Author | Zhao Guangli
On the road to the ultimate dream, every seemingly unrelated technological fruit along the way is enhancing human understanding of quantum computing and helping scientists gain the ability to manipulate qubits and quantum systems. In 2003, physicists Jonathan Dowling and Gerard Milburn proposed the famous “Second Quantum Revolution”.
Nearly 20 years later, quantum superiority has become a reality, and quantum computing seems to usher in a stage of technological breakthroughs, becoming one of the hottest topics in science and engineering. All signs are suggesting that the turning point of the second quantum revolution is approaching.
Climbing “high precision”
Just yesterday (March 24), the quantum laboratory of Alibaba Damo Academy from China announced its newly developed new type of superconducting quantum chip, which achieved 99.72% control accuracy of two-bit gates on the chip, reaching this level. The world’s best level of bit-like.
The latest new quantum chip announced by Ali Dharma Academy
About 2 months ago, a team from the University of New South Wales in Australia achieved a 99.37% fidelity of silicon quantum computing double qubits;
A team from Delft University of Technology in the Netherlands achieved a two-bit gate with 99.65% fidelity by using the electron spin of silicon/silicon germanium alloy quantum dots;
The Japanese RIKEN team also used the quantum dot two-electron system to achieve 99.51% control accuracy of the two-qubit gate.
Despite using different quantum platforms, quantum scientists around the world seem to want to go further and further in the precision of qubit manipulation.
This is because manipulation accuracy is a core indicator for measuring the performance of quantum chips. If the precision of quantum manipulation is not high, errors will accumulate during calculation, and the ability to surpass classical calculation cannot be achieved.
The top performance that quantum computing can achieve in human history has proven its “quantum superiority”: In 2019, Google released the superconducting quantum chip “Plane Suzuki”, which shocked the world with 53 effective bits; in the following two years, from Pan Jianwei’s team from the University of Science and Technology of China has successively released “Nine Chapters” with 76 photons and “Zu Chongzhi No. 2” with 56 superconducting quanta, successfully achieving “quantum superiority” on two types of platforms.
No matter how advanced the bits are, the high-precision manipulation of qubits is always the cornerstone for realizing valuable quantum computing. Therefore, the latest breakthroughs from China, Australia, the Netherlands and Japan will be particularly noticeable.
Shi Yaoyun, head of the Quantum Laboratory of Bodhidharma, told the China Science News that the two issues of “higher precision” and “more bits” have their own unique challenges and are not completely independent. “For the latter to achieve large-scale quantum computing, high-precision multi-bit chips must also be used, and when the scale of the system becomes larger, it will become more difficult to maintain the same accuracy.”
Looking for “new bits”
In the search for higher-quality and easier-to-manipulate qubits, scientists often work tirelessly to improve performance by one-thousandth.
The latest breakthrough of DAMO Academy’s quantum laboratory is based on a new type of quantum bit, fluxonium. The previous two-bit gate control accuracy of this bit was 99.2%, which was recorded by a research team from the University of Maryland in the United States. Bodhidharma raised this indicator to 99.72%, which is close to the 99.85%-99.86% achieved by traditional bit transmon.
The latest new quantum chip announced by Ali Dharma Academy
As a new type of superconducting quantum, fluxonium belongs to the epigenetic force. In the past, the industry was more familiar with the relatively mature transmon, which is also the superconducting quantum used by international leading teams such as Google and IBM.
Compared with the charge-type transmon, the magnetic-flux-type fluxonium is more resistant to the interference caused by charge noise and dielectric loss, and the fluxonium is also closer to an ideal 2-level system. Therefore, if the new fluxonium bits are used, quantum computing can achieve higher control accuracy, which is crucial to advancing fault-tolerant quantum computing and even the practical application of quantum computing.
Therefore, for the theoretically better “high precision” possibility, superconducting quantum computing research groups from the Quantum Laboratory of Bodhidharma Institute, University of Maryland, Princeton University, University of Chicago, UC Berkeley, MIT/Lincoln Lab, etc. are all in the world. At the APS March Meeting 2022, one of the largest physics academic conferences, a total of dozens of reports on fluxonium were shared.
The DAMO Academy on the fluxonium platform has improved the absolute value of the previous highest accuracy by 0.52%, which is equivalent to a 65% reduction in noise, which has preliminarily proved the theoretical potential of fluxonium. Shi Yaoyun concluded: “fluxonium is no longer a demonstration principle in academia. The rough toy has become an industrial-grade weapon that can compete with mainstream platforms.”
The DAMO Academy’s exploration of quantum computing has also provided valuable lessons for scientists around the world.
In their latest paper, the Karlsruhe Institute of Technology research team in Germany summarized the success of superconducting quantum computing in industry in the first sentence, citing work from IBM, Rigetti, Alibaba and Google.
At the APS March Meeting 2022, the research team from the Massachusetts Institute of Technology also compared and analyzed the data and characteristics of the two-bit gate manipulation announced by the DAMO Academy team and the DAMO Academy Quantum Laboratory team.
APS2022 March Meeting site
It seems that fluxonium is becoming a new whirlwind from academia to industry. Will this new type of fluxonium qubit replace transmon and become the mainstream of the industry?
No one can tell. In the era of the second quantum revolution, the most indispensable thing seems to be uncertainty.
Shi Yaoyun told reporters that the realization of quantum computing is still in the stage of basic research and convolutional engineering, and there is no ability to achieve practical applications beyond the classics. “The reason why we say the roundabout is because the specific technical goals and paths of engineering are still being explored, and it is expected that there will be many turns.” He said.
After laying a certain technical foundation for “high precision”, the goal of “multi-bit” was also placed on the table of the quantum computing team of Dharma Academy.
“We are indeed starting multi-bit work.” Shi Yaoyun said: “The laboratory has been focusing on high precision for the past three years, but our next stage goal is ‘scalable high precision’.”
According to him, the number of bits that the DAMO Academy Quantum Laboratory will try is not to maximize this number, or to conduct a “bit number contest”, but to discover and overcome the main factors affecting accuracy in the scale-up process.
“So our work in the future will not have a lot of bits.” Shi Yaoyun said that other colleagues’ achievements in multi-bit have verified the reachability of known technologies in multi-bit integration, but what has not yet been solved is how to Achieving high accuracy on such a large system. “We hope to understand and solve the core problems that this goal will encounter with the smallest cost, that is, the smallest scale chip.”
Editor | Zhao Lu
Typesetting | Guo Gang