Breakthrough in Particle Control Creates Special Half-Vortex Rotation
A breakthrough in the control of a type of particle known as the polariton has created a highly specialized form of rotation.
PQI faculty Andrew Daley and David Snoke and their colleages at Princeton University conducted a test in which they were able to arrange the particles into a 'ring geometry' form in a solid-state environment. The result was a half-vortex in a 'quantized rotation' form.
Andrew Daley, PhD and David Snoke, PhD
Polaritons are propagating states in certain solid-state systems that couple directly to light signals. This work, published in the March 2015 Issue of PNAS, gives a clear observation of quantized circulation of a polariton condensate in a ring; spontaneous quantized circulation is one of the key tests of true superfluidity. The quantized circulation seen here is a new type that is only possible in a spinor condensate in a ring geometry. Because polariton condensates can be made relatively easily in solid-state systems that can operate up to room temperature, the door is open to all kinds of superfluid effects of light in optical communications.
This experiment had previously been possible only with the use of ultra-cold atoms, a fraction of a degree above absolute zero, but new techniques enabled the researchers to perform the test at higher temperatures. This made for a simpler, more efficient system which could feed into research for new technologies.
Professor Andrew Daley was part of the research team and worked on the underlying model of the experiment, which was performed in Pittsburgh.
He said: "This type of controlled experiment is fundamental science but also has applications in quantum technology; much of our research revolves around controlling and understanding these quantum systems. This type of research led in the past to the understanding of building a transistor or a laser.
Top: Interference patterns with from left to right one more fringe on the bottom than on the top of the ring, an equal number of fringes on the top and bottom of the ring, and one more fringe on the top, respectively.
Bottom: Phase maps extracted from the interference patterns with from left to right counterclockwise circulation, no net circulation, and clockwise circulation, respectively.
"Fringes were seen across the entire image of the ring we created, showing that we were controlling the polaritons in a coherent way and that they were displaying collective behaviour, as opposed to behaving as individuals. We were then able to demonstrate unusual states where the particles rotated in the ring at rates that were quantized. The phenomena we observed, known as half-vortices, are peculiar to situations where two different kinds of particles rotate in a superfluid--that is, the particles also must flow with no resistance.
"In this experiment, the polaritons had a much longer lifetime than in previous experiments, which made this collective behavior possible. The ring made in our work can be created relatively easily in solid-state systems that can operate up to room temperature; this opens the door to all kinds of other superfluid light effects, which could have applications in optical communications."
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