Showing papers in "Journal of Physics B in 2012"
TL;DR: In this article, the authors present an introduction to the interaction of light and matter on the attosecond timescale and the theoretical description of ultra-short time delays and relate these to the phase of extreme ultraviolet (XUV) light pulses and to the asymptotic phaseshifts of photoelectron wave packets.
Abstract: This tutorial presents an introduction to the interaction of light and matter on the attosecond timescale. Our aim is to detail the theoretical description of ultra-short time delays and to relate these to the phase of extreme ultraviolet (XUV) light pulses and to the asymptotic phaseshifts of photoelectron wave packets. Special emphasis is laid on time-delay experiments, where attosecond XUV pulses are used to photoionize target atoms at well-defined times, followed by a probing process in real time by a phase-locked, infrared laser field. In this way, the laser field serves as a 'clock' to monitor the ionization event, but the observable delays do not correspond directly to the delay associated with single-photon ionization. Instead, a significant part of the observed delay originates from a measurement induced process, which obscures the single-photon ionization dynamics. This artefact is traced back to a phaseshift of the above-threshold ionization transition matrix element, which we call the continuum-continuum phase. It arises due to the laser-stimulated transitions between Coulomb continuum states. As we shall show here, these measurement-induced effects can be separated from the single-photon ionization process, using analytical expressions of universal character, so that eventually the attosecond time delays in photoionization can be accessed.
308 citations
TL;DR: In this article, experimental and theoretical tools to excite, study and understand strongly interacting Rydberg gases are reviewed, with a focus on the excitation of dense ultracold atomic samples close to, or within quantum degeneracy, high-lying S-states of rubidium.
Abstract: We review experimental and theoretical tools to excite, study and understand strongly interacting Rydberg gases. The focus lies on the excitation of dense ultracold atomic samples close to, or within quantum degeneracy, high-lying Rydberg states. The major part is dedicated to highly excited S-states of rubidium, which feature an isotropic van der Waals potential. Nevertheless, the setup and the methods presented are also applicable to other atomic species used in the field of laser cooling and atom trapping. (Some figures may appear in colour only in the online journal)
273 citations
TL;DR: In this paper, a general mathematical definition for non-Markovianity in the quantum regime and a measure for the degree of memory effects in the dynamics of open systems, which are based on the exchange of information between system and environment are presented.
Abstract: The basic features of the dynamics of open quantum systems, such as the dissipation of energy, the decay of coherences, the relaxation to an equilibrium or non-equilibrium stationary state, and the transport of excitations in complex structures are of central importance in many applications of quantum mechanics. The theoretical description, analysis and control of non-Markovian quantum processes play an important role in this context. While in a Markovian process an open system irretrievably loses information to its surroundings, non-Markovian processes feature a flow of information from the environment back to the open system, which implies the presence of memory effects and represents the key property of non-Markovian quantum behaviour. Here, we review recent ideas developing a general mathematical definition for non-Markovianity in the quantum regime and a measure for the degree of memory effects in the dynamics of open systems, which are based on the exchange of information between system and environment. We further study the dynamical effects induced by the presence of system–environment correlations in the total initial state and design suitable methods to detect such correlations through local measurements on the open system.
155 citations
TL;DR: In this paper, the carrier envelope phase effects of femtosecond laser pulses were investigated for electron rescattering at sharp metal tips, and the authors presented detailed theory models that support this interpretation.
Abstract: Nanometre-scale metal tips irradiated by femtosecond laser pulses represent ultrafast electron sources. The combination of the laser pulse and the tip offers the possibility of extending attosecond science from atomic or molecular gases to surfaces of solid nanoemitters. We first review this emerging research field focusing on electron rescattering at sharp metal tips. In particular, we investigate the carrier?envelope phase effects that reveal attosecond emission dynamics. Furthermore, we present detailed theory models that support this interpretation.
137 citations
TL;DR: In this paper, the quantum properties of light were studied in the context of cavity quantum electrodynamics with quantum gases, where the quantum statistical natures of both light and ultracold matter play equally important roles.
Abstract: Although the study of ultracold quantum gases trapped by light is a prominent direction of modern research, the quantum properties of light were widely neglected in this field. Quantum optics with quantum gases closes this gap and addresses phenomena where the quantum statistical natures of both light and ultracold matter play equally important roles. First, light can serve as a quantum nondemolition probe of the quantum dynamics of various ultracold particles from ultracold atomic and molecular gases to nanoparticles and nanomechanical systems. Second, due to the dynamic light?matter entanglement, projective measurement-based preparation of the many-body states is possible, where the class of emerging atomic states can be designed via optical geometry. Light scattering constitutes such a quantum measurement with controllable measurement back-action. As in cavity-based spin squeezing, the atom number squeezed and Schr?dinger cat states can be prepared. Third, trapping atoms inside an optical cavity, one creates optical potentials and forces, which are not prescribed but quantized and dynamical variables themselves. Ultimately, cavity quantum electrodynamics with quantum gases requires a self-consistent solution for light and particles, which enriches the picture of quantum many-body states of atoms trapped in quantum potentials. This will allow quantum simulations of phenomena related to the physics of phonons, polarons, polaritons and other quantum quasiparticles.
125 citations
TL;DR: In this article, a generalized phase-matching model is proposed for the generation of high-order harmonics using laser pulse energies in the few-μJ range at high repetition rates.
Abstract: We investigate the generation of high-order harmonics using laser pulse energies in the few-μJ range at high repetition rates. We analyse how the conversion efficiency is influenced by the tight focusing geometry required for the generation of high-order harmonics under these conditions. A generalized phase-matching model allows us to discuss macroscopic phase effects independent of focal length. We present experimental results using the example of a 100 kHz laser system to generate harmonics up to the 27th order in Ar with a photon flux up to 3 × 109 photons s−1 into one harmonic order. High-repetition-rate femtosecond or even attosecond light sources open new possibilities for a broad range of applications such as time-resolved photoelectron spectroscopy and microscopy in the extreme ultraviolet regime.
120 citations
TL;DR: In this article, the authors focus on spin squeezing in atomic systems and give an introduction to its concepts and discuss its generation in Bose-Einstein condensates, as well as the experimental requirements necessary for the generation and direct detection of coherent spin squeezing.
Abstract: Squeezed states, special kinds of entangled states, are known as a useful resource for quantum metrology. In interferometric sensors, they allow us to overcome the ‘classical’ projection noise limit stemming from the independent nature of the individual photons or atoms within the interferometer. Motivated by the potential impact on metrology as well as by fundamental questions in the context of entanglement, a lot of theoretical and experimental effort has been made to study squeezed states. The first squeezed states useful for quantum-enhanced metrology have been proposed and generated in quantum optics, where the squeezed variables are the coherences of the light field. In this tutorial, we focus on spin squeezing in atomic systems. We give an introduction to its concepts and discuss its generation in Bose–Einstein condensates. We discuss in detail the experimental requirements necessary for the generation and direct detection of coherent spin squeezing. Two exemplary experiments demonstrating adiabatically prepared spin squeezing based on motional degrees of freedom and diabatically realized spin squeezing based on internal hyperfine degrees of freedom are discussed.
110 citations
TL;DR: In this paper, it was shown that a correlated environment is capable to simulate non-Markovian evolutions leading to any indivisible qubit channel, and the corresponding master equation can be derived to generate a continuous time non-markovian dynamics implementing the universal NOT gate.
Abstract: A sequence of controlled collisions between a quantum system and its environment (composed of a set of quantum objects) naturally simulates (with arbitrary precision) any Markovian quantum dynamics of the system under consideration. In this paper we propose and study the problem of simulation of an arbitrary quantum channel via collision models. We show that a correlated environment is capable to simulate non-Markovian evolutions leading to any indivisible qubit channel. In particular, we derive the corresponding master equation generating a continuous time non-Markovian dynamics implementing the universal NOT gate being an example of the most non-Markovian quantum channels. (Some figures may appear in colour only in the online journal)
106 citations
TL;DR: In this article, a real-time, single-shot carrier-envelope phase (CEP) tagging technique for few-cycle pulses was developed and combined with cold-target recoil-ion momentum spectroscopy and velocity-map imaging to investigate and control CEP-dependent processes with attosecond resolution.
Abstract: A precise, real-time, single-shot carrier–envelope phase (CEP) tagging technique for few-cycle pulses was developed and combined with cold-target recoil-ion momentum spectroscopy and velocity-map imaging to investigate and control CEP-dependent processes with attosecond resolution. The stability and precision of these new techniques have allowed for the study of intense, few-cycle, laser-matter dynamics with unprecedented detail. Moreover, the same stereo above-threshold ionization (ATI) measurement was expanded to multi-cycle pulses and allows for CEP locking and pulse-length determination. Here we review these techniques and their first applications to waveform characterization and control, non-sequential double ionization of argon, ATI of xenon and electron emission from SiO2 nanospheres.
88 citations
TL;DR: In this article, the authors describe the generation of high-order elliptically and circularly polarized harmonic spectra in an aligned H+2 molecule ion by a combination of two-colour ultrashort intense laser fields from numerical solutions of the corresponding time-dependent Schrodinger equation (TDSE).
Abstract: We describe the generation of high-order elliptically and circularly polarized harmonic spectra in an aligned H+2 molecule ion by a combination of two-colour ultrashort intense laser fields from numerical solutions of the corresponding time-dependent Schrodinger equation (TDSE). In intense bichromatic circularly and linearly or circularly polarized laser pulses with intensity I0 and angular frequencies ω0 and 2ω0, it is found that maximum molecular high-order harmonic generation (MHOHG) energies are functions of the molecular internuclear distance. Based on a classical model of laser-induced electron collisions with neighbouring ions, the optimal values of the pulse relative carrier envelope phase , the molecular internuclear distance R and the angle of molecular alignment to the laser polarization axis are obtained for efficiently producing MHOHG spectra with the maximum harmonic energy Ip + 13.5Up, where Ip is the ionization potential of the molecule and Up = I0/4meω20 is the ponderomotive energy of the continuum electron at intensity I0 and frequency ω0 of the laser pulse. The results have been confirmed from corresponding TDSE nonperturbative numerical simulations. The polarization property of the generated harmonics is also presented. The mechanism of MHOHG is further characterized with a Gabor time frequency analysis. It is confirmed that a single collision trajectory of the continuum electron with neighbouring ions dominates in the MHOHG processes. The high efficiency of the proposed MHOHG scheme provides a possible source for production of elliptically and/or circularly polarized attosecond extreme ultraviolet pulses. Circularly polarized attosecond pulses can also be generated by using intense ultrashort circularly polarized laser pulses in combination with static electric fields of comparable intensity for H+2 at equilibrium. A time frequency analysis also confirms the role of single recollisions as the dominant mechanism of the generation of circularly polarized harmonics.
80 citations
TL;DR: In this article, the authors introduce the moving medium analogy for black holes and demonstrate how dispersion can be incorporated into this generalized framework, which can be used for the trans-planckian problem of the origin of the radiation in high frequencies.
Abstract: Hawking radiation, despite being known to theoretical physics for nearly 40 years, remains elusive and undetected. It also suffers, in its original context of gravitational black holes, from practical and conceptual difficulties. Of particular note is the trans-Planckian problem, which is concerned with the apparent origin of the radiation in absurdly high frequencies. In order to gain better theoretical understanding and, it is hoped, experimental verification of Hawking radiation, much study is being devoted to laboratory systems which use moving media to model the spacetime geometry of black holes, and which, by analogy, are also thought to emit Hawking radiation. These analogue systems typically exhibit dispersion, which regularizes the wave behaviour at the horizon at the cost of a more complicated theoretical framework. This tutorial serves as an introduction to Hawking radiation and its analogues, developing the moving medium analogy for black holes and demonstrating how dispersion can be incorporated into this generalized framework. (Some figures may appear in colour only in the online journal)
TL;DR: A review of experimental and theoretical studies of the threshold photoionization of the heavier rare-gas atoms is presented, with particular emphasis on the autoionization resonances in the spectral region between the lowest two ionization thresholds 2P3/2 and 2P1/2.
Abstract: A review of experimental and theoretical studies of the threshold photoionization of the heavier rare-gas atoms is presented, with particular emphasis on the autoionization resonances in the spectral region between the lowest two ionization thresholds 2P3/2 and 2P1/2, accessed from the ground or excited states. Observed trends in the positions, widths and shapes of the autoionization resonances depending on the atomic number, the principal quantum number n, the orbital angular momentum quantum number l and further quantum numbers specifying the fine- and hyperfine-structure levels are summarized and discussed in the light of ab initio and multichannel quantum defect theory calculations. The dependence of the photoionization spectra on the initially prepared neutral state are also discussed, including results on the photoionization cross sections and photoelectron angular distributions of polarized excited states. The effects of various approximations in the theoretical treatment of photoionization in these systems are analysed. The very large diversity of observed phenomena and the numerous anomalies in spectral structures associated with the threshold ionization of the rare-gas atoms can be described in terms of a limited set of interactions and dynamical processes. Examples are provided illustrating characteristic aspects of the photoionization, and sets of recommended parameters describing the energy-level structure and photoionization dynamics of the rare-gas atoms are presented which were extracted in a critical analysis of the very large body of experimental and theoretical data available on these systems in the literature.
TL;DR: In this paper, the interaction between a three-level atom and a quantized single-mode field with intensity-dependent coupling in a "Kerr medium" was studied, and the effects of the intensity dependent coupling, Kerr medium and detuning parameters on the depth and domain of the atom-field state vector were investigated.
Abstract: In this paper, we study the interaction between a three-level atom and a quantized single-mode field with ‘intensity-dependent coupling’ in a ‘Kerr medium’. The three-level atom is considered to be in a Λ-type configuration. Under particular initial conditions, which may be prepared for the atom and the field, the dynamical state vector of the entire system will be explicitly obtained, for the arbitrary nonlinearity function f(n) associated with any physical system. Then, after evaluating the variation of the field entropy against time, we will investigate the quantum statistics as well as some of the nonclassical properties of the introduced state. During our calculations we investigate the effects of intensity-dependent coupling, Kerr medium and detuning parameters on the depth and domain of the nonclassicality features of the atom–field state vector. Finally, we compare our obtained results with those of V-type three-level atoms.
TL;DR: In this paper, the authors discuss how structures can be determined through correlated x-ray scattering measurements, with an emphasis on dilute suspensions of identical bioparticles, using a free-electron laser.
Abstract: It was suggested more than three decades ago that the three-dimensional structure of one particle may be determined using the simultaneous x-ray scattering from many randomly oriented copies ab initio, without modelling of a priori information. This may be possible, provided sufficiently brief and intense x-ray pulses that can ?outrun? the effects of radiation damage and simultaneously produce significant signal within ?snapshot? diffraction patterns. Because the ensemble of particles is static throughout the snapshot exposure, solution scattering patterns contain angular intensity fluctuations and thus differ from conventional isotropic scattering patterns. X-ray free-electron lasers may be able to provide the x-ray source properties that are required to make such experiments feasible. In this tutorial we discuss how structures might be determined through correlated x-ray scattering measurements, with an emphasis on dilute suspensions of identical bioparticles.
TL;DR: In this article, the authors review the current state of tabletop extreme ultraviolet (XUV) sources based on high harmonic generation (HHG) in femtosecond enhancement cavities (fsEC), including current technical challenges to increasing the photon flux and maximum photon energy produced by this type of system.
Abstract: We review the current state of tabletop extreme ultraviolet (XUV) sources based on high harmonic generation (HHG) in femtosecond enhancement cavities (fsEC). Recent developments have enabled generation of high photon flux (1014 photons s?1) in the XUV, at high repetition rates (>50?MHz) and spanning the spectral region from 40 to 120?nm. This level of performance has enabled precision spectroscopy with XUV frequency combs and promises further applications in XUV spectroscopic and photoemission studies. We discuss the theory of operation and experimental details of the fsEC and XUV generation based on HHG, including current technical challenges to increasing the photon flux and maximum photon energy produced by this type of system. Current and future applications for these sources are also discussed.
TL;DR: In this paper, the authors studied beating dark?dark solitons as a prototypical coherent structure that emerges in two-component Bose?Einstein condensates, and showed their connection to the dark?bright soliton via SO(2) rotation, and infer from it both their intrinsic beating frequency and their frequency of oscillation inside a parabolic trap.
Abstract: Motivated by recent experimental results, we study beating dark?dark (DD) solitons as a prototypical coherent structure that emerges in two-component Bose?Einstein condensates. We showcase their connection to dark?bright solitons via SO(2) rotation, and infer from it both their intrinsic beating frequency and their frequency of oscillation inside a parabolic trap. We identify them as exact periodic orbits in the Manakov limit of equal inter- and intra-species nonlinearity strengths with and without the trap and showcase the persistence of such states upon weak deviations from this limit. We also consider large deviations from the Manakov limit illustrating that this breathing state may be broken apart into dark?anti-dark soliton states. Finally, we consider the dynamics and interactions of two beating DD solitons in the absence and in the presence of the trap, inferring their typically repulsive interaction.
TL;DR: In this paper, the entanglement of the ground state and several singlet and triplet excited states of the helium atom was computed using high-quality, state-of-the-art wavefunctions.
Abstract: We compute the entanglement of the ground state and several singlet and triplet excited states of the helium atom using high-quality, state-of-the-art wavefunctions. The behaviour of the entanglement of the helium eigenstates is similar to that observed in some exactly soluble two-electron systems. In particular, the amount of entanglement exhibited by the eigenstates tends to increase with energy.
TL;DR: In this paper, the authors report the extension of hollow-core fiber pulse compression to longer wavelengths and demonstrate the beneficial effect of few-cycle pulses which enable higher saturation intensities on target compared to multicycle pulses.
Abstract: We report the extension of hollow-core fibre pulse compression to longer wavelengths. High-energy multi-cycle infrared pulses are generated via optical parametric amplification and subsequently broadened in the fibre. 2.5-cycle pulses at the Signal wavelength (1.4 ?m) and 1.6-cycle pulses at the Idler wavelength (1.8 ?m) in the sub-millijoule regime have been generated. New compression schemes can be applied at 1.8 ?m and beyond. In this manner, 1.6-cycle carrier envelope phase stable pulses were generated by linear propagation in the anomalous dispersion regime of bulk glass which surprisingly enables compression below its third-order dispersion limit. Furthermore, a dispersion-free way of controlling the carrier envelope phase is demonstrated. Moreover, we experimentally confirm the increase in high-harmonic cut-off energy with driving laser wavelength and demonstrate the beneficial effect of few-cycle pulses which enable higher saturation intensities on target compared to multi-cycle pulses. It will be an ideal tool for future synthesis of isolated attosecond pulses in the sub-keV regime. With this laser source, we revealed for the first time multi-electron effects in high harmonic generation in xenon.
TL;DR: In this paper, a nonlinear Jaynes-Cummings model (NJCM) is proposed to describe the interaction of a two-level atom with a single mode of the electromagnetic field in the presence of a non-linear Kerr-like medium.
Abstract: Based on the f-oscillator formalism, we introduce a nonlinear Jaynes–Cummings model (NJCM) which is constructed from the standard JCM by deforming the single-mode field operators. Such a generalization of the JCM describes the interaction of a two-level atom with a single mode of the electromagnetic field in the presence of a nonlinear Kerr-like medium. Since the medium is modelled as an f-oscillator, it is possible to consider the field f-coherent states (nonlinear coherent states) and their evolution.
TL;DR: In this paper, the authors analyse how imperfections in single-photon detectors impact the characterization of photon-pair sources and perform exact calculations to reveal the effects of multi-pair emissions and of noisy, non-unit efficiency, nonphoton-number resolving detections on the Cauchy-Schwarz parameter, on second-order auto-correlation and cross correlation functions, and on the visibilities of both Hong-Ou-Mandel and Bell-like interferences.
Abstract: We analyse how imperfections in single-photon detectors impact the characterization of photon-pair sources. We perform exact calculations to reveal the effects of multi-pair emissions and of noisy, non-unit efficiency, nonphoton-number resolving detections on the Cauchy–Schwarz parameter, on the second-order auto-correlation and cross-correlation functions, and on the visibilities of both Hong–Ou–Mandel and Bell-like interferences. We consider sources producing either two-mode squeezed states or states with a Poissonian photon distribution. The proposed formulas are useful in practice to determine the impacts of multi-pair emissions and dark counts in standard tests used in quantum optics.
TL;DR: In this article, long-range dipole-dipole and quadrupole-quadrupole interactions between pairs of Rydberg atoms are calculated perturbatively for calcium, strontium and ytterbium within the Coulomb approximation.
Abstract: Long-range dipole–dipole and quadrupole–quadrupole interactions between pairs of Rydberg atoms are calculated perturbatively for calcium, strontium and ytterbium within the Coulomb approximation. Quantum defects, obtained by fitting existing laser spectroscopic data, are provided for all S, P, D and F series of strontium and for the 3P2 series of calcium. The results show qualitative differences with the alkali metal atoms, including isotropically attractive interactions of the strontium 1S0 states and a greater rarity of Forster resonances. Only two such resonances are identified, both in triplet series of strontium. The angular dependence of the long-range interaction is briefly discussed.
TL;DR: In this article, a double optical gating method was used to demonstrate high-order harmonics from carbon plasma using the extreme ultraviolet continuum covered 17 −25 eV. The observation of such a continuum is the first step towards the generation of high-flux single attosecond pulses from plasma harmonics.
Abstract: We demonstrated continuum high-order harmonics from carbon plasma using the double optical gating method. The extreme ultraviolet continuum covered 17‐25 eV. The observation of such continuum is the first step towards the generation of high-flux single attosecond pulses from plasma harmonics. (Some figures may appear in colour only in the online journal)
TL;DR: In this paper, a class of Markovian dynamics using the concept of a divisible dynamical map is characterized and a family of criteria which can distinguish Markovians and non-Markovians is provided.
Abstract: We characterize a class of Markovian dynamics using the concept of a divisible dynamical map. Moreover, we provide a family of criteria which can distinguish Markovian and non-Markovian dynamics. These Markovianity criteria are based on a simple observation that Markovian dynamics implies monotonic behaviour of several well-known quantities such as distinguishability of states, fidelity, relative entropy and genuine entanglement measures.
TL;DR: In this article, high-order harmonic generation in graphite-ablated plasmas was systematically studied using ultrashort (3.5 and 30 fs) laser pulses.
Abstract: High-order harmonic generation in graphite-ablated plasmas was systematically studied using ultrashort (3.5 and 30 fs) laser pulses. We observed the efficient frequency conversion of 3.5 fs Ti:sapphire laser pulses in the range of 15-26 eV. Stabilization of the harmonic yield at a 1 kHz pulse repetition rate was accomplished using a rotating graphite target. We also show the results of harmonic generation in carbon plasma using 1300 nm, 40 ps pulses, which allowed the extension of the harmonic cutoff while maintaining a comparable conversion efficiency to the case of 780 nm driving radiation. The time-of-flight mass spectrometric analysis of the plasma components and the scanning electron microscopy of plasma debris under optimal conditions for harmonic generation suggest the presence of small carbon clusters (C10-C30 )i n the plasma plume at the moment of femtosecond pulse propagation, which further aggregate on nearby substrates. We present the results of plasma spectroscopy obtained under unoptimized plasma conditions that elucidate the reduction in harmonic signal. We also present calculations of plasma concentration under different excitation conditions of the ablated graphite target. (Some figures may appear in colour only in the online journal)
TL;DR: In this article, experimental studies of the optical properties and decoherence for Tm3+:LiNbO3, Pr3 +:LiNiBO3 and KTP bulk crystals for quantum memory applications are reported.
Abstract: Optical waveguides in rare-earth-doped crystals are one of the most promising systems for practical implementations of quantum memory To further develop these systems, detailed understanding of these materials is required We report experimental studies of the optical properties and decoherence for Tm3+:LiNbO3, Pr3+:LiNbO3, Er3+:LiNbO3 and Er3+:KTiOPO4 (KTP) bulk crystals for quantum memory applications and discuss potential differences between the properties of the bulk single crystals and optical waveguides These systems include the rare-earth ions most commonly exploited in quantum memory studies incorporated into two of the most technologically significant waveguide host materials Photon echo methods were used to study decoherence as a function of temperature, applied magnetic field strength, dopant concentration and excitation wavelength Decoherence mechanisms were investigated and modelled to interpret the observed behaviour Spectral hole burning was used to characterize Stark and Zeeman effects Bulk crystal properties were compared and contrasted to the properties of doped waveguides
TL;DR: In this paper, the yield of strong-field ionization, by a linearly polarized probe pulse, is studied experimentally and theoretically as a function of the relative orientation between the laser field and the molecule.
Abstract: The yield of strong-field ionization, by a linearly polarized probe pulse, is studied experimentally and theoretically as a function of the relative orientation between the laser field and the molecule. Experimentally, carbonyl sulphide (OCS), benzonitrile and naphthalene molecules are aligned in one or three dimensions before being singly ionized by a 30 fs laser pulse centred at 800 nm. Theoretically, we address the behaviour of these three molecules. We consider the degree of alignment and orientation and model the angular dependence of the total ionization yield by molecular tunnelling theory accounting for the Stark shift of the energy level of the ionizing orbital. For naphthalene and benzonitrile, the orientational dependence of the ionization yield agrees well with the calculated results, in particular, we observe that ionization is maximized when the probe laser is polarized along the most polarizable axis. For OCS the observation of the maximum ionization yield when the probe is perpendicular to the internuclear axis contrasts the theoretical results.
TL;DR: In this paper, the authors report on recent cross section results for positron scattering from molecular oxygen (O2) using a positron spectrometer in the energy range from 0.1 to 50 eV and with an energy resolution of the positron beam of ∼ 0.25 eV.
Abstract: We report on recent cross section results for positron scattering from molecular oxygen (O2). Total cross sections (TCSs) were measured with a positron spectrometer in the energy range from 0.1 to 50 eV and with an energy resolution of the positron beam of ∼0.25 eV. In addition, TCSs as well as elastic and inelastic integral cross sections were computed within the independent atom model and screening corrected additivity rule approach, with both dipole and dipole plus quadrupole polarization potentials, between 1 and 1000 eV impact energy. An overall fair level of accord is found between the experimental TCS and that calculated with the model that includes the quadrupole term. Comparison to earlier measurements shows very good agreement with the present measured TCS and fair agreement with the TCS computed with our most physical model above ∼8 eV. Conversely, we find only a marginal level of accord when comparing our experimental TCS with previous computations, while the present TCS calculated with the dipole plus quadrupole potentials appears to agree reasonably well with most of the existing theoretical results above ∼100 eV.
TL;DR: In this paper, the photoionization spectra of A@C60 atoms are largely insensitive to the degree η of diffuseness of the potential borders, in a reasonably broad range of ηs.
Abstract: A perceived advantage for the replacement of a discontinuous square-well pseudo-potential, which is often used by various researchers as an approximation to the actual C60 cage potential in calculations of endohedral atoms A@C60, by a more realistic diffuse potential is explored. The photoionization of endohedral H@C60 and Xe@C60 is chosen as the case study. The diffuse potential is modelled by a combination of two Woods–Saxon potentials. It is demonstrated that photoionization spectra of A@C60 atoms are largely insensitive to the degree η of diffuseness of the potential borders, in a reasonably broad range of ηs. These spectra are found to be insensitive to discontinuity of the square-well potential as well. Both potentials result in practically identical calculated spectra. New numerical values for the set of square-well parameters, which lead to a better agreement between experimental and theoretical data for A@C60 spectra, are recommended for future studies.
TL;DR: It is pointed to the fact that two sufficient but not necessary signatures of non-Markovianity of a classical process find their natural quantum counterpart in recently introduced measures of quantum non-Johnstonianity.
Abstract: We consider the issue of non-Markovianity of a quantum dynamics starting from a comparison with the classical definition of Markovian processes We point to the fact that two sufficient but not necessary signatures of non-Markovianity of a classical process find their natural quantum counterpart in recently introduced measures of quantum non-Markovianity This behaviour is analysed in detail for quantum dynamics which can be built taking as input a class of classical processes
TL;DR: In this article, the authors demonstrate the generation of high-energy sub-2-cycle laser pulses generated through hollow core fiber pulse compression using two independent methods: spectral phase interferometry (SPI) and spatially encoded ancilla beams.
Abstract: We demonstrate the generation of high-energy sub-2-cycle laser pulses generated through hollow core fibre pulse compression. We demonstrate their full characterization with two independent methods. For all-optical characterization in amplitude and spectral phase, we employ spatially encoded arrangement spectral phase interferometry for direct electric-field reconstruction using spectrally filtered ancilla beams to characterize the sub-4-fs pulses with spatial resolution. For field-sensitive pulse characterization, we generate isolated attosecond pulses around 93 eV. The attosecond pulse as well as the infrared few-cycle pulse is characterized in amplitude and phase using the frequency resolved optical gating for complete reconstruction of the attosecond bursts technique. We find good agreement between the two methods.