By Marlene Cimons, National Science Foundation
Experimental physicist Markus Greiner always is searching for new and interesting states of matter. “In the long run, these states of matter might lead to new materials with fantastic properties you can’t even imagine yet,” he says.
Greiner, associate physics professor at Harvard University and the recent winner of a prestigious $500,000 “no strings attached” MacArthur Fellowship--popularly known as a “genius” grant--wants to better understand the spatial organization of ultra cold atoms with the goal of learning more about condensed matter physics and quantum mechanics.
“It’s pretty cool stuff,” he says, no pun intended. “But it is far from the everyday world, and hard to grasp for the public.”
Ultimately, the research could lead to new materials for more effective superconductors, as well as new magnetic substances that could speed up computer development. “There seems to be a big world of quantum matter that hasn’t been explored yet,” Greiner says. “So far, we are missing the tools, so we are creating artificial forms of quantum matter to start to get more insights.”
The National Science Foundation-funded scientist uses an instrument that traps thousands of ultra-cold atoms in ordered two-dimensional arrays, or lattices, prompting the atoms to act like electrons in a solid-state crystal, and making it easier to observe quantum phenomena, such as superconductivity.
He has created a quantum gas microscope that allows direct visualization of each individual atom within the two-dimensional optical lattice. He and his research team then can simulate how solid-state crystals transition between insulating and superconducting states, as well as study quantum magnetism.
The atoms must become very, very cold to become a quantum gas. The researchers cool them to a temperature of -273 degrees Celsius, which “is extremely close to absolute zero temperature, the coldest you can ever get, much colder even than outer space,” Greiner says.
“We use laser beams to slow the atoms down tremendously,” he says. “At room temperature, they fly at about the speed of sound. By slowing them down, we cool them down. As the atoms reach temperatures close to absolute zero, you might think that everything comes to a standstill, but instead quantum mechanics takes over. It turns out that each particle is a little wave. When we slow it down, the wave gets larger and larger. Ultimately, they form what is called a ‘Bose Einstein’ condensate, first described by Satyendra Nath Bose and Albert Einstein, where all the atoms lose their individual identity and collectively form a big matter wave at an extremely cold temperature.”
If you load this big wave into a lattice, it creates a state “where each atom is everywhere at the same time,” he says. “That is the magic of quantum mechanics. We have these little atoms that move in this artificial crystal we created, like an egg carton where balls can hop from one side to another. But our atoms aren’t doing exactly that; they go into a state in which each atom is in all of these wells at the same time. It’s very counter-intuitive.”
In fact, “it’s pretty amazing if you try to wrap your mind around it,” he adds.
The research is a starting point to develop new and innovative states of matter, and observe the particles interacting with each other in different ways, he says. “We have already done a few things,” he says. “The Bose Einstein condensate in the lattice is a superfluid which can flow without resistance--a certain quantum state related to superconductivity--and it will keep on flowing forever.”
With this material, “you can transition from one state to another and create new states of matter,” he adds. “You can go from a superfluid to an insulator, from something with no resistance to something with no flow, and you can even create new magnetic states. In that case, each atom behaves like a little compass needle, but each needle points in different directions at the same time. This is quantum magnetism.”