Long-Lived Dipolar Molecules and Feshbach Molecules in a 3D Optical Lattice

We have realized long-lived ground-state polar molecules in a 3D optical lattice, with a lifetime of up to 25 s, which is limited only by off-resonant scattering of the trapping light. Starting from a 2D optical lattice, we observe that the lifetime increases dramatically as a small lattice potential is added along the tube-shaped lattice traps. The 3D optical lattice also dramatically increases the lifetime for weakly bound Feshbach molecules. For a pure gas of Feshbach molecules, we observe a lifetime of greater than 20 s in a 3D optical lattice; this represents a 100-fold improvement over previous results. This lifetime is also limited by off-resonant scattering, the rate of which is related to the size of the Feshbach molecule. Individually trapped Feshbach molecules in the 3D lattice can be converted to pairs of K and Rb atoms and back with nearly 100% efficiency.

Figure 1

Loss of ground-state KRb molecules as a function of time in a 3D lattice with depths of 56, 56, and 70 $E_R$ in $x$, $y$, and $z$, respectively, where $E_R={\hslash }^2{k}^2/2m$ is the KRb recoil energy, $k$ is the magnitude of the lattice beam wave vector, and $m$ the molecular mass. Neglecting the very short time points (red solid circles), the number of molecules for times larger than 1 s (black solid circles) are fit to a single exponential decay, yielding a $1/e$ lifetime of $16.3\pm 1.5\mathrm{s}$. Inset: Lifetime in an isotropic lattice with a depth of 50 $E_R$, with (blue open squares, 0.17 D) and without (black squares, 0 D) an applied electric field. The lifetimes at 0.17 D ($15\pm 4\mathrm{s}$) and 0 D agree within uncertainty.

Figure 2

Lifetime of KRb ground-state molecules in an optical lattice. Black circles: $x$ and $y$ lattice beams are fixed at 56 $E_R$ per beam, while $z$ is varied from 0 to 136 $E_R$ (1 $E_R$ corresponds to a lattice intensity $I=0.025\mathrm{kW}/{\mathrm{cm}}^2$). The lifetime reaches a maximum of $25\pm 5\mathrm{s}$ when the $z$ lattice depth is 34 $E_R$ (point b). For higher lattice intensities, the lifetime decreases, which is consistent with loss due to off-resonant light scattering (dashed line). The open circles correspond to 3D lattices where the radial confinement was also varied. The red squares correspond to lifetimes measured with an additional traveling-wave beam at 1064 nm illuminating the molecules in the 3D lattice. Point c (d) corresponds to the 3D lattice of point a with an intensity of $3.2\mathrm{kW}/{\mathrm{cm}}^2$ (b with $3.7\mathrm{kW}/{\mathrm{cm}}^2$) plus the additional beam intensity of $2.3\mathrm{kW}/{\mathrm{cm}}^2$ ($3.5\mathrm{kW}/{\mathrm{cm}}^2$). Solid lines: see text.

Figure 3

Lifetime of Feshbach molecules and confinement-induced molecules measured as a function of $B$. A purified sample of Feshbach molecules is held in an isotropic 3D optical lattice (50 $E_R$ per beam, 20 kHz trap frequency). Near the Feshbach resonance, the loss rate due to photon scattering can be modeled (solid line) as a weighted sum of the free atom loss rate ${\Gamma }_{\mathrm{atom}}$ and a higher loss rate for tightly bound molecules ${\Gamma }_{\mathrm{molecule}}$. The grey shaded area indicates the single-atom lifetime, and its uncertainty, measured for the same experimental conditions. Inset: Lifetime of Feshbach molecules in a 3D lattice as a function of the trap intensity, at 545.8 G (blue stars) and 543.18 G (green diamonds). The dashed and solid line fits are used to extract the scattering rates.