Increased dimensionality of Raman cooling in a slightly nonorthogonal optical lattice

Abstract

We experimentally study the effect of a slight nonorthogonality in a two-dimensional optical lattice onto resolved-sideband Raman cooling. We find that when the trap frequencies of the two lattice directions are equal, the trap frequencies of the combined potential exhibit an avoided crossing and the corresponding eigenmodes are rotated by 45 • relative to the lattice beams. Hence, tuning the trap frequencies makes it possible to rotate the eigenmodes such that both eigenmodes have a large projection onto any desired direction in the lattice plane, in particular, onto the direction along which Raman cooling works. Using this, we achieve two-dimensional Raman ground-state cooling in a geometry where this would be impossible, if the eigenmodes were not rotated. Our experiment is performed with a single atom inside an optical resonator but this is inessential and the scheme is expected to work equally well in other situations.

Ground-state cooling of a single atom inside a high-bandwidth cavity

“…The running-wave Raman beam is sent along y, with DT y off, such that only odd-order sidebands along z are observed. They change the motional state by ∆n z = ±1, ±3, ..., while the carrier transition is suppressed [28,29]. The noise peaks ("servo bumps") of our Raman laser phase-locked loop appear as additional features at ±1.3 MHz of any Raman transition, but they are mainly visible for the strong heating sideband.…”

Raman Imaging of Atoms Inside a High-bandwidth Cavity

“…Also, the convenient cavity cooling technique [39] does not exist for κ γ, it is switched off by the large cavity decay. Alternative cooling schemes compatible with high bandwidth cavities and restricted FFPC geometries have been established previously using Raman sideband cooling techniques [40,41]. Here we show that the detection of the repumper fluorescence (which is not subject to the Purcell effect) emitted during the Raman cooling cycles, provides enough intensity to allow imaging of the atoms trapped in a 3D lattice superposed with the cavity field.…”

“…Raman spectrum of a single atom in the 3D lattice after 5 ms of continuous Raman sideband cooling (cRSC), addressing the overlapped cooling sidebands with a single Raman-beam pair (see main text and Appendix B). The usage of the intra-cavity field as a Raman beam highly suppresses unwanted off-resonant carrier transitions [40,41]. We observe the cooling efficacy by a motional ground state population > 85 % in each direction estimated from sideband imbalance, and by single-atom 1/e trapping lifetimes of ∼ 1 min.…”

“…B). Note that usage of the intra-cavity field as one of the Raman beams not only solves the problem of optical access, but also suppresses off-resonant coupling on the carrier transition [40,41].…”

Non-adiabatic Storage of Short Light Pulses in an Atom-Cavity System

“…One of the lattices acts as a conveyor belt [22] to transport atoms from a magneto-optical trap (MOT) into the cavity. Confinement in the zdirection is provided by the intra-cavity, blue-detuned lock laser field at 770 nm, which is additionally used for stabilizing the resonator length and for carrier-free Raman cooling in three dimensions [23,24]. As a result, the atom is located with sub-wavelength precision at an antinode of the cavity mode driven by the input pulse.…”