Approaching Superconductor-Cold Atom Hybrid Quantum Circuits

利用天然或人造原子中的量子相干是一个非常热门的话题，不仅是从基础科学的角度来看，特别是因为它在量子计算、量子模拟或量子传感等领域具有潜在的应用前景。在这个提议中，重点放在由超导体和冷原子组成的混合系统上。一旦实现耦合，人们就结合了两种非常通用的技术--固态和量子光学--这两种技术允许在固态和原子端操纵单个量子系统，并有可能用从微波到光学频率的光子来操纵系统。这种混合系统虽然难以实现，但从根本上来说是非常有吸引力的，因为它将宏观对象(超导量子比特、谐振器)与真实原子耦合在一起。从应用的角度来看，在量子信息的背景下，人们可以设想一种混合系统，其中信息由快速超导电路处理，并存储在冷原子云中，充当量子存储器。冷原子(无论是基态原子、玻色-爱因斯坦凝聚态(BEC)或高激发里德堡原子)耦合到超导谐振器上，可以进一步实现新型量子门，实现微波-光学换能器和芯片上的微脉泽。该提议建立在我们合作运营的现有冷原子/超导体混合装置(分别在4.2K和30MK下运行)的基础上。应推进冷原子与超导结构的耦合，并将4.2K时实现的概念转移到MK环境中，以实现子系统之间的相干耦合。在原子方面，主要关注里德堡原子，提供各种共振跃迁，并允许与谐振器和/或基于约瑟夫森结的器件进行强烈的电偶极耦合。在超导方面，我们将开发包含捕获原子结构的芯片、优化为与里德堡原子强耦合的谐振器以及基于约瑟夫森结的器件(SQUID，量子比特)。Nb或Al基超导芯片的设计将使它们与磁捕获原子的技术兼容。最好的设计将转移到30MK冷原子/超导体装置中。

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.