JETP Letters最新文献

The possibility of forming a bright–dark terahertz acoustic bullet at the second-harmonic generation in a paramagnetic crystal placed in an external magnetic field is investigated. Such a bullet is a narrow beam of a double-frequency elastic strain field of, along which a dark nanosecond-duration spot, where the strain field is absent, propagates at the speed of sound. The important role of temporal dispersion caused by spin–phonon coupling and spatial dispersion caused by the discreteness of the crystal lattice in the formation of the bullet is emphasized. It is shown that the formation of the bullet in the absence of phase- and group-velocity matching is possible in the presence of upper bounds on the time duration of the dark spot and on the transverse size of the acoustic beam.

We propose a theoretical concept for creating a linear array of dark optical nanotraps in a cylindrical nanohole in a high-refractive-index dielectric film. It is rigorously shown that due to breaking the transversality of plane waves in the nanohole region, a linear chain of deep 3D dark (blue-detuned) trap configurations for neutral atoms, with sizes of less than 50 nm, a period of less than 100 nm and an effective depth of more than 10 mK at an intensity of just 10 kW/cm² is formed in the nanohole. The predicted effect could open up new directions in the field of cold atom manipulation and quantum computing on neutral atoms.

We investigate the shift caused by asymmetry of spectroscopic lineshape in atomic interferometers, which has not previously been discussed in the scientific literature. This asymmetry arises because laser field is frequency-chirped not only during the free-evolution intervals of atoms, but also during the Ramsey pulses. As a result, the effective detuning from the working atomic transition during the pulses also depends on the chirping rate, which, in turn, leads to the lineshape-asymmetry-caused shift (LACS). It is shown that this shift has an inverse cubic dependence of  ( propto 1{text{/}}{{T}^{3}}) on the duration of the interval between the Ramsey pulses T, which markedly contrasts with the ( propto 1{text{/}}{{T}^{2}}) dependence typical in atomic interferometry. Therefore, the metrological importance of this shift substantially increases for compact atomic interferometers with a short baseline. For example, for interferometers-gravimeters using two-photon transitions in rubidium atoms, at (T sim 1) ms we estimate the LACS shift and its variations at the level of 0.1–1 mGal, while for (T sim 100) μs this can reach a value of 0.1–1 Gal.

A cylindrical microresonator based on standard silica optical fibers is a promising simple platform for creating nonlinear devices, but it requires high pump power to observe nonlinear effects. This paper examines the feasibility of magnetron sputtering thin films from silicon and silicon nitride layers with a high nonlinear refractive index. It is shown that during sputtering the Q-factor drops to 10⁵ and 10⁶ for silicon and silicon nitride films, respectively.

This work is devoted to solving the problem of processing numerical sequences using variational quantum algorithms implemented on a noisy intermediate-scale quantum computer. The quantum computing platform is an integrated circuit based on superconducting artificial atoms. The architecture of the quantum recurrent neural network is constructed using single- and two-qubit operations. At the simulation stage, we investigated the trainability of the model as a function of the number of qubits, as well as the encoded into the qubit states data amount and the encoding method. A comparison with classical architectures showed that on current quantum processors it is possible to achieve a prediction quality on the chosen machine-learning task that is comparable to that of models implemented on classical processors.

The effect of nanosecond magnetic pulses on a photon echo signal in the Er³⁺-doped YLiF₄ and LuLiF₄ samples has been considered. A strong dependence of the photon echo intensity on the parameters of the magnetic pulse and the direction of variation of the external magnetic field H has been found. The application of magnetic pulses can increase the echo intensity by a factor of 5–6. The irreversibility (nonreciprocity) effect is explained by the occurrence of the spatial dispersion of the permittivity.

The parameters of narrowband lasing in a random fiber laser on stimulated Raman scattering (Raman laser) with feedback based on Rayleigh scattering, which are necessary for the implementation of ultra-high-resolution spectroscopy with a scanning single-pixel spectrum analyzer, have been analyzed. It has been shown that the correct subpixel approximation requires the mode lifetime ≥0.5 ms, intermodal interval ≥2.5 GHz, and a sufficient mode density in the unit spectral range. The laser parameters meet these requirements, which makes it possible to achieve an effective increase in the spectral resolution (to the instrument sampling step up to 1 pm).

An effective Kugel–Khomskii-type model that can be applied to analyze the magnetic and orbital order in the Sr₂VO₄ compound is formulated. For the case of infinitely large crystal field splitting (the difference of the energy of the (xy) state from the energies of the xz and yz states), the phase diagram describing the ground state of the model in the variables of spin–orbit coupling and Hund’s exchange is determined. A quantum phase transition is described, and an equation for the phase boundary between a state exhibiting both the hidden magnetic and orbital long-range orders and a weakly ferromagnetic state with concurrent antiferro-orbital order with the same amplitude is derived. These long-range orders are described in terms of octupole moments constructed from the components of the total magnetic moment.

The morphology and phase composition of a concentration series of HfO₂–(x) mol % Yb₂O₃ (x = 0, 5, 10, 15, 30) nanoparticles, obtained by a coprecipitation method, have been studied. The characteristics of thermal radiation, arising in ZrO₂–30 mol % Yb₂O₃ and HfO₂–30 mol % Yb₂O₃ nanoparticles exposed to laser radiation with the wavelength ({{lambda }_{{{text{exc}}}}} = 980{kern 1pt} ) nm and a high power density, have been comparatively analyzed. The cytotoxicity of HfO₂–(x) mol % Yb₂O₃ ((x = 15), 30) nanoparticles has been studied. It has been demonstrated that an increase in the content of Yb₂O₃ in particles from 15 to 30 mol % and the effect of 980-nm laser radiation on them double a cytotoxic effect of these particles relative to the Mh22 cell line.

A method for analyzing the spectra of isobaric analog multiplets of nuclei has been developed on the basis of the ab initio approach of the no-core shell model. Doublets of ⁵He–⁵Li five-nucleon resonant states with excitation energies E* ≤ 30 MeV, total angular momenta J ≤ 5/2, and isospin T = 1/2. For all table levels of these nuclei, the corresponding theoretically calculated levels have been found. The calculations of the differences of the binding energies of isobaric analog pairs and their comparison with experimental data have allowed us to significantly expand the list of reliably established levels of the ⁵He and ⁵Li nuclei and to prove the need to correct the tables of spectroscopic data.