Resonant control of spin dynamics in ultracold quantum gases by microwave dressing

We study experimentally interaction-driven spin oscillations in optical lattices in the presence of an off-resonant microwave field. We show that the energy shift induced by this microwave field can be used to control the spin oscillations by tuning the system either into resonance to achieve near-unity contrast or far away from resonance to suppress the oscillations. Finally, we propose a scheme based on this technique to create a flat sample with either singly or doubly occupied sites, starting from an inhomogeneous Mott insulator, where singly and doubly occupied sites coexist.

Figure 1

(Color online) An off-resonant microwave field with approximately $\pi$ polarization and frequency ${\omega }_{\mu w}$ $\left(\mathrm{a}\right)$ is used to control the detuning for coherent spin oscillations in optical lattices. Case $\left[\mathrm{b}\right(1\left)\right]$ corresponds to zero or weak microwave intensity. With properly chosen microwave parameters, one can compensate this detuning and achieve full resonance $\left[\mathrm{b}\right(2\left)\right]$ or overcompensate to suppress the spin-changing collisions $\left[\mathrm{b}\right(3\left)\right]$.

Figure 2

(Color online) $\left(\mathrm{a}\right)$ Absorption image of an expanded cloud after $t_{\mathrm{osc}}=0\mathrm{ms}$ (upper image) and $t_{\mathrm{osc}}=15\mathrm{ms}$ (lower image). The dashed line indicates the box used to fit the $m=0$ component. $\left(\mathrm{b}\right)$ Horizontal cut through the lower image in $\left(\mathrm{a}\right)$ (black line). Subtracting a Gaussian fit (red dashed line) to the $m=0$ component yields a new image (blue line) used to count separately the population in $m=\pm 1$ by integration.

Figure 3

(Color online) Spin oscillations at a magnetic field $B=0.4\mathrm{G}$. $\left(\mathrm{a}\right)$ Spin oscillations without microwave dressing (squares), for a resonant dressing (circles), and for an overcompensated dressing (triangles). The dashed, solid, and dotted lines are fit to the data (see text). $\left(\mathrm{b}\right)$ and $\left(\mathrm{c}\right)$ Period and amplitude of the oscillation (circles), together with a fit to the expected Rabi dependence.

Figure 4

(Color online) Spin oscillations recorded for a magnetic field $B=1.2\mathrm{G}$. Filled circles denote the population in the Zeeman substate $m=0$, and hollow circles the sum of the populations in substates $m=\pm 1$.

Figure 5

(Color online) Illustration of the proposed scheme to create a homogeneous MI with only singly occupied sites starting from a sample with singly and doubly occupied Mott plateaus. After a spin oscillation half-period, atoms in singly occupied sites are transferred into the upper hyperfine level. Another spin oscillation half-period brings back atoms in doubly occupied sites to $\mid F=1,m=0⟩$, while a second microwave pulse is used to transfer atoms in singly occupied sites to $\mid F=1,m=-1⟩$. Another spin oscillation nearly creates the homogeneous $n=1$ system, the only difference being a supplementary atom in $\mid F=1,m=+1⟩$ in doubly occupied sites. This can be corrected by transferring these atoms to $F=2$, where a resonant laser beam can be used to remove them out of the trap.