C. Wilen

High-Fidelity Measurement of a Superconducting Qubit using an On-Chip Microwave Photon Counter

  1. A. Opremcak,
  2. C. H. Liu,
  3. C. Wilen,
  4. K. Okubo,
  5. B. G. Christensen,
  6. D. Sank,
  7. T. C. White,
  8. A. Vainsencher,
  9. M. Giustina,
  10. A. Megrant,
  11. B. Burkett,
  12. B. L. T. Plourde,
  13. and R. McDermott
We describe an approach to the high-fidelity measurement of a superconducting qubit using an on-chip microwave photon counter. The protocol relies on the transient response of a dispersively
coupled measurement resonator to map the state of the qubit to „bright“ and „dark“ cavity pointer states that are characterized by a large differential photon occupation. Following this mapping, we photodetect the resonator using the Josephson Photomultipler (JPM), which transitions between classically distinguishable flux states when cavity photon occupation exceeds a certain threshold. Our technique provides access to the binary outcome of projective quantum measurement at the millikelvin stage without the need for quantum-limited preamplification and thresholding at room temperature. We achieve raw single-shot measurement fidelity in excess of 98% across multiple samples using this approach in total measurement times under 500 ns. In addition, we show that the backaction and crosstalk associated with our measurement protocol can be mitigated by exploiting the intrinsic damping of the JPM itself.
arxiv pdf

Measurement of a Superconducting Qubit with a Microwave Photon Counter

  1. A. Opremcak,
  2. I. V. Pechenezhskiy,
  3. C. Howington,
  4. B. G. Christensen,
  5. M. A. Beck,
  6. E. Leonard Jr.,
  7. J. Suttle,
  8. C. Wilen,
  9. K. N. Nesterov,
  10. G. J. Ribeill,
  11. T. Thorbeck,
  12. F. Schlenker,
  13. M.G. Vavilov,
  14. B. L. T. Plourde,
  15. and R. McDermott
Fast, high-fidelity measurement is a key ingredient for quantum error correction. Conventional approaches to the measurement of superconducting qubits, involving linear amplification
of a microwave probe tone followed by heterodyne detection at room temperature, do not scale well to large system sizes. Here we introduce an alternative approach to measurement based on a microwave photon counter. We demonstrate raw single-shot measurement fidelity of 92%. Moreover, we exploit the intrinsic damping of the counter to extract the energy released by the measurement process, allowing repeated high-fidelity quantum non-demolition measurements. Crucially, our scheme provides access to the classical outcome of projective quantum measurement at the millikelvin stage. In a future system, counter-based measurement could form the basis for a scalable quantum-to-classical interface.
arxiv pdf