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Project titleInteraction of twisted light with individual atoms and atomic ensembles

Research area 02 - PHYSICS AND SPACE SCIENCES, 02-602 - Quantum field theory, quantum mechanics

Keywordsatom, molecule, twisted photon, orbital angular momentum, spin, polarization, scattering, ionization, quantum electrodynamics, quantum optics, phase vortex, topological charge

Annotation
We plan to study a number of electromagnetic processes with elementary particles (first of all, with photons) in quantum states with an orbital angular momentum with respect to a propagation axis -- with the so-called twisted particles. Whereas the conserving quantum numbers of the usual photons are three projections of the momentum and a helicity, the twisted photons are characterized with another set of quantum numbers: a longitudinal momentum, an absolute value of the transverse momentum, the helicity, and a projection of the total angular momentum onto the propagation direction. Such photons have been generated in a number of laboratories and they have found applications in classical and quantum optics, in microscopy, non-invasive diagnostics, physics of new nano-materials, in astrophysics, biology, etc. They also offer new possibilities for obtaining new information about the atomic structure and the electromagnetic interaction, in particular, for strong fields characteristic for ions of the heavy atoms. During 25 years, passed from the first experiments with the twisted photons and from the beginning of their application, this field from a beautiful but somewhat exotic island of laser physics has become a vast field of activity embracing many branches of atomic physics. The most important applications for this project lie in quantum and classical information, optical traps, and in study of the atomic systems on quantum level. The development of new applications of the twisted photons, especially in the X-ray range, is hampered by the lack of the consistent quantum-electrodynamical description of interaction of the twisted beams with atoms, ions, molecules, and atomic ensembles. The current project aims at the development of such a theory and of its applications in the fundamental problems of atomic and molecular physics. We plan to investigate interaction of the twisted light with the separate atoms (ions), confined in an ion trap, and with the atomic ensembles and molecules. For the single-atom scenario, we will pay attention to transitions between the bound states and the ionization in a region of the quasi-stationary (autoionization) states, selection rules and probabilities of which can effectively be changed due to the presence of the twisted photons' orbital angular momentum. Furthermore, absorption of the twisted light will allow one to attenuate the light (Stark) shift of the atomic levels and, therefore, it can be an effective tool for managing the prohibited dipole transitions in atomic clocks. For interaction of the twisted light with atomic ensembles, we will concentrate, in particular, on the Hanle effect in atomic vapor and will develop a theory of photoionization of molecules. Currently, the Budker Institute for Nuclear Physics SB RAS (Novosibirsk) is the only Russian institution where experimental studies with the twisted photons in the THz region are being performed. We support contacts with the experimenters, in particular, with the experimental groups in the above Institute for Nuclear Physics and in the Physikalisch-Technische Bundesanstalt (Braunschweig, Germany). We plan to formulate our results in a way convenient for comparison with the data at hand and with the future experiments.

Expected results
An analytical model for describing processes of excitation and ionization of atoms by twisted photons, including angular distributions and spin of the emitted electrons. This model will allow one to study non-dipole effects in atomic photoionization in more detail and to make concrete quantitative predictions on the magnitude of the effects, in particular, for the resonance photoionization. Study of the non-dipole effects in atomic ionization by twisted light will provide a new view on the entanglement of the atomic structure and the properties of light. The model to be developed will allow one to suggest new accurate methods for studying the interaction of the optical radiation with the multielectron atoms and will be crucially important for planning and analyzing forthcoming experiments, in particular, at Braunschweig Technical University. An analytical model for describing transitions induced by the twisted light in atomic clocks. These results will help in planning and conducting experiments with the single trapped ions. In these experiments the twisted light is used to induce the transitions, prohibited in a dipole approximation. Our calculations will facilitate the choice of a right geometry for these experiments. One of the key parameters for the future measurements is an angle between the ion quantization axis and the direction of the twisted light beam. Furthermore, the polarization state of the twisted light can influence the probability of the corresponding transitions. A generalized Weizsäcker-Williams method for describing equivalent twisted photons of the field of a twisted charged particle as a function of their energy and virtuality. The consistent accounting for the spin state and the vorticity of the equivalent photons. Application of the developed method for calculations of the more complicated processes of radiation, including Bremsstrahlung of the twisted electrons on nuclei, and of scattering with the initial twisted electrons and other particles, electromagnetic field of which is represented as a set of virtual twisted photons instead of the usual plane waves. An analytical theory of interaction of the twisted photons with molecules of an arbitrary symmetry group. Currently, the corresponding theoretical studies, to the best of our knowledge, are absent. Estimates of the vorticity effects for selected molecules in extreme ultraviolet and X-ray regions and recommendations for conducting the corresponding experiments. The results can make an essential contribution to the development of atomic and molecular physics with twisted photons and of quantum optics; they can also advance the development of the theory of quantum phenomena with non-classical light, as well as of the new applications in micro- and nano-manipulation, in microscopy, biology, quantum technologies, physics of new materials, and so forth.

Annotation of the results obtained in 2023
1. A complete description of the final quantum state of a system of two particles of different types in the processes of Vavilov-Cherenkov radiation in a medium with a refractive index and emission of a virtual photon by a relativistic electron carrying a non-zero projection of orbital angular momentum is obtained. The second process is considered as a generalization of the model of equivalent photons with angular momentum to virtual particles. The final state wave function is derived in a symmetrical form and presented in coordinate and momentum representations. The possibility of registering final particles with a non-zero projection of the total angular momentum has been established both for the case of a plane-wave initial electron and for a twisted one. It is shown that the law of conservation of total angular momentum is satisfied. For Vavilov-Cherenkov radiation, a factor has been calculated that characterizes the degree of linear polarization of a final photon with an arbitrary twistedness. For the processes of emission of equivalent photons, the relevant expressions are given for the number and average polarization of the resulting equivalent twisted photons. 2. A theoretical model has been developed for the quantum description emission of a twisted photon by a charged particle in magnetic field. The wave function of a emitted photon is obtained without specifying the detector and it is shown that it corresponds to a «twisted» Bessel beam. It is demonstrated that the majority of the emitted photons are twisted with the angular momentum projection of the order of 1. Transitions with emission of a photon with zero or negative angular momentum projection onto the direction of the magnetic field are generally strongly suppressed. Transitions between different spin states have been studied, and the well-known self-polarization effect has been reproduced. 3. The formulas, previously not presented in the literature, for the matrix element and photoelectron angular distribution in the process of multiphoton ionization of an atomic target by Bessel waves were obtained. It is shown that the expressions allow analytical integration over the impact parameter with a uniform or Gaussian distribution of target atoms; however, it is more convenient from an applied point of view to introduce a special form factor calculated for specific parameters of the process under investigation. 4. General formulas are obtained for the statistical tensors of the photoelectron and photo-ion formed during the ionization of a target of uniformly distributed unpolarized atoms by Bessel light. Based on these formulas, expressions were constructed for the polarization components of the photoelectron spin, as well as for the orientation and alignment of the residual ion. In the dipole approximation, the question about the dependence of the photoelectron spin polarization value during ionization of the 4p shell of a krypton atom on various fine structure states of the residual ion on the angle of emission of the photoelectron, the opening angle of the Bessel beam cone and the type of beam polarization (circular and linear) is considered. 5. It has been demonstrated that, due to randomness of the molecule orientation in space, the effects of twisting of the incident radiation when the molecule is ionized by Bessel light disappear upon averaging. To detect such effects, it is necessary to conduct an experiment with a molecule strictly fixed along the axis of the propagating Bessel beam and, in addition to the photoelectron, to record all decay products of the molecular ion.

Publications

1. D. Grosman, N. Sheremet, I. Pavlov, D. Karlovets Elastic scattering of Airy electron packets on atoms PHYSICAL REVIEW A, 107, 062819 (year - 2023) https://doi.org/10.1103/PhysRevA.107.062819

2. D.V. Karlovets, S.S. Baturin, G. Geloni, G.K. Sizykh, V.G. Serbo Shifting physics of vortex particles to higher energies via quantum entanglement EUROPEAN PHYSICAL JOURNAL C, 83:372 (year - 2023) https://doi.org/10.1140/epjc/s10052-023-11529-4

3. M.D. Kiselev, E.V. Gryzlova, A.N. Grum-Grzhimailo Angular distribution of photoelectrons generated in atomic ionization by twisted radiation PHYSICAL REVIEW A, 108, 023117 (year - 2023) https://doi.org/10.1103/PhysRevA.108.023117

Annotation of the results obtained in 2021
1. A theory has been developed for calculating photoelectron angular distributions (PADs) formed during the interaction of atoms with twisted radiation in the form of Bessel beams for the cases of circular and linear polarizations. We obtained the transformation that makes it possible to reconstruct the PAD in the case of the photoionization by twisted light from the PAD in the case of the photoionization by plane-wave radiation. 2. A generalization of the Weizsäcker-Williams method has been obtained for relativistic charged particles with angular momentum and the general formulas have been derived for the number of equivalent twisted photons of the electromagnetic field of a relativistic charged particle. The model developed allows one, in particular, to describe transfer of the angular momentum from an initial twisted particle (electron, positron, hadron, etc.) to the final one during scattering, annihilation or Bremsstrahlung, when the virtual particles can also carry angular momentum. 3. Based on the obtained analytical formulas, PADs due to photoionization of a helium atom in the region of the quadrupole 2p2 [1D2] and dipole 2s2p [1P1] autoionization resonances are constructed. We carried out the analysis of the constructed PADs’ evolution during scanning of the investigated energy region in terms of the photon energy and at different values of the twisted radiation cone angle θc. It is shown that the angular distributions can acquire new features of asymmetry with the increasing angle θc. 4. A theoretical model has been developed for calculating the process of resonant scattering of a twisted photon with angular momentum by a relativistic atom or an ion. Within an example of the simplest 1s -> 2p -> 1s electric dipole transition, it is shown that the vorticity is conserved with a good accuracy during scattering, while the photon energy is increased and it can reach the X-ray or even gamma-ray range when the incoming photon has an energy of the order of 1 eV. A principal possibility has been confirmed to create a fabric of the hard X-ray twisted photons at the Large Hadron Collider (LHC), which would be an analog of the corresponding source of such photons in the THz range at the Budker Institute for Nuclear Physics (SB RAS) in Novosibirsk and it would have numerous potential applications in nuclear and particle physics. 5. A carbon monoxide molecule CO has been found to be the most promising molecule for further investigation of the interaction of twisted light with molecules. For this molecule, there is a large amount of reliable information about the characteristics of its interaction with plane-wave radiation, which will allow us to make reliable predictions for the planned experiments.

Publications

1. Dmitry V. Karlovets, Valeriy G. Serbo, and Andrey Surzhykov Wave function of a photon produced in the resonant scattering of twisted light by relativistic ions Physical Review A, Vol. 104, pp. 023101-1 -- 023101-8. (year - 2021) https://doi.org/10.1103/PhysRevA.104.023101

2. Valeriy G. Serbo, Andrey Surzhykov, and Andrey Volotka Resonant Scattering of Plane-Wave and Twisted Photons at the Gamma Factory Annalen der Physik, Vol. 2021, pp. 2100199 (1-14) (year - 2021) https://doi.org/10.1002/andp.202100199

Annotation of the results obtained in 2022
1. A theoretical model has been developed to take into account the effects of quantum coherence and entanglement in the scattering of twisted light by charged particles, including protons and ions. The role of the process of post-selection of final particles in the scattering of twisted light and the transfer of angular momentum to final particles depending on the measurement process and the choice of the detector state has been studied. 2. High-precision wave functions of atoms and ions of neon and krypton were obtained by a series of calculations using the multiconfiguration Hartree-Fock method. The found wave functions were used to elucidate the characteristics of spectroscopic features (Cooper minima, autoionization resonances) and the regularities of their change in the processes of photoionization from the ground and excited states of these atoms. Knowing the positions and characteristics (profile, depth, q-index) of various spectroscopic features allows us to study in the most accurate way the mutual influence of dipole and non-dipole contributions to the differential and integral characteristics of the photoionization process, including that caused by the twisted radiation. 3. A general theoretical model has been developed to take into account the influence of quantum coherence and entanglement in the scattering of twisted and untwisted particles of arbitrary mass, energy and spin on other particles, including leptons and hadrons, as well as ions and nuclei. The role of the process of post-selection of final particles in the process of Vavilov-Cherenkov radiation, nonlinear Compton scattering and undulator radiation, elastic scattering of muons and protons, depending on the measurement process and the choice of the detector state, has been studied. It is shown that in a process with two final particles of any kind, the lack of measurement of the momentum azimuthal angle of one final particle (or its measurement with a large error - the so-called generalized measurements) leads to the fact that the state of the other particle as it is (i.e. regardless of the detector properties) turns out to be twisted. This technique can be used to generate relativistic vortex particles (including hadrons and nuclei) at accelerators, high-power lasers and free electron lasers (XFEL, etc.) 4. The model of equivalent photons with angular momentum is generalized to virtual particles. On the example of the Vavilov-Cherenkov radiation process, the wave function of a finite system of two particles (an electron and a photon) is obtained as it is, i.e. without assumptions about the detectors of both particles. It is shown that the photon part of the wave function is generally a superposition of states with total angular momentum m+1/2 and m-1/2, where m is the projection of the total angular momentum of an electron (m=1/2 for an ordinary "plane-wave" electron) . The process of Vavilov-Cherenkov radiation is related to the problem of the twisted state of a virtual photon emitted by an electron, since in both problems the square of the 4-momentum of the photon k^2 is different from zero. Thus, for strongly twisted electrons with m>>1/2, the electron's vorticity is almost completely transferred to the virtual photon, which can be used, for example, in calculations of the scattering of vortex electrons by protons. 5. The polarization properties of the transition radiation of an electron crossing a two-dimensional photonic crystal consisting of subwavelength particles arranged in a flat lattice are studied. It is shown that the polarization properties of transition radiation on a photonic crystal differ significantly from those for the ordinary transition radiation and the Smith-Purcell radiation. The theory developed contains the coordinates of the particles that make up the photonic crystal, which makes it possible to consider structures of a finite size, both symmetric and asymmetric. For asymmetric targets, the polarization of radiation turns out to be very sensitive to the electron trajectory, which can manifest itself when radiation is generated by electron packets with a complex spatial structure (including vortex electrons).

Publications

1. D. Sergeeva, D.Garaev, A. Tishchenko Polarized grating transition radiation from a 2D photonic crystal Journal of the Optical Society of America B, Vol. 39, Issue 12, pp. 3275-3282 (year - 2022) https://doi.org/10.1364/JOSAB.471124

2. Karlovets D., Baturin S., Geloni G., Sizykh G., Serbo V. Generation of vortex particles via generalized measurements European Physical Journal C, Том 82, Выпуск 11 (year - 2022) https://doi.org/10.1140/epjc/s10052-022-10991-w

3. M.M. Popova, S.N. Yudin, E.V. Gryzlova, M.D. Kiselev, A.N. Grum-Grzhimailo ATTOSECOND INTERFEROMETRY INVOLVING DISCRETE STATES Journal of Experimental and Theoretical Physics, - (year - 2022)

4. Popova M., Kiselev M., Burkov S., Gryzlova E., Grum-Grzhimailo A. Spectroscopic Peculiarities at Ionization of Excited 2p5(2PJf )3s[K]0,1,2 States of Ne: Cooper Minima and Autoionizing Resonances Atoms (MDPI), Том 10, выпуск 102 (year - 2022) https://doi.org/10.3390/atoms10040102

5. - Неточность поможет закрутить релятивистские частицы N+1, - (year - )

6. - В ИТМО придумали, как закручивать частицы с помощью свойства квантовой запутанности ITMO/NEWS, - (year - )