Related papers: Experimental Observation of Purity-Like Invariants of Multi-photon States in Linear Optics

Experimental Observation of Purity-Like Invariants of Multi-photon States in Linear Optics

URL: http://arxiv.org/abs/2506.12857v1
Date: Sun, 15 Jun 2025 14:17:42 GMT
Title: Experimental Observation of Purity-Like Invariants of Multi-photon States in Linear Optics
Abstract summary: Linear optical networks (LONs) with multi-photon inputs offer a powerful platform for advanced quantum technologies.<n>We show that the overall state purity decomposes into three distinct invariants -- each arising from either single-photon dynamics or the multi-photon interference.
Score: 9.649931243211384
License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
Abstract: Linear optical networks (LONs) with multi-photon inputs offer a powerful platform for advanced quantum technologies. However, the number of degrees of freedom of a LON is far fewer than the dimensionality of the multi-photon multi-mode Fock space, therefore it cannot implement arbitrary unitary evolutions on multi-photon states. Understanding these intrinsic constraints is essential for the preparation, manipulation, and measurement of multi-photon states with LONs. Although several properties of the multi-photon state have been shown to be invariant under LON unitary evolution, their physical interpretation remains elusive. Here, we introduce a Hermitian transfer matrix approach to explore the multi-photon evolution, revealing that the overall state purity decomposes into three distinct invariants -- each arising from either single-photon dynamics or the multi-photon interference. We experimentally observe these purity-like invariants by preparing distinct initial states, applying LON unitaries, and measuring the resulting invariants. Our results not only confirm their conservation but also provide valuable insights into multi-photon state evolution in linear optics.

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