Scientists have succeeded for the first time in realizing a time crystal that spontaneously breaks continuous time translation symmetry. The researchers, from the Institute of Laser Physics at the University of Hamburg, reported their observation in a study published on June 9, 2022, in the journal Science.
The idea of a time crystal goes back to Nobel laureate Franck Wilczek, who first proposed the phenomenon. Similar to water spontaneously turning into ice around the freezing point, thereby breaking the translation symmetry of the system, the time translation symmetry in a dynamical many-body system spontaneously breaks when a time crystal is formed.
In recent years, scientists have already observed discrete or Floquet time crystals in periodically driven closed and open quantum systems. “In all previous experiments, however, the continuous-time translation symmetry is broken by a time-periodic drive,” says Dr. Hans Keßler from Prof. Andreas Hemmerich’s group at the Cluster of Excellence “CUI: Advanced Imaging of Matter.” “The challenge for us was to realize a system that spontaneously breaks the continuous time translation symmetry.”
Using a Bose-Einstein condensate inside an optical high-finesse cavity
In their experiment, the researchers used a Bose-Einstein condensate inside an optical high-finesse cavity. Using a time-independent pump, they observed a limit cycle phase which is characterized by emergent periodic oscillations of the intracavity photon number accompanied by the atomic density cycling through recurring patterns.
They discovered that the time phase of the oscillations takes random values between 0 and 2π, as expected for spontaneously broken continuous symmetry. By identifying the stability area in the relevant parameter space and showing the persistence of the limit cycle oscillations even in the presence of strong temporal perturbations, the experimenters demonstrated the robustness of the dynamic phase.
Reference: “Observation of a continuous time crystal” by Phatthamon Kongkhambut, Jim Skulte, Ludwig Mathey, Jayson G. Cosme, Andreas Hemmerich and Hans Keßler, 9 June 2022, Science.