Research drawing on the quantum “anti-butterfly effect” solves a long-standing experimental problem in physics and establishes a way to benchmark the performance of quantum computers.
“Using the simple, robust protocol we’ve developed, we can determine the level at which quantum computers can effectively process information, and apply it to information loss in other complex quantum systems, too, ” said Bin Yan, a quantum theorist at Los Alamos National Laboratory.
Yan is the corresponding author of the paper on benchmarking information scrambling published today in Physical Review Letters. “Our protocol quantifies information scrambling in a quantum system and clearly distinguishes it from false positive signals in the noisy background due to quantum decoherence,” he said.
Noise in the form of decoherence removes all quantum information in a complex system such as a quantum computer as it interacts with the surrounding environment. Information scrambling through quantum chaos, on the other hand, spreads information throughout the system, protects it and allows it to be retrieved.
Coherence is a quantum state that enables quantum computing, and decoherence refers to the loss of that state as information escapes the surrounding environment.
“Our method, which captures the quantum anti-butterfly effect we discovered two years ago, transforms a system forward and backward in time in a loop, so we can apply it to any system with time-varying dynamics, including quantum computers. and quantum simulators that use cold atoms,” said Yan.
The Los Alamos group demonstrated the protocol with simulations on IBM cloud-based quantum computers.
The inability to distinguish decoherence from information scrambling has prevented experimental research into the phenomenon. First studied in black-hole physics, information scrambling has proven relevant to a wide range of research areas, including quantum chaos in many-body systems, phase transitions, quantum machine learning and quantum computing. . Experimental platforms for studying information scrambling include superconductors, trapped ions and cloud-based quantum computers.
Practical application of the quantum anti-butterfly effect
Yan and co-author Nikolai Sinitsyn published a paper in 2020 proving that the development of quantum processes backwards on a quantum computer to destroy information in the simulated past causes a small change if back to the present. In contrast, a classical-physics system erases information irretrievably during the back-and-forth time loop.
Building on this discovery, Yan, Sinitsyn and co-author Joseph Harris, a graduate student at the University of Edinburgh who works in his current role as a participant at the Los Alamos Quantum Computing Summer School, developed the protocol. It prepares a quantum system and subsystem, evolves the entire system forward in time, causes a change in another subsystem, then evolves the system backward in the same amount of time. Measuring the overlapping information between two subsystems shows how much information is preserved by scrambling and how much is lost by decoherence.
Materials provided by DOE/Los Alamos National Laboratory. Note: Content may be edited for style and length.