Electric-field Quantum Sensing using a Photogenerated Spin-correlated Electron-hole Pair in a Charge-transfer Molecule*

Quantum sensing (QS) has garnered increasing attention due to the promise of unmatched sensitivity and atomic-scale resolution. In recent years, the quantum control of molecular magnets (MM) has opened new opportunities in QS, due to their structural reproducibility, and access to uniquely molecular degrees of freedom, including the interaction between spins and electric fields (SEI). Among different MMs, photon-induced spin-correlated radical pairs have attracted much interest due to the possibility for the creation of well-define initial molecular spin states, allowing QS at elevated temperatures. In this work, we demonstrate the QS of electric fields using a spin-correlated electron-hole (eh) pair embedded in a charge-transfer (CT) molecule (ACRSA). An electron spin echo sequence, comprising an optical initialization and a DC electric field pulse of varying duration, is employed throughout the study. The intra-molecule magnetic dipolar interaction of the ACRSA photoinduced CT state is strongly correlated to the interaction within the electric dipole moment of the eh pair, enabling a direct correlation between the electric and spin degrees of freedom. This is experimentally probed by monitoring the E-field-induced coherent modulation to the echo. Our method allows for the detection of variations in the EPR frequency with kHz resolution. These results prove CT molecules displaying SEI can function as electric-field quantum sensors.