Quantum computers take a step forward thanks to spin centers | UCR News

Quantum computers, which use the laws of quantum mechanics, can solve urgent problems in a wide range of fields, from medicine to machine learning, that are too complex for classical computers. Quantum simulators are devices made of interacting quantum units that can be programmed to simulate complex models of the physical world. Scientists can then gain information about these models, and by extension, the real world, by changing the interactions in a controlled way and measuring the resulting behavior of the quantum simulators.

In a paper published in Physical Review B, selected by the journal as an editors’ proposal, a research team led by the University of California, Riverside, proposed a chain of quantum magnetic objects, called spin centers, that, in the presence of an external magnetic field, can quantum-simulate diverse magnetic phases of matter, as well as transitions between those phases.

“We are designing new devices that house spin centers that can be used to simulate and explore interesting physical phenomena that cannot be fully explored using classical computers,” said Shan-Wen Tsai, a professor of physics and astronomy who led the research team. “Spin centers in solid-state materials are localized quantum objects with enormous untapped potential for designing new quantum simulators.”

According to Troy Losey, Tsai’s graduate student and the paper’s lead author, advances in these devices could enable the study of more efficient ways to store and transmit information, as well as develop methods needed to create quantum computers that operate at room temperature.

“We have many ideas on how to improve spin-center quantum simulators beyond this initially proposed device,” he said. “Applying these new ideas and considering more complex spin-center arrangements could help create quantum simulators that are easy to build and operate while still being able to simulate new and significant physics.”

Below, Tsai and Losey answer some questions about the research:

Q: What is a quantum simulator?

Tsai: It’s a device that uses the unusual behaviors of quantum mechanics to simulate interesting physics that are too difficult for a regular computer to compute. Unlike quantum computers, which operate with qubits and universal gate operations, quantum simulators are designed individually to simulate/solve specific problems. By trading the universal programmability of quantum computers for the richness of different quantum interactions and geometrical arrangements, quantum simulators can be easier to implement and provide new applications for quantum devices, which is important because quantum computers are not yet widely usable.

A spin center is an atom-sized magnetic object that can be placed in a crystal. It can store quantum information, communicate with other spin centers, and be controlled by lasers.

Q: What are the uses of this work?

Losey: We can build the proposed quantum simulator to simulate exotic magnetic phases of matter and phase transitions between them. These phase transitions are very interesting because during these transitions the behaviors of very different systems become identical, which means that there are fundamental physical phenomena that connect these different systems.

The techniques used to build this device could also be used in spin-center quantum computers, which are a leading candidate for the development of room-temperature quantum computers, whereas most quantum computers require extremely low temperatures to operate. Furthermore, our device assumes that the spin centers are arranged in a straight line, but it is possible to arrange the spin centers in up to 3-dimensional arrays. This could enable the study of spin-based information devices that are more efficient than the methods currently used by computers.

Because quantum simulators are easier to build and operate than quantum computers, we can now use quantum simulators to solve certain problems that ordinary computers cannot solve while we wait for quantum computers to become more sophisticated. However, this does not mean that quantum simulators can be built without challenges, because we are only now good enough at manipulating spin centers, growing pure crystals, and working at low temperatures to build the quantum simulator we propose.