We present experimental results on a dispersive scheme for reading out aJosephson phase qubit. A capacitively shunted dc-SQUID is used as a nonlinearresonator which is inductively coupled to the qubit. We detect the flux stateof the qubit by measuring the amplitude and phase of a microwave pulsereflected from the SQUID resonator. By this low-dissipative method, we reducethe qubit state measurement time down to 25 microseconds, which is much fasterthan using the conventional readout performed by switching the SQUID to itsnon-zero dc voltage state. The demonstrated readout scheme allows for readingout multiple qubits using a single microwave line by employingfrequency-division multiplexing.
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