Howard M. Wiseman

Implementation of a canonical phase measurement with quantum feedback

  1. Leigh S. Martin,
  2. William P. Livingston,
  3. Shay Hacohen-Gourgy,
  4. Howard M. Wiseman,
  5. and Irfan Siddiqi
Much of modern metrology and communication technology encodes information in electromagnetic waves, typically as an amplitude or phase. While current hardware can perform near-ideal
measurements of photon number or field amplitude, to date no device exists that can even in principle perform an ideal phase measurement. In this work, we implement a single-shot canonical phase measurement on a one-photon wave packet, which surpasses the current standard of heterodyne detection and is optimal for single-shot phase estimation. By applying quantum feedback to a Josephson parametric amplifier, our system adaptively changes its measurement basis during photon arrival and allows us to validate the detector’s performance by tracking the quantum state of the photon source. These results provide an important capability for optical quantum computing, and demonstrate that quantum feedback can both enhance the precision of a detector and enable it to measure new classes of physical observables.
arxiv pdf

Detector dependency of diffusive quantum monitorings

  1. Shakib Daryanoosh,
  2. Howard M. Wiseman,
  3. and Jay M. Gambetta
Continuous measurements play a pivotal role in the study of dynamical open quantum systems. `Dyne‘ detections are among the most widespread and efficient measurement schemes,
and give rise to quantum diffusion of the conditioned state. In this work we study under what conditions the detector dependency of the conditional state of a quantum system subject to diffusive monitoring can be demonstrated experimentally, in the sense of ruling our any detector-independent pure-state dynamical model for the system. We consider an arbitrary number L of environments to which the system is coupled, and an arbitrary number K of different types of dyne detections. We prove that non-trivial necessary conditions for such a demonstration can be determined efficiently by semi-definite programming. To determine sufficient conditions, different physical environmental couplings and Hamiltonians for a qubit, and different sets of diffusive monitorings are scrutinized. We compare the threshold efficiencies that are sufficient in the various cases, as well as cases previously considered in the literature, to suggest the most feasible experimental options.
arxiv pdf