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The Quantum-Dot-Confined Dark Exciton as a Semiconductor Spin Qubit

Emma Schmigdall, University of Washington
Thursday, May 5, 2016 - 12:30am to 1:30am
PAT C-520
​On-demand initialization and resetting of qubits and their coherent control are basic

requirements for quantum information processing (QIP). A semiconductor quantum

dot is a convenient QIP platform, due to the fact that its potential well confines single

carriers, whose spins can be used as matter qubits, and optical recombination of these

confined carriers allows coupling to photonic qubits.

A quantum-dot-confined dark exciton (DE) is an electron hole pair with

parallel spins. Since photons barely interact with the electronic spin, the DE is almost

optically inactive and has a very long lifetime, making it an interesting quantum dot

qubit candidate. We demonstrate for the first time that the quantum dot-confined DE

forms a long lived (more than 1 μs) integer spin qubit which, despite its optical

inactivity, can be deterministically initiated [1-2] and fully controlled [1] by short

optical pulses, several orders of magnitude shorter than the life and coherence time (at

least 100 ns) of this qubit. We also demonstrate that the DE can be reset from the

quantum dot via optical pumping [3] and that it can be used to generate entangled

photons [4].

[1] Schwartz, Schmidgall et al. Phys. Rev. X 5, 011009 (2015).
[2] Schwartz et al. Phys. Rev. B 92, 201201R (2015).
[3] Schmidgall et al. Appl. Phys. Lett. 106, 193101 (2015).
[4] Lindner and Rudolph, Phys. Rev. Lett. 103, 113602 (2009).​