Quantum Optics Seminar by Stephan Smolka – Niels Bohr Institute - University of Copenhagen

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Quantum Optics Seminar by Stephan Smolka

The interaction between a local energy level and a continuum of states leads to fascinating quantum phenomena such as the Kondo effect [1] or Fano-type quantum interference. We demonstrate quantum interference between a discrete quantum dot energy level and a nearby Fermi reservoir that is modified by the scattering potential of the exciton hole [2]. This Fano interference is detected with resonant absorption measurements by continuously tuning the neutral exciton energy level with respect to the Fermi reservoir. Strikingly, we observe - in addition to the direct quantum dot transition – an indirect transition, i.e. the generation of a hole in the quantum dot and absorption of an electron in the Fermi reservoir. The measured lineshape shows a pronounced asymmetry as well as a broadening originating from the tunnel coupling between dot and the Fermi reservoir [3]. When the energy of the neutral exciton excitation is in the vicinity of or above the Fermi energy, the charge of the photo-excited quantum dot hole cannot be fully screened by the optically excited electron and generates a scattering potential for the free electrons of the Fermi reservoir. This scattering potential modifies the wave-function of the Fermi reservoir and leads to a quench dynamics after absorption - a Fermi edge singularity. The experimental data are found to be in very good agreement with our numerical model allowing us to determine the non-trivial phase between the absorption of the discrete quantum level and the continuum of states [4]. The quantum interference between a quantum dot and the Fermi reservoir is an important step to study the interplay between coherent laser excitation and an interacting many-body system. 

[1] C. Latta, F. Haupt, et al., Quantum quench of Kondo correlations in optical absorption, Nature 474, 627 (2011).

[2] M. Heyl, et al., X-ray edge singularity in optical spectra of quantum dots, Phys. Rev. B 85, 155413 (2012).

[3] N. Kleemans, et al. Many-body exciton states in self-assembled quantum dots coupled to a Fermi sea, Nature Physics 6, 534-538 (2010).

[4] L. N. Oliveira, Fano antiresonances in x-ray-absorption spectroscopy, Phys. Rev. B 32, 696 (1985).