Light-atom interfaces have been of fundamental interest due to their varied applications as magnetometers, atomic clocks, and as fundamental building blocks for quantum communication and cryptography. Especially room temperature atomic ensembles have drawn much interest as they offer experimental simplicity while not relying on cryogenic cooling. These practical advantages make room-temperature atomic ensembles a promising candidate and experimental platform within the field of quantum optics in terms of potential scalability. This thesis focuses on two applications of room-temperature atomic ensembles: on-demand single-photon generation and storage, as well as quantum-enhanced sensing. Both applications exploit the atomic ensembles’ collective spin state. This thesis covers our on-demand room-temperature single-photon source with built-in memory exploiting a herald-retrieve scheme. We observe a conditional auto-correlation as low as g⁽²⁾ _RR|W=1 = 0.20 ± 0.07 verifying the singlephoton character of our source. Further, high cross-correlations of g⁽²⁾_WR = 10 ± 1 between the heralding and retrieval light fields confirm the success of our protocol, indicating highly non-classical correlations between the heralding and retrieval scattered photons. The herald-retrieve scattered photons maintain non-classical correlations for a duration of 0.68 ± 0.08 ms. The second application covered in this thesis is quantum-enhanced magnetic induction tomography (QMIT). We introduce the technique of stroboscopic back-action evasion along with conditional spin-squeezing to the well known technique of magnetic induction tomography. We test this new quantum enhanced measurement protocol in a proof-of-principle experiment. We verify the quantum enhancement by observing 42% lower quantum noise exploiting conditional spin-squeezing of x2 = (-1.8 ± 0.1) dB between unconditional and conditional measurement, corresponding to a signal-to-noise improvement from 0.72 to 1.2.