Measurement and control in superconducting qubits: from the quantum Zeno effect to quantum enhanced metrology

The quantum Zeno effect is a feature of measurement-driven quantum evolution where frequent measurement inhibits the decay of a quantum state. We will explore how the opposite effect; the anti-Zeno effect - where frequent measurement accelerates decay - can also emerge from frequent measurement. The emergence of one effect or the other elucidates the nature of quantum measurement and the role measurement plays in controlling quantum evolution. In a second experiment, we investigate how control over a single qubit can be used achieve a quantum speedup in the precision of frequency measurements, demonstrating a frequency sensitivity that improves as 1/T2, where T is the duration of the experiment.
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