QUROPE Quantum Information Processing and Communication in Europe

Photonic Boson Sampling in a Tunable Circuit
M. A. Broome, A. Fedrizzi, S. Rahimi-Keshari, J. Dove, S. Aaronson, T. C. Ralph and A. G. White
Science 339, 794-798 (2013) and

Integrated multimode interferometers with arbitrary designs for photonic boson sampling
A. Crespi, R. Osellame, R. Ramponi, D. J. Brod, E. F. Galvao, N. Spagnolo, C. Vitelli, E. Maiorino, P. Mataloni and F. Sciarrino
Nature Photonics 7, 545-549 (2013) and

Experimental boson sampling
M. Tillmann, B. Daki, R. Heilmann, S. Nolte, A. Szameit and P. Walther
Nature Photonics 7, 540-544 (2013) and

Boson Sampling on a Photonic Chip
J. B. Spring, B. J. Metcalf, P. C. Humphreys, W. S. Kolthammer, X.-M. Jin, M. Barbieri, A. Datta, N. Thomas-Peter, N. K. Langford, D. Kundys, J. C. Gates, B. J. Smith, P. G. R. Smith and I. A. Walmsley
Science 339, 798-801 (2013)

Universal quantum computers promise a dramatic increase in computation power over classical computers,
for example the ability to factor numbers exponentially faster than any known classical algorithm. Their fullsize
realization remains challenging and this motivates the question of whether one can show a separation
between classical and quantum computation without requiring a full scale universal quantum computer. One
candidate approach, put forward by Aaronson and Arkhipov, involves only the interference of single photons
in random linear optical networks. Sampling the bosonic output distribution from such a network, known as
the 'Boson Sampling' problem, is strongly believed to be classically intractable (requiring an exponential
amount of time in the number of modes classically). Since such a scheme requires only linear optics and not
measurement based interactions or adaptive feed forward techniques it provides an idea intermediate
scenario that can be tested to provide strong evidence of a quantum speedup before a full scale quantum
computer is feasible.

The four above works, demonstrated for the first time small scale proof of concept experiments of Boson
Sampling. All four groups manufactured integrated interferometers with varying numbers of modes, and
were able to obtain the output distribution when either three or four photons were sent through the network.
In each case the groups verified that the final distribution was consistent with the predictions of Boson
Sampling. These works pave the way for scaling up to larger optical networks where a definitive
demonstration of the power of quantum computations is hoped to be seen.