Approaching Superconductor-Cold Atom Hybrid Quantum Circuits

利用自然或人造原子中的量子相干性是一个非常热门的话题，不仅从基础科学的角度来看，而且因为它在量子计算、量子模拟或量子传感等领域的潜在应用。在这个提议中，重点是由超导体和冷原子组成的混合系统。一旦实现了耦合，人们就可以将两种非常通用的技术——固态和量子光学——结合起来，允许在固态和原子方面操纵单个量子系统，并有可能用从微波到光学频率的光子来操纵系统。这个混合系统虽然很难实现，但从基本的角度来看是非常有吸引力的，因为它将宏观物体（超导量子比特、谐振器）与真实的原子耦合在一起。从应用的角度来看，在量子信息的背景下，人们可以设想一个混合系统，其中信息由快速超导电路处理并存储在冷原子云中，作为量子存储器。冷原子（基态原子，玻色-爱因斯坦凝聚物（BECs）或高激发里德伯原子）耦合到超导谐振器可以进一步实现新的量子门，实现微波到光的换能器和片上微脉泽。该提案建立在现有的冷原子/超导体混合装置（分别运行在4.2 K和30 mK）的基础上。推进冷原子与超导结构的耦合，将4.2 K下实现的概念转移到mK环境中，实现子系统之间的相干耦合。在原子方面，主要焦点将放在里德伯原子上，提供各种各样的谐振跃迁，并允许对谐振器和/或基于约瑟夫森结的设备进行强电偶极耦合。在超导方面，我们将开发包含捕获原子结构的芯片，优化了与里德伯原子强耦合的谐振器和基于约瑟夫森结的器件（squid，量子位）。基于铌或铝的超导芯片将被设计成与磁性捕获原子的技术兼容。最好的设计将转移到30 mK冷原子/超导体装置。

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.