Tristan Brown

Detailed, interpretable characterization of mid-circuit measurement on a transmon qubit

  1. Piper C. Wysocki,
  2. Luke D Burkhart,
  3. Madeline H. Morocco,
  4. Corey I. Ostrove,
  5. Riley J. Murray,
  6. Tristan Brown,
  7. Jeffrey M. Gertler,
  8. David K. Kim,
  9. Nathan E. Miller,
  10. Bethany M. Niedzielski,
  11. Katrina M. Sliwa,
  12. Robin Blume-Kohout,
  13. Gabriel O. Samach,
  14. Mollie E. Schwartz,
  15. and Kenneth M. Rudinger
Mid-circuit measurements (MCMs) are critical components of the quantum error correction protocols expected to enable utility-scale quantum computing. MCMs can be modeled by quantum
instruments (a type of quantum operation or process), which can be characterized self-consistently using gate set tomography. However, experimentally estimated quantum instruments are often hard to interpret or relate to device physics. We address this challenge by adapting the error generator formalism — previously used to interpret noisy quantum gates by decomposing their error processes into physically meaningful sums of „elementary errors“ — to MCMs. We deploy our new analysis on a transmon qubit device to tease out and quantify error mechanisms including amplitude damping, readout error, and imperfect collapse. We examine in detail how the magnitudes of these errors vary with the readout pulse amplitude, recover the key features of dispersive readout predicted by theory, and show that these features can be modeled parsimoniously using a reduced model with just a few parameters.
arxiv pdf

Trade off-Free Entanglement Stabilization in a Superconducting Qutrit-Qubit System

  1. Tristan Brown,
  2. Emery Doucet,
  3. Diego Ristè,
  4. Guilhem Ribeill,
  5. Katarina Cicak,
  6. Joe Aumentado,
  7. Ray Simmonds,
  8. Luke Govia,
  9. Archana Kamal,
  10. and Leonardo Ranzani
Quantum reservoir engineering is a powerful framework for autonomous quantum state preparation and error correction. However, traditional approaches to reservoir engineering are hindered
by unavoidable coherent leakage out of the target state, which imposes an inherent trade off between achievable steady-state state fidelity and stabilization rate. In this work we demonstrate a protocol that achieves trade off-free Bell state stabilization in a qutrit-qubit system realized on a circuit-QED platform. We accomplish this by creating a purely dissipative channel for population transfer into the target state, mediated by strong parametric interactions coupling the second-excited state of a superconducting transmon and the engineered bath resonator. Our scheme achieves a state preparation fidelity of 84% with a stabilization time constant of 339 ns, leading to the lowest error-time product reported in solid-state quantum information platforms to date.
arxiv pdf