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.
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