Electric field suppression of ultracold confined chemical reactions

We consider ultracold collisions of polar molecules confined in a one-dimensional optical lattice. Using a quantum scattering formalism and a frame transformation method, we calculate elastic and chemical quenching rate constants for fermionic molecules. Taking ${}^{40}\mathrm{K}$${}^{87}\mathrm{Rb}$ molecules as a prototype, we find that the rate of quenching collisions is enhanced at zero electric field as the confinement is increased but that this rate is suppressed when the electric field is turned on. For molecules with 500 nK of collision energy, for realistic molecular densities, and for achievable experimental electric fields and trap confinements, we predict lifetimes for KRb molecules to be $1$ s. We find a ratio of elastic to quenching collision rates of about $100$, which may be sufficient to achieve efficient evaporative cooling of polar KRb molecules.

Figure 1

Collision of ${}^{40}\mathrm{K}$${}^{87}\mathrm{Rb}$ molecules in the ground state of a confining trap. The elastic (blue) and quenching (red) rate coefficients are plotted as a function of the dipole moment $d$ for $\nu =50$ kHz (upper panel) and $\nu =1000$ kHz (lower panel), for a fixed collision energy of $E_c=500$ nK. A pure 2D SC formula (thin blue line) and a pure 2D Born approximation (BA) formula (dashed blue line) have also been reported from Ticknor [24].

Figure 2

Barrier height $V_b$ as a function of the dipole moment $d$ for $\nu =50$ kHz (solid line) and $\nu =1000$ kHz (dashed line).