NIST Researchers Help Design a Prototype Quantum Computer

Researchers have created a prototype quantum computer with a record number of qubits—the analog of bits in an ordinary computer—capable of performing logical operations. The feat promises to be an important step towards building a practical quantum computer.

The work, led by scientists at Harvard University, included researchers from the Massachusetts Institute of Technology in Cambridge and QuEra Computing Inc. in Boston, in collaboration with theorists at the National Institute of Standards and Technology (NIST) and the Joint Center for Quantum Information and Computer Science (QuICS), a research partnership between NIST and the University of Maryland,

For certain problems, quantum computing may offer an advantage over ordinary computing because qubits are not restricted to the specific “1”’sand “0”s” of ordinary bits, but can be in a superposition of the two, potentially storing and encoding much more information. However, qubits are notoriously fragile, their quantum states easily disturbed by interactions with their environment and prone to errors.

To minimize errors, the researchers used the principle of quantum entanglement, in which many physical qubits are linked together to form a “logical qubit” in which information is distributed among numerous qubits rather than stored in a single, potentially faulty one. In the team’s study, two closely spaced energy levels in single atoms of rubidium served as the physical qubits, which were moved around by laser light to associate with other qubits.

This entanglement strategy, known as a quantum error correction code, worked well in reducing errors. But it remained unclear how to best link groups of qubits in different ways.

That’s where theorists Michael Gullans of NIST and Dominik Hangleiter of QuICS came in. Experts in the theory of logical qubits and quantum algorithms, the researchers created the choreography that combined and reshuffled logical qubits in complex ways so that they formed quantum circuits that could tackle certain kinds of computations.

“You could say we designed a dance, a new dance, for the individual qubits so they were able to perform new types of computations,” Gullans noted.

The dance enabled 228 individual qubits to form 48 logical qubits, the largest number of logical qubits in a quantum circuit to date. ‘

“This will greatly accelerate the progress towards large-scale useful quantum computers and techniques,” said collaborator Dolev Bluvstein of Harvard.

The algorithm also provides a possible way to determine whether a particular operation performed on a quantum computer truly offers an advantage over an ordinary computer, Hangleiter said. Proving the so-called “quantum advantage” will be crucial to assessing progress.

The researchers described their work in an article posted December 6 online in Nature. A Harvard news story provides further details about the work.

Paper: Dolev Bluvstein, Simon J. Evered, Alexandra A. Geim, Sophie H. Li, Hengyun Zhou, Tom Manovitz, Sepehr Ebadi, Madelyn Cain, Marcin Kalinowski, Dominik Hangleiter, J. Pablo Bonilla Ataides, Nishad Maskara, Iris Cong, Xun Gao, Pedro Sales Rodriguez, Thomas Karolyshyn, Giulia Semeghini, Michael J. Gullans, Markus Greiner, Vladan Vuletić & Mikhail D. Lukin. Logical quantum processor based on reconfigurable atom arrays Nature, published online Dec. 6, 2023. DOI: https://doi.org/10.1038/s41586-023-06927-3.