Wilczek's idea has been a subject of debate for years. While some researchers considered time crystals impossible, others sought ways to create them under special conditions. Now, a remarkable time crystal has been successfully developed at Tsinghua University in China, supported by TU Wien in Austria. The team utilized laser light and unique Rydberg atoms, which have diameters hundreds of times larger than typical atoms. The findings were recently published in "Nature Physics."
Spontaneous Symmetry Breaking
The ticking of a clock exemplifies a periodic movement, but it requires someone to start it. In contrast, a time crystal should spontaneously generate periodicity without any initial physical difference between moments in time.
"The tick frequency is predetermined by the physical properties of the system, but the times at which the tick occurs are completely random; this is known as spontaneous symmetry breaking," explains Prof Thomas Pohl from the Institute of Theoretical Physics at TU Wien.
Prof. Pohl led the theoretical research that resulted in the discovery of a time crystal at Tsinghua University. In the experiment, laser light was directed into a glass container filled with rubidium gas, and the light's intensity at the container's other end was measured.
"This is actually a static experiment in which no specific rhythm is imposed on the system," says Thomas Pohl. "The interactions between light and atoms are always the same, the laser beam has a constant intensity. But surprisingly, it turned out that the intensity that arrives at the other end of the glass cell begins to oscillate in highly regular patterns."
Giant Atoms
The experiment's success depended on preparing the atoms in a specific manner. Electrons orbit an atom's nucleus along different paths based on their energy. When energy is added to an atom's outermost electron, it can orbit much farther from the nucleus, creating Rydberg atoms with giant electron shells.
"If the atoms in our glass container are prepared in such Rydberg states and their diameter becomes huge, then the forces between these atoms also become very large," explains Thomas Pohl. "And that in turn changes the way they
interact with the laser. If you choose laser light in such a way that it can excite two different Rydberg states in each atom at the same time, then a feedback loop is generated that causes spontaneous oscillations between the two atomic states. This in turn also leads to oscillating light absorption." The giant atoms naturally develop a regular rhythm, which translates into the oscillating light intensity observed at the container's end.
"We have created a new system here that provides a powerful platform for deepening our understanding of the time crystal phenomenon in a way that comes very close to Frank Wilczek's original idea," says Thomas Pohl. "Precise, self-sustained oscillations could be used for sensors, for example. Giant atoms with Rydberg states have already been successfully used for such techniques in other contexts."
Research Report:Dissipative time crystal in a strongly interacting Rydberg gas
Related Links
Vienna University of Technology
Understanding Time and Space
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