LSU Physicists Build the First Quantum Material That Sorts Light's Quantum States at Room Temperature

Physicists at Louisiana State University have built a material that can tell different quantum states of light apart and route them along separate paths while keeping their quantum character intact — and it does so at room temperature, without the bulky refrigeration that most quantum hardware demands.

The device, reported in Nature, is what the team calls a quantum statistical plasmonic metacrystal: a gold film deposited on a glass chip and thinner than a human hair, into which researchers carved hundreds of microscopic slits using focused ion beams. Each slit functions as an artificial atom, or meta-atom, and together they form a crystal with no natural counterpart. The arrangement of those engineered atoms, rather than the chemistry of gold, determines how the material treats incoming light.

"Our crystal essentially acts as a statistical filter on quantum states," said Riley B. Dawkins, a recent LSU Ph.D. graduate now an NRC postdoctoral research associate at NIST. Different quantum states of light — distinguished by their photon statistics rather than by color or polarization — are directed along different pathways through the metacrystal, each preserving its characteristics on the way through. The researchers describe the result as robust transport of quantum information at room temperature, and say it is the first time that has been achieved.

Temperature is the constraint the work is aimed at. Most quantum systems hold their fragile states only near absolute zero, and the dilution refrigerators that get them there dominate the size, cost and complexity of a quantum machine. A component that sorts and moves quantum states on a chip at ambient temperature sidesteps that overhead entirely — and plasmonic structures, which confine light to metal surfaces at scales smaller than its own wavelength, are one of the few routes to doing quantum optics in a space that small.

The research was led by Omar S. Magaña-Loaiza, an associate professor of physics at LSU, whose Quantum Photonics Group has spent years on the statistical properties of light. Co-authors include Chenglong You, a former LSU postdoctoral researcher now a professor at the University of Electronic Science and Technology of China, and Jannatul Ferdous, a graduate student in the group.

The team points to quantum computing without refrigeration, secure quantum communication networks and ultrasensitive sensors as targets. A less obvious one comes next in the lab: solar cells. Light arriving from the sun carries its own photon statistics, and a material that sorts light by those statistics could, in principle, help a cell make better use of what falls on it. The group has said enhancing solar efficiency is the next phase of the research.