Deterministic Quantum State Transfer and Generation of Remote Entanglement using Microwave Photons

  1. Philipp Kurpiers,
  2. Paul Magnard,
  3. Theo Walter,
  4. Baptiste Royer,
  5. Marek Pechal,
  6. Johannes Heinsoo,
  7. Yves Salathé,
  8. Abdulkadir Akin,
  9. Simon Storz,
  10. Jean-Claude Besse,
  11. Simone Gasparinetti,
  12. Alexandre Blais,
  13. and Andreas Wallraff
Sharing information coherently between nodes of a quantum network is at the foundation of distributed quantum information processing. In this scheme, the computation is divided into
subroutines and performed on several smaller quantum registers connected by classical and quantum channels. A direct quantum channel, which connects nodes deterministically, rather than probabilistically, is advantageous for fault-tolerant quantum computation because it reduces the threshold requirements and can achieve larger entanglement rates. Here, we implement deterministic state transfer and entanglement protocols between two superconducting qubits fabricated on separate chips. Superconducting circuits constitute a universal quantum node capable of sending, receiving, storing, and processing quantum information. Our implementation is based on an all-microwave cavity-assisted Raman process which entangles or transfers the qubit state of a transmon-type artificial atom to a time-symmetric itinerant single photon. We transfer qubit states at a rate of 50kHz using the emitted photons which are absorbed at the receiving node with a probability of 98.1±0.1% achieving a transfer process fidelity of 80.02±0.07%. We also prepare on demand remote entanglement with a fidelity as high as 78.9±0.1%. Our results are in excellent agreement with numerical simulations based on a master equation description of the system. This deterministic quantum protocol has the potential to be used as a backbone of surface code quantum error correction across different nodes of a cryogenic network to realize large-scale fault-tolerant quantum computation in the circuit quantum electrodynamic architecture.

Itinerant microwave photon detector

  1. Baptiste Royer,
  2. Arne L. Grimsmo,
  3. Alexandre Choquette-Poitevin,
  4. and Alexandre Blais
The realization of a high-efficiency microwave single photon detector is a long-standing problem in the field of microwave quantum optics. Here we propose a quantum non-demolition,
high-efficiency photon detector that can readily be implemented in present state-of-the-art circuit quantum electrodynamics. This scheme works in a continuous fashion, gaining information about the arrival time of the photon as well as about its presence. The key insight that allows to circumvent the usual limitations imposed by measurement back-action is the use of long-lived dark states in a small ensemble of inhomogeneous artificial atoms to increase the interaction time between the photon and the measurement device. Using realistic system parameters, we show that large detection fidelities are possible.