A photon-based method for demonstrating the advantage of quantum over classical machines can handle photon loss, facilitating experiments.

A race is on to build a quantum computer that solves difficult problems much faster than a classical computer—a milestone dubbed quantum supremacy [1]. Runners in this race, however, are faced with a hazy finish line, which can move closer as quantum machines and algorithms improve or further away as their classical counterparts catch up. An experiment led by Jian-Wei Pan of the University of Science and Technology in China [2] nudges the racers forward for now. Inspired by a theoretical proposal, the researchers confirmed that a promising method for demonstrating quantum supremacy, known as boson sampling with photons (Fig. 1), produces useful output even as photons leak from the system. This means that researchers don’t have to “toss away” the output of a sampling experiment when photons are lost, as was previously assumed [3], allowing for faster computations and bringing a demonstration of quantum supremacy closer to reality.

When will we have a useful quantum computer?