Strongly non-linear interaction between non-classical light and a blockaded Rydberg atomic ensemble

We investigate the interaction between non-classical light with a tunable multiphoton component and a highly nonlinear medium based on cold Rydberg atoms. The non-classical field emitted by a DLCZ quantum memory is stored using Rydberg electromagnetically induced transparency, experiencing strong nonlinear response due to the dipole blockade. We show that the storage efficiency in the Rydberg ensemble decreases as function of the multiphoton strength of the input field, as a result of the nonlinearity. We also show that the autocorrelation function $g^{(2)}(0)$ of the retrieved field after storage in the Rydberg state is considerably reduced, leading to the first demonstration of single photon filtering with non-classical input light. Finally, we develop a simple simulation that allows us to model the effect of our medium on the input state. This work is a step towards matter-mediated photon-photon interactions with non-classical light

Transfert efficace d’intrication entre photons et mémoires quantiques

This PhD thesis focuses on the development of highly-efficient quantum memories based on large ensemble of cold cesium atoms with the ability to store photonic quantum states and retrieve it on demand, a key ingredient for large scale quantum networks. We first illustrate how memory parameters influence the performance of such a network. Specifically, we identify that a highly efficient memory is a stringent requirement. We then focus on how to optimize the efficiency of such memories by explaining the physics at play. We describe several experimental techniques to increase the absorption in our atomic ensemble, limit the temperature to a low value and optimize the magnetic environment. In this setup, by using the cesium D1-line, we first demonstrate the storage of single photons with an efficiency of η = (87 ± 5)%. This is the maximal achievable value at this optical depth, and also the highest efficiency ever achieved for single-photon storage in a quantum memory regardless of the platform considered. Finaly, we demonstrate an efficient mapping of single-photon entanglement into and out of two quantum memories, with an overall entanglement transfer of λ = (80 ± 20)% without background correction, a three-fold increase as compared to prior work. This work constitute an essential requirement to build large-scale networks.Cette thèse porte sur le développement de mémoires quantiques efficaces basées sur des ensembles d’atomes froids. Ces mémoires, qui ont la capacité de stocker un état quantique photonique pour le récupérer sur demande après un temps défini, constituent un élément central pour la construction de réseaux quantiques à grande échelle. Nous commençons par expliquer pourquoi une mémoire quantique est importante dans ce contexte, et nous expliquons de quelle façon l’efficacité d’une mémoire est un paramètre crucial, qui se doit d’être proche de l’unité pour mener à bien des applications réalistes. Nous nous concentrons ensuite sur l’optimisation de ce paramètre en expliquant notamment comment l’absorptivité des atomes et la transition choisie influe sur l’efficacité. Dans le but de préparer notre ensemble d’atomes à agir comme une mémoire quantique efficace, plusieurs techniques expérimentales sont aussi présentées. Nous démontrons finalement deux expériences de stockage quantique sur la ligne D1 du césium. La première est le stockage de photons uniques avec une efficacité record de η = (87±5)%. Ensuite, nous étendons ce résultat à un stockage d’intrication photonique et nous démontrons un transfert d’intrication avec une efficacité de transfert de λ = (80 ± 20)%. Ces résultats constituent une avancée essentielle vers la construction d’un réseau quantique de grande échelle

Efficient reversible entanglement transfer between light and quantum memories

International audienceReversible entanglement transfer between light and matter is a crucial requisite for the ongoing developments of quantum information technologies. Quantum networks and their envisioned applications, e.g., secure communications beyond direct transmission, distributed quantum computing, or enhanced sensing, rely on entanglement distribution between nodes. Although entanglement transfer has been demonstrated, a current roadblock is the limited efficiency of this process that can compromise the scalability of multi-step architectures. Here we demonstrate the efficient transfer of heralded single-photon entanglement into and out of two quantum memories based on large ensembles of cold cesium atoms. We achieve an overall storage-and-retrieval efficiency of 85% together with a preserved suppression of the twophoton component of about 10% of the value for a coherent state. Our work constitutes an important capability that is needed toward large scale networks and increased functionality