PhD Defense: Rebecca Schmieg

Collective Spin-Oscillators for Light-Atom Interfaces 

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  verifying the single-photon character of our source. Further, high cross-correlations of etween 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 wellknown 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  = (-1.8  0.1) dB between unconditional and conditional measurement, corresponding to a signal-to-noise improvement from 0.72 to 1.2.

Link to Zoom: 
https://ucph-ku.zoom.us/j/66808116335?pwd=ajhybGZqNFlsYS9Pb0o5L3FoeXFqdz09

Meeting ID: 668 0811 6335
Passcode: 653674