Protocols for optimal readout of qubits using a continuous quantum nondemolition measurement

By Jay M. Gambetta, W. Braff, Andreas Wallraff, Steven M. Girvin, Robert J. Schoelkopf. 2007

165 citations recorded by the source corpus.

We study how the spontaneous relaxation of a qubit affects a continuous quantum nondemolition measurement of the initial state of the qubit. Given some noisy measurement record {psi}, we seek an estimate of whether the qubit was initially in the ground or excited state. We investigate four different measurement protocols, three of which use a linear filter (with different weighting factors) and a fourth which uses a full nonlinear filter that gives the theoretically optimal estimate of the initial state of the qubit. We find that relaxation of the qubit at rate 1/T{sub 1} strongly influences the fidelity of any measurement protocol. To avoid errors due to this decay, the measurement must be completed in a time that decrease linearly with the desired fidelity while maintaining an adequate signal to noise ratio. We find that for the nonlinear filter the predicted fidelity, as expected, is always better than the linear filters and that the fidelity is a monotone increasing function of the measurement time. For example, to achieve a fidelity of 90%, the box car linear filter requires a signal to noise ratio of {approx}30 in a time T{sub 1}, whereas the nonlinear filter only requires a signal to noisemore » ratio of {approx}18.« less

Subfields: Artificial Intelligence, Atomic and Molecular Physics, and Optics

View Paper: https://www.semanticscholar.org/paper/49fc3121c990836a64294ceff3dd70034a60086f

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Citations in the corpus

Introduction to quantum noise, measurement, and amplification (2008, background): “A. Importance of QND measurements The fact that QND measurements are repeatable is of fundamental practical importance in overcoming detector inefficiencies (Gambetta et al., 2007).”
Dispersive optomechanics: a membrane inside a cavity (2008, background): “ts ground state and then shutting o the cooling beam while an energy measurement is made. Note that the somewhat related situation of QND measurement of qubit energy was studied theoretically in Ref. [36]. 5.1. Model and measurement sensitivity in the zero-damping limit The quantity measured in the ”
Rapid High-fidelity Multiplexed Readout of Superconducting Qubits (2018, background): “Choosing this quantity as a mode-matched filter is known to provide near optimal filter efficiency for a given readout frequency and power [43, 44].”
Rapid High-Fidelity Single-Shot Dispersive Readout of Superconducting Qubits (2017, background): “5 independent of all other parameters [31], see Fig.”