How Frank Wilczek’s Mind of Physics Caught Time Crystals
The discovery of a Nobel Prize laureate and MIT physics professor
In 2010, Frank Wilczek was preparing for a class on physics symmetries, particularly crystalline symmetry. New ideas about the relationships between space and time arose in his mind when he thought about the organized arrangement of atoms that is repeating in crystals like diamond and quartz.
How do crystals behave throughout time, and what is that classified as, he pondered in his mind.
He introduced higher dimensional crystals, converting three-dimensional crystals into four-dimensional objects by including time as a physical dimension. In his imagination, a substance would move between states and return to its initial state at regular intervals of time rather than cycling back and forth.
Since the time crystal behaves differently as its system is translated across time, this object violates the law of time translation symmetry, which states that the laws of physics behave the same regardless of time.
A time crystal is a new phase of matter that would repeat in time infinitely without any energy input. This idea seemed wild but Frank Wilczek proposed this concept by publishing papers in 2012 on quantum time crystals. Patrick Bruno of the European Synchrotron Radiation Facility in Grenoble, France objected in 2013 to the creation of time crystals from physical systems.
One problem arises, Wilczek’s idea of a time crystal would function as a perpetual motion machine which violates the laws of thermodynamics. A 2014 proof ultimately demonstrated it to fail, just like all other perpetual motion machines.
In 2015, physicists from the University of California, Berkeley, and the University of Tokyo proved that no physical system in its lowest energy state is capable of producing a time crystal similar to the one hypothesized by Frank Wilczek, similar to the objection from Bruno. This 2015 paper claimed that since it is impossible to stop an oscillating system from losing energy, the oscillating state must eventually degrade and is therefore not in equilibrium.
The physicists also suggested that periodic time crystal behavior might be present in a system that has been driven out of equilibrium. This study demonstrates that to violate time translation symmetry, another symmetry must be violated with a periodic driving force.
During this time, a group of researchers at Princeton were studying Floquet systems which are periodically driven systems, and how many-body localized systems react when periodically driven like Floquet systems. They discovered that by applying specific laser stimulation to a confined chain of spins, they move between two different many-body localized states in an endless cycle without absorbing any net energy from the laser. Their discovery was called a pi spin-glass phase finding this new phase of matter without knowing it was a time crystal yet, and they released a preprint in 2015.
In June 2016, they published an updated version of their research with the connection between their discovery and time crystals.
While that was going on, a former graduate student of Wilczek’s formed a group and released a preprint theorizing the existence of Floquet time crystals using the Princeton researcher’s group discovery as an example.
These floquet time crystals behave similarly to the time crystals predicted by Frank Wilczek, with the exception that they only do so when being periodically driven by an outside energy source. Since this system is many-body localized, its spins cannot reach equilibrium. But rather than heating up, it continually oscillates back and forth between localized states.
A little after the Princeton group wrote about their theoretical finding of the first instance of floquet time crystals, the graduate student and their team released a paper in August 2016 highlighting symmetry, time, the breaking of time translation symmetry, and expanding the idea of a Floquet time crystal.
The race to create a time crystal has begun with the graduate student’s team collaborating with Christopher Monroe at the University of Maryland using ions trapped by electromagnetic fields and reporting turning the trapped ions into a “prethermal” time crystal in June 2021.
The problem is that because of the breakdown of the cyclical behavior, this time crystal steadily deteriorates and cannot last indefinitely.
The Princeton group decided to search elsewhere for their answers. In 2019, Google announced their Sycamore quantum computer had completed a task in 200 seconds that would take a regular computer 10,000 years to finish. The group reached out to a theorist at Google about collaborating on the time crystal project, and he and his colleagues agreed to work together.
To understand what this group did, we need a little bit of background on quantum computers and how they work. Quantum computers use quantum bits “qubits”, which can simultaneously store data as a 1 and 0. With two possible energy states, representing either an up or down spin, the team used 20 qubits made of superconducting aluminum for their time crystal.
The researchers set the spins up or down arbitrarily and randomized the qubits’ interaction strengths to closely interact and achieve many-body localization. They sent in pulsed coherent microwave light and the spins oscillated back and forth without the system absorbing or releasing any energy.
The system of spins was observed to alternate between two many-body localized states after running thousands of demonstrations.
The findings were published in November 2021 by scientists from Stanford University, Google Quantum AI, the Max Planck Institute for Physics of Complex Systems, and Oxford University on how they created a time crystal using Google’s Sycamore quantum computing hardware.
Among all these findings, a team at the Delft University of Technology in the Netherlands reported that they built a Floquet time crystal. They did not use a quantum processor, rather the nuclear spins of carbon atoms in a diamond making their system smaller than the one in Google’s quantum processor.
Being the first out-of-equilibrium phase, the Floquet time crystal opens up numerous opportunities for physicists all around the world, shifting our scientific emphasis from the world and what we can obtain from it to what we can produce with it.
References:
- Wolchover, Natalie. “Eternal Change for No Energy: A Time Crystal Finally Made Real.” Quanta Magazine, 17 Dec. 2021, https://www.quantamagazine.org/first-time-crystal-built-using-googles-quantum-computer-20210730/#newsletter.
- Wolchover, Natalie. “‘Time Crystals’ Could Upend Physicists’ Theory of Time.” Wired, Conde Nast, 30 Apr. 2013, https://www.wired.com/2013/04/time-crystals/.
- Ball, Philip. “In Search of Time Crystals.” Physics World, 24 July 2018, https://physicsworld.com/a/in-search-of-time-crystals/.
- Kubota, Taylor. “Stanford Physicists Help Create Time Crystals with Quantum Computers.” Stanford News, 30 Nov. 2021, https://news.stanford.edu/2021/11/30/time-crystal-quantum-computer/.
- “Time Crystals: A New Phase of Matter — and a Breakthrough for Quantum Computing?” YouTube, DW News, 19 Aug. 2021, https://www.youtube.com/watch?v=EfSbC2Y0WPo.
- “BREAKING: New Phase of Matter.” YouTube, Physics Girl, 15 June 2022, https://www.youtube.com/watch?v=ieDIpgso4no.
