SOQS: Superposition of Quantum States for Selective Detection of Dipolar Frequency Multiples in Pulsed EPR Spectroscopy

Pulsed electron paramagnetic resonance (EPR) spectroscopy provides a means for determining nanometer-range distance distributions between paramagnetic centers. The method relies on the measurement of dipolar coupling frequencies, while the lowest resolved dipolar frequency sets the upper limit for distance determination. We explore the possibility of increasing the upper distance limit by accessing the dipolar frequency multiples from the selective excitation of transitions with ΔMS > 1. Such transitions arise from the superposition of quantum states (SOQS) and provide up to four times the dipolar frequency, and up to 60% increase in the upper distance limit. This has been demonstrated through spin dynamics calculations for the triplet state of a xanthene chromophore and experimentally for NV– centers in diamond. Future steps toward the practical application are discussed.