TIME CRYSTAL ARRIVES

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 TIME CRYSTAL ARRIVES

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• Google's announcement: Researchers at Google in collaboration with physicists at Stanford, Princeton and other universities say that they have used Google’s quantum computer to demonstrate a genuine “time crystal.” (In addition, a separate research group claimed earlier this month to have created a time crystal in a diamond.)
• What is a Time Crystal: A novel phase of matter that physicists have strived to realize for many years, a time crystal is an object whose parts move in a regular, repeating cycle, sustaining this constant change without burning any energy. The consequence is you evade the second law of thermodynamics! That law says disorder always increases. (disorder = entropy)
• Out of equilibrium, new phase: Time crystals are also the first objects to spontaneously break “time-translation symmetry,” the usual rule that a stable object will remain the same throughout time. A time crystal is both stable and ever-changing, with special moments that come at periodic intervals in time. The time crystal is a new category of phases of matter, expanding the definition of what a phase is. All other known phases, like water or ice, are in thermal equilibrium: Their constituent atoms have settled into the state with the lowest energy permitted by the ambient temperature, and their properties don’t change with time. The time crystal is the first “out-of-equilibrium” phase: It has order and perfect stability despite being in an excited and evolving state.
• Quantum computing's first practical use: Google’s quantum computing team made headlines in 2019 when they performed the first-ever computation that ordinary computers weren’t thought to be able to do in a practical amount of time. Yet that task was contrived to show a speedup and was of no inherent interest. The new time crystal demo marks one of the first times a quantum computer has found gainful employment. Researchers seem to have fulfilled the original hope for quantum computers. 
• Richard Feynman: In his 1982 paper proposing the devices, the physicist Richard Feynman argued that they could be used to simulate the particles of any imaginable quantum system. A time crystal exemplifies that vision. It’s a quantum object that nature itself probably never creates, given its complex combination of delicate ingredients. Imaginations conjured the recipe, stirred by nature’s most baffling laws.
• First time: The Nobel Prize­winning physicist Frank Wilczek conceived the idea in 2012, while teaching a class about ordinary (spatial) crystals. “If you think about crystals in space, it’s very natural also to think about the classification of crystalline behavior in time,” he said. 

1. Consider a diamond, a crystalline phase of a clump of carbon atoms. The clump is governed by the same equations everywhere in space, yet it takes a form that has periodic spatial variations, with atoms positioned at lattice points. Physicists say that it “spontaneously breaks space-translation symmetry.” Only minimum-energy equilibrium states spontaneously break spatial symmetries in this way.
2. Wilczek envisioned a multi-part object in equilibrium, much like a diamond. But this object breaks time-translation symmetry: It undergoes periodic motion, returning to its initial configuration at regular intervals.
3. Something that’s as stable as this is unusual, and special things become useful.
4. Wilczek’s proposed time crystal was profoundly different from, say, a wall clock — an object that also undergoes periodic motion. Clock hands burn energy and stop when the battery runs out. A Wilczekian time crystal requires no input and continues indefinitely, since the system is in its ultra-stable equilibrium state.

• Google's quantum jump: In 2019, Google announced that its Sycamore quantum computer had completed a task in 200 seconds that would take a conventional computer 10,000 years. The Sycamore processor contains as its fundamental building blocks exactly the things we need to realize the Floquet time crystal. Google quickly agreed to collaborate on the time crystal project. 
• What these are: Quantum computers aren’t the next generation of supercomputers — they’re something else entirely. 

1. Quantum computers consist of “qubits” — essentially controllable quantum particles, each of which can maintain two possible states, labeled 0 and 1, at the same time. 
2. When qubits interact, they can collectively juggle an exponential number of simultaneous possibilities, enabling computing advantages.
3. Google’s qubits consist of superconducting aluminum strips. Each has two possible energy states, which can be programmed to represent spins pointing up or down. 
4. The main advantage of the machine over its competitors is its ability to tune the strengths of interactions between its qubits. This tunability is key to why the system could become a time crystal: The programmers could randomize the qubits’ interaction strengths, and this randomness created destructive interference between them that allowed the row of spins to achieve many-body localization. The qubits could lock into a set pattern of orientations rather than aligning.
5. The researchers gave the spins arbitrary initial configurations, such as: up, down, down, up, and so on. Pumping the system with microwaves flipped up-pointing spins to down and vice versa. By running tens of thousands of demos for each initial configuration and measuring the states of the qubits after different amounts of time in each run, the researchers could observe that the system of spins was flipping back and forth between two many-body localized states.

• Phase: The hallmark of a phase is extreme stability. Ice stays as ice even if the temperature fluctuates. Indeed, the researchers found that microwave pulses only had to flip spins somewhere in the ballpark of 180 degrees, but not exactly that much, for the spins to return to their exact initial orientation after two pulses, like little boats righting themselves. Furthermore, the spins never absorbed or dissipated net energy from the microwave laser, leaving the disorder of the system unchanged.
• One more: On July 5, 2021, a team based at the Delft University of Technology in the Netherlands reported that they built a Floquet time crystal not in a quantum processor, but out of the nuclear spins of carbon atoms in a diamond. The Delft system is smaller and more limited than the time crystal realized in Google’s quantum processor.

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