Phase-Coherent Dynamics of a Superconducting Flux Qubit with Capacitive-Bias Readout

摘要: We present a systematic study of the phase coherent dynamics superconducting three-Josephson-junction flux qubit. The qubit state is detected with integrated-pulse method, which variant pulsed switching-dc-superconducting quantum interference device (SQUID) method. In this scheme, dc SQUID bias current pulse applied via capacitor instead resistor, giving rise to narrow bandpass pure low-pass filter configuration electromagnetic environment. Measuring one and same both setups allows direct comparison. With capacitive method about four times faster switching pulses an increased visibility are achieved. Furthermore, deliberate engineering environment, minimizes noise due circuit, facilitated. Right at degeneracy point, coherence limited by energy relaxation. find two main contributions. White limits relaxation contributes dephasing far from point. $1∕f$ dominant source in vicinity optimal influence also supported nonrandom beatings Ramsey spin echo decay traces. Numeric simulations coupled qubit-oscillator system indicate that these resonant interaction least pointlike fluctuator, especially strongly