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arXiv:2601.12173 · Optics Express

State Engineering via Nonlinear Interferometry with Linear Spectral Phases

Cody Charles Payne, Elaganuru Bashaiah, Markus Allgaier

quant-phphysics.opticsSubmitted Jan 17, 2026• Announced Jan 20, 2026• 0 citations
v1 · Jan 17, 2026v2 · May 11, 2026
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Abstract

Many protocols within quantum cryptography, communications, and computing require the ability to generate entangled states as well as spectral qudits. Nonlinear interferometry is a viable way to engineer these complex quantum states of light. However, it is difficult to achieve a high level of control over spectral correlations. Here, we present a protocol utilizing a nonlinear interferometer with linear spectral phases that can generate both high-dimensional spectral qudits and high-dimensional entangled states. We model the effect of loss and loss of overlap on interference visibility and thereby on the states generated.

DOI
10.1364/OE.590780

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Many protocols within quantum cryptography, communications, and computing require the ability to generate entangled states as well as spectral qudits. Nonlinear interferometry is a viable way to engineer these complex quantum states of light. However, it is difficult to achieve a high level of control over spectral correlations. Here, we present a protocol utilizing a nonlinear interferometer with linear spectral phases that can generate both high-dimensional spectral qudits and high-dimensional entangled states. We model the effect of loss and loss of overlap on interference visibility and thereby on the states generated.
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Recently, a method of engineering the quantum states with a nonlinear interferometer was proposed to achieve precise state engineering for near-ideal single-mode operation and near-unity efficiency (L. Cui et al., Phys. Rev. A 102, 033718 (2020)), and the high-purity bi-photon states can be created without degrading brightness and collection efficiency. Here, we study the coarse or fine tunability of the nonlinear interference method to match constructive interference patterns into a transmission window of standard 100-GHz DWDM channels. The joint spectral intensity spectrum is measured for various conditions of the nonlinear interference effects. We show that the method has coarse- and fine-tuning ability while maintaining its high spectral purity. We expect that our results expand the usefulness of the nonlinear interference method. The photon-pair generation engineered via this method will be an excellent practical source of the quantum information process.
Nonlinear quantum interferometry is widely used in photonic quantum sensing applications to perform measurements with undetected photons. While continuous wave (cw) lasers are typically used to generate correlated photon pairs, pulsed laser pumping can enhance the generation efficiency for photon pairs and enable time-resolved measurements. However, the finite spectral linewidth of pulsed lasers leads to imperfect frequency correlation between generated photon pairs, which can affect the sensitivity of nonlinear interferometry. In this work, we investigate the effect of the finite linewidth of a pump laser on the visibility of spectral domain interference in a nonlinear quantum interferometer where signal photons are detected using a dispersive spectrometer. The proposed theory quantitatively predicts the visibility as a function of optical path difference for a pump source with arbitrary spectrum. As a demonstration, we construct an experimental setup to obtain quantum interference using both cw and pulsed laser excitations under the same experimental conditions. At large optical path differences, a fine interference fringe pattern with high contrast is observed with cw laser excitation, whereas with pulsed laser pumping, the visibility decreases as the optical path delay increases, and the interference fringes appear almost washed out. Our quantitative analysis is useful for determining appropriate pulsed laser parameters for designing nonlinear interferometers for quantum sensing applications using a dispersive spectrometer.