Decoding scrambled quantum information that was never encoded: An experimental demonstration
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Abstract
Quantum information scrambling (QIS) describes the rapid spread of initially localized information across an entire quantum many-body system through entanglement generation. Once scrambled, the original local information becomes encoded globally, inaccessible from any single subsystem. In this work, we introduce a protocol that enables information scrambling into the past, allowing decoding even before the original information is generated. This protocol is achieved by simulating a closed timelike curve (a theoretical construct in which particles can traverse backward in time) using postselection methods. Remarkably, the postselected outcome corresponds to a paradox-free trajectory that enables consistent time travel and reliable information recovery. Furthermore, the success probability is governed by out-of-time-ordered correlations, which is a standard measure of QIS. We present a quantum circuit design and experimentally implement our protocol on cloud-based Quantinuum and IBM quantum processors. Our approach illuminates a unique quantum task: retrieving information encoded in the future without altering the past.