Martin Weides

Concentric transmon qubit featuring fast tunability and site-selective Z coupling

  1. Jochen Braumüller,
  2. Martin Sandberg,
  3. Michael R. Vissers,
  4. Andre Schneider,
  5. Steffen Schlör,
  6. Lukas Grünhaupt,
  7. Hannes Rotzinger,
  8. Michael Marthaler,
  9. Alexander Lukashenko,
  10. Amadeus Dieter,
  11. Alexey V. Ustinov,
  12. Martin Weides,
  13. and David P. Pappas
We present a planar qubit design based on a superconducting circuit that we call concentric transmon. While employing a simple fabrication process using Al evaporation and lift-off
lithography, we observe qubit lifetimes and coherence times in the order of 10us. We systematically characterize loss channels such as incoherent dielectric loss, Purcell decay and radiative losses. The implementation of a gradiometric SQUID loop allows for a fast tuning of the qubit transition frequency and therefore for full tomographic control of the quantum circuit. The presented qubit design features a passive direct Z coupling between neighboring qubits, being a pending quest in the field of quantum simulation.
arxiv pdf

Multi-photon dressing of an anharmonic superconducting many-level quantum circuit

  1. Jochen Braumüller,
  2. Joel Cramer,
  3. Steffen Schlör,
  4. Hannes Rotzinger,
  5. Lucas Radtke,
  6. Alexander Lukashenko,
  7. Ping Yang,
  8. Michael Marthaler,
  9. Lingzhen Guo,
  10. Alexey V. Ustinov,
  11. and Martin Weides
We report on the investigation of a superconducting anharmonic multi-level circuit that is coupled to a harmonic readout resonator. We observe multi-photon transitions via virtual energy
levels of our system up to the fifth excited state. The back-action of these higher-order excitations on our readout device is analyzed quantitatively and demonstrated to be in accordance with theoretical expectation. By applying a strong microwave drive we achieve multi-photon dressing of our system which is dynamically coupled by a weak probe tone. The emerging higher-order Rabi sidebands and associated Autler-Townes splittings involving up to five levels of the investigated anharmonic circuit are observed. Experimental results are in good agreement with master equation simulations.
arxiv pdf

Long-lived, radiation-suppressed superconducting quantum bit in a planar geometry

  1. Martin Sandberg,
  2. Michael R. Vissers,
  3. Tom Ohki,
  4. Jiansong Gao,
  5. Jose Aumentado,
  6. Martin Weides,
  7. and David P. Pappas
We present a superconducting qubit design that is fabricated in a 2D geometry over a superconducting ground plane to enhance the lifetime. The qubit is coupled to a microstrip resonator
for readout. The circuit is fabricated on a silicon substrate using low loss, stoichiometric titanium nitride for capacitor pads and small, shadow-evaporated aluminum/aluminum-oxide junctions. We observe qubit relaxation and coherence times ($T_1$ and $T_2$) of 11.7 $pm$ 0.2 $mu$s and 8.7 $pm$ 0.3 $mu$s, respectively. Calculations show that the proximity of the superconducting plane suppresses the otherwise high radiation loss of the qubit. A significant increase in $T_1$ is projected for a reduced qubit-to-superconducting plane separation.
arxiv pdf