The reappearance of Rabi rotations finally measured

When a semiconductor quantum dot is optically driven, the population of the excitonic state undergoes Rabi oscillations. In realistic systems, however, these oscillations are not perfectly coherent. The interaction with longitudinal acoustic phonons leads to a damping of the oscillation amplitude.

When short laser pulses are used for excitation, this coherent control appears as Rabi rotations, where the exciton population oscillates as a function of the pulse intensity. The coupling to phonons modifies this behavior in an intriguing way. First, the Rabi rotations are strongly damped as the pulse intensity increases. But for even larger pulse areas, the oscillation amplitude recovers.

This non-monotonic behavior was predicted theoretically in 2007 in Phys. Rev. Lett. and later observed experimentally. In our recent work, we were happy to provide the theoretical calculations complementing new experimental measurements performed in the Jöns group at the University of Paderborn, using quantum dots grown by the Rastelli group at JKU Linz.

Together, theory and experiment show the characteristic reappearance of Rabi rotations at high pulse intensities and highlight the subtle role of phonon interactions in the coherent control of semiconductor quantum dots.

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