  Photonic quantum memory is the core element in quantum information processing
(QIP). For the scalable and convenient practical applications, great efforts
have been devoted to the integrated quantum memory based on various waveguides
fabricated in solids. However, on-demand storage of qubits, which is an
essential requirement for QIP, is still challenging to be implemented using
such integrated quantum memory. Here we report the on-demand storage of
time-bin qubits in an on-chip waveguide memory on the surface of a
$^{151}$Eu$^{3+}$:Y$_2$SiO$_5$ crystal, utilizing the Stark modulated atomic
frequency comb protocol. A qubit storage fidelity of $99.3\%\pm0.2\%$ is
obtained with a input of 0.5 photons per pulse, far beyond the highest fidelity
achievable using the classical measure-and-prepare strategy. The developed
integrated quantum memory with the on-demand retrieval capability, represents
an important step towards practical applications of integrated quantum nodes in
quantum networks.
