Search results for "Tunnelling"
showing 10 items of 218 documents
Coherent Spin Dependent Landau-Zener Tunneling in Mixed Valence Dimers
2011
In this contribution we introduce the concept of single molecule ferroelectric based on the vibronic pseudo Jahn-Teller model of mixed valence dimeric clusters belonging to the Robin and Day class II compounds. We elucidate the main factors controlling the nonadiabatic Landau-Zener tunneling between the low lying vibronic levels induced by a pulse of the electric field. The transition probabilities are shown to be dependent on the both time of the pulse and the total spin of the cluster. A possibility to control the spin-dependent Landau-Zener tunneling by applying a static magnetic field is discussed.
Resonant Tunneling in 2D Waveguides in Magnetic Field
2021
Chapter 7 presents an asymptotic and numerical studies of resonant tunneling in a two-dimensional waveguide with two-narrows in magnetic field. It is supposed that the electron energy is between the first and the second thresholds.
Quantum dot state initialization by control of tunneling rates
2019
We study the loading of electrons into a quantum dot with dynamically controlled tunnel barriers. We introduce a method to measure tunneling rates for individual discrete states and to identify their relaxation paths. Exponential selectivity of the tunnel coupling enables loading into specific quantum dot states by tuning independently energy and rates. While for the single-electron case orbital relaxation leads to fast transition into the ground state, for electron pairs triplet-to-singlet relaxation is suppressed by long spin-flip times. This enables the fast gate-controlled initialization of either a singlet or a triplet electron pair state in a quantum dot with broad potential applicati…
Arrays of normal metal tunnel junctions in weak Coulomb blockade regime
1995
Universal features of I–V characteristics of one‐dimensional arrays of normal metal tunnel junctions have been tested against inhomogenities in the junction parameters, number of junctions in the array, and magnetic field. We find that the differential conductance versus bias voltage obeys the analytic form to within 1% if the fabrication errors are smaller than 10% in junction areas, and if the array has more than ten junctions. Furthermore, the universal relation is insensitive to magnetic field at least up to 8 T.
Control of Localization and Suppression of Tunneling by Adiabatic Passage
2004
We show that a field of frequency $\ensuremath{\omega}$ combined with its second harmonic $2\ensuremath{\omega}$ driving a double-well potential allows us to localize the wave packet by adiabatic passage, starting from the delocalized ground state. The relative phase of the fields allows us to choose the well of localization. We can suppress (and restore) the tunneling subsequently by switching on (and off) abruptly the fields at well-defined times. The mechanism relies on the fact that the dynamics is driven to an eigenstate of the Floquet Hamiltonian which is a localized state.
Probing High Frequency Noise with Macroscopic Resonant Tunneling
2011
We have developed a method for extracting the high-frequency noise spectral density of an rf-SQUID flux qubit from macroscopic resonant tunneling (MRT) rate measurements. The extracted noise spectral density is consistent with that of an ohmic environment up to frequencies $~$4 GHz. We have also derived an expression for the MRT line shape expected for a noise spectral density consisting of such a broadband ohmic component and an additional strongly peaked low-frequency component. This hybrid model provides an excellent fit to experimental data across a range of tunneling amplitudes and temperatures.
The Holographic Interpretation of Hawking Radiation
2007
Holography gives us a tool to view the Hawking effect from a new, classical perspective. In the context of Randall-Sundrum braneworld models, we show that the basic features of four-dimensional evaporating solutions are nicely translated into classical five-dimensional language. This includes the dual bulk description of particles tunneling through the horizon.
On cosmic quantum tunneling from “nothing”
2015
We extend to a general Λ-Eriedmann-Lemaitre-Robertson-Walker (ΛFLRW) a previous result by Vilenkin and others according to which a closed de Sitter universe could be created from "nothing". More specifically, our main result is that only the closed ΛFLRW universe (but not the open and flat ones) could be created from a corresponding instanton, that is, from the corresponding solution with signature +4 of the Einstein field equations. Before getting this result the suitable corresponding instantons are calculated. The result is in accordance with previous results by another authors obtained by different methods.
Behaviour of Interacting Protons: The Average-Mass Approach to its Study and its Possible Biological Relevance
1973
Among all other kinds of ions occurring in the solid, liquid and living states of matter, positive hydrogen ions (which we shall henceforth call protons for brevity) are singled out by their exceptionally small mass. This is the reason for their specific property of tunnelling through potential barriers, which in turn is responsible for such properties as hydrogen bonding. This is also responsible for the unique properties exhibited in many cases by (sub)systems of interacting protons. Examples are the intriguing properties of liquid water and ice [1]; the para-ferroelectric transition in hydrogen-bonded ferroelectrics [2]; the cooperative transitions in ammonium salts [3] and in hexamine h…
Photodetachment o F- by a few-cycle circularly polarized laser field
2009
We report on calculations of the above threshold detachment of F(-) by a few-cycle circularly polarized laser field, discussing the effects of both the carrier-envelope relative phase and the number of the cycle contained in a pulse on the angular distribution of ejected photoelectron. The results are analyzed in terms of a two-step semiclassical model: after the electrons are detached through tunnelling their motion is determined by the electric field pulse according to the classical dynamics laws. Anisotropies in the angular distributions of the electrons ejected on the plane perpendicular to the laser propagation direction are found that depend on the number of cycle of the laser pulse.