Controlled Interferometric Test of Quantum Coherence under Equal PathDistinguishability: Discrete Energy Exchange versus Continuous Dispersion

Abstract

Abstract The relation between interference visibility and path distinguishability is a core pillar of quantum complementarity and decoherence theory. In standard quantum mechanics, all coherence decay in interferometric systems is attributed exclusively to path information leakage, which establishes a one-to-one relation between environmental distinguishability and fringe visibility. However, a fundamental question remains experimentally untested: whether discrete quantized energy exchange between light and matter can degrade quantum coherence independently of path distinguishability. In this work, we propose a high-precision cavity-QED experiment based on a Mach–Zehnder interferometer to decouple interaction modality from path information. A single trapped Rb atom inside an optical cavity is placed in one interferometer arm, enabling fully switchable light–matter interaction regimes: resonant discrete energy exchange and far-detuned continuous dispersive interaction. To eliminate systematic artifacts, we employ environmental state tomography to rigorously equalize the path distinguishability in both operational regimes. Furthermore, we systematically compensate all linear dynamical differences between resonant and dispersive cavity responses, including group delay, spectral distortion, and temporal mode mismatch. With all standard decoherence and dynamical contributions precisely calibrated, standard quantum mechanics predicts identical interference visibility for resonant and dispersive interactions. In contrast, a physically motivated alternative conjecture suggests that discrete energy exchange can induce intrinsic coherence suppression even at fixed path distinguishability. The two scenarios yield experimentally distinguishable visibility differences. Our scheme utilizes mature single-atom cavity quantum optics techniques without low-temperature superconducting devices, providing a robust and accessible platform to resolve this long-standing open question in quantum interferometry. The complete optical layout, timing sequence, tomography calibration, statistical criteria, and error suppression strategies are presented. This experiment offers a decisive experimental benchmark for the fundamental relationship between light–matter interaction type and quantum coherence.