Exploring the limits of multiplexed photon-pair sources for the preparation of pure single-photon states

Current sources of heralded single photons based on nonlinear optics operate in a probabilistic manner. In order to build quantum-enhanced devices based around the use of single photons, compact, turn-key and deterministic sources are required. A possible solution is to multiplex a number of sources to increase the single-photon generation probability and in so doing reducing the waiting time to deliver large numbers of photons simultaneously, from independent sources. Previously it has been shown that, in the ideal case, 17 multiplexed sources allow deterministic generation of heralded single photons [Christ and Silberhorn, Phys. Rev. A 85, 023829 (2012)]. Here we extend this analysis to include undesirable effects of detector inefficiency and photon loss on a number of multiplexed sources using a variety of different detectors for heralding. We compare these systems for fixed signal-to-noise ratio to allow a direct comparison of performance for real- world heralded single photon sources.Comment: 10 pages, 7 figures. Equation 18 changed to include power of a half in the binomial facto

Temporal Loop Multiplexing: A resource efficient scheme for multiplexed photon-pair sources

Single photons are a vital resource for photonic quantum information processing. However, even state-of-the-art single photon sources based on photon-pair generation and heralding detection have only a low probability of delivering a single photon when one is requested. We analyse a scheme that uses a switched fibre delay loop to increase the delivery probability per time bin of single photons from heralded sources. We show that, for realistic experimental parameters, combining the output of up to 15 pulses can yield a performance improvement of a factor of 10. We consider the future performance of this scheme with likely component improvements.Comment: 5 pages, 4 figure

Cyclic fatigue damage characteristics observed for simple loadings extended to multiaxial life prediction

Fully reversed uniaxial strain controlled fatigue tests were performed on smooth cylindrical specimens made of 304 stainless steel. Fatigue life data and cracking observations for uniaxial tests were compared with life data and cracking behavior observed in fully reversed torsional tests. It was determined that the product of maximum principle strain amplitude and maximum principle stress provided the best correlation of fatigue lives for these two loading conditions. Implementation of this parameter is in agreement with observed physical damage and it accounts for the variation of stress-strain response, which is unique to specific loading conditions. Biaxial fatigue tests were conducted on tubular specimens employing both in-phase and out-of-phase tension torsion cyclic strain paths. Cracking observations indicated that the physical damage which occurred in the biaxial tests was similar to the damage observed in uniaxial and torsional tests. The Smith, Watson, and Topper parameter was then extended to predict the fatigue lives resulting from the more complex loading conditions

Disability and Skill Mismatch

This paper integrates two strands of literature on overskilling and disability using the 2004 British Workplace Employment Relations Survey (WERS). It finds that the disabled are significantly more likely to be mismatched in the labour market, to suffer from a pay penalty and to have lower job satisfaction, the effects being stronger for the work-limited disabled. Giving workers more discretion over how they perform their work would significantly reduce these negative effects.skills, disability, job matching, earnings, job satisfaction

Acoustofluidics 9: Modelling and applications of planar resonant devices for acoustic particle manipulation

This article introduces the design, construction and applications of planar resonant devices for particle and cell manipulation. These systems rely on the pistonic action of a piezoelectric layer to generate a one dimensional axial variation in acoustic pressure through a system of acoustically tuned layers. The resulting acoustic standing wave is dominated by planar variations in pressure causing particles to migrate to planar pressure nodes (or antinodes depending on particle and fluid properties). The consequences of lateral variations in the fields are discussed, and rules for designing resonators with high energy density within the appropriate layer for a given drive voltage presente

Efficient Hamiltonian programming in qubit arrays with nearest-neighbour couplings

We consider the problem of selectively controlling couplings in a practical quantum processor with always-on interactions that are diagonal in the computational basis, using sequences of local NOT gates. This methodology is well-known in NMR implementations, but previous approaches do not scale efficiently for the general fully-connected Hamiltonian, where the complexity of finding time-optimal solutions makes them only practical up to a few tens of qubits. Given the rapid growth in the number of qubits in cutting-edge quantum processors, it is of interest to investigate the applicability of this control scheme to much larger scale systems with realistic restrictions on connectivity. Here we present an efficient scheme to find near time-optimal solutions that can be applied to engineered qubit arrays with local connectivity for any number of qubits, indicating the potential for practical quantum computing in such systems.Comment: 5 pages, 5 figures. Shortened and clarified from previous versio