Molecule Quantum Optics

In our lab, we are building a new experimental platform to trap, cool, and control individual polar molecules, with the long-term goal of turning them into a programmable tweezer array for quantum science. Our molecule of choice is calcium monofluoride (CaF), a diatomic molecule whose rich internal structure and permanent electric dipole moment make it especially attractive for quantum applications. CaF has long lived rotational states and its electric dipole moment allows for strong interaction between ground state molecules, opening the door to exciting new physics.

We're particularly interested in using molecular rotational states for error-protected qubit encoding, exploring molecular Rydberg states, and studying cavity quantum electrodynamics with cold molecules. This work sits at the intersection of quantum metrology, nonlinear quantum optics, and molecular physics. Thus, this project is a collaborative effort between three research groups in Bonn- Quantum Metrology, Nonlinear Quantum Optics and Nanophysics and Quantum Photonics.

We will produce a beam of cold CaF molecules by laser-ablating a calcium target inside a cryogenic buffer gas cell cooled to 1.8 K, where it reacts with sulphur hexafluoride (SF₆). The hot molecules interact with cold helium gas cooled to 4 K, also introduced into the cell, cooling it down to low kelvin regime. Then the molecules exit the cell at around 150 m/s, thus producing a molecular beam.

We plan on using a frequency-chirped slowing laser to bring the molecules down to about 10 m/s, slow enough to be captured in a magneto-optical trap (MOT). A blue-detuned, dual-frequency MOT scheme  can then cool the molecules further, into the microkelvin regime. Due to the presence of rotational and vibrational energy levels, the whole process will require 5 distinct lasers, addressing 20 individual optical transitions! Once cooled, the molecules are transported via a moving optical dipole trap into a dedicated tweezer chamber, where we will capture them in an optical tweezer array, and do exciting physics.