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ICS

Semiconductor devices for emergent photonic and quantum technologies

Speaker: Jonathan Finley (Walter Schottky Institut, TU Munich, Germany)
Date: Friday 9 October 2015
Time: 15:00
Venue: WX3.14

In this talk, I will discuss several research themes pursued in my group in which the photonic and electronic properties of III-V semiconductor nanostructures are tailored to facilitate emergent photonic and quantum technologies. I will start by discussing experiments related to quantum information technologies in which we use ultrafast optical methods to the spin coherence of excitations in individual, optically active quantum dots (QDs). Coherent optical control of the exciton spin wavefunction with very high (>95%) fidelity is possible, simply by varying the polarization of picosecond optical pulses [1,2]. Optical charge storage experiments facilitate the generation of single electron spins and the study of their interaction with the environment for timescales ranging from a few picoseconds up to ~1ms. These experiments elucidate the processes responsible for spin decoherence in III-V quantum dots [3] and allow us to implement a new approach for harnessing quantum effects in solid state qubits via measurements of the 3rd order time-correlations of a single electron spin qubit confined in a semiconductor QD. Such measurements allow for the direct determination of both, ensemble and quantum dephasing times, T2* and T2, with only repeated projective measurements of the qubit state without the need for coherent spin control. Our focus will then move to nanostructures for integrated (quantum) photonics. We will discuss how slow light phenomena in GaAs photonic crystal waveguides can be used to efficiently direct single photons into propagating waveguide modes on a chip [4,5] and illustrate how one can generate, transport and detect quantum light in-situ using integrated NbN superconducting single photon detectors attached to waveguides [6]. Finally, time permitting we will explore the lasing properties of III-V coreshell nanowires grown site-selectively using MBE on silicon substrates [7,8] in which ultra-fast pump probe spectroscopy [9] reveals self-induced Rabi pulsation.
[1] Muller, K. et al. All optical quantum control of a spin-quantum state and ultrafast transduction into an electric current. Sci. Rep. 3, 1906 (2013).
[2] Muller, K. et al. Probing ultrafast carrier tunneling dynamics in individual quantum dots and molecules. ANNALEN DER PHYSIK 525, 49 (2012).
[3] Bechtold, A. et al. Three-stage decoherence dynamics of an electron spin qubit in an optically active quantum dot. Nature Physics (2015). doi:10.1038/nphys3470
[4] Laucht, A. et al. A Waveguide-Coupled On-Chip Single-Photon Source. Phys. Rev. X 2, 011014 (2012).
[5] Reichert, T. Development of mesa based ultra high current density and ultra low leakage current diodes and investigation of Germanium islands. 1 (2014).
[6] Reithmaier, G. et al. On-Chip Generation, Routing, and Detection of Resonance Fluorescence. Nano 150710123855007 (2015). doi:10.1021/acs.nanolett.5b01444
[7] Mayer, B., Rudolph, D., Schnell, J. & Morkotter, S. Lasing from individual GaAs-AlGaAs core-shell nanowires up to room temperature. Nature 4, 1 (2013).
[8] Loitsch, B. et al. Tunable Quantum Confinement in Ultrathin, Optically Active Semiconductor Nanowires Via Reverse-Reaction Growth. Adv. Mater. 27, 2195 (2015).
[9] Roder, R. et al. Ultrafast Dynamics of Lasing Semiconductor Nanowires. Nano Lett. 15, 4637 (2015).