# A breakthrough in error mitigation for quantum computers

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Researchers at the Advanced Quantum Testbed (AQT) at Lawrence Berkeley National Laboratory have demonstrated that an experimental method known as random compilation (CR) can dramatically reduce error rates in quantum algorithms and lead to computations more precise and stable quantum. More than just a theoretical concept for quantum computing, the groundbreaking experimental results of the multidisciplinary team are published in *Physical examination X*.

The experiments at AQT were performed on a four-qubit superconducting quantum processor. Researchers have shown that CR can suppress one of the most serious types of errors in quantum computers: coherent errors.

Akel Hashim, AQT researcher involved in the experimental breakthrough and a graduate student at the University of California, Berkeley, explained, â€œWe can perform quantum computations in this era of Intermediate-Scale Noisy Quantum Computing (NISQ), but these are very error prone from many different sources, and do not last very long due to the decoherence, ie loss of information, of our qubits. ”

Coherent errors have no analogue in classical calculations. These types of errors are systematic and result from imperfect control of qubits on a quantum processor, and can constructively or destructively interfere with a quantum algorithm. Because of this, it is extremely difficult to predict their final impact on the performance of an algorithm.

While in theory coherent errors can be corrected or avoided with perfect analog control, they tend to get worse as more qubits are added to a quantum processor due to the “crosstalk” between signals. intended to control neighboring qubits.

First conceptualized in 2016, the RC protocol does not attempt to correct or correct consistent errors. Instead, RC alleviates the problem by randomizing the direction in which coherent errors impact qubits, so that they behave as if it were some form of stochastic noise. RC achieves this by creating, measuring, and combining the results of many logically equivalent quantum circuits, thereby averaging the impact that coherent errors can have on a single quantum circuit.

â€œWe know that on average stochastic noise will consistently occur at the same average error rate, so we can reliably predict what the results will be from the average error rates. Stochastic noise will never have a worse impact on our system than the average error rate. something that is not true for consistent errors, the impact of which on algorithm performance may be worse than their average error rates suggest. ”

Hashim used the signal-to-noise ratio analogy in astronomy to compare the impact of coherent errors versus stochastic noise in quantum computing. The longer a telescope operates, the more the signal will grow relative to the noise, as the signal will build up coherently on itself, while the noise – being inconsistent and uncorrelated – will grow much slower.

Coherent errors in quantum algorithms can build up through constructive interference and often grow faster than stochastic noise. However, the experimental proof of RC has shown that consistent errors in quantum algorithms can be controlled to grow at a much slower rate.

The AQT team worked closely with the original creators of the protocol, Joseph Emerson and Joel Wallman, who co-founded Quantum Benchmark, Inc. (recently acquired by Keysight Technologies) to tackle the problem of analytics. comparative and error mitigation in quantum computing systems. .

â€œNot having to design the software ourselves to run the RC protocol ultimately saved us a lot of time and resources and allowed us to focus on the experimental work,â€ Hashim said.

By bringing together researchers and partners from the quantum information science community in the United States and around the world, AQT enables the exploration and development of quantum computing based on one of the leading technologies , superconducting circuits.

â€œRC is a universal protocol for gate-based quantum computing, which is independent of specific error models and hardware platforms,â€ Hashim described. â€œThere are many applications and classes of algorithms that can benefit from CR. Our collaborative research has demonstrated that RC strives to improve algorithms in the NISQ era, and we expect it to continue to be a useful protocol beyond NISQ. It is important to have this successful demonstration in our toolbox at AQT. We can now deploy it on other user projects on the test bench.

Adding logical qubits to the Sycamore quantum computer reduces the error rate

**More information:**

Akel Hashim et al, Random compilation for scalable quantum computing on a noisy superconducting quantum processor,

*Physical examination X*(2021). DOI: 10.1103 / PhysRevX.11.041039

Provided by Lawrence Berkeley National Laboratory

**Quote**: Crucial leap in error mitigation for quantum computers (2021, December 9) retrieved December 9, 2021 from https://phys.org/news/2021-12-crucial-error-mitigation-quantum.html

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