Nondestructive imaging of an ultracold lattice gas
Y. S. Patil, S. Chakram, L. M. Aycock, and M. Vengalattore
Physical Review A, 90, 033422 (2014)
arXiv:1404.5583 (2014)

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.

Bibtex

@article{patilRamanImaging2014,
title = {Nondestructive imaging of an ultracold lattice gas},
author = {Patil, Y. S. and Chakram, S. and Aycock, L. M. and Vengalattore, M.},
journal = {Phys. Rev. A},
volume = {90},
issue = {3},
pages = {033422},
numpages = {4},
year = {2014},
month = {Sep},
publisher = {American Physical Society},
doi = {10.1103/PhysRevA.90.033422},
url = {http://link.aps.org/doi/10.1103/PhysRevA.90.033422}
}

Figure 1

(a) Lattice imaging scheme: An atom within a lattice site is cooled to the ground state |g⟩≡|F=1,mF=+1;ν=0⟩ via RSC. An auxiliary imaging beam promotes the atom out of this state to a fluorescing state, which is subsequently cooled back to |g⟩. Repeated cycles of this process extract fluorescence from the atom while continually restoring the atom to |g⟩; (b) The near-resonance optical fields used in the imaging sequence. A cooling beam (RSC) with σ+ and π components cools and optically pumps the atom into the dark state |g⟩. A σ− beam induces fluorescence by bringing the atom out of the dark state. (c) Raman fluorescence image of a gas of 1.5×10^6 atoms obtained within 15 ms. The field of view is 250μm × 250μm.

Figure 2

Spatially resolved sideband spectroscopy of the lattice gas following the imaging sequence yielding ⟨n⟩=0.01+0.03−0.01. Inset: A time-of-flight absorption image of the ultracold gas following an intense interrogation pulse at the two-photon resonance. The divot near the center of the atomic distribution shows the location and relative size of the beams used for sideband spectroscopy. The field of view is 600 μm ×600 μm.

Figure 3

Regimes of fluorescence acquisition rates for non-destructive imaging. (a) Measured temperature of the lattice gas in a pulsed imaging sequence, in units of the vibrational frequency ωL. The temperature during the fluorescence pulse grows (red) with increasing fluorescence rates while RSC rapidly cools the atoms back to the ground state (blue). (b) Measured atom number following the imaging sequence. At low fluorescence rates, the atom number is conserved indicating negligible levels of tunneling across sites. As the fluorescence rate is increased, the increasing temperature during the fluorescence pulse causes tunneling followed by light-induced loss. The shaded area represents the critical fluorescence rate for the onset of tunneling as identified by our measurements of light-induced loss. Inset: Evolution of atom number immediately following an intense fluorescence pulse (Γf=6×10^5 per s) shows that RSC quickly (within 100 μs) binds the atoms to the ground state of a lattice site thereby drastically suppressing tunneling.

Figure 4

The fraction of atoms remaining after the imaging sequence (Nf/Ni) vs fluorescence rates for lattice depths of U0/Er=14.6,24.9,36.7 and 76.2 (left to right). Inset: An estimate of the maximum fluorescence acquisition rate Γf,max per atom vs s = U0/Er.