  We present experimental results on a dispersive scheme for reading out a
Josephson phase qubit. A capacitively shunted dc-SQUID is used as a nonlinear
resonator which is inductively coupled to the qubit. We detect the flux state
of the qubit by measuring the amplitude and phase of a microwave pulse
reflected from the SQUID resonator. By this low-dissipative method, we reduce
the qubit state measurement time down to 25 microseconds, which is much faster
than using the conventional readout performed by switching the SQUID to its
non-zero dc voltage state. The demonstrated readout scheme allows for reading
out multiple qubits using a single microwave line by employing
frequency-division multiplexing.
