Rapid Exchange Cooling with Calcium Ions

In trapped ion quantum information, maintaining low ion temperature of computational ions is key to performing high fidelity gates. However, sympathetic cooling, the current standard in the field, is both slow and experimentally complex. In this work, we experimentally study the technique of dynamic exchange cooling. The protocol utilizes a bank of cold ions to cool the hotter computational ions. Both the coolant and computational ions are of the same atomic species. The Coulomb interaction mediates an energy exchange between a coolant ion and a computational ion. We test this concept with two ions, showing that the process is efficient and fast. We remove over 96% (as many as 100 quanta) of axial motional energy from a computational ion. The resonant energy transfer to a coolant ion takes just 5.8 µs. The process can be repeated for additional cooling. Moreover, we verify that re-cooling the coolant ion does not decohere the computational ion.

This work was done in collaboration with Los Alamos National Laboratory.