Top publication! Alibaba sets world record for superconducting double quantum bit gate fidelity
In 1900, the famous physicist Kelvin said in a lecture, "The beauty and clarity of the kinetic theory, which asserts that heat and light are both modes of motion, is now eclipsed by two dark clouds."
These "two dark clouds" later gave rise to the theory of relativity and to quantum mechanics.
More than a century later, although physicists have not yet fully unlocked the secrets of the clouds, but mankind has initially learned to use them, quantum computing is an important area of exploration and application of quantum theory.
Quantum computing is completely different from classical computing. While conventional computers can understand binary instructions consisting of 0s or 1s, quantum bits can be both 0s and 1s, like "Schrödinger's cat" in a cardboard box.
Inside the dilution chiller of the quantum lab of Dharma Academy
Quantum computing has the potential to surpass traditional computing. For example, for a particular quantum problem that would take a supercomputer more than 10,000 years to solve, it may take only 200 seconds to get the answer using quantum computing.
On July 8, Alibaba Dharma Institute's research on a new quantum bit platform was published in the latest issue of Physical Review Letters, the top journal of physics in the world, and was selected as an "Editor's Choice".
The journal reviewed the results of the Dharma Institute, which can be considered a milestone in the field, as it achieves a high accuracy comparable to the mainstream transmon quantum bits in a single system with a new type of bit fluxonium.
Screenshot from the website of Physical Review Letters
In the exploration of quantum computing, Dharma Institute's Quantum Lab has chosen a new type of quantum bit, fluxonium, which is very different from the transmon bits used by most of the industry in terms of bit construction. fluxonium offers the advantage of higher manipulation accuracy and is more complex in the actual chip preparation.
Dharma Institute's new quantum bit fluxonium design layout
The bit constructions of fluxonium and transmon are different.
1) fluxonium uses the magnetic flux of a toroidal circuit as the quantum bit, and represents the 1 and 0 states of the quantum bit by the antisymmetric and symmetric superposition states in the clockwise and counterclockwise directions of the toroidal current in it, respectively.
2) transmon is used whether to excite the electromagnetic oscillation in the circuit as the expression of the 1 and 0 states of the quantum bit.
3) In terms of bit construction, fluxonium is more resistant to interference from external charge noise than transmon and is closer to an ideal 2-energy system. At the practical level, however, the high manipulation accuracy of fluxonium is more difficult to achieve than that of transmon. For example, a transmon bit requires only 1~2 Josephson junctions (a key circuit element for preparing quantum bits), while a fluxonium bit requires nearly 100 or more Josephson junctions.
The published results of the Dharma Institute have significantly improved the accuracy of two-bit gate manipulation to 99.72%, which is the highest level of similar bits in the world; and implemented other basic operations required for fault-tolerant quantum computing, such as reset, read/write, and single-bit gate, in a single system with robustness and high accuracy. These results show that the theoretical advantages of fluxonium can be translated into industrial practice, and are a concentrated demonstration of the results of the quantum lab of Dharmakaya on various topics such as theory, design, simulation, materials, preparation and control.
Dharma Institute two-bit (fluxonium) quantum chip
The achievement of this research relies on breakthroughs and innovations in multiple topics in theory, design, simulation, materials, preparation and control. Recently, the Dharma Institute shared eight academic presentations at the 2022APS Annual Meeting, a global physics event, announcing multiple results in these areas.
Materials: The Dharma Institute has invented a new method to fabricate quantum devices using an epitaxial system of titanium aluminum nitride (TAN) material, which can achieve a dramatic increase in dynamic inductance despite extremely low microwave losses. This material is expected to be the core component of the next generation of fluxoinum chips at the Dharma Institute.
Preparation: On another chip preparation topic, the superconducting quantum bits based on titanium nitride prepared in the Quantum Lab of Dharmakaya Institute can reproducibly reach 300 microseconds in the most critical performance index of coherence time, which is a world class level.
Design: A core issue in the automation of quantum chip design is to enhance the speed of simulation and computation. In this topic, the surface integral equation-based superconducting quantum chip electromagnetic simulation tool developed by Dharma Institute has achieved two orders of magnitude acceleration in the calculation of circuit parameters and interface losses compared to the commonly used finite element method, which greatly accelerates the design optimization of quantum chips.
Control: In another effort to significantly improve the design capability of large-scale quantum chips, the Dharma Institute has integrated both chip optimization and quantum manipulation into a gradient optimization framework to efficiently and jointly optimize bit design solutions and bit manipulation solutions in a larger parameter space.
Compilation: Dharmakaya has also validated its own optimization scheme for the overall computational performance of superconducting quantum chips on fluxonium, including a single-bit gate general optimization compilation scheme for superconducting architectures, and an on-the-fly optimal compilation scheme for another native manipulation SQiSW gate on superconducting chips. The optimization scheme can significantly improve the overall performance index of the quantum chip.
Shi Yao-cheng, head of the Quantum Lab at Dharmakaya, said, "In the future, we are expected to do the same complex computation with fewer bits, or with the same number of bits, to do the computation that no one else can do." In the future, Dharma Institute Quantum Lab will deepen its efforts to explore the core technology of fault-tolerant quantum computing with fluxonium as a platform for scalable high precision and a differentiated innovation path.
About Alibaba Dharmakaya Quantum Lab.
