December 4, 2022

Bin Yan, pictured here, Nikolai Sinitsyn and Joseph Harris developed a new method that determines how much information is lost from a quantum system to decoherence and how much is preserved through information encryption. Credit: Los Alamos National Laboratory

Research based on the quantum “anti-butterfly effect” solves a long-standing experimental problem in physics and establishes a method for benchmarking the performance of quantum computers.

“Using the simple, robust protocol we developed, we can determine the extent to which quantum computers can process information effectively, and it also applies to information loss in other complex quantum systems,” said Bin Yan, a quantum theorist at Los Alamos National. Laboratory.

Yan is the corresponding author of an article on encrypting information through benchmarking, published today in Physical Assessment Letters. “Our protocol quantifies information scrambling in a quantum system and unambiguously distinguishes it from fake positive signals in the noisy background caused by quantum decoherence,” he said.

Noise in the form of decoherence erases all quantum information in a complex system such as a quantum computer, because it couples with the environment. On the other hand, information clambering through the quantum chaos spreads information about the system, protecting it and making it available for retrieval.

Coherence is a quantum state that enables quantum computing, and decoherence refers to the loss of that state when information leaks into the environment.

“Our method, which is based on the quantum anti-butterfly effect we discovered two years ago, evolves a system forward and backward through time in a single loop so that we can apply it to any system with time reversal of dynamics, including quantum computers and quantum simulators that use cold atoms,” Yan said.

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The Los Alamos team demonstrated the protocol with simulations on IBM cloud-based quantum computers.

The inability to distinguish decoherence from the encryption of information has hampered experimental research on the phenomenon. First studied in black hole physics, the encryption of information has proved relevant in a wide range of research areas, including quantum chaos in many-body systems, phase transition, quantum machine learning, and quantum computing. Experimental platforms for studying information encryption include superconductors, embedded 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 showing that quantum processes evolving backwards on a quantum computer to damage information in the simulated past causes little change when they return to the present. A classical physical system, on the other hand, smears out the information irretrievably during the back-and-forth time loop.

Building on this discovery, Yan, Sinitsyn, and co-author Joseph Harris, a graduate student from the University of Edinburgh who worked on the current paper as a participant in 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, and then evolves the system backward during the same time. Measuring the overlap of information between the two subsystems shows how much information is preserved through scrambling and how much is lost through decoherence.

Finding coherence in quantum chaos

More information:
Joseph Harris et al, Benchmarking Information Scrambling, Physical Assessment Letters (2022). DOI: 10.1103/PhysRevLett.129.050602

Quote: Anti-butterfly effect enables new benchmarking of quantum computer performance (2022, July 26) retrieved July 26, 2022 from

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