Long Distance Entanglement Generation in 2D Networks

We consider 2D networks composed of nodes initially linked by two-qubit mixed states. In these networks we develop a global error correction scheme that can generate distance-independent entanglement from arbitrary network geometries using rank two states. By using this method and combining it with the concept of percolation we also show that the generation of long distance entanglement is possible with rank three states. Entanglement percolation and global error correction have different advantages depending on the given situation. To reveal the trade-off between them we consider their application on networks containing pure states. In doing so we find a range of pure-state schemes, each of which has applications in particular circumstances: For instance, we can identify a protocol for creating perfect entanglement between two distant nodes. However, this protocol can not generate a singlet between any two nodes. On the other hand, we can also construct schemes for creating entanglement between any nodes, but the corresponding entanglement fidelity is lower.Comment: 10 pages, 9 figures, 1 tabl

Online interactive assessment with short free-text questions and tailored feedback

A linguistically based authoring tool has been used to write e-assessment questions requiring short free-text answers of up to about 20 words in length (typically a single sentence). The answer matching is sophisticated and students are provided with instantaneous targeted feedback on incorrect and incomplete responses. They are able to use this feedback in reattempting the question. Seventy-five questions of this type have been offered to students on an entry-level interdisciplinary science module and they have been well received. Students have been observed attempting the questions and have been seen to respond in differing ways to both the questions themselves and the feedback provided. The answer matching has been demonstrated to be of similar or greater accuracy than specialist human markers. The software described is all either open source or commercially available, but the purpose of this paper is not to advertise these products but rather to encourage reflection on e-assessment's potential to support student learning

Singlet Generation in Mixed State Quantum Networks

We study the generation of singlets in quantum networks with nodes initially sharing a finite number of partially entangled bipartite mixed states. We prove that singlets between arbitrary nodes in such networks can be created if and only if the initial states connecting the nodes have a particular form. We then generalize the method of entanglement percolation, previously developed for pure states, to mixed states of this form. As part of this, we find and compare different distillation protocols necessary to convert groups of mixed states shared between neighboring nodes of the network into singlets. In addition, we discuss protocols that only rely on local rules for the efficient connection of two remote nodes in the network via entanglement swapping. Further improvements of the success probability of singlet generation are developed by using particular forms of `quantum preprocessing' on the network. This includes generalized forms of entanglement swapping and we show how such strategies can be embedded in regular and hierarchical quantum networks.Comment: 17 pages, 21 figure

The Optical Excitation of Zigzag Carbon Nanotubes with Photons Guided in Nanofibers

We consider the excitation of electrons in semiconducting carbon nanotubes by photons from the evanescent field created by a subwavelength-diameter optical fiber. The strongly changing evanescent field of such nanofibers requires dropping the dipole approximation. We show that this leads to novel effects, especially a high dependence of the photon absorption on the relative orientation and geometry of the nanotube-nanofiber setup in the optical and near infrared domain. In particular, we calculate photon absorption probabilities for a straight nanotube and nanofiber depending on their relative angle. Nanotubes orthogonal to the fiber are found to perform much better than parallel nanotubes when they are short. As the nanotube gets longer the absorption of parallel nanotubes is found to exceed the orthogonal nanotubes and approach 100% for extremely long nanotubes. In addition, we show that if the nanotube is wrapped around the fiber in an appropriate way the absorption is enhanced. We find that optical and near infrared photons could be converted to excitations with efficiencies that may exceed 90%. This may provide opportunities for future photodetectors and we discuss possible setups.Comment: 14 pages, 14 figure

Excitation of N2 and N2/+/ band systems by electrons. 1 - Absolute transition probabilities

Absolute transition probabilities for neutral and ionic molecular nitroge

Excitation of N2 and N2/+/ systems by electrons. 2 - Excitation cross sections and N2 1PG low pressure afterglow

Characteristics of Meinel systems excited by electrons and measurement of transition probabilities, excitation cross sections, and afterglow effect

Letter to Charles Adams regarding the North Carolina Library Association, September 23, 1963

A letter from Winston Broadfoot to Charles Adams regarding a report on the activities of the North Carolina Library Association Constitution and Bylaws Committee

Letter to Andy Orr regarding the North Carolina Library Association Constitution and Bylaws Committee, March 3, 1963

A letter from Winston Broadfoot to Andy Orr regarding changes and additions to the Constitution and Bylaws of the North Carolina Library Association

Letter to Carlton West regarding the North Carolina Library Association Constitution and Bylaws Committee, February 20, 1963

A letter from Winston Broadfoot to Carlton West regarding the activities and proposed meeting of the North Carolina Library Association Constitution and Bylaws Committee

Letter to Elizabeth Hughey regarding the Constitution and Bylaws of the North Carolina Library Association, September 4, 1961

A letter from Winston Broadfoot to Elizabeth Hughey regarding the Constitution and Bylaws of the North Carolina Library Association