糖心视频

(糖心视频Org.com) -- Harvard physicists have expanded the possibilities for quantum engineering of novel materials such as high-temperature superconductors by coaxing ultracold atoms trapped in an optical lattice -- a light crystal -- to self-organize into a magnet, using only the minute disturbances resulting from quantum mechanics. The research, published in the journal Nature, is the first demonstration of such a 鈥渜uantum magnet鈥� in an optical lattice.

As modern technology depends more and more on materials with exotic quantum mechanical properties, researchers are coming up against a natural barrier.
鈥淭he problem is that what makes these materials useful often makes them extremely difficult to design,鈥漵aid senior author Markus Greiner, an associate professor in Harvard鈥檚 Department of 糖心视频ics. 鈥淭hey can become entangled, existing in multiple configurations at the same time. This hallmark of quantum mechanics is difficult for normal computers to represent, so we had to take another approach.鈥�

That approach is using a so-called 鈥渜uantum simulator鈥� 鈥� the properties of a quantum material are simulated with an artificial quantum system that can behave similarly, but that is easier to manipulate and observe.

The physicists found that when they applied a force to a crystal formed by ultracold atoms trapped in an optical lattice, a Mott insulator, the atoms behaved like a chain of little magnets that repelled one another, in the presence of an external magnetic field that sought to align them.

鈥淲hen the external magnetic field was strong, all of the magnets aligned to it, forming a paramagnet,鈥� said co-author Jonathan Simon, a postdoctoral fellow in physics. 鈥淲hen we reduced the magnetic field, the magnets spontaneously anti-aligned to their neighbors, producing an antiferromagnet.鈥�

While such self-organization is common in everyday materials, it typically depends on temperature to jostle the system into the new order, like shaking a Boggle game to help the dice settle, the researchers say. 鈥淏ut the temperature was so low that thermal fluctuations were absent,鈥� explained Simon. 鈥淥ur fluctuations arose from quantum mechanics.鈥�

When quantum mechanics takes over, things get bizarre. 鈥淨uantum fluctuations can make the magnets point in multiple directions simultaneously,鈥� Greiner said. 鈥淭his 鈥榪uantum weirdness鈥� gives rise to many of the fascinating properties of quantum magnets.鈥�

Greiner and his colleagues used a quantum gas microscope to observe individual magnets at temperatures of one billionth of a degree above absolute zero (-273 Celsius). They were able to watch as quantum fluctuations flipped the magnets around, turning a paramagnet into an antiferromagnet and back again.

鈥淥bserving quantum magnetism in a cold gas is a crucial first step toward quantum simulation of real magnetic materials,鈥� Greiner said. 鈥淭here remain many exciting questions to answer, and we have only just scratched the surface. By studying the bizarre and wonderful ways that quantum mechanics works, we open new perspectives not only for developing novel high-tech materials, but also for quantum information processing and computation.鈥�