The successful observation of a time crystal using Google’s quantum computing hardware has recently been reported. Time crystals, first proposed in 2012, are delicate quantum systems that have structures whose lowest-energy states are periodic in both time and space. The name comes from the analogy to a physical crystal, such as a diamond, which has atoms that are arranged periodically in space.
The notion of a crystal that is periodic in time may be somewhat unintuitive. How does a time crystal compare to, for example, a pendulum clock, whose pendulum returns to the same place in a periodic manner? The difference lies in the fact that as the clock’s pendulum mechanically swings, it loses energy, while a time crystal can “swing” between states without energy input or output. It should be noted that this means the time crystal’s entropy does not increase, and thus, despite its periodicity, a time crystal cannot be used to create a perpetual motion machine.
What scientists may be able to do with time crystals still remains to be seen, as time crystals are incredibly exotic states of matter that are not found in nature. However, being able to reliably implement these rare crystals is expected to lead to exciting avenues for study. Indeed, the demonstration of a time crystal is both a triumph for theoretical physics and another landmark for quantum computing. As quantum processors become more sophisticated in the future, more discoveries of new physics and chemistry may too be realized.
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