1,327 research outputs found
Voltage controlled nuclear polarization switching in a single InGaAs quantum dot
Sharp threshold-like transitions between two stable nuclear spin
polarizations are observed in optically pumped individual InGaAs self-assembled
quantum dots embedded in a Schottky diode when the bias applied to the diode is
tuned. The abrupt transitions lead to the switching of the Overhauser field in
the dot by up to 3 Tesla. The bias-dependent photoluminescence measurements
reveal the importance of the electron-tunneling-assisted nuclear spin pumping.
We also find evidence for the resonant LO-phonon-mediated electron
co-tunneling, the effect controlled by the applied bias and leading to the
reduction of the nuclear spin pumping rate.Comment: 5 pages, 2 figures, submitted to Phys Rev
Optimizing Replica Exchange Moves For Molecular Dynamics
In this short note we sketch the statistical physics framework of the replica
exchange technique when applied to molecular dynamics simulations. In
particular, we draw attention to generalized move sets that allow a variety of
optimizations as well as new applications of the method.Comment: 4 pages, 3 figures; revised version (1 figure added), PRE in pres
Fast preparation of single hole spin in InAs/GaAs quantum dot in Voigt geometry magnetic field
The preparation of a coherent heavy-hole spin via ionization of a
spin-polarized electron-hole pair in an InAs/GaAs quantum dot in a Voigt
geometry magnetic field is investigated. For a dot with a 17 ueV bright-exciton
fine-structure splitting, the fidelity of the spin preparation is limited to
0.75, with optimum preparation occurring when the effective fine-structure of
the bright-exciton matches the in-plane hole Zeeman energy. In principle,
higher fidelities can be achieved by minimizing the bright-exciton
fine-structure splitting.Comment: 8 pages, 10 figs, published PRB 85 155310 (2012
The new physics of non-equilibrium condensates: insights from classical dynamics
We discuss the dynamics of classical Dicke-type models, aiming to clarify the
mechanisms by which coherent states could develop in potentially
non-equilibrium systems such as semiconductor microcavities. We present
simulations of an undamped model which show spontaneous coherent states with
persistent oscillations in the magnitude of the order parameter. These states
are generalisations of superradiant ringing to the case of inhomogeneous
broadening. They correspond to the persistent gap oscillations proposed in
fermionic atomic condensates, and arise from a variety of initial conditions.
We show that introducing randomness into the couplings can suppress the
oscillations, leading to a limiting dynamics with a time-independent order
parameter. This demonstrates that non-equilibrium generalisations of polariton
condensates can be created even without dissipation. We explain the dynamical
origins of the coherence in terms of instabilities of the normal state, and
consider how it can additionally develop through scattering and dissipation.Comment: 10 pages, 4 figures, submitted for a special issue of J. Phys.:
Condensed Matter on "Optical coherence and collective phenomena in
nanostructures". v2: added discussion of links to exact solution
Fast optical preparation, control, and readout of a single quantum dot spin
We propose and demonstrate the sequential initialization, optical control, and readout of a single spin trapped in a semiconductor quantum dot. Hole spin preparation is achieved through ionization of a resonantly excited electron-hole pair. Optical control is observed as a coherent Rabi rotation between the hole and charged-exciton states, which is conditional on the initial hole spin state. The spin-selective creation of the charged exciton provides a photocurrent readout of the hole spin state. © 2008 The American Physical Society
Control of polarization and mode mapping of small volume high Q micropillars
We show that the polarization of the emission of a single quantum dot embedded within a microcavity pillar of elliptical cross section can be completely controlled and even switched between two orthogonal linear polarizations by changing the coupling of the dot emission with the polarized photonic modes. We also measure the spatial profle of the emission of a series of pillars with
different ellipticities and show that the results can be well described by simple theoretical modeling
of the modes of an infinite length elliptical cylinder
Stacked low-growth-rate InAs quantum dots studied at the atomic level by cross-sectional scanning tunneling microscopy
Continuous wave observation of massive polariton redistribution by stimulated scattering in semiconductor microcavities
A massive redistribution of the polariton occupancy to two specific wave vectors is observed under conditions of continuous wave excitation of a semiconductor microcavity.
The “condensation” of the polaritons to the two specific states arises from stimulated scattering at final
state occupancies of order unity. The stimulation phenomena, arising due to the bosonic character of
the polariton quasiparticles, occur for conditions of resonant excitation of the lower polariton branch.
High energy nonresonant excitation, as in most previous work, instead leads to conventional lasing in
the vertical cavity structure
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