Contactless photoconductivity-detected electron spin resonance of P donors in isotopically purified Si

Coherence times of electron spins bound to phosphorus donors have been measured, using a standard Hahn echo technique, to be up to 20 ms in isotopically pure silicon with [P]$= 10^{14}$ cm$^{-3}$ and at temperatures $\leq 4$K. Although such times are exceptionally long for electron spins in the solid state, they are nevertheless limited by donor electron spin-spin interactions. Suppressing such interactions requires even lower donor concentrations, which lie below the detection limit for typical electron spin resonance (ESR) spectrometers. Here we describe an alternative method for phosphorus donor ESR detection, exploiting the spin-to-charge conversion provided by the optical donor bound exciton transition. We characterise the method and its dependence on laser power and use it to measure a coherence time of $T_2 = 130$ms for one of the purest silicon samples grown to-date ([P]$= 5\times 10^{11}$cm$^{-3}$). We then benchmark this result using an alternative application of the donor bound exciton transition: optically polarising the donor spins before using conventional ESR detection at 1.7~K for a sample with [P]$= 4\times10^{12}$cm$^{-3}$, and measuring in this case a $T_2$ of 350 ms

Narrow optical linewidths in erbium implanted in TiO2_2

Atomic and atom-like defects in the solid-state are widely explored for quantum computers, networks and sensors. Rare earth ions are an attractive class of atomic defects that feature narrow spin and optical transitions that are isolated from the host crystal, allowing incorporation into a wide range of materials. However, the realization of long electronic spin coherence times is hampered by magnetic noise from abundant nuclear spins in the most widely studied host crystals. Here, we demonstrate that Er$^{3+}$ ions can be introduced via ion implantation into TiO$_2$, a host crystal that has not been studied extensively for rare earth ions and has a low natural abundance of nuclear spins. We observe efficient incorporation of the implanted Er$^{3+}$ into the Ti$^{4+}$ site (40% yield), and measure narrow inhomogeneous spin and optical linewidths (20 and 460 MHz, respectively) that are comparable to bulk-doped crystalline hosts for Er$^{3+}$. This work demonstrates that ion implantation is a viable path to studying rare earth ions in new hosts, and is a significant step towards realizing individually addressed rare earth ions with long spin coherence times for quantum technologies

Therapeutic DNA vaccine induces broad T cell responses in the gut and sustained protection from viral rebound and AIDS in SIV-infected rhesus macaques.

Immunotherapies that induce durable immune control of chronic HIV infection may eliminate the need for life-long dependence on drugs. We investigated a DNA vaccine formulated with a novel genetic adjuvant that stimulates immune responses in the blood and gut for the ability to improve therapy in rhesus macaques chronically infected with SIV. Using the SIV-macaque model for AIDS, we show that epidermal co-delivery of plasmids expressing SIV Gag, RT, Nef and Env, and the mucosal adjuvant, heat-labile E. coli enterotoxin (LT), during antiretroviral therapy (ART) induced a substantial 2-4-log fold reduction in mean virus burden in both the gut and blood when compared to unvaccinated controls and provided durable protection from viral rebound and disease progression after the drug was discontinued. This effect was associated with significant increases in IFN-γ T cell responses in both the blood and gut and SIV-specific CD8+ T cells with dual TNF-α and cytolytic effector functions in the blood. Importantly, a broader specificity in the T cell response seen in the gut, but not the blood, significantly correlated with a reduction in virus production in mucosal tissues and a lower virus burden in plasma. We conclude that immunizing with vaccines that induce immune responses in mucosal gut tissue could reduce residual viral reservoirs during drug therapy and improve long-term treatment of HIV infection in humans

Correlates of physical activity among community-dwelling adults aged 50 or over in six low- and middle-income countries

Background: Considering that physical activity is associated with healthy ageing and helps to delay, prevent, or manage a plethora of non-communicable diseases in older adults, there is a need to investigate the factors that influence physical activity participation in this population. Thus, we investigated physical activity correlates among community-dwelling older adults (aged ≥50 years) in six low- and middle-income countries. Methods: Cross-sectional data were analyzed from the World Health Organization’s Study on Global Ageing and Adult Health. Physical activity was assessed by the Global Physical Activity Questionnaire. Participants were dichotomized into low (i.e., not meeting 150 minutes of moderate physical activity per week) and moderate-to-high physically active groups. Associations between physical activity and a range of correlates were examined using multivariable logistic regressions. Results: The overall prevalence (95%CI) of people not meeting recommended physical activity levels in 34,129 participants (mean age 62.4 years, 52.1% female) was 23.5% (22.3%-24.8%). In the multivariable analysis, older age and unemployment were significant sociodemographic correlates of low physical activity. Individuals with low body mass index (<18.5kg/m2), bodily pain, asthma, chronic back pain, chronic obstructive pulmonary disease, hearing problems, stroke, visual impairment, slow gait, and weak grip strength were less likely to meet physical activity targets in the overall sample (P<0.05). The associations varied widely between countries. Conclusion: Our data illustrates that a multitude of factors influence physical activity target achievement in older adults, which can inform future interventions across low- and middle-income countries to assist people of this age group to engage in regular physical activity. Future prospective cohort studies are also required to investigate the directionality and mediators of the relationships observed

SPIN AND OPTICAL CHARACTERIZATION OF DEFECTS IN GROUP IV SEMICONDUCTORS FOR QUANTUM MEMORY APPLICATIONS

This thesis is focused on the characterization of highly coherent defects in both silicon and diamond, particularly in the context of quantum memory applications. The results are organized into three parts based on the spin system: phosphorus donor electron spins in silicon, negatively charged nitrogen vacancy color centers in diamond (NV-), and neutrally charged silicon vacancy color centers in diamond (SiV0). The first part on phosphorus donor electron spins presents the first realization of strong coupling with spins in silicon. To achieve this, the silicon crystal was made highly pure and highly isotopically enriched so that the ensemble dephasing time, T2*, was long (10 µs). Additionally, the use of a 3D resonator aided in realizing uniform coupling, allowing for high fidelity spin ensemble manipulation. These two properties have eluded past implementations of strongly coupled spin ensembles and have been the limiting factor in storing and retrieving quantum information. Second, we characterize the spin properties of the NV- color center in diamond in a large magnetic field. We observe that the electron spin echo envelope modulation originating from the central 14N nuclear spin is much stronger at large fields and that the optically induced spin polarization exhibits a strong orientation dependence that cannot be explained by the existing model for the NV- optical cycle, we develop a modification of the existing model that reproduces the data in a large magnetic field. In the third part we perform characterization and stabilization of a new color center in diamond, SiV0, and find that it has attractive, highly sought-after properties for use as a quantum memory in a quantum repeater scheme. We demonstrate a new approach to the rational design of new color centers by engineering the Fermi level of the host material. The spin properties were characterized in electron spin resonance, revealing long spin relaxation and spin coherence times at cryogenic temperature. Additionally, we observe that the optical emission is highly coherent, predominately into a narrow zero phonon line that is stable in frequency. The combination of coherent optical and spin degrees of freedom has eluded all previous solid state defects

Optically Detected Magnetic Resonance in Neutral Silicon Vacancy Centers in Diamond via Bound Exciton States

Neutral silicon vacancy (SiV0) centers in diamond are promising candidates for quantum networks because of their excellent optical properties and long spin coherence times. However, spin-dependent fluorescence in such defects has been elusive due to poor understanding of the excited state fine structure and limited off-resonant spin polarization. Here we report the realization of optically detected magnetic resonance and coherent control of SiV0 centers at cryogenic temperatures, enabled by efficient optical spin polarization via previously unreported higher-lying excited states. We assign these states as bound exciton states using group theory and density functional theory. These bound exciton states enable new control schemes for SiV0 as well as other emerging defect systems

Replication Data for: Observation of an environmentally insensitive solid state spin defect in diamond

Engineering coherent systems is a central goal of quantum science. Color centers in diamond are a promising approach, with the potential to combine the coherence of atoms with the scalability of a solid state platform. We report a color center that shows insensitivity to environmental decoherence caused by phonons and electric field noise: the neutral charge state of silicon vacancy (SiV0). Through careful material engineering, we achieve over 80% conversion of implanted silicon to SiV0. SiV0 exhibits spin-lattice relaxation times approaching one minute and coherence times approaching one second. Its optical properties are excellent, with approximately 90% of its emission into the zero-phonon line and near-transform-limited optical linewidths. These combined properties make SiV0 a promising defect for quantum networks