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Quantum computers

Making complex calculations with light

Quantum computers that can complete various tasks are still far from reality. But by the time the next decade rolls around, we may see quantum computers with limited functionalities, but that even so use the quantum properties of light to execute complex calculations within a few days when the same process would take years for normal computers. This is the long-term goal of a collaboration between Brazilian and Italian researchers: theoretical physicists Ernesto Galvão and Daniel Brod from the Physics Institute at the Universidade Federal Fluminense (UFF), in the city of Niterói, state of Rio de Janeiro, and the teams of experimental physicists headed by Paolo Mataloni and Fabio Sciarrino at the Sapienza University of Rome and by Roberto Osellame at the Institute for Photonics and Nanotechnologies in Milan. In 2012, the researchers demonstrated a way of making mathematical calculations using a glass microchip in which three light particles – known as photons – simultaneously travel through a circuit of five intertwining paths (see Pesquisa FAPESP Issue No. 209). In June 2014, Nature Photonics published the team’s most recent results, including higher-complexity calculations made by a bigger microchip, in which up to three photons go through one nine-path circuit and another 13-path one. The physicists also used a new statistical test to verify the results of their calculations. The more photons and pathways in the circuit, the harder it is to use conventional computers to check the calculations performed by the chip.