An entirely new and efficient model of quantum computer — the boson-sampling computer — was successfully prototyped, bringing scientists a leap forward in the world of quantum computing. Quantum computers work by manipulating quantum objects as, for example, individual photons, electrons or atoms, and by harnessing the unique features of the quantum world. This particular feature promises a dramatic increase in speed over classical computers; they are designed to complete tasks that even a supercomputer would not be able to handle. Despite a rapid development of quantum technology over the past several years, the development of such a machine has proved difficult to achieve. Scientists from the University of Vienna, in collaboration with a team from the University of Jena in Germany, have set about using photons, a particular type of bosons, based on their high mobility. Together, the researchers inserted photons into a complex optical network, where they could propagate along many different paths. The optical network — the central part of the University of Vienna boson-sampling computer. According to the laws of quantum physics, the photons seem to take different paths simultaneously, as shown in the image. Courtesy of ©Philip Walther Group, University of Vienna. “According to the laws of quantum physics, the photons seem to take all possible paths at the same time,” said Philip Walther of the University of Vienna’s physics faculty. “This is known as superposition. Amazingly, one can record the outcome of the computation rather trivially: One measures how many photons exit in which output of the network.” Because a classical computer relies on an exact description of the optical network to calculate the propagation of the photons through this circuit, it is ultimately unable to calculate a few dozen photons and an optical network with a hundred inputs and outputs. However, the prototype boson-sampling computer that the investigators built — based on a theoretical proposal by scientists at MIT in Cambridge, Mass. — can achieve this calculation. “It is crucial to verify the operation of a boson-sampling computer by comparing its outcome with the predictions of quantum physics,” said Max Tillmann, first author of the study. “Fortunately, for small enough systems, classical computers are still able to accomplish this.” The investigators successfully demonstrated that their realization of the boson-sampling computer works with high precision; this achievement gives rise to the hope that the first outperformance of conventional computers may not be too far off. The results appeared online in Nature Photonics (doi: 10.1038/nphoton.2013.102). It will appear in a print edition in July. For more information, visit: www.univie.ac.at/en