Quantum RAM Potentially Unlocked With Time Crystals

In 2016, two separate groups of researchers claimed to have created the first time crystals – originally proposed by Nobel Prize­-winning physicist Frank Wilczek in 2012. The first of those groups was helmed by Google engineers in collaboration with researchers from Stanford, Princeton and other universities. Their results, published in Nature, claimed to have created the exotic phase of matter within a quantum computer. In a true demonstration of convergence, another, unrelated team of researchers announced the creation of the world’s first time crystal inside a diamond that same year. Now, as covered by Interesting Engineering, scientists with the Aalto University in Finland have created a system(opens in new tab) where two of these time crystals interact – cracking the doors ever so slightly towards a RAM-like equivalent for quantum computing.

In pop culture, Muse’s song “The 2nd Law: Isolated System” states that “in an isolated system, entropy can only increase” – a reference to the second law of thermodynamics, which essentially states that all systems tend to disorder over a sufficient enough time. Time crystals apparently strain this concept by enabling the creation of perpetual motion machines – they move in a periodic, repeating cycle, sustaining a predictable and constant pattern of changing states without burning or creating energy. If you’ve ever seen a Newton Cradle, a popular executive toy, you can see how this works in your mind’s eye.

A schematic of Newton's Cradle

Schematic of a Newton Cradle. This image serves merely as an illustration, and is an oversimplification of the actual physics. (Image credit: Wikipedia)

To create their system, the researchers cooled a quantity of helium-3, an isotope of helium that becomes a superfluid when cooled to a fraction above absolute zero (minus 459.67 degrees Fahrenheit, or minus 273 degrees Celsius). Being a superfluid, there’s no viscosity, which means no energy is lost to friction, thus allowing time crystal’s movement to continue indefinitely.

In the experiment, the “indefinitely” equated to a pretty finite 1,000 seconds (nearly 17 minutes) of coherence. But in quantum, where coherence times typically hover around a few milliseconds (depending on qubit type, hardware configurations, and operational procedures), it’s the quantum equivalent of several lifetimes.

A schematic on time crystals

The superfluid is contained in a quartz glass cylinder. The magnon time crystal (blue blob) is trapped in the middle of the container by the combined effect of a static magnetic field, created using a pinch coil (green wire loop), and by the spatial distribution of the superfluid orbital momentum (small green arrows). The coherency of the time crystal’s magnetisation is observed using transverse pick-up coils. The ripple on the superfluid free surface is added for illustrational purposes. (Image credit: Aalto University)

Since no energy is spontaneously created, time crystals obey the principle of conservation of energy, and are described as achieving “motion without energy”. They still need a driver of sort (a laser or another medium) to sustain their state, or they’d fall towards equilibrium and cease their perpetual motion. But since this happens without energy actually being added to the system in any way – not even as heat – no new physics need apply. And as an added bonus, the new research posits that these interlinked time crystals could eventually be made to operate at room temperature, doing away with expensive and complex cooling systems – such as IBM’s Goldeneye – that are a requirement for some types of qubits.

Yet physicists and industry experts are still coming to grips with how exactly this technology will unfold. And yet, the time crystals’ long-lived stability is already bringing eyes upon this new phase of matter. Speaking with Quanta Magazine,  Roderich Moessner, director of the Max Planck Institute for the Physics of Complex Systems in Dresden, Germany, and a co-author on the original Google paper, credited time crystals’ stability as something that’s especially unusual in the field of quantum computing – and human ingenuity tends to make useful things out of the unusual.

Florian Preis, physicist and engineer at Quantum Brilliance – known for its room-temperature, diamond-based qubits – said that time crystal’s unusually long stability times, along with predictability, could theoretically open up the door to the quantum equivalent of RAM memory. This stability through time is what gives them the sci-fi flair of time crystals.

These long coherence times stand in contrast with the fundamental element of quantum computing – the qubit – whose fickleness has industry juggernauts and quantum specialists such as IBM, MicrosoftIonQ, and others racing against one another towards quantum supremacy. Risking oversimplification, a number of qubits (quantum transistors) can produce the equivalent complexity of CPU cores – hence the term Quantum Processing Unit (QPU). Perhaps time crystals will eventually unlock quantum computing’s analog to system RAM – encoding information that’s available for a long enough period of time to be operated on by qubits themselves.

“Everyone knows that perpetual motion machines are impossible,” Samuli Autti, a research fellow and lecturer in physics at Lancaster University in the United Kingdom, said in a statement to Ram Rayong. “However, in quantum physics, perpetual motion is okay as long as we keep our eyes closed,” he finished.

It seems that blinking too is an indispensable part of quantum physics.


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