On the possibility of observing nonadiabatic atomic transitions in a laser field and their application to nanolithography

The scheme of an experiment has been proposed to observe nonadiabatic atomic transitions in the standingwave laser field and splitting of atomic wave packets on the nodes of the standing wave induced by these transitions in a certain range of optical detuning. The effect can be implemented in atomic-optical nanolithography for making spatial atomic structures with a period much smaller than the optical wavelength.     

Quantum carpets woven by cold atoms in a laser field

Propagation of wave packets of cold two-level atoms in a standing-wave laser field can be interpreted in the dressed-state basis as motion in two optical potentials. The three distinct regimes of the wavepacket motion are specified by the ratio of the squared atom–laser detuning to the normalized Doppler shift. We calculate the momentum and position probability densities, which form patterns with minima and maxima of probability both in the momentum and the position spaces known as quantum carpets. At small and large detunings, the atomic motion is substantially adiabatic, and the quantum carpets have a simple form. At intermediate detunings, the wave packet moves nonadiabatically, splitting at each node of the standing wave, which causes a proliferation or branching of atomic trajectories with a single atom. Nonadiabatic transitions produce beautiful quantum carpets with a rich structure.     

Dynamics of spontaneous radiation of atoms scattered by a resonance standing light wave

The scattering of atoms by a resonance standing light wave is considered under conditions when the lower of two resonance levels is metastable, while the upper level rapidly decays due to mainly spontaneous radiative transitions to the nonresonance levels of an atom. The diffraction scattering regime is studied, when the Rabi frequency is sufficiently high and many diffraction maxima are formed due to scattering. The dynamics of spontaneous radiation of an atom is investigated. It is shown that scattering slows down substantially the radiative decay of the atom. The regions and characteristics of the power and exponential decay are determined. The adiabatic and nonadiabatic scattering regimes are studied. It is shown that the wave packets of atoms in the metastable and resonance excited states narrow down during scattering. A limiting (minimal) size of the wave packets is found, which is achieved upon nonadiabatic scattering in the case of a sufficiently long interaction time.     

Coherent transport of neutral atoms in spin-dependent optical lattice potentials

We demonstrate the controlled coherent transport and splitting of atomic wave packets in spin-dependent optical lattice potentials. Such experiments open intriguing possibilities for quantum state engineering of many body states. After first preparing localized atomic wave functions in an optical lattice through a Mott insulating phase, we place each atom in a superposition of two internal spin states. Then state selective optical potentials are used to split the wave function of a single atom and transport the corresponding wave packets in two opposite directions. Coherence between the wave packets of an atom delocalized over up to seven lattice sites is demonstrated.     

Proliferation of atomic wave packets at the nodes of a standing light wave

A quantum analysis is presented of the motion and internal state of a two-level atom in a strong standing-wave light field. Coherent evolution of the atomic wave-packet, atomic dipole moment, and population inversion strongly depends on the ratio between the detuning from atom-field resonance and a characteristic atomic frequency. In the basis of dressed states, atomic motion is represented as wave-packet motion in two effective optical potentials. At exact resonance, coherent population trapping is observed when an atom with zero momentum is centered at a standing-wave node. When the detuning is comparable to the characteristic atomic frequency, the atom crossing a node may or may not undergo a transition between the potentials with probabilities that are similar in order of magnitude. In this detuning range, atomic wave packets proliferate at the nodes of the standing wave. This phenomenon is interpreted as a quantum manifestation of chaotic transport of classical atoms observed in earlier studies. For a certain detuning range, there exists an interval of initial momentum values such that the atom simultaneously oscillates in an optical potential well and moves as a ballistic particle. This behavior of a wave packet is a quantum analog of a classical random walk of an atom, when it enters and leaves optical potential wells in a seemingly irregular manner and freely moves both ways in a periodic standing light wave. In a far-detuned field, the transition probability between the potentials is low, and adiabatic wave-packet evolution corresponding to regular classical motion of an atom is observed.     

Velocity selective trapping of atoms in a frequency-modulated laser field

The wavefunction of a moderately cold atom in a stationary near-resonant standing light wave delocalizes very fast due to wave packet splitting. However, we show that frequency modulation of the field may suppress packet splitting for some atoms having specific velocities in a narrow range. These atoms remain localized in a small space for a long time. We propose that in a real experiment with cold atomic gas this effect may decrease the velocity distribution of atoms (the field traps the atoms with such specific velocities while all other atoms leave the field).     

Coherent Interband and Intersubband Dynamics in Terahertz-Driven GaAs Quantum Wells

We theoretically investigate the optical absorption spectra and charge density by subjecting a GaAs quantum well to both an intense terahertz (THz)-frequency driving field and an optical pulse within the theory of density matrix. In presence of a strong THz field, the optical transitions in quantum well subbands are altered by the THz field. The alteration has a direct impact on the optical absorption and the charge density. The excitonic peak splitting and THz optical sideband in the absorption spectra show up when changing the THz field intensity and/or frequency. The Autler-Towns splitting is a result from the THz nonlinear dynamics of confined excitons. On the other hand, the carrier charge density is created as wave packets formed by coherent superposition of several eigenstates. The charge density exhibitsquantum beats for short pulses and/or wider wells and is modulated by the THz field.     

Quantum memory based on optical subradiance: Optimization of the signal-to-noise ratio

A scheme for creating subradiant states in an extended system of atoms, based on the use of an external inhomogeneous electric field, is proposed. It is shown that the maximum signal-to-noise ratio at the output of a quantum memory device using such subradiant states for data storage is obtained when the temporal shape of recorded single-photon wave packets (quantum information carriers) is a time-reversed pulse characteristic of a resonant atomic system. In this case, the quantum memory efficiency tends to unity in the limit of large optical thickness of the resonant medium.     

Controlled splitting of an atomic wave packet

We propose a simple scheme capable of adiabatically splitting an atomic wave packet using two independent translating traps. Implemented with optical dipole traps, our scheme allows a high degree of flexibility for atom interferometry arrangements and highlights its potential as an efficient and high fidelity atom optical beam splitter.     

Observation of nonspreading wave packets in an imaginary potential

We propose and experimentally demonstrate a method to prepare a nonspreading atomic wave packet. Our technique relies on a spatially modulated absorption constantly chiseling away from an initially broad de Broglie wave. The resulting contraction is balanced by dispersion due to Heisenberg's uncertainty principle. This quantum evolution results in the formation of a nonspreading wave packet of Gaussian form with a spatially quadratic phase. Experimentally, we confirm these predictions by observing the evolution of the momentum distribution. Moreover, by employing interferometric techniques, we measure the predicted quadratic phase across the wave packet. Nonspreading wave packets of this kind also exist in two space dimensions and we can control their amplitude and phase using optical elements.     

沟道效应作用下中性原子在激光驻波场中的沉积特性研究

基于半经典理论,建立了中性原子与激光驻波场相互作用的模型,分析了中性原子在激光驻波场沟道效应作用下运动轨迹及沉积特性,探讨了球差、色差和原子束发散角对沉积条纹的影响. 得到了上述三种影响因素下纳米光栅的半高宽分别为0.532,12.16,96.70 nm. 仿真结果表明,随着原子束发散角度的增加,沉积条纹的对比度将会下降,当原子束发散角分别为0.1 mard时,其对比度为85.2：1,发散角为0.3 mrad时,条纹对比度为5.33：1,而当发散角增加至0.5 mrad以上时,沉积条纹将会出现分裂现象,导致条纹的恶化. 关键词： 激光驻波场 纳米光栅 沟道效应     

Storage of quantum optical information based on the intracavity polaritons under the Bose-Einstein condensation condition

The propagation of optical wave packets in the atomic medium that is placed inside the cavity is considered under the conditions for the strong coupling of atoms and the quantized field. Primary attention is paid to the mechanisms for the formation of coherent polaritons determined by the bound state of the optical field and atomic medium at the lower branch of the dispersion curves of these states. Significant variations (slowing) in the group velocity of the optical wave packets under quasi-condensation (or true condensation) conditions of polaritons are analyzed. An algorithm for the spatially distributed quantum recording, storage, and readout of the information related to the wave packet propagation is proposed.     

Dynamics of Electronic Rydberg Wave Packets in the Presence of Laser-induced Core Transitions

Recent theoretical work on the dynamics of electronic Rydberg wave packets under the influence of laser-induced core transitions is reviewed. The discussion focuses on the intricate interplay between laser-modified electron correlation effects, radiative damping by the ionic core and the time evolution of electronic Rydberg wave packets. Via the stimulated light force this interplay manifests itself also in the atomic center of mass motion. A unified theoretical framework is provided by combining methods of quantum defect theory, stochastic techniques and semiclassical path expansions.     

An Approach to Construct Wave Packets with Complete Classical-Quantum Correspondence in Non-relativistic Quantum Mechanics

We introduce a method to construct wave packets with complete classical and quantum correspondence in one-dimensional non-relativistic quantum mechanics. First, we consider two similar oscillators with equal total energy. In classical domain, we can easily solve this model and obtain the trajectories in the space of variables. This picture in the quantum level is equivalent with a hyperbolic partial differential equation which gives us a freedom for choosing the initial wave function and its initial slope. By taking advantage of this freedom, we propose a method to choose an appropriate initial condition which is independent from the form of the oscillators. We then construct the wave packets for some cases and show that these wave packets closely follow the whole classical trajectories and peak on them. Moreover, we use de-Broglie Bohm interpretation of quantum mechanics to quantify this correspondence and show that the resulting Bohmian trajectories are also in complete agreement with their classical counterparts.     

A nanofiber-based optical conveyor belt for cold atoms

We demonstrate optical transport of cold cesium atoms over millimeter-scale distances along an optical nanofiber. The atoms are trapped in a one-dimensional optical lattice formed by a two-color evanescent field surrounding the nanofiber, far red- and blue-detuned with respect to the atomic transition. The blue-detuned field is a propagating nanofiber-guided mode while the red-detuned field is a standing-wave mode which leads to the periodic axial confinement of the atoms. Here, this standing wave is used for transporting the atoms along the nanofiber by mutually detuning the two counter-propagating fields which form the standing wave. The performance and limitations of the nanofiber-based transport are evaluated and possible applications are discussed.     

The Sagnac effect: 20 years of development in matter-wave interferometry

Since the first atom interferometry experiments in 1991, measurements of rotation through the Sagnac effect in open-area atom interferometers have been investigated. These studies have demonstrated very high sensitivity that can compete with state-of-the-art optical Sagnac interferometers. Since the early 2000s, these developments have been motivated by possible applications in inertial guidance and geophysics. Most matter-wave interferometers that have been investigated since then are based on two-photon Raman transitions for the manipulation of atomic wave packets. Results from the two most studied configurations, a space-domain interferometer with atomic beams and a time-domain interferometer with cold atoms, are presented and compared. Finally, the latest generation of cold atom interferometers and their preliminary results are presented.     

Optical orientation by linearly polarized light in intersubband quantum-well transitions

The absorption of linearly polarized light in low-dimensional semiconductor structures is investigated. It is shown that the absorption under consideration can give rise to spin orientation of free carriers. A theory of this optical orientation by linearly polarized light is developed for resonant intersubband optical transitions in n-type quantum wells. It is demonstrated that, in the vicinity of the resonance, the optical orientation undergoes spectral inversion, namely, the electron spin orientation reverses sign with increasing frequency. This behavior can be accounted for by the spin-orbit subband splitting, which is linear in the wave vector, and by the energy and quasi-momentum conservation laws.     

Spin-charge separation in cold fermi gases: a real time analysis

Using the adaptive time-dependent density-matrix renormalization group method for the 1D Hubbard model, the splitting of local perturbations into separate wave packets carrying charge and spin is observed in real time. We show the robustness of this separation beyond the low-energy Luttinger liquid theory by studying the time evolution of single particle excitations and density wave packets. A striking signature of spin-charge separation is found in 1D cold Fermi gases in a harmonic trap at the boundary between liquid and Mott-insulating phases. We give quantitative estimates for an experimental observation of spin-charge separation in an array of atomic wires.     

运动三能级原子与驻波激光场斜交相互作用的理论分析

分析了一个运动的三能级原子与一个驻波激光场地斜交相互作用时的动量传递行为。结果表明，当原子和光场由于多普勒效应满足一定条件时，将产生受激拉曼跃迁。如果作用光相对于原子而言为一个“π／２脉冲”光时，那么经过作用后，原子将处于一个相干迭加态，其中一个态与加始相同。     

The effect of spin-orbit splitting on the valence band density of states of lead

Tight-binding calculations are reported for the valence bands of lead, with and without spin-orbit splitting in the 6p bands. The addition of spin-orbit interaction is necessary to reproduce the two-peaked structure in the 6p density of states observed in X-ray photoemission, in contrast to the assertion by Breeze that crystal-field effects alone are enough. The observed splitting is, however, only fortuitously nearly equal to the atomic spin-orbit splitting. The tight-binding band structure, with spin-orbit splitting, gives better overall agreement with optical, Fermi surface, and photoemission data than did any of the three earlier band structures.