Storing, single photons in broadband vapor cell quantum memories

Single photons are an essential resource for realizing quantum technologies. Together with compatible quantum memories granting control over when a photon arrives, they form a foundational component both of quantum communication and quantum information processing. Quality solid-state single photon sources deliver on the high bandwidths and rates required for scalable quantum technology, but require memories that match these operational parameters. In this thesis, I report on quantum memories based on electromagnetically induced transparency and built in warm rubidium vapor, with such fast and high bandwidth interfaces in mind. I also present work on a heralded single photon source based on parametric downconversion in an optical cavity, operated in a bandwidth regime of a few 100s of megahertz. The systems are characterized on their own and together in a functional interface. As the photon generation process is spontaneous, the memory is implemented as a fully reactive device, capable of storing and retrieving photons in response to an asynchronous external trigger. The combined system is used to demonstrate the storage and retrieval of single photons in and from the quantum memory. Using polarization selection rules in the Zeeman substructure of the atoms, the read-out noise of the memory is considerably reduced from what is common in ground-state storage schemes in warm vapor. Critically, the quantum signature in the photon number statistics of the retrieved photons is successfully maintained, proving that the emission from the memory is dominated by single photons. We observe a retrieved single-photon state accuracy of $g_{c,\,\text{ret}}^{(2)}=0.177(23)$ for short storage times, which remains $g_{c,\,\text{ret}}^{(2)}<0.5$ throughout the memory lifetime of $680(50)\,$ns. The end-to-end efficiency of the memory interfaced with the photon source is $\eta_{e2e}=1.1(2)\,\%$, which will be further improved in the future by optimizing the operating regime. With its operation bandwidth of $370\,$MHz, our system opens up new possibilities for single-photon synchronization and local quantum networking experiments at high repetition rates

Simple atomic quantum memory suitable for semiconductor quantum dot single photons

Quantum memories matched to single photon sources will form an important cornerstone of future quantum network technology. We demonstrate such a memory in warm Rb vapor with on-demand storage and retrieval, based on electromagnetically induced transparency. With an acceptance bandwidth of $\delta f$ = 0.66~GHz the memory is suitable for single photons emitted by semiconductor quantum dots. In this regime, vapor cell memories offer an excellent compromise between storage efficiency, storage time, noise level, and experimental complexity, and atomic collisions have negligible influence on the optical coherences. Operation of the memory is demonstrated using attenuated laser pulses on the single photon level. For 50 ns storage time we measure $\eta_{\textrm{e2e}}^{\textrm{50ns}} = 3.4(3)\%$ \emph{end-to-end efficiency} of the fiber-coupled memory, with an \emph{total intrinsic efficiency} $\eta_{\textrm{int}} = 17(3)\%$. Straightforward technological improvements can boost the end-to-end-efficiency to $\eta_{\textrm{e2e}} \approx 35\%$; beyond that increasing the optical depth and exploiting the Zeeman substructure of the atoms will allow such a memory to approach near unity efficiency. In the present memory, the unconditional readout noise level of $9\cdot 10^{-3}$ photons is dominated by atomic fluorescence, and for input pulses containing on average $\mu_{1}=0.27(4)$ photons the signal to noise level would be unity

Single-Photon Storage in a Ground-State Vapor Cell Quantum Memory

Interfaced single-photon sources and quantum memories for photons together form a foundational component of quantum technology. Achieving compatibility between heterogeneous, state-of-the-art devices is a long-standing challenge. We built and successfully interfaced a heralded single-photon source based on cavity-enhanced spontaneous parametric down-conversion in ppKTP and a matched memory based on electromagnetically induced transparency in warm $^{87}$Rb vapor. The bandwidth of the photons emitted by the source is 370 MHz, placing its speed in the technologically relevant regime while remaining well within the acceptance bandwidth of the memory. Simultaneously, the experimental complexity is kept low, with all components operating at or above room temperature. Read-out noise of the memory is considerably reduced by exploiting polarization selection rules in the hyperfine structure of spin-polarized atoms. For the first time, we demonstrate single-photon storage and retrieval in a ground-state vapor cell memory, with $g_{c,\text{ret}}^{(2)}=0.177(23)$ demonstrating the single-photon character of the retrieved light. Our platform of single-photon source and atomic memory is attractive for future experiments on room-temperature quantum networks operating at high bandwidth.Comment: 9 pages, 5 figure

An efficient, tunable, and robust source of narrow-band photon pairs at the 87^{87}Rb D1 line

We present an efficient and robust source of photons at the $^{87}$Rb D1-line (795 nm) with a narrow bandwidth of $\delta=226(1)$ MHz. The source is based on non-degenerate, cavity-enhanced spontaneous parametric down-conversion in a monolithic optical parametric oscillator far below threshold. The setup allows for efficient coupling to single mode fibers. A heralding efficiency of $\eta_{\mathrm{heralded}}=45(5)$ % is achieved, and the uncorrected number of detected photon pairs is $3.8 \times 10^{3}/(\textrm{s mW})$. For pair generation rates up to $5\times 10^{5}/$s, the source emits heralded single photons with a normalized, heralded, second-order correlation function $g^{(2)}_{c}<0.01$. The source is intrinsically stable due to the monolithic configuration. Frequency drifts are on the order of $\delta/20$ per hour without active feedback on the emission frequency. We achieved fine-tuning of the source frequency within a range of $> 2$ GHz by applying mechanical strain.Comment: 6 pages, 4 figure

An atomic memory suitable for semiconductor quantum dot single photons

Summary form only given. Quantum networks consist of many quantum memory nodes that are interconnected via photonic links, transporting single photons carrying quantum information. In the future, such quantum networks may enable: high-speed quantum cryptography for unconditionally secure communication; large-scale quantum computers; and quantum simulators that will allow for exponential speed-up in solving specific complex problems. A promising route towards functional quantum network nodes is the heterogeneous approach [1], where different and separately optimized physical systems are used for single photon generation and storage. For example semiconductor quantum dots may be used as efficient, fast and deterministic single photon sources, while atomic ensembles allow for efficient storage of these photons.We demonstrate a photonic memory in warm Rb vapour with on-demand storage and retrieval, based on electromagnetic induced transparency (EIT). The memory is suitable for storing single photons emitted by a GaAs droplet quantum dots [2] embedded into a state-of-the-art photonic structures [3]. With our experiments we close the gap between low speed quantum memories with acceptance bandwidth well below 100 MHz and ultra-high speed memories with acceptance bandwidth above 1 GHz. We find that in this intermediate regime vapour cell memories offer an excellent compromise between storage efficiency, storage time and experimental complexity

Fertility concerns, preservation strategies and quality of life in young women with breast cancer: Baseline results from an ongoing prospective cohort study in selected European Centers.

OBJECTIVES Most research addressing needs and concerns of young patients with breast cancer (≤40 years) is retrospective. The HOHO European protocol is a prospective multicenter cohort study of young women with newly diagnosed breast cancer, about fertility, psychosocial and quality of life concerns. Here we report the baseline data and focus on predictors of fertility concerns. MATERIALS AND METHODS Patient surveys and medical record review were used. The baseline survey included sociodemographic, medical and treatment data as well as questions on fertility concerns and preservation strategies. Subscales from the CAncer Rehabilitation Evaluation System-Short Form (CARES-SF) were administered to measure specific quality of life aspects. Uni- and multivariable modeling were used to investigate predictors of greater fertility concern. RESULTS Among 297 eligible respondents, 67% discussed fertility issues before starting therapy, 64% were concerned about becoming infertile after treatment, and 15% decided not to follow prescribed therapies. Fifty-four percent of women wished future children before diagnosis; of these, 71% still desired biologic children afterwards. In multivariable analysis, not having children was the only patient characteristic significantly associated with fertility concerns at diagnosis. Twenty-seven percent used fertility preservation strategies. Women who received chemotherapy reported greater physical (p = 0.021) and sexual difficulties (p = 0.039) than women who did not. Women who were married or had a partner reported less psychosocial problems than single women (p = 0.039). CONCLUSIONS Young women with newly diagnosed breast cancer have several concerns, including, but not limited to, fertility. The HOHO European study provides valuable information to develop targeted interventions

Fertility concerns, preservation strategies and quality of life in young women with breast cancer: Baseline results from an ongoing prospective cohort study in selected European Centers

Objectives: Most research addressing needs and concerns of young patients with breast cancer (≤40 years) is retrospective. The HOHO European protocol is a prospective multicenter cohort study of young women with newly diagnosed breast cancer, about fertility, psychosocial and quality of life concerns. Here we report the baseline data and focus on predictors of fertility concerns. Materials and methods: Patient surveys and medical record review were used. The baseline survey included sociodemographic, medical and treatment data as well as questions on fertility concerns and preservation strategies. Subscales from the CAncer Rehabilitation Evaluation System-Short Form (CARES-SF) were administered to measure specific quality of life aspects. Uni- and multivariable modeling were used to investigate predictors of greater fertility concern. Results: Among 297 eligible respondents, 67% discussed fertility issues before starting therapy, 64% were concerned about becoming infertile after treatment, and 15% decided not to follow prescribed therapies. Fifty-four percent of women wished future children before diagnosis; of these, 71% still desired biologic children afterwards. In multivariable analysis, not having children was the only patient characteristic significantly associated with fertility concerns at diagnosis. Twenty-seven percent used fertility preservation strategies. Women who received chemotherapy reported greater physical (p = 0.021) and sexual difficulties (p = 0.039) than women who did not. Women who were married or had a partner reported less psychosocial problems than single women (p = 0.039). Conclusions: Young women with newly diagnosed breast cancer have several concerns, including, but not limited to, fertility. The HOHO European study provides valuable information to develop targeted interventions