Science1 publisher2 min readPublished
Quantum fluctuations melt a spin glass into SYK criticality in a new PRL solution
At very low temperature, quantum fluctuations can unfreeze a spin glass instead of locking it tighter, and the state on the other side is the fast, entangled one the SYK model uses to describe black holes.
The Scientist · Science desk
What happened
- A team led by University at Buffalo physicists published a mathematical solution for how a frustrated quantum magnet can move from ultraslow dynamics to ultrafast, highly entangled behavior resembling a black hole's.
- The solution links spin glasses, where atomic magnets point in disordered directions and freeze effectively in place, to the entangled states described by the Sachdev-Ye-Kitaev model.
- The group reached the result with quantum field theory built on an unconventional way of representing spins, following the glass down into temperatures that have resisted mathematical description.
- The study appeared Sept. 17 in Physical Review Letters, with Jamir Marino, an assistant professor of physics at Buffalo, as senior author.
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Why it matters
- constraint The solvable object is an infinite-range model. Any laboratory test has to establish that the crossover survives when spins couple only to nearby spins.
- decision Groups that measure spin glasses at their lowest accessible temperatures now have a prediction that cuts against the expectation of deeper freezing, aimed exactly at the regime where their data are thinnest.
- capability If matter really does cross over this way, one system would hold information still at one temperature and scramble it at another. That tuning, Marino says, could help control storage and spread of information.
- precedent SYK criticality appearing inside a Heisenberg spin glass makes the model a target for condensed-matter theory and not only for work on gravity analogues.
Quantum fluctuations disrupt the locked arrangement of spins, and eventually the particles become so highly entangled that they lose their individual identities [11]. The two ends of that crossover are useful for opposite reasons. In the glassy state, disordered spins respond to a disturbance so slowly that information stays trapped for long periods. That is why spin glasses turn up both in schemes for preserving information and in the hard optimization problems of artificial intelligence [7]. At the other end, particles are entangled strongly enough that information scrambles among them, similar to the way information is scrambled in a black hole [8].
"You normally think that lowering the temperature will freeze something even more," Marino said. "But here, the quantum effects can essentially melt the spin glass and take you from extremely slow dynamics to extremely fast dynamics." [12]
"We've essentially found the math that describes how matter can go from among the slowest states in quantum dynamics to among the fastest," Marino said [3]. The paper's title is more specific about what was solved: "Crossover to Sachdev-Ye-Kitaev Criticality in an Infinite-Range Quantum Heisenberg Spin Glass" [14].
Infinite range is the tractable case, and it is the case the field-theory treatment handles [10][14]. The phys.org account describes a mathematical solution and names no candidate material or temperature scale for testing it [15]. A group that wanted to look for this crossover in a real magnet would have to pick the magnet. It would also have to work out whether spins that only feel their neighbours cross over the same way.
Subir Sachdev, the Herchel Smith Professor of Physics at Harvard, first proposed the SYK model with Jinwu Ye, and he collaborated on this paper [5]. The first author, Hossein Hosseinabadi, did the work as a graduate student in Marino's lab at Buffalo and is now a distinguished postdoctoral scholar at the Max Planck Institute for the Physics of Complex Systems in Germany [6].
The group wanted to know what happens to a spin glass as quantum fluctuations grow at extremely low temperatures, a regime whose behaviour has been difficult to describe mathematically [9].
Marino's stated payoff is control. Understanding the transition and the states in between "could ultimately help better control the storage and spread of information in quantum technologies," he said [13].
What to watch
- Whether anyone proposes a specific short-range frustrated magnet as the platform, with a temperature scale attached.
- Whether independent groups reproduce the crossover using a different spin representation or numerics rather than the same field-theory route.
- What observable would separate SYK-like scrambling from ordinary glassy slowing in a real low-temperature sample.