Scientists find a way to improve the performance of quantum computers


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USC scientists have developed a theoretical method to improve the performance of quantum computers, an important step to evolve a technology that can solve some of the biggest challenges in society.

The method solves a weakness that hinders the performance of next-generation computers by eliminating erroneous calculations while increasing the fidelity of results, a crucial step before machines can outperform conventional computers as expected. Called "dynamic decoupling", it ran on two quantum computers, was easier and more reliable than other solutions and was accessible via the cloud, a first for dynamic decoupling.

This technique involves administering staccato bursts of tiny focused energy pulses to compensate for ambient disturbances that damage sensitive computations. The researchers indicated that they were able to maintain a quantum state up to three times longer than would be the case in an uncontrolled state.

"It's a step forward," said Daniel Lidar, professor of electrical engineering, chemistry and physics at USC and director of the USC Center for Quantum Information Science and Technology (CQIST). "Without removing mistakes, quantum computing can surpass classic computing."

The results were published today in the journal Letters of physical examination. Lidar is Viterbi Engineering Professor at USC and corresponding author of the study; He led a team of researchers at CQIST, a collaboration between the USC Viterbi School of Engineering and the USC Dornsife School of Letters, Arts and Sciences. Rigetti Computing, an IBM and Bay Area startup, provided cloud access to their quantum computers.

Quantum computers are fast but fragile

Quantum computers have the potential to render today's super computers obsolete and to propel advances in medicine, finance and defense. They exploit the speed and behavior of atoms, which operate in a radically different way than silicon computer chips, to perform seemingly impossible calculations.

Quantum computing has the potential to optimize new drug therapies, models for climate change and designs for new machines. They can accelerate the delivery of products, reduce the costs of manufactured products and improve transportation efficiency. They are powered by qubits, subatomic work tools and components of quantum computing.

But the qubits are as capricious as the high-performance race cars. They are fast and state of the art, but they are prone to errors and need stability to support calculations. When they do not work properly, they produce poor results, which limits their capabilities compared to traditional computers. Scientists all over the world still have to get a "quantum advantage – the point where a quantum computer surpasses the performance of a conventional computer in any task.

The problem is "noise," a catch-all descriptor for disturbances such as sound, temperature, and vibration. This can destabilize the qubits, which creates a "decoherence", a disturbance that disrupts the duration of the quantum state, which reduces the time that a quantum computer can perform to perform a task while getting some precise results.

"Noise and decoherence have a big impact and ruin calculations, and a quantum computer with too much noise is useless," said Lidar. "But if you can eliminate noise problems, you're starting to get to the point where quantum computers are becoming more useful than conventional computers."

USC Research Expands on Multiple Quantum Computing Platforms

USC is the only university in the world to have a quantum computer. its 1098 qubit quantum D-Wave rings are specialized in solving optimization problems. It is part of the USC-Lockheed Martin Center for Quantum Computing, located at the USC Institute of Information Sciences. However, the latest research findings were obtained not on the D-Wave machine, but on smaller-scale general-purpose quantum computers: IBM's 16-bit QX5 and Rigetti's 19-bit Throat.

To achieve dynamic decoupling (DD), the researchers bathed the superconducting qubits with meticulously focused minute pulses of minute electromagnetic energy. By manipulating the impulses, the scientists were able to wrap the qubits in a microenvironment, sequestered – or decoupled – from surrounding ambient noise, thus perpetuating a quantum state.

"We have tried a simple mechanism to reduce errors in machines that have proven effective," said Bibek Pokharel, PhD student in Electrical Engineering at USC Viterbi and first author of the study.

The time sequences of the experiments were extremely small, with 200 pulses of up to 600 nanoseconds. A billionth of a second, or a nanosecond, is the time it takes for light to walk one foot.

For IBM quantum computers, final fidelity increased threefold from 28.9% to 88.4%. According to the study, the improvement in the final fidelity of the Rigetti quantum computer was 17%, from 59.8 to 77.1. Scientists have tested how long loyalty improvement can be maintained and found that the pulse count still improved things for Rigetti's computer, while there was a limit of about 100 pulses for the IBM computer.

Overall, the results show that the DD method works better than other methods of quantum error correction that have been tried so far, Lidar said.

"To the best of our knowledge," the researchers wrote, "this equates to the first unequivocal demonstration of a successful mitigation of decoherence in cloud-based superconducting qubit platforms (…). the lessons learned will be widely applicable "

The challenges of the race for quantum supremacy

The quest for the supremacy of quantum computing is a geopolitical priority for Europe, China, Canada, Australia and the United States. The benefit of acquiring the first computer that makes all other computers obsolete would be huge and would confer economic, military and public health benefits to the winner.

Congress is considering two new bills to establish the United States as a leader in quantum computing. In September, the House of Representatives passed the National Quantum Initiative Act, which provides $ 1.3 billion over five years to stimulate research and development. He would create a national quantum coordination office at the White House to oversee research at the national level. Senator Kamala Harris' quantum computing research bill, D-Calif., Directs the Department of Defense to lead a quantum computing effort.

"Quantum computing is the next technological frontier that will change the world and we can not afford to fall behind," Harris said in his prepared remarks. "This could create jobs for the next generation, cure diseases and, most importantly, make our country stronger and safer … Without adequate research and coordination on quantum computing, we are likely to fall behind about our global competition in the race for cyberspace, which leaves us vulnerable to attacks from our opponents, "she said.

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More information:
Bibek Pokharel et al., Demonstration of fidelity enhancement using dynamic decoupling with superconducting Qubits, Letters of physical examination (2018). DOI: 10.1103 / PhysRevLett.121.220502

Journal reference:
Letters of physical examination

Provided by:
University of Southern California

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