Momentum States Research Articles

Shell model study of nuclear structure in 63,65,67Ga

Shell model calculations have been performed in [Formula: see text] model space using two different interactions viz. jj44bpn and jun45pn to explore nuclear structure in [Formula: see text]Ga. Calculated excitation energies are compared with previously reported experimental values and a good agreement has been observed. Transitions strengths are also calculated using two sets of effective charges for proton and neutron and are compared with nearby [Formula: see text]Zn isotopes. Occupation probabilities of protons and neutrons corresponding to individual orbitals (namely [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] orbital), and dominant particle configurations for individual spin states have been presented as well. Calculations suggest major role of intruder [Formula: see text] orbital in constructing the wave functions of higher angular momentum states, whereas, the lower excited states are mainly dominated by contributions from [Formula: see text] orbitals.

Accurate calculation of multipole polarizabilities for one-electron atom in Debye plasmas

The electric multipole polarizabilities of one-electron atoms embedded in weakly coupled Debye plasmas are calculated in the non-relativistic framework. The static dipole, quadrupole, octopole, and hexadecapole polarizabilities for hydrogen atoms in both ground and excited states at a variety of Debye screening parameters are calculated in high precision based on the sum-over-states method, where the system bound and continuum states are produced by employing the generalized pseudospectral method. It is shown that the contribution of bound states to the polarizability decreases with increasing the plasma screening strength, whereas the contribution of continuum states is enhanced. At very small screening parameters where the plasma environment starts to take effect, it is found that the 2l-pole polarizability for s-wave states with principle quantum number n≥l+1 has an abrupt change from its non-screening value to infinity. We attribute such a phenomenon to the sudden non-degeneracy of different angular momentum states in the n shell. With continuously increasing the screening strength, the polarizabilities for n≥l+1 states decrease to certain values and, eventually, they approach to infinity at the critical screening parameter. For states with n≤l, the 2l-pole polarizabilities show regular enhancement from the non-screening value to infinity. The present results are compared with other theoretical calculations available in the literature and it is shown that our work has established by now the most accurate predictions of multipole oscillator strengths and polarizabilities for one-electron atoms in Debye plasmas.

Population transfer to high angular momentum states in infrared-assisted XUV photoionization of helium

An extreme-ultraviolet (XUV) laser pulse consisting of harmonics of a fundamental near-infrared (NIR) laser frequency is combined with the NIR pulse to systematically study two-color photoionization of helium atoms. A time-resolved photoelectron spectroscopy experiment is carried out where energy- and angle-resolved photoelectron distributions are obtained as a function of the NIR intensity and wavelength. Time-dependent Schrödinger equation calculations are performed for the conditions corresponding to the experiment and used to extract residual populations of Rydberg states resulting from excitation by the XUV + NIR pulse pair. The residual populations are studied as a function of the NIR intensity (3.5 × 1010 − 8 × 1012 W cm−2) and wavelength (760–820 nm). The evolution of the photoelectron distribution and the residual populations are interpreted using an effective restricted basis model, which includes the minimum set of states relevant to the features observed in the experiments. As a result, a comprehensive and intuitive picture of the laser-induced dynamics in helium atoms exposed to a two-color XUV–NIR light field is obtained.

Collective modes and gapped momentum states in liquid Ga: Experiment, theory, and simulation

Collective excitations in liquids are important for understanding liquid dynamical and thermodynamic properties. Gapped momentum states (GMS) are a notable feature of liquid dynamics predicted to operate in the transverse sector of collective excitations. Here, we combine inelastic neutron scattering experiments, theory and molecular dynamics modelling to study collective excitations and GMS in liquid Ga in a wide range of temperature and $k$-points. We find that all three lines of enquiry agree for the longitudinal sector of liquid dynamics. In the transverse sector, the experiments agree with theory, modelling as well as earlier X-ray experiments at larger $k$, whereas theory and modelling agree in a wide range of temperature and $k$-points. We observe the emergence and development of the $k$-gap in the transverse sector which increases with temperature and inverse of relaxation time as predicted theoretically.

How Exciton Interactions Control Spin-Depolarization in Layered Hybrid Perovskites.

Using circularly polarized broadband transient absorption, time-resolved circular photoluminescence, and transient Faraday rotation spectroscopy, we report that spin-dependent interactions have a significant impact on exciton energies and spin depolarization times in layered Ruddlesden-Popper hybrid metal-halide perovskites. In BA2FAPb2I7, we report that room-temperature spin lifetimes are largest (3.2 ps) at a carrier density of ∼1017 cm-3 with increasing depolarization rates at higher exciton densities. This indicates that many-body interactions reduce spin-lifetimes and outcompete the effect of D'yakonov-Perel precessional relaxation that has been previously reported at lower carrier densities. We further observe a dynamic circular dichroism that arises from a photoinduced polarization in the exciton distribution between total angular momentum states. Our findings provide fundamental and application relevant insights into the spin-dependent exciton-exciton interactions in layered hybrid perovskites.

The effect of astigmatism induced by refraction on the orbital angular momentum of light

We use the Fourier transform and Snell’s law to demonstrate how refraction at a flat interface induces astigmatism and transforms the spatial distribution of a stigmatic beam. Refraction makes the beam parameters for the transverse dimensions perpendicular and parallel to the plane of incidence grow differently and gives rise astigmatism. The decompositions of the orbital angular momentum of the beam before and after refraction are different. A single-value state of orbital angular momentum of the incident photon in a Laguerre–Gaussian mode is transformed into a superposition state.

Numerical Analysis of Multi-Phase Flow around Supercavitating Body at Various Cavitator Angle of Attack and Ventilation Mass Flux

Cavitation flow is an important issue in many areas of mechanical engineering. In this study, the natural and ventilated cavitation analyses were performed using the developed code for the cavitation flow analysis. The governing equation is the Navier-Stokes equation based on a homogeneous mixture model. This model assumes that all fluids are in an equilibrium state of momentum. The momentum equations are solved using the homogeneous mixture phase, although the continuity equations are solved in the liquid, vapor, and gas phases, separately. Computational analysis was performed for the different injection conditions and inflow velocity conditions under the same conditions as the experiments. The comparison between the cavitation shape and the drag showed good agreement with the experiments. Based on this, this study predicted the change of cavitation shape according to the change of cavitator angle of attack.

Design a photonic crystal fiber of guiding terahertz orbital angular momentum beams in optical communication

In this letter, a hollow core ring based circular photonic crystal fiber (PCF) is explored and proposed with stably supporting terahertz (THz) orbital angular momentum (OAM) states transmission. The proposed PCF is discussed, investigated, analyzed and simulated with optical properties in a terahertz frequency spectrum ranging from 0.20 THz to 0.55 THz. The OAM and THz communication-based parameters of the fiber are deliberated extensively under various conditions through using the full vector finite element method (FEM). Some significant parameters of PCF like effective refractive index difference, dispersion profile, confinement loss, effective mode area, numerical aperture, power fraction and isolation effects are numerically discussed for the first time with their effects and applications on the THz OAM transmission. The mentioned PCF has supported 48 OAM modes with a large effective refractive index difference up to 10−3. The confinement loss of the PCF around 10−10 dB/cm, and the average dispersion profile variation is 1.0055 ps/THz/cm. Besides, the highest numerical aperture and power fraction of the PCF are 0.35 and 99.7882%, respectively. Also, a higher isolation power effect around 267 dB, and crosstalk less than −14 dB are obtained for the PCF. Moreover, this kind of PCF would be a robust candidate for efficient THz OAM transmission, high capacity and high feasibility of optical fiber communications.

Direct discrimination of structured light by humans

We predict and experimentally verify an entoptic phenomenon through which humans are able to perceive and discriminate optical spin-orbit states. Direct perception and discrimination of these particular states of light with polarization-coupled spatial modes is possible through the observation of distinct profiles induced by the interaction between polarization topologies and the radially symmetric dichroic elements that are centered on the foveola in the macula of the human eye. A psychophysical study was conducted where optical states with a superposition of right and left circular polarization coupled to two different orbital angular momentum (OAM) values ([Formula: see text] and [Formula: see text]) were directed onto the retina of participants. The number of azimuthal fringes that a human sees when viewing the spin-orbit states is shown to be equal to the number (N) of radial lines in the corresponding polarization profile of the beam, where [Formula: see text] The participants were able to correctly discriminate between two states carrying OAM [Formula: see text] and differentiated by [Formula: see text] and [Formula: see text], with an average success probability of 77.6% (average sensitivity [Formula: see text], [Formula: see text], [Formula: see text]). These results enable methods of robustly characterizing the structure of the macula, probing retina signaling pathways, and conducting experiments with human detectors and optical states with nonseparable modes.

Propensity rules and interference effects in laser-assisted photoionization of helium and neon

We investigate the angle-resolved photoelectron spectra from laser-assisted photoionization for helium and neon atoms using an ab initio method based on time-dependent surface flux and configuration interaction singles. We find that the shape of the distributions can be interpreted using a propensity rule, an intrinsic difference in the absorption and the emission processes, as well as interference effects between multiple paths to the final angular momentum state. The difference between absorption and emission is hidden in the first sideband in neon due to the multiple competing m channels, while in the second sideband a qualitative difference between absorption and emission is observed. In the m-resolved case, a clear difference is observed already in the first sideband, as exemplified in helium and m-resolved neon.

Single Photon Orbital Angular Momentum Transfer Based on Information Processing Technology

The orbital angular momentum state (OAM) of the photon can be theoretically evaluated from minus infinity to infinity, and the different orbital angular momentum states are orthogonal to each other. Therefore, in recent years, it has attracted wide attention from the academic circle and the industry. The purpose of this paper is to study the characteristics of single photon orbital angular momentum transfer based on information processing technology and to provide Suggestions for its technical optimization. Based on the characteristics of the angular momentum state of photon orbit, this paper studies its application and related problems in information processing and transmission. In this paper, quantum multiuser communication technology is studied, and a multiuser communication scheme based on photon orbital angular momentum state is proposed. The scheme takes advantage of the orthogonality of different orbital angular momentum states of the photon and assumes that the sender and receiver share a pair of entangled orbital angular momentum states. On this basis, the spatial light modulator is used to modulate it to the entangled photon of the sender, so that the sending photon carries all the user’s information at the same time. Finally, the receiver accurately extracts the information of each sender by measuring the coincidence count and according to the specific receiving rules. Numerical simulation and experimental results show that the coincidence rate of different coding schemes is between 0 and 0.66, which proves the feasibility of the scheme.

Noise cancellation system for shaking optical lattice by controlling optical path.

We present a simple way to control the phase of an optical lattice by detecting the interference signal of two beams. The optical lattice is intentionally shaken by varying the relative phase of the beams. However, the lattice may also be shaken by unwanted variations of the relative optical path length, e.g., due to mirror vibrations. The purpose of the servo is to attenuate these unwanted variations while the intended shaking remains. We demonstrate that the servo changes the relative phase between beams and follows the intended shaking function with 99% accuracy. The bandwidth for the acceptable attenuation of unwanted shaking, -13 dB, is measured to 1.2 kHz to control the atomic Bloch state. The servo will be implemented to attenuate the unknown system vibrations for a shaken lattice and engineer the momentum state of atoms trapped in the lattice. This idea can also be applied to any time varying experiment.

Reducing orbital angular momentum crosstalk of the Bessel–Gaussian beam for underwater optical communications

We derive analytical expressions of the probabilities for the signal and the crosstalk orbital angular momentum (OAM) states of a high order Bessel–Gaussian beam used in underwater optical communications. Our numerical results show that the probabilities of the signal and crosstalk OAM states are affected by the propagation distance and the parameters of the oceanic turbulence. The receiver aperture can be used to reduce the probabilities of the crosstalk OAM states and the probability of the detected signal OAM states keeps almost unchanged. Our results may improve the quality of optical communications systems.

Conjugate photoelectron recapture peaks in the high resolution Auger electron spectra following near-threshold Ar 2p photoionization

We have observed formation of Rydberg series superimposed on the Ar (L3M2,3M2,3) Auger electron spectral profile with photoexcitation just above the 2p−13/2 photoionization threshold. This is due to the recapture of photoelectrons induced by post-collision interaction between the Auger electron and photoelectron: Ar+ 2p−13/2 + e− → Ar+ 3p−2ml + e−. The intensity distribution of the angular momentum state resolved Rydberg peaks revealed prominent conjugate peaks due to angular momentum exchange between photoelectrons and Auger electrons in the process. In addition, we measured the 2p−13/2nl → 3p−2ml + e− resonant Auger spectra with high resolution below the 2p−13/2 threshold. Our results showed that conjugate shake-up/down 2p−13/2nd → 3p−2mp + e− processes are stronger than the direct 2p−13/2nd → 3p−2ms, (m−1)d + e− processes in the spectator Auger processes, implying a strong angular momentum exchange effect between photoelectron and Auger electron.

Covariant calculation of a two-loop test of nonrelativistic QCD factorization

We test the nonrelativistic QCD factorization conjecture for inclusive quarkonium production at two loops by carrying out a covariant calculation of the nonrelativistic quantum chromodynamics (NRQCD) long-distance matrix element (LDME) for a heavy-quark pair in an $S$-wave, color-octet state to fragment into a heavy-quark pair in a color-singlet state of arbitrary orbital angular momentum. The NRQCD factorization conjecture for the universality of the LDME requires that infrared divergences that it contains be independent of the direction of the Wilson line that appears in its definition. We find this to be the case in our calculation. The results of our calculation differ in some respects from those of a previous calculation that was carried out by Nayak, Qiu, and Sterman using light-cone methods. We have identified the sources of some of these differences. The results of both calculations are consistent with the NRQCD factorization conjecture. However, the general principle that underlies this confirmation of NRQCD factorization at two-loop order has yet to be revealed.

Reflection and transmission of a Bessel vortex beam by a stratified uniaxial anisotropic slab

The reflection and transmission of a Bessel vortex beam incident on a stratified uniaxial anisotropic slab are analytically solved by use of the expansion of cylindrical vector wave functions (CVWFs). This work is an extension of our previous paper, in which the reflection and transmission of a Bessel vortex beam incident on a homogeneous uniaxial anisotropic slab were studied. A closed form of the expansion coefficients of the reflected and transmitted beams for a stratified slab is derived. Taking a three-layered uniaxial anisotropic slab as an example, the characteristics of the reflected and transmitted beams and its influencing factors are numerically analyzed, including the magnitude profiles of the electric field components, the energy conversion between the two transverse electric components, and the distortion of orbital angular momentum (OAM) states. The results indicate that the effects of the dielectric properties of each layer on the magnitude profiles of the reflected field components are prominent, while those of the transmitted beams are opposite, which could be applied in the design of optical devices. Compared with other polarization modes, the polarization perturbation for the circularly polarized caseis very slight. As for the oblique incidence, an increase of the incident angle can obtain a high-quality reflected beam with fewer derived OAM states, and the lossy media can also do the same. Since the uniaxial anisotropic media has many applications in optical communication, radar detection, microwave device manufacture, etc., and vortex beams are proved to increase the channel capacity of an optical communication systems, these numerical results are of use in optical communications, for example, reducing the crosstalk in optical communication.

Sorting full angular momentum states with Pancharatnam-Berry metasurfaces based on spiral transformation.

Full angular momentum states constitute a complete and higher state space of a photon, which are significant not only for fundamental study of light but also for practical applications utilizing cylindrical optics such as optical fibers. Here we propose and demonstrate a simple yet effective scheme of combining the spiral transformation with Pancharatnam-Berry (PB) metasurfaces for high-resolution sorting of full angular momentum states. The scheme is verified by successfully sorting full angular momentum states with 7 orbital angular momentum states and 2 spin angular momentum states via numerical simulations and experiments. We expect that our work paves the way for simple high-resolution sorting of full angular momentum states, which could be highly useful in both classical and quantum information systems.

Optomechanical detection of light with orbital angular momentum.

We present the design of an optomechanical device that allows sensitive transduction of the orbital angular momentum of light. An optically induced twist imparted on the device is detected using a photonic crystal cavity optomechanical system. This device allows the measurement of the orbital angular momentum of light when photons are absorbed by the mechanical element or the detection of the presence of photons when they are scattered into new orbital angular momentum states by a sub-wavelength grating patterned on the device. Such a system allows the detection of optical pulses with an l = 1 orbital angular momentum field that have an average photon number of 3.9 × 103 at a 5 MHz repetition rate, assuming that detector noise is not limiting measurement sensitivity. This scheme can be extended to higher order orbital angular momentum states.

Laser spectroscopy of pionic helium atoms.

Charged pions1 are the lightest and longest-lived mesons. Mesonic atoms are formed when an orbital electron in an atom is replaced by a negatively charged meson. Laser spectroscopy of these atoms should permit the mass and other properties of the meson to be determined with high precision and could place upper limits on exotic forces involving mesons (as has been done in other experiments on antiprotons2-9). Determining the mass of the π- meson in particular could help to place direct experimental constraints on the mass of the muon antineutrino10-13. However, laser excitations of mesonic atoms have not been previously achieved because of the small number of atoms that can be synthesized and their typically short (less than one picosecond) lifetimes against absorption of the mesons into the nuclei1. Metastable pionic helium (π4He+) is a hypothetical14-16 three-body atom composed of a helium-4 nucleus, an electron and a π- occupying a Rydberg state of large principal (n≈16) and orbital angular momentum (l≈n-1) quantum numbers. The π4He+ atom is predicted to have an anomalously long nanosecond-scale lifetime, which could allow laser spectroscopy to be carried out17. Its atomic structure is unique owing to the absence of hyperfine interactions18,19 between the spin-0 π- and the 4He nucleus. Here we synthesize π4He+ in a superfluid-helium target and excite the transition (n,l)=(17,16)→(17,15) of the π--occupied π4He+ orbital at anear-infrared resonance frequency of 183,760 gigahertz. The laser initiates electromagnetic cascade processes that end with the nucleus absorbing the π- and undergoing fission20,21. The detection of emerging neutron, proton and deuteron fragments signals the laser-induced resonance in the atom, thereby confirming the presence of π4He+. This work enables the use of theexperimental techniques of quantum opticsto study ameson.

High-purity orbital angular momentum states from a visible metasurface laser

Orbital angular momentum (OAM) from lasers holds promise for compact, at-source solutions for applications ranging from imaging to communications. However, conjugate symmetry between circular spin and opposite helicity OAM states (±l) from conventional spin–orbit approaches has meant that complete control of light’s angular momentum from lasers has remained elusive. Here, we report a metasurface-enhanced laser that overcomes this limitation. We demonstrate new high-purity OAM states with quantum numbers reaching l = 100 and non-symmetric vector vortex beams that lase simultaneously on independent OAM states as much as Δl = 90 apart, an extreme violation of previous symmetric spin–orbit lasing devices. Our laser conveniently outputs in the visible, producing new OAM states of light as well as all previously reported OAM modes from lasers, offering a compact and power-scalable source that harnesses intracavity structured matter for the creation of arbitrary chiral states of structured light. A metasurface laser generates orbital angular momentum states with quantum numbers reaching l = 100. Simultaneous output vortex beams, with Δl as great as 90, are demonstrated in the visible regime.