New analog quantum computers to solve previously unsolvable problems

Physicists have invented a new type of analog quantum computer capable of solving difficult physics problems that the most powerful digital supercomputers cannot.

New research published in Natural Physics by collaborating scientists from Stanford University in the United States and University College Dublin (UCD) in Ireland has shown that a new type of highly specialized analog computer, whose circuits include quantum components, can solve cutting-edge problems in quantum physics that were previously out of reach. When scaled up, such devices might be able to shed light on some of the most important unsolved problems in physics.

For example, scientists and engineers have long wanted to gain a better understanding of superconductivity because existing superconducting materials, such as those used in MRI machines, high-speed trains, and energy-efficient long-distance power grids, do not work. currently only at extremely low temperatures. , limiting their wider use. The holy grail of materials science is to find superconducting materials at room temperature, which would revolutionize their use in a host of technologies.

Dr Andrew Mitchell is Director of the UCD Center for Quantum Engineering, Science and Technology (C-QuEST), a theoretical physicist at the UCD School of Physics and co-author of the paper.

He said: “Some problems are simply too complex to be solved by even the fastest classical digital computers. Accurate simulation of complex quantum materials such as high-temperature superconductors is a really important example – this kind of computation far exceeds current capabilities because of the exponential computation time and memory requirements needed to simulate realistic model properties.”

“However, the technological and technical advances driving the digital revolution have brought with them the unprecedented ability to control matter at the nanoscale. This has allowed us to design specialized analog computers, called ‘quantum simulators’. , which solve specific models of quantum physics by taking advantage of the inherent quantum mechanical properties of its nanoscale components.Although we have not yet been able to build a general-purpose programmable quantum computer with sufficient power to solve all open problems in physics, what we can now do is build custom-made analog devices with quantum components capable of solving specific quantum physics problems.”

The architecture of these new quantum devices involves hybrid metal-semiconductor components embedded in a nanoelectronic circuit, designed by researchers from Stanford, UCD and the Department of Energy’s SLAC National Accelerator Laboratory (located at Stanford). The Stanford Nanoscience Experimental Group, led by Professor David Goldhaber-Gordon, built and operated the device, while theory and modeling were done by Dr Mitchell of UCD.

Professor Goldhaber-Gordon, who is a research fellow at the Stanford Institute for Materials and Energy Sciences, said: “We are always creating mathematical models that we hope will capture the essence of the phenomena that interest, but even if we believe they’re right, they often cannot be resolved in a reasonable time.”

With a quantum simulator, “we have these knobs to turn that no one has ever had before,” Professor Goldhaber-Gordon said.

Why analog?

The essential idea of ​​these analog devices, Goldhaber-Gordon said, is to build some sort of hardware analogy to the problem you want to solve, rather than writing computer code for a programmable digital computer. For example, suppose you want to predict the movements of planets in the night sky and the timing of eclipses. You could do this by building a mechanical model of the solar system, where someone turns a crank, and interlocking rotating gears represent the movement of the moon and planets.

In fact, such a mechanism was discovered in an ancient shipwreck off a Greek island dating back over 2000 years. This device can be considered as a very first analog computer.

Not to be overlooked, analog machines were used until the end of the 20th century for mathematical calculations that were too difficult for the most advanced digital computers of the time.

But to solve quantum physics problems, devices must involve quantum components. The new Quantum Simulator architecture involves electronic circuits with nanoscale components whose properties are governed by the laws of quantum mechanics. It is important to note that many such components can be made, each behaving essentially identical to the others.

This is crucial for the analog simulation of quantum materials, where each of the electronic circuit components is a proxy for a simulated atom and behaves like an “artificial atom”. Just as different atoms of the same type in a material behave identically. , just like the various electronic components of the analog computer.

The new design therefore offers a unique path to scale the technology from individual units to large arrays capable of simulating bulk quantum matter. Moreover, the researchers showed that new microscopic quantum interactions can be engineered into such devices. The work is a step towards developing a new generation of scalable solid-state analog quantum computers.

Quantum firsts

To demonstrate the power of analog quantum computing using their new Quantum Simulator platform, the researchers first studied a simple circuit comprising two quantum components coupled together.

The device simulates a model of two atoms coupled together by a particular quantum interaction. By adjusting the electrical voltages, the researchers were able to produce a new state of matter in which the electrons appear to have only a third of their usual electrical charge, called “Z3 parafermions”. These elusive states have been proposed as the basis for future topological quantum computing, but never before created in the laboratory in an electronic device.

“By scaling up the quantum simulator from two to more nanoscale components, we hope we can model much more complicated systems than current computers can handle,” said Dr Mitchell. “This could be the first step in finally unraveling some of the most puzzling mysteries in our quantum universe.”