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This theoretical study demonstrates that coherently controlled quantum probes can extract more information about quantum many-body systems than conventional response theory methods. The researchers show that quantum probes can access properties like fluctuations, non-equilibrium structures, and entanglement entropy through their reduced dynamics, which encode anti-commutator and mixed-order correlations not available through traditional spectroscopy. Importantly, the required probe resources scale with the complexity of target correlations rather than system size, and entangled probes can measure properties like von Neumann entropy.
Why it matters
This work establishes a new operational framework for characterizing quantum materials and many-body systems that goes beyond current spectroscopic techniques. The findings could improve quantum sensing technologies and provide more efficient methods for studying complex quantum systems without requiring full tomography or simulation.
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arXiv:2607.11829v1 Announce Type: cross
Abstract: Which properties of a quantum many-body system are operationally accessible is a central question underlying spectroscopy, thermodynamics, and quantum information science. Conventional response theory answers this question within a system-only paradigm: one perturbs and measures the matter itself, obtaining susceptibility built from causally ordered nested commutators. Here we show that coherently controlled quantum probes, when measured at the end, define a strictly larger operational learning framework beyond that accessible from response theory. We establish this through a quantum-circuit description that unifies spectroscopy, probe microscopy, and probe-based quantum technologies within a common operational framework, from which we develop quantum protocols for learning many-body properties from probe readout only. This advantage arises because the reduced dynamics of quantum probes generically encode anti-commutator and mixed-order correlators of the target; therefore, measurements on the probe provide access to fluctuations, non-equilibrium structure, and entanglement entropy that are in general not accessible through response functions or a single probe alone. Moreover, we demonstrate that entangled probes can access many-body properties such as von Neumann entropy. We prove that the required probe resources scale with the complexity of the target correlations rather than with the size of the many-body system. Quantum probes are therefore not merely more sensitive sensors but provide a new way to learn many-body properties distinct from those of tomography or quantum simulation.
Source: Quantum probe advantage in learning many-body systems