LAKE WALES, Fla. ‐ Future quantum computers need reliable arrays of consistently encoded single-photon sources, which many investigators assumed would come from quantum dots. However, University of Tsukuba researchers now contend that doped gallium arsenide (GaAs) semiconductors provide nearly identically encoded single photon sources more reliably than quantum dots.
"We believe that our demonstration is an essential step toward future quantum information processing using impurities in III-V compound semiconductors," said Michio Ikezawa, a professor at University of Tsukuba, in a paper written with co-authors Liao Zhang, Yoshiki Sakuma and Yasuaki Masumoton that appears in the AIP's journal Applied Physics Letters. The paper is titled Quantum interference of two photons emitted from a luminescence center in GaAs:N.
Indistinguishability versus Δ. The red dots are obtained from two-photon interference (TPI) measurements. The black dashed line shows the estimated value of VTPI by T1 and T2
The III-V compound GaAs was doped with nitrogen (N), as indicated in the article's title. According to the authors, they can better supply arrays of single-photon sources with what is called wave-packet overlap (nearly perfect matching of energy, space, time and polarization) of each photon emitted.
The University of Tsukuba researchers collaborated with Japan’s National Institute for Materials Science (also in Tsukuba) to dope GaAs with nitrogen impurities in order to make them into arrays of consistency encoded single-photon emitters. The novel mechanism of emission is called isoelectronic traps. Because of the homogeneity of the doped GaAs material, its isoelectronic traps produce arrays of matched single-photon emitters more easily than quantum dots, according to the researchers. To boot, the quantum-encoded single-photons have an unusually long coherence time, which is another requirement for future quantum computers.
Using the Hong–Ou–Mandel effect in nitrogen doped GaAs, two identical photons entered a 50:50 beam splitter, one in each input port, to demonstrate that they were identically encoded by extinguishing each other thus creating an interferometer that accurately measured bandwidth, path lengths and timing.
The researchers claimed their experiment was the world's first demonstration of measurement confirmed identical photons emitted from III-V semiconductors with higher quality and longer coherence times than quantum dots.
Next, the group intends to increase the indistinguishability of their photon-emitting arrays by finding a way to suppress the high-speed relaxation mechanism exhibited in their experiment.
— R. Colin Johnson, Advanced Technology Editor, EE Times