Optical size resonances in nanostructures

The existence of optical size resonances in atomic nanostructures is proved. The properties of optical size resonances strongly depend on the interatomic distances and on the polarization of an external radiation field. The properties of linear and nonlinear size resonances are considered in the case of two-dimensional nanostructures. The linear optical size resonances are described based on a closed system of equations for dipole oscillators and nonlocal field equations taking into account the dipole-dipole interactions of atoms in the radiation field. Using a stationary solution to these equations, it is demonstrated that two isotropic atoms with definite intrinsic frequencies form an anisotropic system in the radiation field, possessing two or four size resonances depending on whether the component atoms are identical or different. The nanostructure composed of two different atoms possesses two size resonances with positive dispersion and two other resonances with negative dispersion. The frequencies of the size resonances significantly differ from the intrinsic frequencies of isolated atoms entering into the nanostructure. By changing the angle of incidence of the external wave, it is possible to excite various size resonances. The properties of nonlinear optical size resonances excited by an intense radiation field were theoretically and numerically studied using the modified Bloch equations and nonlocal field equations. Dispersion relationships for the nonlinear resonances were derived and the inversion properties of atoms in the nanostructure were studied for various polarizations of the external optical wave.     

Optical holography of nanostructure diatomic objects for different polarizations of the external wave and dimensional resonances

For the combined system of equations of field and atomic variables for two different atoms in the ground state, a stationary solution is obtained, which takes into account their dipole-dipole interaction in the field of external emission. Atoms are treated as linear dipole oscillators with different natural frequencies and linear polarizabilities. Formulas for effective polarizabilities of atoms in a nanostructure object, whose dispersion properties substantially differ from the dispersion properties of isolated atoms in the region of their natural resonances, are obtained. It is found that a nanostructure object consisting of two different atoms has four dimensional resonances, whose frequencies strongly depend on the interatomic separation and the object orientation with respect to the direction of propagation of an external wave. Using interference from the coherent field of dipoles of a small object with a reference coherent wave in a certain plane of observation points in the wave region far from a small object, an optical hologram of a small object is obtained. It is shown by numerical experiments that a small object forms interference fringes with good contrast, which makes possible the use of optical quasi-resonant emission for the development of a nondestructive method of study of small objects.     

Dimensional Resonances in Biatomic Nanostructures and the Characteristics of Their Holograms

A self-consistent problem of determining the field at the location of atoms in a nanostructural object and also at different observation points beyond a group of atoms (a small object) in the wave and near zones is solved on the basis of a system of compatible equations for the light-wave electric field strength and optical equations for linear dipole oscillators. We proved the existence of two dimensional resonances in the nanostructural object that consists of two identical atoms, with each having a single isolated resonance. We show that the properties of dimensional resonances depend strongly on small displacements of atoms with respect to one another. Formulas are obtained for effective polarizabilities of atoms in the small object. Optical plane holograms of the small object were obtained by interference of the coherent field of the dipoles of the small object and of the reference coherent wave in a certain plane of observation points far from the small object in the wave zone at frequencies corresponding to dimensional resonances.     

Nonlinear steady-state sized resonances in diatomic nanostuctural objects

A new solution to modified Bloch equations for a diatomic quantum system consisting of two identical interacting atoms in a field of high-intensity continuous radiation is obtained. On the basis of this solution, the existence of nonlinear sized resonances whose properties strongly depend on the atomic spacing, on the polarization of the external field of radiation, and on the initial inversions of atoms constituting a nanostructural object is shown. Dispersion dependences of induced dipole moments and inversions of atoms of the object are investigated theoretically in the region of sized resonances for various irradiation conditions.     

On the capabilities of sub-Doppler photoionization spectroscopy in thin gas cells

A high-sensitivity photoionization method of registration of narrow sub-Doppler resonances in the spectral distribution of a flow of metastable atoms (or molecules) excited from the ground quantum term by a monochromatic laser beam propagating at normal incidence through an ultrathin gas cell (with a micrometer-scale or even nanoscale gas layer thickness) is proposed. Based on density matrix equations for atomic particles, various mechanisms of broadening of the considered resonances, such as time-of-flight, field, and Doppler broadening, are analyzed. The requirements for laser beam parameters and gas cell dimensions that allow obtaining the narrowest resonances are established. The proposed method can be used in ultrahigh resolution spectroscopy of atoms and molecules, as well as high-precision optical frequency standards.     

Dynamic control of light propagation and optical switching through an RF-driven cascade-type atomic medium

We study nonlinear optical behaviors in pulse propagation through a medium consisting of four-level cascade-type cold atoms, where a radio-frequency (RF) field couples upper two-folded levels and double-dark resonances (DDRs) can arise. By numerically solving the coupled Bloch-Maxwell equations for atom and field simultaneously in space and time, we demonstrate dynamic control of light propagation and optical switching in such a four-level atomic medium. The proposed scheme may have potential applications in the design of optical switching and optical storage devices.     

As much of cosmology as is possible

This article traces the development of optical pumping from the ideas first elaborated by Kastler in 1950. It deals with the general characteristics of optical pumping, the optical ‘magnetization’ of gases and vapours, spin exchange, metastability exchange, orientation by collision, multiple quantum resonances, atomic coherences, quantum beats, and dressed atoms: and concludes with a note on laser spectroscopy.     

Optical holography of diatomic small nanostructure objects and the near-field effect: Dimensional resonances at normal incidence of external optical radiation on a small object

The interaction of an atomic group occupying a volume with linear dimensions which are considerably smaller than the length of an external light wave is considered. On the basis of the joint set of equations for the electric field strength of the light wave and the optical equations for linear dipole oscillators, the self-consistent problem of determination of the field at the points of location of the atoms, as well as at different points of observation outside the atomic group (a small object) in the wave and near-field zones, is solved. An optical plane hologram of a small object is obtained by way of interference of the coherent field of dipoles of the object and a reference coherent wave in a certain plane of observation points far from the object in the wave zone. It is shown with the help of numerical experiments that a small object forms interference fringes with a good contrast, which allows one to use optical quasi-resonant emission for the development of a nondestructive method of investigation of small objects.     

Three-fermion problems in optical lattices

We present exact results for the spectra of three fermionic atoms in a single well of an optical lattice. For the three lowest hyperfine states of 6Li atoms, we find a Borromean state across the region of the distinct pairwise Feshbach resonances. For 40K atoms, nearby Feshbach resonances are known for two of the pairs, and a bound three-body state develops towards the positive scattering-length side. In addition, we study the sensitivity of our results to atomic details. The predicted few-body phenomena can be realized in optical lattices in the limit of low tunneling.     

Dipole emission of a nanostructure system composed of two atoms and dimensional resonances

A stationary solution is obtained for the joint system of equations for atomic and field variables for two different atoms with dipole-dipole interaction in the radiation field taking into account the common radiative friction. The atoms are treated as an Lorentz oscillator with one isolated resonance. The interaction of atoms in the radiation field forms four dimensional resonances at frequencies that are substantially different from the natural frequencies of isolated atoms. Two of the four dimensional resonances are characterized by negative dispersion, and the intensity of dipole emission at these frequencies may be increased with respect to the intensity of emission at the frequencies of natural atomic resonances by a factor of about 10¹².     

Dynamics of moving interacting atoms in a laser radiation field and optical size resonances

The forces acting on interacting moving atoms exposed to resonant laser radiation are calculated. It is shown that the forces acting on the atoms include the radiation pressure forces as well as the external and internal bias forces. The dependences of the forces on the atomic spacing, polarization, and laser radiation frequency are given. It is found that the internal bias force associated with the interaction of atomic dipoles via the reemitted field may play an important role in the dynamics of dense atomic ensembles in a light field. It is shown that optical size resonances appear in the system of interacting atoms at frequencies differing substantially from transition frequencies in the spectrum of atoms. It is noted that optical size resonances as well as the Doppler frequency shift in the spectrum of interacting atoms play a significant role in the processes of laser-radiation-controlled motion of the atoms.     

Sub-doppler absorption resonances induced in a gas cell by transverse optical pumping

New sub-Doppler resonances at central frequencies of atomic (molecular) transitions that appear in the spectrum of absorption of the probe optical radiation under the influence of optical pumping propagating in the orthogonal direction through a relatively narrow area of a cylindrical cell containing dilute gas medium are discovered and analyzed. These resonances are induced by specific optical pumping of atoms as they fly freely from the inner cell surface through the pumped region toward the probe optical beam. The obtained mathematical relations are used to investigate the dependence of the discussed resonances on the intensity and spatial distribution of the localized optical pumping. The proposed method could allow reducing the Doppler broadening of the detected spectral lines by the factor equal to the ratio of the effective width of the narrow pumped region to the cell radius. The obtained results may find application in high-resolution spectroscopy of atoms (molecules), as well as for laser-frequency stabilization by using the discovered sub- Doppler resonances.     

Observation of high-order quantum resonances in the kicked rotor

Quantum resonances in the kicked rotor are characterized by a dramatically increased energy absorption rate, in stark contrast to the momentum localization generally observed. These resonances occur when the scaled Planck's constant Planck's [over ]=r/s 4pi, for any integers r and s. However, only the variant Planck's [over ]=r2pi resonances are easily observable. We have observed high-order quantum resonances (s>2) utilizing a sample of low energy, noncondensed atoms and a pulsed optical standing wave. Resonances are observed for variant Planck's [over ]=r/16 4pi for integers r=2-6. Quantum numerical simulations suggest that our observation of high-order resonances indicate a larger coherence length (i.e., coherence between different wells) than expected from an initially thermal atomic sample.     

激光减速原子束频标的建议

本文提出一个激光减速的碱金属原子束频标的方案。用共振激光束对原子束同时进行减速和选态,使原子速率降到10m/s以下,而光抽运作用使原子自动集中到基态超精细结构中具有最大磁量子数的塞曼子能级上。为避免重力场中束轨迹下垂,用偏转磁铁或多束激光使束由水平转成垂直向上,然后用级联磁共振使原子过渡到频标所需的m_F=0能级。利用原子上升和重力场中自由下落两次通过单个微波谐振腔而取得Ramsey共振信号,线宽约为¹Hz。信号用另一束激光检测。予期这种频标的稳定度和准确度可比现有束型频标提高一个数量级以上。文中详细讨论了激光减速和选态的方法,克服横向加热效应的措施,实现级联磁共振的办法,以及获得垂直束装置的设计等。     

Dynamics of interaction between two-level atoms in a laser field and linear stationary optical dimensional resonances

Formulas for radiative forces acting on the atoms of a diatomic object in a field of external laser radiation are obtained with allowance made for the interatomic dipole-dipole interaction. It is shown that one can control the motion of the atoms by gradually varying the frequency of external laser radiation due to the presence of optical dimensional resonances in the spectrum of the diatomic object.     

Optical size resonances in structured atomic systems on the surface and inside of isotropic media

It is shown that linear stationary optical size resonances can be used for high-precision measurement of the spatial distribution of atoms in structured atomic systems on the surface and inside of isotropic optical media by changing the frequency and the polarization of external continuous optical radiation.     

Maslov’s asymptotic methods in problems of the theory of optical lattices

Application of Maslov’s asymptotic methods to equations that arise in the theory of optical lattices was considered. The occurrence of a small parameter in the Schrödinger equations with potentials of three-dimensional and controlled optical lattice was investigated and the conditions of application of Maslov’s asymptotic methods for solving these equations was determined. Consideration of different conditions imposed on the parameters in these potentials led to the use of two different methods for solving the arising equations: Maslov’s method of a complex germ and Maslov’s operator-valued method of a complex germ. Expressions that can be used to calculate the desired characteristics of the atomic systems under consideration in optical lattices were derived.     

Quantum entanglement via optical control of atom-atom interactions

Two-photon optical transitions combined with long-range dipole-dipole interactions can be used for the coherent manipulation of multiatom collective states. We show that it is possible to induce optical resonances accompanied by the generation of entangled superpositions of such atomic states. Resonances of this kind can be used to implement quantum logic gates using optically excited single atoms (impurities) in the condensed phase.     

Multiple frequency modulation for low-light atom measurements in an optical cavity

We present a frequency modulation scheme to detect atoms dispersively in a high-finesse optical cavity at low-light levels with immunity to cavity length fluctuations. We use multiple cavity resonances to provide common mode noise rejection, keeping the high intensity carrier off-resonant from all cavity modes. The method has applications in atomic squeezed state generation and quantum metrology.     

On the possibilities of sub-Doppler atomic spectroscopy in multilayer gas cells

Possibilities of high-resolution spectroscopy of atoms (or molecules) for optical pumping and probing with the use of a proposed cell with a series of plane-parallel thin gas layers between spatially separated regions of this cell are theoretically studied. It is shown that efficient velocity selection of optically pumped atoms is possible in view of their characteristic transit and collisional relaxation in such a cell, which leads to the formation of narrow sub-Doppler resonances in absorption of a probe monochromatic wave. The resolution of this spectroscopic method is analyzed in the cases of stationary and definite nonstationary optical pumping of atoms by broadband radiation for different geometrical parameters of these cells and pumping intensity. The proposed multilayer gas cell is a compact analog of a large number of parallel atomic (molecular) beams and can be the basis for new high-precision and compact optical frequency standards.