Appearance Of Quantum Research Articles

Observation of novel in-gap states on alkali metal dosed Ti2O3 film

Alkali metal dosing has nowadays been extensively used in angle-resolved photoemission spectroscopy (ARPES) for the in situ surface electron doping of materials to provide access to the unoccupied states. This technique also gives rise to nontrivial physical phenomena, such as the appearance of quantum well states and effects due to alkali metal intercalation. Here, we uncovered a previously unobserved type of electronic behavior induced by alkali metal dosing. By employing ARPES to study the evolution of the electronic structure of the Ti2O3 thin film upon rubidium (Rb) dosing, we found that the electron chemical potential of the system remains unchanged throughout the process. Interestingly, a series of electron-like band dispersions first appear with Rb dosing. A further increase in the Rb dosage leads to the eventual disappearance of the electron-like bands and the emergence of a set of hole-like bands. Our finding enriches the phenomenology brought about by alkali metal surface dosing, suggesting a novel functionality of this popular surface doping technique.

A hybrid classical-quantum workflow for natural language processing

Natural language processing (NLP) problems are ubiquitous in classical computing, where they often require significant computational resources to infer sentence meanings. With the appearance of quantum computing hardware and simulators, it is worth developing methods to examine such problems on these platforms. In this manuscript we demonstrate the use of quantum computing models to perform NLP tasks, where we represent corpus meanings, and perform comparisons between sentences of a given structure. We develop a hybrid workflow for representing small and large scale corpus data sets to be encoded, processed, and decoded using a quantum circuit model. In addition, we provide our results showing the efficacy of the method, and release our developed toolkit as an open software suite.

Формирование InAs/GaP-гетероструктур с квантовыми ямами на подложках кремния методом молекулярно-лучевой эпитаксии

Possibility of formation of pseudomorphous quantum well consisting of InGaAsP quaternary alloy during InAs deposition on GaP/Si epitaxial film surface with developed relief is demonstrated. Investigations of quantum well were performed by transmission electron microscopy and spectroscopy of cw photoluminescence. The appearance of quantum well segments of 2 types with different width and composition InGaAsP is demonstrated. Width increasing is accompanied by decreasing of In and As atoms fraction. Lateral sizes of quantum well segments are not lower than 20 nm. Different photoluminescence bands are corresponds to quantum well segments. Observed phenomenon are explained in the framework of suggestion about strain induced surface reorganization during InAs heteroepitaxy on terraced GaP surface.

Momentum Distribution Functions in Quark-Gluon Plasma

Based on the constituent quasiparticle model of the quark-gluon plasma (QGP), the Wigner function is presented in the form of a color path integral. The Monte Carlo calculations of the quark and gluon densities, pair correlation functions and the momentum distribution functions for strongly coupled QGP plasma in thermal equilibrium at barion chemical potential equal to zero have been carried out. Analysis of the pair correlation functions points out on arising glueballs and related gluon bound states. Comparison results between the momentum distribution functions and Maxwell-Boltzmann distributions show the significant influence of the interparticle interaction on the high energy asymptotics of the momentum distribution functions resulting in the appearance of quantum “tails”.

Composite Nature of Layered Hybrid Perovskites: Assessment on Quantum and Dielectric Confinements and Band Alignment.

Layered hybrid organic-inorganic perovskites (HOPs) have re-emerged as potential technological solutions for next-generation photovoltaic and optoelectronic applications. Their two-dimensional (2D) nature confers them a significant flexibility and results in the appearance of quantum and dielectric confinements. Such confinements are at the origin of their fascinating properties, and understanding them from a fundamental level is of paramount importance for optimization. Here, we provide an in-depth investigation of band alignments of 2D HOP allowing access to carriers' confinement potentials. 2D HOPs are conceptualized as composite materials in which pseudoinorganic and -organic components are defined. In this way, computational modeling of band alignments becomes affordable using first-principles methods. First, we show that the composite approach is suitable to study the position-dependent dielectric profiles and enables clear differentiation of the respective contributions of inorganic and organic components. Then we apply the composite approach to a variety of 2D HOPs, assessing the impact on the confinement potentials of well and barrier thickness, of the nature of the inorganic well, and of structural transitions. Using the deduced potentials, we further discuss the limitations of the effective mass approximation, scrutinizing the electronic properties of this family of composite materials. Our simulations demonstrate type-I dominant band alignment in 2D HOPs. Finally, we outline design principles on band alignment toward achieving specific optoelectronic properties. Thus, we present alternative theoretical methods to inspect the properties of 2D hybrid perovskites and expect that the composite approach will be applicable to other classes of layered materials.

Observation of quantum beat oscillations and ultrafast relaxation of excitons confined in GaAs thin films by controlling probe laser pulses

We study the quantum beats and relaxation dynamics of exciton center-of-mass motion confined in GaAs thin films by a reflection-type pump-probe technique. By using spectrally narrowed probe pulses with energies comparable with the exciton energy separation, oscillations caused by quantum beats between the confined excitons and ultrafast responses which are shorter than their lifetime appear. This appearance of quantum beats does not result from the so-called detection process. Our results demonstrate that the reduction of the destructive interference of the probe pulse in the sample is a key factor to observe the excitonic quantum beats.

Maximally discordant mixed states of two qubits

We study the relative strength of classical and quantum correlations, as measured by discord, for two-qubit states. Quantum correlations appear only in the presence of classical correlations, while the reverse is not always true. We identify the family of states that maximize the discord for a given value of the classical correlations and show that the largest attainable discord for mixed states is greater than for pure states. The difference between discord and entanglement is emphasized by the remarkable fact that these states do not maximize entanglement and are, in some cases, even separable. Finally, by random generation of density matrices uniformly distributed over the whole Hilbert space, we quantify the frequency of the appearance of quantum and classical correlations for different ranks.

Gravitational Descendants in Symplectic Field Theory

It was pointed out by Y. Eliashberg in his ICM 2006 plenary talk that the rich algebraic formalism of symplectic field theory leads to a natural appearance of quantum and classical integrable systems, at least in the case when the contact manifold is the prequantization space of a symplectic manifold. In this paper we generalize the definition of gravitational descendants in SFT from circle bundles in the Morse-Bott case to general contact manifolds. After we have shown using the ideas in Okounkov and Pandharipande (Ann Math 163(2):517–560, 2006) that for the basic examples of holomorphic curves in SFT, that is, branched covers of cylinders over closed Reeb orbits, the gravitational descendants have a geometric interpretation in terms of branching conditions, we follow the ideas in Cieliebak and Latschev (http://arixiv.org/abs/0706.3284v2 [math.s6], 2007) to compute the corresponding sequence of Poisson-commuting functions when the contact manifold is the unit cotangent bundle of a Riemannian manifold.

Quantum many‐body phenomena in coupled cavity arrays

AbstractThe increasing level of experimental control over atomic and optical systems gained in recent years has paved the way for the exploration of new physical regimes in quantum optics and atomic physics, characterised by the appearance of quantum many‐body phenomena, originally encountered only in condensed‐matter physics, and the possibility of experimentally accessing them in a more controlled manner. In this review article we survey recent theoretical studies concerning the use of cavity quantum electrodynamics to create quantum many‐body systems. Based on recent experimental progress in the fabrication of arrays of interacting micro‐cavities and on their coupling to atomic‐like structures in several different physical architectures, we review proposals on the realisation of paradigmatic many‐body models in such systems, such as the Bose‐Hubbard and the anisotropic Heisenberg models. Such arrays of coupled cavities offer interesting properties as simulators of quantum many‐body physics, including the full addressability of individual sites and the accessibility of inhomogeneous models.

Nonlinear magneto-optical probing of magnetic interfaces

Magnetization induced effects in the nonlinear optical (second harmonic generation) response appear to be a very sensitive probe of magnetic interface properties. This leads to attractive applications for the study of magnetic multilayer structures and also leads to new modes of nonlinear magneto-optical imaging. PACS: 42.65.-k; 78.20.Ls; 75.70.Cn Some of the most exciting recent discoveries in magnetism, such as the giant magneto-resistance (GMR) and the oscillatory exchange coupling, are related to the properties of multilayers of alternating ferromagnetic and paramagnetic layers. For magnetic recording on the other hand, antiferromagnetic biasing of ferromagnetic films is used (spin-valve structures). The interfaces between these layers appear to play an essential role for these phenomena and consequently for the device properties based on them [1]. The well known magneto-optical Kerr effect (MOKE) is based on the changes in the linear susceptibility as a function of the magnetization. As this results in a (small) rotation of the polarization of light traveling through a magnetic material, it yields a probe for the bulk magnetization. Though very sensitive and even applicable to monolayers, MOKE is not interface specific. Magnetization induced second harmonic generation (MSHG) is a new nonlinear magneto-optical technique that combines interface sensitivity with huge magneto-optical effects [2] (up to three orders of magnitude times their linear equivalent). These effects are due to the simultaneous breaking of inversion symmetry (at interfaces) and time-reversal symmetry (by the magnetization), which lead to the appearance of even and respectively, odd tensor components in the magnetization that are of comparable magnitude. Because of the latter, the relative phase between these contributions plays an important role [3]. The higher-order nonlinear optical tensor is also responsible for the appearance of essentially new magneto-optical effects that have no equivalent in the linear case [4]. Since the initial theoretical predictions of Ru-Pin Pan et al. [5] and Hubner et al. [6], there have been a large number of experimental studies that have demonstrated the interface sensitivity as well as new and large magneto-optical effects (for example, Kerr rotations close to 90◦). An overview of these results can be found in a number of review papers [7– 9]. In this paper I will concentrate on some of the more recent developments and future challenges of this new technique. Because most magnetically ordered materials are centrosymmetric in their bulk form, MSHG is a particularly useful probe to study the magnetic properties of the interfaces in magnetic multilayer systems. A great challenge for this nonlinear magneto-optical technique is to correlate structural and electronic interface properties with their magnetic properties. Using MSHG, we have found that the spin orientation at the interface of CoNi/Pt multilayers can be different from the bulk due to specific preparation conditions. By a careful analysis of the experimental data, a correlation between increasing interface roughness and a canting spin orientation at the interface could be observed. MSHG has also been shown to be extremely sensitive to the appearance of quantum well states in ultra thin overlayer or spacer films [10]. We have studied several combinations of noble metal overlayers (Au, Ag, Cu) on a variety of magnetic materials (Co, Fe). Spectroscopic MSHG studies of these quantum well states show strong peculiarities of the oscillatory MSHG response. We have also observed QWS within thin Fe films, though here the effects on the MSHG response appear to be much weaker. These combined results reveal the complexity and the role of the interplay between electronic bandstructure, dipole matrix elements and the symmetry of the wavefunction of the quantum well states [11]. Nonlinear magneto-optics also appears to give promising new possibilities for nonlinear optical imaging [12]. We have used this to study the switching behaviour in thin CoNi films which may be used for magnetic recording. 1 Magnetization induced second harmonic generation The optical second harmonic polarization P (2ω) of a magnetic medium is generally described by a third rank polar tensor χcr ijk for the crystallographic contribution and a fourth

Growth, structure and properties of ultra-thin copper films on a V(110) surface

In this work we study the evolution and electronic properties of copper ultra-thin films grown at room temperature on a V(110) single crystal surface using angle-resolved ultraviolet photoemission spectroscopy (ARUPS), X-ray photoemission spectroscopy (XPS), Auger electron spectroscopy (AES) and low-energy electron diffraction (LEED). Up to 5 monolayers (5 ML) the films grow in an imperfect layer-by-layer mode; this being more pronounced at coverages above 2 ML. The LEED studies show that films up to 2 ML coverage grow pseudomorphically, forming thus a body-centered cubic (bcc)-copper film. The 5 ML film shows no clear LEED pattern, although the appearance of quantum well states (QWS) at 1.1 and 1.9 eV binding energy in the ARUPS spectrum suggests that the film as a whole is rather well ordered. Dispersion of the Cu 3d bands of the 5 ML film follows the calculated dispersion of the bcc copper along the ΓN high symmetry axis. The 2 ML film also shows a QWS (at 1.8 eV) of very high intensity. Annealing affects significantly only the films of coverages higher than 2 ML: clusters are formed on the 2 ML thick copper overlayer. These findings contribute also to a better understanding of the results obtained by thermal treatment of ultra-thin vanadium films grown on a Cu(100) surface, in which case a segregated copper film is formed on top of the bcc-vanadium film. The work function of the clean and ordered V(110) surface is found to be 4.65±0.08 eV.