Frequency Multiplexing for Quasi-Deterministic Heralded Single-Photon Sources

Single-photon sources based on optical parametric processes have been used extensively for quantum information applications due to their flexibility, room-temperature operation and potential for photonic integration. However, the intrinsically probabilistic nature of these sources is a major limitation for realizing large-scale quantum networks. Active feedforward switching of photons from multiple probabilistic sources is a promising approach that can be used to build a deterministic source. However, previous implementations of this approach that utilize spatial and/or temporal multiplexing suffer from rapidly increasing switching losses when scaled to a large number of modes. Here, we break this limitation via frequency multiplexing in which the switching losses remain fixed irrespective of the number of modes. We use the third-order nonlinear process of Bragg scattering four-wave mixing as an efficient ultra-low noise frequency switch and demonstrate multiplexing of three frequency modes. We achieve a record generation rate of $4.6\times10^4$ multiplexed photons per second with an ultra-low $g^{2}(0)$ = 0.07, indicating high single-photon purity. Our scalable, all-fiber multiplexing system has a total loss of just 1.3 dB independent of the number of multiplexed modes, such that the 4.8 dB enhancement from multiplexing three frequency modes markedly overcomes switching loss. Our approach offers a highly promising path to creating a deterministic photon source that can be integrated on a chip-based platform.Comment: 28 pages, 9 figures. Comments welcom

Presence of two types of flowers with respect to nectar sugar in two gregariously flowering species

Many species of animal-pollinated flowers are known to vary widely in the nectar content of flowers. Some proportion of flowers in many species is apparently nectarless, and such flowers are believed to be 'cheaters'. Cheating may explain a part of the variability in nectar content. If cheating exists as a qualitatively different strategy then we expect bimodality in the distribution of nectar content of flowers. It has been shown in a multispecies study that gregarious species have a higher proportion of cheater flowers. We studied the frequency distribution of total nectar sugar in two gregariously flowering species Lantana camara and Utricularia purpurascens, which differed in other floral and ecological characters. At the population level, both the species showed significant bimodality in the total sugar content of flowers. The obvious sources of heterogeneity in the data did not explain bimodality. In Lantana camara, bimodality was observed within flowers of some of the individual plants sampled. In Utricularia purpurascens the proportion of nectarless flowers was more in high-density patches, suggesting that the gregariousness hypothesis may work within a species as well. The results support the hypothesis of cheating as a distinct strategy since two distinct types of flowers were observed in both the species. The effect of density in Utricularia purpurascens also supports the gregariousness hypothesis

A quantum electromechanical interface for long-lived phonons

Controlling long-lived mechanical oscillators in the quantum regime holds promises for quantum information processing. Here, we present an electromechanical system capable of operating in the GHz-frequency band in a silicon-on-insulator platform. Relying on a novel driving scheme based on an electrostatic field and high-impedance microwave cavities based on TiN superinductors, we are able to demonstrate a parametrically-enhanced electromechanical coupling of ${g/2 \pi} = 1.1$ MHz, sufficient to enter the strong-coupling regime with a cooperativity of $\mathcal{C} = 1200$. The absence of piezoelectric materials in our platform leads to long mechanical lifetimes, finding intrinsic values up to $\tau_\text{d} = 265~ \mu$s ($Q = 8.4 \times {10}^6$ at $\omega_\mathrm{m}/2\pi = 5$ GHz) measured at low-phonon numbers and millikelvin temperatures. Despite the strong parametric drives, we find the cavity-mechanics system in the quantum ground state by performing sideband thermometry measurements. Simultaneously achieving ground-state operation, long mechanical lifetimes, and strong coupling sets the stage for employing silicon electromechanical resonators as memory elements and transducers in hybrid quantum systems, and as a tool for probing the origins of acoustic loss in the quantum regime

Albiglutide and cardiovascular outcomes in patients with type 2 diabetes and cardiovascular disease (Harmony Outcomes): a double-blind, randomised placebo-controlled trial

Background: Glucagon-like peptide 1 receptor agonists differ in chemical structure, duration of action, and in their effects on clinical outcomes. The cardiovascular effects of once-weekly albiglutide in type 2 diabetes are unknown. We aimed to determine the safety and efficacy of albiglutide in preventing cardiovascular death, myocardial infarction, or stroke. Methods: We did a double-blind, randomised, placebo-controlled trial in 610 sites across 28 countries. We randomly assigned patients aged 40 years and older with type 2 diabetes and cardiovascular disease (at a 1:1 ratio) to groups that either received a subcutaneous injection of albiglutide (30–50 mg, based on glycaemic response and tolerability) or of a matched volume of placebo once a week, in addition to their standard care. Investigators used an interactive voice or web response system to obtain treatment assignment, and patients and all study investigators were masked to their treatment allocation. We hypothesised that albiglutide would be non-inferior to placebo for the primary outcome of the first occurrence of cardiovascular death, myocardial infarction, or stroke, which was assessed in the intention-to-treat population. If non-inferiority was confirmed by an upper limit of the 95% CI for a hazard ratio of less than 1·30, closed testing for superiority was prespecified. This study is registered with ClinicalTrials.gov, number NCT02465515. Findings: Patients were screened between July 1, 2015, and Nov 24, 2016. 10 793 patients were screened and 9463 participants were enrolled and randomly assigned to groups: 4731 patients were assigned to receive albiglutide and 4732 patients to receive placebo. On Nov 8, 2017, it was determined that 611 primary endpoints and a median follow-up of at least 1·5 years had accrued, and participants returned for a final visit and discontinuation from study treatment; the last patient visit was on March 12, 2018. These 9463 patients, the intention-to-treat population, were evaluated for a median duration of 1·6 years and were assessed for the primary outcome. The primary composite outcome occurred in 338 (7%) of 4731 patients at an incidence rate of 4·6 events per 100 person-years in the albiglutide group and in 428 (9%) of 4732 patients at an incidence rate of 5·9 events per 100 person-years in the placebo group (hazard ratio 0·78, 95% CI 0·68–0·90), which indicated that albiglutide was superior to placebo (p<0·0001 for non-inferiority; p=0·0006 for superiority). The incidence of acute pancreatitis (ten patients in the albiglutide group and seven patients in the placebo group), pancreatic cancer (six patients in the albiglutide group and five patients in the placebo group), medullary thyroid carcinoma (zero patients in both groups), and other serious adverse events did not differ between the two groups. There were three (<1%) deaths in the placebo group that were assessed by investigators, who were masked to study drug assignment, to be treatment-related and two (<1%) deaths in the albiglutide group. Interpretation: In patients with type 2 diabetes and cardiovascular disease, albiglutide was superior to placebo with respect to major adverse cardiovascular events. Evidence-based glucagon-like peptide 1 receptor agonists should therefore be considered as part of a comprehensive strategy to reduce the risk of cardiovascular events in patients with type 2 diabetes. Funding: GlaxoSmithKline

Frequency Domain Quantum Processing via Four-Wave Mixing

158 pagesOptical photons are excellent flying qubits for future long-distance quantum networks due to negligible decoherence at room temperature. To date, quantum photonic technologies have focused on processing the spatial, temporal and polarization degrees of freedom of light. However, frequency encoding of information has had a profound impact on classical telecommunications, creating mature low-loss fiber-based and integrated photonics hardware that can be exploited to address challenges of scalability in photonic quantum networks. In this dissertation, we use tools from nonlinear optics to realize coherent frequency domain processing of single photons. We use quantum frequency conversion via Bragg scattering four-wave mixing (BS-FWM) to manipulate the spectral and temporal properties of single photons. We use an implementation of BS-FWM that achieves close to unity efficiency and ultra-low noise to develop a powerful toolbox that combines advantages of frequency encoding, fiber and integrated photonic technologies and nonlinear optics for scaling future quantum networks. The first application discussed in this thesis is a frequency-multiplexed single-photon source. Deterministic, high-quality sources of single photons are a crucial requirement for scalable photonic quantum information processing (QIP). The most widely used single-photon sources are based on nonlinear parametric processes that are inherently probabilistic. Active feed-forward switching and multiplexing of such probabilistically generated photons can be used to generate photons on demand if a sufficiently large number of modes are multiplexed. Schemes based on spatial and temporal multiplexing however suffer from prohibitive switching losses that significantly limit their performance. We implemented an alternative scheme based on frequency multiplexing that breaks this limitation. We used BS-FWM as a ‘frequency switch’ to multiplex frequency modes of a broadband probabilistic single-photon source. We demonstrated a 220\% enhancement in single-photon generation rate while maintaining low noise properties ($g^{(2)}$ = 0.07) essential for quantum applications. This approach has a unique potential to create a deterministic source of single photons on a chip-based integrated photonics platform. The next application we discuss is Hong-Ou-Mandel (HOM) interference with photons of distinct colors. In this work, we combine frequency-entangled photons generated on-chip together with Bragg-scattering four-wave mixing (BS-FWM) in fiber to demonstrate frequency-domain HOM interference with 95\% visibility. BS-FWM coherently couples distinct frequency modes while preserving all quantum properties of the input fields and can therefore be used to create an active, tunable ‘frequency beam splitter (FBS)’. We observe a rich two-photon interference pattern including quantum beating, previously observed with cold-atomic systems. Remarkably, we observe high fidelity interference even though the photons propagate for much longer than their mutual coherence time, confirming that this is truly a two-photon interference phenomenon. In addition to fundamental novelty, this work establishes four-wave mixing as a tool for selective, high-fidelity two-photon operations in the frequency domain, which combined with integrated single photon sources provides a building block for frequency multiplexed photonic quantum networks. This demonstration will also enable applications such as frequency domain boson sampling, which we discuss in detail in this dissertation. Finally, we demonstrate a single-photon level time lens with picosecond resolution using BS-FWM. We discuss the conditions under which broadband phase-matching can be achieved with BS-FWM. A time lens draws on space-time duality and imparts a quadratic phase shift on the input signal. With this setup, we achieve a temporal magnification factor of 158 and resolve single-photon level pulses separated by 2.2 ps. Finally, we show that the temporal phase imparted by the BS-FWM pumps can be generalized to realize significantly more complex, unitary operations on broadband temporal modes. In particular, we use numerical optimization via steepest gradient descent to demonstrate temporal mode sorting of field orthogonal but intensity overlapping Hermite-Gaussian temporal modes. These results show that BS-FWM is a powerful tool for temporal mode quantum processing at the single-photon level

Resonance Fluorescence of a Chiral Artificial Atom

We demonstrate a superconducting artificial atom with strong unidirectional coupling to a microwave photonic waveguide. Our artificial atom is realized by coupling a transmon qubit to the waveguide at two spatially separated points with time-modulated interactions. Direction-sensitive interference arising from the parametric couplings in our scheme results in a nonreciprocal response, where we measure a forward/backward ratio of spontaneous emission exceeding 100. We verify the quantum nonlinear behavior of this artificial chiral atom by measuring the resonance fluorescence spectrum under a strong resonant drive and observing well-resolved Mollow triplets. Further, we demonstrate chirality for the second transition energy of the artificial atom and control it with a pulse sequence to realize a qubit-state-dependent nonreciprocal phase on itinerant photons. Our demonstration puts forth a superconducting hardware platform for the scalable realization of several key functionalities pursued within the paradigm of chiral quantum optics, including quantum networks with all-to-all connectivity, driven-dissipative stabilization of many-body entanglement, and the generation of complex nonclassical states of light

Fractional N-Phase Locked Loop using

Abstract: Literature survey of Phase Locked Loop reflects that many researchers have applied different techniques like digital and analog simulation by applying mathematical/logical relations to design the Phase Locked Loop (PLL). Researchers have undertaken different systems, processes or phenomena with regard to design and attempted to find the unknown parameters and analyzed PLL. Since in the real world today VLSI/CMOS is in very much in demand, it is observed that very few researchers have undertaken the work for designing PLL using CMOS/VLSI technology,,after the careful study of reported work. In the proposed work, low power PLL with multiple outputs is designed with stability of system and there are no fractional spurs in the output spectrum of the fractional-N phase locked loop. Keywords-Phase Locked Loop; Sigma-Delta modulation; Frequency Synthesizer; Fractional-N; Phase Noise I