A team of quantum computer physicists at UNSW Sydney has developed an atomic-scale quantum processor to simulate the behavior of a small organic molecule, solving a challenge posed some 60 years ago by theoretical physicist Richard Feynman.
The achievement, which came two years ahead of schedule, represents a major milestone in the race to build the world’s first quantum computer and demonstrates the team’s ability to control the quantum states of electrons and atoms in silicon at an outstanding level yet to be achieved. has not been reached before.
In an article published today in the journal: Naturethe researchers described how they could mimic the structure and energy states of the organic compound polyacetylene – a repeating chain of carbon and hydrogen atoms distinguished by alternating single and double carbon bonds.
Lead researcher and former Australian of the Year, Scientia Professor Michelle Simmons, said the team at Silicon Quantum Computing, one of UNSW’s most exciting startups, has built a quantum integrated circuit made up of a chain of 10 quantum dots to simulate the precise location of atoms in the polyacetylene chain.
“If you go back to the 1950s, Richard Feynman said you can’t understand how nature works unless you can build matter at the same length scale,” said Prof. Simmons.
“And that’s what we do. We literally build it from the bottom up, mimicking the polyacetylene molecule by placing atoms in silicon at the exact distances that represent the carbon-carbon single and double bonds.”
The study was based on measuring the electric current through an intentionally constructed 10-quantum-dot replica of the polyacetylene molecule as each new electron moved from the source output of the device to the drain — the other end of the circuit.
To be doubly sure, they simulated two different strands of the polymer chains.
In the first device, they cut a fragment of the chain to leave double bonds at the end, yielding 10 peaks in the current. In the second device, they cut another fragment of the chain to leave single bonds at the end that only gave rise to two peaks in the current. The current passing through each chain was therefore dramatically different due to the different bond lengths of the atoms at the end of the chain.
The measurements not only matched the theoretical predictions, they matched perfectly.
“What it shows is that you can literally mimic what’s really happening in the real molecule. And that’s why it’s exciting because the signatures of the two chains are very different,” said Prof. Simmons.
“Most of the other quantum computer architectures out there don’t have the ability to engineer atoms with sub-nanometer precision or have the atoms sit that close.
“And that means we can now begin to understand more and more complicated molecules based on placing the atoms as if they were mimicking the real physical system.”
standing on the edge
According to Prof. Simmons, it was no coincidence that a carbon chain of 10 atoms was chosen, because that falls within the limit of what a classic computer can calculate, with up to 1024 individual interactions of electrons in that system. Raising it to a 20-point chain would increase the number of possible interactions exponentially, making it difficult for a classical computer to solve.
“We’re almost at the limit of what classic computers can do, so it’s like stepping off the edge into the unknown,” she says.
“And here’s the exciting thing, we can now make bigger devices that go beyond a classic computer can model. So we can look at molecules that have not been simulated before. We will be able to understand the world in a different way, by tackling fundamental questions that we have never been able to solve before.”
One of the questions Prof. Simmons alluded to is about understanding and mimicking photosynthesis — how plants use light to create chemical energy for growth. Or insight into how to optimize the design of catalysts for fertilizers, a process that currently involves a lot of energy and costs.
“So there are huge implications for fundamentally understanding how nature works,” she said.
Future quantum computers
Much has been written about quantum computers over the past three decades, with the billion dollar question always being, “but when can we see one?”
Prof. dr. Simmons says the development of quantum computers is on a similar trajectory to how classical computers evolved — from a transistor in 1947 to an integrated circuit in 1958, then small computer chips that were incorporated into commercial products such as calculators about five years later.
“And so we’re now replicating that roadmap for quantum computers,” says Prof. Simmons.
“We started with a single atomic transistor in 2012. And this latest result, achieved in 2021, is the equivalent of the atomic-scale quantum integrated circuit two years earlier. If we attribute it to the evolution of classical computer science, we can’ predicting again that in five years we should have some sort of commercial result from our technology.”
One of the benefits of the UNSW/SQC team’s research is that the technology is scalable because it manages to use fewer components in the circuit to control the qubits — the basic bits of quantum information.
“In quantum systems, you need something that creates the qubits, some kind of structure in the device that allows you to shape the quantum state,” says Prof. Simmons.
“In our system, the atoms themselves create the qubits, requiring fewer elements in the circuitry. We only needed six metal gates to control the electrons in our 10-point system — in other words, we have fewer gates than there are. active device components While most quantum computing architectures require nearly double the number or more of the control systems to move the electrons in the qubit architecture.”
With fewer components packed tightly together, the amount of interference with the quantum states is minimized, allowing devices to scale up to create more complex and powerful quantum systems.
“So that very low physical port density is also very exciting for us, because it shows that we have this nice clean system that we can manipulate, maintaining consistency over long distances with minimal overhead in the ports. So it’s valuable for scalable quantum computers.”
Looking ahead, Prof. Simmons and her colleagues will investigate larger compounds that may have been theoretically predicted but have never been simulated and fully understood, such as superconductors at high temperatures.
M. Kiczynski et al, Engineering topological states in atom-based semiconductor quantum dots, Nature (2022). DOI: 10.1038/s41586-022-04706-0
University of New South Wales
Quote: Scientists develop quantum processor to emulate a small organic molecule (June 2022, June 23) Retrieved June 24, 2022 from https://phys.org/news/2022-06-scientists-quantum-processor-emulate-small.html
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