Excited-state orbital angular momentum enables all-optical molecular spin coherence.

Area of Science:

• Quantum sensing
• Molecular spectroscopy
• Spin dynamics

Background:

• Paramagnetic molecules offer unique quantum sensing capabilities.
• Optical initialization and readout of spin dynamics are crucial for their application.
• Previous methods required high-symmetry molecules with ground-state orbital angular momentum.

Purpose of the Study:

• To demonstrate ultrafast spin coherence measurements in non-octahedral molecules.
• To establish excited-state orbital angular momentum as an optical interface for spin-photon coupling.
• To enable all-optical detection of electron paramagnetic resonance (EPR) spectra and magnetic fields.

Main Methods:

• Ultrafast pump-probe polarization spectroscopy.
• Circularly polarized excitation of axial tungsten(v)-oxo complexes.
• Time-domain detection of spin coherence at room temperature.

Main Results:

• Achieved room-temperature spin coherence lasting several nanoseconds.
• Demonstrated optical detection of EPR spectra, including g value anisotropy.
• Enabled solution-phase DC magnetic field detection down to 5 mT.

Conclusions:

• Excited-state orbital angular momentum provides an optical interface in lower-symmetry complexes.
• This work establishes a route to ultrafast, all-optical spin spectroscopy.
• Paves the way for quantum sensing with chemically tunable coordination complexes.