Using the Dark Side of Excitons for Quantum Computing

New experiments demonstrate a more efficient and scalable method for using dark excitons in quantum information processing

Article ID: 687125

Released: 20-Dec-2017 7:05 AM EST

Source Newsroom: American Institute of Physics (AIP)

  • Credit: Tobias Heindel



In new experiments, however, not only can researchers read the spin states of dark excitons, but they can also do it more efficiently than before. Their demonstration, described this week in APL Photonics, from AIP Publishing, can help researchers scale up dark exciton systems to build larger devices for quantum computing. 



If the electron and hole have opposite spins, the two particles can easily recombine and emit a photon. These electron-hole pairs are called bright excitons. But if they have the same spins, the electron and hole cannot easily recombine. The exciton can’t emit light and is thus called a dark exciton. 

This darkness is part of why dark excitons are promising qubits. Because dark excitons cannot emit light, they can't relax to a lower energy level. Therefore, dark excitons persist with a relatively long life, lasting for over a microsecond -- a thousand times longer than a bright exciton and long enough to function as a qubit. 

Still, the darkness poses a challenge. Because the dark exciton is closed off to light, you can't use photons to read the spin states -- or any information a dark exciton qubit may contain. 



Like in the 2010 experiments, the new ones measure dark excitons inside quantum dots. But unlike the earlier study, the new experiments use a microlens that fits over an individual quantum dot that was selected in advance. The lens allows researchers to capture and measure more photons, crucial for larger-scale quantum information devices. Their approach also lets them choose the brightest quantum dots to measure. 




The article, "Accessing the dark exciton spin in deterministic quantum-dot microlenses," is authored by Tobias Heindel, Alexander Thoma, Ido Schwartz, Emma R. Schmidgall, Liron Gantz, Dan Cogan, Max Strauss, Peter Schnauber, Manuel Gschrey, Jan-Hindrik Schulze, Andre Strittmatter, Sven Rodt, David Gershoni and Stephan Reitzenstein. The article appeared in the journal APL Photonics Dec. 19, 2017 (DOI: 10.1063/1.5004147) and can be accessed at http://aip.scitation.org/doi/full/10.1063/1.5004147


APL Photonics is the dedicated home for open access multidisciplinary research from and for the photonics community. The journal publishes fundamental and applied results that significantly advance the knowledge in photonics across physics, chemistry, biology and materials science. See http://scitation.aip.org/content/aip/journal/app




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