Physicists take big step in race to quantum computing
Team develops simulator with 256 qubits, largest of its kind ever created


Date:
July 9, 2021
Source:
Harvard University
Summary:
A team of physicists has developed a special type of quantum
computer known as a programmable quantum simulator capable of
operating with 256 quantum bits, or 'qubits.'


FULL STORY ==========================================================================
A team of physicists from the Harvard-MIT Center for Ultracold Atoms
and other universities has 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 toward building large-scale quantum machines
that could be used to shed light on a host of complex quantum processes
and eventually help bring about real-world breakthroughs in material
science, communication technologies, finance, and many other fields,
overcoming research hurdles that are beyond the capabilities of even
the fastest supercomputers today. Qubits are the fundamental building
blocks on which 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 to
thus far," said Mikhail Lukin, the George Vasmer Leverett Professor
of Physics, co- director of the Harvard Quantum Initiative, and one
of the senior authors of the study published today in the journal
Nature. "We are entering a completely new part of the quantum world."
According to Sepehr Ebadi, a physics student in the Graduate School of
Arts and Sciences and the study's lead author, it is the combination
of system's unprecedented size and programmability that puts it at the
cutting edge of the race for a quantum computer, which harnesses the
mysterious properties of matter at extremely small scales to greatly
advance processing power. Under the right circumstances, the increase
in qubits means the system can store and process exponentially more
information than the classical bits on which standard computers run.

"The number of quantum states that are possible with only 256 qubits
exceeds the number of atoms in the solar system," Ebadi said, explaining
the system's vast size.

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



========================================================================== These experiments provide powerful insights on the quantum physics
underlying material properties and can help show scientists how to design
new materials with exotic properties.

The project uses a significantly upgraded version of a platform the
researchers developed in 2017, which was capable of reaching a size
of 51 qubits. That older system allowed the 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 the 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 the
atoms in defect-free patterns and create programmable shapes like square, honeycomb, or triangular lattices to engineer different interactions
between the qubits.

"The workhorse of 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 tweezer beams," said Ebadi. "These devices
are essentially the same as what is used inside a computer projector to
display images on a screen, but we have adapted them to be a critical
component of our quantum simulator." The initial loading of the atoms
into the optical tweezers is random, and the researchers must move the
atoms around to arrange them into their target geometries. The researchers
use a second set of moving optical tweezers to drag the atoms to their
desired locations, eliminating the initial randomness.

Lasers give the researchers complete control over the positioning of
the 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 along with
Massachusetts Institute of Technology Professor Vladan Vuleti?, and
scientists from Stanford, the University of California Berkeley, the
University of Innsbruck in Austria, the Austrian Academy of Sciences,
and QuEra Computing Inc. in Boston.

"Our work is part of a really intense, high-visibility global race to
build bigger and better quantum computers," said Tout Wang, a research associate in physics at Harvard and one of the paper's authors. "The
overall effort [beyond our own] has top academic research institutions
involved and major private- sector investment from Google, IBM, Amazon,
and many others." The 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
matter to solving challenging real-world problems that can be naturally
encoded on the qubits.

"This work enables a vast number of new scientific
directions," Ebadi said. "We are nowhere near
the limits of what can be done with these systems." ========================================================================== Story Source: Materials provided by Harvard_University. Original written
by Juan Siliezar.

Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. 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, Mikhail D. Lukin. Quantum phases of matter
on a 256-atom programmable quantum simulator. Nature, 2021; 595
(7866): 227 DOI: 10.1038/s41586-021-03582-4 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/07/210709104157.htm

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