Biercuk, Michael J.

Date: Monday, June 15, 2015
Time: 11:00
Place: ETH Zurich, Hönggerberg, HPF G 6
Host: Jonathan Home

Predicting the future of noisy qubits

Michael J. Biercuk
University of Sydney, Australia

The uncontrolled evolution of qubits in the presence of a noisy environment poses a major challenge to the development of quantum information systems.  Nonetheless, similar circumstances are common in classical technologies, and a wide range of techniques have been developed in the discipline of control theory to provide stability to dynamically unstable systems.  We discuss experimental  demonstrations using trapped ions of a suite of quantum-control theoretic techniques to predict and control the evolution of qubits subject to semiclassical decoherence.  Our work includes the development of generalized transfer functions permitting the prediction of a qubit's ensemble-average evolution during an arbitrary operation and shows how this construct can be leveraged to produce noise-suppressing filters derived from a sequence of open-loop control operations (qubit rotations).  Further, we employ concepts from optimal estimation to predict a qubit's evolution in real time due to external decoherence, based on a time-stamped series of projective measurements qubit.  This technique, closely related to Kalman filtering, permits us to predict and perform feedforward compensation to offset the undesired evolution - again, in real time.  Finally, we describe how this suite of techniques can be made compatible with quantum computing control hardware, and touch on architectural impacts of our findings.