Quantum state tomography of quietly pumped semiconductor lasers for optical communications and enhanced sensing performance
Description
Quantum communications is the most mature field of quantum technologies, leveraging the properties of quantum mechanics for securing the keys exchanged between distant parties. While the typical encoding of quantum information has been performed in discrete alphabets such as the polarization of light, encoding quantum information in continuous variables such as the quadratures of the electromagnetic field [1] is advantageous as the equipment required is found off-the-shelf and readily available in optical communications laboratories [2,3].
A limiting contribution for continuous variable quantum communications is the shot noise, which occurs during photodetection and limits the information that can be securely transmitted. Squeezed states [4], which can reduce the noise of the transmitted light below shot noise, enable the development of novel CV quantum communication protocols. Squeezed states also play a crucial role in other quantum technology fields such as quantum sensing [5] and quantum computing [6,7]. While squeezed states are usually generated by nonlinear optical processes in materials such as LiNbO3 or KTP[8], a promising alternative way to generate squeezed states uses a constant current source for electrically pumping a laser. Indeed, as demonstrated in our group, this pumping is consistent with amplitude squeezing [9,10].
This project is aimed at the experimental tomography of the quantum fields produced by semiconductor-based light sources: quantum dot and quantum well lasers, as well as semiconductor-based frequency combs. The squeezed states will then be used to improve CV-QKD protocols over long distances (>100 km) with secret key rates exceeding 100 Mbit/s. This program therefore fills a strategic gap and positions itself at the scientific frontier. The project could also lead to the development of novel quantum sensors exploiting the enhanced experimental sensitivity afforded by squeezed light.
Finally, the project leverages the joint expertise of two research teams within the LTCI at Télécom Paris and the COPL at Université Laval. The development of the project is multifaceted and includes the theoretical modelling of the squeezing phenomena, the digital signal processing necessary for its estimation.
Bibliography
Bibliography
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[2] Usenko, V. C. et al. arXiv 2501.12801 (2025).
[3] Braunstein, S. L. & van Loock, P. Rev. Mod. Phys. 77, 513–577 (2005).
[4] Leonhardt, U. Measuring the Quantum State of Light (Cambridge Univ. Press, 1997).
[5] Aasi, J. et al. Astrophys. J. 785, 119 (2014).
[6] Zhong, H.-S. et al. Science 370, 1460–1463 (2020).
[7] Larsen, M. V. et al. Nature 642, 587–591 (2025).
[8] Breitenbach, G. Quantum State Reconstruction of Classical and Nonclassical Light (PhD thesis, Univ. Konstanz, 1998).
[9] Zhao, S. et al. Phys. Rev. Research 6, L032021 (2024).
[19] Ding, S. et al., APL Quantum 1, 026102 (2024).
