M. Jerger

Dispersive Qubit Readout with Intrinsic Resonator Reset

  1. M. Jerger,
  2. F. Motzoi,
  3. Y. Gao,
  4. C. Dickel,
  5. L. Buchmann,
  6. A. Bengtsson,
  7. G. Tancredi,
  8. Ch. Warren,
  9. J. Bylander,
  10. D. DiVincenzo,
  11. R. Barends,
  12. and P. A. Bushev
A key challenge in quantum computing is speeding up measurement and initialization. Here, we experimentally demonstrate a dispersive measurement method for superconducting qubits that
simultaneously measures the qubit and returns the readout resonator to its initial state. The approach is based on universal analytical pulses and requires knowledge of the qubit and resonator parameters, but needs no direct optimization of the pulse shape, even when accounting for the nonlinearity of the system. Moreover, the method generalizes to measuring an arbitrary number of modes and states. For the qubit readout, we can drive the resonator to ∼102 photons and back to ∼10−3 photons in less than 3κ−1, while still achieving a T1-limited assignment error below 1\%. We also present universal pulse shapes and experimental results for qutrit readout.
arxiv pdf

Probing the TLS Density of States in SiO Films using Superconducting Lumped Element Resonators

  1. S. T. Skacel,
  2. Ch. Kaiser,
  3. S. Wuensch,
  4. H. Rotzinger,
  5. A. Lukashenko,
  6. M. Jerger,
  7. G. Weiss,
  8. M. Siegel,
  9. and A. V. Ustinov
We have investigated dielectric losses in amorphous SiO thin films under operating conditions of superconducting qubits (mK temperatures and low microwave powers). For this purpose,
we have developed a broadband measurement setup employing multiplexed lumped element resonators using a broadband power combiner and a low-noise amplifier. The measured temperature and power dependences of the dielectric losses are in good agreement with those predicted for atomic two-level tunneling systems (TLS). By measuring the losses at different frequencies, we found that the TLS density of states is energy dependent. This had not been seen previously in loss measurements. These results contribute to a better understanding of decoherence effects in superconducting qubits and suggest a possibility to minimize TLS-related decoherence by reducing the qubit operation frequency.
arxiv pdf

Anisotropic rare-earth spin ensemble strongly coupled to a superconducting resonator

  1. S. Probst,
  2. H. Rotzinger,
  3. S. Wünsch,
  4. P. Jung,
  5. M. Jerger,
  6. M. Siegel,
  7. A. V. Ustinov,
  8. and P. A. Bushev
Interfacing photonic and solid-state qubits within a hybrid quantum architecture offers a promising route towards large scale distributed quantum computing. Ideal candidates for coherent
qubit interconversion are optically active spins magnetically coupled to a superconducting resonator. We report on a cavity QED experiment with magnetically anisotropic Er3+:Y2SiO5 crystals and demonstrate strong coupling of rare-earth spins to a lumped element resonator. In addition, the electron spin resonance and relaxation dynamics of the erbium spins are detected via direct microwave absorption, without aid of a cavity.
arxiv pdf