give a natural explanation of
the absence of the zero bias peak as well as other features observed in the
vortex tunneling spectra of high-Tc cuprates.Comment: 4 pages 3 figures, minor corrections, to appear in Phys Rev
Heralded Noiseless Amplification of a Photon Polarization Qubit
Non-deterministic noiseless amplification of a single mode can circumvent the
unique challenges to amplifying a quantum signal, such as the no-cloning
theorem, and the minimum noise cost for deterministic quantum state
amplification. However, existing devices are not suitable for amplifying the
fundamental optical quantum information carrier, a qubit coherently encoded
across two optical modes. Here, we construct a coherent two-mode amplifier, to
demonstrate the first heralded noiseless linear amplification of a qubit
encoded in the polarization state of a single photon. In doing so, we increase
the transmission fidelity of a realistic qubit channel by up to a factor of
five. Qubit amplifiers promise to extend the range of secure quantum
communication and other quantum information science and technology protocols.Comment: 6 pages, 3 figure
Noiseless Linear Amplification and Distillation of Entanglement
The idea of signal amplification is ubiquitous in the control of physical
systems, and the ultimate performance limit of amplifiers is set by quantum
physics. Increasing the amplitude of an unknown quantum optical field, or more
generally any harmonic oscillator state, must introduce noise. This linear
amplification noise prevents the perfect copying of the quantum state, enforces
quantum limits on communications and metrology, and is the physical mechanism
that prevents the increase of entanglement via local operations. It is known
that non-deterministic versions of ideal cloning and local entanglement
increase (distillation) are allowed, suggesting the possibility of
non-deterministic noiseless linear amplification. Here we introduce, and
experimentally demonstrate, such a noiseless linear amplifier for
continuous-variables states of the optical field, and use it to demonstrate
entanglement distillation of field-mode entanglement. This simple but powerful
circuit can form the basis of practical devices for enhancing quantum
technologies. The idea of noiseless amplification unifies approaches to cloning
and distillation, and will find applications in quantum metrology and
communications.Comment: Submitted 10 June 200
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