605 research outputs found
Remote Macroscopic Entanglement on a Photonic Crystal Architecture
The outstanding progress in nanostructure fabrication and cooling
technologies allows what was unthinkable a few decades ago: bringing
single-mode mechanical vibrations to the quantum regime. The coupling between
photon and phonon excitations is a natural source of nonclassical states of
light and mechanical vibrations, and its study within the field of cavity
optomechanics is developing lightning-fast. Photonic crystal cavities are
highly integrable architectures that have demonstrated the strongest
optomechanical coupling to date, and should therefore play a central role for
such hybrid quantum state engineering. In this context, we propose a realistic
heralding protocol for the on-chip preparation of remotely entangled mechanical
states, relying on the state-of-the-art optomechanical parameters of a
silicon-based nanobeam structure. Pulsed sideband excitation of a Stokes
process, combined with single photon detection, allows writing a delocalised
mechanical Bell state in the system, signatures of which can then be read out
in the optical field. A measure of entanglement in this protocol is provided by
the visibility of a characteristic quantum interference pattern in the emitted
light.Comment: 8 pages, 5 Figure
Weak localization in macroscopically inhomogeneous two-dimensional systems: a simulation approach
A weak-localization effect has been studied in macroscopically inhomogeneous
2D system. It is shown, that although the real phase breaking length tends to
infinity when the temperature tends to zero, such a system can reveal a
saturated behavior of the temperature dependence of that parameter, which is
obtained from the standard analysis of the negative magnetoresistance and
usually identified by experimentalists with the phase braking length.Comment: 5 pages, 4 figure
Simple mechanisms that impede the Berry phase identification from magneto-oscillations
The phase of quantum magneto-oscillations is often associated with the Berry
phase and is widely used to argue in favor of topological nontriviality of the
system (Berry phase ). Nevertheless, the experimentally determined
value may deviate from arbitrarily, therefore more care should be
made analyzing the phase of magneto-oscillations to distinguish trivial systems
from nontrivial. In this paper we suggest two simple mechanisms dramatically
affecting the experimentally observed value of the phase in three-dimensional
topological insulators: (i) magnetic field dependence of the chemical
potential, and (ii) possible nonuniformity of the system. These mechanisms are
not limited to topological insulators and can be extended to other
topologically trivial and non-trivial systems.Comment: 9 pages, 4 figures, in published version the title was change
Interference quantum correction to conductivity of Al xGa 1-xAs/GaAs double quantum well heterostructures near the balance
We present the results of experimental investigations of the interference quantum correction to the conductivity of the gated double quantum well Al xGa 1-xAs/GaAs/Al xGa 1-xAs heterostructures. Analyzing the positive magnetoconductiv-ity we obtain the interwell transition rate and the phase relaxation rate under the conditions when one and two quantum wells are occupied. It has been found that the interwell transition rate resonantly depends on the difference between the electron densities in the wells in accordance with the theoretical estimate. The central point, however, is that the dephasing rate in the lower quantum well is independent of whether the upper quantum well contributes to the conductivity or not. The results obtained are interpreted within framework of the recent theory for the dephasing and electron-electron interaction in the double well structures [Burmistrov I S, Gornyi I V and Tikhonov K S 2011 Phys. Rev. B 84 075338]
Negative polarizability of 2D electrons in HgTe quantum well
The polarizability of electrons occupying the lowest subband of spatial
quantization in CdTe/CdHgTe/CdTe quantum wells is calculated. It is
shown that polarizability in the quantum well without cadmium is negative,
i.e., the displacement of an electron in an electric field applied
perpendicularly to the quantum well plane is opposite to the force acting on
it. The negative polarizability of 2D electrons can reduce the dielectric
constant of quantum wells by up to percent.Comment: 4 pages, 4 figure
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