Andreas Wallraff (ETH Zurich, Switzerland)
Superconducting circuits are a prime contender for realizing universal quantum computation and solving noisy intermediate-scale quantum (NISQ) problems on fault-tolerant or non-error-corrected quantum processors, respectively. In this talk, I will present elements of an architecture which allows for fast, high-fidelity, single shot qubit read-out , for unconditional reset , and can be multiplexed . Integrating multiple qubits in a single device, we evaluate performance metrics such as the single and two-qubit gate fidelity and the qubit readout fidelity. We also test the performance of the architecture in parity measurements with real-time feedback, which is a basic element of a error correcting code. To provide a potential avenue for extending monolithic chip-based architectures for quantum information processing, we employ the circuit elements of our architecture to implement a deterministic state transfer and entanglement generation protocol . Our protocol is based on an all-microwave process, which entangles or transfers the state of a superconducting qubit with a time-symmetric itinerant single photon exchanged between individually packaged chips connected by a transmission line. We transfer qubit states at rates of 50 kHz, absorb photons at the receiving node with near unit probability, and achieve transfer process fidelities and on demand remote entanglement state fidelities of about 80 %. We also show that time bin encoding can be used to further improve these quantum communication metrics . Sharing information coherently between physically separated chips in a network of quantum computing modules may be an essential element for realizing a viable extensible quantum information processing system.
 T. Walter et al., Phys. Rev. Applied 7, 054020 (2017)  P. Magnard et al., Phys. Rev. Lett. 121, 060502 (2018)  J. Heinsoo et al., Phys. Rev. Applied 10, 034040 (2018)  P. Kurpiers et al., Nature 558, 264-267 (2018)  P. Kurpiers et al., arXiv:1811.07604 (2018)
This research was performed in a collaboration between J.-C. Besse, A. Akin, S. Gasparinetti, J. Heinsoo, P. Kurpiers, P. Magnard, M. Pechal, B. Royer, Y. Salathe, S. Storz, T. Walter, A. Blais, C. Eichler, and A. Wallraff.