Input-output formulation of quantum light spectroscopy

Liwen Ko; Robert L. Cook; K. Birgitta Whaley

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arXiv · 2609.38533

Input-output formulation of quantum light spectroscopy

Liwen Ko·Robert L. Cook·K. Birgitta Whaley

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Abstract

We develop an input-output formulation of quantum light spectroscopy (QLS) by combining the input-output theory, commonly used in quantum optics, with the perturbative expansion method for nonlinear spectroscopy, commonly used in chemical physics. The use of the input-output relation provides physical intuition for how matter systems alter the photon input field. As examples, we consider linear spectroscopy, fluorescence, intra-beam $G^{(2)}$, and Hong-Ou-Mandel correlation. For certain initial photon states, we show that signal expectation values can be evaluated non-perturbatively. For general initial photon states, the signals can be computed via a perturbative expansion of the input-output relation. The input-output relation reduces the work needed to perturbatively expand the optical signal, allowing for cleaner derivations and clearer physical interpretations.

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Liwen Ko, Robert L. Cook, K. Birgitta Whaley. 2026-09-29. Input-output formulation of quantum light spectroscopy. https://arxiv.org/abs/2609.38533

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