Maximilian Kristen

Random telegraph fluctuations in granular microwave resonators

  1. Maximilian Kristen,
  2. Jan Nicolas Voss,
  3. Micha Wildermuth,
  4. Hannes Rotzinger,
  5. and Alexey V. Ustinov
Microwave circuit electrodynamics of disordered superconductors is a very active research topic spawning a wide range of experiments and applications. For compact superconducting circuit
elements, the transition to an insulating state poses a limit to the maximum attainable kinetic inductance. It is therefore vital to study the fundamental noise properties of thin films close to this transition, particularly in situations where a good coherence and temporal stability is required. In this paper, we present measurements on superconducting granular aluminum microwave resonators with high normal state resistances, where the influence of the superconductor to insulator phase transition is visible. We trace fluctuations of the fundamental resonance frequency and observe, in addition to a 1/f noise pattern, a distinct excess noise, reminiscent of a random telegraph signal. The excess noise shows a strong dependency on the resistivity of the films as well as the sample temperature, but not on the applied microwave power.
arxiv pdf

Amplitude and frequency sensing of microwave fields with a superconducting transmon qudit

  1. Maximilian Kristen,
  2. Andre Schneider,
  3. Alexander Stehli,
  4. Tim Wolz,
  5. Sergey Danilin,
  6. Hsiang S. Ku,
  7. David P. Pappas,
  8. Alexey V. Ustinov,
  9. and Martin Weides
Experiments with superconducting circuits require careful calibration of the applied pulses and fields over a large frequency range. This remains an ongoing challenge as commercial
semiconductor electronics are not able to probe signals arriving at the chip due to its cryogenic environment. Here, we demonstrate how the on-chip amplitude and frequency of a microwave field can be inferred from the ac Stark shifts of higher transmon levels. In our time-resolved measurements, we employ a simple quantum sensing protocol, i.e. Ramsey fringes, allowing us to detect the amplitude of the systems transfer function over a range of several hundreds of MHz with an energy sensitivity on the order of 10−4. Combined with similar measurements for the phase of the transfer function, our sensing method can facilitate the microwave calibration of high fidelity quantum gates necessary for working with superconducting quantum circuits. Additionally, the potential to characterize arbitrary microwave fields promotes applications in related areas of research, such as quantum optics or hybrid microwave systems including photonic, mechanical or magnonic subsystems.
arxiv pdf