We report a study of the entanglement between the quantized photon field and an atom arising in the photo-ionization process. Our approach is based on an ab initio solution of the time-dependent ...Schrödinger equation (TDSE) describing the quantum evolution of a bipartite system consisting of the atom and the quantized electromagnetic field. Using the solution of the TDSE, we calculate the reduced photon density matrix, which we subsequently use to compute entanglement entropy. We explain some properties of the entanglement entropy and propose an approximate formula for the entanglement entropy based on the analysis of the density matrix and its eigenvalues. We present the results of a comparative study of the entanglement in the photo-ionization process for various ionization regimes, including the tunneling and the multiphoton ionization regimes.
Abstract
We describe an approach to the description of the time-development of the process of strong field ionization of atoms based on the calculation of the joint probability of occurrence of two ...events, event B being finding atom in the ionized state after the end of the laser pulse, event A being finding a particular value of a given physical observable at a moment of time inside the laser pulse duration. As an example of such an physical observable we consider lateral velocity component of the electron’s velocity. Our approach allows us to study time-evolution of the lateral velocity distribution for the ionized electron during the interval of the laser pulse duration. We present results of such a study for the cases of target atomic systems with short range Yukawa and Coulomb interactions.
The ability to synthesize VO2 in the form of single-crystalline nanobeams and nano- and microcrystals uncovered a number of previously unknown aspects of the metal−insulator transition (MIT) in this ...oxide. In particular, several reports demonstrated that the MIT can proceed through competition between two monoclinic (insulating) phases M1 and M2 and the tetragonal (metallic) R phase under influence of strain. The nature of such phase behavior has been not identified. Here we show that the competition between M1 and M2 phases is purely lattice-symmetry-driven. Within the framework of the Ginzburg−Landau formalism, both M phases correspond to different directions of the same four-component structural order parameter, and as a consequence, the M2 phase can appear under a small perturbation of the M1 structure such as doping or stress. We analyze the strain-controlled phase diagram of VO2 in the vicinity of the R−M2−M1 triple point using the Ginzburg−Landau formalism and identify and experimentally verify the pathways for strain-control of the transition. These insights open the door toward more systematic approaches to synthesis of VO2 nanostructures in desired phase states and to use of external fields in the control of the VO2 phase states. Additionally, we report observation of the triclinic T phase at the heterophase domain boundaries in strained quasi-two-dimensional VO2 nanoplatelets, and theoretically predict phases that have not been previously observed.
Metastable alloys based on the Ti–Nb system are considered promising candidates to replace the biomaterials currently used in medicine. Several very promising alloys like TNTM, TNZT, etc., were ...recently developed by adding Zr, Ta, Mo, Fe, or other elements to the Ti–Nb system. However, only a few fundamental studies were devoted to the structural characterisation of Ti–Nb alloys in the as-cast state. In this study, we analyze the microstructure, the phase transformations, the lattice parameters, the interaction of different phases, and Young's modulus of a wide range of Ti–Nb alloys produced by suction casting. The structure of experimental samples was investigated using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and synchrotron X-ray diffraction (SXRD) analysis. The samples with a Nb content of less than 17.5 wt % consisted of α′ phase. The pure α’’ phase was observed only in the alloy with 17.5 wt % Nb. The alloys with an intermediate content of Nb (20–30 wt %) contained a mixture of α’’, β and ω phases. The samples with 30–35 wt % Nb consisted of a mix of β and ω phases. The samples with 37.5 and 45 wt % Nb included two types of β phase. In addition to the regular β phase, a little detectable amount of bcc phase was observed with a larger lattice parameter named βminor. The mechanical properties strongly depended on the phase composition. We found that for α’’-dominated alloys, there is a correlation between Young's modulus and orthorhombicity and c/a ratio of α’’ phase. The lowest Young's modulus (47 GPa) was observed in the alloy with 17.5 wt % Nb, which has orthorhombicity close to unity and c/a ratio close to 1.58.
•High orthorhombicity and low c/a ratio of α’’ phase result in low Young's modulus.•Small volume change in β→ω transformation causes a high Young's modulus.•Two different β metastable phases have been observed in Nb rich alloys.•Lattice strains in β→ω transformations are smaller than in β→α′/α″ transformations.
Abstract
We combine IR pump and XUV probe laser pulses to visualize the Kramers–Henneberger (KH) state of the potassium atom. We demonstrate that ionization of such an atom exhibits some ...molecular-like features such as low order interference maxima in photoelectron momentum spectra. The locations of these maxima allow to estimate spatial dimensions of the KH atom and can be used for accurate calibration of high intensity laser fields. At the same time, we show that an analogy between the KH atom and a homo-nuclear diatomic molecule cannot be extended too far. In particular, higher order interference maxima are very difficult to observe in the case of the KH state. We attribute this to a particular structure of the KH potential which does not confine electron motion to a well-defined potential well unlike in real diatomic molecules.
Color centers with long-lived spins are established platforms for quantum sensing and quantum information applications. Color centers exist in different charge states, each of them with distinct ...optical and spin properties. Application to quantum technology requires the capability to access and stabilize charge states for each specific task. Here, we investigate charge state manipulation of individual silicon vacancies in silicon carbide, a system which has recently shown a unique combination of long spin coherence time and ultrastable spin-selective optical transitions. In particular, we demonstrate charge state switching through the bias applied to the color center in an integrated silicon carbide optoelectronic device. We show that the electronic environment defined by the doping profile and the distribution of other defects in the device plays a key role for charge state control. Our experimental results and numerical modeling evidence that control of these complex interactions can, under certain conditions, enhance the photon emission rate. These findings open the way for deterministic control over the charge state of spin-active color centers for quantum technology and provide novel techniques for monitoring doping profiles and voltage sensing in microscopic devices.
We aimed to screen children aged 18–48 months in the general population of nine Russian regions for risk of mental, behavioral and developmental disorders (MBDDs) including autism spectrum disorders ...(ASD) using an original screening tool. The prevalence of the risk for MBDDs is 1307:10,000 (13.07%), the prevalence of clinically verified cases of MBDDs is 151:10,000 (1.51%), whereas the prevalence of ASD among them is 18:10,000 (0.18%). Basing on our results, the screening procedures are already integrated into the Russian primary care system since the end of 2019. Screening of the risk for MBDDs including ASD in Russia among children in the general pediatric population is a promising area of preventive medicine.
Metabolic intervention strategy of epilepsy treatment has been gaining broader attention due to accumulated evidence that hypometabolism, manifested in humans as reduced brain glucose consumption, is ...a principal factor in acquired epilepsy. Therefore, targeting deficient energy metabolism may be an effective approach for treating epilepsy. To confront this pathology we utilized pyruvate, which besides being an anaplerotic mitochondrial fuel possesses a unique set of neuroprotective properties as it: (i) is a potent reactive oxygen species scavenger; (ii) abates overactivation of Poly ADP-ribose polymerase 1 (PARP-1); (iii) facilitates glutamate efflux from the brain; (iv) augments brain glycogen stores; (v) is anti-inflammatory; (vi) prevents neuronal hyperexcitability; and (vii) normalizes the cytosolic redox state. In vivo, chronic oral pyruvate administration completely abolished established epileptic phenotypes in three accepted and fundamentally different rodent acquired epilepsy models. Our study reports metabolic correction by pyruvate as a potentially highly effective treatment of acquired epilepsies.
•Metabolic correction by pyruvate was utilized for epilepsy treatment.•Chronic pyruvate administration halts epilepsy in three different rodent models.•Pyruvate provides a strong general anti-epileptic effect in acquired epilepsies.
Abstract
Dielectric losses are one of the key factors limiting the coherence of superconducting qubits. The impact of materials and fabrication steps on dielectric losses can be evaluated using ...coplanar waveguide (CPW) microwave resonators. Here, we report on superconducting CPW microwave resonators with internal quality factors systematically exceeding 5 × 10
6
at high powers and 2 × 10
6
(with the best value of 4.4 × 10
6
) at low power. Such performance is demonstrated for 100-nm-thick aluminum resonators with 7–10.5 um center trace on high-resistivity silicon substrates commonly used in Josephson-junction based quantum circuit. We investigate internal quality factors of the resonators with both dry and wet aluminum etching, as well as deep and isotropic reactive ion etching of silicon substrate. Josephson junction compatible CPW resonators fabrication process with both airbridges and silicon substrate etching is proposed. Finally, we demonstrate the effect of airbridges’ positions and extra process steps on the overall dielectric losses. The best quality factors are obtained for the wet etched aluminum resonators and isotropically removed substrate with the proposed ultrasonic metal edge microcutting.
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