Exploring Molecular Orbital Pseudospins as All-Optical Quantum Sensors

Recent developments in molecular qubits have focused on transitions among electron spin states interfaced with optical electronic transitions for better sensing resolutions. However, molecular electronic states can also form pseudospins, and using them as qubits would bypass the additional step of spin-optical interfacing. In this work, we discuss whether precessions of molecular orbital pseudospins under environmental influence can allow for all-optical quantum sensing via optical pump-probe spectroscopy. We find that these oscillations can survive rotational averaging and can be detected in isotropic environments. Unfortunately, fast electronic decoherence is likely to constrain measurements to environmental quantities that strongly influence orbital pseudospins, which are uncommon. This pitfall may be mitigated by further molecular engineering, which can be faster than spin-based qubits, given the high ab initio predictability of molecular electronic states.