From The University of Chicago: “Using two different elements creates new possibilities in hybrid atomic quantum computers”

From The University of Chicago

Mar 29, 2022
Meredith Fore

Left: A hybrid array of cesium atoms (yellow) and rubidium atoms (blue). Right: The customizability of the researchers’ technique enables them to place the atoms anywhere, allowing them to create this image of Chicago landmarks Willis Tower and the Cloud Gate. The scale bar in both images is 10 micrometers. Image by Bernien Lab.

New technique allows researchers to measure a single atom without disturbing its neighbors.

Qubits, the building blocks of quantum computers, can be made from many different technologies. One way to make a qubit is to trap a single neutral atom in place using a focused laser-a technique that won the Nobel Prize in 2018.

But to make a quantum computer out of neutral atom qubits many individual atoms must be trapped in place by many laser beams. So far, these arrays have only been constructed from atoms of a single element, out of concern that making an array out of two elements would be prohibitively complex.

But for the first time, University of Chicago researchers have created a hybrid array of neutral atoms from two different elements, significantly broadening the system’s potential applications in quantum technology. The results were funded in part by the NSF Quantum Leap Challenge Institute Hybrid Quantum Architectures and Networks (HQAN), and published in Physical Review X.

“There have been many examples of quantum technology that have taken a hybrid approach,” said Hannes Bernien, lead researcher of the project and assistant professor in University of Chicago’s Pritzker School of Molecular Engineering. “But they have not been developed yet for these neutral atom platforms. We are very excited to see that our results have triggered a very positive response from the community, and that new protocols using our hybrid techniques are being developed.”

Double the potential

While man made qubits such as superconducting circuits require quality control to stay perfectly consistent, neutral atoms made from a single element all have exactly the same properties, making them ideal, consistent candidates for qubits.

But since every atom in the array has the same properties, it’s extremely difficult to measure a single atom without disturbing its neighbors—they’re all on the same frequency, so to speak.

“There have been quite a few milestone experiments over the last few years showing that atomic array platforms are extremely well suited for quantum simulation and also quantum computation,” Bernien said. “But measurements on these systems tend to be destructive, since all the atoms have the same resonances. This new hybrid approach can be really useful in this case.”

In a hybrid array made of atoms of two different elements any atom’s nearest neighbors can be atoms of the other element, with completely different frequencies. This makes it much easier for researchers to measure and manipulate a single atom without any interference from the atoms around it.

It also allows researchers to sidestep a standard complication of atomic arrays; it is very difficult to hold an atom in one place for very long.

“When you do these experiments with the single atoms, at some point, you lose the atoms,” Bernien said. “And then you always have to re-initialize your system by first making a new, cold cloud of atoms and waiting for individual ones to get trapped by the lasers again. But because of this hybrid design, we can do experiments with these species separately. We can be doing an experiment with atoms of one element, while we refresh the other atoms, and then switch so we always have qubits available.”

Making a bigger quantum computer

The hybrid array created by Bernien’s group contains 512 lasers: 256 loaded with cesium atoms and 256 with rubidium atoms. As quantum computers go, this is a lot of qubits: Google and IBM, whose quantum computers are made of superconducting circuits rather than trapped atoms, have only gotten up to about 130 qubits. Though Bernien’s device is not yet a quantum computer, quantum computers made from atomic arrays are much easier to scale up, which could lead to some important new insights.

“We actually don’t know what happens when you scale up a very coherent system that you can isolate very well from the environment,” Bernien said. “This trapped atom approach can be a wonderful tool to explore large-system quantum effects in unknown regimes.”

The hybrid nature of this array also opens the door to many applications that wouldn’t be possible with a single species of atom. Since the two species are independently controllable, the atoms of one element can be used as quantum memory while the other can be used to make quantum computations, taking on the respective roles of RAM and a CPU on a typical computer.

“Our work has already inspired theoreticians to think about new protocols for it, which is exactly what I hoped,” Bernien said. “I hope it will inspire people to think about how these tools can be used for measurements and state control. We have already seen really cool protocols that that we are very interested in implementing on these arrays.”

The first author on the paper was postdoctoral researcher Kevin Singh. Other authors were UChicago graduate students Shraddha Anand, Andrew Pocklington and Jordan Kemp.

See the full article here .

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The University of Chicago is an urban research university that has driven new ways of thinking since 1890. Our commitment to free and open inquiry draws inspired scholars to our global campuses, where ideas are born that challenge and change the world.

We empower individuals to challenge conventional thinking in pursuit of original ideas. Students in the College develop critical, analytic, and writing skills in our rigorous, interdisciplinary core curriculum. Through graduate programs, students test their ideas with University of Chicago scholars, and become the next generation of leaders in academia, industry, nonprofits, and government.

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In all we do, we are driven to dig deeper, push further, and ask bigger questions—and to leverage our knowledge to enrich all human life. Our diverse and creative students and alumni drive innovation, lead international conversations, and make masterpieces. Alumni and faculty, lecturers and postdocs go on to become Nobel laureates, CEOs, university presidents, attorneys general, literary giants, and astronauts. The University of Chicago is a private research university in Chicago, Illinois. Founded in 1890, its main campus is located in Chicago’s Hyde Park neighborhood. It enrolled 16,445 students in Fall 2019, including 6,286 undergraduates and 10,159 graduate students. The University of Chicago is ranked among the top universities in the world by major education publications, and it is among the most selective in the United States.

The university is composed of one undergraduate college and five graduate research divisions, which contain all of the university’s graduate programs and interdisciplinary committees. Chicago has eight professional schools: the Law School, the Booth School of Business, the Pritzker School of Medicine, the School of Social Service Administration, the Harris School of Public Policy, the Divinity School, the Graham School of Continuing Liberal and Professional Studies, and the Pritzker School of Molecular Engineering. The university has additional campuses and centers in London, Paris, Beijing, Delhi, and Hong Kong, as well as in downtown Chicago.

University of Chicago scholars have played a major role in the development of many academic disciplines, including economics, law, literary criticism, mathematics, religion, sociology, and the behavioralism school of political science, establishing the Chicago schools in various fields. Chicago’s Metallurgical Laboratory produced the world’s first man-made, self-sustaining nuclear reaction in Chicago Pile-1 beneath the viewing stands of the university’s Stagg Field. Advances in chemistry led to the “radiocarbon revolution” in the carbon-14 dating of ancient life and objects. The university research efforts include administration of DOE’s Fermi National Accelerator Laboratory and DOE’s Argonne National Laboratory, as well as the U Chicago Marine Biological Laboratory in Woods Hole, Massachusetts (MBL). The university is also home to the University of Chicago Press, the largest university press in the United States. The Barack Obama Presidential Center is expected to be housed at the university and will include both the Obama presidential library and offices of the Obama Foundation.

The University of Chicago’s students, faculty, and staff have included 100 Nobel laureates as of 2020, giving it the fourth-most affiliated Nobel laureates of any university in the world. The university’s faculty members and alumni also include 10 Fields Medalists, 4 Turing Award winners, 52 MacArthur Fellows, 26 Marshall Scholars, 27 Pulitzer Prize winners, 20 National Humanities Medalists, 29 living billionaire graduates, and have won eight Olympic medals.

The University of Chicago is enriched by the city we call home. In partnership with our neighbors, we invest in Chicago’s mid-South Side across such areas as health, education, economic growth, and the arts. Together with our medical center, we are the largest private employer on the South Side.

Research

According to the National Science Foundation, University of Chicago spent $423.9 million on research and development in 2018, ranking it 60th in the nation. It is classified among “R1: Doctoral Universities – Very high research activity” and is a founding member of the Association of American Universities and was a member of the Committee on Institutional Cooperation from 1946 through June 29, 2016, when the group’s name was changed to the Big Ten Academic Alliance. The University of Chicago is not a member of the rebranded consortium, but will continue to be a collaborator.

The university operates more than 140 research centers and institutes on campus. Among these are the Oriental Institute—a museum and research center for Near Eastern studies owned and operated by the university—and a number of National Resource Centers, including the Center for Middle Eastern Studies. Chicago also operates or is affiliated with several research institutions apart from the university proper. The university manages DOE’s Argonne National Laboratory, part of the United States Department of Energy’s national laboratory system, and co-manages DOE’s Fermi National Accelerator Laboratory, a nearby particle physics laboratory, as well as a stake in the Apache Point Observatory in Sunspot, New Mexico.
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SDSS Telescope at Apache Point Observatory, near Sunspot NM, USA, Altitude 2,788 meters (9,147 ft).

Apache Point Observatory, near Sunspot, New Mexico Altitude 2,788 meters (9,147 ft).
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Faculty and students at the adjacent Toyota Technological Institute at Chicago collaborate with the university. In 2013, the university formed an affiliation with the formerly independent Marine Biological Laboratory in Woods Hole, Mass. Although formally unrelated, the National Opinion Research Center is located on Chicago’s campus.