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SUMMARY:Predicting the Future of Noisy Qubits
DESCRIPTION: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.  This technique, closely related to Kalman filtering, permits us to predict and perform feedforward compensation to offset the undesired evolution, providing enhanced stabilization.  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.
LOCATION:IQOQI lecture hall
DTSTART:20150619T091500
DTEND:20150619T101500
TZID: Europe/Vienna
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