Microwave shielding of ultracold polar molecules with imperfectly circular polarization

We investigate the use of microwave radiation to produce a repulsive shield between pairs of ultracold polar molecules and prevent collisional losses that occur when molecular pairs reach short range. We carry out coupled-channels calculations on $\mathrm{RbCs}+\mathrm{RbCs}$ and $\mathrm{CaF}+\mathrm{CaF}$ collisions in microwave fields. We show that effective shielding requires predominantly circular polarization but can still be achieved with elliptical polarization that is around 90% circular.

Figure 1

Probability of RSR (a) and rate coefficient for microwave-induced loss (b) in $\mathrm{RbCs}+\mathrm{RbCs}$ collisions with microwave detuning $\mathrm{\Delta }=0$, as a function of Rabi frequency, $\mathrm{\Omega }$, and ellipticity angle, $\xi$.

Figure 2

Probability of RSR (a) and rate coefficient for microwave-induced loss (b) in $\mathrm{CaF}+\mathrm{CaF}$ collisions with microwave detuning $\mathrm{\Delta }=0$, as a function of Rabi frequency, $\mathrm{\Omega }$, and ellipticity angle, $\xi$.

Figure 3

Adiabatic potential curves for $\mathrm{RbCs}+\mathrm{RbCs}$ with $\mathrm{\Omega }=0.2$ MHz and fixed orientation $\theta$ as indicated in the legend. The different panels correspond to (a) circular polarization for $\mathrm{\Omega }\ll \mathrm{\Delta }$, (b) linear polarization for $\mathrm{\Omega }\ll \mathrm{\Delta }$, (c) circular polarization for $\mathrm{\Omega }\gg \mathrm{\Delta }$, and (d) linear polarization for $\mathrm{\Omega }\gg \mathrm{\Delta }$.

Figure 4

Probabilities for reaching short range [(a), (c), (e), left-hand column] and rates of microwave-induced loss [(b), (d), (f), right-hand column] as a function of Rabi frequency and fixed orientation $\theta$. Panels (a) and (b) are for ${\sigma }^{+}$ circular polarization, panels (c) and (d) are for ${\sigma }_x$ linear polarization, and panels (e) and (f) are for elliptical polarization with $\xi =0.2\pi /4$.