17,727 research outputs found
Correspondence between continuous variable and discrete quantum systems of arbitrary dimensions
We establish a mapping between a continuous variable (CV) quantum system and
a discrete quantum system of arbitrary dimension. This opens up the general
possibility to perform any quantum information task with a CV system as if it
were a discrete system of arbitrary dimension. The Einstein-Podolsky-Rosen
state is mapped onto the maximally entangled state in any finite dimensional
Hilbert space and thus can be considered as a universal resource of
entanglement. As an explicit example of the formalism a two-mode CV entangled
state is mapped onto a two-qutrit entangled state.Comment: 4 pages, 1 figure, revised version, an example adde
Inferring effective interactions from the local density of states: application to STM data from BiSrCaCuO
While the influence of impurities on the local density of states (LDOS) in a
metal is notoriously non-local due to interference effects, low order moments
of the LDOS in general can be shown to depend only on the local structure of
the Hamiltonian. Specifically, we show that an analysis of the spatial
variations of these moments permits one to ``work backwards'' from scanning
tunneling microscopy (STM) data to infer the local structure of the underlying
effective Hamiltonian. Applying this analysis to STM data from the high
temperature superconductor, BiSrCaCuO, we find that
the variations of the electro-chemical potential are remarkably small (i.e.,
the disorder is, in a sense, weak) but that there are large variations in the
local magnitude of the d-wave gap parameter.Comment: 7 pages, 7 figure
Simple Scheme for Efficient Linear Optics Quantum Gates
We describe the construction of a conditional quantum control-not (CNOT) gate
from linear optical elements following the program of Knill, Laflamme and
Milburn [Nature {\bf 409}, 46 (2001)]. We show that the basic operation of this
gate can be tested using current technology. We then simplify the scheme
significantly.Comment: Problems with PDF figures correcte
Board interlocks and the diffusion of disclosure policy
We examine whether board connections through shared directors influence firm disclosure policies. To overcome endogeneity challenges, we focus on an event that represents a significant change in firm disclosure policy: the cessation of quarterly earnings guidance. Our research design allows us to exploit the timing of director interlocks and therefore differentiate the director interlock effect on disclosure policy contagion from alternative explanations, such as endogenous director-firm matching or strategic board stacking. We find that firms are more likely to stop providing quarterly earnings guidance if they share directors with previous guidance stoppers. We also find that director-specific experience from prior guidance cessations matters for disclosure policy contagion. The positive effect of interlocked directors on the likelihood of quarterly earnings guidance cessation is particularly strong for firms with interlocked directors who experienced positive outcomes from prior guidance cessation decisions. Overall, our evidence is consistent with interlocked directors serving as conduits for information sharing that leads to the spread of corporate disclosure policies
Band theory in the context of the Hamilton-Jacobi formulation
In the one-dimensional periodic potential case, we formulate the condition of
Bloch periodicity for the reduced action by using the relation between the wave
function and the reduced action established in the context of the equivalence
postulate of quantum mechanics. Then, without appealing to the wave function
properties, we reproduce the well-known dispersion relations which predict the
band structure for the energy spectrum in the Kr\"onig-Penney model.Comment: 10 pages, no figure
Quasiparticle spectroscopy and high-field phase diagrams of cuprate superconductors -- An investigation of competing orders and quantum criticality
We present scanning tunneling spectroscopic and high-field thermodynamic
studies of hole- and electron-doped (p- and n-type) cuprate superconductors.
Our experimental results are consistent with the notion that the ground state
of cuprates is in proximity to a quantum critical point (QCP) that separates a
pure superconducting (SC) phase from a phase comprised of coexisting SC and a
competing order, and the competing order is likely a spin-density wave (SDW).
The effect of applied magnetic field, tunneling current, and disorder on the
revelation of competing orders and on the low-energy excitations of the
cuprates is discussed.Comment: 10 pages, 5 figures. Accepted for publication in the International
Journal of Modern Physics B. (Correspondence author: Nai-Chang Yeh, e-mail:
[email protected]
Raman spectroscopy of InN films grown on Si
We have used Raman spectroscopy to study indium nitride thin films grown by
molecular beam epitaxy on (111) silicon substrates at temperatures between 450
and 550 C. The Raman spectra show well defined peaks at 443, 475, 491, and 591
cm{-1}, which correspond to the A_1(TO), E_1(TO), E_2^{high}, and A_1(LO)
phonons of the wurtzite structure, respectively. In backscattering normal to
the surface the A_1(TO) and E_1(TO) peaks are very weak, indicating that the
films grow along the hexagonal c axis. The dependence of the peak width on
growth temperature reveals that the optimum temperature is 500 C, for which the
fullwidth of the E_2^{high} peak has the minimum value of 7 cm{-1}. This small
value, comparable to previous results for InN films grown on sapphire, is
evidence of the good crystallinity of the films.Comment: 3 pages, 1 eps figure, RevTe
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