  Determining the state of a qubit on a timescale much shorter than its
relaxation time is an essential requirement for quantum information processing.
With the aid of a new type of non-degenerate parametric amplifier, we
demonstrate the continuous detection of quantum jumps of a transmon qubit with
90% fidelity in state discrimination. Entirely fabricated with standard
two-step optical lithography techniques, this type of parametric amplifier
consists of a dispersion engineered Josephson junction (JJ) array. By using
long arrays, containing $10^3$ JJs, we can obtain amplification at multiple
eigenmodes with frequencies below $10~\mathrm{GHz}$, which is the typical range
for qubit readout. Moreover, by introducing a moderate flux tunability of each
mode, employing superconducting quantum interference device (SQUID) junctions,
a single amplifier device could potentially cover the entire frequency band
between 1 and $10~\mathrm{GHz}$.
