Abstract Interaction of atoms with twisted light is the subject of intense experimental and theoretical investigation. In almost all studies, the atom is viewed as a localized probe of the twisted light field. However, as argued in this paper, conceptually novel effects will arise if light‐atom interaction is studied in the double‐twisted regime with delocalized atoms, that is, either via twisted light absorption by atom vortex beam, or via two‐twisted‐photon spectroscopy of atoms in a non‐vortex but delocalized state. Even for monochromatic twisted photons and for an infinitely narrow line, absorption will occur over a finite range of detuning. Inside this range, a rapidly varying absorption probability is predicted, revealing interference fringes induced by two distinct paths leading to the same final state. The number, location, height, and contrast of these fringes can give additional information on the excitation process which would not be accessible in usual spectroscopic settings. Visibility of the predicted effects will be enhanced at the future Gamma factory thanks to the large momenta of ions.
Abstract Interaction of atoms with twisted light is the subject of intense experimental and theoretical investigation. In almost all studies, the atom is viewed as a localized probe of the twisted light field. However, as argued in this paper, conceptually novel effects will arise if light‐atom interaction is studied in the double‐twisted regime with delocalized atoms, that is, either via twisted light absorption by atom vortex beam, or via two‐twisted‐photon spectroscopy of atoms in a non‐vortex but delocalized state. Even for monochromatic twisted photons and for an infinitely narrow line, absorption will occur over a finite range of detuning. Inside this range, a rapidly varying absorption probability is predicted, revealing interference fringes induced by two distinct paths leading to the same final state. The number, location, height, and contrast of these fringes can give additional information on the excitation process which would not be accessible in usual spectroscopic settings. Visibility of the predicted effects will be enhanced at the future Gamma factory thanks to the large momenta of ions.
The physics of optical vortices, also known as twisted light, is now a well-established and a growing branch of optical physics with a number of important applications and significant interdisciplinary connections.Optical vortex fields of widely varying forms and degrees of complexity can be realised in the laboratory by a host of different means.The interference between such beams with designated orbital angular momenta and optical spins (the latter is associated with wave polarisations) can be structured to conform to various geometrical arrangements.The focus of this review is on how such tailored forms of light can exert a controllable influence on atoms with which they interact.The main physical effects involve atoms in motion due to application of optical forces.The now mature area of atom optics has had notable successes both of fundamental nature and in applications such as atom lasers, atom guides and Bose-Einstein condensates.The concepts in atom optics encompass not only atomic beams interacting with light, but atomic motion in general as influenced by optical and other fields.Our primary concern in this review is on atoms in structured light where, in particular, the twisted nature of the light is made highly complex with additional features due to wave polarisation.These features bring to the fore a variety of physical phenomena not realisable in the context of atomic motion in more conventional forms of laser light.Atoms near resonance with such structured light fields become subject to electromagnetic fields with complex polarisation and phase distributions, as well as intricately structured intensity gradients and radiative forces.From the combined effect of optical spin and orbital angular momenta, atoms may also experience forces and torques involving an interplay between the internal and centre of mass degrees of freedom.Such interactions lead to new forms of processes including scattering, trapping and rotation and, as a result, they exhibit characteristic new features at the micro-scale and below.A number of distinctive properties involving angular momentum exchange between the light and the atoms are highlighted, and prospective applications are discussed.Comparison is made between the theoretical predictions in this area and the corresponding experiments that have been reported to date.
We investigate absorption and scattering of structured light by atoms, treating the photon and the atomic center of mass as spatially localized wave packets. We show that vortex photons can transfer orbital angular momentum (OAM) to the atomic center of mass with near-perfect efficiency in head-on collisions when the impact parameter b is smaller than the atomic transverse coherence length σ, which ranges from nanometers to sub-micrometer scales. Larger offsets result in a shifted mean OAM and a finite variance, both controlled by the ratio b/σ. The wave-packet nature of light enables electronic transitions that violate standard selection rules, albeit with a clear hierarchy where the dipole transition dominates. For femtosecond pulses, the finite spatial coherence of the photon leads to measurable shaping of the resonant absorption lines. We demonstrate a transverse recoil of the atom in a vicinity of the photonic vortex, dubbed "the superkick", and its dual effect - "the selfkick" - when an initially twisted atomic packet experiences recoil upon absorbing a gaussian photon. These phenomena are within reach of experimental capabilities using structured light in combination with cold atomic beams and ions in Penning traps, providing a route to the controlled generation and manipulation of non-gaussian atomic packets.
We investigate absorption and scattering of structured light by atoms, treating the photon and the atomic center of mass as spatially localized wave packets. We show that vortex photons can transfer orbital angular momentum (OAM) to the atomic center of mass with near-perfect efficiency in head-on collisions when the impact parameter b is smaller than the atomic transverse coherence length σ , which ranges from nanometers to sub-micrometer scales. Larger offsets result in a shifted mean OAM and a finite variance, both controlled by the ratio b / σ . The wave-packet nature of light enables electronic transitions that violate standard selection rules, albeit with a clear hierarchy where the dipole transition dominates. For femtosecond pulses, the finite spatial extent of the photon leads to measurable shaping of the resonant absorption lines. We demonstrate a transverse recoil of the atom in a vicinity of the photonic vortex, dubbed “the superkick,” and its dual effect—“the selfkick”—when an initially twisted atomic packet experiences recoil upon absorbing a Gaussian photon. These phenomena are within reach of experimental capabilities using structured light in combination with cold atomic beams and ions in Penning traps, providing a route to the controlled generation and manipulation of non-Gaussian atomic packets.
Theoretical work has already established the existence of a light-induced torque acting on the centre of mass of an atom, ion or molecule immersed in twisted light, where the transition frequency is suitably detuned from that of the twisted light beam. The twisted beam carries l units of orbital angular momentum per photon, and the steady-state saturation form of the torque is also determined by the width of the upper state in the atomic transition. It has been shown that, to leading order, the transfer of orbital angular momentum can only occur between the twisted light and the centre of mass motion. We argue here that, for small linewidth, the full time-dependence of the torque is needed to account correctly for the dynamics of atoms in a twisted light beam. We outline the theoretical framework needed to derive this full time-dependence, applying the theory to the motion in a twisted light beam of Eu3+ ions, which possess a particularly narrow linewidth state. For relatively large linewidth, the steady-state forces and torque are appropriate, but the processes of cooling and trapping require the application of several suitably oriented twisted beams. The description of atomic motion in multiple twisted beams demands the application of special coordinate transformations. We show how to construct the appropriate transformation matrices to represent a twisted light beam propagating in an arbitrary direction, and we proceed to investigate the cooling and trapping of Mg+ ions in sets of pairs of counter-propagating twisted beams in two-dimensional and three-dimensional molasses configurations.
Twisted light has received a lot of attention in recent years. And there are justified reasons for this. The properties of twisted light are unusual and differ fundamentally from the plane-wave properties. The phase fronts of these light beams have a helical structure, giving them the name twisted. This helical phase structure originates from the well-defined orbital angular momentum (OAM) that they carry along their propagation direction and in addition to the spin angular momentum (SAM). Moreover, they have a characteristic intensity profile, which consists of concentric rings with a central minimum, and a phase singularity in the beam center. This thesis is based on two main parts, each dealing with a different aspect of twisted light. These investigations are carried out using Bessel beams, one type of twisted light. Twisted light beams are cylindrically symmetrical. Therefore, they are defined on the basis of circularly polarized light. This fact leads to the first question: Is it possible to generate twisted light in other polarization states? In this work, we derive how this can be achieved by using the superposition principle and how this can be used to construct linearly, radially, or azimuthally polarized Bessel beams. The focus in the second part is on excitations of atoms by twisted Bessel beams. In particular, we analyze how the use of twisted light can modify individual atomic multipole transitions. The obtained results show that for an efficient modification a precise localization of the target atom is required. In the last chapter, both aspects are combined. We analyze transitions between magnetic hyperfine states in a single trapped atom (or ion), which is exposed to an additional external magnetic field. The presented calculations for these multipole excitations are based on a formalism that accounts for the alignment of the applied external magnetic field with respect to the light propagation direction, and additionally different polarization states of the radiation field are considered. The obtained results indicate that twisted light could be of particular interest for precision experiments. One possible application is the use in single-ion clocks. The work shows that high multipole orders of the vortex beams allow excitations in the intensity minimum in the center of these beams without causing large disturbances, and thus may enable a significant reduction of the light shift in atomic transitions.
A form of quantum control is proposed by applying twisted light, also known as optical vortex beams, to drive ultranarrow atomic transitions in neutral Ca, Mg, Yb, Sr, Hg, and Cd bosonic isotopes. This innovative all-optical spectroscopic method introduces spatially tailored electric and magnetic fields to fully rewrite atomic selection rules, reducing simultaneously probe-induced frequency shifts and additional action of external ac and dc field distortions. A twisted-light focused probe beam produces strong longitudinal electric and magnetic fields along the laser propagation axis, which opens the $^{1}S_{0}\ensuremath{\rightarrow}^{3}P_{0}$ doubly forbidden clock transition with a high E1M1 two-photon excitation rate. This long-lived clock transition is thus immune to nonscalar electromagnetic perturbations. Zeeman components of the M2 magnetic quadrupole $^{1}S_{0}\ensuremath{\rightarrow}^{3}P_{2}$ transition considered for quantum computation and simulation are now selectively driven by transverse or longitudinal field gradients with vanishing electric fields. These field gradients are manipulated by the mutual action of orbital and spin angular momentum of the light beam and are used in presence of tunable vector and tensor polarizabilities. A combination of these two different twisted-light induced clock transitions within a single quantum system, at the same magic wavelength and in presence of a common thermal environment, significantly reduces systematic uncertainties. Furthermore, it generates an optical synthetic frequency which efficiently limits the blackbody radiation shift and its variations at room temperature. Engineering light-matter interaction by optical vortices merged with composite pulses will ultimately benefit experimental atomic and molecular platforms targeting an optimal coherent control of quantum states, reliant quantum simulation, novel approaches to atomic interferometry, and precision tests of fundamental theories in physics and high-accuracy optical metrology.