S. Probst

Magnetic resonance with squeezed microwaves

  1. A. Bienfait,
  2. P. Campagne-Ibarcq,
  3. A. Holm-Kiilerich,
  4. X. Zhou,
  5. S. Probst,
  6. J.J. Pla,
  7. T. Schenkel,
  8. D. Vion,
  9. D. Esteve,
  10. J.J.L. Morton,
  11. K. Moelmer,
  12. and P. Bertet
Although vacuum fluctuations appear to represent a fundamental limit to the sensitivity of electromagnetic field measurements, it is possible to overcome them by using so-called squeezed
states. In such states, the noise in one field quadrature is reduced below the vacuum level while the other quadrature becomes correspondingly more noisy, as required by Heisenberg’s uncertainty principle. Squeezed optical fields have been proposed and demonstrated to enhance the sensitivity of interferometric measurements beyond the photon shot-noise limit, with applications in gravitational wave detection. They have also been used to increase the sensitivity of atomic absorption spectroscopy, imaging, atom-based magnetometry, and particle tracking in biological systems. At microwave frequencies, cryogenic temperatures are required for the electromagnetic field to be in its vacuum state. Squeezed microwaves have been produced, used for fundamental studies of light-matter interaction and for enhanced sensing of a mechanical resonator, and proposed to enhance the sensitivity of the readout of superconducting qubits. Here we report the use of squeezed microwave fields to enhance the sensitivity of magnetic resonance spectroscopy of an ensemble of electronic spins. Our scheme consists in sending a squeezed vacuum state to the input of a cavity containing the spins while they are emitting an echo, with the phase of the squeezed quadrature aligned with the phase of the echo. We demonstrate a total noise reduction of 1.2\,dB at the spectrometer output due to the squeezing. These results provide a motivation to examine the application of the full arsenal of quantum metrology to magnetic resonance detection.
arxiv pdf

Microwave multimode memory with an Er3+:Y2SiO5 spin ensemble

  1. S. Probst,
  2. H. Rotzinger,
  3. A. V. Ustinov,
  4. 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. In that respect, hybrid
quantum systems combining circuit QED with ions doped into solids are an attractive platform. There, the ions serve as coherent memory elements and reversible conversion elements of microwave to optical qubits. Among many possible spin-doped solids, erbium ions offer the unique opportunity of a coherent conversion of microwave photons into the telecom C-band at 1.54μm employed for long distance communication. In our work, we perform a time-resolved electron spin resonance study of an Er3+:Y2SiO5 spin ensemble at milli-Kelvin temperatures and demonstrate multimode storage and retrieval of up to 16 coherent microwave pulses. The memory efficiency is measured to be 10−4 at the coherence time of T2=5.6μs.
arxiv pdf

Efficient and robust analysis of complex scattering data under noise in microwave resonators

  1. S. Probst,
  2. F. B. Song,
  3. P. A. Bushev,
  4. A. V. Ustinov,
  5. and M. Weides
Superconducting microwave resonators are reliable circuits widely used for detection and as test devices for material research. A reliable determination of their external and internal
quality factors is crucial for many modern applications, which either require fast measurements or operate in the single photon regime with small signal to noise ratios. Here, we use the circle fit technique with diameter correction and provide a step by step guide for implementing an algorithm for robust fitting and calibration of complex resonator scattering data in the presence of noise. The speedup and robustness of the analysis are achieved by employing an algebraic rather than an iterative fit technique for the resonance circle.
arxiv pdf

Hybrid quantum circuit with implanted erbium ions

  1. S. Probst,
  2. N. Kukharchyk,
  3. H. Rotzinger,
  4. A. Tkalcec,
  5. S. Wünsch,
  6. A. D. Wieck,
  7. M. Siegel,
  8. A. V. Ustinov,
  9. and P. A. Bushev
We report on hybrid circuit QED experiments with focused ion beam implanted Er3+ ions in Y2SiO5 coupled to an array of superconducting lumped element microwave resonators. The Y2SiO5
crystal is divided into several areas with distinct erbium doping concentrations, each coupled to a separate resonator. The coupling strength is varied from 5 MHz to 18.7 MHz, while the linewidth ranges between 50 MHz and 130 MHz. We confirm the paramagnetic properties of the implanted spin ensemble by evaluating the temperature dependence of the coupling. The efficiency of the implantation process is analyzed and the results are compared to a bulk doped Er:Y2SiO5 sample. We demonstrate the successful integration of these engineered erbium spin ensembles with superconducting circuits.
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