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).