Atomic switches: atomic-movement-controlled nanodevices for new types of computing

Abstract

Atomic switches are nanoionic devices that control the diffusion of metal cations and their reduction/oxidation processes in the switching operation to form/annihilate a metal atomic bridge, which is a conductive path between two electrodes in the on-state. In contrast to conventional semiconductor devices, atomic switches can provide a highly conductive channel even if their size is of nanometer order. In addition to their small size and low on-resistance, their nonvolatility has enabled the development of new types of programmable devices, which may achieve all the required functions on a single chip. Three-terminal atomic switches have also been developed, in which the formation and annihilation of a metal atomic bridge between a source electrode and a drain electrode are controlled by a third (gate) electrode. Three-terminal atomic switches are expected to enhance the development of new types of logic circuits, such as nonvolatile logic. The recent development of atomic switches that use a metal oxide as the ionic conductive material has enabled the integration of atomic switches with complementary metal-oxide-semiconductor (CMOS) devices, which will facilitate the commercialization of atomic switches. The novel characteristics of atomic switches, such as their learning and photosensing abilities, are also introduced in the latter part of this review.     

N-level Atom Interacting with Single-mode Radiation Field: An Exactly Solvable Model with Multiphoton Transitions and Intensity-dependent Coupling

Abstract

We study the dynamics of an N-level atom coupled in a lossless cavity to a single-mode near-resonant quantized field. The atomic levels are coupled by the multiphoton transitions and the coupling constants between the field and the atomic levels are supposed to be intensity dependent. We find the exact solution for the state vector describing the dynamics of the atom-plus-field system. As an illustration we use the model for studying (i) the time evolution of the atomic occupation probability with the initially coherent field and (ii) the light squeezing, when the cavity field is initially in the vacuum state and the atom is prepared in the atomic ‘coherent state’ (a superposition of atomic states).     

Highly Excited Hydrogen in Strong D.C. Electric Fields: Atomic Engineering

Abstract

We excite atomic hydrogen from the ground state via a three-photon process to high-lying excited states in the presence of strong d.c. electric fields. The external field is used to manipulate, control, and design specific atomic structures. We can construct nearly ‘one-dimensional’ atoms whose electronic distributions are highly extended along the field, and which may have enormous electric dipole moments (‘giant-dipole atoms’).     

Influence of inhomogeneous broadening on group velocity in coherently pumped atomic vapour

Abstract

We studied experimentally the influence of thermal atomic motion on light propagation in a vacuum atomic vapour cell above room temperature. We found that atomic motion introduces sizable changes in the spectral properties of the medium, such as dispersion and absorption, if the conditions for coherent population trapping are fulfilled. In particular, studying the group delay of light in the atomic vapour, we confirm the theoretical predictions of Kocharovskaya et al. (2001, Phys. Rev. Lett., 86, 628) and demonstrate that a coherent atomic medium has light dragging abilities large enough to make feasible the realization of frozen light based on atomic motion. We also demonstrate that dragging can be observed in measurements of the electromagnetically induced transparency resonance width, as well as in group delay measurements.     

General formalism of interaction of a three-level atom with cavity fields in the Kerr-like medium

Abstract

A general formalism of a three-level atom interacting with one-mode or two-mode cavity fields in a Kerr-like medium is presented. Dynamic behaviours of the atomic occupation probabilities and the transfer phenomena are investigated numerically in two typical cases. Our results show that the transfer phenomena may depend on the initial conditions.     

Generalized Bloch-Siegert Shift in a Squeezed Vacuum

Abstract

The time evolution of the atomic dipole moment of a two-level atom damped by an off-resonance squeezed vacuum is studied. Our results are valid for arbitrary detuning between the carrier frequency of the squeezed vacuum and the atomic transition frequency and show that the atomic dipole moment can oscillate with two dominant frequencies. These frequencies are shifted from their central values by an amount which is proportional to the degree of squeezing. We show that this shift of the frequencies is the exact equivalent of the optical Bloch-Siegert shift in the case of the ordinary vacuum damping without the rotating-wave approximation.     

On the Global Efficiency of the Laser Optical Excitation of a Fast Atomic Beam

Abstract

The interaction of a fast atomic beam and a laser beam that crosses at right angles has been considered. We have studied the competition between the Doppler effect, due to the angular divergence of the atomic beam and the effect of the laser light intensity distribution. For low laser power values, an optimum waist size can be determined. For higher laser power values, the conditions for a maximum global efficiency are outlined.     

The Effect of Continuum-continuum Transitions on Laser-induced Continuum Structures

Abstract

Laser induced continuum structures (LICS) can be produced by a strong laser embedding an excited atomic bound state into a flat atomic continuum, leading to a tunable resonance of adjustable width that can be probed by a second laser. If this second laser is of similar intensity to the embedding laser then the distinction between the two becomes artificial and saturation effects become important. In this paper the effect on LICS of transitions caused by both lasers between the original atomic continuum and a second atomic continuum are studied in the Markoff approximation by means of Laplace transform methods and allowing for the ionization of each atomic state by both laser fields. Formal results correct to all orders are also given in terms of a T-matrix approach. Numerical calculations are presented showing the effects on the LICS resonant structures of continuum-continuum coupling processes. Significant changes to the Fano profiles (second laser weak) and to coherence holes (second laser strong) occur. Analytical results are also given.     

Cavity field spectrum for multiphoton Jaynes-Cummings model

Abstract

The field spectra in an ideal cavity for the multiphoton Jaynes-Cummings model are studied. The analytical expression for the spectrum is obtained from the finite double-Fourier transform of the two-time field correlation function. The spectral differences between the initial coherent and initial thermal states are discussed, and the comparisons between the field spectra and atomic emission spectra for k = 2, 3 and 4 are presented. It is shown that the kth power of the photon annihilation operator and atomic lowering operator are subjected to identical forms of a second-order differential equation, in which the coefficients consist of the constants of motion. The field spectrum in the cavity and the emission spectrum of the atom for the initial vacuum state are compared.     

Equivalence of interaction hamiltonians in the electric dipole approximation

Abstract

The interaction of an atomic system with an externally applied electromagnetic field can be treated in the electric dipole approximation by means of either the minimal coupling (p · A) or direct coupling (d · E) Hamiltonian. It is shown that both methods lead to identical and unambiguous predictions for observable quantities as long as the atomic wavefunctions are transformed when used in the minimal-coupling formulation. The physical meaning of kinetic momentum is used to show that the atomic states must be described by wavefunctions calculated in the absence of an electromagnetic field when using the d · E (but not the p · A) form of the interaction Hamiltonian. When, however, observables are calculated using the common approximations of resonance atomic physics – the two-level approximation and the rotatingwave approximation – the two formulations can lead to measurably different results. This point is illustrated by calculating the induced polarization (and hence the refractive index) of an atomic system for the two exactly soluble cases of the harmonic oscillator and the hydrogen atom.     

Spontaneous emission of a driven five-level atom in a defective photonic crystal

Abstract

The free space spontaneous emission spectra of a driven five-level atom embedded in a defective double-band photonic band-gap material are investigated. The effect of quantum interference on the spontaneous emission spectra and its nature are discussed. It is shown that the nature of quantum interference in the presence of the driving field and defect mode may be destructive or constructive depending on the initial atomic coherency.     

Atomic motion in a standing-wave squeezed light field

Abstract

We investigate atomic motion in the standing-wave field of a cavity driven by coherent light plus broad-band-squeezed vacuum. We assume the bad-cavity limit and adiabatically eliminate the cavity mode, deriving a master equation for the atomic variables alone. From this master equation we study the (one-dimensional) atomic motion both in the semiclassical approximation and using quantum Monte Carlo wavefunction simulations. The light force and momentum diffusion are shown to be strongly dependent on the relative phase between the coherent and squeezed fields and, using a dressedstate analysis, we identify observable effects unique to the reduced quantum noise that characterizes squeezed-vacuum light.     

Possible Role Played by the Fullerene‐like Structures of Interstellar Carbon Dust in the Formation of Molecular Hydrogen in Space

Abstract

After a general introduction to the problem of formation of molecular hydrogen from atomic hydrogen in the interstellar medium and in the dense molecular clouds in particular, and after the explanation of the key role played by the surfaces on this process, it is proposed that the most suitable carbon surface for the formation of molecular hydrogen (from the radiative association process of atomic hydrogen) can be represented by carbon black rather than by graphite. Furthermore, it is proposed that the fullerene‐like structures present in the carbon black graphene sheets are the reaction sites where molecular hydrogen may be formed.     

Quantum effects in the transient dynamics of a many mode Jaynes-Cummings model

Abstract

Phenomenology and mechanisms of energy exchange, due to induced atomic processes of absorption and emission, are investigated in the evolution of a two-mode Jaynes-Cummings model. One field mode is initially in a highly coherent populated state and the other one is initially empty. The field mode exchanges energy with the atom by two mechanisms, related to very different atomic dynamics, which operate in complementary phases of the system evolution. One mechanism determines the energy exchanges which involve only the populated mode and the atom. The other is responsible for mode-mode photon exchanges and becomes relevant when the first mechanism is quenched. Thus there is no competition between the atomic emission in the empty mode and processes involving the atom and the highly populated mode. Quantum features related to entanglement of atom and field states are discussed. Cooperative effects between the two field modes and their incompatibility with the predictions of neo-classical theory are evidenced.     

Simple theory of microwave induced transparency in atomic and molecular systems

Abstract

In recent years the idea of electromagnetically induced transparency in atomic systems using a microwave coupling field has been discussed. We present theoretical work on how this may be achieved in both Doppler systems, and by extension in non-Doppler broadened systems. By considering the specific example of atomic rubidium we demonstrate the feasibility and practical difficulties of such an experiment. By considering systems with appropriate rotational-vibration structure we conclude that microwave induced transparency in gas vapours is more readily achievable in molecular systems.     

Initial peak on the time dependence of the heterogeneous recombination velocity of hydrogen atoms at the surface of phosphor crystals

The radical recombination luminescence of phosphor crystals in strong atomic fluxes was investigated. An initial emission intensity peak was observed whose amplitude depends on the magnitude of the atomic flux, the phosphor crystal temperature, and the interval between switching the atomic source off and on. Pis’ma Zh. Tekh. Fiz. 24, 54–59 (February 12, 1998)     

Atomic interference in the micromaser and statistical properties of the micromaser field

Abstract

In this paper we report on atomic interferometry in the micromaser. The atomic inversion is recorded while scanning the cavity frequency across the atomic resonance. For high pump rates, interference patterns are observed on the low-frequency wing of the maser line. The interferences are due to the non-adiabatic mixing of dressed states of the atoms at the entrance and exit holes of the maser cavity, leading to a Ramsey-type two-field interaction. Furthermore, statistical properties of the maser field are investigated via a measurement of the statistics of the pump atoms that leave the maser cavity. Theoretical expressions for the time dependence of the Fano–Mandel parameter Q _A(t) are compared with the experimental data. We demonstrate, that metastability of the maser field and atomic interference strongly influence the approach to a steady-state value of Q _A(t).     

Effects of Atomic Coherence on Collapses and Revivals in the Binomial State of the Field

Abstract

The effects of the coherence between the states of a two-level atom on the phenomenon of collapses and revivals in an undamped binomial state of the electromagnetic field are investigated. It is found that the Rabi oscillations exhibit qualitatively different behaviour for different phases of coherence between the levels. This behaviour in the binomial state of the field is in contrast with that in a coherent state field, in which case the Rabi oscillations are qualitatively the same for all values of the coherence between the two atomic levels.     

High order harmonic generation: The role of the acceleration matrix elements and of the bound and continuum transitions

Abstract

The electromagnetic spectrum emitted by a one-dimensional atom driven by a strong laser field is obtained by use of the acceleration form and interpreted by means of few general properties of the matrix elements of the acceleration operator. We show that the emission occurs essentially in a region near the atomic core where the acceleration is significant and we investigate the role of the various emission channels arising from interference effects between transitions involving the bare atomic levels.