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The procedure of scrambling a couple of eggs—breaking them, beating the yolk and whites, pouring the mixture into a skillet, and stirring—may take a few minutes. One can observe the procedure unfolding and gain insights into how the scrambling transpires. Now, a recent theoretical article in Science reveals that, under appropriate circumstances, the subatomic counterpart of eggs could become scrambled in an instant.
“Quantum dynamics possess the capability to scramble at a rate that is exponentially quicker than any dynamics found in the classical realm,” states lead author Thomas Schuster, a Sherman Fairchild Postdoctoral Scholar Research Associate in Theoretical Physics at Caltech. Schuster collaborated on the project with Hsin-Yuan (Robert) Huang (PhD ’24), an assistant professor of theoretical physics at Caltech and a William H. Hurt scholar.
“This is quite unexpected and contradicts our intuition,” Schuster remarks. “We assumed it would require more time.”
In any quantum material, the various subatomic particles that compose it interact and experience distinctly quantum phenomena, such as entanglement and superposition. As a quantum system evolves over time, the state of the system and the information it embodies becomes progressively tangled as different components of the system become entangled with each other.
Generating quantum randomness serves as a valuable tool in quantum cryptography, as well as in the exploration of quantum systems in general. Schuster aimed to investigate how challenging or simple it would be to comprehend quantum states once the information began to scramble.
As Schuster, Huang, and their colleague Jonas Haferkamp of Harvard University and Saarland University in Germany formulated a mathematical proof regarding the difficulty of understanding a quantum system as it scrambles, they realized they had discovered something further: that quantum systems rapidly become completely unrecognizable—what scientists refer to as “maximally random.”
“This ultra-rapid scrambling happens when quantum systems can navigate through the landscape of all possibilities,” Huang clarifies. “Nothing in the classical domain mimics this scrambling behavior, and even some limited quantum realms, such as those confined to real numbers, fail to replicate this. The superfast scrambling implies it is significantly more challenging to learn about the system’s evolution time, entanglement, and other characteristics than we previously believed.”
On a positive note, this outcome may assist in future quantum applications, including those in cryptography as well as in the pursuit of establishing quantum advantage—empirical demonstrations in which quantum computers excel beyond their classical equivalents.
For instance, Google evidenced quantum advantage in 2019 using the same kind of quantum randomness generated in this research.
“This finding indicates that quantum devices can showcase quantum advantage utilizing considerably smaller quantum circuits than previously expected,” Huang remarks. “This may permit a wider range of quantum devices to gain quantum advantages.”
The study titled “Random unitaries in extremely low depth” received funding from the Walter Burke Institute for Theoretical Physics at Caltech, Harvard, MIT, the US Department of Energy Quantum Systems Accelerator, and Caltech’s Institute for Quantum Information and Matter (IQIM), a US National Science Foundation Physics Frontier Center.
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