Sharpening the Features of Optical Lattices

Abstract

We report on the experimental realization of a conservative optical lattice for cold atoms with a subwavelength spatial structure. The potential is based on the nonlinear optical response of three-level atoms in laser-dressed dark states, which is not constrained by the diffraction limit of the light generating the potential. The lattice consists of a one-dimensional array of ultranarrow barriers with widths less than 10 nm, well below the wavelength of the lattice light, physically realizing a Kronig-Penney potential. We study the band structure and dissipation of this lattice and find good agreement with theoretical predictions. Even on resonance, the observed lifetimes of atoms trapped in the lattice are as long as 44 ms, nearly 10 5 times the excited state lifetime, and could be further improved with more laser intensity. The potential is readily generalizable to higher dimensions and different geometries, allowing, for example, nearly perfect box traps, narrow tunnel junctions for atomtronics applications, and dynamically generated lattices with subwavelength spacings. DOI: 10.1103/PhysRevLett.120.083601 Coherent control of the position and motion of atoms with light has been a primary enabling technology in the physics of ultracold atoms. The paradigmatic examples of conservative optical potentials are the optical dipole trap and optical lattices, generated by far off-resonant laser fields, with the ac-Stark shift of atomic levels as the underlying mechanism. The spatial resolution for such optical potential landscapes is determined by the diffraction limit, which is of the order of the wavelength of light λ. This fundamentally limits optical manipulation of atoms. For example, in quantum simulation with atoms in optical lattices, the minimum lattice constant is λ=2, setting the energy scale for Hubbard models for both hopping (kinetic energy) and interaction of atoms, with challenging temperature requirements to observe quantum phases of interest [1]. Developing tools to overcome the diffraction limit, allowing coherent optical manipulation of atoms on the subwavelength scale, is thus an outstanding challenge. Following recent proposals [2-4], we report below first experiments demonstrating coherent optical potentials with subwavelength spatial structure, by realizing a KronigPenney-type optical lattice with barrier widths below λ=50.In the quest to beat the diffraction limit, several ideas have been proposed to create coherent optical potentials with subwavelength structure. These include Fourier synthesis of lattices using multiphoton Raman transitions [5,6], optical or radio-frequency dressing of optical potentials [7,8], and trapping in near-field guided modes with nanophotonic systems [9,10] (although they suffer from decoherence induced by nearby surfaces). An alternative approach uses the spatial dependence of the nonlinear atomic response associated with the dark state of a three-level system [11][12][13][14][15][16] as a means to realize subwavelength atomic addressing and excitation. The subw...