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arXiv · 2609.16623

Terahertz two-dimensional coherent spectroscopy: unlocking coherent quantum intraband nonlinear dynamics

Se Jin Park·In Hyeok Choi·Jeong Woo Han
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Abstract

Quantum materials host a rich spectrum of low-energy collective excitations- phonons, magnons, plasmons, polaritons, and Higgs modes- that fundamentally govern their emergent properties, but remain inaccessible to conventional linear THz spectroscopy when nonlinear pathways overlap or non-perturbative dynamics emerge. Terahertz two-dimensional coherent spectroscopy (THz-2DCS), realized through phase-stable high-field THz pulse sequences, directly resolves this challenge by delivering phase-resolved multidimensional spectra that uniquely disentangle coherent intraband nonlinear quantum dynamics from incoherent backgrounds. Here, we establish a unified theoretical framework by using density-matrix formalism combined with the optical Bloch equations, from which nonlinear pathways are systematically derived and visualized on the Bloch sphere. This framework provides insight into low-energy nonlinear dynamics exhibiting homogeneous or inhomogeneous broadening depending on the scattering mechanism, enabling the interpretation of nonlinear signals in both the perturbative regime, described by a susceptibility expansion, and the non-perturbative regime. Building on this foundation, we comprehensively survey THz-2DCS investigations of nonlinear plasmon, phonon, magnon, and polariton. Finally, we outline future opportunities, including integration with optical-pump THz-probe platforms for nonequilibrium quantum control.

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Se Jin Park, In Hyeok Choi, Jeong Woo Han. 2026-09-15. Terahertz two-dimensional coherent spectroscopy: unlocking coherent quantum intraband nonlinear dynamics. https://arxiv.org/abs/2609.16623

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