Preserving quantum information is crucial for the advancement of quantum computing systems. However, interacting quantum systems are inherently chaotic and abide by the laws of thermodynamics, which eventually lead to information loss. Physicists have long known about a peculiar exception called dynamical freezing, where quantum systems, when agitated at precisely calibrated frequencies, can evade these laws. The pressing question has been: how long can this phenomenon delay the inevitable march of thermodynamics?
While not indefinite, Cornell physicists have made a groundbreaking discovery, determining that the frozen state can be stabilized for a surprisingly long duration. Using a new mathematical framework, they have demonstrated that this state can be maintained long enough to serve as a viable strategy for preserving information in quantum systems. This finding is particularly promising for maintaining coherence in quantum computers as the number of qubits scales up to the millions.
Understanding Dynamical Freezing
“It’s like asking, how do you evade the laws of physics from eventually taking over?” said Debanjan Chowdhury, associate professor of physics in the College of Arts and Sciences. “Imagine that you had a hot cup of coffee that even without a heater stayed hot. Or a block of ice placed on a heater that never melts. Is that even possible? This has been one of the big open problems in the field of quantum many-body systems.”
Chowdhury, along with his research group, discovered through analytical calculations that while quantum systems can be driven to maintain information for extremely long periods—potentially approaching the age of the universe—the frozen state is not permanent and will eventually thermalize through exceedingly rare quantum processes.
“There is something special about this effect,” Chowdhury said. “It doesn’t last forever, but now we can calculate precisely how long the protection persists. The time scales are exponentially long in the presence of the drive. There is a very, very long time over which the information can be preserved.”
The Mechanism Behind the Freeze
Their paper, titled “Floquet Thermalization via Instantons Near Dynamical Freezing,” was published in Physical Review X on February 27. The co-first authors are Haoyu Guo, Bethe/KIC postdoctoral fellow with Cornell’s Laboratory of Atomic and Solid State Physics (LAASP), and Rohit Mukherjee, former Fulbright visiting fellow.
On why the drive needs to persist, Mukherjee explained, “The system does not stay naturally frozen on its own. Think of a playground swing: If you give it small, well-timed pushes over and over, you can keep its motion controlled in a particular way. Here, the periodic drive is like those regular pushes.”
This research reveals theoretically how coherence ultimately fades. “Most of the time the system remains stable, but every so often it makes a sudden quantum jump to a different state,” Guo noted. “Imagine a ball sitting quietly in a valley that unexpectedly shows up in the next valley over—not by rolling uphill, but by passing through the mountain itself, something only quantum physics allows.”
Implications for Quantum Computing
Chowdhury emphasized that the continued periodic drive at precisely tuned frequencies causes a subtle quantum mechanical cancellation of processes that lead to chaos. “What we see here is like noise-canceling headphones for quantum chaos,” he said.
While this work is theoretical, it has significant experimental implications, directly connecting to ongoing efforts across various quantum computing platforms. As quantum processors grow larger, preserving coherence becomes dramatically harder; a single unstable qubit can trigger cascading errors across millions of interacting components.
“With a few qubits, control is manageable,” Chowdhury said. “With millions, even small chaotic processes can avalanche. We need strategies that remain effective as systems scale.”
Dynamical freezing is not the only strategy for preserving quantum information. However, it is a particularly promising one for scaling up from a handful of qubits interacting to millions in a real device in the future.
“This work shows that dynamical freezing does not manifest as a violation of thermodynamics, but as a finely balanced state, poised between order and chaos, whose lifetime can now be predicted from first principles,” Chowdhury concluded.
The research was supported by the Alfred P. Sloan Foundation, the National Science Foundation, and a New Frontier Grant from the College of Arts and Sciences.
Kate Blackwood is a writer for the College of Arts and Sciences.
