Curator's Take
This work tackles a fundamental challenge in understanding quantum many-body systems: how to efficiently track information as it scrambles throughout a quantum system using only simple, practical measurements. Rather than requiring exotic optimal measurements that are difficult to implement, the researchers show that basic randomized Pauli measurements—the kind already used in quantum error correction—can effectively probe information scrambling dynamics. The approach successfully distinguishes between key quantum phenomena like many-body localization and quantum scarring, potentially offering experimentalists a powerful new tool for characterizing their quantum simulators and processors. This represents an important step toward making quantum information scrambling studies accessible to near-term quantum devices, where complex measurement schemes remain challenging to implement.
— Mark Eatherly
Summary
In quantum many-body dynamics, locally encoded information typically scrambles across the entire system, becoming inaccessible to local probes. The upper bound of accessible information of local probes can be characterized by the Holevo information via optimal measurement. In this work, we investigate the information dynamics of quantum scrambling utilizing local randomized probes, quantified by the averaged accessible information (AAI). We derive an analytical expression for the AAI under Haar-random measurements and demonstrate that it is a function of purity of local reduced density matrix. Operationally, we employ the classical shadow protocol, using only single-qubit randomized Pauli measurements, to efficiently extract the AAI across extended subsystems. Through numerical simulations across diverse many-body paradigms, we show that the AAI can reveal distinct scrambling behaviors, resolving phenomena that range from dynamical confinement and ballistic transport to persistent scar revivals and many-body localization. This work highlights a pragmatic paradigm shift--from relying on optimal measurements to utilizing randomized local probes--for the characterization of complex quantum information dynamics.