Connecting two ‘time crystals’ in a superfluid of helium-3, barely a ten-thousandth of a degree above absolute zero, could be a huge step towards a new kind of quantum computer.
Time crystals are bizarre structures of atoms, whose existence was only predicted in 2012, with experimental evidence a few years later. In a normal crystal, such as diamond or salt, the atoms are arranged in a regularly repeating spatial pattern – a lattice or similar framework. And like most materials, the atoms stop shaking when they’re in their ground state — their lowest possible energy level.
Time crystals, on the other hand, are made up of atoms that repeat in time rather than space, oscillating or spinning back and forth, even in their ground state. They can maintain this movement continuously, without requiring energy or wasting energy.
In doing so, these time crystals can defy a concept known as: entropy† The second law of thermodynamics describes entropy as how a system becomes more disorderly over time. As an example, consider the orbits of the planets around the Sun† For simplicity, we imagine that they move in a clockwork sequence and always return to the same place in their respective orbits. In reality, however, things are messy: the gravity of the other planets, or passing stars, can pull and pull on the planets, making subtle changes in their orbits.
Hence the orbits of the planets are naturally chaotic. A small change in one can potentially have a big impact on all of them. The system becomes disordered over time – the entropy of the system increases.
Time crystals can negate the effects of entropy because of a quantum mechanical principle known as ‘localization of many objects’. If an atom in the time crystal feels a force, it only affects that atom. Therefore, the change is considered localized rather than global (system-wide). As a result, the system does not become chaotic and theoretically the repeating oscillations can go on forever.
“Everyone knows that perpetuum mobile is impossible,” said Samuli Autti, a research fellow and lecturer in physics at Lancaster University in the United Kingdom, in a statement. pronunciation† “In quantum physics, however, perpetual motion is okay as long as we keep our eyes closed.”
Autti, who led the research, refers to Heisenberg’s uncertainty principle, which alludes to how, when a quantum system is observed and measured, its quantum wave function collapses. Due to their quantum mechanical nature, time crystals can only work with 100% efficiency if they are completely isolated from their environment. This requirement limits the amount of time they can observe until they break down completely due to the wavefunction collapse.
However, Autti’s team managed to connect two time crystals together by a quantity helium-3, an isotope of helium. Helium-3 is special because, when cooled to a fraction above absolute zero (minus 459.67 degrees Fahrenheit or minus 273 degrees Celsius), the isotope becomes a superfluid, which not many materials can. In a superfluid, there is no viscosity, so no kinetic energy is lost through friction, allowing motions — like those of the atoms in a time crystal — to continue indefinitely.
Autti’s team, working at Aalto University in Finland, then manipulated the helium-3 atoms to create two time crystals that interacted with each other. In addition, they observed this time crystal pairing for a record time, about 1,000 seconds (nearly 17 minutes), which corresponds to billions of periods of oscillating or spinning motion of the atoms, before the wave function of the time crystals decayed.
“It turns out that putting the two together works beautifully,” Autti said.
The findings create a promising line of research for developing a fully functional quantum computer† While a normal computer’s bits are binary – 1s or 0s, on or off – the processing speed of quantum computers is much faster because they use ‘qubits’, which can be 1 and 0 at the same time, on and off. One way to build a quantum computer would be to connect numerous time crystals together, each designed to act like a qubit. Therefore, this first experiment to connect two time crystals has created the basic building block of a quantum computer.
Previous experiments have already shown that certain time crystals can operate at room temperature, rather than having to be cooled to near absolute zero, making their construction even easier. The next task, Autti’s team said, is to show that logic gates, which are functions that allow a computer to process information, can operate between two or more time crystals.
The research was published on June 2 in the journal nature communication (opens in new tab)†