by James Mitchell Crow

Chao-Yang Lu is a quantum physicist at the University of Science and Technology of China in Hefei, China. Credit: Dave Tacon for

*Nature*

In my laboratory, we develop quantum computers based on single photons, the fundamental particles of light. In 2020, our computer was the first worldwide to demonstrate ‘quantum advantage’: it completed a calculation in 200 seconds that would take a conventional supercomputer more than 2 billion years.

Today’s computers and mobile phones perform calculations using a binary code of 1s and 0s. Their silicon transistors can be only ever in either the 1 or the 0 state: on or off. But if we use fundamental particles such as photons to perform calculations, quantum effects come into play. In the quantum world, where a wave-like photon can be in two places at once, you can have 1 and 0 simultaneously. Quantum computers can take advantage of this ‘superposition’ to solve certain problems exponentially faster than classical computation can.

Here, I am looking through the control electronics part of our quantum computer. The control electronics ‘phase lock’ our photons so that they arrive in the computer together, with 15-nanometre precision. The machine performs calculations on the basis of the photons’ interactions.

When I accepted a professorship at the University of Science and Technology of China, my first quantum machine could control only six single photons. By 2020, my team had a machine that could control up to 76, and demonstrate quantum advantage. We are now up to 130 photons.

Quantum advantage used to be called quantum ‘supremacy’. It is very good that the new terminology has been adopted.

The problem that our computer solved to show quantum advantage is very abstract, a mathematical proof. My next steps are to scale the computer to control more photons — maybe 200 in the near term — and to reconfigure it for real-world applications, such as accelerating drug development by accurately predicting the interactions between candidate drugs and their targets.

*Nature*610, 412 (2022)

See: https://www.nature.com/articles/d41586-022-03205-6?utm_source=Nature+Briefing&utm_campaign=29d3e71c37-briefing-dy-20221011&utm_medium=email&utm_term=0_c9dfd39373-29d3e71c37-46554234

Quantum advantage has demonstrated and measured success to process a real-world problem faster on a quantum computer than on a classic computer. QPUs (quantum processing units) are now becoming scalable enough to run some of the larger real-world problems. Quantum supremacy refers to the demonstrated and measured ability to process a problem faster on a quantum computer than on a classic computer. It’s, any problem, not a real-world problem which is a different situation that deserves a different perspective.

Quantum computers can not read any additional data once they start running a problem. They ingest each variable into a single qubit and then run the computations. So you need a quantum computer with enough qubits to be able to hold all of your data variables. For example, if you have 25,000 variables as part of your logistics problem you need a quantum computer that can then process 25,000 variables.

"Quantum computing will have a revolutionary impact on our understanding of quantum systems and will be good at solving intrinsically quantum problems. For example, it can help us solve physics problems where quantum mechanics and the interrelation of materials or properties are important. At an atomic level, quantum computing simulates nature and therefore could help us find new materials or identify new chemical compounds for drug discovery. It holds the promise of being able to take on problems that could take a normal computer billions of years to solve and do it in second," according to Mark Potter, SVP and CTO of Hewlett Packard Enterprise and director of Hewlett Packard Labs.

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