Exchange Of Orbital Angular Momentum Research Articles

Inverse Optically-Induced Ring Currents in Ring-Shaped Molecules.

Permanent electronic ring currents are supported within manifolds of ΓE degenerate excited electronic states as E± = Ex ± iEy excitations. In [ Phys. Rev. Res. 2021, 3, L042003] we showed the existence of inverse-current manifolds, where the direction of the electronic ring current in each degenerate state E± is opposite to the circular polarization of the generating light fields. This vibronic effect is caused by the exchange of orbital angular momentum between the electrons and the vibrational modes with the required symmetry. Here we consider the case of fixed nuclei and find that ring-shaped molecular systems possess inverse-current manifolds on a purely electronic-structure basis, i.e., without intervention of vibronic coupling. The effect is explained first on a tight-binding model with cyclic symmetry and then considering the ab initio electronic structure of benzene and sym-triazine. A framework for discriminating regular- and inverse-current ΓE manifolds in molecules using quantum chemistry calculations is provided.

Auxiliary-cavity-enhanced quantum estimation of optorotational-coupling strength.

A scheme is proposed to achieve significantly enhanced quantum estimation of optorotational-coupling (ORC) strength by coupling a driven auxiliary cavity to a Laguerre-Gaussian (L-G) rotational cavity, where the ORC originates from the exchange of orbital angular momentum between a L-G light and rotational mirror. The results indicate that, by appropriately designing the auxiliary-cavity mechanism, the estimation error of the ORC parameter is significantly reduced, and revealing the estimation precision has a much stronger thermal noise and dissipation robustness in comparison with the unassisted case. Our study paves the way toward achieving high-precision quantum sensors.

A five-level cold atomic system for the orbital angular momentum exchange based on a four-wave mixing setup

In this paper, we suggest a theoretical model for the exchange of the orbital angular momentum (OAM) state of laser fields in a real cold atomic system for realization in an experimental setup. By using four-wave mixing (FWM) processes, we study the spatial dependence of the new weak generated signal light under electromagnetically induced transparency conditions when one of the laser lights becomes an optical vortex. We discuss the spatial dependence of FWM processes via experimental parameters for different conditions of the OAM of vortex light. We have found that the intensity and phase distributions of the new generated light depends strongly on the OAM number of the optical vortex light. Moreover, we investigate the absorption spectrum of the new generated signal light for different OAM of the optical vortex light. Our obtained results may have potential applications in quantum information science.

Observation of Anomalous Orbital Angular Momentum Transfer in Parametric Nonlinearity.

Orbital angular momentum (OAM) conservation plays an important role in shaping and controlling structured light with nonlinear optics. The OAM of a beam originating from three-wave mixing should be the sum or difference of the other two inputs because no light-matter OAM exchange occurs in parametric nonlinear interactions. Here, we report anomalous OAM transfer in parametric upconversion, in which a Hermite-Gauss mode signal interacts with a specially engineered pump capable of astigmatic transformation, resulting in Laguerre-Gaussian mode sum-frequency generation (SFG). The anomaly here refers to the fact that the pump and signal both carry no net OAM, while their SFG does. We reveal experimentally that there is also an OAM inflow to the residual pump, having the same amount of that to the SFG but with the opposite sign, and thus holds system OAM conservation. This unexpected OAM selection rule improves our understanding of OAM transfer among interacting waves and may inspire new ideas for controlling OAM states via nonlinear optics.

Understanding the flare emission in CF Tucanae using TESS

Abstract Chromospherically active binaries are important in the understanding of the origins of optical flares. Since studies of flares in binaries are important, we perform a detailed analysis of 11 flares emitted by the RS CVn binary source CF Tucanae using the Transiting Exoplanet Survey Satellite (TESS). We assume a 10000 K blackbody spectrum to determine the flare energies, which were noted to be ∼0.29–2.86 × 1035 erg. We also fitted optical flares with a fast rise with an exponential decay burst profile and decay times were used to estimate the flare scale lengths. Three flares among them mandate a double burst model and another two exhibit complex flare features. Spot areas were found to be ∼1022 cm2 and associated magnetic energies were found to be ∼1036–37 erg. This excess of magnetic energy indicates that the flares release only a small fraction of the magnetic energy of the dominant spot but may indicate a lack of connection between the flares and the dominant spot. We also study the periodic variations using the times of minima obtained from TESS data along with previous values. The optical periodic variation requires a parabola and a sinusoidal function to get the best fit. A new periodic modulation of Pmod ∼ 28.64 ± 1.82 yr was observed and we attempt to explain this using a magnetic activity cycle. We conclude that CF Tuc exhibits complex flares and its periodic modulation varies, probably due to the exchange of spin and orbital angular momentum in the binary.

Rotational mirror–mirror entanglement via dissipative atomic reservoir in a double-Laguerre–Gaussian-cavity system

We propose a new scheme to prepare macroscopic entanglement between two rotating mirrors using dissipative atomic reservoir in a double-Laguerre–Gaussian-cavity system. The two-level atomic system driven by a strong field, acts as a single pathway of Bogoliubov dissipation to push the two original cavity modes into the desirable entangled state under the near-resonant conditions. Successively, the photon–photon entanglement can be transferred to mirror–mirror entanglement through the exchange of orbital angular momentum. In essence, the macroscopic entanglement is originated from the dissipative atomic reservoir rather than the radiation torque, thereby it is usually robust against environmental noises. The present scheme provides a feasible way to realize stable entanglement between spatially separated mirrors with high capacity, which may find potential applications in remote quantum communications.

Highly efficient exchange of orbital angular momentum of light via electron spin coherence

In this letter we analysed the efficient exchange of orbital angular momentum (OAM) of light in a double V-type semiconductor quantum well via electron spin coherence. We found that due to the four-wave mixing (FWM) mechanism the OAM state of the vortex light can transfer from applied lights to a new generated signal beam when the efficiency of the FWM processes is enough high. We also shown that the absorption spectrum of the new generated light depends on the OAM number and azimuthal angle of the optical vortex light. We realized that for some specific parametric conditions the absorption spectrum of the generated light becomes negative which corresponds to the lasing without inversion.

Tidally induced migration of TESS gas giants orbiting M dwarfs

ABSTRACT According to core-accretion formation models, the conditions under which gas giants will form around M dwarfs are very restrictive. Also, the correlation of the occurrence of these planets with the metallicity of host stars is still unknown due to the intrinsic faintness of M dwarfs in the optical and some intricacies in their spectra. Interestingly, NASA’s Transiting Exoplanet Survey Satellite (TESS) mission has started to create a growing sample of these systems, with 11 observed planets located in close-in orbits: contrary to what is expected for low-mass stars. Tidal interactions with the host star will play a key role in determining the fate of these planets, so by using the measured physical and orbital characteristics of these M-dwarf systems we numerically analyse the exchange of rotational and orbital angular momentum, while constraining the energy dissipation in each system to calculate whether host stars are spun up or spun down, depending on the relationship between the gain and loss of angular momentum by the stellar rotation. We also study the coupled orbital and physical evolution of their gas giant companion and calculate orbital circularization time-scales, as well as the time needed to undergo orbital decay from their current orbital position to the Roche limit. The thorough study of tidal processes occurring over short and long time-scales in star–planet systems like those studied here, can help constrain tidal dissipation rates inside the star and planet, complement tidal theories, and improve estimations of unconstrained properties of exoplanetary systems.

Exchange of orbital angular momentum of light via noise-induced coherence

The noise-induced coherence created via the quantum interference of incoherent radiation in atomic three-level systems of V and \ensuremath{\Lambda} types driven by a pair of weak laser pulses is shown to result in exchange of optical vortices. In the three- level V-type atom-light coupling the system is populated in its ground level, while in the \ensuremath{\Lambda} model the system is initially prepared in an electromagnetically induced transparency state. By solving the quantum optical Maxwell-Bloch equations and with quantum interference of incoherent radiation present, we show that the orbital angular momentum (OAM) of the vortex probe beam can be transferred to a generated signal field. While the exchange efficiency in the V configuration is higher, the losses are less in the \ensuremath{\Lambda} scheme when we consider such a noise-induced coherence. We further discuss the effects of phase mismatching and inhomogeneous broadening on the energy conversion between light beams carrying OAM.

Acoustic polarization singularities arising under torsion and orbital angular momentum exchange at the backward collinear acousto-optic diffraction: a case of crystals with point symmetry 3m

Acoustic polarization singularities arising under torsion and orbital angular momentum exchange at the backward collinear acousto-optic diffraction: a case of crystals with point symmetry 3m

Acoustic polarization singularities arising under torsion and orbital angular momentum exchange at the backward collinear acousto-optic diffraction: a case of crystals with point symmetry 3m. Errata

Acoustic polarization singularities arising under torsion and orbital angular momentum exchange at the backward collinear acousto-optic diffraction: a case of crystals with point symmetry 3m. Errata

Entanglement and coherence in a hybrid Laguerre–Gaussian rotating cavity optomechanical system with two-level atoms

We theoretically investigate quantum entanglement and coherence in a hybrid Laguerre–Gaussian rotating cavity optomechanical system with two-level atoms, where cavity and mechanical modes are coupled through the exchange of orbital angular momentum. Our study shows that the injection of atoms with a suitable choice of the physical parameters can significantly improve the degree of optomechanical entanglement in all aspects. In the study of quantum coherence research, we show more comprehensively the negative and positive effects of atoms on the coherence. The result obtained is that only when the atom is significantly off-resonant to driving field, the coupling strength in between the atoms and light field increases and the quantum coherence can be enhanced, otherwise it will reduce quantum coherence. In addition, the atomic decay suppresses quantum coherence phenomenon.

Orbital angular momentum transfer in molecular magnets

We study the propagation of probe pulses carrying orbital angular momentum (OAM) in a crystal of molecular magnets characterized by a double-$\mathrm{\ensuremath{\Lambda}}$ light-matter coupling scheme. The model is based on the four-wave mixing (FWM) of applied fields interacting with the magnetic dipole moment of the molecular magnets. We consider the light-matter interaction under the situation where a weak probe field carries an optical vortex and investigate the exchange of optical vortices between different frequencies via the FWM in the microwave region. The propagation of OAM beams with nonzero radial indices is then explored. It is found that the conservation of both azimuthal and radial indices is satisfied over the swapping of OAM states of light. Superimposing two initially weak OAM modes with different topological charges creates specific vortex beams with a very characteristic form. The resulting beam contains a central vortex as well as several singly charged peripheral vortices distributed at the same radial distance from the center of the light beam. This complex pattern of vortices arises because the intensity radius of two interfering OAM modes is different. It is shown that the boundary region of intensity dominance of two OAM modes can be controlled by the molecular magnets parameters and strong cw electromagnetic fields. Our proposed scheme may provide a route to study the solid systems suitable for quantum technologies as well as for OAM exchange devices for quantum information processing.

Quadrupole absorption rate for atoms in circularly-polarized optical vortices

Twisted light beams, or optical vortices, have been used to drive the circular motion of microscopic particles in optical tweezers and have been shown to generate vortices in quantum gases. Recent studies have established that electric quadrupole interactions can mediate an orbital angular momentum exchange between twisted light and the electronic degrees of freedom of atoms. Here we consider a quadrupole atomic transition mediated by a circularly-polarized optical vortex. We evaluate the transfer rate of the optical angular momentum to a Ca+ ion involving the 42S1∕2→32D5∕2 quadrupole transition and explain how the polarization state and the topological charge of the vortex beam determine the selection rules.

Derivation of Einstein–Cartan theory from general relativity

This paper derives the elements of classical Einstein–Cartan theory (EC) from classical general relativity (GR) in two ways. (I) Derive discrete versions of torsion (translational holonomy) and the spin-torsion field equation of EC from one Kerr solution in GR. (II) Derive the field equations of EC as the continuum limit of a distribution of many Kerr masses in classical GR. The convergence computations employ “epsilon-delta” arguments, and are not as rigorous as convergence in Sobolev norm. Inequality constraints needed for convergence restrict the limits from continuing to an infinitesimal length scale. EC enables modeling exchange of intrinsic and orbital angular momentum, which GR cannot do. Derivation of EC from GR strengthens the case for EC and for new physics derived from EC.

Laguerre-Gaussian optical sum-sideband generation via orbital angular momentum exchange

Laguerre-Gaussian optical sum-sideband generation via orbital angular momentum exchange has been studied analytically beyond the linearized approach. We obtain the analytical expression for the amplitudes of these signals within the semiclassical approximation. The pump power dependence of Laguerre-Gaussian sum-sideband generation is discussed, and we find that Laguerre-Gaussian sum-sideband generation can be remarkable even at low power through the satisfaction of matching conditions. The matching conditions for Laguerre-Gaussian sum-sideband generation in an optorotational system are discussed and summarized in detail, and the physical interpretation of matching conditions is discussed. The role of the topological charge value $l$ on the sum-sideband generation is studied, which exhibits a saturation effect for the peak value of the normalized amplitude and consequently limits further improvement of the Laguerre-Gaussian sum-sideband generation. Our results may find applications in Laguerre-Gaussian optical frequency comb and communications and provide a potential method for the determination of the orbital angular momentum of light fields with high topological charges.

Quadrupole absorption rate and orbital angular momentum transfer for atoms in optical vortices

Recent experiments involving the interaction of optical vortices with atoms in quadrupole transitions have been shown to be accompanied by the exchange of orbital angular momentum (OAM) between the electronic states of the atom and the optical vortex field. Earlier work by both theory and experiment had ruled out the transfer of a vortex OAM to the electronic degrees of freedom in an electric dipole atomic transition and it has been confirmed that the lowest multipolar order involving an OAM transfer to the electronic motion is indeed the electric quadrupole. Hitherto, the quadrupole transition involving optical vortices has not been quantified and we have thus set out to evaluate the absorption rate accompanied by an OAM transfer with reference to the $6^2S_{1/2}\rightarrow 5^2D_{5/2}$ in Cs when caesium atoms are subject to the field of a linearly polarized optical vortex. Our results assuming typical experimentally accessible parameters indicate that the absorption rate for moderate light intensities is smaller than the quadrupole spontaneous emission rate, but should still be within the measurement capabilities of modern spectroscopic techniques.

Reconfigurable orbital angular momentum exchange assisted by dual-area mirror

By using the orthogonality of the orbital angular momentum (OAM) beam and the characteristics of its annular intensity distribution, a method for separating the OAM beam from the Gaussian beam is proposed. This method uses a dual-area mirror in an OAM multiplexed data link. Experiments show that the topological charge of the multiplexed OAM beams can be reconfigured with the aid of a dual-area mirror. Compared with previous separation methods, this method is low cost, easy to implement, easy to integrate, and can freely control the direction of the separated beam. Furthermore, it can considerably reduce the optical power loss and is expected to reduce the bit error rate in the optical communication link.

Manipulation and exchange of light with orbital angular momentum in quantum-dot molecules

We study the interaction of laser pulses carrying orbital angular momentum (OAM) with structural asymmetry quantum dot molecules characterized by four energy levels. We demonstrate how the inter-dot tunneling endows exchange of optical vortices between different frequencies. We consider a case where a weak probe beam has an optical vortex and thus has a zero intensity at the center. The presence of tunneling coupling generates an additional weak laser beam with the same vorticity as that of the incident vortex beam. We analyze conditions for the vortex of the initial beam to be transferred efficiently to the generated beam. The propagation of Laguerre-Gaussian (LG) beams possessing OAM states characterized by both azimuthal and radial indices is then investigated for the case where the strong control beam is also an OAM mode. It is shown that the conservation of OAM states is always satisfied over the OAM exchange process. Yet, an abnormal case is observed in which the radial index induces some intensity patterns of the generated beam which differs from a pure LG beam of incident beams. Analytical solutions are provided to elucidate such effects induced by radial indices on propagation characteristics of OAM beams. When superimposing two initially present weak OAM modes, it is observed that the resulting optical vortices move about the beam axis as the light propagates, forming a sort of "constellation" around the center. The shift in axis of such a composite pulses is due to the effect of inter-dot tunneling which is controlled by an external electric voltage. The optical angular momenta may add a new degree of freedom in the study of solid systems suitable for quantum technologies.

Laguerre–Gauss and Hermite–Gauss soft X-ray states generated using diffractive optics

Light’s capacity to carry angular momentum is integral to our knowledge of physics and ability to probe matter. In addition to spin, photons can occupy free-space orbital angular momentum eigenstates1,2. Visible light orbital angular momentum is used in quantum information experiments, super-resolution microscopy, optical tweezers and angular momentum transfer to atoms in optical lattices3,4. Soft X-ray orbital angular momentum applications, slowed by the lack of suitable optics and the rarity of coherent X-ray sources, could enable the direct alteration of atomic states through orbital angular momentum exchange, and methods to study the electronic properties of quantum materials. We have made soft X-ray diffractive optics that generate single Laguerre–Gauss modes, observed carrying up to 30ħ angular momentum per photon, or their superpositions. We also present Hermite–Gauss diffractive optics and a soft X-ray orbital angular momentum analyser. These tools could enable both the manipulation and finer characterization of topologically complex electronic matter, such as magnetic skyrmions. Robust methods for creating and analysing soft X-ray modes, with as much as 30ħ angular momentum per photon, are demonstrated.