Defining a fermionic lattice using spin and momentum instead of spatial coordinates opens the door for interacting-fermion simulations with more complex lattice geometries.
Synthetic magnetism in cold atomic gases opened the doors to many exciting novel physical systems and phenomena. Ubiquitous are the methods used for the creation of synthetic magnetic fields. They include rapidly rotating Bose-Einstein condensates employing the analogy between the Coriolis and the Lorentz force, and laser-atom interactions employing the analogy between the Berry phase and the Aharonov-Bohm phase. Interestingly, radiation pressure - being one of the most common forces induced by light - has not yet been used for synthetic magnetism. We experimentally demonstrate a synthetic Lorentz force, based on the radiation pressure and the Doppler effect, by observing the centre-of-mass motion of a cold atomic cloud. The force is perpendicular to the velocity of the cold atomic cloud, and zero for the cloud at rest. Our novel concept is straightforward to implement in a large volume, for a broad range of velocities, and can be extended to different geometries.
Physical systems with high ground state degeneracy, such as electrons in large magnetic fields [1, 2] and geometrically frustrated spins [3], provide a rich playground for exploring emergent many-body phenomena. Quantum simulations with cold atoms offer new prospects for exploring complex phases arising from frustration and interactions [4-7] through the direct engineering of these ingredients in a well-controlled environment [8, 9]. Advances in band structure engineering, through the use of sophisticated lattice potentials made from interfering lasers, have allowed for explorations of kagome [10] and Lieb [11] lattice structures that support high-degeneracy excited energy bands. The use of internal states as synthetic dimensions [12] offers even greater flexibility in creating nontrivial band structures [13-17]. Here, using synthetic lattices based on laser-coupled atomic momentum states, we perform the first exploration of high-degeneracy ground bands in a cold atom system. By combining nearest- and next-nearest-neighbour tunnellings, we form an effective zigzag lattice that naturally supports kinetic frustration and nearly-flat quartic energy bands. In a quartic band structure with time-reversal symmetry (TRS) broken by a synthetic magnetic flux, the quench dynamics of our atoms reveal hallmark signatures of spin-momentum locking. Under preserved TRS, we demonstrate the extreme sensitivity of a nearly-flat ground band to added disorder. Furthermore, we show that the ground state localisation properties are strongly modified by an added flux, relating to a flux-dependent mobility edge due to multi-range tunnelling. Our work constitutes the first quantum simulation study on the interplay of topology and disorder [18], and opens the door to studying emergent phenomena driven by frustrated kinetics and atomic interactions
We experimentally realize a spin-momentum lattice with a homogeneously trapped Fermi gas. The lattice is created via cyclically rotated atom-laser couplings between three bare atomic spin states, and are such that they form a triangular lattice in a synthetic spin-momentum space. We demonstrate the lattice and explore its dynamics with spin- and momentum-resolved absorption imaging. This platform will provide new opportunities for synthetic spin systems and the engineering of topological bands. In particular, the use of three spin states in two spatial dimensions would allow the simulation of synthetic magnetic fields of high spatial uniformity, which would lead to ultranarrow Chern bands that support robust fractional quantum Hall states.