1,216 research outputs found
Optimizing optical Bragg scattering for single-photon frequency conversion
We develop a systematic theory for optimising single-photon frequency
conversion using optical Bragg scattering. The efficiency and phase-matching
conditions for the desired Bragg scattering conversion as well as spurious
scattering and modulation instability are identified. We find that third-order
dispersion can suppress unwanted processes, while dispersion above the fourth
order limits the maximum conversion efficiency. We apply the optimisation
conditions to frequency conversion in highly nonlinear fiber, silicon nitride
waveguides and silicon nanowires. Efficient conversion is confirmed using full
numerical simulations. These design rules will assist the development of
efficient quantum frequency conversion between multicolour single photon
sources for integration in complex quantum networks.Comment: 9 pages, 14 figure
An All Optical Fibre Quantum Controlled-NOT Gate
We report the first experimental demonstration of an optical controlled-NOT
gate constructed entirely in fibre. We operate the gate using two heralded
optical fibre single photon sources and find an average logical fidelity of 90%
and an average process fidelity of 0.83<F<0.91. On the basis of a simple model
we are able to conclude that imperfections are primarily due to the photon
sources, meaning that the gate itself works with very high fidelity.Comment: 4 pages, 4 figures, comments welcom
Hybrid photonic circuit for multiplexed heralded single photons
A key resource for quantum optics experiments is an on-demand source of
single and multiple photon states at telecommunication wavelengths. This letter
presents a heralded single photon source based on a hybrid technology approach,
combining high efficiency periodically poled lithium niobate waveguides,
low-loss laser inscribed circuits, and fast (>1 MHz) fibre coupled
electro-optic switches. Hybrid interfacing different platforms is a promising
route to exploiting the advantages of existing technology and has permitted the
demonstration of the multiplexing of four identical sources of single photons
to one output. Since this is an integrated technology, it provides scalability
and can immediately leverage any improvements in transmission, detection and
photon production efficiencies.Comment: 5 pages, double column, 3 figure
Ultra-compact optical auto-correlator based on slow-light enhanced third harmonic generation in a silicon photonic crystal waveguide
The ability to use coherent light for material science and applications is
directly linked to our ability to measure short optical pulses. While
free-space optical methods are well-established, achieving this on a chip would
offer the greatest benefit in footprint, performance, flexibility and cost, and
allow the integration with complementary signal processing devices. A key goal
is to achieve operation at sub-Watt peak power levels and on sub-picosecond
timescales. Previous integrated demonstrations require either a temporally
synchronized reference pulse, an off-chip spectrometer, or long tunable delay
lines. We report the first device capable of achieving single-shot time-domain
measurements of near-infrared picosecond pulses based on an ultra-compact
integrated CMOS compatible device, with the potential to be fully integrated
without any external instrumentation. It relies on optical third-harmonic
generation in a slow-light silicon waveguide. Our method can also serve as a
powerful in-situ diagnostic tool to directly map, at visible wavelengths, the
propagation dynamics of near-infrared pulses in photonic crystals.Comment: 20 pages, 6 figures, 38 reference
Integrated spatial multiplexing of heralded single photon sources
The non-deterministic nature of photon sources is a key limitation for single
photon quantum processors. Spatial multiplexing overcomes this by enhancing the
heralded single photon yield without enhancing the output noise. Here the
intrinsic statistical limit of an individual source is surpassed by spatially
multiplexing two monolithic silicon correlated photon pair sources,
demonstrating a 62.4% increase in the heralded single photon output without an
increase in unwanted multi-pair generation. We further demonstrate the
scalability of this scheme by multiplexing photons generated in two waveguides
pumped via an integrated coupler with a 63.1% increase in the heralded photon
rate. This demonstration paves the way for a scalable architecture for
multiplexing many photon sources in a compact integrated platform and achieving
efficient two photon interference, required at the core of optical quantum
computing and quantum communication protocols.Comment: 10 pages, 3 figures, comments welcom
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An Extended Culture System that Supports Human Primordial Germ Cell-like Cell Survival and Initiation of DNA Methylation Erasure.
The development of an in vitro system in which human primordial germ cell-like cells (hPGCLCs) are generated from human pluripotent stem cells (hPSCs) has been invaluable to further our understanding of human primordial germ cell (hPGC) specification. However, the means to evaluate the next fundamental steps in germ cell development have not been well established. In this study we describe a two dimensional extended culture system that promotes proliferation of specified hPGCLCs, without reversion to a pluripotent state. We demonstrate that hPGCLCs in extended culture undergo partial epigenetic reprogramming, mirroring events described in hPGCs in vivo, including a genome-wide reduction in DNA methylation and maintenance of depleted H3K9me2. This extended culture system provides a new approach for expanding the number of hPGCLCs for downstream technologies, including transplantation, molecular screening, or possibly the differentiation of hPGCLCs into gametes by in vitro gametogenesis
Willingness of Private Physicians to Be Involved in Smallpox Preparedness and Response Activities
Background. The public health system continues its efforts to prepare for bioterrorist events, such as a smallpox outbreak, but may need to call on other health professionals to ensure sufficient capacity to implement preparedness plans. Objective. The goal was to understand the willingness of primary care physicians to participate in possible smallpox pre- or post-event activities. Methods. A 23-question mail survey was sent to a national random sample of 727 internists and 720 family physicians. After three mailings, a one-page version of the survey was sent to nonrespondents. Results. Response rates were 26% for questions common to both surveys and 22% for questions on the longer survey only. Respondents to the survey expressed moderate support for participating in certain smallpox pre- and post-event activities. Under a pre-event scenario, many providers would be willing to vaccinate first responders in their practice, and roughly one-third would be willing to vaccinate patients in their practice or to work in a public health clinic as a vaccinator. Most physicians, however, would be unwilling to be vaccinated themselves. Under post-event conditions, most providers would be willing to vaccinate their own patients, and many would vaccinate other community members in their practice. Conclusions. Despite the low response rate, information from this study on the smallpox preparedness activities in which physicians are most willing to participate can help to inform efforts by public health officials and private physicians to collaborate on bioterrorism preparedness efforts.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/63165/1/bsp.2005.3.16.pd
Intrinsically narrowband pair photon generation in microstructured fibres
In this paper we study the tailoring of photon spectral properties generated
by four-wave mixing in a birefringent photonic crystal fibre (PCF). The aim is
to produce intrinsically narrow-band photons and hence to achieve high
non-classical interference visibility and generate high fidelity entanglement
without any requirement for spectral filtering, leading to high effective
detection efficiencies. We show unfiltered Hong-Ou-Mandel interference
visibilities of 77% between photons from the same PCF, and 80% between separate
sources. We compare results from modelling the PCF to these experiments and
analyse photon purities.Comment: 23 pages, 17 figures, Comments Welcom
Money, Well-Being, and Loss Aversion: Does an Income Loss Have a Greater Effect on Well-Being Than an Equivalent Income Gain?
Higher income is associated with greater well-being, but do income gains and losses affect well-being differently? Loss aversion, whereby losses loom larger than gains, is typically examined in relation to decisions about anticipated outcomes. Here, using subjective-well-being data from Germany (N = 28,723) and the United Kingdom (N = 20,570), we found that losses in income have a larger effect on well-being than equivalent income gains and that this effect is not explained by diminishing marginal benefits of income to well-being. Our findings show that loss aversion applies to experienced losses, challenging suggestions that loss aversion is only an affective-forecasting error. By failing to account for loss aversion, longitudinal studies of the relationship between income and well-being may have overestimated the positive effect of income on well-being. Moreover, societal well-being might best be served by small and stable income increases, even if such stability impairs long-term income growth
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