A. Fedorov

Realization of Deterministic Quantum Teleportation with Solid State Qubits

  1. L. Steffen,
  2. A. Fedorov,
  3. M. Oppliger,
  4. Y. Salathe,
  5. P. Kurpiers,
  6. M. Baur,
  7. G. Puebla-Hellmann,
  8. C. Eichler,
  9. and A. Wallraff
Transferring the state of an information carrier from a sender to a receiver is an essential primitive in both classical and quantum communication and information processing. In a quantum
process known as teleportation the unknown state of a quantum bit can be relayed to a distant party using shared entanglement and classical information. Here we present experiments in a solid-state system based on superconducting quantum circuits demonstrating the teleportation of the state of a qubit at the macroscopic scale. In our experiments teleportation is realized deterministically with high efficiency and achieves a high rate of transferred qubit states. This constitutes a significant step towards the realization of repeaters for quantum communication at microwave frequencies and broadens the tool set for quantum information processing with superconducting circuits.
arxiv pdf

Exploring the Effect of Noise on Geometric Phases using Superconducting Qubits

  1. S. Berger,
  2. M. Pechal,
  3. A. A. Abdumalikov Jr.,
  4. C. Eichler,
  5. L. Steffen,
  6. A. Fedorov,
  7. A. Wallraff,
  8. and S. Filipp
We make use of a superconducting qubit to study the effects of noise on adiabatic geometric phases. The state of the system, an effective spin one-half particle, is adiabatically guided
along a closed path in parameter space and thereby acquires a geometric phase. By introducing artificial fluctuations in the control parameters, we measure the geometric contribution to dephasing for a variety of noise powers and evolution times. Our results clearly show that only fluctuations which distort the path lead to geometric dephasing. In a direct comparison with the dynamic phase, which is path-independent, we observe that the adiabatic geometric phase is less affected by noise-induced dephasing. This observation directly points towards the potential of geometric phases for quantum gates or metrological applications.
arxiv pdf

Geometric phases in superconducting qubits beyond the two-level-approximation

  1. S. Berger,
  2. M. Pechal,
  3. S. Pugnetti,
  4. A. A. Abdumalikov Jr,
  5. L. Steffen,
  6. A. Fedorov,
  7. A. Wallraff,
  8. and S. Filipp
Geometric phases, which accompany the evolution of a quantum system and depend only on its trajectory in state space, are commonly studied in two-level systems. Here, however, we study
the adiabatic geometric phase in a weakly anharmonic and strongly driven multi-level system, realised as a superconducting transmon-type circuit. We measure the contribution of the second excited state to the two-level geometric phase and find good agreement with theory treating higher energy levels perturbatively. By changing the evolution time, we confirm the independence of the geometric phase of time and explore the validity of the adiabatic approximation at the transition to the non-adiabatic regime.
arxiv pdf