397 research outputs found
Entanglement and criticality in translational invariant harmonic lattice systems with finite-range interactions
We discuss the relation between entanglement and criticality in
translationally invariant harmonic lattice systems with non-randon,
finite-range interactions. We show that the criticality of the system as well
as validity or break-down of the entanglement area law are solely determined by
the analytic properties of the spectral function of the oscillator system,
which can easily be computed. In particular for finite-range couplings we find
a one-to-one correspondence between an area-law scaling of the bi-partite
entanglement and a finite correlation length. This relation is strict in the
one-dimensional case and there is strog evidence for the multi-dimensional
case. We also discuss generalizations to couplings with infinite range.
Finally, to illustrate our results, a specific 1D example with nearest and
next-nearest neighbor coupling is analyzed.Comment: 4 pages, one figure, revised versio
Non-ionizing radiation hardness of CMOS Monolithic Active Pixel Sensors manufactured in a 0.18m CMOS process
Resonance-like piezoelectric electron-phonon interaction in layered structures
We show that mismatch of the piezoelectric parameters between layers of
multiple-quantum well structures leads to modification of the electron-phonon
interaction. In particular, short-wavelength phonons propagating perpendicular
to the layers with wavevector close to , where is the period of
the structure, induce a strong smoothly-varying component of the
piezo-potential. As a result, they interact efficiently with 2D electrons. It
is shown, that this property leads to emission of collimated
quasi-monochromatic beams of high-frequency acoustic phonons from hot electrons
in multiple-quantum well structures. We argue that this effect is responsible
for the recently reported monochromatic transverse phonon emission from
optically excited GaAs/AlAs superlattices, and provide additional experimental
evidences of this.Comment: 6 pages, 7 figure
Weighted complex projective 2-designs from bases: optimal state determination by orthogonal measurements
We introduce the problem of constructing weighted complex projective
2-designs from the union of a family of orthonormal bases. If the weight
remains constant across elements of the same basis, then such designs can be
interpreted as generalizations of complete sets of mutually unbiased bases,
being equivalent whenever the design is composed of d+1 bases in dimension d.
We show that, for the purpose of quantum state determination, these designs
specify an optimal collection of orthogonal measurements. Using highly
nonlinear functions on abelian groups, we construct explicit examples from d+2
orthonormal bases whenever d+1 is a prime power, covering dimensions d=6, 10,
and 12, for example, where no complete sets of mutually unbiased bases have
thus far been found.Comment: 28 pages, to appear in J. Math. Phy
Electron-phonon interaction via Pekar mechanism in nanostructures
We consider an electron-acoustic phonon coupling mechanism associated with
the dependence of crystal dielectric permittivity on the strain (the so-called
Pekar mechanism) in nanostructures characterized by strong confining electric
fields. The efficiency of Pekar coupling is a function of both the absolute
value and the spatial distribution of the electric field. It is demonstrated
that this mechanism exhibits a phonon wavevector dependence similar to that of
piezoelectricity and must be taken into account for electron transport
calculations in an extended field distribution. In particular, we analyze the
role of Pekar coupling in energy relaxation in silicon inversion layers.
Comparison with the recent experimental results is provided to illustrate its
potential significance
Phonon spectroscopy with chirped shear and compressive acoustic pulses
Picosecond duration compressive and shear phonon wave packets injected into (311) GaAs slabs transform after propagation through ∼1  mm into chirped acoustic pulses with a frequency increasing in time due to phonon dispersion. By probing the temporal optical response to coherent phonons in a near surface layer of the GaAs slab, we show that phonon chirping opens a transformational route for high-sensitivity terahertz and subterahertz phonon spectroscopy. Temporal gating of the chirped phonon pulse allows the selection of a narrow band phonon spectrum with a central frequency up to 0.4 THz for longitudinal and 0.2 THz for transverse phonons
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