Klaus Ensslin

Large-bandwidth transduction between an optical single quantum-dot molecule and a superconducting resonator

  1. Yuta Tsuchimoto,
  2. Zhe Sun,
  3. Emre Togan,
  4. Stefan Fält,
  5. Werner Wegscheider,
  6. Andreas Wallraff,
  7. Klaus Ensslin,
  8. Ataç İmamoğlu,
  9. and Martin Kroner
Quantum transduction between the microwave and optical domains is an outstanding challenge for long-distance quantum networks based on superconducting qubits. For all transducers realized
to date, the generally weak light-matter coupling does not allow high transduction efficiency, large bandwidth, and low noise simultaneously. Here we show that a large electric dipole moment of an exciton in an optically active self-assembled quantum dot molecule (QDM) efficiently couples to a microwave field inside a superconducting resonator, allowing for efficient transduction between microwave and optical photons. Furthermore, every transduction event is heralded by a single-photon pulse generated at the QDM resonance, which can be used to generate entanglement between distant qubits. With an on-chip device, we demonstrate a sizeable single-photon coupling strength of 16 MHz. Thanks to the fast exciton decay rate in the QDM, the transduction bandwidth reaches several 100s of MHz.
arxiv pdf

Strong Coupling Cavity QED with Gate-Defined Double Quantum Dots Enabled by a High Impedance Resonator

  1. Anna Stockklauser,
  2. Pasquale Scarlino,
  3. Jonne Koski,
  4. Simone Gasparinetti,
  5. Christian Kraglund Andersen,
  6. Christian Reichl,
  7. Werner Wegscheider,
  8. Thomas Ihn,
  9. Klaus Ensslin,
  10. and Andreas Wallraff
The strong coupling limit of cavity quantum electrodynamics (QED) implies the capability of a matter-like quantum system to coherently transform an individual excitation into a single
photon within a resonant structure. This not only enables essential processes required for quantum information processing but also allows for fundamental studies of matter-light interaction. In this work we demonstrate strong coupling between the charge degree of freedom in a gate-detuned GaAs double quantum dot (DQD) and a frequency-tunable high impedance resonator realized using an array of superconducting quantum interference devices (SQUIDs). In the resonant regime, we resolve the vacuum Rabi mode splitting of size 2g/2π=238 MHz at a resonator linewidth κ/2π=12 MHz and a DQD charge qubit dephasing rate of γ2/2π=80 MHz extracted independently from microwave spectroscopy in the dispersive regime. Our measurements indicate a viable path towards using circuit based cavity QED for quantum information processing in semiconductor nano-structures.
arxiv pdf