In this series, researchers answer three questions about their latest results in the fields of quantum, AI, and data science. Editor’s note: Responses may be edited for length or clarity.
Summary
Researchers with Oak Ridge National Laboratory and Duke University have developed a scalable quantum error mitigation (QEM) protocol for noisy-intermediate-scale quantum (NISQ) hardware. NISQ systems are the current state of the art but can be plagued by environmental interference and quantum decoherence. Scientists are extending the quantum advantage of these early systems with a variety of QEM methods. In Quantum Science and Technology, the team describes their QEM hardware technique, which resulted in decreased noise and improved algorithmic resilience in superconducting circuits.
Citation
Leyton-Ortega, V., Majumder, S., Pooser, R.C. (2022) “Quantum error mitigation by hidden inverses protocol in superconducting quantum devices.” Quantum Science and Technology Volume: 8 Number: 1 DOI: 10.1088/2058-9565/aca92d
Q&A with Vicente Leyton-Ortega
(1) What was the problem you set out to solve?
Quantum computers are vulnerable to disturbances that can result in mistakes in their calculations. The main disturbances are called coherent noise and incoherent noise. Coherent noise is caused by changes in the system that runs the calculation, affecting how the quantum state evolves. Incoherent noise comes from interactions between the parts of the quantum computer and a dissipative environment. We are working to find ways to prevent mistakes caused by coherent noise without making the mitigation more complicated.
(2) What was the solution, and how did you reach it?
We have a unique approach to tackling errors in quantum computation. We view quantum gates as a blend of an ideal gate and its imperfections. To mitigate these imperfections, we reverse the pulse structure that represents the quantum gate. This means that if we need to apply the same gate twice, we can invert one of the gates and neutralize any imperfection by matching them with the imperfections of the inverse. This new method reduces the impact of noise and enhances the accuracy of quantum computations. By inverting the pulse structure that represents the quantum gate, we effectively cancel out most of the errors that would have been present in the original gate.
(3) How do your results impact the field going forward?
This breakthrough in the development of quantum computers brings us closer to reliable and sturdy systems that can be used in various applications, ranging from cryptography to optimization.
We discovered a significant enhancement in the variational quantum eigensolver algorithm through the application of the hidden inverse. In our experiment, we calculated the ground state energy of the H2 molecule as the test problem and observed improved results in the learning path. The reduction of coherent errors positively impacts the optimization process in variational quantum algorithms. This innovative protocol, the hidden inverse, also has the potential to make a big difference in the characterization of other types of noise in quantum devices. By minimizing the effects of coherent noise, we can help advance the development of robust and reliable quantum systems.