Measurement and control of a superconducting quantum processor with a fully-integrated radio-frequency system on a chip

  1. Mats O. Tholén,
  2. Riccardo Borgani,
  3. Giuseppe Ruggero Di Carlo,
  4. Andreas Bengtsson,
  5. Christian Križan,
  6. Marina Kudra,
  7. Giovanna Tancredi,
  8. Jonas Bylander,
  9. Per Delsing,
  10. Simone Gasparinetti,
  11. and David B. Haviland
We describe a digital microwave platform called Presto, designed for measurement and control of multiple quantum bits (qubits) and based on the third-generation radio-frequency system
on a chip. Presto uses direct digital synthesis to create signals up to 9 GHz on 16 synchronous output ports, while synchronously analyzing response on 16 input ports. Presto has 16 DC-bias outputs, 4 inputs and 4 outputs for digital triggers or markers, and two continuous-wave outputs for synthesizing frequencies up to 15 GHz. Scaling to a large number of qubits is enabled through deterministic synchronization of multiple Presto units. A Python application programming interface configures a firmware for synthesis and analysis of pulses, coordinated by an event sequencer. The analysis integrates template matching (matched filtering) and low-latency (184 – 254 ns) feedback to enable a wide range of multi-qubit experiments. We demonstrate Presto’s capabilities with experiments on a sample consisting of two superconducting qubits connected via a flux-tunable coupler. We show single-shot readout and active reset of a single qubit; randomized benchmarking of single-qubit gates showing 99.972% fidelity, limited by the coherence time of the qubit; and calibration of a two-qubit iSWAP gate.

Multipartite entanglement in a microwave frequency comb

  1. Shan W. Jolin,
  2. Gustav Andersson,
  3. J. C. Rivera Hernández,
  4. Ingrid Strandberg,
  5. Fernando Quijandría,
  6. Joe Aumentado,
  7. Riccardo Borgani,
  8. Mats O. Tholén,
  9. and David B. Haviland
Significant progress has been made with multipartite entanglement of discrete qubits, but continuous variable systems may provide a more scalable path toward entanglement of large ensembles.
We demonstrate multipartite entanglement in a microwave frequency comb generated by a Josephson parametric amplifier subject to a bichromatic pump. We find 64 correlated modes in the transmission line using a multifrequency digital signal processing platform. Full inseparability is verified in a subset of seven modes. Our method can be expanded to generate even more entangled modes in the near future.