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arXiv:2601.07157

Strong coupling of virtual negative states in the Kapitza-Dirac effect

Qianlong Wang, Sven Ahrens, Baifei Shen

quant-phSubmitted Jan 12, 2026• Announced Jan 13, 2026
v1 · Jan 12, 2026v2 · May 19, 2026
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Abstract

Negative states are an intrinsic property of relativistic quantum theory and related to anti-particles in the context of the Dirac sea concept. We show that negative states can dominantly contribute to the diffraction amplitude in the quantum dynamics of the two-photon Kapitza-Dirac effect. We draw our conclusion by investigating solutions from time-dependent perturbation theory, where the perturbative solutions are in match with numeric solutions of the relativistic quantum system and also with the numeric and analytic solutions from the relativistic equations of motion of a classical point-like electron in an external standing wave light field. While our numeric solutions assume a strong laser field, the analytic solutions indicate that negative state coupling remains dominant for arbitrary low field amplitudes, where in the single-photon case (Compton scattering) negative state coupling can be mathematically associated with the interaction of a virtual electron-positron pair in the context of a quantized theory in old-fashioned perturbation theory.

Journal reference
Physical Review A 113, 052221 (2026)
DOI
10.1103/nlzn-11yf
Comments
14 pages, 5 figures

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