Quantum dots and entanglement Tobias Huber Thanks to

Quantum dots and entanglement Tobias Huber

Thanks to… Uni Innsbruck Institute for exp. physics Gregor Weihs Ana Predojević Max Prilmüller Stephanie Grabher Daniel Föger Harishankar Jayakumar Thomas Kauten Michael Sehner Uni Innsbruck Institute for theo. physics Helmut Ritsch Laurin Ostermann Hashem Zoubi Uni Olomouc Ivo Straka Miroslav Ježek Radim Filip JQI @ NIST & UMD Glenn Solomon CNRC Canada Dan Dalacu Philip Poole Uni Bordeaux Philippe Tamarat Brahim Louis Uni Waterloo Milad Koshnegar Hamed Majedi Uni Würzburg Christian Schneider Sven Höfling Uni Stuttgart Markus Müller Peter Michler Uni Innsbruck Staff Carina-Theresa Oberhöler Armin Sailer Christoph Wegscheider Anton Schönherr

Why care about quantum light? Communication Interferometry www. scienceabc. com Optical quantum computing Imaging www. ligo. caltech. edu/page/ligo-detectors Metrology Fundamental new physics youtube. com, NIST J. Carolan et al. Science www. rp-photonics. com sciencealert. com

Outline • Quantum dots (QD) • (Two photon) entanglement • Polarization entangled photons • Time-bin entangled photons • 2 photon resonant excitation • Hyper-entanglement

Quantum dots • Semiconductor structure • confined in all 3 dimensions Bryant and Solomon, Optics of quantum dots and wires, 2005 ©JQI Bryant and Solomon, Optics of quantum dots and wires, 2005

Quantum dot states Electronic structure: Confined states: X – Exciton XX – Biexciton X+(-) – Charged exciton (trion) XX+(-) – Charged biexciton Excitation process:

Entanglement •

Polarization entanglement from QDs H … horizontally polarized photon V … vertically polarized photon • Fine-structure splitting S must be small • or fast detection to resolve phase change Minimize S by: • Finding a round quantum dot • E-field (Gerardot et al. APL 90, 041101 (2007), Muller et al. PRL 103, 217402 (2009)) • B-field (Kowalik et al. PRB 75, 195340 (2007) • Strain (Trotta et al. PRB 88, 155312 (2013) • Thermal annealing (Ellis et al. APL 90, 011907 (2007))

Reconstructed density matrix Polarization entanglement Fidelity F=0. 81(6) Concurrence C=0. 71(5) Experiment Theory

Time-bin entanglement

2 photon resonant excitation of the biexciton Jayakumar et al. Phys. Rev. Lett. 110, 135505 (2013) Huber et al. Phys. Rev. B 93, 201301(R) (2016) Resonant excitation allows to create time bin entangled phtons

Reconstructed density matrix Time-bin entanglement Fidelity F=0. 87(4) Concurrence C=0. 76(8) Experiment Theory

2 photon resonant excitation • What is it good for? • deterministic generation of photon pairs Jayakumar et al. Phys. Rev. Lett. 110, 135505 (2013) • improved indistinguishability improves from 0 to 0. 39 Huber et al. New J. Phys. 17 123025 (2015) • coherent control enables e. g. creation of time bin entangled photons Jayakumar et al. Nature Communications 5, 4251 (2014) • improved polarization entanglement fidelity improves from 0. 72 to 0. 81 Müller et al. Nature Photonics 8, 224– 228 (2014)

Hyper-entanglement •

Hyper-entanglement analysis •

Analysis II and setup

Full hyper-entangled matrix Full reconstruction Theory Fidelity F=0. 55(4) 17