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We report the observation of the controlled expansion of a two-dimensional (2D) quantum gas confined onto a curved shell-shaped surface. We start from the ellipsoidal geometry of a dressed quadrupole trap and introduce a novel gravity compensation mechanism enabling to explore the full ellipsoid. The zero-point energy of the transverse confinement manifests itself by the spontaneous emergence of an annular shape in the atomic distribution. The experimental results are compared with the solution of the three-dimensional Gross–Pitaevskii equation and with a 2D semi-analytical model. This work evidences how a hidden dimension can affect dramatically the embedded low-dimensional system by inducing a change of topology.

Free space atom-interferometry traditionally suffers from the large distances that atoms have to fall in order to achieve long interaction times. Trapped atom interferometry is emerging as a powerful way of achieving long interaction times in a reduced experimental volume. Here, we demonstrate bi-chromatic adiabatic magnetic shell traps as a novel tool for matterwave interferometry. We dress the magnetic hyperfine states of the F = 1 and F = 2 Rubidium 87 Bose-Einstein Condensates thus creating two independently controllable shell traps of which we use the F = 1 , m ¯ F = − 1 〉 and F = 2 , m ¯ F = 1 〉 adiabatic states. Using microwave pulses, we put atoms originally loaded into one of the two shell-traps into a superposition between the two shell traps. Since the two traps can be manipulated independently, their position and vertical curvature can be matched, thus creating a good starting point for an atom interferometer. This interferometer can be sensitive to spatially varying electric or magnetic fields, which could be DC or RF magnetic fields or microwaves. We demonstrate that the trap-matching afforded by the independent control of the shell traps allows for a tenfold increase in coherence times when compared to adiabatic potentials created by a single RF-frequency. For large-radius shells the atoms are confined to a 2D surface enabling highly sensitive imaging matterwave interferometers.

We dress atoms with multiple-radiofrequency (RF) fields and investigate the spectrum of transitions driven by an additional probe field. A complete theoretical description of this rich spectrum is presented, in which we find allowed transitions and determine their amplitudes using the resolvent formalism. Experimentally, we observe transitions up to sixth order in the probe field using RF spectroscopy of Bose-Einstein condensates trapped in single- and multiple-RF-dressed potentials. We find excellent agreement between theory and experiment, including the prediction and verification of previously unobserved transitions, even in the single-RF case.

At present, much attention is paid to the dielectric engineering of the material of the surrounding matrix and low-dimensional structures, which makes it possible to purposefully change their properties and optimize the characteristics of semiconductor devices. The aim of this work is a theoretical study of the influence of the pair interaction of quantum dots (QDs), as well as their interaction with the surrounding matrix through 2D dissipative tunneling, on the photodielectric effect (PDE) associated with the excitation of an impurity complex A + + e in a QD system in an external electric field. Interaction of an electron with a hole in an impurity complex A + + e in a QD has been considered in the adiabatic approximation. The dispersion equations for a hole in an impurity complex A + + e in the presence of an external electric field and 2D dissipative tunneling for the s - and p -states of an electron in a QD are obtained within the framework of the zero-range potential model in the effective mass approximation. The influence of the electric field on the ground state of an electron in a QD has been taken into account in the second order of the perturbation theory. The probability of 2D dissipative tunneling is calculated in the one-instanton semiclassical approximation. The relative change in dielectric permittivity has been calculated in the dipole approximation. PDE field-dependence curves have been plotted for InSb QDs. It is shown that the PDE field dependence at a certain value of the strength of an external electric field and the parameters of 2D dissipative tunneling has a characteristic kink associated with the effect of 2D bifurcation, when, under the action of an electric field, the double-well oscillatory potential simulating the “QD–surrounding matrix” system is transformed and the tunnel transfer mode changes from synchronous to asynchronous. It has been established that there are irregular oscillations on the PDE curves in the vicinity of the 2D bifurcation point, which are associated with the regime of quantum beats. It is shown that the amplitude of the oscillations increases with increasing phonon mode frequency and temperature, while the break point shifts towards weaker fields. It has been found that an increase in the constant of interaction with the contact medium, as well as with the constant of the pair interaction of QDs, leads to the suppression of the PDE.

On the basis of modelling not empirical quantum calculations of geometrical and electronic structure of some isomers of substituted benzoic acids are investigated regularity in behaviour of parameters of the adiabatic potential a carboxyl fragment.

Despite using potential energy surfaces, multivariable functions on molecular configuration space, to comprehend chemical dynamics for decades, the real happenings in molecules occur in phase space, in which the states of a classical dynamical system are completely determined by the coordinates and their conjugate momenta. Theoretical and numerical results are presented, employing alanine dipeptide as a model system, to support the view that geometrical structures in phase space dictate the dynamics of molecules, the fingerprints of which are traced by following the Hamiltonian flow above saddles. By properly selecting initial conditions in alanine dipeptide, we have found internally free rotor trajectories the existence of which can only be justified in a phase space perspective. This article is part of the theme issue 'Modern theoretical chemistry'.

Effect of tunneling decay for the quasi-stationary A+-state, in an impurity complex A+ + e (a hole, localized on a neutral acceptor, interacting with an electron, localized in the ground state of a quantum dot) on the photodielectric effect, associated with the excitation of impurity complexes A+ + e in a quasi-zerodimensional structure, has been studied in the zero-radius potential model in the one-instanton approximation. Calculation of the binding energy of a hole in an impurity complex A+ + e was performed in the zero radius potential model in the adiabatic approximation. It is shown that as the probability of dissipative tunneling increases, the binding energy of a hole in a complex A+ + e decreases, which is accompanied by an increase in the effective localization radius of the impurity complex and, accordingly, an increase in the magnitude of the photodielectric effect. The spectral dependence of the photodielectric effect has been calculated in the dipole approximation taking into account the dispersion of the quantum dot radius. A high sensitivity of the magnitude of the photodielectric effect to such parameters of dissipative tunneling as the frequency of the phonon mode, temperature, and coupling constant with the contact medium, has been revealed.

Structural-dynamic models of aspirin are proposed on the basis of non-empirical quantum calculations of geometrical and electronic structure. In this work, the parameters of the adiabatic potential are determined, and the interpretation of the vibrational states of the compound under study is proposed. Structural-dynamic models of its isomers are constructed, the signs of their spectral identification are revealed. The conformational structure of the molecules of the substance under study was analyzed. The choice of the method and the basis for calculating the fundamental vibration frequencies and band intensities in the IR and Raman spectra are substantiated. A method for estimating anharmonic vibrations using cubic and flat force constants is described. The article presents the results of a numerical experiment; the geometrical parameters of the molecules, such as the lengths of the valence bonds and the magnitudes of the angles between them, are determined. The frequencies of the vibrational states and the magnitudes of their integrated intensities are obtained. The interpretation of isomer vibrations is given and compared with the available experimental data. General regularities in the behavior of spectral bands of different isomers are shown. Frequencies that can be used to identify the isomer from the vibrational spectra of molecules are proposed. The calculation was carried out by the DFT/B3LYP density functional quantum method. It is shown that this method can be used to model the geometrical parameters of molecules and the electronic structure of various substituted benzoic acid. It allows to construct structural-dynamic models of the specified class of compounds on the basis of numerical calculations.

The pseudo Jahn-Teller effect (PJTE) is employed in C 8 AH 8 (A = O, S, Se, Te), and C 8 EH 8 + 1 (E = N, P, As, Sb) with planar configurations to show symmetry breaking phenomena (SBP) in heteronine analogues, and to explain why molecules with (C 2v ) high-symmetry configurations cannot maintain planarity and pucker to their (C 2 ) and (C s ) lower-symmetry structures, respectively. To investigate this phenomenon, geometry optimization and frequency calculations through the density functional B3LYP method using the cc-pVTZ basis set (for Te, and Sb cc-pVTZ-PP) were carried out for all compounds in the series. The state average-complete active space self-consistent field wave-function method was employed to calculate the electronic ground and several low-lying excited states to specify the adiabatic potential energy surface along the a 2 and b 1 puckering nuclear displacements. The PJTE (A 1  + A 2  + A 1 ′)  a 2 and (A 1  + B 1  + A 1 ′)  b 1 problems were formulated as the effects originating via the PJTE theorem. Moreover, replacing hydrogen atoms in C 8 NH 9 , a stable planar structure, with fluorine ligands demonstrated that SBP occur from C 2v to C 2 symmetry. Furthermore, thermochemical calculations via B3LY/cc-pVTZ illustrated that the planarity of the C 8 E ring is restored in C 8 EH 8 − (E = P, As, Sb) anions ,with the change in free energy corresponding to spontaneous deprotonation reactions as 23.67 kJ mol −1 , 21.88 kJ mol −1 , and 16.57 kJ mol −1 , respectively. In fact, despite C 8 EH 8 + 1 having a donor electron-pair and potentially being Lewis base compounds, it acts as a Bronsted-Lowry acid releasing a H + proton instead in this case.

Ultracold atomic gases in periodic potentials are powerful platforms for exploring quantum physics in regimes dominated by many-body effects as well as for developing applications that benefit from quantum mechanical effects. Further advances face a range of challenges including the realization of potentials with lattice constants smaller than optical wavelengths as well as creating schemes for effective addressing and manipulation of single sites. In this paper we propose a dressed-based scheme for creating periodic potential landscapes for ultracold alkali atoms with the capability of overcoming such difficulties. The dressed approach has the advantage of operating in a low-frequency regime where decoherence and heating effects due to spontaneous emission do not take place. These results highlight the possibilities of atom-chip technology in the future development of quantum simulations and quantum technologies, and provide a realistic scheme for starting such an exploration.