Quantum technologies are poised to disrupt a multitude of sectors through their revolution in communication, computation and sensing. At the heart of many of these applications is the need for light-matter interfaces to utilise the benefits of the individual systems. Unfortunately, many matter-based systems have stringent spectral requirements for efficient interaction with light, thus highlighting the need for narrow bandwidth quantum states. In this thesis we investigate the generation of narrowband single photons from a cavity-enhanced spontaneous parametric downconversion (SPDC) source. The novel approach to birefringence compensation in this source---the half-wave plate `flip-trick'---enables this source to lock to the pump of the SPDC process to achieve resonance with the pump and both downconverted modes, with a locking scheme that is pumping the SPDC process 100\% of the time, thereby always probabilistically generating photons. We characterise this source to produce a two-photon linewidth of γtp = (410 ± 6) kHz, with measured spectral brightness of B = (7.5 ± 0.8) × 106 pairs/(sMHzmW) in its multimode state, corresponding to a single-mode spectral brightness of BSM = (6.0 ± 0.6) × 103 pairs/(sMHzmW). A minimum value for the second-order auto-correlation function was measured with 0.003 mW pump power to g(2)s,s|i(0) = 0.016 ± 0.002, indicating very few higher-number photon contributions in the heralded state. The indistinguishability of the photons was then investigated with Hong-Ou-Mandel (HOM) interference measurements. When matched in all degrees of freedom, including arrival time to the interfering beamsplitter, a visibility of V = (98.4 ± 1.7)% was observed. Interestingly, due to the mode-locked nature of our source and subsequent long coherence time, we can add a temporal delay between the two arms of SPDC and still see second-order quantum interference even while the photons are separated by a time delay of τ = 347.8 ns. The half-wave plate `flip-trick' also creates a unique output state from our source that is able to produce phase-sensitive NOON state super-resolution fringes around specific time delays. Single frequency mode single photons are often required for further application, so we attempt to characterise our source from multimode, to `several-mode', to single-mode. We investigate different configurations of filtering and find filtering the heralding photon seems preferable. Spectrally filtering multi-mode photons changes the output of the source to appear to use a lower pump power, thus reducing the count rate without maintaining similar higher-order number state contributions to the equivalent pump power for an unfiltered source. Near single-mode output is achieved, although experimental complexities and COVID-19 prevented further investigation. With single-mode output we were able to demonstrate, for the first time, the storage and recall of single photon states out of Gradient Echo Memory, a quantum memory protocol suitable to atomic ensembles with demonstrated high efficiency with weak coherent states. Although insufficient filtering of the control beam excluded measurements of the quantum nature of the recalled state, we observe the clear delay of a recalled signal, with a recall efficiency of (84 ± 3)%, at 4 μs, comparable to the current best performing quantum memory demonstrations. Those experiments relied on complex experimental setups with cold atoms in high vacuum systems and operated with low duty-cycles. Our system is hot and ever-ready, making it easier to scale and ready for integration with a network system. To our knowledge, this is the most efficient warm-vapour memory to surpass the no-cloning theorem for storage up to 13 μs.