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 $GaAs/Ga_{1-x}Al_xAs$ 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