title: Broadband optical cooling of molecular rotors from room temperature to the ground state.
abstract: Laser cycling of resonances can remove entropy from a system via spontaneously emitted photons, with electronic resonances providing the fastest cooling timescales because of their rapid spontaneous relaxation. Although atoms are routinely laser-cooled, even simple molecules pose two interrelated challenges for cooling: every populated rotational-vibrational state requires a different laser frequency, and electronic relaxation generally excites vibrations. Here we cool trapped AlH(+) molecules to their ground rotational-vibrational quantum state using an electronically exciting broadband laser to simultaneously drive cooling resonances from many different rotational levels. Undesired vibrational excitation is avoided because of vibrational-electronic decoupling in AlH(+). We demonstrate rotational cooling on the 140(20) ms timescale from room temperature to 3.8(-0.3)(+0.9) K, with the ground-state population increasing from ~3 to 95.4(-2.1)(+1.3)%. This cooling technique could be applied to several other neutral and charged molecular species useful for quantum information processing, ultracold chemistry applications and precision tests of fundamental symmetries.
authors.affiliation: Department of Physics and Astronomy, Northwestern University, 2145 Sheridan Road, Evanston, Ilinois 60208, USA.
authors.forename: Chien-Yu
authors.initials: CY
authors.lastname: Lien
authors.affiliation: Department of Physics and Astronomy, Northwestern University, 2145 Sheridan Road, Evanston, Ilinois 60208, USA.
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Seck
authors.affiliation: Department of Physics and Astronomy, Northwestern University, 2145 Sheridan Road, Evanston, Ilinois 60208, USA.
authors.forename: Yen-Wei
authors.initials: YW
authors.lastname: Lin
authors.affiliation: 1] Department of Physics and Astronomy, Northwestern University, 2145 Sheridan Road, Evanston, Ilinois 60208, USA [2].
authors.forename: Jason H V
authors.initials: JH
authors.lastname: Nguyen
authors.affiliation: Department of Physics and Astronomy, Northwestern University, 2145 Sheridan Road, Evanston, Ilinois 60208, USA.
authors.forename: David A
authors.initials: DA
authors.lastname: Tabor
authors.affiliation: Department of Physics and Astronomy, Northwestern University, 2145 Sheridan Road, Evanston, Ilinois 60208, USA.
authors.forename: Brian C
authors.initials: BC
authors.lastname: Odom