Klemens Hammerer

Spatially Adiabatic Frequency Conversion in Optoelectromechanical Arrays

  1. Ondřej Černotík,
  2. Sahand Mahmoodian,
  3. and Klemens Hammerer
Faithful conversion of quantum signals between microwave and optical frequency domains is crucial for building quantum networks based on superconducting circuits. Optoelectromechanical
systems, in which microwave and optical cavity modes are coupled to a common mechanical oscillator, are a promising route towards this goal. In these systems, efficient, low-noise conversion is possible using mechanically dark mode of the fields but the conversion bandwidth is limited to a fraction of the cavity linewidth. Here, we show that an array of optoelectromechanical transducers can overcome this limitation and reach a bandwidth that is larger than the cavity linewidth. The coupling rates are varied throughout the array so that the mechanically dark mode of the propagating fields adiabatically changes from microwave to optical or vice versa. Our approach opens a new route towards frequency conversion with optomechanical systems.
arxiv pdf

Measurement-Induced Long-Distance Entanglement of Superconducting Qubits using Optomechanical Transducers

  1. Ondřej Černotík,
  2. and Klemens Hammerer
While superconducting systems provide a promising platform for quantum computing, their networking poses a considerable challenge as they cannot be interfaced directly to light–the
natural carrier for transmission of quantum signals through channels at room temperature. Here, we show that remote superconducting qubits can be prepared in entangled states by coupling them to mechanical oscillators whose positions are monitored with optical fields. Continuous homodyne detection of light provides information on the total spin of the two qubits such that entangled qubit states can be post-selected. Entanglement generation is possible without ground state cooling of the mechanical oscillators for systems with an optomechanical cooperativity moderately larger than unity; in addition, our setup tolerates a substantial loss of photons in transmission. The approach is scalable to generation of multipartite entanglement and represents a crucial step towards quantum networks with nodes using superconducting circuits.
arxiv pdf