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Quantum computers: what to expect in the Qubits of future

August 27th, 2021

Quantum computers: what to expect in the Qubits of future

August 27th, 2021

A team of physicists from the Harvard-MIT Center for Supercold Atoms and other universities has developed a special type of quantum computer known as a programmable quantum simulator that can work with 256 quantum bits, or “qubits.”

This system is an important step towards building large-scale quantum machines that can be used to illuminate a set of complex quantum processes and ultimately lead to real advances in materials science, communication technologies, finance, and many more. Other fields help. Overcoming research barriers beyond the capabilities of today’s fastest supercomputers. Qubits are the basic blocks on which quantum computers run and are the source of their enormous processing power.

“It takes the field to a new field that no one has ever been in before,” says Mikhail Lukin, professor of physics at George Wassmer Livert, co-director of the Harvard Quantum Project and co-author of the study. Which is published today 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 the lead author of the study, it combines unprecedented system size and programming that puts it at the forefront of competition for a quantum computer. It uses the mysterious properties of the material on a very small scale to dramatically improve processing power. Under the right conditions, increasing the qubit means that the system can store and process more information than the classic bits that standard computers run on.

Using the strange capabilities of quantum mechanics, qubits are the foundation of technologies that are potentially changing the world, such as new powerful types of computers or highly accurate sensors.

Qubits (short for quantum bits) are often made of semiconductor materials similar to our everyday electronics. But an interdisciplinary team of chemists and physicists at Northwestern University and the University of Chicago has developed a new way to create custom qubits: the chemical synthesis of molecules that encode quantum information in their magnetic or “rotational” state.

What quantum computers can do for us? 

This new bottom-up approach could eventually lead to quantum systems that have tremendous flexibility and control, paving the way for next-generation quantum technology.

“Chemical synthesis allows atomic control over the structure of qubits,” says Dana Friedman, a professor of chemistry at the Weinberg Northwestern School of Arts and Sciences. “Molecular chemistry creates a new paradigm for quantum information science.” He co-led the research with his colleague David Oshalum of the Pritzker School of Molecular Engineering at the University of Chicago.

The results were published in the November issue of Science.

“This is proof of the concept of a powerful and scalable quantum technology,” says Oshalom, a Liu family professor of molecular engineering. “We can use molecular design techniques to create new systems at the atomic scale for quantum information science. Bringing these two communities together will increase the interest and potential to improve quantum computing and detection.”

Oshalom is also the director of Q-NEXT, the Ministry of Energy’s National Quantum Information Science Research Center, which was established in August and is led by Argonne National Laboratory. Friedman, along with two other Northwestern masters, is a member of the new center.

Qubits work by using a phenomenon called superposition. While the classic bits used in ordinary computers are 1 or 0 in size, the qubit can be 1 and 0 at the same time.

The team wanted to find a new bottom-up approach to developing molecules whose spin mode could be used as qubits and could easily interact with the outside world. To do this, they used metal chromium molecules to create a state of rotation that they could control with light and microwaves.

By stimulating molecules with precisely controlled laser pulses and measuring the light emitted, they can “read” the rotation of molecules after stacking, “reading” the need for use in quantum technology.

By changing several different atoms in these molecules through synthetic chemistry, they were also able to change their optical and magnetic properties and highlight the promise of custom molecular qubits.

“Over the past decades, addressable optical rotations in semiconductors have been very powerful for applications involving advanced quantum detection,” says Oshalum. “Transforming the physics of these systems into a molecular architecture opens up a powerful synthetic chemistry toolbox to activate new capabilities that we have just begun to discover.”

“Our results open up a whole new field of synthetic chemistry,” Friedman said. “We show that artificially controlled symmetry and connection create qubits that can be repaired in the same way as semiconductor defects. Our bottom-up approach is to operate both individual units and qubits.” The designer “makes it possible for applications to easily aim and create controllable quantum state matrices that enable scalable quantum systems.”

A potential application for these molecules could be quantum sensors designed to target specific molecules. Such sensors can detect specific cells in the body, detect when food is spoiled, or even detect hazardous chemicals.

This top-down approach can also help integrate quantum technology with existing classical technologies.

“Some of the challenges to quantum technology can be addressed with this different bottom-up approach,” said Sam Bayliss, an ATSchalom postdoctoral researcher and lead author of the paper. “The use of molecular systems in light-emitting diodes was a transformative change; something similar to molecular qubits might happen.”

Daniel Lorenza, a graduate student at Friedman Lab and the first author, sees tremendous potential for chemical innovation in space. “This specific chemical control of the environment around qubits provides a valuable feature for integrating addressable molecular qubits into a wide range of environments,” he said.

“The number of quantum states that are only possible with 256 qubits is greater than the number of atoms in the solar system,” Ebadi said of the system’s large size.

The simulator has now enabled researchers to observe several bizarre quantum states of matter that had not previously been experimentally performed, and conducted a quantum phase transition study so accurately that it served as a textbook of how it works. Magnetism worked at the quantum level.

These experiments provide valuable insights into the quantum physics that underlie the properties of materials and can help scientists design new materials with strange properties.

The project uses a significantly improved version of a platform developed by researchers in 2017, which can reach 51 qubits. That old system allowed researchers to take super-cold rubidium atoms and arrange them in a specific order using a single-dimensional set of separate focused lasers called optical tweezers.

This new system allows atoms to be collected in two-dimensional arrays of light tweezers. This increases the system size from 51 to 256 qubits. Using tweezers, researchers can arrange atoms into integrated patterns and create programmable shapes such as squares, honeycombs or triangular lattices to design different interactions between qubits.

“The working platform of this new platform is a device called a space light modulator, which is used to form an optical wave to produce hundreds of concentrated tweezers,” Ebadi said. “These devices are essentially the same devices used inside a computer projector to display images on the screen, but we have adapted them as one of the most important components of our quantum simulator.”

The initial charge of atoms in optical tweezers is random, and researchers must move the atoms to target them in geometry. Researchers use a second moving light tweezers to pull the atoms to their desired location, eliminating the initial accident. Lasers give researchers complete control over the position of atomic qubits and their coherent quantum manipulation.

What we aim to achieve in the field of quantum electronics.

Other co-authors of the study include Harvard professors Subir Sachdoff and Marcus Greiner, who worked on the project with Professor Vladan Volti, a professor at the Massachusetts Institute of Technology, and scientists at Stanford, the University of California at 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 and highly visible global competition to build bigger and better quantum computers,” said Tutt Wang, a Harvard physics researcher and co-author of the paper. “Overall effort [beyond us] has leading academic research institutes and significant private sector investment from Google, IBM, Amazon and many more.”

Researchers are currently working to improve the system by improving laser control over qubits and further system planning. They are also actively exploring how to use the system for new applications, from exploring the strange shapes of quantum matter to solving challenging real-world problems that can be naturally encoded in qubits.

“This makes possible a new set of scientific aspects,” Ebadi said. “We are by no means close to what can be done with these systems.”

This work is supported by the Super Cold Atoms Center, the National Science Foundation, the Vannevar Bush College Fellowship, the US Department of Energy, the Naval Research Bureau, the MURI Army Research Bureau, and the DARPA ONISQ program.

Article by:

Armin Vali

Adapted from: Science daily.

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