The dream of creating game-changing quantum computers—supermachines that encode information in single atoms rather than conventional bits—has been hampered by the formidable challenge known as quantum error correction.
In a paper recently published in Nature, researchers from Harvard University, the University of Maryland and other institutions demonstrated a new system capable of detecting and removing errors below a key performance threshold, potentially providing a workable solution to the problem.
“For the first time, we combined all essential elements for a scalable, error-corrected quantum computation in an integrated architecture,” said Mikhail Lukin, co-director of the Quantum Science and Engineering Initiative, Joshua and Beth Friedman University Professor, and senior author of the new paper. “These experiments—by several measures the most advanced that have been done on any quantum platform to date—create the scientific foundation for practical large-scale quantum computation.”
In their paper, the team demonstrated a “fault tolerant” system using 448 atomic quantum bits manipulated with an intricate sequence of techniques to detect and correct errors.
The key mechanisms include physical entanglement, logical entanglement, logical magic, and entropy removal. For example, the system employs the trick of “quantum teleportation”—transferring the quantum state of one particle to another elsewhere without physical contact.
Michael Gullans, an adjunct assistant professor of physics at the University of Maryland with an adjunct appointment in the University of Maryland Institute for Advanced Computer Studies (UMIACS), co-authored the study. He worked closely with Shayan Majidy, a postdoctoral fellow at Harvard, on the theoretical design of the quantum error correction and algorithms implemented in the paper.
“The paper is a first of its kind demonstration of an architecture for neutral atoms that realizes a scalable fault-tolerant quantum computer. We then explore the physical principles behind the operation of this device,” said Gullans, who is a physicist at the National Institute of Standards and Technology and a Fellow in the Joint Center for Quantum Information and Computer Science (QuICS).
Gullans says to think of a fault-tolerant quantum computer as a thermodynamic machine (like a refrigerator), where entropy is produced during the computation that is self-consistently removed from the system without destroying the fragile quantum correlations. The paper’s researchers studied this process of entropy removal, generation, and preservation of quantum correlations in several different scenarios.
Gullans is also a senior investigator in the NSF Quantum Leap Challenge Institute for Robust Quantum Simulation (RQS) where he co-leads the research challenge of quantum simulations facing the environment. RQS supported this project through a supplemental funding grant senior investigator Mikhail Lukin at Harvard to the institute.
“This work strongly connects to the mission of RQS to use quantum simulators to understand and control open quantum systems,” said Gullans. “We are using this neutral atom platform to understand the physical principles behind scalable quantum computing.”