Peter J. Leek

High Coherence in a Tileable 3D Integrated Superconducting Circuit Architecture

  1. Peter A. Spring,
  2. Shuxiang Cao,
  3. Takahiro Tsunoda,
  4. Giulio Campanaro,
  5. Simone D. Fasciati,
  6. James Wills,
  7. Vivek Chidambaram,
  8. Boris Shteynas,
  9. Mustafa Bakr,
  10. Paul Gow,
  11. Lewis Carpenter,
  12. James Gates,
  13. Brian Vlastakis,
  14. and Peter J. Leek
We report high qubit coherence as well as low crosstalk and single-qubit gate errors in a superconducting circuit architecture that promises to be tileable to 2D lattices of qubits.
The architecture integrates an inductively shunted cavity enclosure into a design featuring non-galvanic out-of-plane control wiring and qubits and resonators fabricated on opposing sides of a substrate. The proof-of-principle device features four uncoupled transmon qubits and exhibits average energy relaxation times T1=149(38) μs, pure echoed dephasing times Tϕ,e=189(34) μs, and single-qubit gate fidelities F=99.982(4)% as measured by simultaneous randomized benchmarking. The 3D integrated nature of the control wiring means that qubits will remain addressable as the architecture is tiled to form larger qubit lattices. Band structure simulations are used to predict that the tiled enclosure will still provide a clean electromagnetic environment to enclosed qubits at arbitrary scale.
arxiv pdf

Realization of a Carbon-Nanotube-Based Superconducting Qubit

  1. Matthias Mergenthaler,
  2. Ani Nersisyan,
  3. Andrew Patterson,
  4. Martina Esposito,
  5. Andreas Baumgartner,
  6. Christian Schönenberger,
  7. G. Andrew D. Briggs,
  8. Edward A. Laird,
  9. and Peter J. Leek
Hybrid circuit quantum electrodynamics (QED) involves the study of coherent quantum physics in solid state systems via their interactions with superconducting microwave circuits. Here
we present an implementation of a hybrid superconducting qubit that employs a carbon nanotube as a Josephson junction. We realize the junction by contacting a carbon nanotube with a superconducting Pd/Al bi-layer, and implement voltage tunability of the qubit frequency using a local electrostatic gate. We demonstrate strong dispersive coupling to a coplanar waveguide resonator via observation of a resonator frequency shift dependent on applied gate voltage. We extract qubit parameters from spectroscopy using dispersive readout and find qubit relaxation and coherence times in the range of 10−200 ns.
arxiv pdf

Coherence and Decay of Higher Energy Levels of a Superconducting Transmon Qubit

  1. Michael J. Peterer,
  2. Samuel J. Bader,
  3. Xiaoyue Jin,
  4. Fei Yan,
  5. Archana Kamal,
  6. Ted Gudmundsen,
  7. Peter J. Leek,
  8. Terry P. Orlando,
  9. William D. Oliver,
  10. and Simon Gustavsson
We present measurements of coherence and successive decay dynamics of higher energy levels of a superconducting transmon qubit. By applying consecutive π-pulses for each sequential
transition frequency, we excite the qubit from the ground state up to its fourth excited level and characterize the decay and coherence of each state. We find the decay to proceed mainly sequentially, with relaxation times in excess of 20 μs for all transitions. We also provide a direct measurement of the charge dispersion of these levels by analyzing beating patterns in Ramsey fringes. The results demonstrate the feasibility of using higher levels in transmon qubits for encoding quantum information.
arxiv pdf