  Photonic polarization qubits are widely used in quantum computation and
quantum communication due to the robustness in transmission and the easy qubit
manipulation. An integrated quantum memory for polarization qubits is a
fundamental building block for large-scale integrated quantum networks.
However, on-demand storing polarization qubits in an integrated quantum memory
is a long-standing challenge due to the anisotropic absorption of solids and
the polarization-dependent features of microstructures. Here we demonstrate a
reliable on-demand quantum memory for polarization qubits, using a
depressed-cladding waveguide fabricated in a 151Eu3+: Y2SiO5 crystal. The
site-2 151Eu3+ ions in Y2SiO5 crystal provides a near-uniform absorption for
arbitrary polarization states and a new pump sequence is developed to prepare a
wideband and enhanced absorption profile. A fidelity of 99.4\pm0.6% is obtained
for the qubit storage process with an input of 0.32 photons per pulse, together
with a storage bandwidth of 10 MHz. This reliable integrated quantum memory for
polarization qubits reveals the potential for use in the construction of
integrated quantum networks.

Quantum Physics