Scientists find a way to improve the performance of quantum computers

The method corrects a weakness that hinders the performance of next-generation computers by eliminating erroneous calculations while increasing the fidelity of results, a crucial step for machines to outperform as expected. Called "dynamic decoupling", it works on two quantum computers, proves easier and more reliable than other remedies and is accessible via the cloud, which is a first for dynamic decoupling.

This technique delivers staccato bursts of tiny focused energy. pulses to compensate for ambient disturbances that spoil sensitive calculations. The researchers said they were able to maintain a quantum state up to three times longer than 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 errors, quantum computing can in no way exceed conventional computing."

The results were published today in the journal Physical Review Letters . 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. IBM and Bay Area start-up Rigetti Computing provided cloud access to their quantum computers.

Quantum computers are fast but fragile

Quantum computers can potentially render current supercomputers obsolete and breakthroughs in medicine. , financial and defense capabilities. They exploit the speed and behavior of atoms, which work in a radically different way than silicon computer chips, to perform seemingly impossible calculations.

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

But qubits are as capricious as 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 have yet to obtain a "quantum advantage – the point where a quantum computer surpbades any conventional computer."

The problem is "noise," a catch-all descriptor for disturbances such as sound, temperature and vibrations, it can destabilize qubits, which creates a "decoherence", a disturbance that disrupts the duration of the quantum state, which reduces the time available to a quantum computer to obtain accurate results [19659005] "Noise and decoherence have a huge impact. Calculations, and a quantum computer with too much noise is useless, "explained Lidar. But if you can eliminate noise-related problems, you're starting to get to the point where quantum computers are becoming more useful than conventional computers. "[19659005] USC research covers several platforms of quantum computing

The USC is the only university in the world to have a quantum computer: its quantum annealer D-Wave of 1098 qubits specializes in this field.Lving optimization problems.It is part of the USC-Lockheed Martin Center for Quantum Computing, located at the Institute of Science and Technology. USC information. However, the latest research findings were obtained not on the D-Wave machine, but on versatile quantum computers on a smaller scale: the 16-bit QX5 from IBM and Rigetti's 19-bit template

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

"We tried a simple mechanism to reduce errors in machines to be 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, up to 200 pulses up to 600 nanoseconds. A billionth of a second, or a nanosecond, represents the time it takes for light to travel 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 the improvement in fidelity could be maintained and found that the pulse count still improved things for the Rigetti computer, while there was a limit of about 100 pulses for the IBM computer.

Overall, the results show that the DD method works better. According to Lidar, "to our knowledge," he added, "this is the first unequivocal demonstration of the successful mitigation of decoherence in qubit superconducting systems in cloud platforms … we hope the Lessons Learned Will Have Broad Applicability. "

The Challenge of the Race to Quantum Supremacy

The quest for the supremacy of quantum computing is a geopolitical priority for the world. Europe, China, Canada, Australia and the United States. An advantage acquired by acquiring the first computer rendering all other computers obsolete would be enormous and confer on the winner economic, military and public health benefits

Congress considers two new bills to establish the United States in as a leader in quantum computing. In September, the House of Representatives pbaded 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. The law on quantum computing research of Senator Kamala Harris, D-Calif., Orders the Ministry 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, Physical Review Letters (2018). DOI: 10.1103 / PhysRevLett.121.220502