Crystalline solids such as diamond have a hallmark property: their structure is periodic in space. For much of the past decade, physicists have wondered whether a similarly robust, repeating structure might also exist in time. By analogy with spatial crystals, this structure is known as a time crystal, and whereas diamonds may be forever, time crystals are both forever and forever changing.
Researchers have proposed several physical systems that could host time crystals, including platforms like nitrogen-vacancy (NV) centres and trapped ions. Most recently, a collaboration between researchers at QuTech, TU Delft and UC Berkeley demonstrated long-lived period-doubling oscillations in carbon-13 NV centres across a variety of initial conditions. However, each of these previous platforms lacked the full slate of capabilities to necessary to realize (and verify) a genuine time crystal.
Now, researchers at Google Quantum AI and Stanford University in the US have constructed a time crystal on Google’s Sycamore quantum processor, demonstrating that these exotic objects constitute their own distinct phase of matter. To do so, they ran a series of “experiments” on Sycamore, treating the computer as a laboratory to test whether their proposed time crystal met certain requirements. The result is the first to experimentally verify that a phase of matter can exist outside of thermal equilibrium. It also shows that even in today’s world of noisy intermediate scale quantum (NISQ) computing, quantum processors already have important implications for our understanding of physics.
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