Generating Molecular Rovibrational Coherence by Two-Photon Femtosecond Photoassociation of Thermally Hot Atoms

Abstract

The formation of diatomic molecules with rotational and vibrational coherence is demonstrated experimentally in free-to-bound two-photon femtosecond photoassociation of hot atoms. In a thermal gas at a temperature of 1000 K, pairs of magnesium atoms, colliding in their electronic ground state, are excited into coherent superpositions of bound rovibrational levels in an electronically excited state. The rovibrational coherence is probed by a time-delayed third photon, resulting in quantum beats in the UV fluorescence. A comprehensive theoretical model based on ab initio calculations rationalizes the generation of coherence by Franck-Condon filtering of collision energies and partial waves, quantifying it in terms of an increase in quantum purity of the thermal ensemble. Our results open the way to coherent control of a binary reaction.

Training Schrödinger’s cat: quantum optimal control

“…In the context of coherent control of a chemical reaction, the bimolecular process of bond formation using femtosecond lasers remained more elusive [214][215][216][217][218][219][220][221] than bond breaking. Its coherent control was demonstrated only very recently [222].…”

Laser cooling of rotation and vibration by optical pumping

“…For atoms at room temperature, the PA process does not allow to resolve the excited state level structure because the width of the Maxwell-Boltzmann kinetic energy distribution of the atoms, k B T (k B is the Boltzman constant and T the temperature of the atomic sample), is much larger than the energy spacing in the excited state [31]. On the contrary, due to the extremely narrow width of the thermal distribution of ultracold atoms (k B T ≈ h × 2 MHz at T ≈ 100 µK), smaller than the energy spacing between molecular bound levels, and more importantly, very often narrower than the level width of the excited states, photo-association of cold atoms has proven to be a powerful tool for high-resolution molecular spectroscopy [32].…”

Maximizing hole coherence in ultrafast photoionization of argon with an optimization by sequential parametrization update

“…(ω max + ω min ), (13) where ω ∈ IR is the circular frequency returned by the optimization algorithm, whereas ω new , which is guaranteed to be in the interval ]ω min ,ω max [ by Eq. (13), is the one used for the propagation.…”

“…As with any coherent spectroscopy, the degree of coherence of the state that will be transiently probed is a crucial resource [13]. However, the transient interaction between the photoion and the photoelectron introduces decoherence of the hole states even in one-photon ionization with attosecond pulses [12].…”