JETP Letters最新文献

This paper establishes a connection between the Hawking temperature of spacetime horizons and global topological invariants, specifically the Euler characteristic of Wick-rotated Euclidean spacetimes. This is demonstrated for both de Sitter and Schwarzschild, where the compactification of the near-horizon geometry allows for a direct application of the Chern–Gauss–Bonnet theorem. For de Sitter, a simple argument connects the Gibbon–Hawking temperature of the Bunch–Davies state to the global thermal de Sitter temperature. This establishes that spacetime thermodynamics are a consequence of the geometrical structure of spacetime itself, therefore suggesting a deep connection between global topology and semi-classical analysis.

The storage of a signal of a single-photon source based on spontaneous parametric down-conversion in a periodically poled MgO:PPLN crystal in a quantum memory based on an atomic frequency comb in an isotopically pure (^{{{text{143}}}}{text{Nd}}{kern 1pt} {text{:}}{kern 1pt} {{{text{Y}}}^{{text{7}}}}{text{Li}}{{{text{F}}}_{{text{4}}}}) crystal has been demonstrated.

Coherent state quantum cryptography protocols are of interest due to their easy implementation. However, the security proof of such protocols against all attacks can be tricky because of the attenuation in the communication channel that can be exploited by an eavesdropper. In this work, an attack on the subcarrier wave quantum cryptography protocol has been built, which generalizes the photon number splitting attack. The efficiency of the attack has been analyzed, in particular, for the case where the eavesdropper does not have quantum memory.

In this paper, we present the results of studies of the phonon and relaxation subsystems in the relaxor ferroelectric crystal PbCo_1/3Nb_2/3O₃ (PCN) using Raman scattering in the temperature range from 650 to 80 K, including the regions of “diffuse phase transition” with a maximum permittivity ({{T}_{m}} approx 250{kern 1pt} ) K at a frequency of 1 kHz and charge phase separation in the vicinity of 170 K. It has been shown that the polarized spectra of PCN are similar to those observed in relaxor ferroelectrics with a perovskite structure. The analysis of the temperature behavior of the main phonon modes and anisotropic quasielastic light scattering revealed anomalies in the region corresponding to the onset (({{T}_{2}} sim 230{kern 1pt} ) K) and final formation (({{T}_{3}} sim 170{kern 1pt} ) K) of charge phase separation, determined by the presence of Co²⁺ and Co³⁺ ions in the PCN crystal. Anomalies in the evolution of the Raman spectra near the temperature of the relative permittivity maximum ({{T}_{m}}), which are characteristic of relaxor ferroelectrics, were not observed in PCN. The dynamics of polar nanoregions, which determine the behavior of quasielastic light scattering, differ from those observed in the model relaxor ferroelectric PbMg_1/3Nb_2/3O₃ (PMN).

The properties of dilute, compensated “weak” electrolytes on the example of the binary mixture “acid + alkali + water” have been discussed within the framework of phenomenological energy statistics. The concepts of weak donors and acceptors have been consistently defined at the energy level. A natural criterion of donor–acceptor agreement has been formulated by analyzing tabular data on the dissociation constants K_d(T) and K_a(T) in Ostwald’s dilution law for weak acids and alkalis (these constants are defined below). The fundamental role of the existence and possibilities of observing the compensation effect in binary electrolytes in determining the main energy parameters of phenomenological statistics of dilute weak hosts is emphasized.

The electronic structure and magnetic properties of thin-film (Co,Fe)/MgO heterostructures have been examined using the GGA + U method. It has been found that the epitaxial strain in the Co layer leads to the antiferromagnetic order, which can deteriorate the polarization characteristics of the (Co, Fe)/MgO interface. The simulation of the extension of bcc Co lattice has shown that the change in the long-range order from ferromagnetic to antiferromagnetic can be caused by an increase in the interatomic distance.

To study the crystal structure of the Si(111) 2 × 2-(Bi,Mg) surface reconstruction, formed during the adsorption of magnesium on the Si(111) (sqrt 3 times sqrt 3 )-Bi surface phase, ab initio calculations have been performed. The stoichiometric composition of the unit cell of the 2 × 2 surface reconstruction has been determined. Using the calculated formation energies, the most stable structures for the two-dimensional Bi(_{X})Mg(_{Y}) alloy have been identified. It has been shown that the structural model with the configuration (X = 2) and (Y = 4) is in good agreement with the low-energy electron diffraction and scanning tunneling microscopy results observed for the reconstructed Si(111) 2 × 2-(Bi,Mg) surface.

A mathematical model has been proposed for an optical trap, in which a nanoparticle is captured by the field of a standing wave formed upon reflection of a photon jet from a dielectric surface. The equations of motion for the nanoparticle under the action of a trap field in the presence of viscous friction in the medium (liquid) have been formulated. The conditions for stable capture of a nanoparticle in the trap have been estimated analytically. The role of friction in the stability of the trap has been analyzed by numerically solving the equations of motion.

Grazing incidence X-ray diffraction (GIXRD) data have indicated that the orthorhombic (Pmn{{2}_{1}}) phase previously detected in a 10–20 nm buried ferroelectric HfO₂:Al₂O₃ (10:1) layer of silicon-on-insulator and silicon-on-sapphire structures after annealing at (T > 950)°C for 1 h is absent after 30 s stepwise rapid thermal annealing treatments. Instead, stressed textured ferroelectric layers thermally stable up to 1000°C are formed with the {111} and {002} orientations for silicon and sapphire substrates, respectively, in the rhombohedral r(R3) or orthorhombic (Pca{{2}_{1}}) phases, which are not manifested in GIXRD patterns. The high remnant polarization in silicon-on-insulator structures indicates that the rhombohedral r(R3) phase is favorable.

We introduce statistical models for each of the three main sources of barren plateaus: nonlocality of the observable, entanglement of the initial state, and circuit expressivity. For instance, non-local observables are modeled by random Pauli operators, which lead to barren plateaus with probability exponentially close to one. These models are complementary to the conventional deterministic ones, and often simpler to analyze. Using this framework, we show that in the barren plateau regime any two Pauli observables are anti-concentrated with high probability in the following sense. While each of the observables is localized in an exponentially small parameter subspace, these regions are essentially independent, so that their overlap is yet exponentially smaller than each subspace. This invites to rethink the structure of quantum landscapes with barren plateaus and approaches to their optimization, including warm-start strategies.