77 research outputs found
Schrodinger cat animated on a quantum computer
We present a quantum algorithm which allows to simulate chaos-assisted
tunneling in deep semiclassical regime on existing quantum computers. This
opens new possibilities for investigation of macroscopic quantum tunneling and
realization of semiclassical Schr\"odinger cat oscillations. Our numerical
studies determine the decoherence rate induced by noisy gates for these
oscillations and propose a suitable parameter regime for their experimental
implementation.Comment: research at Quantware MIPS Center http://www.quantware.ups-tlse.fr ;
revtex, 4 pages, 4 figure
Floquet theory of microwave absorption by an impurity in two dimensional electron gas
We investigate the dynamics of a two-dimensional electron gas (2DEG) under
circular polarized microwave radiation in presence of dilute localized
impurities. Inspired by recent developments on Floquet topological insulators
we obtain the Floquet wavefunctions of this system which allow us to predict
the microwave absorption and charge density responses of the electron gas, we
demonstrate how these properties can be understood from the underlying
semiclassical dynamics even for impurities with a size of around a magnetic
length. The charge density response takes the form of a rotating charge density
vortex around the impurity that can lead to a significant renormalization of
the external microwave field which becomes strongly inhomogeneous on the scale
of a cyclotron radius around the impurity. We show that this in-homogeneity can
suppress the circular polarization dependence which is theoretically expected
for MIRO but which was not observed in MIRO experiments on semiconducting
2DEGs. Our explanation, for this so far unexplained polarization independence,
has close similarities with the Azbel'-Kaner effect in metals where the
interaction length between the microwave field and conduction electrons is much
smaller than the cyclotron radius due to skin effect generating harmonics of
the cyclotron resonance
Hall detection of time-reversal symmetry breaking under AC electric driv ing
In a four terminal sample microscopic time-reversibility leads to symmetry
relations between resistance measurements where the role of current and voltage
leads are exchanged. These reciprocity relations are a manifestation of general
Onsager-Casimir symmetries in equilibrium systems. We investigate
experimentally the validity of time reversal symmetry in a
Hall bar irradiated by an external AC field, at zero
magnetic field. For inhomogeneous AC fields we find strong deviations from
reciprocity relations and show that their origin can be understood from the the
billiard model of a Hall junction. Under homogeneous irradiation the symmetry
is more robust, indicating that time-reversal symmetry is preserved
Magnetization of ballistic quantum dots induced by a linear-polarized microwave field
On a basis of extensive analytical and numerical studies we show that a
linear-polarized microwave field creates a stationary magnetization in
mesoscopic ballistic quantum dots with two-dimensional electron gas being at a
thermal equilibrium. The magnetization is proportional to a number of electrons
in a dot and to a microwave power. Microwave fields of moderate strength create
in a one dot of few micron size a magnetization which is by few orders of
magnitude larger than a magnetization produced by persistent currents. The
effect is weakly dependent on temperature and can be observed with existing
experimental techniques. The parallels between this effect and ratchets in
asymmetric nanostructures are also discussed.Comment: 10 pages, 11 figs, research at http://www.quantware.ups-tlse.f
Synchronization theory of microwave induced zero-resistance states
We develop the synchronization theory of microwave induced zero-resistance
states (ZRS) for two-dimensional electron gas in a magnetic field. In this
theory the dissipative effects lead to synchronization of cyclotron phase with
driving microwave phase at certain resonant ratios between microwave and
cyclotron frequencies. This synchronization produces stabilization of electron
transport along edge channels and at the same time it gives suppression of
dissipative scattering on local impurities and dissipative conductivity in the
bulk, thus creating the ZRS phases at that frequency ratios. The electron
dynamics along edge and around circular disk impurity is well described by the
Chirikov standard map. The theoretical analysis is based on extensive numerical
simulations of classical electron transport in a strongly nonlinear regime. We
also discuss the value of activation energy obtained in our model and the
experimental signatures that could establish the synchronization origin of ZRS.Comment: revtex, 15 pages, 17 fig
Coupling between Rydberg states and Landau levels of electrons trapped on liquid helium
We investigate the coupling between Rydberg states of electrons trapped on a
liquid Helium surface and Landau levels induced by a perpendicular magnetic
field. We show that this realises a prototype quantum system equivalent to an
atom in a cavity, where their coupling strength can be tuned by a parallel
magnetic field. We determine experimentally the renormalisation of the atomic
transition energies induced by the coupling to the cavity, which can be seen as
an analogue of the Lamb shift. When the coupling is sufficiently strong the
transition between the ground and first excited Rydberg states splits into two
resonances corresponding to dressed states with vacuum and one photon in the
cavity. Our results are in quantitative agreement with the energy shifts
predicted by the effective atom in a cavity model where all parameters are
known with high accuracy
Strong screening in the plum pudding model
We study a generalized Thomson problem that appears in several condensed
matter settings: identical point-charge particles can penetrate inside a
homogeneously charged sphere, with global electro-neutrality. The emphasis is
on scaling laws at large Coulombic couplings, and deviations from mean-field
behaviour, by a combination of Monte Carlo simulations and an analytical
treatment within a quasi-localized charge approximation, which provides
reliable predictions. We also uncover a local overcharging phenomenon driven by
ionic correlations alone
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