System Bits: Jan. 13

A team of MIT researchers has built an array of light detectors sensitive enough to register the arrival of individual light particles, or photons, and mounted them on a silicon optical chip — these could be critical components of quantum computing devices.

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Quantum computational circuits
MIT researchers have built an array of light detectors sensitive enough to register the arrival of photons and mounted them on a silicon optical chip, which could be critical components of quantum computing devices.

They pointed out that single-photon detectors are notoriously temperamental. For example, of 100 deposited on a chip using standard manufacturing techniques, only a handful will generally work. As such, the team has defined a procedure for fabricating and testing the detectors separately and then transferring those that work to an optical chip built using standard manufacturing processes.

Along with 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.

Quantum mechanics dictates that tiny physical particles are, counterintuitively, able to inhabit mutually exclusive states at the same time, and a computational element made from such a particle — known as a quantum bit, or qubit — could thus represent zero and one simultaneously. If multiple qubits are “entangled,” meaning that their quantum states depend on each other, then a single quantum computation is, in some sense, like performing many computations in parallel.

Further, with most particles, entanglement is difficult to maintain, but it’s relatively easy with photons but it is for this reason that optical systems are a promising approach to quantum computation. They note that 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.

llustration of superconducting detectors on arrayed waveguides on a photonic integrated circuit for detection of single photons. (Source: MIT)

llustration of superconducting detectors on arrayed waveguides on a photonic integrated circuit for detection of single photons.
(Source: MIT)