Subrecoil cavity cooling towards degeneration (Vol. 45 No.2)

Single-particle momentum distribution for bosons in a ring cavity. The initially broad distribution is cavity-cooled to |p| = 0, ±1hk momentum states.

Cavity assisted cooling has become a valuable tool to implement cavity-QED with ultra cold quantum gases, trapped ions and optomechanical elements. Injecting a red-detuned laser extracts kinetic energy from the particles to create cavity photons, which leak out of the resonator, carrying away energy and effectively cooling the system. In contrast to conventional laser cooling, this method works without resonant excitation and spontaneous emission, eliminating photon re-absorption and making it applicable to a wide class of polarisable particles with final temperatures only limited by the cavity line-width.

We present a detailed numerical analysis of the cooling dynamics involving a cavity with energy uncertainty below the recoil energy. Motivated by a recent Hamburg experiment demonstrating targeted cooling on the subrecoil scale, we embrace a tailored sequence of laser pulses transferring the particles from a thermal state towards the ground state reaching subrecoil kinetic energies. The few particle simulations give encouraging prospects to implement condensation of a quantum gas via cavity cooling and exhibit genuine quantum correlations distinguishing fermions and bosons.

A broad momentum distribution is cooled to generate a large ground state population. Each step of a laser pulse sequence with optimized detunings transfers specific momentum states irreversibly towards lower momenta.

R. M. Sandner, W. Niedenzu and H. Ritsch, “Subrecoil cavity towards degeneration: a numerical study”, EPL, 104, 43001 (2013)
[Abstract]