Alternate Scheme for Optical Cluster-State Generation without Number-Resolving Photon Detectors

We design a controlled-phase gate for linear optical quantum computing by using photodetectors that cannot resolve photon number. An intrinsic error-correction circuit corrects errors introduced by the detectors. Our controlled-phase gate has a 1/4 success probability. Recent development in cluster-state quantum computing has shown that a two-qubit gate with non-zero success probability can build an arbitrarily large cluster state with only polynomial overhead. Hence, it is possible to generate optical cluster states without number-resolving detectors and with polynomial overhead.Comment: 10 pages, 4 figures, 4 tables; made significant revisions and changed forma

Two qubits can be entangled in two distinct temperature regions

We have found that for a wide range of two-qubit Hamiltonians the canonical-ensemble thermal state is entangled in two distinct temperature regions. In most cases the ground state is entangled; however we have also found an example where the ground state is separable and there are still two regions. This demonstrates that the qualitative behavior of entanglement with temperature can be much more complicated than might otherwise have been expected; it is not simply determined by the entanglement of the ground state, even for the simple case of two qubits. Furthermore, we prove a finite bound on the number of possible entangled regions for two qubits, thus showing that arbitrarily many transitions from entanglement to separability are not possible. We also provide an elementary proof that the spectrum of the thermal state at a lower temperature majorizes that at a higher temperature, for any Hamiltonian, and use this result to show that only one entangled region is possible for the special case of Hamiltonians without magnetic fields.Comment: 6 pages, 4 figures, many new result

Quantum Computation as Geometry

Quantum computers hold great promise, but it remains a challenge to find efficient quantum circuits that solve interesting computational problems. We show that finding optimal quantum circuits is essentially equivalent to finding the shortest path between two points in a certain curved geometry. By recasting the problem of finding quantum circuits as a geometric problem, we open up the possibility of using the mathematical techniques of Riemannian geometry to suggest new quantum algorithms, or to prove limitations on the power of quantum computers.Comment: 13 Pages, 1 Figur

Oil Market Modelling: A Comparative Analysis of Fundamental and Latent Factor Approaches

International audienceWe formally compare fundamental factor and latent factor approaches to oil price modelling. Fundamental modelling has a long history in seeking to understand oil price movements, while latent factor modelling has a more recent and limited history, but has gained popularity in other financial markets. The two approaches, though competing, have not formally been compared as to effectiveness. For a range of short-medium-and long-dated WTI oil futures we test a recently proposed five-factor fundamental model and a Principal Component Analysis latent factor model. Our findings demonstrate that there is no discernible difference between the two techniques in a dynamic setting. We conclude that this infers some advantages in adopting the latent factor approach due to the difficulty in determining a well specified fundamental model

Motivating student learning

Abstract After more than 20 years in various sales and marketing roles, I have recently changed careers to lecturing business studies subjects within the HETAC framework. I decided to use the opportunity to conduct an action research project to address student engagement and explore strategies to encourage the students to take ownership of the learning by engaging in classroom activities. My concern therefore resulted in the following action research question: ‘If students are encouraged to engage in open discussions regarding the course content, will this motivate them to take ownership of their own learning?’ The methodology applied in this research uses the five phases of Susmans action research model (1983). The five stages includes: diagnosing, action planning, taking action, evaluating, specifying learning and then repeating the process multiple times. I undertook two action research cycles to explore and respond to this question during a six week period which began in March 2011. My students were a small group (9 students) studying their 1st year of a higher certificate course in business studies. Having gathered data from cycle 1 and reflecting upon it, I commenced my second action research cycle responding to the learning and further needs which emerged during cycle 1. During this research I uncovered unexpected issues which are outlined in my findings: for example, differing learning cultures between second and third level education. I expect that the issues uncovered are not unique to my small group of students and other lecturers have had similar experiences and I hope that the recommendations provided in this report will be of use to the reader

Endogenous lysophosphatidic acid (LPA1) receptor agonists demonstrate ligand bias between calcium and ERK signalling pathways in human lung fibroblasts

Background and Purpose Human lung fibroblasts (HLF) express high levels of the LPA1 receptor, a GPCR that responds to the endogenous lipid mediator, lysophosphatidic acid (LPA). Several molecular species or analogues of LPA exist and have been detected in biological fluids such as serum and plasma. The most widely expressed of the LPA receptor family is the LPA1 receptor, which predominantly couples to Gq/11, Gi/o and G12/13 proteins. This promiscuity of coupling raises the possibility that some of the LPA analogues may bias the LPA1 receptor towards one signalling pathway over another. Experimental Approach Here, we have explored the signalling profiles of a range of LPA analogues in HLF that endogenously express the LPA1 receptor. HLF were treated with LPA analogues and receptor activation monitored via calcium mobilization and ERK phosphorylation. Key Results These analyses demonstrated that the 16:0, 17:0, 18:2 and C18:1 LPA analogues appear to exhibit ligand bias between ERK phosphorylation and calcium mobilization when compared with 18:1 LPA, one of the most abundant forms of LPA that has been found in human plasma. Conclusion and Implications The importance of LPA as a key signalling molecule is shown by its widespread occurrence in biological fluids and its association with disease conditions such as fibrosis and cancer. These findings have important, as yet unexplored, implications for the (patho-) physiological signalling of the LPA1 receptor, as it may be influenced not only by the concentration of endogenous ligand but the isoform as well

A high-frequency analysis of price resolution and pricing barriers in equities on the adoption of a new currency

We use ultra high frequency (trade by trade) data to demonstrate that equity price clustering and pricing predictability around psychologically important prices in Greece switches away from drachma-focused with the introduction of the euro, but does not immediately switch to euroclustering. The change in trader price focus around the euro introduction addresses an open debate in the clustering literature on whether the presence of clustering is a bias related to the current prices or anchoring to past prices. Our findings of a decline in drachma clustering, but lack of switch to euro effects supports the case for clustering being a trading feature that is slow to transfer to new pricing regimes. A key advantage of the ultra high frequency dataset is we arealso able to demonstrate the presence of psychological pricing barriers related to each currency that are not detectable in daily data