Full quantum control of enantiomer-selective state transfer in chiral molecules despite degeneracy

Abstract

The driven quantum asymmetric top is an important paradigm in molecular physics with applications ranging from quantum information to chiral-sensitive spectroscopy. A key prerequisite for these applications is the ability to completely control the rotational dynamics. The inherent degeneracy of quantum rotors poses a challenge for quantum control since selecting a particular rotational state cannot be achieved by spectral selection alone. Here, we prove complete controllability for rotational states of an asymmetric top belonging to degenerate values of the orientational quantum number M. Based on this insight, we construct a pulse sequence that energetically separates population in degenerate M-states. Introducing the concept of enantio-selective controllability, we determine the conditions for complete enantiomer-specific population transfer in chiral molecules and construct pulse sequences for the example of propanediol and carvone molecules for population initially distributed over degenerate M-states. Our work shows how to leverage controllability analysis for the solution of practical quantum control problems.

Increasing ion yield circular dichroism in femtosecond photoionisation using optimal control theory

“…15 Prospects for control are even more promising for M3WM where complete enantiomer-specific population transfer is possible if a suitable combination of frequencies and polarization for the electric fields driving the three-wave mixing process is chosen. 16 These recent successes in enhancing chiral signatures with shaped pulses strongly suggest that interference between different excitation pathways may be a promising avenue to increase the contrast also in CD experiments. However, PECD and M3WM are pure electric dipole effects to first order, which leads to strong transitions and the possibility to attain high contrast with moderate laser intensities.…”

Discrimination of enantiomers for chiral molecules using analytically designed microwave pulses

“…The details about the technical treatment of such a cyclic three-level system for chiral molecules and the theoretical calculation of transition dipole moments between rotational states can be found in ref. 36 and 55.…”

“…We should note that the cyclic three-level model gives a qualitative understanding of ESST, which at a finite temperature depends on the M J -states 0 degeneracies. 55,56 As demonstrated in the latest experiment work, 57 the effect of M J -states could be overcome by cooling down the molecules to an ultracold or a low temperature while selecting the initial rotational level in the electronic and vibrational ground state of the most abundant conformer via optical pumping. To that end, triple resonant linearly polarized microwave pulses with orthogonal polarization directions involve multiple M J values will lead to the system with at least four states, which can be decomposed into two equivalent cyclic three-level systems 36 or into a cyclic three-level system and an uncoupling two-level system.…”

Ultrafast chirality: the road to efficient chiral measurements

“…Let us consider a locally chiral field with frequencies o 1 , o 2 and o 3 = o 1 + o 2 polarized along x, y and z, respectively. 90,95,97,99,101,102,109,132 The first (achiral) pathway is associated with the linear response at frequency o 3 , which is not sensitive to chirality, and leads to polarization at o 3 along z. The second (chiral) pathway corresponds to sum-frequency generation, a secondorder process that records the molecular handedness: the medium absorbs one o 1 photon and one o 2 photon from the field components polarized in the xy plane, generating polarization at frequency o 3 along z (Fig.…”

“…99) together with Schnell and coworkers, 95 who demonstrated an alternative implementation. Leibscher, Koch and co-workers 97,98,157 are developing optimal control protocols of enantio-sensitive state transfer in chiral microwave fields.…”