Identifying Single Molecule Dynamics in Real Time via Time-Resolved Coherent Anti-Stokes Raman Scattering

By enhancing the local response of a single molecule with a dipolar nano-antenna, the vibrational dynamics at the single molecule limit can be measured in real time, by Time-Resolved Coherent Anti-Stokes Raman Scattering (TR-CARS). Such measurements involve the preparation and subsequent probing of vibrational wavepackets on the ground electronic state. In contrast to ensemble measurements, the vibrational coherence of a single molecule is not subject to dephasing; it exhibits dynamic phase and amplitude noise due to the~collapse of the wavepacket upon measurement. Continuous measurements of the amplitude noise distribution as a function of phase delay, allows the complete reconstruction of the state of the system. Under ambient conditions, repeated measurements of a single molecule coherence reduces to a statistical state of a system coupled to the thermal bath. The signature of the statistical state of a single molecule is characteristic, distinct from that of two, or three, or many; and this can be directly demonstrated through measurements.