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MIT Team Slashes Errors in Two-Qubit Gates

By Becky Bracken posted 21 Jun 2021

Expanding on the existing tunable coupler technique, a team at the MIT Engineering Quantum Systems demonstrated a new approach to reducing gate errors in quantum systems to nearly 100 percent fidelity.

The team said the breakthrough is the key in creating the robust hardware necessary to power sophisticated quantum systems. The research was recently published in Physical Review X.

The new approach eliminates error-producing, undesirable interactions in two-qubit gates between the qubits themselves and the tunable coupler, which is used to turn qubits on and off to control them.

“We have now taken the tunable coupler concept further and demonstrated near 99.8 percent fidelity for the two major types of two-qubit gates, known as Controlled-Z gates and iSWAP gates,” MIT’s William D. Oliver, an associate professor of electrical engineering and computer science said. “Higher-fidelity gates increase the number of operations one can perform, and more operations translates to implementing more sophisticated algorithms at larger scales.”

The researchers explained they used the coupler’s higher energy levels to negate the error-causing, problematic interactions. Qubit errors can be easily addressed by building in redundancy, Oliver explained but that only works if the gates themselves are reliable.

“The most lenient thresholds today are around 99 percent,” Oliver said. “However, in practice, one seeks gate fidelities that are much higher than this threshold to live with reasonable levels of hardware redundancy.”

Other proposals circulating in the development of quantum hardware systems to drive down error rates include AWS’s idea to use concatated cat codes and IBM’s bug hunting code.

As teams all over the world work on the problem, each breakthrough is a step closer to the elusive “quantum supremacy goal.”

MIT thinks their solution which pairs efficient circuit compilation and improved algorithms can make a difference.

Taken together, the principles and demonstrations we present will help resolve major challenges facing quantum computing hardware for contemporary applications.

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