Controlling Polar Molecules
Figure 1. Controlling polar molecules in optical
potentials using electric and magnetic fields.
We study trapping conditions for ultracold neutral molecules, such that pairs of internal states experience identical trapping potentials. These conditions have potential applications in experiments with diatomic polar molecules in optical traps. The implications are particularly striking for the use of two rotational states of a polar molecule as quantum bits. This application is susceptible to decoherence due to intensity fluctuations in the optical trapping lasers when the dynamic polarizability of these levels are different as is generally the case. We show that this limitation can be removed by adjusting the experimental parameters to guarantee that the dynamic polarizabilities are equal. Moreover, for a quantum bit implementation relying on a spatially varying electric field to ensure individual addressability, it should be possible to use trapping light polarized at a ``magic angle'' relative to the static electric field and, thereby, eliminate a potentially dangerous source of decoherence.
In the presence of both static electric and cw laser fields a polar molecule has an anisotropic dynamic polarizability. This anisotropy of the molecular levels manifests itself as a dependence on the relative orientation of the polarization of the trapping laser and the electric field. Then by applying a magnetic field, quadrupole and Zeeman interactions further mix states. The combined action of these three fields can be a powerful tool with which to manipulate and control ultracold molecules trapped in an optical potential.
We performed a theoretical study of the internal rovibronic and hyperfine quantum states of the KRb molecule when both magnetic and electric fields as well as non-resonant trapping lasers are applied. Understanding the effect of changing the relative orientation or polarization of these three fields is of crucial importance for creation of decoherence-free subspaces built from two or more ro-vibronic and hyperfine states.
Phys. Rev. A 82, 063421 (2010);
Phys. Rev. Lett. 109, 230403 (2012);
Mol. Phys. 111, 1731 (2013).