Study Opens New Avenue for Exploring Gauge Field-Induced Topological Physics

Gauge fields describe the basic interactions between charged particles and are responsible for various emergent topological phases of matter. This concept recently has been further generalized to charge neutral systems by engineering an analog Hamiltonian that governs the effective dynamics of neutral particles subject to magnetic fields.

Very recently, the discrete momentum states of 87Rb atoms with untunable interaction are exploited as lattice spatial dimensions to implement a two-leg ladder with tunable gauge fields. However, for the interaction energy that is comparable to the tunneling strength between the synthetic lattice sites, the interaction would affect the noninteracting single-particle physics.

In a new paper published in Light Science & Application, a team of scientists, led by Professor Suotang Jia from State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, China have demonstrated the experimental realization of an atom-optically synthetic gauge field in a momentum-space two-leg ladder for a noninteracting Bose gas of Cs atoms.

They studied the gauge flux dependent populations of atoms in the synthetic lattice sites and observed the gauge field induced chiral atomic currents in the two-leg ladder. They also studied the dependence of chiral current on the inter-leg coupling. In addition, they constructed an inhomogeneous gauge field and found the controllable atomic transport in the ladder with the inhomogeneous gauge fields.

Their experimental results are in qualitative agreement with the theoretical simulations, which were obtained by the single-particle tight binding model. Due to the use of a noninteracting Bose gas, their study lays the groundwork for using a clean synthetic lattice to study the gauge fields in synthetic dimensions and the topologic physics.

In their experiment, a two-leg ladder was synthesized for a noninteracting Bose gas by using three significant techniques: (1) They created a Bose gas of Cs atoms in a quasi-1D optical trap by a hybrid evaporation, and used a broad Feshbach resonance to tune the scattering length of ultracold atoms for achieving a 1D momentum-state lattice in the noninteracting regime; (2) The 1D momentum-state lattice was formed by driving a series of two-photon Bragg transitions to achieve the nearest-neighbor couplings between the discrete atomic momentum states. (3) They used the next-nearest-neighbor couplings with four-photon processes to increase the connections between synthetic lattice sites, which enables the mapping of a single 1D momentum-state lattice into a two-leg ladder.

Gauge fields were synthesized by locally tuning the intra-leg hopping phase in the ladder. They implemented homogeneous and inhomogeneous synthetic gauge fields, and studied the dynamics of atomic transport in the two-leg ladder subject to these two kinds of gauge fields. Based on the tunable inter-leg couplings in the ladder, they studied the variation of the observed chiral atomic current with the inter-leg coupling, and this is significant for a better understanding of chiral feature under gauge fields in a two-leg ladder.

In compared to the previous synthetic gauge fields in the two-leg ladder, these scientists summarized the significant differences in their system:

"Our synthetic lattice that can be flexibly tuned into the noninteracting regime has provided a clean platform for investigating various single-article physical models. Our study opens an avenue for exploring the synthetic gauge field and topological physics in presence of tunable interactions."

"We used a single 1D momentum-state lattice to synthesize a two-leg ladder in 2D, and this enlarges the tool box of implementing synthetic dimensions."


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