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Harvard-MIT Quantum Computing Breakthrough – “We are entering a whole new part of the quantum world”

Advanced Quantum Computer concept

Team develops 256 qubits simulator, 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 can be used to shed light on a range of complex quantum processes and ultimately help create real-world breakthroughs in materials science, communications technology, economics and many other areas. , overcome research barriers that lie beyond the capabilities of even the fastest supercomputers today. Qubits are the basic building blocks where quantum computers run and the source of their massive processing power.

“This moves the field into a new domain where no one has ever been so far,”

; said Mikhail Lukin, George Vasmer Leverett Professor of Physics, co-director of the Harvard Quantum Initiative, and one of the senior authors of the study. published July 7, 2021 in the journal Nature. “We are entering a whole new part of the quantum world.”

Dolev Bluvstein, Mikhail Lukin and Sepehr Ebadi

Dolev Bluvstein (from left), Mikhail Lukin and Sepehr Ebadi developed a special type of quantum computer known as a programmable quantum simulator. Ebadi customizes the device that allows them to create the programmable optical tweezers. Credit: Rose Lincoln / Harvard Staff Photographer

According to Sepehr Ebadi, a physics student at the Graduate School of Arts and Sciences and the study’s lead author, it is the combination of the system’s unprecedented size and programmability that puts it at the forefront of a quantum computer that exploits mysterious properties of material in extremely small scales to greatly promote processing power. Under the right circumstances, the increase in qubits means that the system can store and process exponentially more information than the classic bits that standard computers run on.

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

Already, the simulator has allowed scientists to observe several exotic quantum states of matter that had never before been realized experimentally, and to perform a quantum phase transition study so precisely that it serves as a textbook example of how magnetism works at the quantum level.

Funny Atom Video

By arranging them in sequential frames and taking pictures of single atoms, scientists can even make funny atomic videos. Credit: Greetings from the Lukin Group

These experiments provide strong insight into the quantum physics that underlies material properties, and can help researchers design new materials with exotic properties.

The project uses a markedly upgraded version of a platform that the researchers developed in 2017, which was able to reach a size of 51 qubits. The older system allowed scientists 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 makes it possible to assemble the atoms in two-dimensional arrays of optical tweezers. This increases the achievable system size from 51 to 256 qubits. Using tweezers, scientists can arrange the atoms in flawless patterns and create programmable shapes such as square, honeycomb, or triangular grids to construct different interactions between qubits.

Dolev Bluvstein

Dolev Bluvstein looks at 420 mm laser, which allows them to control and wind Rydberg atoms. Credit: Harvard University

“The workhorse for this new platform is a device called the spatial light modulator, which is used to shape an optical wavefront to produce hundreds of individually focused optical tweezers,” said Ebadi. “These devices are pretty much the same as those used inside a computer projector to display images on a screen, but we’ve adapted them to be a critical component of our quantum simulator.”

The initial load of the atoms in the optical tweezers is random, and scientists have to move the atoms around to arrange them in their target geometries. The scientists use a different set of moving optical tweezers to pull the atoms to their desired locations, eliminating the initial randomness. Lasers give scientists complete control over the location of atomic qubits and their coherent quantum manipulation.

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

“Our work is part of a truly intense, highly visible global race to build bigger and better quantum computers,” said Tout Wang, a physics research assistant at Harvard and one of the paper’s authors. “The overall effort [beyond our own] has top academic research institutions involved and large private investments from Google, IBM, Amazon and many others. ”

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

“This work enables a large number of new scientific directions,” said Ebadi. “We are not near the limits of what can be done with these systems.”

Reference: “Quantum phases of matter on a 256-atom programmable quantum simulator” 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, 7 July 2021, Nature.
DOI: 10.1038 / s41586-021-03582-4

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

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