4,195 research outputs found
Sequential modular position and momentum measurements of a trapped ion mechanical oscillator
The non-commutativity of position and momentum observables is a hallmark
feature of quantum physics. However this incompatibility does not extend to
observables which are periodic in these base variables. Such modular-variable
observables have been suggested as tools for fault-tolerant quantum computing
and enhanced quantum sensing. Here we implement sequential measurements of
modular variables in the oscillatory motion of a single trapped ion, using
state-dependent displacements and a heralded non-destructive readout. We
investigate the commutative nature of modular variable observables by
demonstrating no-signaling-in-time between successive measurements, using a
variety of input states. In the presence of quantum interference, which we
enhance using squeezed input states, measurements of different periodicity show
signaling-in-time. The sequential measurements allow us to extract two-time
correlators for modular variables, which we use to violate a Leggett-Garg
inequality. The experiments involve control and coherence of multi-component
superpositions of up to 8 coherent, squeezed or Fock state wave-packets.
Signaling-in-time as well as Leggett-Garg inequalities serve as efficient
quantum witnesses which we probe here with a mechanical oscillator, a system
which has a natural crossover from the quantum to the classical regime.Comment: 6 pages, 3 figures and supplemental informatio
Bell measurements as a witness of a dualism in entanglement
We show how a property of dualism, which can exist in the entanglement of
identical particles, can be tested in the usual photonic Bell measurement
apparatus with minor modifications. Two different sets of coincidence
measurements on the same experimental setup consisting of a Hong-Ou-Mandel
interferometer demonstrate how the same two-photon state can emerge
entanglement in the polarization or the momentum degree of freedom depending on
the dynamical variables used for labeling the particles. Our experiment
demonstrates how the same source can be used as both a polarization entangled
state, as well as a dichotomic momentum entangled state shared between distant
users Alice and Bob in accordance to which sets of detectors they access. When
the particles become distinguishable by letting the information about one of
the variables to be imprinted in yet another (possibly inaccessible) system or
degree of freedom, the feature of dualism is expected to vanish. We verify this
feature by polarization decoherence (polarization information in environment)
or arrival time difference, which both respectively destroy one of the dual
forms of entanglement.Comment: 5 pages, 4 figure
Pulsed force sequences for fast phase-insensitive quantum gates in trapped ions
We show how to create quantum gates of arbitrary speed between trapped ions,
using a laser walking wave, with complete insensitivity to drift of the optical
phase, and requiring cooling only to the Lamb-Dicke regime. We present pulse
sequences that satisfy the requirements and are easy to produce in the
laboratory.Comment: 11 pages, 3 figure
A review of knowledge: inter-row hoeing & its associated agronomy in organic cereal & pulse crops
The aim of this project was to establish the âstate of the artâ for inter-row hoeing and its associated agronomic practices in organic cereal and pulse crops. To achieve this a detailed review of literature was undertaken.
âą To facilitate inter-row cultivation in cereal and pulse crops, some adjustment of row spacing may be required. For cereals, drilling crops in 25 cm rows can reduce yield compared with normal drilling practice, primarily due to greater intra-specific competition amongst the crop (i.e. competition between crop plants).
âą The yield penalty resulting from widely spaced crop rows can be minimised using a number of approaches, depending on the drill:
1. Reducing the seed rate in widely spaced crop rows can help to minimise excessive intra-specific competition.
2. Band sowing the crop in wide rows can also help to minimise intra-specific competition as the seed is distributed over a greater area.
3. Using a twin-row arrangement can completely overcome the yield penalty.
âą The recommended row spacing for peas (up to 20 cm) and beans (up to 35 cm) does not require any further adjustment for inter-row hoeing.
âą Recent developments in automated guidance of inter-row hoeing equipment mean that weeding operations can now be conducted a much higher speeds (10 km h-1). This has highlighted the limitations of some of the cultivators currently used (e.g. âAâ blades), as excessive soil throw can occur at this high speed. Rolling cultivators may prove to be the most suitable at high forward speeds. For manually guided hoes working at slower speeds (5 km h-1), âAâ and âLâ blades offer an effective low cost solution.
âą In terms of the timing of inter-row hoeing, it is suggested that weeding operations should be conducted at an early stage in the growing season, as the weeds that emerge with or shortly after the crop are the ones that pose the most significant threat for crop yield. Weeding on two occasions can provide better levels of weed control than weeding once, but weeding more frequently offered little additional benefit. Reductions of weed biomass of up to 99 % have been reported as a result of inter-row hoeing, although this has not always resulted in a positive crop yield response. This is probably due to crop damage resulting from inaccurate hoeing, a problem that can be overcome with automated guidance.
âą There is some evidence to suggest that mechanical weeding operations can mineralise soil bound nitrogen.
âą The impact of inter-row hoeing on ground nesting birds is uncertain. Early indications suggest that skylarks prefer to nest directly adjacent to or in the crop row rather than between rows.
The information contained within this review should enable farmers to make best use of inter-row hoeing in their arable crops.
There are a number of areas that require further research and development:
âą The interaction of seed rate and row spacing needs to be confirmed in organic systems.
âą Relatively little is known about the mechanisms of weed kill and the detailed interaction between the cultivator blade, the weed and the soil. This is particularly important with the new automated guidance equipment that allows weeding at high forward speeds.
âą The timing and frequency of inter-row hoeing has received very little attention. The optimum weed control timings are based on small-plot crop:weed competition studies and need to be verified under field scale management with inter-row hoeing equipment.
âą Finally, the impact of inter-row hoeing and widely spaced crop rows on ground-nesting birds has not been looked at directly, but is of importance.
Please see the main report for a more detailed summary before the full text
Quantum control of the motional states of trapped ions through fast switching of trapping potentials
We propose a new scheme for supplying voltages to the electrodes of
microfabricated ion traps, enabling access to a regime in which changes to the
trapping potential are made on timescales much shorter than the period of the
secular oscillation frequencies of the trapped ions. This opens up
possibilities for speeding up the transport of ions in segmented ion traps and
also provides access to control of multiple ions in a string faster than the
Coulomb interaction between them. We perform a theoretical study of ion
transport using these methods in a surface-electrode trap, characterizing the
precision required for a number of important control parameters. We also
consider the possibilities and limitations for generating motional state
squeezing using these techniques, which could be used as a basis for
investigations of Gaussian-state entanglement.Comment: Accepted by New Journal of Physic
Les groupes de femmes : outils de changement personnel et de développement
Cet article traite des groupes de femmes axĂ©s sur le partage du vĂ©cu, la rĂ©solution de problĂšmes ou la croissance personnelle. On y retrouve les groupes de thĂ©rapie/croissance animĂ©s par des intervenantes fĂ©ministes, les groupes axĂ©s sur le soutien et l'aide mutuelle entre les membres et ceux qui ajoutent, Ă l'une ou l'autre de ces orientations, un objectif de conscientisation. Parmi les obstacles que ces groupes peuvent rencontrer, on retrouve la difficultĂ© de concilier le soutien et le dĂ©fi ainsi que l'autonomie et la dĂ©pendance, de mĂȘme que certains problĂšmes reliĂ©s au choix d'un leadership appropriĂ©, au rythme de changement Ă adopter ainsi qu'aux diffĂ©rences culturelles entre les membres. Pour surmonter ces obstacles, il faut faire face aux contradictions entre l'idĂ©ologie fĂ©ministe et la rĂ©alitĂ© quotidienne des femmes, et accorder une attention particuliĂšre Ă la planification des groupes
Evaluating On-Farm Biodiversity: A Comparison of Assessment Methods
Strategies to stop the loss of biodiversity in agriculture areas will be more successful if farmers have the means to understand changes in biodiversity on their farms and to assess the effectiveness of biodiversity promoting measures. There are several methods to assess on-farm biodiversity but it may be difficult to select the most appropriate method for a farmerâs individual circumstances. This study aims to evaluate the usability and usefulness of four biodiversity assessment methods that are available to farmers in Switzerland. All four methods were applied to five case study farms, which were ranked according to the results. None of the methods were able to provide an exact statement on the current biodiversity status of the farms, but each method could provide an indication, or approximation, of one or more aspects of biodiversity. However, the results also showed that it is possible to generate different statements on the state of biodiversity on the same farms by using different biodiversity assessment methods. All methods showed strengths and weaknesses so, when choosing a method, the purpose of the biodiversity assessment should be kept in the foreground and the limitations of the chosen methods should be considered when interpreting the outcomes
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