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Outline (a) and micrograph (b) of the qubit. The phase qubit consists of the standard circuit elements in parallel—a Josephson junction, an inductor and a capacitor all capacitively coupled to a feedline via a coupling capacitor. An optical micrograph of the qubit depicts the actual layout of circuit. (c) Shows the readout schematic, The qubit flux bias and microwave lines (S1,S2) are sufficiently filtered and attenuated to ensure sufficiently low electron temperatures. A HEMT at the 4 K stage amplifies the outgoing microwave signal.
Experimental pulse sequence. The flux bias and qubit microwave pulse follow standard phase qubit protocols. The microwave read-out pulse is applied after the measurement pulse is executed for a duration of .
Frequency response of the phase qubit for negative (black) and positive (white) reset pulses. When the qubit is hysteretic two resonance frequencies are observed, consistent with the L and R configurations. The lower frequency response corresponds to the configuration in which the qubit is operated, and the other, , corresponds to the configuration in which the phase particle tunneled during the measurement pulse. The read-out is performed by observing the presence or absence of resonance response at .
(a) Rabi oscillations and (b) an energy relaxation curve of the qubit. Note that no absolute scale is shown as we are presently not performing a single shot measurement.
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