Anomalous spreading of power-Law quantum wave packets

We introduce power-law tail quantum wave packets. We show that they can be seen as eigenfunctions of a Hamiltonian with a physical potential. We prove that the free evolution of these packets presents an asymptotic decay of the maximum of the wave packets which is anomalous for an interval of the characterizing power-law exponent. We also prove that the number of finite moments of the wave packets is a conserved quantity during the evolution of the wave packet in the free space.     

Transmission times of wave packets tunneling through barriers

The transmission of wave packets through barriers by tunneling is studied in detail by the method of quantum molecular dynamics. The distribution of the arrival times of a tunneling packet in front of and behind a barrier and the momentum distribution function of the packet are calculated. The average position and average momentum of the packet and their spread are investigated. It is found that below the barrier a part of the packet is reflected, and a Gaussian barrier increases the average momentum of the transmitted packet and its spread in momentum space. Zh. éksp. Teor. Fiz. 115, 1872–1889 (May 1999)     

Resonant tunneling of spin-wave packets via quantized states in potential wells

We have studied the tunneling of spin-wave pulses through a system of two closely situated potential barriers. The barriers represent two areas of inhomogeneity of the static magnetic field, where the existence of spin waves is forbidden. We show that for certain values of the spin-wave frequency corresponding to the quantized spin-wave states existing in the well formed between the barriers, the tunneling has a resonant character. As a result, transmission of spin-wave packets through the double-barrier structure is much more efficient than the sequent tunneling through two single barriers.     

Velocity and natural spreading of wave packets in mean fields

The propagation of quantum mechanical wave packets in a mean field is discussed and illustrated in one-dimensional models. Nonlocal as well as energy-dependent mean fields are considered. The group velocity and the rate of natural spreading are compared with those which correspond to the propagation in free space.     

Holography of wave packets

We describe the principles of holographic storage and reconstruction of ultrashort light pulses using spectrally nonselective media. This can be achieved by the application of a 3-D recording medium and by the holography of waves produced by spatial spectral decomposition of light pulses. We also describe various transformations of optical temporal signals based on holographic spectral filtering and nonlinear interaction of spectral decomposition waves.     

Resonant tunneling field-effect transistors

We report an experimental project to incorporate double-barrier tunnel structures into three-terminal devices. These devices have the negative-differential-resistance (NDR) features of the double barrier, and the added flexibility of a third controlling electrode. One way to make such a device involves the series combination of a double-barrier tunnel structure with a field-effect transistor. We have realized this concept in two types of devices, using samples grown by metalorganic chemical vapor deposition. The devices consist of a GaAsAl_xGa_1−xAs double-barrier tunneling heterostructure, the current through which is controlled by either an integrated vertical field-effect transistor or a planar metal-semiconductor field effect transistor. The voltage location and peak-to-valley current ratio of the NDR present in the source-drain circuit can be modulated with gate voltage. Experimental results for four samples are presented.     

Resonant tunneling properties of heterostructures

A general theory of resonance tunneling in planar structures, independent of the detailed form of the “well”, is developed. The transmission probability versus energy is Lorentzian, near each quasi-local level, with a width that is simply related to the lifetime for escape from the local state, the wave-packet transit time, and the dynamical response time. The charge-accumulation effect is estimated.     

Resonantly scattered wave packets

The effect of a resonant scattering on the shape of a (spherical) wave packet is investigated for the illustrative case of an incident packet Lorentzian in momentum. In the elastic case, packets both broader and narrower than the resonance are considered, and the relation of their time-delays to the Wigner-Eisenbud estimate elucidated. The effects on the elastically-scattered packet of (a) a double-pole resonance and (b) inelasticity are obtained as well.     

Resonant inversion of tunneling magnetoresistance

Resonant tunneling via localized states in the barrier can invert magnetoresistance in magnetic tunnel junctions. Experiments performed on electrodeposited Ni/NiO/Co nanojunctions of area smaller than 0.01 microm(2) show that both positive and negative values of magnetoresistance are possible. Calculations based on Landauer-Büttiker theory explain this behavior in terms of disorder-driven statistical variations in magnetoresistance with a finite probability of inversion due to resonant tunneling.     

Resonant tunneling through Andreev levels

We use a semiclassical approach for analyzing the tunneling transport through a normal conductor in contact with superconducting mirrors. Our analysis of the electron–hole propagation along semiclassical trajectories shows that resonant transmission through Andreev levels is possible resulting in an excess, low-energy quasiparticle contribution to the conductance. The excess conductance oscillates with the phase difference between the superconductors having maxima at odd multiples of π for temperatures much below the Thouless temperature.     

Resonant tunneling single electron transistors

We use a modulation-doped double barrier heterostructure to fabricate a resonant tunneling single electron transistor. Irregular Coulomb blockade oscillations are observed when the gate voltage is swept to vary one-by-one the number of electrons in the dot close to 'pinch-off'. The oscillation period is not regular, and generally becomes longer as the electron number is decreased down to zero, reflecting the growing importance of electron-electron interactions and size quantization. Negative differential resistance associated with resonant tunneling through zero-dimensional states is pronounced for a dot holding just a few electrons. The temperature dependence of the Coulomb blockade oscillations and that for the negative differential resistance are not the same. This highlights the different effects of charging and resonant tunneling on the transport characteristics.     

Resonant tunneling of illuminated multi-insulator diodes

The current–voltage (I–V) characteristics of two different Metal–Insulator–Metal (MIM) diodes with three insulator layers were calculated and compared. The effect of illumination, or the photon-assisted tunneling was considered with the Tien–Gordon model. Our calculations indicate that, by carefully designing the insulating layers of the MIM diodes, the resonant tunneling phenomena can be tuned effectively in the diodes with quantum well structures. The results also show that the minimum shift of the illuminated current depends not only on the intensity of the photons incident but also on the diode structures, or the parameters of the insulators and so on.     

Resonance-assisted decay of nondispersive wave packets

We present a quantitative semiclassical theory for the decay of nondispersive electronic wave packets in driven, ionizing Rydberg systems. Statistically robust quantities are extracted combining resonance-assisted tunneling with subsequent transport across chaotic phase space and a final ionization step.     

State reconstruction of one-dimensional wave packets

76 , 1985 (1996)] for quantum-state reconstruction of one-dimensional non-relativistic wave packets from position observations. We illuminate the theoretical background of the technique and show how to extend the procedure to the continuous part of the spectrum. Received: 7 July 1997     

Transverse compression of two-photon wave packets

A method for generating two-photon wave packets (biphotons) with a small width of the spatial intensity correlation function (correlation radius) has been considered. We propose to prepare a two-photon wave packet inhomogeneously broadened in the angle by means of spontaneous parametric down-conversion in an inhomogeneous crystal. Such biphotons are not diffraction limited; i.e., their correlation radius is much larger than the inverse width of the spatial spectrum. However, the correlation radius of such a biphoton decreases as the biphoton propagates in free space, and transverse compression occurs at a certain distance from the crystal; i.e., the biphoton becomes diffraction limited.     

On the theory of wave packets

In this paper we discuss some aspects of the theory of wave packets. We consider a popular noncovariant Gaussian model used in various applications and show that it predicts too slow a longitudinal dispersion rate for relativistic particles. We revise this approach by considering a covariant model of Gaussian wave packets, and examine our results by inspecting a wave packet of arbitrary form. A general formula for the time dependence of the dispersion of a wave packet of arbitrary form is found. Finally, we give a transparent interpretation of the disappearance of the wave function over time due to the dispersion—a feature often considered undesirable, but which is unavoidable for wave packets. We find, starting from simple examples, proceeding with their generalizations and finally by considering the continuity equation, that the integral over time of both the flux and probability densities are asymptotically proportional to the factor 1/|x|² in the rest frame of the wave packet, just as in the case of an ensemble of classical particles.