Sketch of the optical cavity showing the BoseEinstein condensate in its centre. Credit: Keler et al.
A time crystal is an exotic and unique phase of matter that was first predicted by Frank Wilczek, an American physicist in 2012. Time crystals can be considered as temporal analogs to more traditional space crystals. Both are based upon repeating patterns and are therefore time crystals.
Time crystals don't form repetitive patterns in three-dimensional (3D), space like space crystals. Instead, they are characterised by changes over time that follow a specific pattern. These exotic phases of matter have been realized by some researchers, but they have not been possible to achieve until now in closed systems. The question arose as to whether time crystals can also be realized in open systems in the presence dissipation or decoherence.
The University of Hamburg's Institute of Laser Physics recently discovered a time crystal within an open quantum system. The paper published in Physical Review Letters could have important implications in the study of exotic phase of matter in quantum systems.
Hans Keler, one the researchers involved in the study, stated that the primary goal of his research was to examine dynamical phases known for their ability to change over time in an ordered manner. My Ph.D. studies were conducted by my co-workers and I. We studied the phase transition between a homogenous BEC and a self-ordered, super-radiant phase. Also, we looked at how the system reacts to a qunch from one steady state.
Keler and his collaborators discovered that no physical state is inherently stable. Therefore, they decided to continue their research on dynamical phases of matter. These are basically transitions in which materials alter their properties over time.
Researchers' latest study had the main goal of realizing a dissipative-time crystal in a laboratory environment. They used a quantum manybody system that was strongly coupled to an optical cavity in the narrow band to accomplish this.
Sketch of the optical cavity showing the BoseEinstein condensate in its centre. Credit: Keler et al.
Keler explained that it was essential for our experiments to have the light field inside of the resonator as well as the density of many-body systems evolve on the same footing. This is determined by the cavity band width (and frequency corresponding with a single photonic recoil respectively). This is a unique situation in our atom cavity system, and it opens up the possibility of studying dynamic phases.
Real physical systems cannot be isolated completely from their environment, so they are vulnerable to dissipation, i.e. loss or waste energy. It is therefore difficult, if not impossible, to create quantum systems that can be closed for any length of time. Keler and his team were inspired to try to realize a time crystal within an open quantum system.
Keler stated that the time crystals found in different groups had to be isolated from the environment because dissipation can have the unfavorable effect of melting them. The unique feature of the time crystal in our atom cavity setup is its positive role as a preventive mechanism for dissipation. It helps stabilize the system's dynamics. Our most significant achievement is therefore the demonstration of time crystalline order within an open system.
This team of researchers has recently demonstrated that a discrete-time crystal can exist within an open and driven atom-cavity. Keler and his coworkers are currently trying to create a continuous time crystal with the same atom cavity system that was used in their previous work.
This continuous dissipative-time crystal is different from the discrete dissipative crystal that they have recently discovered. The former oscillates even without a time-periodic driving force. The oscillation results in the spontaneous breaking of a continuous time-translationsymmetry by the new crystal they are studying.
Keler said, "As we suggested for the scenario outlined by our recent paper," that our atom-cavity will switch to a condition of matter characterized periodic oscillations at an intrinsic frequency. "The relative phase for oscillations occurring in such a crystal can take any value between 0 to 2 pi. This is quite different from discrete crystals where the relative phase can only either be 0 or pi. A continuous time crystal is similar to a solid crystal because they both have continuous symmetry.
Continue reading Searching for discrete times crystals in classical multi-body systems
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