Harvard-MIT quantum computing breakthrough – “We are entering a whole new part of the quantum world”

The team is developing a simulator with 256 qubits, the largest of its kind ever created.

A team of physicists from the Harvard-MIT Center for Ultracold Atoms and other universities have developed a special type of quantum computer known as a programmable quantum simulator capable of operating with 256 quantum bits, or “qubits.”

The system marks a major step towards building large-scale quantum machines that could be used to shed light on a multitude of complex quantum processes and possibly help achieve real-world breakthroughs in materials science, technology and technology. communication, finance and many other fields, overcoming research hurdles that are beyond the capabilities of today’s fastest supercomputers. Qubits are the fundamental building blocks on which quantum computers operate and the source of their enormous processing power.

“This moves the field into a new area where no one has ever been before,” said Mikhail Lukin, George Vasmer Leverett physics professor, co-director of the Harvard Quantum Initiative and one of the lead authors of the study. published on July 7, 2021 in the journal Nature. “We are entering a whole new part of the quantum world. “

According to Sepehr Ebadi, a physics student at the Graduate School of Arts and Sciences and lead author of the study, it’s the combination of the system’s unprecedented size and programmability that puts it at the forefront of the race for a quantum computer, which harnesses the mysterious properties of matter at extremely small scales to dramatically advance processing power. Under the right circumstances, increasing qubits means the system can store and process more information exponentially than the conventional bits that standard computers run on.

“The number of quantum states possible with just 256 qubits exceeds the number of atoms in the solar system,” Ebadi said, explaining the large size of the system.

Already, the simulator has allowed researchers to observe several exotic quantum states of matter that had never been achieved experimentally before, and to perform a quantum phase transition study so precise that it serves as a classic example of the functioning of magnetism at the quantum level.

These experiments provide powerful information about the quantum physics underlying the properties of materials and can help show scientists how to design new materials with exotic properties.

The project uses a significantly improved version of a platform developed by researchers in 2017, capable of reaching a size of 51 qubits. This ancient system allowed researchers to capture ultra-cold rubidium atoms and arrange them in a specific order using a one-dimensional array of individually focused laser beams called optical tweezers.

This new system allows atoms to be assembled in two-dimensional arrays of optical tweezers. This increases the achievable system size from 51 to 256 qubits. Using the tweezers, researchers can arrange atoms in flawless patterns and create programmable shapes such as square, honeycomb, or triangular arrays to design different interactions between qubits.

“The workhorse of this new platform is a device called a spatial light modulator, which is used to shape an optical wavefront to produce hundreds of individually focused tweezer optical beams,” Ebadi said. “These devices are essentially the same devices used inside a computer projector to display images on a screen, but we have adapted them to become an essential component of our quantum simulator.”

The initial loading of atoms in the optical tweezers is random, and researchers must move the atoms to arrange them in their target geometries. Researchers use a second set of movable optical tweezers to drag atoms to desired locations, eliminating the initial randomness. Lasers give researchers full control over the positioning of atomic qubits and their coherent quantum manipulation.

Other lead authors on the study include Harvard professors Subir Sachdev and Markus Greiner, who worked on the project with Professor Vladan Vuletić of the Massachusetts Institute of Technology, and scientists at Stanford, University of California at Berkeley. , University of Innsbruck in Austria, Academy of Sciences and QuEra Computing Inc. in Boston.

“Our work is part of a very intense, high-visibility global race to build bigger and better quantum computers,” said Tout Wang, associate physics researcher at Harvard and one of the authors of the article. “The overall effort [beyond our own] has the best academic research institutions involved and major private sector investments from Google, IBM, Amazon and many more.

Researchers are currently working to improve the system by improving laser control over the qubits and making the system more programmable. They are also actively exploring how the system can be used for new applications, ranging from exploring exotic forms of quantum matter to solving difficult real-world problems that can be naturally coded on qubits.

“This work allows a lot of new scientific directions,” Ebadi said. “We are far from the limits of what can be done with these systems. “

Reference: “Quantum phases of matter on a programmable quantum simulator with 256 atoms” by Sepehr Ebadi, Tout T. Wang, Harry Levine, Alexander Keesling, Giulia Semeghini, Ahmed Omran, Dolev Bluvstein, Rhine Samajdar, Hannes Pichler, Wen Wei Ho , Soonwon Choi, Subir Sachdev, Markus Greiner, Vladan Vuletić and Mikhail D. Lukin, July 7, 2021, Nature.
DOI: 10.1038 / s41586-021-03582-4

This work was supported by the Center for Ultracold Atoms, the National Science Foundation, the Vannevar Bush Faculty Fellowship, the US Department of Energy, the Office of Naval Research, the Army Research Office MURI, and the DARPA ONISQ program.