Synthetic Magnetic Fields for Ultracold Neutral Atoms

Atomic Bose–Einstein condensates (BECs) can be used to study many-body phenomena, such as superconductivity, that occur in more complex systems. However, many intriguing phenomena occur for charged particles in a magnetic field, and BECs are neutral. This drawback can be avoided by rotating the neutral system to create a synthetic magnetic field, but such fields are of limited strength. Lin et al. report a method of optically synthesizing magnetic fields for ultracold neutral atoms that is not subject to the limitations of the rotational approach. The method has the potential to generate the high fields required to reach the quantum Hall regime, which would enable studies of topological quantum computation. Atomic Bose–Einstein condensates can be used to study many-body phenomena that occur in more complex material systems; however, the charge neutrality of these systems prevents intriguing phenomena that occur for charged particles in a magnetic field. Rotation can be used to create a synthetic magnetic field, but such fields are of limited strength. An optically synthesized magnetic field for ultracold neutral atoms that is not subject to the limitations of rotating systems is now experimentally realized. Neutral atomic Bose condensates and degenerate Fermi gases have been used to realize important many-body phenomena in their most simple and essential forms1,2,3, without many of the complexities usually associated with material systems. However, the charge neutrality of these systems presents an apparent limitation—a wide range of intriguing phenomena arise from the Lorentz force for charged particles in a magnetic field, such as the fractional quantum Hall effect in two-dimensional electron systems4,5. The limitation can be circumvented by exploiting the equivalence of the Lorentz force and the Coriolis force to create synthetic magnetic fields in rotating neutral systems. This was demonstrated by the appearance of quantized vortices in pioneering experiments6,7,8,9 on rotating quantum gases, a hallmark of superfluids or superconductors in a magnetic field. However, because of technical issues limiting the maximum rotation velocity, the metastable nature of the rotating state and the difficulty of applying stable rotating optical lattices, rotational approaches are not able to reach the large fields required for quantum Hall physics10,11,12. Here we experimentally realize an optically synthesized magnetic field for ultracold neutral atoms, which is evident from the appearance of vortices in our Bose–Einstein condensate. Our approach uses a spatially dependent optical coupling between internal states of the atoms, yielding a Berry’s phase13 sufficient to create large synthetic magnetic fields, and is not subject to the limitations of rotating systems. With a suitable lattice configuration, it should be possible to reach the quantum Hall regime, potentially enabling studies of topological quantum computation.