A multi-qubit quantum network node for quantum communication and computation

• Applicant: Dr. Stephan Welte
• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 539838695

In this project, I propose to implement a versatile quantum network node for novel quantum communication and computation applications. The goal is to integrate an optical cavity with an array of tweezers containing individual neutral rubidium atoms. Within this framework, the atoms in the cavity represent stationary carriers of quantum information while photons serve as flying carriers of quantum information. These photons, upon exiting the cavity, are free to propagate to other network nodes in glass fibers. In the last decade, both the fields of cavity quantum electrodynamics and optical tweezers have been awarded with Nobel prizes (Serge Haroche 2012, Arthur Ashkin 2018). An amalgamation of these experimental platforms within a single setup will enable a plethora of new experiments. The versatility of the tweezer platform allows to deterministically load a well-defined number of atoms into the cavity and position them at positions of maximal coupling to the cavity mode. Furthermore, a reservoir of atoms can be stored in tweezers outside of the cavity mode, which allows for rapid replacement of an intra-cavity atom in the event of atom loss. This feature is not available in any state-of-the-art setup. The inherent all-to-all connectivity provided by the common coupling of all atomic qubits to the same cavity mode facilitates the execution of multi-qubit quantum gates in a single step via the reflection of a single photon from the cavity. This mechanism is independent of the number of qubits and can be harnessed to execute an N-qubit Toffoli gate. This gate can, for example, be used to implement entanglement swapping in a quantum repeater link. I will furthermore focus on the generation of highly entangled states of light, such as multidimensional cluster states. For the generation of these states, individual control of the intra-cavity atoms is a necessary prerequisite. Lastly, I intend to produce optical Gottesman-Kitaev-Preskill states, which serve as basis states for encoding quantum information in a bosonic mode. Although it has been demonstrated theoretically that these states exhibit promising features in quantum error correction protocols, their deterministic generation in the optical domain has yet to be demonstrated. To achieve these goals, my group and I will build a novel experimental apparatus at the 5th Institute of Physics at the University of Stuttgart. Here, we will develop the necessary tools for precise individual atom control and thoroughly explore the potential of the new setup for novel quantum computing and quantum network protocols. After the successful implementation of this setup and the demonstration of its key properties, the design of the new network node can be replicated, allowing for the connection of multiple nodes to form a quantum network.

• DFG Programme: Independent Junior Research Groups
• International Connection: Denmark, Netherlands, Switzerland
• Major Instrumentation: Diode Laser ; EMCCD Camera ; Laser 1064nm ; ULE Cavities
• Instrumentation Group: 5430 Hochgeschwindigkeits-Kameras (ab 100 Bilder/Sek) ; 5700 Festkörper-Laser ; 5770 Lichtmodulatoren, Elektrooptik, Magnetooptik
• Cooperation Partners: Professor Dr. Johannes Borregaard; Dr. Jacob Hastrup; Professor Dr. Jonathan Home