Physicists Develop Quantum Magnet

Harvard physicists at the Greiner Lab recently devised a “quantum magnet” that could aid with the development of high-temperature superconductors and quantum computers and may thereby expand the possibilities for future material science engineering.

“The idea is then we provide some feedback—by studying the matter from a fundamental microscopic perspective—to the people who actually do real material science,” Physics Research Assistant Waseem S. Bakr said. “We help them choose which materials might be suitable candidates for things that might have applications in technology.”

The bigger objective, said Post-Doctoral Fellow in Physics Jonathan Simon, is to “understand real materials that are too complicated to simulate on real computers.”

The quantum magnet is governed by quantum mechanics rather than classical mechanics, according to Bakr, which enables particles to exist in superpositions—meaning they can exist in multiple states simultaneously. Bakr and Simon emphasized the application of the quantum magnet in high-temperature superconductors, which allow the transfer of energy without dissipation.

“The magnet’s ability to exist in multiple states at a time makes it invaluable to constructing the high temperature superconductors,” Simon said. “The classical picture of this has been well-developed and understood over the last 100 years but, recently, we’ve been reaching a limit where you need to see non-classical correlations and entanglements—the concept of existing in multiple states at one time—between the electrons to understand the behaviors of the materials.”

Although quantum phase transitions have been observed before in 2001, this magnet spurred the first observation of a quantum phase transition in a magnetic system with cold atoms, according to Bakr. While traditional phase transitions occur when temperature is altered, quantum phase transitions result when other physical parameters of a system are changed.

“A difficulty we encountered was reaching a limit where thermal fluctuations aren’t a problem,” Simon said. “Thermal fluctuations can drive phase transitions and they can, more importantly for us, destroy the initial magnet.”

Although Simon said there was a lot of controversy over whether temperatures this cold would be accessible, the researchers were able to reach temperatures that approximated 100 trillionths of a degree Kelvin.

“In the end, we want to make new materials, and it turns out that ultra-cold atoms can be very good simulators of the same physics that happens in the real material,” Bakr said, adding that the frigid temperatures allow scientists to more closely control the parameters of the system.

The development of the magnet should also aid the larger efforts of the physics community to develop a quantum computer, which can be much faster than a classical computer at certain types of computations.

Markus Greiner, senior author of the research paper and Associate Professor of Physics, is out of town and could not be reached for comment.