Engineering strong interactions between quantum systems is essential for many phenomena of quantum physics and technology. Typically, strong coupling relies on short-range forces or on placing the systems in high-quality electromagnetic resonators, which restricts the range of the coupling to small distances. We used a free-space laser beam to strongly couple a collective atomic spin and a micromechanical membrane over a distance of 1 meter in a room-temperature environment. The coupling is highly tunable and allows the observation of normal-mode splitting, coherent energy exchange oscillations, two-mode thermal noise squeezing, and dissipative coupling. Our approach to engineering coherent long-distance interactions with light makes it possible to couple very different systems in a modular way, opening up a range of opportunities for quantum control and coherent feedback networks.
Observations are collected under particular conditions. Suppose the conditions vary.How reliable are then the original observations? We propose a measure of reliability and deduce its explicit form for quantum systems from the principles of information theory and also from physical principles. The deduced measure reflects devel proximity)) and thus is simply related to devel curvature)), devel dynamics. and asusceptibility>). We illustrate its use in the context of perturbed molecular vibrations.
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