Nondestructive imaging of an ultracold lattice gas

Abstract

We demonstrate the nondestructive imaging of a lattice gas of ultracold bosons. Atomic fluorescence is induced in the simultaneous presence of degenerate Raman sideband cooling. The combined influence of these processes controllably cycles an atom between a dark state and a fluorescing state while eliminating heating and loss. Through spatially resolved sideband spectroscopy following the imaging sequence, we demonstrate the efficacy of this imaging technique in various regimes of lattice depth and fluorescence acquisition rate. Our work provides an important extension of quantum gas imaging to the nondestructive detection, control and manipulation of atoms in optical lattices. In addition, our technique can also be extended to atomic species that are less amenable to molasses-based lattice imaging.PACS numbers: 37.10. Jk,67.85.Hj,03.75.Lm, The creation, control and manipulation of ultracold atomic gases in tailored optical potentials has spurred enormous interest in harnessing these mesoscopic quantum systems to the realization of ultracold analogues of correlated electronic materials [1,2], studies of nonequilibrium dynamics in isolated quantum many-body systems [3] and quantum metrology [4]. The dilute nature of these gases and the weak interactions impose stringent restrictions on the energy, entropy and means of manipulating and probing these systems. This has led to the development of novel techniques to cool and image these gases at ever increasing levels of precision and resolution. In this context, the in situ imaging of lattice gases at high spatial resolution has emerged as a powerful tool for the study of Hubbard models [5][6][7][8] and quantum information processing [9].Here, we demonstrate a nondestructive imaging technique for ultracold lattice gases. The scheme relies on extracting fluorescence from the atoms while simultaneously cooling them to the lowest band of the lattice via Raman sideband cooling (RSC) [10][11][12]. Through a combination of sideband spectroscopy and time-of-flight measurements, we demonstrate broad regimes of fluorescence acquisition rates and lattice depths for which the imaging scheme preserves the spatial location, the spin state and the vibrational occupancy of the lattice gas.The principle of the imaging sequence is depicted in Fig. 1. Raman sideband cooling is employed to cool individual atoms within an optical lattice to the lowest vibrational band while simultaneously pumping the atoms to the high field seeking state. In the case of 87 Rb atoms used in our study, this state is denoted by |g = |F = 1, m F = 1; ν = 0 where ν is the vibrational state of the atom within a lattice site. Importantly, this state is a dark state with respect to the optical fields used for Raman cooling. As such, the atoms do not emit any fluorescence while in this ground state. Fluorescence is induced in these atoms by shining a circularly polarized (σ − ) beam resonant with the F = 1 → F = 0 (D2) transition. Simultaneous use of RSC mitigates the increase in temperature caused by this fluor...

Ultracold Atoms Out of Equilibrium

“…Experiments thus rely on the repeated preparation of many atomic clouds with identical initial conditions, which are let to evolve for different times. However, also less invasive techniques are possible, ranging from phase contrast imaging [39], imaging based on the Faraday effect [85], imaging of lattice gases using Raman sideband cooling [86], to more exotic techniques, such as electron microscopy of quantum gases [87,88]. One the one hand, these techniques enable a repeated probing of the same system.…”

Quantum-Gas Microscope for Fermionic Atoms

“…Raman sideband cooling has previously been used to cool 87 Rb and 133 Cs atoms in lattices and in optical tweezers to large ground-state populations [20][21][22][23][24][25][26][27]. Here, we realize continuous Raman sideband cooling of 40 K using two states from the ground hyperfine manifolds, jai ¼ jF ¼ 9=2; m F ¼ −9=2i and jbi ¼ j7=2; −7=2i, which form an approximate two-level system.…”

“…Previous microscope experiments in Hubbard-type lattices [13][14][15] cool via optical molasses. In contrast, we employ 3D Raman sideband cooling [19][20][21][22][23][24][25][26][27], in which Raman transitions on vibration-lowering sidebands are combined with optical pumping to provide cooling. Our method therefore not only achieves site-resolved imaging, but also leaves a large fraction of the atoms [72(3)%] in the 3D motional ground state of each lattice site.…”

Imaging and addressing of individual fermionic atoms in an optical lattice

“…Instead, dark-state coherence establishes an EIT window that suppresses carrier scattering, while creating an absorption resonance at the red trap sideband, thereby cooling the tightly bound atoms [27,36]. Multicolor Raman sideband cooling realizes a similar mechanism [37][38][39], and has also been used for the site-resolved imaging of fermionic atoms [24,25]. Figure 4 describes our implementation of EIT cooling.…”