Google has created a unique state of matter inside its quantum computer that could, in theory, flip between two configurations without expending energy.
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In collaboration with physicists from Stanford, Princeton, and several other Universities, researchers from Google have used the tech giant's quantum computer to create a rare state of matter called a “time crystal.”
The research, described in a paper published on the repository ArVix, details the production of the time crystal, which not only demonstrates the capacity of the quantum computer to solve real-world problems but also delivers a state of matter that could be important in quantum computers in the future.
The development follows the revelation from a separate team of researchers that they had created a time crystal sealed with a diamond.
Time crystals represent a state of matter that physics has strived to create for many years. Its realization has significant implications as it represents matter that spontaneously breaks so-called time-translation symmetry (TTS) — the concept that the laws of physics are unchanged — invariant — under such a transformation, and possibly even the second law of thermodynamics.
What Are Time Crystals?
An aspect of condensed matter physics, a time crystal is a quantum system of particles with a unique and important quality. In their lowest energy state, the particles that comprise a time crystal are in a constant and repetitive motion.
The phase of matter now called a time crystal was first proposed in 2015 by a group of physicists from Princeton and Loughborough University in the United Kingdom. The name was coined by a separate team from Station Q and the University of California shortly afterward.
The time crystal system can’t lose energy, because it’s already in its ground state — the state of lowest possible energy. That means that technically the particles making up a time crystal have motion without energy.
The articles in a time crystal move in a regularly repeating pattern, a state of constant change, without consuming energy. Physicists say that this might actually allow time crystals to at least seem to defy the second law of thermodynamics. The law says the disorder, or entropy, of a closed system, can only increase.
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This is the law of physics that precludes perpetual motion machines, devices that can continue operations without the need for additional energy input. The reason this is possible for a time crystal is that it is a system existing in the quantum realm, in which energy is not depleted by elements like friction.
By breaking TTS time crystals also challenge the idea that a stable remains the same as time progresses. Think of a state of matter like water in liquid or solid form. In thermal equilibrium, these states are marked by atoms settled into a state in which the temperature determines the lowest energetic state. The properties of these states don’t change unless something like a rise in temperature changes them.
A time crystal manages to be both stable and constantly changing. This makes it the first out-of-equilibrium phase of matter we’ve discovered, possessing both order and stability while being in a changing state.
How to Make a Time Crystal
The race to create a time crystal has been intense. Many teams have attempted to demonstrate the pages of matter, but their states have, thus far, lacked one or another of the properties that define a time crystal proper.
Despite the lack of total success in this endeavor, researchers have suggested that a quantum computer, like that belonging to Google, could be the ideal place to generate such a state of matter.
Finally doing this with Google’s Sycamore, a quantum processor comprised of 54 qubits — the basic unit of quantum computing just as bits are the basic unit of traditional computing — is an important practical demonstration of its computing power.
Google’s time crystal may meet the definition of such a system closer than any other. The team used 20 qubits to represent a data chain of random particle spins — a type of magnetic angular momentum found on the quantum scale.
Using interference between the particles to effectively “freeze” them in place, the researchers saw that the qubits simultaneously reversed their spin in unison and then return back to their original configuration.
The qubits repeated this configuration switching, representing what the team says is a true time-crystal.
As for what this means for quantum computing, the ironic thing about such systems is that it has long been proposed that quantum computers could be the only way to model a quantum system that is comprised of many particles. This work appears to be the first demonstration of that ability.
Time crystals could also be of practical use for quantum computers increasing reliability and accuracy. Because of their delicate stability, time crystals could also be used as an accurate measurement tool used to probe electrical and magnetic external fields.
References and Further Reading
Google Quantum AI and collaborators, [2021], “Observation of Time-Crystalline Eigenstate Order on a Quantum Processor.” https://arxiv.org/pdf/2107.13571.pdf
Randall. J., Bradley. C. E., van der Gronden. F. V., et al, [2021], “Observation of a many-body-localized discrete time crystal with a programmable spin-based quantum simulator. https://arxiv.org/pdf/2107.00736.pdf
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