Femtosecond coherence and quantum control of single molecules at room temperature

Quantum-mechanical phenomena, such as electronic coherence and entanglement, play a key role in several remarkably efficient natural processes including ultrafast electronic energy transfer and charge separation in photosynthetic light-harvesting. To gain insight into such dynamic processes of biomolecules it is vital to reveal relations between structural and quantum-mechanical properties. However, ensemble experiments targeting ultrafast coherences are hampered by the large intrinsic heterogeneity in these systems at physiological conditions, and single-molecule techniques have not been available until now. Here we show, by employing femtosecond pulse-shaping techniques, that quantum coherences in single organic molecules can be created, probed and manipulated at ambient conditions even in highly disordered solid environments. We find broadly distributed coherence decay times for different individual molecules giving direct insight into the structural heterogeneity of the local surroundings. Most importantly, we induce Rabi oscillations and control the coherent superposition state in a single molecule, thus carrying out a basic femtosecond single-qubit operation at room temperature.