Such arrays are crucial components of devices that use photons to perform quantum computations; however,single-photon detectors are notoriously temperamental: Of 100 deposited on a chip using standard manufacturing techniques, only a handful will generally work. In a paper in Nature Communications, the researchers at MIT and elsewhere describe a procedure for fabricating and testing the detectors separately and then transferring those that work to an optical chip built using standard manufacturing processes.

In addition to yielding much denser and larger arrays, the approach also increases the detectors' sensitivity. In experiments, the researchers found that their detectors were up to 100 times more likely to accurately register the arrival of a single photon than those found in earlier arrays.

With most particles, entanglement is difficult to maintain, but it's relatively easy with photons. For that reason, optical systems are a promising approach to quantum computation. But any quantum computer--say, one whose qubits are laser-trapped ions or nitrogen atoms embedded in diamond--would still benefit from using entangled photons to move quantum information around.

"Because ultimately one will want to make such optical processors with maybe tens or hundreds of photonic qubits, it becomes unwieldy to do this using traditional optical components," says Dirk Englund, the Jamieson Career Development Assistant Professor in Electrical Engineering and Computer Science at MIT and corresponding author on the new paper. "It's not only unwieldy but probably impossible, because if you tried to build it on a large optical table, simply the random motion of the table would cause noise on these optical states. So there's been an effort to miniaturize these optical circuits onto photonic integrated circuits."