Researchers in collaboration with Google might have used Google's quantum computer to create an entirely new phase of matter, a time crystal.
Time crystals have the ability to cycle between two states in an infinite loop without losing energy. This allows them to avoid one of the most fundamental laws of physics, the second law, which says that the disorder or entropy of an isolated system must always rise. These time crystals are so stable that they resist dissolution into randomness despite being in constant flux.
According to a July 28th research article published to the preprint database arXiv, scientists were able create the time crystal in approximately 100 seconds using qubits (quantum computing’s version of traditional computer bits) within the core of Google’s Sycamore quantum processor.
Related: 12 amazing quantum physics experiments
This strange new phase of matter is exciting for physicists. It also reveals a new world of physical behaviors.
Curt von Keyserlingk (a University of Birmingham physicist who wasn't involved in the study) said that "this was a huge surprise." "This is something that you would never have predicted if you asked someone 30 years, 20 years or even 10 decades ago."
Because they bypass the second law in thermodynamics, which is one of the most important laws in physics, time crystals are fascinating to physicists. It says that entropy, which is a rough analog for disorder in a system, always increases. You need to invest more energy in order to make things more organized.
This tendency to disorderly grow can explain many things. For example, it's much easier to mix ingredients than to separate them again. Or why headphones get tangled up in the pockets of your pants. It sets the arrow for time. The past universe is always more orderly than the present. For example, a reversed video will likely look odd to you because you are witnessing an incongruous reversal.
According to the second law of thermodynamics, all systems will eventually reach a state of greater disorder. In this state energy is distributed evenly throughout the system. (Image credit Universal History Archive/Universal Images Group via Getty Images.
This rule doesn't apply to time crystals. Instead of "thermalizing" slowly to reach thermal equilibrium so their energy or temperature is evenly distributed throughout the surrounding environment, time crystals get stuck between two energy states that are above that equilibrium state and cycle back and forth indefinitely between them.
Von Keyserlingk described this unusual behavior by describing a sealed container containing coins that has been shaken a million thousand times. The coins bounce off each other and ricochet, and then become more chaotic. Eventually, the shaking stops and the box is opened. Inside, the coins are in a random arrangement with half facing up and half facing downward. This random configuration, with half of the coins facing up and half facing down, can be expected regardless of how the coins were arranged in the box.
The "box" in Google's Sycamore allows us to view the qubits of the quantum processor just like our coins. The qubits can either be heads or tails like coins. They can also be a 1 or 0, one of the possible positions in a 2-state system, or a strange mix of probabilities called a superposition. Von Keyserlingk explains that time crystals are unique in that they cannot be shaken or moved from one state to the next. They can only flip the crystal from its original state to its second, and then back to its starting state.
Von Keyserlingk stated, "It just kind of flip-flops." It doesn't look random. It just gets stuck. It acts as if it recalls how it looked at first, and then it repeats the pattern over time.
A time crystal can be described as a pendulum which never stops swinging.
"Even though you physically isolate a pendulum completely from the universe so there's no friction or air resistance, it will eventually cease to exist." It's because of the second rule of thermodynamics." Achilleas Lazaridis, a University of Loughborough physicist, explained Live Science. He was one of the first to discover the possibility of the new phase and was also a member of Live Science's 2015 scientific team. "Energy begins out concentrated at the center of the pendulum's mass. But there are all of these internal degrees, like the way the atoms vibrate within the rod, that it will eventually transfer into.
It's impossible for large-scale objects to behave like time crystals without sounding absurd. This is because there are only two rules that allow time crystals to exist: the strange and surreal rules of quantum mechanics.
Quantum objects behave like both point particles and little waves simultaneously. The magnitude of the waves in any particular region of space represents the probability of finding a particle there. Randomness, such as random defects in crystal structures or programmed randomness between qubits' interaction strengths, can cause a particle’s probability wave to cancel out in any given region. The particle is rooted in place and unable to move, change state or thermalize its surroundings.
This localization process was used by the researchers as the foundation for their experiment. The scientists used 20 strips of superconducting aluminium for their qubits and programmed each one to one of two possible states. By blasting a microwave beam across the strips, the scientists were able drive their qubits into flipping states. The researchers repeated the experiment for thousands of times and stopped at various points to record their qubits' current states. They found that the qubits were only flipping between two configurations. The researchers had also made a time crystal to record the qubits' heat absorption.
The key clue was that the time crystal they saw was a phase. To be considered a phase, something must be stable against fluctuations. While solids won't melt if temperatures change, liquids won't evaporate or freeze as quickly as slight fluctuations. The same thing happens if the microwave beam used for flipping the qubits from one state to another was adjusted slightly to get within the 180 degree limit required to complete a flip. However, the qubits still flipped to the opposite state.
Lazarides stated that it is not true that you can't be exactly at 180 degrees to scramble them. "It [the Time Crystal] magically will always tip slightly in, even though you make slight mistakes."
The breaking of physical symmetries is another hallmark of transitioning from one phase to the next. This refers to the notion that the laws and physics of physics apply to all objects at any given point in time or space. Water molecules follow the same physical laws as other liquids at all points in space and direction. However, if water is cooled enough, it can transform into ice. Ice molecules will choose regular points along a crystal structure to arrange themselves. The spatial symmetry of water is suddenly broken when water molecules choose which points in space they want to occupy.
Time crystals can be made crystals in space in the same way that ice is transformed into a crystal by breaking spatial symmetry. The row of qubits will initially experience continuous symmetry between all moment in time, but this is before they transform into the time crystal phase. The periodic cycle of microwave beam cuts the constant conditions experienced in the qubits into discrete packets, making the beam's symmetry a discrete-time-translation symmetry. By flipping at twice the wavelength of the beam's wavelength, the qubits can break the laser's discrete time-translationsymmetry. This is the first time we have seen qubits do this.
This weirdness makes time crystals full of new physics. Sycamore's control over experimental setups may make it an ideal platform to further investigate. However, it is possible to improve upon this system. Google's quantum computer must be isolated from the environment in order to prevent qubits from going through a process called "decoherence". This eventually causes the quantum localization effects to break down and destroy the time crystal. Researchers are currently working to isolate the processor and reduce the effects of decoherence. However, it is unlikely that they will be able to eliminate the effect forever.
Google's experiment will likely continue to be the best way to study the time crystals in the future, despite this. Many other projects have made convincingly similar time crystals using diamonds, superfluids of helium-3, quasiparticles called magnetons, and BoseEinstein condensates. However, these crystals are too fast to allow for detailed analysis.
Although theoretical newness is a problem for crystal physicists, it can be a double-edged weapon. Physicists are currently struggling to find clear uses for the crystals, although von Keyserlingk suggested they could be used as precise sensors. The crystals could also be used to store more information or create quantum computers that are faster.
In another sense, however, time crystals could be the most important application of time. They enable scientists to explore the limits of quantum mechanics.
Lazarides stated that quantum mechanics allows one to design and study the natural world, as well as to look at the limitations of quantum mechanics. "If something isn't found in nature, it doesn't necessarily mean that it won't exist. We just created it."
Original publication on Live Science
