We present a scheme for generating a synthetic magnetic field and spin-orbit coupling via Raman coupling in highly magnetic lanthanide atoms such as dysprosium. Employing these atoms offers several advantages for realizing strongly correlated states and exotic spinor phases. The large spin and narrow optical transitions of these atoms allow the generation of synthetic magnetic fields that are an order of magnitude larger than those in the alkali metals, but with considerable reduction of the heating rate for equal Raman coupling. The effective Hamiltonian of these systems differs from that of the alkali metals' by an additional nematic coupling term, which leads to a phase transition in the dressed states as detuning varies. For high-spin condensates, spin-orbit coupling leads to a spatially periodic structure, which is described in a Majorana representation by a set of points moving periodically on a unit sphere. We name this a ``Majorana spinor helix,'' in analogy to the persistent spin-$\frac{1}{2}$ helix observed in electronic systems.
We present a scheme for generating a synthetic magnetic field and spin-orbit coupling via Raman coupling in highly magnetic lanthanide atoms such as dysprosium. Employing these atoms offers several advantages for realizing strongly correlated states and exotic spinor phases. The large spin and narrow optical transitions of these atoms allow the generation of synthetic magnetic fields that are an order of magnitude larger than those in the alkali metals, but with considerable reduction of the heating rate for equal Raman coupling. The effective Hamiltonian of these systems differs from that of the alkali metals' by an additional nematic coupling term, which leads to a phase transition in the dressed states as detuning varies. For high-spin condensates, spin-orbit coupling leads to a spatially periodic structure, which is described in a Majorana representation by a set of points moving periodically on a unit sphere. We name this a ``Majorana spinor helix,'' in analogy to the persistent spin-21 helix observed in electronic systems.
Ultracold gases are remarkably versatile and controllable systems with untapped potential to emulate a variety of quantum phenomena [1]. Atoms are, however, electrically neutral and therefore it is highly desirable to make them behave as charged particles. This capability has recently been demonstrated in a series of recent experiments [2–4]. Although many challenges remain ahead, atoms exposed to synthetic gauge field offer great opportunities for the realization of new classes of quantum materials with custom-designed properties, and with unforeseen applications. The first implementation of an effective magnetic field was accomplished by rotating an atomic cloud [5]. In the rotating frame of reference, an atom experiences the Coriolis force that emulates the Lorentz force experienced by a charged particle in a uniform magnetic field. Large vortex lattices have been created in this way, however, so far the strength of the effective magnetic field achieved by rotation is too weak to lead to new physics. An alternative approach invokes the vector potential, A, that induces a geometric phase as a charged particle moves around a closed loop. This notion of geometric phase can be adapted to a neutral atom that slowly moves in the presence of laser fields. If the lasers are chosen to ‘dress’ the internal atomic levels, so that the dressed eigenstates become position dependent, the center of mass adiabatically evolves according the operator p-A, instead of just p = −iℏ∇. The atom thus effectively moves as a charged particle in a magnetic field B = ∇ × A (see Fig. 1a). Exploiting this idea series of experiments have implemented artificial magnetic and electric fields [2–4]. The idea has also been implemented in the presence of a superimposed periodic optical lattice potential (see Fig. 1b). In this case, the length scale imposed by the lattice competes with the one associated with the magnetic field and can lead to frustration, manifested as an energy spectrum with fractal characteristics [2,3]. Light induced synthetic gauge fields: (a) A gas of neural atoms (green oval) can behave as a gas of charged particles when it is illuminated by a pair of laser beams (red arrows) that imparts momentum to the atoms and couples their internal (.|↑.〉, .|↓.〉) and motional degrees of freedom. The Raman beams that induce transitions between internal states also transfer two units of their linear momentum 2kL. This leads to the formation of dressed states (superpositions of states with different internal levels and center of mass momenta) which experience a modified kinetic energy, with an effective vector potential. If the effective vector potential has nonzero curl, the atoms move as charged particles in a magnetic field. (b) In the presence of an optical lattice potential, Raman beams can also induce an effective vector potential. In this case, the lattice is engineered so that along one direction atoms can tunnel between adjacent lattice sites (Jlight) only by absorbing and emitting photons from the beams. The imparted momentum from the lasers produces path-dependent phases that resemble the magnetic flux accumulated by a charged particle as it moves in a closed loop. The flux accumulated by the atoms when they move around a single unit cell, ϕ, can be significant (equivalent to the one generated by a real magnetic field of thousands tesla in an electronic system) and induce a fractal energy spectrum. Generalizations to emulate non-Abelian gauge potentials, associated in many cases to spin-orbit coupling can emerge when the geometric phase is replaced by a matrix acting on the internal Hilbert space [2–5]. This happens if there is a manifold of degenerate dressed states, such that even for arbitrarily slow motion, after traveling around a contour the particle ends up in a different internal state. Although various proposals for generating non-Abelian potentials exist, they remain to be implemented. On the other hand, Abelian spin-orbit coupling, arising from the momentum kicks imparted on the atom by the laser photons that drive internal transitions, has been realized in several laboratories using different laser configurations in alkali-metal (one outer electron) and alkaline-earth (two outer electrons) atoms [2–5]. There is a great vista ahead. For example, the inclusion of collisions or dipolar interactions will open a window to engineer fractional Hall liquids, unconventional superfluids and interacting topological phases. The creation of dynamical gauge fields important in many areas of physics such as quantum chromodynamics is also an open direction. The time is just ripe for investigating rich and unexplored physics with synthetic gauge fields for ultracold matter.
Abstract Ultracold atoms endowed with tunable spin-orbital-angular-momentum coupling (SOAMC) represent a promising avenue for delving into exotic quantum phenomena. Building on recent experimental advancements, we propose the generation of synthetic gauge fields, and by including exotic vortex phases within spinor Bose–Einstein condensates, employing a combination of a running wave and Laguerre–Gaussian laser fields. We investigate the ground-state characteristics of the SOAMC condensate, revealing the emergence of exotic vortex states with controllable orbital angular momenta. It is shown that the interplay of the SOAMC and conventional spin-linear-momentum coupling induced by the running wave beam leads to the formation of a vortex state exhibiting a phase stripe hosting single multiply quantized singularity. The phase of the ground state will undergo the phase transition corresponding to the breaking of rotational symmetry while preserving the mirror symmetry. Importantly, the observed density distribution of the ground-state wavefunction, exhibiting broken rotational symmetry, can be well characterized by the synthetic magnetic field generated through light interaction with the dressed spin state. Our findings pave the way for further exploration into the rotational properties of stable exotic vortices with higher orbital angular momenta against splitting in the presence of synthetic gauge fields in ultracold quantum gases.
The implementation of the fractional quantum Hall effect in ultracold atomic quantum gases remains, despite substantial advances in the field, a major challenge. Since atoms are electrically neutral, a key ingredient is the generation of sufficiently strong artificial gauge fields. Here we theoretically investigate the synthetization of such fields for bosonic erbium atoms by phase imprinting with two counterpropagating optical Raman beams. Given the nonvanishing orbital angular momentum of the rare-earth atomic species erbium in the electronic ground state and the availability of narrow-line transitions, heating from photon scattering is expected to be lower than in atomic alkali-metal species. We give a parameter regime for which strong synthetic magnetic fields with good spatial homogeneity are predicted. We also estimate the size of the Laughlin gap expected from the s-wave contribution of the interactions for typical experimental parameters of a two-dimensional atomic erbium microcloud. Our analysis shows that cold rare-earth atomic ensembles are highly attractive candidate systems for experimental explorations of the fractional quantum Hall regime.
Encoding a dimension in the internal degree of freedom of an atom provides an interesting tool for quantum simulation, facilitating the realization of artificial gauge fields. We propose an extension of the synthetic dimension toolbox, making it possible to encode two dimensions within a large atomic spin. The protocol combines first- and second-order spin couplings such that the spin projection m and the remainder r=m (mod 3) of its Euclidian division by 3 act as orthogonal coordinates on a synthetic cylinder. It is suited for an implementation with lanthanide atoms, which feature a large electronic spin and narrow optical transitions for applying the required spin couplings. This method is useful for simulating geometries with periodic boundary conditions and engineering various types of topological systems evolving in high dimensions.
The interactions between light and matter are strongly enhanced when atoms are placed in high-finesse quantum cavities, offering tantalizing opportunities for generating exotic new quantum phases. In this work we show that both spin-orbit interactions and strong synthetic magnetic fields result when a neutral atom is confined within a ring cavity, whenever the internal atomic states are coupled to two off-resonant counter-propagating modes. We diagonalize the resulting cavity polariton Hamiltonian and find characteristic spin-orbit dispersion relations for a wide range of parameters. An adjustable uniform gauge potential is also generated, which can be converted into a synthetic magnetic field for neutral atoms by applying an external magnetic field gradient. Very large synthetic magnetic fields are possible, as the strength is proportional to the (average) number of photons in each of the cavity modes. The results suggest that strong-coupling cavity quantum electrodynamics can be a useful environment for the formation of topological states in atomic systems.
With the advent of ultracold atomic gases experimentally realized by laser cooling techniques nearly 40 years ago, the doors to accessing novel physical behaviour have been opened wide and far. Experimentally, research in this domain started with alkali atoms, proceeded with alkaline earth atoms, and only more recently embarked on atoms with higher complexity of their spectrum, as e.g. the highly dipolar lanthanide atomic species erbium and dysprosium. Those elements possess a non-vanishing orbital angular momentum in the ground state, leading to ample advantages for the manipulation with far-detuned laser light in phase imprinting schemes, as losses due to spontaneous scattering can be suppressed radically in comparison to the case of alkali atomic species. This beneficial behaviour will be used in the future for the generation of synthetic magnetic fields for electrically neutral erbium atoms aimed at investigating fractional quantum Hall physics. This thesis describes in the first part the generation of an atomic erbium Bose-Einstein condensate in a hybrid crossed optical dipole trap. The main purpose of this endeavor was an enhancement of absolute atom number of the degenerate ensemble and long-term stability of the experimental setup with respect to the use of a single beam dipole trap. A comparison of the here achieved results with respect to those achieved in only a single CO2 laser beam dipole trap is illustrated. In the second part of this thesis a theoretical evaluation of the generation of synthetic magnetic fields for ultracold erbium atoms in prospect for experimental investigations of fractional quantum Hall physics is presented. One of the most promising techniques for the realization of strong synthetic magnetic fields is by phase imprinting via Raman manipulation. Here for the theoretical calculation of such fields with erbium atoms a compared to earlier work on alkali atoms new modified optical Raman coupling scheme in a σ+ - σ- beam polarization configuration is chosen. It is shown that sufficiently high field strengths with good spatial homogeneity can be reached for experimentally viable parameters. Additionally, an estimation for the expected Laughlin gap in the proposed erbium atomic fractional quantum Hall system is given.