Proposed Coherent Trapping of a Population of Electrons in a C60 Molecule Induced by Laser Excitation

This Letter demonstrates the possibility of generating coherent population trapping in C60. Similar to a three-level Λ system, C60 has a forbidden transition between the highest occupied molecular orbital (HOMO) (|a⟩) and the lowest unoccupied molecular orbital (LUMO) (|c⟩), but a dipole-allowed transition between HOMO and LUMO+1 (|b⟩) and between |b⟩ and |c⟩. We employ two cw laser fields, one coupling and one probe. The strong coupling field is switched on first to resonantly excite the transition between |b⟩ and |c⟩. After a delay, the probe is switched on; the coherent interaction between the coupling and probe fields traps the population in |a⟩ and |c⟩. This forms a partially dark state in C60, analogous to that in atomic vapors. Turning off the coupling field restores C60’s absorption. Pulsed lasers work as well. We use two pulses to steer the system into a dark state; when we send in a cw probe field, the electric polarization of C60 plunges by five times, in comparison with the noncontrol case. This should be detectable experimentally