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See detailCooperative spontaneous emission from indistinguishable atoms in arbitrary motional quantum states
Damanet, François ULg; Braun, Daniel; Martin, John ULg

in Physical Review A (2016), 94

We investigate superradiance and subradiance of indistinguishable atoms with quantized motional states, starting with an initial total state that factorizes over the internal and external degrees of ... [more ▼]

We investigate superradiance and subradiance of indistinguishable atoms with quantized motional states, starting with an initial total state that factorizes over the internal and external degrees of freedom of the atoms. Due to the permutational symmetry of the motional state, the cooperative spontaneous emission, governed by a recently derived master equation [F. Damanet et al., Phys. Rev. A 93, 022124 (2016)], depends only on two decay rates γ and γ0 and a single parameter dd describing the dipole-dipole shifts. We solve the dynamics exactly for N = 2 atoms, numerically for up to 30 atoms, and obtain the large-N limit by a mean-field approach. We find that there is a critical difference γ0 − γ that depends on N beyond which superradiance is lost. We show that exact nontrivial dark states (i.e., states other than the ground state with vanishing spontaneous emission) only exist for γ = γ0 and that those states (dark when γ = γ0) are subradiant when γ < γ0. [less ▲]

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See detailQuantum calculation of the Vavilov-Cherenkov radiation by twisted electrons
Ivanov, Igor ULg; Serbo, Valery; Zaytsev, Vladimir

in Physical Review A (2016), 93

We present a detailed quantum electrodynamical description of Vavilov-Cherenkov radiation emitted by a relativistic twisted electron in the transparent medium. Simple expressions for the spectral and ... [more ▼]

We present a detailed quantum electrodynamical description of Vavilov-Cherenkov radiation emitted by a relativistic twisted electron in the transparent medium. Simple expressions for the spectral and spectral-angular distributions as well as for the polarization properties of the emitted radiation are obtained. Unlike the plane-wave case, the twisted electron produces radiation within the annular angular region, with enhancement towards its boundaries. Additionally, the emitted photons can have linear polarization not only in the scattering plane but also in the orthogonal direction. We find that the Vavilov-Cherenkov radiation emitted by an electron in a superposition of two vortex states exhibits a strong azimuthal asymmetry. Thus, the Vavilov-Cherenkov radiation offers itself as a convenient diagnostic tool of such electrons and complements the traditional microscopic imaging. [less ▲]

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See detailMaster equation for collective spontaneous emission with quantized atomic motion
Damanet, François ULg; Braun, Daniel; Martin, John ULg

in Physical Review A (2016), 93

We derive a Markovian master equation for the internal dynamics of an ensemble of two-level atoms including all effects related to the quantization of their motion. Our equation provides a unifying ... [more ▼]

We derive a Markovian master equation for the internal dynamics of an ensemble of two-level atoms including all effects related to the quantization of their motion. Our equation provides a unifying picture of the consequences of recoil and indistinguishability of atoms beyond the Lamb-Dicke regime on both their dissipative and conservative dynamics, and applies equally well to distinguishable and indistinguishable atoms. We give general expressions for the decay rates and the dipole-dipole shifts for any motional states, and we find closed-form formulas for a number of relevant states (Gaussian states, Fock states, and thermal states). In particular, we show that dipole-dipole interactions and cooperative photon emission can be modulated through the external state of motion. [less ▲]

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See detailBreakdown of Anderson localization in the transport of Bose-Einstein condensates through one-dimensional disordered potentials
Dujardin, Julien ULg; Engl, Thomas; Schlagheck, Peter ULg

in Physical Review A (2016), 93

We study the transport of an interacting Bose–Einstein condensate through a 1D correlated disorder potential. We use for this purpose the truncated Wigner method, which is, as we show, corresponding to ... [more ▼]

We study the transport of an interacting Bose–Einstein condensate through a 1D correlated disorder potential. We use for this purpose the truncated Wigner method, which is, as we show, corresponding to the diagonal approximation of a semiclassical van Vleck–Gutzwiller representation of this many-body transport process. We also argue that semiclassical corrections beyond this diagonal approximation are vanishing under disorder average, thus confirming the validity of the truncated Wigner method in this context. Numerical calculations show that, while for weak atom-atom interaction strengths Anderson localization is preserved with a slight modification of the localization length, for larger interaction strengths a crossover to a delocalized regime exists due to inelastic scattering. In this case, the transport is fully incoherent. [less ▲]

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See detailAnticoherence of spin states with point-group symmetries
Baguette, Dorian ULg; Damanet, François ULg; Giraud, Olivier et al

in Physical Review A (2015), 92

We investigate multiqubit permutation-symmetric states with maximal entropy of entanglement. Such states can be viewed as particular spin states, namely anticoherent spin states. Using the Majorana ... [more ▼]

We investigate multiqubit permutation-symmetric states with maximal entropy of entanglement. Such states can be viewed as particular spin states, namely anticoherent spin states. Using the Majorana representation of spin states in terms of points on the unit sphere, we analyze the consequences of a point-group symmetry in their arrangement on the quantum properties of the corresponding state. We focus on the identification of anticoherent states (for which all reduced density matrices in the symmetric subspace are maximally mixed) associated with point-group-symmetric sets of points. We provide three different characterizations of anticoherence and establish a link between point symmetries, anticoherence, and classes of states equivalent through stochastic local operations with classical communication. We then investigate in detail the case of small numbers of qubits and construct infinite families of anticoherent states with point-group symmetry of their Majorana points, showing that anticoherent states do exist to arbitrary order. [less ▲]

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See detailScattering of twisted relativistic electrons by atoms
Serbo, Valery; Ivanov, Igor ULg; Fritzsche, Stephan et al

in Physical Review A (2015), 92

The Mott scattering of high-energetic twisted electrons by atoms is investigated within the framework of the first Born approximation and Dirac's relativistic equation. Special emphasis is placed on the ... [more ▼]

The Mott scattering of high-energetic twisted electrons by atoms is investigated within the framework of the first Born approximation and Dirac's relativistic equation. Special emphasis is placed on the angular distribution and longitudinal polarization of the scattered electrons. In order to evaluate these angular and polarization properties we consider two experimental setups in which the twisted electron beam collides with either a single well-localized atom or macroscopic atomic target. Detailed relativistic calculations have been performed for both setups and for the electrons with kinetic energy from 10 to 1000 keV. The results of these calculations indicate that the emission pattern and polarization of outgoing electrons differ significantly from the scattering of plane-wave electrons and can be very sensitive to the parameters of the incident twisted beam. In particular, it is shown that the angular- and polarization-sensitive Mott measurements may reveal valuable information about both the transverse and longitudinal components of the linear momentum and the projection of the total angular momentum of twisted electron states. Thus, the Mott scattering emerges as a diagnostic tool for the relativistic vortex beams. [less ▲]

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See detailElastic and inelastic transmission in guided atom lasers: A truncated Wigner approach
Dujardin, Julien ULg; Argüelles, Arturo; Schlagheck, Peter ULg

in Physical Review A (2015), 91

We study the transport properties of a Bose-Einstein condensate formed by an ultracold gas of bosonic atoms that is coupled from a magnetic trap into a one-dimensional waveguide. Our theoretical approach ... [more ▼]

We study the transport properties of a Bose-Einstein condensate formed by an ultracold gas of bosonic atoms that is coupled from a magnetic trap into a one-dimensional waveguide. Our theoretical approach to tackling this problem is based on the truncated Wigner method for which we assume the system to consist of two semi-infinite noninteracting leads and a finite interacting scattering region with two constrictions modeling an atomic quantum dot. The transmission is computed in the steady-state regime and we find a good agreement between truncated Wigner and matrix-product state calculations. We also identify clear signatures of inelastic resonant scattering by analyzing the distribution of energy in the transmitted atomic-matter wave beam. [less ▲]

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See detailIsotope shifts and hyperfine structure of the laser-cooling Fe I 358-nm line
Huet, Nicolas ULg; Pettens, Manon; Bastin, Thierry ULg

in Physical Review A (2015), 92

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See detailOperational entanglement families of symmetric mixed N-qubit states
Bastin, Thierry ULg; Mathonet, Pierre ULg; Solano, Enrique

in Physical Review A (2015), 91

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See detailControl of molecular dynamics with zero-area fields. application to molecular orientation and photodissociation
Sugny, Dominique; Vranckx, Stéphane; Ndong, Mamadou et al

in Physical Review A (2014), 90

The constraint of time-integrated zero area on the laser field is a fundamental requirement, both theoretically and experimentally, in the control of molecular dynamics. By using techniques of local and ... [more ▼]

The constraint of time-integrated zero area on the laser field is a fundamental requirement, both theoretically and experimentally, in the control of molecular dynamics. By using techniques of local and optimal control theory, we show how to enforce this constraint in two benchmark control problems, namely, molecular orientation and photofragmentation. The origin and the physical implications for the dynamics of this zero-area control field are discussed. [less ▲]

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See detailMultiqubit symmetric states with maximally mixed one-qubit reductions
Baguette, Dorian ULg; Bastin, Thierry ULg; Martin, John ULg

in Physical Review A (2014), 90

We present a comprehensive study of maximally entangled symmetric states of arbitrary numbers of qubits in the sense of the maximal mixedness of the one-qubit reduced density operator. A general criterion ... [more ▼]

We present a comprehensive study of maximally entangled symmetric states of arbitrary numbers of qubits in the sense of the maximal mixedness of the one-qubit reduced density operator. A general criterion is provided to easily identify whether given symmetric states are maximally entangled in that respect or not. We show that these maximally entangled symmetric (MES) states are the only symmetric states for which the expectation value of the associated collective spin of the system vanishes, as well as in corollary the dipole moment of the Husimi function. We establish the link between this kind of maximal entanglement, the anticoherence properties of spin states, and the degree of polarization of light fields. We analyze the relationship between the MES states and the classes of states equivalent through stochastic local operations with classical communication (SLOCC). We provide a nonexistence criterion of MES states within SLOCC classes of qubit states and show in particular that the symmetric Dicke state SLOCC classes never contain such MES states, with the only exception of the balanced Dicke state class for even numbers of qubits. The 4-qubit system is analyzed exhaustively and all MES states of this system are identified and characterized. Finally the entanglement content of MES states is analyzed with respect to the geometric and barycentric measures of entanglement, as well as to the generalized N-tangle. We show that the geometric entanglement of MES states is ensured to be larger than or equal to 1/2, but also that MES states are not in general the symmetric states that maximize the investigated entanglement measures. [less ▲]

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See detailNonlinear Schrödinger wave equation with linear quantum behavior
Richardson, Christopher ULg; Schlagheck, Peter ULg; Martin, John ULg et al

in Physical Review A (2014), 89

We show that a nonlinear Schroedinger wave equation can reproduce all the features of linear quantum mechanics. This nonlinear wave equation is obtained by exploring, in a uniform language, the transition ... [more ▼]

We show that a nonlinear Schroedinger wave equation can reproduce all the features of linear quantum mechanics. This nonlinear wave equation is obtained by exploring, in a uniform language, the transition from fully classical theory governed by a nonlinear classical wave equation to quantum theory. The classical wave equation includes a nonlinear classicality enforcing potential which when eliminated transforms the wave equation into the linear Schro ̈dinger equation. We show that it is not necessary to completely cancel this nonlinearity to recover the linear behavior of quantum mechanics. Scaling the classicality enforcing potential is sufficient to have quantumlike features appear and is equivalent to scaling Planck’s constant. [less ▲]

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See detailLogic operations in a doped solid driven by stimulated Raman adiabatic passage
Beil, F.; Halfmann, T.; Remacle, Françoise ULg et al

in Physical Review A (2011), 83

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See detailToward scalable information processing with ultracold polar molecules in an electric field: a numerical investigation
Bomble, Laëtitia; Pellegrini, Philippe; Ghesquière, Pierre et al

in Physical Review A (2010), 82

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See detailCircular dielectric cavity and its deformation
Dubertrand, Rémy ULg; Bogomolny, E; Djellali, N et al

in Physical Review A (2008), 77

The construction of perturbation series for slightly deformed dielectric circular cavity is discussed in detail. The obtained formulas are checked on the example of cut disks. A good agreement is found ... [more ▼]

The construction of perturbation series for slightly deformed dielectric circular cavity is discussed in detail. The obtained formulas are checked on the example of cut disks. A good agreement is found with direct numerical simulations and far-field experiments. [less ▲]

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See detailC 1s and N 1s core excitation of aniline: Experiment by electron impact and ab initio calculations
Duflot, D.; Flament, J. P.; Giuliani, Alexandre et al

in Physical Review A (2007), 75(5), 052719

Core shell excitation spectra of aniline at the carbon and nitrogen 1s edges have been obtained by inner-shell electron energy-loss spectroscopy recorded under scattering conditions where electric dipolar ... [more ▼]

Core shell excitation spectra of aniline at the carbon and nitrogen 1s edges have been obtained by inner-shell electron energy-loss spectroscopy recorded under scattering conditions where electric dipolar conditions dominate, with higher resolution than in the previous studies. They are interpreted with the aid of ab initio configuration interaction calculations. The spectrum at the C 1s edge is dominated by an intense pi(*) band. The calculated chemical shift due to the different chemical environment at the carbon 1s edge calculated is in agreement with the experimental observations within a few tenths of an eV. The transition energies of the most intense bands in the C 1s excitation spectrum are discussed at different levels of calculations. In the nitrogen 1s excitation spectrum the most intense bands are due to Rydberg-valence transitions involving the sigma(*)-type molecular orbitals, in agreement with the experiment. This assignment is different from that of extended Huckel molecular orbital calculations. The geometries of the core excited states have been calculated and compared to their equivalent core molecules and benzene. [less ▲]

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See detailLaser-probing measurements and calculations of lifetimes of the 5d D-2(3/2) and 5d D-2(5/2) metastable levels in BaII
Gurell, J.; Biémont, Emile ULg; Blagoev, K. et al

in Physical Review A (2007), 75(5), 1-6

The two metastable levels 5d(2)D(3/2) and 5d(2) D-5/2 in Ba II both show extremely long lifetimes of the order of several tens of seconds each. This has been found both by experiments and by theoretical ... [more ▼]

The two metastable levels 5d(2)D(3/2) and 5d(2) D-5/2 in Ba II both show extremely long lifetimes of the order of several tens of seconds each. This has been found both by experiments and by theoretical predictions. The small transition probabilities associated with these two levels make them interesting and challenging for theoreticians as well as for experimentalists. Several calculations and measurements of these two lifetimes have been made previously but discrepancies between the results are present. This article presents values of ??? = 89.4 +/- 15.6 s for the D-2(3/2) level and ??? = 32.0 +/- 4.6 s for the D-2(5/2) level measured in a beam-laser experiment performed at the ion storage ring CRYRING. These values are supported by our new calculations resulting in ???= 82.0 s for the D-2(3/2) level and ???= 31.6 s for the D-2(5/2) level. [less ▲]

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See detailInferring periodic orbits from spectra of simply shaped microlasers
Lebental, M; Djellali, N; Arnaud, C et al

in Physical Review A (2007), 76

Dielectric microcavities are widely used as laser resonators and characterizations of their spectra are of interest for various applications. We experimentally investigate microlasers of simple shapes ... [more ▼]

Dielectric microcavities are widely used as laser resonators and characterizations of their spectra are of interest for various applications. We experimentally investigate microlasers of simple shapes ͑Fabry-Perot, square, pentagon, and disk͒. Their lasing spectra consist mainly of almost equidistant peaks and the distance between peaks reveals the length of a quantized periodic orbit. To measure this length with a good precision, it is necessary to take into account different sources of refractive index dispersion. Our experimental and numerical results agree with the superscar model describing the formation of long-lived states in polygonal cavities. The limitations of the two-dimensional approximation are briefly discussed in connection with microdisks. [less ▲]

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See detailDisentanglement of magnetic field mixing reveals the spontaneous M2 decay rate for a metastable level in Xe+
Schef, P.; Lundin, P.; Biémont, Emile ULg et al

in Physical Review A (2005), 72(2),

We have investigated the radiative decay of the metastable level 5d(4)D(7/2) in Xe+. Theoretically we find the decay to be heavily dominated by an M2 transition and not by M1/E2 transitions. Lifetime ... [more ▼]

We have investigated the radiative decay of the metastable level 5d(4)D(7/2) in Xe+. Theoretically we find the decay to be heavily dominated by an M2 transition and not by M1/E2 transitions. Lifetime measurements of 5d(4)D(7/2) in a storage ring are difficult since magnetic mixing of the metastable with a short-lived level quenches its population. Decay rates were determined at different magnetic field strengths (B) in order to allow a nonlinear extrapolation to B=0. The experimental lifetime of 2.4 +/- 0.8 s was in agreement with the calculated value, but much smaller than previously estimated. [less ▲]

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See detailRadiative lifetime and transition probabilities in CdI and CdII
Xu, H. L.; Persson, A.; Svanberg, S. et al

in Physical Review A (2004), 70(4), 1-14

Radiative lifetimes of 11 levels belonging to the 5s5p P-1(1)o 5snd D-3(1,2) (n=6-9) and 5sns S-3(1) (n=7,8) series of Cd I, and of 5 levels of Cd II (i.e., 4d(10)5p P-2(1/2.3/2)o, 4d(10)6s S-2(1/2), and ... [more ▼]

Radiative lifetimes of 11 levels belonging to the 5s5p P-1(1)o 5snd D-3(1,2) (n=6-9) and 5sns S-3(1) (n=7,8) series of Cd I, and of 5 levels of Cd II (i.e., 4d(10)5p P-2(1/2.3/2)o, 4d(10)6s S-2(1/2), and 4d(10)5d D-2(3/2,5/2)) have been measured using the time-resolved laser-induced fluorescence technique. Free neutral and singly ionized cadmium atoms have been generated by laser ablation. Single- or two-step excitation processes were considered to populate the levels under study. Branching fractions of Cd II transitions have been measured by laser-induced breakdown spectroscopy. Transition probabilities and oscillator strengths for Cd I and Cd II spectral lines originating from the above states as well as from the 4d(9)5 s(22)D(3/2,5/2) states of Cd II have been deduced by combining the experimental lifetimes and theoretical branching fractions obtained in multiconfigurational relativistic Hartree-Fock calculations taking core-polarization effects into account. [less ▲]

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