Measurement-driven quantum clock implemented with a superconducting qubit

We demonstrate a quantum clock implemented with a superconducting transmon qubit dispersively coupled to an open co-planar resonator for qubit state readout. The cavity and qubit are driven by coherent fields and readout resonator output is monitored with a quantum-noise-limited amplifier and further analysed to generate a clock signal. We show that the quantum clock, near zero temperature, can be partly driven by entropy reduction through measurement, and is necessarily subject to quantum noise. Weak continuous measurement induces sustained coherent oscillations (with fluctuating period) in the conditional moments. Strong continuous measurement leads to an aperiodic cycle of quantum jumps. Both regimes constitute a clock with a signal extracted from the observed measurement current. This signal is analysed to demonstrate the relation between clock period noise and dissipated power for measurement-driven quantum clocks. We show that the thermodynamic limit of clock accuracy is the rates of energy dissipation and entropy generation.