The rapid advancement of quantum technologies, has emphasised the need for the generation of robust and reliable quantum states, as well as it’s proper characterisation. By employing continuous variable (CV) encoding of quantum information, it is possible to harness the inherent properties of light fields to generate tailored quantum states on demand. In this paradigm, CV multimode light presents itself as a remarkable platform for quantum technologies: a large number of modes –spectral and spatial degrees of freedom– can be used to encode large amounts of information, while the modes can straightforwardly be measured using interferometric methods. At the Multimode Quantum Optics group - LKB(MQO-LKB), we specialise in generating CV-multimode states by using frequency combs and second-order nonlinear interactions, together with the characterisation of desired properties.

In this talk, we will discuss about characterisation methods to identify desired properties on quantum states, namely, Gaussian and non-gaussianity. I will begin by introducing the
types of multimode states generated experimentally. Next, I will discuss detection schemes that reveals these properties. First, I will present the implementation of a certification protocol for identifying non-gaussian features of a state generated via modeselective photon subtraction [1,2]. Second, I will share preliminary results on pulse-bypulse homodyne detection, showing its potential for scalable and high-rate quantum information processing [3,4].

1) U Chabaud, G Roeland, M Walschaers, F Grosshans, V Parigi, D Markham and N Treps, Phys. Rev. X Quantum 2, 020333 (2021).
2) U Chabaud, D Markham and F Grosshans, Phys.Rev.Lett. 124, 063605 (2020).
3) Roman-Rodriguez, Victor, et al. "Multimode squeezed state for reconfigurable quantum networks at telecommunication wavelengths." Physical Review Research 6.4 (2024): 043113.
4) Kouadou, Tiphaine, et al. "Spectrally shaped and pulse-by-pulse multiplexed multimode squeezed states of light." APL Photonics 8.8 (2023).