Approaching Superconductor-Cold Atom Hybrid Quantum Circuits

• Applicant: Professor Dr. Reinhold Kleiner
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2019 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 421077991

Exploiting quantum coherence in natural or artificial atoms is a very hot topic, not only in view of fundamental science but particularly because of potential applications in fields like quantum computing, quantum simulation or quantum sensing. In this proposal the focus is on hybrid systems consisting of superconductors and cold atoms. Once coupling is achieved, one has combined two very versatile technologies - solid state and quantum optics - that allow manipulation of individual quantum systems both on the solid state and the atomic side, with the possibility to manipulate the system with photons ranging from microwave to optical frequencies. The hybrid system, although challenging to realize, is very attractive from a fundamental perspective, since it couples macroscopic objects (superconducting qubits, Resonators) with real atoms. In view of applications, in the context of quantum information one can envision a hybrid system where information is processed by a fast superconducting circuit and stored in a cloud of cold atoms, serving as a quantum memory. Cold atoms (either ground state atoms, Bose-Einstein condensates (BECs) or highly excited Rydberg atoms) coupled to superconducting resonators could furthermore enable the implementation of novel quantum gates, the realization of a microwave-to-optical transducer and on-chip micro masers. The proposal builds on existing hybrid cold atom/superconductor setups (operating at 4.2 K and 30 mK, respectively) run by our collaboration. The coupling of cold atoms and superconducting structures shall be pushed forward and concepts realized at 4.2 K shall be transferred to the mK environment, in order to achieve coherent coupling between the subsystems. On the atomic side, the main focus will be on Rydberg atoms, offering a large variety of resonant transitions and allowing for strong electric dipolar coupling to resonators and/or Josephson junction based devices. On the superconducting side we will develop chips containing structures to trap atoms, resonators optimized for strong coupling to Rydberg atoms and Josephson junction-based devices (SQUIDs, qubits). The Nb or Al based superconducting chips will be designed such that they are compatible with the techniques to magnetically trap atoms. The best designs will be transferred to the 30 mK cold atom/superconductor setup.

• DFG Programme: Research Grants
• Co-Investigator: Professor Dr. József Fortágh