Northwestern University researchers develop new tool to analyze large quantum superconducting circuits


September 14, 2021 – The next generation of computing and information processing resides in the fascinating world of quantum mechanics. Quantum computers are expected to be able to solve large-scale and extremely complex problems that are beyond the capacity of today’s most powerful supercomputers.

New research tools are needed to advance the field and fully develop quantum computers. Today, researchers at Northwestern University have developed and tested a theoretical tool to analyze large superconducting circuits. These circuits use superconducting quantum bits, or qubits, the smallest units of a quantum computer, to store information.

Circuit size is important because protection against harmful noise tends to come at the cost of increased circuit complexity. Currently, there are few tools that address the modeling of large circuits, which makes the Northwestern method an important contribution to the research community.

“Our framework draws on methods originally developed for studying electrons in crystals and allows us to obtain quantitative predictions for circuits that were previously difficult or impossible to access,” said Daniel Weiss, correspondent and first author of the article. He is a fourth year student in the research group of Jens Koch, an expert in superconducting qubits.

Koch, associate professor of physics and astronomy at Weinberg College of Arts and Sciences, is a member of the Superconducting Quantum Materials and Systems Center (SQMS) and the Co-design Center for Quantum Advantage (C2AQ). The two national centers were established last year by the US Department of Energy (DOE). SQMS focuses on the construction and deployment of a state-of-the-art quantum computer based on superconducting technologies. VS2Quality assurance builds the fundamental tools needed to create scalable, distributed, and fault-tolerant quantum computing systems.

“We are delighted to contribute to the missions pursued by these two DOE centers and to add to Northwestern’s visibility in the field of quantum information science,” said Koch.

In their study, Northwestern researchers illustrate the use of their theoretical tool by extracting from a protected circuit quantitative information impossible to obtain with conventional techniques.

The details were published on September 13 in the open access journal Physical Review Research.

The researchers specifically studied the protected qubits. These qubits are shielded from damaging noise by design and could result in coherence times (how long quantum information is retained) that are much longer than current state-of-the-art qubits.

These superconducting circuits are necessarily large, and the Northwestern tool is a way to quantify the behavior of these circuits. There are existing tools that can analyze large superconducting circuits, but each only works well when certain conditions are met. The Northwestern method is complementary and works well when these other tools can give suboptimal results.

The research was funded by the Army Research Office (contract n ° W911NF-17-C-0024).

The title of the article is “Variational tight binding method for the simulation of large superconducting circuits”.

Source: Megan Fellman, Northwestern University

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