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New way of designing circuits could lead to large-scale quantum computers

Illustration of light blue dots travelling in the dark.
The new findings could enable larger and more complicated circuits – crucial to unlocking the enormous computational power of quantum computers. Photo: Unsplash.

By utilising quantum mechanics, a quantum computer can solve computational problems that today's supercomputers cannot. But there are problems. As the circuits in quantum computers get bigger, they become more difficult to control. Researchers have demonstrated a new way to construct quantum circuits for individual light particles. This could enable larger and more complex circuits – crucial to unlocking the enormous computational power of quantum computers.

Optical circuits are a technology that uses light to transmit and process information. These circuits are different from traditional electronic circuits that use electrical signals. Optical circuits will be crucial to developing future technologies such as unhackable communication networks and ultra-fast quantum computers. However, as circuits become larger and more complex, they become more difficult to control and manufacture, affecting their performance. In a new study published in the scientific journal Nature Physics, an international team of researchers, including Lund University, has taken an ingenious technological step towards solving the problem.

“We have developed a versatile option for constructing optical circuits using a process that occurs spontaneously in nature. By exploiting the natural scattering behaviour of light in an optical fibre, we were able to program circuits in very precise ways,” said Armin Tavakoli, a physics researcher at Lund University.

Thinner than a strand of hair

The team conducted their research using commercial optical fibres used worldwide to carry the internet to our homes and businesses. These fibres are thinner than a strand of hair and use light to transmit data. In the study, the researchers managed to encode an enormous amount of information in a single particle of light, unleashing enormous computational power.

The idea is to exploit a natural process in nature: the propagation of light in optical fibres. 
“In order to avoid a complicated manipulation of the quantum state of the light particles coming out at the other end of an optical fibre, we managed to manipulate them, tame the disorder and use the entanglement of two light particles as a resource”, says Armin Tavakoli.

Manipulating light particles

Drug development, climate forecasting and space research are just some of the areas where the scientific community expects quantum computers to play an important role in the coming years. But also in machine learning and artificial intelligence – areas where optical circuits are used to process huge amounts of data very quickly. Being able to manipulate light particles and maintain more precise control as the circuits get bigger will be a key element in the development of future full-scale quantum computers.

“Quantum technology is almost mainstream today. By mapping how light particles can be manipulated, it is possible to implement this technology and create useful and programmable circuits for individual quantum particles with many degrees of freedom. This is a new and exciting approach in the development of optical quantum computers”, says Armin Tavakoli.

In addition to Lund University, Heriot-Watt University, Sapienza University of Rome and the University of Twente participated in the work. The experiment was conducted at Heriot-Watt University.

The study “Inverse design of high-dimensional quantum optical circuits in a complex medium” is published in the scientific journal Nature Physics.

Facts: Quantum computers

A quantum computer is a computing device that uses quantum mechanics to perform multiple calculations simultaneously, enough to solve problems that today's supercomputers cannot. The advantage of quantum computers over regular computers lies in their basic building blocks. In traditional computers, the smallest information carrier is a bit that can take on the value of 0 or 1. Quantum computers are instead made up of quantum bits that can have both the value of 0 and 1 at the same time, thanks to a quantum property called superposition.