Towards interfacing single photons emitted from Dibenzoterrylene with rubidium ensemble quantum memories

Photonic quantum information processing is a pivotal aspect of the emerging quantum tech- nology landscape, with a wide range of applications in quantum computing, communication, simulation and sensing. The use of single photons for these applications is of immense interest, but requires both the generation of single photons and the ability to interact them separately, often relying on probabilistic processes. The first part of this thesis showcases work on the generation of single photons, utilizing an organic molecule, Dibenzoterrylene (DBT), doped into an anthracene (Ac) crystal. We will in- troduce a comprehensive theoretical framework for characterizing these molecules, and present experimental results where the wavlength of emission from DBT is tuned through three dif- ferent tuning mechanisms. Additionally, we will explore techniques for enhancing the emission properties of DBT, before finally demonstrating single photon emission from DBT in a novel host matrix: para-Terphenyl. In the second part of this thesis, we shift our focus to quantum memories - critical devices capable of storing and on-demand recall of quantum states of light, required to overcome the limitations of probabilistic photon-photon interactions. We will derive equations of motion governing the memory interaction with single photons and an ensemble of atoms. Next, we will explore methods for optimizing the memory interaction, while increasing the complexity of our model to more accurately resemble an interface between photons emitted from DBT/Ac and a rubidium (Rb) vapour, near resonant with the DBT/Ac. Finally, we will present the major challenges facing these systems and potential avenues for overcoming them. The results presented in this thesis pave the way for interfacing photons emitted from DBT with quantum memories based on a Rb ensemble.Open Acces

Single-photon-level sub-Doppler pump-probe spectroscopy of rubidium

We propose and demonstrate pump-probe spectroscopy of rubidium absorption which reveals the sub-Doppler hyperfine structure of the $^{5}$S$_{1/2} \leftrightarrow$ $^{5}$P$_{3/2}$ (D2) transitions. The counter propagating pump and probe lasers are independently tunable in frequency, with the probe operating at the single-photon-level. The two-dimensional spectrum measured as the laser frequencies are scanned shows fluorescence, Doppler-broadened absorption dips and sub-Doppler features. The detuning between the pump and probe lasers allows compensation of the Doppler shift for all atomic velocities in the room temperature vapor, meaning we observe sub-Doppler features for all atoms in the beam. We detail a theoretical model of the system which incorporates fluorescence, saturation effects and optical pumping and compare this with the measured spectrum, finding a mean absolute percentage error of 4.17\%. In the future this technique could assist in frequency stabilization of lasers, and the single-photon-level probe could be replaced by a single photon source.Comment: 5 page paper, 4 page supplemental material. Comments welcom

Economic history and econometrics: a cautionary note from the hyperinflation front

We seek to add a cautionary note to the growing appetite for quantitative economic history. Our lightning rod is the money demand estimation undertaken by Michael, Nobay and Peel (MNP) (1994) over the last months of Germany's hyperinflation. MNP apply to less than eighteen months of data an econometric technique designed for long-run time series and use a questionably-defined real wage series as an inappropriate proxy for real income. Given the popularity of applying modern time-series methods to hyperinflations, MNPs work provides a timely reminder that there is no substitute for knowing the historical setting and knowing the data.