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Quantum enhancement in computation, communication, and sensing relies on the generation and control of nonclassical states. Generation of such photonic nonclassical states useful for quantum technology is discussed in the context of quantum state engineering and reservoir engineering. Quadratic Hamiltonians generate and preserve Gaussian states, whose dynamics are completely determined by the first and second moments of the canonical bosonic operators. There are numerous applications of the Gaussian states, but their capabilities are fundamentally limited. Achieving stronger nonclassical properties and quantum advantage requires quantum state engineering or reservoir engineering. As an example of the former case experimental generation of non-Gaussian states after photon addition and subtraction is discussed [1]. Such states are shown to possess photon-number fluctuations in twin beams as well as the corresponding signal and idler beams below the classical limit. These engineered states provide a versatile and experimentally accessible platform for the direct comparison of different quantum operations aimed at producing highly nonclassical and entangled states. Potential of reservoir engineering for singularity enhanced quantum sensing is illustrated by an example of two-mode Gaussian state [2]. The presented framework provides practical guidelines for engineering nonclassical and non-Gaussian states in platforms relevant to quantum communication, sensing, and information processing.
[1] K. Thapliyal, J. Peřina Jr., O. Haderka, V. Michálek, and R. Machulka, Experimental characterization of multimode photon-subtracted twin beams, Phys. Rev. Res. 6, 013065 (2024).
[2] K. Thapliyal, J. Peřina Jr., G. Chimczak, A. Kowalewska-Kudlaszyk, A. Miranowicz, Multiple quantum exceptional, diabolical, and hybrid points in multimode bosonic systems: I. Inherited and genuine singularities, Quantum 9, 1932 (2025).