Machine Heart Report
Editor: Zhang Qian, Zenan
Australian quantum computing company SQC has created an integrated quantum circuit that can accurately simulate a small organic polyacetylene molecule quantum state , which will help create new materials. The study appeared in the new issue of Nature.
6 On June 23, Australian quantum computing company SQC (Silicon Quantum Computing) announced the launch of the world's first quantum integrated circuit. This is a circuit that contains all the basic components on a classic computer chip, but the volume is on the quantum scale.
SQC team used this quantum processor to accurately simulate the quantum state of an organic polyacetylene molecule - ultimately demonstrating the effectiveness of the new quantum system modeling technology.
"This is a major breakthrough," said SQC founder Michelle Simmons. Because there may be a lot of interactions between atoms , classic computers today are even difficult to simulate relatively small molecules. The development of SQC atomic-level circuit technology will enable companies and their customers to build a range of new materials quantum models, whether it is drugs, battery materials or catalysts. It won't take long to start implementing new materials that have never existed before. ”
The research results were published in the new issue of Nature magazine.
Paper link: https://www.nature.com/articles/s41586-022-04706-0
Replicate the classic computer
on the quantum level, just like an ordinary (classic) computer, quantum computer uses transistor to encode information. However, unlike classical computers, the transistors of quantum computers are on the quantum scale—so small as the size of only one atom. Classic computers use bits 0 and 1, while quantum transistors use a mixture of 0, 1 or 0 and 1 to encode quantum information.
engineers can use the quantum effect of single atom transistor for calculations. But in the quantum world, things are not that simple.
In the quantum world, particles exist in the form of "superposition states" - their positions, momentum and other physical properties are not defined by a single value, but are expressed by probability. Through superposition, qubit can store multi-dimensional computing data that is much more complex than ordinary bits.
Therefore, quantum computers are expected to be thousands or even millions of times faster than classic computers, and the efficiency of performing calculations is even much higher than the most powerful classic computers.
However, they have other magical features.
When the superposition state expands to multiple systems or atoms, you will get a " entangled state ", that is, the qubits are associated with each other. When qubits are entangled, their changes affect each other. This quantum effect is expected to be applied to the field of encryption.
But at the same time, this effect also causes trouble for scientists to create available quantum computers.
Most importantly, the probability properties of quantum systems mean they are very prone to errors. Therefore, a major challenge in creating quantum machines is to make them have coherence to reduce noise in the signal. The SQC team believes that it is exactly this problem they cracked.
"To create a quantum computer, we have to work on the atomic scale so that we can touch quantum states and make them coherent and fast," said Michelle Simmons, founder of SQC and corresponding author of the paper.
paper corresponding author Michelle Simmons.
Simmons’ team built the world’s first single-atom transistor in 2012 and made the first atomic scale integrated circuit in 2021. "We're focusing on the next device - before we can make quantum computers that people can use, we need to solve some kind of business-related algorithm. At the beginning, we didn't know what we would show on that circuit.”
The team chose polyacetylene, a carbon-based molecular chain with the chemical formula (C2H2)n, where n represents duplication.
polyacetylene structure diagram. The atoms in
polyacetylene are bound together through the covalent bond . Single bond means that two atoms share one outer electron, and double bond means that two electrons share. The alternation of single and double bonds between carbon atoms in the polyacetylene chain makes this molecule an interesting research object in physicochemistry. The
Su-Schrieffer-Heeger (SSH) model is a well-known molecular theory representation that uses the interaction between atoms and their electrons to explain the physical and chemical properties of compounds. "This is a well-known problem that can be solved with classic computers, because there are only a few atoms in it, and a classic computer can handle all the interactions. But we are trying to solve it now with a quantum system." The stick model of
polyacetylene shows a single and double bond between a carbon atom (dark gray) and a hydrogen atom (light gray).
So how did the SQC team simulate polyacetylene on their quantum devices?
"We asked the processor itself to simulate single and double bonds between carbon atoms ," Simmons explained. "We engineered with subnanometer precision in an attempt to mimic chemical bonds within a silicon system. So that's why it's called a quantum analog simulator."
uses atomic transistors in the machine to simulate covalent bonds in polyacetylene.
According to SSH theory, there are two different situations in polyacetylene, called "topology state" - the name " topology " is because their geometry is different.
In one state, you can cut the link at a single carbon-carbon bond, so there are double bonds at the end of the chain. Alternatively, you can cut off the double bond and leave a single bond at the end of the chain. Because the single bond is long distance, this practice can separate atoms at both ends. These two topological states exhibit completely different behaviors when the current passes through the molecular chain.
This is the theory. "When we make the equipment, we see exactly this behavior. So it's very exciting," said Simmons. Dr Charles Hill, senior lecturer in quantum computing at the University of Melbourne, agrees.
"One of the most promising applications of quantum technology is to use one quantum system to simulate other quantum systems," Hill said. "In this work, the authors considered a chain of ten quantum dots and used them to simulate the so-called SSH model. This is an amazing project. The quantum device used for the demonstration is made with sub-nano precision. This experiment paves the way for the future of simulating larger and more complex quantum systems."
Simmons believes that the advantage of this complex production process is that you are "not creating a new material that you have to invent and figure out how to make it."
"We do have atomic sub-nanometer precision," she added. "The atoms themselves are located in the silicon matrix, so we are building systems with materials that have been used in the semiconductor industry."
"There are only two atoms in the entire device - phosphorus and silicon. We get rid of everything else, all the interfaces, dielectrics, everything that causes problems in other architectures. It's simple conceptually, but obviously it's challenging to make. It's a pretty, Clean, physical, scalable system. "
"The challenge is how to put the atoms in place and you know it's there. It took us ten years to figure out the chemical process that lets the phosphorus atoms enter the silicon matrix and make it protected. (One of them) The technology we used is the scanning tunneling microscope (STM), a lithography tool." "
After placing the silicon plate in vacuum, the team first heated the substrate to 1100°C, then gradually cool to around 350°C to form a flat two-dimensional silicon surface.The silicon is then covered with hydrogen atoms and can be removed selectively individually using the STM tip. Before the whole thing is covered with another layer of silicon, the phosphorus atoms are placed in the newly formed gap in the hydrogen atom layer.
SQC quantum devices modeled at atomic scale.
"That means we can only make one device at a time," Simmons admitted, "but I think it's like a Swiss watch - it can be very precise and needs to be made by hand. My point is that to make a scalable system, you need that precision. If the accuracy is not enough, it's hard to build a quantum state because you don't know what you have. So our point is: Yes, it's slower, but you know what you can get."
Once the device is made, the algorithm chosen by the research team will have "historical significance."
"The simulation algorithm is the dream of Richard Feynman since the 1950s," Simmons explained. "If you want to understand how nature works, you have to build it on that length scale. At the sub-nanometer accuracy, can we simulate single and double bonds of carbon molecules? In fact, we found ourselves using 25 phosphorus atoms, rather than using a single atom to simulate carbon atoms."
The team found that they were able to control electrons to flow along the link.
"So, you have individual and local control and extended control capabilities," Simmons said. "We have shown that it is possible to implement a 10-point link with just six electrodes. Therefore, there are much fewer electrodes than the actual number of points. This is very useful for scaling. Because fundamentally, in quantum computers, you always want to build fewer gates compared to active components, otherwise it will be poorly scalable."
The new device not only complies with the SSH theory, but Simmons believes that quantum computers will soon start to simulate problems beyond the current optimal theory. "It opens a door for something we never imagined before, which is both frightening and exciting," she said.
This device has similar disadvantages as other quantum computers—especially the need for huge cooling systems to keep the operating temperature close to absolute zero, which requires a lot of energy and cost.
Out of trade secrets, Simmons is tight-lipped about the project SQC is working on after the preliminary demonstration. But she still said: We want to apply it to as many different things as possible and see what we can find. ”
Nature The SQC team behind the paper.
"The fact that we can get electrons coherently across the entire link tells us that this is a very quantum-coherent system," she says. "It leads us to believe that its physical system is very stable. It is a proof of the purity of the system, and it leads to many different paths. Making larger physical systems is definitely one of them. Observing spin states rather than charge states is another matter."
Simmons describes this work as a "journey" that demonstrates the interdisciplinary nature of quantum physicists, chemists, engineers and software engineers all involved. "It's an exciting area for young people," she said. "This is a case where basic scientific research projects evolve into practical tools."
reference link:
http://sqc.com.au/2022/06/23/silicon-quantum-computing-announces-worlds-first-quantum-integrated-circuit/
https://cosmosmagazine.com/technology/quantum-computer-coherent-silicon/
