Admittedly, the name Time Crystal may conjure up images of magical things, such as a magic crystal ball or some kind of time travel device. But time crystals are real, though they do feel a bit like magic in some ways.
The concept of time crystals, first proposed by Nobel laureate Frank Wilczek, is actually a unique arrangement of particles that can be in permanent and reciprocating motion in both time and space.
In a recent study, two Australian scientists observed discrete-time crystals (DTCs) on 57 superconducting qubits on a state-of-the-art quantum computer. This is the second study to successfully create a time crystal on a quantum computer after last year's Google team. The paper was recently published in Science Advances.
Time crystals
Time crystals are so valued because they are a new phase of matter, and they are not in equilibrium or steady state, but switch between various states.
Solid crystals, like rock salts and diamonds, are defined by the way their atoms are arranged and repeated in space. In contrast to these everyday "space crystals", the time crystal is a system of particles that repeats over time and space.
Moreover, their state is almost very close to the edge of challenging the laws of physics, as they are somehow "perpetually moving." A time crystal spontaneously and permanently switches back and forth between two different configurations. And the reason why it "almost" violates the laws of physics is because although it is generally assumed that the energy of motion will always dissipate in the process of increasing entropy (a measure of disorder in the system), since we cannot extract energy from the perpetual motion of the time crystal, there is actually no energy dissipation.
To better understand the strangeness here, we can draw an analogy to an everyday scene. When baking, we put flour and sugar in a bowl, and when we stir them together, the entropy increases and the substance becomes more disordered, so that it is no longer flour and sugar, but a mixture of both.
Now, let's imagine a scenario where entropy doesn't increase, no matter how long you mix the two together, all the flour is always on one side of the bowl and the sugar is still on the other side. The time crystal is like an impossible system in which flour and sugar never mix, that is, entropy remains stationary over time. That's why physicists all over the world are excited about time crystals.
However, building a time crystal is not so simple and needs to meet many requirements. In order to avoid heating, that is, flour and sugar are mixed with entropy, the individual components of the time crystal must be isolated from the environment, otherwise the thermal vibration will always destroy the time crystal system.
This sounds very difficult, but in fact, there is already a class of machines that need to isolate their components as much as possible: quantum computers.
Quantum computers
Similar to time crystals, quantum computers use unique particle systems to create a quantum state that can be used to process data. A common technique for isolating fragile quantum states is to keep them at extremely low temperatures.
Last year, researchers from Google and some institutions became the first team to use quantum computers to create time crystals, and published their study in the journal Nature in November 2021. Now, in the new study, physicists Philipp Frey and Stephan Rachel from the University of Melbourne have similarly observed their time crystals in a quantum computer.
The two scientists gained online access through the IBM Quantum Centre at the University of Melbourne, giving them access to the best performing parts (partitions) of IBM's quantum computer.
Turning a quantum computer into a time crystal also satisfies the requirements in other ways. For example, the initial state of the system can be prepared. The states of qubits "0" and "1" can be thought of as "flour and sugar". The different configurations of 0 and 1 are the basis for ordinary computer bits to process information, but in quantum computers, qubits can be a unique superposition of 0s and 1s, thus enhancing the ability to process and calculate information.
Although the quantum simulations on IBM's quantum computer are still somewhat noisy, flawed, or interfering, which confirms that all quantum computers are still prototypes, the study still observed a time crystal in which the configuration of qubits is constantly repeated.
Of the 65 qubits of the chip (black), 57 qubits are used to simulate DTC. | Image source: Science Advance
Fascinating application prospects
This peculiar quantum system is inherently attractive, and there is an obvious application for time crystals. Due to the constant duplication of configurations, this system will never lose memory. That is, it never forgets this initial state. This means that time crystals have the potential to form a perfect quantum memory device.
At the same time, although quantum computers have been predicted to have many application prospects, this research reflects what physicist Richard Feynman envisioned 30 years ago - the use of quantum computers for basic physics research.
But as a new phase of matter, there is still a lot of knowledge about time crystals to be understood, and the more we recognize, the more attractive their applications become. Quantum computers, as a means of creating and studying time crystals, will surely accelerate scientists' understanding in this new quantum race.
#创作团队:
Compile: M ka
Typography: Wenwen
#参考来源:
https://pursuit.unimelb.edu.au/articles/observing-time-crystals
https://theconversation.com/an-ever-ticking-clock-we-made-a-time-crystal-inside-a-quantum-computer-178164
https://www.science.org/doi/10.1126/sciadv.abm7652 #
#图片来源:
Cover image: max pixel
First image: pixabay