Coherent Dynamics of Individual Electrons far from Thermal Equilibrium
The first paper which was funded by the new SFB 1432, written by Philipp Henzler.
Understanding excited quantum systems and manipulating a few charge carriers at a time on fundamental spatio-temporal scales represents the current frontier for technological progress. However, experiments on small quantum systems far from thermal equilibrium remain challenging due to the required sensitivity and femtosecond time resolution. Investigating individual semiconductor quantum dots allows us to study fundamental phenomena such as quantum coherence and relaxation pathways of a well-defined number of excited electrons on such ultrashort timescales.
In the present work, we report on persistent quantum beats between charged exciton states in a single quantum dot investigating the biexcitonic transient absorption. Surprisingly, the excitonic coherence turns out to be protected upon phonon-mediated relaxation of the photoexcited hole and transferred between excited states. Decoherence proceeds only through scattering of the hot-electron which is slowed considerably due to Pauli blocking. This situation results in a difference between hole-phonon scattering and trion dephasing times by almost three orders of magnitude. Modeling the signatures of the spectro-temporal evolution of nonlinear absorption by an analytical theory provides a new understanding of the coupling of light to a resonant system which evolves rapidly in time. In the future, ultrafast quantum logic operations with extremely large processing bandwidth will likely involve such highly excited quantum states. This renders our observations important for the development of upcoming quantum technologies.
Reference:
Femtosecond Transfer and Manipulation of Persistent Hot-Trion Coherence in a Single CdSe/ZnSe Quantum Dot
Philipp Henzler, Christian Traum, Matthias Holtkemper, David Nabben, Marcel Erbe, Doris E. Reiter, Tilmann Kuhn, Suddhassatta Mahapatra, Karl Brunner, Denis V. Seletskiy, and Alfred Leitenstorfer
Phys. Rev. Lett. 126, 067402 (2021)
Link: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.126.067402
DOI: 10.1103/PhysRevLett.126.067402