Rice University theoretical physicist Andriy Nevidomskyy has a decidedly ambitious goal. With support from the Department of Energy (DOE), he’s searching for a way to design an experimental platform that could provide the first tangible evidence of particles called fractons.
“Fractons are unlike any other quantum particles we know of, in that they cannot move in isolation from one another,” Nevidomskyy said. “It came as an immense surprise when they were first theoretically proposed a decade ago because these particles cannot be described in the language of quantum field theory, which holds that all elementary particles move freely through space when left alone.”
Fractons have yet to be experimentally observed in a lab, and Nevidomskyy recently won a three-year grant from DOE’s Office of Basic Energy Sciences to identify experimental platforms that could be used to harbor them.
Fractons are emergent excitations that are believed to arise in certain strongly interacting theoretical models, and they take their name from the word “fractal,” alluding to their geometric arrangement in space. For example, certain theoretical models show quartets of fractons appearing simultaneously at the four corners of a Sierpinski tetrahedron, a nested fractal structure inscribed into a four-sided pyramid.
Fractons also have topological properties that are of intense interest to the quantum computing community. In most physical systems, quantum states are delicate and subject to collapse due to the slightest interference. In quantum computers, where information is stored in the quantum states of particles, information loss due to quantum decoherence is an enormous obstacle. Topological materials are a potential solution because they produce emergent quantum states that are protected from decoherence under certain conditions.
For example, it might be possible to use fractons for quantum information storage, but it would require technology capable of both creating and destroying quartets of fractons, as well as manipulating them to store information in a quantum superposition of states.
“Creating a quartet of fractons would cost potential energy, and if that happened spontaneously, it would spoil the quantum information storage,” Nevidomskyy said. “Fortunately, at sufficiently low temperatures, such a coordinated process would be very unlikely to happen on its own. Since an individual fracton cannot move in isolation from its three ‘partners,’ quantum information could be protected in such a low-temperature device.”
Finding a way to create and observe fractons in an experimental platform is the first step towards the goal of quantum information storage, and the ultimate goal of Nevidomskyy’s DOE-funded research.
“The project is about trying to come up with realistic platforms to realize these particles in an experiment,” Nevidomskyy said. “The principal challenge is overcoming the complexity of the inter-particle interactions that would need to be realized in an experiment to create fracton matter.
“I am thinking of creative ways of doing that, including, in particular, the quantum computation-inspired route: use a sequence of qubits and quantum gates — the so-called quantum circuit — to engineer a quantum state that has the desired properties of the fracton matter.
“It's not an easy task,” he said. “My proposals for such a realization would have to be experimentally tested. But if it works, it will be very exciting.”
Nevidomskyy is a professor in the Department of Physics and Astronomy and a member of both the Rice Quantum Initiative and the Rice Center for Quantum Materials.