Analog quantum computers are a type of quantum computer that work with continuous variables, such as the amplitude and phase of a quantum wave function, to perform calculations.
Physicists have created a new type of analog quantum computer that can handle challenging physics problems that the most powerful digital supercomputers cannot solve.
A groundbreaking study published in Natural physics by a team of researchers from Stanford University in the US and University College Dublin (UCD) in Ireland has revealed that a new type of highly specialized analog computer, equipped with quantum components in its circuits, can solve complex problems in quantum physics that were previously out of reach. If these devices can be scaled up, they have the potential to provide insights into some of the most important unsolved problems in physics.
For example, scientists and engineers have been looking for a deeper understanding of superconductivity for a long time. Currently, superconducting materials, such as those used in MRI machines, high-speed trains and energy-efficient long-distance power grids, only work at extremely low temperatures, hindering their wider applications. The ultimate goal of materials science is to discover materials that exhibit superconductivity at room temperature, which would revolutionize their use in a variety of technologies.
Photomicrograph of the new Quantum Simulator, which features two coupled nano-sized metal-semiconductor components embedded in an electronic circuit. Credit: Pouse, W., Peeters, L., Hsueh, CL et al. Quantum simulation of an exotic quantum critical point in a two-site charged Kondo circuit. Nat. Phys. (2023)
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 for even the fastest digital classical computers to solve. The exact simulation of complex quantum materials such as high-temperature superconductors is a really important example – that kind of computation is well beyond current capabilities because of the exponential computation time and memory requirements required to simulate the properties of realistic models.
Dr Andrew Mitchell is a theoretical physicist at University College Dublin, an Irish Research Council laureate and Director of the UCD Center for Quantum Engineering, Science and Technology (C-QuEST). Credit: UCD Media: photo by Vincent Hoban
“However, the technical and technological advances driving the digital revolution have brought with them the unprecedented ability to control matter on nanoscale. This has allowed us to design specialized analog computers, called “Quantum Simulators,” that solve specific models in quantum physics by exploiting the intrinsic quantum mechanical properties of its nanoscale components. Although we have not yet been able to build an all-purpose programmable quantum computer with sufficient power to solve all open problems in physics, what we can now do is build tailored analog devices with quantum components that can solve specific quantum physics problems. “
The architecture of these new quantum devices involves hybrid metal-semiconductor components embedded in a nanoelectronic circuit, devised by researchers at Stanford, UCD, and the Department of Energy’s SLAC National Accelerator Laboratory (located in Stanford). Stanford’s Experimental Nanoscience Group, led by Professor David Goldhaber-Gordon, built and operated the device, while the theory and modeling was done by Drs. Mitchell at UCD.
Professor Goldhaber-Gordon, who is a researcher at the Stanford Institute for Materials and Energy Sciences, said: “We always make mathematical models that we hope will capture the essence of phenomena we are interested in, but even if we believe that they are correct, they are often not solvable within 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 a kind of hardware analogy to the problem you want to solve, rather than writing some computer code for a programmable digital computer. For example, say you wanted to predict the movements of the planets in the night sky and the timing of eclipses. You can do this by constructing a mechanical model of the solar system, where someone turns a crank, and rotating interlocking gears represent the motion of the moon and planets. In fact, such a mechanism was discovered in an ancient shipwreck off the coast of a Greek island dating back more than 2,000 years. This device can be seen as a very early analog computer.
Not to be sniffed at, analog machines were used right into the late 20th century for mathematical calculations that were too difficult for the most advanced digital computers of the time.
However, to solve quantum physics problems, the 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. Importantly, many such components can be manufactured, each behaving essentially identically to the others. This is crucial for analog simulation of quantum materials, where each of the electronic components in the circuit is a proxy for a atom is simulated and behaves like an “artificial atom”. Just as different atoms of the same type in a material behave identically, so must the different electronic components in the analog computer.
The new design therefore offers a unique path to scale up the technology from individual devices to large networks capable of simulating quantum matter in bulk. In addition, the researchers showed that new microscopic quantum interactions can be engineered in such devices. The work is a step towards developing a new generation of scalable solid-state analog quantum computers.
Quantum first
To demonstrate the power of analog quantum computing with their new Quantum Simulator platform, the researchers first studied a simple circuit consisting of two quantum components coupled together.
The device simulates a model of two atoms linked together by a strange quantum interaction. By adjusting electrical voltages, the researchers were able to produce a new state of matter in which electrons appear to have only a fraction of 1/3 of their usual electrical charge – so-called ‘Z3 parafermions’. These elusive states have been proposed as the basis for future topological quantum computing, but have never before been created in the lab in an electronic device.
“By scaling up the Quantum Simulator from two to many nano-sized components, we hope to be able to model much more complicated systems that today’s computers cannot handle,” said Dr. Mitchell. “This could be the first step in finally unraveling some of the most perplexing mysteries of our quantum universe.”
Reference: “Quantum simulation of an exotic quantum critical point in a two-site charge Kondo circuit” by Winston Pouse, Lucas Peeters, Connie L. Hsueh, Ulf Gennser, Antonella Cavanna, Marc A. Kastner, Andrew K. Mitchell and David Goldhaber -Gordon, 30 Jan 2023, Natural physics.
DOI: 10.1038/s41567-022-01905-4
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