Ultrahigh-vacuum cryostat für hybrid quantum experiments with ultracold Rydberg atoms

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An apparatus for the realization and investigation of quantum hybrid systems consisting of ultracold Rydberg atoms coupled to solid-state electromechanical systems is proposed. The apparatus will be used to investigate fundamental issues in quantum mechanics such as decoherence and transition between classical and quantum physics. At the same time, novel methods for manipulating and transferring quantum information between microwave-based solid-state quantum computers and "flying" qubits encoded in single optical photons will be investigated and developed. The overall apparatus consists centrally of an ultra-high vacuum cryostat in which, on the one hand, magnetically and optically trapped ultracold atoms can be generated and processed and, on the other hand, electromechanical resonators and superconducting circuits can be operated. Other components of the overall apparatus include lasers for optical cooling and trapping and for Rydberg excitation of rubidium atoms, a microwave signal generator, a network analyzer for excitation and readout of the electromechanical systems in the GHz frequency range, and an 8-channel single photon detector for measuring photon-photon correlations and entanglement between optical photons and single microwave photons or phonons in the solid-state system. The proposed components will be combined with a predecessor setup in which Rydberg excitations were studied in a room temperature vacuum chamber. The planned experiments in a cryogenic environment are a fundamentally new approach to exploiting Rydberg-Rydberg interactions and the Rydberg blockade mechanism. Our group has been successfully using this mechanism for several years to generate optical nonlinearities at the single photon level and resulting effective interactions between single photons. This allows the realization of quantum optical switching elements such as transistors and single photon logic gates, which are a central component of quantum information setups. In this new apparatus, the approach we are advancing will be applied to an entirely new quantum system, a micro-mechanical oscillator (MEMS). For example, optical nonlinearity will be used to generate and read out non-classical oscillatory states of the MEMS. In addition to fundamental questions about the quantum mechanics of "large" objects, MEMS in the quantum regime are of great interest as quantum sensors and quantum information storage devices for superconducting quantum computers. In particular, our research project aims at the realization of an optical interface for microwave quantum computers, which enables the networking of these machines over long distances.