Chinese photonic quantum computer demonstrates quantum supremacy

A team of researchers affiliated with several institutions in China have built and tested a photonic quantum computer that demonstrates quantum supremacy. In their article published in the journal Science, the group describes their computer, which they call Jiuzhang, and its performance when sampling Gaussian bosons.

Quantum computers have been in the news lately as scientists try to determine if they can meet expectations. Quantum computers could far outperform conventional machines on some tasks. The goal is to achieve what is now called “quantum supremacy” – where a quantum computer can outperform conventional computers on at least one type of task. So far, only one computer has achieved this feat: Google’s Sycamore device. And because the field is still so new, researchers around the world are working on very different designs. Sycamore was based on qubits represented by superconducting materials. In this new effort, the team in China developed a photon-based quantum computer capable of performing just one specific type of computation: boson sampling.

Boson sampling is a way to calculate the output of a straight line optical circuit that has multiple inputs and outputs. It is achieved by building a machine in which photons are sent through a circuit in parallel, and once inside, are separated by beam splitters. The divided photons continue through the circuit, encountering mirrors and other beam splitters. Notably, if two photons encounter the same separator simultaneously, the two undivided photons will follow one of the paths away from the separator. The process is repeated, resulting in a distribution of numbers that represent the output of the network. Conventional computers get bogged down very quickly when trying to calculate the distributions of such a system. Jiuzhang was designed to handle 100 inputs and 100 outputs using 300 beam splitters and 75 mirrors.

The researchers found that it took Jiuzhang about 200 seconds to provide a response. They noted that it would have taken about 2.5 billion years for the world’s fastest supercomputer to perform the same calculations – a clear example of quantum supremacy.

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