Today, the world's first atomic-scale quantum integrated circuit is born
Australian quantum computing manufacturer Silicon Quantum Computing (SQC) today announced the launch of the world's first quantum integrated circuit (quantum processor) fabricated at the atomic scale and used to solve Richard Feynman's 63 The problem raised years ago [1]. This is achieved by SQC in collaboration with the team of Professor Michelle Simmons of the University of New South Wales, who is the founder of SQC and will officially assume the role of CEO on July 1.
At present, our common quantum computing chips, whether superconducting, ion traps or photonic chips, are visible to the naked eye. SQC says they have built the world's first atomic-scale quantum integrated circuit, which requires tools such as scanning tunneling microscopy to find out.
Intel superconducting quantum chip (top left); Xanadu photonic chip (top right); SQC atomic-scale integrated circuit (bottom). The first two are real photos, and the latter are images under a scanning tunneling microscope.
The Simmons team announced in 2012 that it had produced the world's first single-atom transistor, and proposed the goal of achieving atomic-scale quantum integrated circuits by 2023. Simmons revealed that the goal was actually achieved two years ahead of schedule (the end of 2021). Their processor consists of a chain of 10 quantum dots . In a paper published June 22 in the journal Nature [2], they used this quantum processor to accurately simulate the structure and energy states of the organic compound polyacetylene, finally demonstrating the effectiveness of the team's technique .
Professor Simmons described it as the biggest achievement of her career. "This is a major breakthrough. Today's classical computers have difficulty simulating even relatively small molecules due to the large number of possible interactions between atoms. Advances in SQC atomic-scale circuit technology have allowed the company and its customers to build a range of new materials for Quantum models, whether it's drugs, battery materials or catalysts. It won't be long before we start discovering new materials that have never existed before."
Team Simmons
To realize the first atomic-scale quantum integrated circuits, SQC leverages three separate techniques of atomic engineering:
The first is to make small atomic dots (known as quantum dots) of uniform size so that their energy levels are aligned and electrons can easily pass through them.
The second is the ability to tune the energy levels of each dot individually, but also to tune the energy levels of all dots collectively to control the transfer of quantum information.
The third is that the team was able to control the distance between the dots with sub-nanometer precision, keeping the dots close enough but independent for quantum coherent transport of electrons on the chain.
Prof Simmons said the choice of a carbon chain of 10 atoms was not accidental, as it is within the size range that classical computers can calculate, with as many as 1024 independent electron interactions in the system. If you increase this to a chain of 20 points, the number of possible interactions grows exponentially, making it difficult for classical computers to solve.
"We're getting close to the limits of classical computers, so it's like going from the edge to the unknown," she said.
Renderings from different angles. A chain of 10 quantum dots in an integrated circuit.
Hon Ed Husic, Minister of Industry and Science of Australia, recognized the work of SQC[3], which launched the world's first integrated circuit manufactured at the atomic scale two years ahead of schedule and is a world leader in the development of silicon-based quantum computing status. "Australia's research capabilities provide the foundation for a strong quantum industry both domestically and with our like-minded international partners."
Through the world's first atomic-scale quantum integrated circuit, the Simmons team and SQC solved for the first time that the Nobel Prize winner in physics, who proposed the concept of quantum computing, and the famous theoretical physicist Richard Feynman proposed it 63 years ago. the problem.
In 1959, Feynman asserted in his lecture "Plenty of Room at the Bottom" that if you want to understand how nature works, then you must be able to control matter on the same length scales that make it up—that is, you It must be possible to control matter on the length scale of atoms. Sixty-three years after Feynman first proposed this fundamental theory, Simmons' team proved the conjecture.
The team chose to work with polyacetylene—a carbon-based molecular chain with the chemical formula (C2H2)n , where n represents a repeating pattern of two hydrogen atoms and two carbon atoms.
Symbolic diagram of polyacetylene showing single and double bonds between carbon and hydrogen atoms.
The atoms in polyacetylene are joined by covalent bonds, which are strong molecular bonds where atoms share electrons in the outer shell. A single bond means that two bonded atoms share one outer electron. A double bond represents two shared electrons. The alternating single and double bonds between carbon atoms in the polyacetylene chain make this molecule an interesting object of study in physical chemistry.
The Su-Schrieffer-Heeger (SSH) model is a well-known representation of molecular theory that takes into account the interactions between atoms and their electrons and explains the physical and chemical properties of compounds. "It's a well-known problem that you can solve with a classical computer. The number of atoms that a classical computer can observe all interacting with is very small. But now we're doing it in a quantum system," Simmons said [4].
A club model of polyacetylene showing single and double bonds between carbon atoms (dark grey) and hydrogen atoms (light grey).
How did the team simulate polyacetylene on their quantum device?
"What we're doing is having the actual processor itself simulate carbon-carbon single bonds and carbon-carbon double bonds," Simmons explained. "We're designing with sub-nanometer precision to try to simulate these bonds in a silicon system. That's why. It's called a quantum simulator."
Using atomic transistors in the machine, the researchers simulated covalent bonds in polyacetylene.
According to SSH theory, there are two distinct situations in polyacetylene, called "topological states" - "topological" because of their different geometries.
In the first case, you can cut the chain at the carbon-carbon single bond, so there is a double bond at the end of the chain. In the second case, you sever the double bond, leaving a carbon-carbon single bond at the end of the chain and, due to the long distance of the single bond, separates the two atoms on either end. The two topological states exhibit completely different behaviors when an electric current is passed through the molecular chain.
In this work, the team constructed a chain of ten quantum dots and used them to simulate the so-called SSH model.
"There are only two kinds of atoms in our entire device—phosphorus and silicon," Simmons said. "We took out everything else, all the interfaces, the dielectrics, everything that caused problems in other architectures, and we only had those two kinds of atoms. Simple in concept, but obviously hard to make. It's a nice, clean, physically scalable system.
She added: "The challenge is how to put the atom in place, and then how do you know it's there? It took us a full decade to figure out the chemistry that gets the phosphorus atom into the silicon matrix so that it's protected. The technology we used One is scanning tunneling microscopy (STM), a lithography tool."
After placing a silicon plate in a vacuum, the research team first heated the substrate to 1,100°C and then gradually cooled to around 350°C, creating a flat, two-dimensional silicon surface. The silicon is then covered with hydrogen atoms (which can be selectively removed individually with an STM probe). Phosphorus atoms are placed in the newly formed gaps in the hydrogen layer, and the entire hydrogen layer is then covered by another layer of silicon.
SQC quantum device simulated at the atomic scale.
"Instead of using a single atom to model carbon, we used 25 phosphorus atoms," Simmons said.
The team found that they were able to control the flow of electrons along the chain. They demonstrated that for a chain of 10 points, only 6 electrodes are needed to do this. Therefore, the number of electrodes is much less than the actual number of points. This is great for scaling. Because fundamentally, in a quantum computer, you want fewer gates compared to active components, otherwise it scales poorly. "
Simmons believes that not only does their device conform to SSH theory, but that quantum computers will soon start simulating problems even beyond our best theories. "This opens up a door for us to things we've never imagined before. "
The device suffers from similar drawbacks as other quantum computers—in particular, the high cost and energy consumption of bulky refrigerators, which require temperatures close to absolute zero.
Simmons has avoided talking about SQC's ongoing projects after this initial presentation, citing commercial confidentiality concerns. But she did say: "We want to apply it to as many different fields as possible and see what we can find."
Reference link:
[1] http://sqc.com.au/2022/06/23/silicon-quantum-computing-announces-worlds-first-quantum-integrated-circuit/
[2] https://www.nature.com/articles/s41586-022-04706-0
[3] https://www.minister.industry.gov.au/ministers/husic/media-releases/quantum-breakthrough-fuel-australian-industry
[4] https://cosmosmagazine.com/technology/quantum-computer-coherent-silicon/
