Fundamental aspects of the interaction between quantum dots and light: breakdown of the dipole theory, single-photon superradiance, and decoherence
LTL Quantum Physics Seminar (Nanotalo). Speaker: Dr. P. Tighineanu (Niels Bohr Institute, University of Copenhagen, Denmark).
Semiconductor quantum dots are fascinating quantum emitters that share many properties with atoms such as three-dimensional quantum confinement and discrete spectrum. However, the many-body nature, mesoscopic size, lack of atomic symmetries, and the underlying solid-state habitat are unique features that are unknown to other emitters, and lead to extremely rich physics in quantum dots.
In the first part of this talk we discuss two mesoscopic effects that are mediated by the large physical size of quantum dots: the breakdown of the textbook electric-dipole theory [1-3], which causes quantum dots to interact with the electric and magnetic components of light on the same electronic transition, and single-photon superradiance , which leads to a giant enhancement of light-matter interaction in quantum dots.
In the second part of the talk we discuss the processes that decohere the interaction between quantum dots and light. Controlling the sources of decoherence is challenging due to the underlying solid-state nature, yet pivotal for the realization of coherent qubits in quantum dots. We identify the interaction between quantum dots and phonons as an important dephasing process , and present a microscopic theory for evaluating the coherence of quantum dots placed in realistic nano-photonic structures . We find that the degree of coherence strongly depends on the dimensionality of the nano-structure.
 M. L. Andersen, S. Stobbe, A. S. Sørensen, and P. Lodahl. Strongly modified plasmon-matter interaction with mesoscopic quantum emitters. Nature Physics 7, 215 (2011).
 P. Tighineanu, M. L. Andersen, A. S. Sørensen, S. Stobbe, and P. Lodahl. Probing electric and magnetic vacuum fluctuations with quantum dots. Physical Review Letters 113, 043601 (2014).
 P. Tighineanu, A. S. Sørensen, S. Stobbe, and P. Lodahl. Unraveling the mesoscopic character of quantum dots in nanophotonics. Physical Review Letters 114, 247401 (2015).
 P. Tighineanu, R. S. Daveau, T. B. Lehmann, H. E. Beere, D. A. Ritchie, P. Lodahl, and S. Stobbe. Single-photon superradiance from a quantum dot. Physical Review Letters 116, 163604 (2016).
 E. A. Muljarov, and R. Zimmermann. Dephasing in quantum dots: quadratic coupling to acoustic phonons. Physical Review Letters 93, 237401 (2004).
 P. Tighineanu, C. L. Dreeßen, C. Flindt, P. Lodahl, and A. S. Sørensen. Phonon decoherence of quantum dots in photonic structures: broadening of the zero-phonon line and the role of dimensionality. To be submitted (2017).