A study published in *Nature* on October 22nd proposes that manipulating quantum circuits by reversing information scrambling can probe the characteristics of quantum computers and improve their performance. Scientists measured the quantity of non-temporally correlated components (OTOCs) in a superconducting quantum processor. OTOCs can serve as a tool for understanding quantum computers and for building verifiable demonstrations that surpass the performance of classical computers.

The goal of quantum computing is to build quantum computers with the performance to achieve quantum advantage, outperforming classical computers in specific and desirable practical tasks. Achieving this goal requires solving a series of challenging problems by reducing noise and overcoming defects. One such problem is probing the quantum dynamics of the numerous components in the system to distinguish between real quantum effects and classical noise.These systems are often difficult to study because the behavior of interacting elements is unpredictable and difficult to track, especially when only a subset of components is measured at specific moments. One possible solution involves time inversion: after perturbing the system, the perturbation is allowed to propagate outward, and then the system is inverted to attempt to reverse the information scrambling, thereby obtaining information about the overall system.

In this study, a team from Google Quantum AI and collaborators measured high-order OTOC in a superconducting quantum processor using a time-reversal scheme, a tool for studying how quantum information propagates in multi-particle quantum systems. They found that experimental observables remain sensitive to true quantum effects over sufficiently long timescales to sample a large portion of the processor during the propagation and reversal dynamics. The researchers added that measuring OTOC reveals microscopic properties of quantum systems that are unattainable by classical computing, which they believe enhances the possibility of future demonstrations of robust quantum advantage (such as NMR) using such multi-particle measurements.

Researchers point out that although the circuit used in the demonstration is a simplified model, the scheme can be used in real physical systems.