Samuel Piotr Wolski

Dissipation-based Quantum Sensing of Magnons with a Superconducting Qubit

  1. Samuel Piotr Wolski,
  2. Dany Lachance-Quirion,
  3. Yutaka Tabuchi,
  4. Shingo Kono,
  5. Atsushi Noguchi,
  6. Koji Usami,
  7. and Yasunobu Nakamura
Hybrid quantum devices expand the tools and techniques available for quantum sensing in various fields. Here, we experimentally demonstrate quantum sensing of the steady-state magnon
population in a magnetostatic mode of a ferrimagnetic crystal. Dispersively coupling the magnetostatic mode to a superconducting qubit allows the detection of magnons using Ramsey interferometry with a sensitivity on the order of 10−3 magnons/Hz−−−√. The protocol is based on dissipation as dephasing via fluctuations in the magnetostatic mode reduces the qubit coherence proportionally to the number of magnons.
arxiv pdf

Fast parametric two-gubit gates with suppressed residual interaction using a parity-violated superconducting qubit

  1. Atsushi Noguchi,
  2. Alto Osada,
  3. Shumpei Masuda,
  4. Shingo Kono,
  5. Kentaro Heya,
  6. Samuel Piotr Wolski,
  7. Hiroki Takahashi,
  8. Takanori Sugiyama,
  9. Dany Lachance-Quirion,
  10. and Yasunobu Nakamura
We demonstrate fast two-qubit gates using a parity-violated superconducting qubit consisting of a capacitively-shunted asymmetric Josephson-junction loop under a finite magnetic flux
bias. The second-order nonlinearity manifesting in the qubit enables the interaction with a neighboring single-junction transmon qubit via first-order inter-qubit sideband transitions with Rabi frequencies up to 30~MHz. Simultaneously, the unwanted static longitudinal~(ZZ) interaction is eliminated with ac Stark shifts induced by a continuous microwave drive near-resonant to the sideband transitions. The average fidelities of the two-qubit gates are evaluated with randomized benchmarking as 0.967, 0.951, 0.956 for CZ, iSWAP and SWAP gates, respectively.
arxiv pdf

Entanglement-based single-shot detection of a single magnon with a superconducting qubit

  1. Dany Lachance-Quirion,
  2. Samuel Piotr Wolski,
  3. Yutaka Tabuchi,
  4. Shingo Kono,
  5. Koji Usami,
  6. and Yasunobu Nakamura
The recent development of hybrid systems based on superconducting circuits has opened up the possibility of engineering sensors of quanta of different degrees of freedom. Quantum magnonics,
which aims to control and read out quanta of collective spin excitations in magnetically-ordered systems, furthermore provides unique opportunities for advances in both the study of magnetism and the development of quantum technologies. Using a superconducting qubit as a quantum sensor, we report the detection of a single magnon in a millimeter-sized ferromagnetic crystal with a quantum efficiency of up to~0.71. The detection is based on the entanglement between a magnetostatic mode and the qubit, followed by a single-shot measurement of the qubit state. This proof-of-principle experiment establishes the single-photon detector counterpart for magnonics.
arxiv pdf