Effects of self-phase modulation on weak nonlinear optical quantum gates

A possible two-qubit gate for optical quantum computing is the parity gate based on the weak Kerr effect. Two photonic qubits modulate the phase of a coherent state, and a quadrature measurement of the coherent state reveals the parity of the two qubits without destroying the photons. This can be used to create so-called cluster states, a universal resource for quantum computing. Here, the effect of self-phase modulation on the parity gate is studied, introducing generating functions for the Wigner function of a modulated coherent state. For materials with non-EIT-based Kerr nonlinearities, there is typically a self-phase modulation that is half the magnitude of the cross-phase modulation. Therefore, this effect cannot be ignored. It is shown that for a large class of physical implementations of the phase modulation, the quadrature measurement cannot distinguish between odd and even parity. Consequently, weak nonlinear parity gates must be implemented with physical systems where the self-phase modulation is negligable.Comment: 7 pages, 4 figure

Applications of atomic ensembles in distributed quantum computing

Thesis chapter. The fragility of quantum information is a fundamental constraint faced by anyone trying to build a quantum computer. A truly useful and powerful quantum computer has to be a robust and scalable machine. In the case of many qubits which may interact with the environment and their neighbors, protection against decoherence becomes quite a challenging task. The scalability and decoherence issues are the main difficulties addressed by the distributed model of quantum computation. A distributed quantum computer consists of a large quantum network of distant nodes - stationary qubits which communicate via flying qubits. Quantum information can be transferred, stored, processed and retrieved in decoherence-free fashion by nodes of a quantum network realized by an atomic medium - an atomic quantum memory. Atomic quantum memories have been developed and demonstrated experimentally in recent years. With the help of linear optics and laser pulses, one is able to manipulate quantum information stored inside an atomic quantum memory by means of electromagnetically induced transparency and associated propagation phenomena. Any quantum computation or communication necessarily involves entanglement. Therefore, one must be able to entangle distant nodes of a distributed network. In this article, we focus on the probabilistic entanglement generation procedures such as well-known DLCZ protocol. We also demonstrate theoretically a scheme based on atomic ensembles and the dipole blockade mechanism for generation of inherently distributed quantum states so-called cluster states. In the protocol, atomic ensembles serve as single qubit systems. Hence, we review single-qubit operations on qubit defined as collective states of atomic ensemble. Our entangling protocol requires nearly identical single-photon sources, one ultra-cold ensemble per physical qubit, and regular photodetectors. The general entangling procedure is presented, as well as a procedure that generates in a single step Q-qubit GHZ states with success probability p(success) similar to eta(Q/2), where eta is the combined detection and source efficiency. This is signifcantly more efficient than any known robust probabilistic entangling operation. The GHZ states form the basic building block for universal cluster states, a resource for the one-way quantum computer

Transaction Costs and Cattle Farmers' Choice of Marketing Channels in North-Central Namibia

About 70% of the Namibian population depends on agricultural activities for their livelihood. Moreover, agriculture remains an important sector to Namibia because its national economy is widely dependent on agricultural production. Cattle producers in the Northern Communal Areas (NCAs) have an option to market their cattle via the formal or informal markets. Efforts have been made to encourage producers to market their cattle through the formal market; however, limited improvement has been observed. In this study a number of factors have been analysed to determine its influences on cattle marketing decisions. Factors influencing the marketing decision of whether or not to sell through the formal market are analysed using the Probit model. Factors influencing the proportion of cattle sold through the formal market on condition that a producer uses the formal markets to sell cattle are analysed with the Truncated model. Testing the Tobit model against the alternative of a two-part model is done using Cragg’s model. Empirical results revealed that problems with transport to MeatCo, improved productivity, accessibility to market-related information and access to new information technology, are some factors significantly affecting the decision of whether or not to sell through the formal market. Payment arrangements by MeatCo, animal handling, accessibility to new information technology, age of respondents and lack of access to marketing expertise, are some factors influencing the proportional number of cattle sold through the formal market. The results suggest that substantially more information is obtained by modelling cattle marketing behaviour as a two decision-making instead of a single decision-making framework.Cattle marketing, decision-making, formal markets, transaction costs, Livestock Production/Industries,

A Stochastic Budgeting Analysis of Three Alternative Scenarios to Convert from Beef-Cattle Farming to Game Ranching

The main objective of this paper is to evaluate the profitability and financial feasibility of three alternative scenarios to convert from beef-cattle farming to game ranching. The analyses acknowledge the importance of quantifying the probability of failure or success when making investment decisions. Risk is incorporated into a standard net present value analysis using risk simulation. De-trended historical auction prices of live game and on-the-hoof prices of weaner cattle were used to quantify price variability. The stochastic net present value analyses indicate that game ranching is more profitable than cattle farming. Although an investment in a limited number of common game species is financially feasible, the cash flow analysis indicates a decreasing probability of making more money with game when annual cash flows are compared to those generated by means of cattle farming. Both the high-value game species scenarios are financially unfeasible during the first five years. These infeasibilities stem from a high probability of not covering instalments to finance game purchases, the extent to which these instalments are not covered, and the high probability of shortfalls in consecutive years.Game ranching, profitability, financial feasibility, risk simulation, Agricultural Finance, Farm Management, Livestock Production/Industries,

A logic for model-checking of mean-field models

Recently, many systems consisting of a large number of interacting objects were analysed using the mean-field method, which has only been used for performance evaluation. In this short paper, we apply it to model checking. We define logic, which allows to describe the overall properties of the large system

Habitual accountability routines in the boardroom: How boards balance control and collaboration

open3siCorporate accountability is a complex chain of reporting that reaches from external stakeholders into the organization’s management structure. The transition from external to internal accountability mechanisms primarily occurs at the board of directors. Yet outside of incentive mechanisms, we know surprisingly little about how internal actors (management) are held to account by the representatives of external shareholders (the board). This paper explores the process of accountability at this transition point by documenting the routines used by boards to hold the firm’s management to account. In so doing we develop our understanding of the important transition between internal and external firm accountability.embargoed_20190401Nicholson, Gavin; Pugliese, Amedeo; Bezemer, Pieter JanNicholson, Gavin; Pugliese, Amedeo; Bezemer, Pieter Ja