  Qubit memory that is entangled with photonic qubit is the building block for
long distance quantum repeaters. Cavity enhanced and long lived spin wave
photon entanglement has been demonstrated by applying dual laser beams onto
optical-lattice atoms. However, owing to cross readouts by two beams, retrieval
efficiency of spin wave qubit is decreased by one quarter compared to that of
single mode spin wave at all storage times. Here, by coupling cold atoms to two
modes of a polarization interferometer based cavity, we achieve perfect qubit
retrieval in cavity enhanced and long lived atom photon entanglement. A write
laser beam is applied onto cold atoms, we then create a magnetic field
insensitive spin wave qubit that is entangled with the photonic qubit encoded
onto two arms of the interferometer. The spin wave qubit is retrieved by a read
beam, which avoids the cross readouts. Our experiment demonstrates 540{\mu}s
storage time at 50% intrinsic qubit retrieval efficiency, which is 13.5 times
longer than the best reported result.
