Entanglement decoherence in a gravitational well according to the event formalism

The event formalism is a non-linear extension of quantum field theory designed to be compatible with the closed time-like curves that appear in general relativity. Whilst reducing to standard quantum field theory in flat space-time the formalism leads to testably different predictions for entanglement distribution in curved space. In this paper we introduce a more general version of the formalism and use it to analyse the practicality of an experimental test of its predictions in the earth's gravitational well

Optical Quantum Computation

We review the field of Optical Quantum Computation, considering the various implementations that have been proposed and the experimental progress that has been made toward realizing them. We examine both linear and nonlinear approaches and both particle and field encodings. In particular we discuss the prospects for large scale optical quantum computing in terms of the most promising physical architectures and the technical requirements for realizing them

High-Fidelity Z-Measurement Error Correction of Optical Qubits

We demonstrate a quantum error correction scheme that protects against accidental measurement, using an encoding where the logical state of a single qubit is encoded into two physical qubits using a non-deterministic photonic CNOT gate. For the single qubit input states |0>, |1>, |0>+|1>, |0>-|1>, |0>+i|1>, and |0>-i|1> our encoder produces the appropriate 2-qubit encoded state with an average fidelity of 0.88(3) and the single qubit decoded states have an average fidelity of 0.93(5) with the original state. We are able to decode the 2-qubit state (up to a bit flip) by performing a measurement on one of the qubits in the logical basis; we find that the 64 1-qubit decoded states arising from 16 real and imaginary single qubit superposition inputs have an average fidelity of 0.96(3).Comment: 4 pages, 4 figures, comments welcom

The impacts for stone curlews of increased traffic on the A11. Model and predictions

Stone curlew nest density in the Breckland region of Eastern England was shown to be negatively related to ‘nearby’ housing density and ‘nearby’ trunk road traffic (based on new traffic data for the period 1988-2006). However, no statistically significant additional relationship with non-trunk A-road traffic could be detected. We recommend using the statistical modelling predictions in the report Table 5 as the best currently available estimates of the potential effect of a 70% increase in A11 average daily (March-August)two-way traffic above the average All traffic levels in 2002-06. The predicted effect of a 70% increase in A11 traffic is for a reduction from current observed nest numbers on suitable arable land of 3.7% with no changes in housing density or 4.9% when combined with the predicted effect of housing options. A reduction of 7.3% is predicted for semi-natural grassland and SSSI habitats. Taking both semi-natural grassland/SSSI and arable habitats together, the observed total average nest numbers for the period 2002-2006 was 221.4, and the prediction following a 70% increase in traffic on the A11 is 210.8, a reduction of 10.6 nests (4.8%)

Conditional two mode squeezed vacuum teleportation

We show, by making conditional measurements on the Einstein-Podolsky-Rosen (EPR) squeezed vacuum, that one can improve the efficacy of teleportation for both the position difference, momentum sum and number difference, phase sum continuous variable teleportation protocols. We investigate the relative abilities of the standard and conditional EPR states, and show that by conditioning we can improve the fidelity of teleportation of coherent states from below to above the $\bar{F} = 2/3$ boundary.Comment: 18 pages, RevTeX4, 10 figures postscrip

Loophole-free Bell test based on local precertification of photon's presence

A loophole-free violation of Bell inequalities is of fundamental importance for demonstrating quantum nonlocality and long-distance device-independent secure communication. However, transmission losses represent a fundamental limitation for photonic loophole-free Bell tests. A local precertification of the presence of the photons immediately before the local measurements may solve this problem. We show that local precertification is feasible by integrating three current technologies: (i) enhanced single-photon down-conversion to locally create a flag photon, (ii) nanowire-based superconducting single-photon detectors for a fast flag detection, and (iii) superconducting transition-edge sensors to close the detection loophole. We carry out a precise space-time analysis of the proposed scheme, showing its viability and feasibility.Comment: REVTeX4, 7 Pages, 1 figur

Quantum Computation with Coherent States, Linear Interactions and Superposed Resources

We show that quantum computation circuits with coherent states as the logical qubits can be constructed using very simple linear networks, conditional measurements and coherent superposition resource states

Guidance and Control in a Josephson Charge Qubit

In this paper we propose a control strategy based on a classical guidance law and consider its use for an example system: a Josephson charge qubit. We demonstrate how the guidance law can be used to attain a desired qubit state using the standard qubit control fields.Comment: 9 pages, 5 figure

Quantum Sampling Problems, BosonSampling and Quantum Supremacy

There is a large body of evidence for the potential of greater computational power using information carriers that are quantum mechanical over those governed by the laws of classical mechanics. But the question of the exact nature of the power contributed by quantum mechanics remains only partially answered. Furthermore, there exists doubt over the practicality of achieving a large enough quantum computation that definitively demonstrates quantum supremacy. Recently the study of computational problems that produce samples from probability distributions has added to both our understanding of the power of quantum algorithms and lowered the requirements for demonstration of fast quantum algorithms. The proposed quantum sampling problems do not require a quantum computer capable of universal operations and also permit physically realistic errors in their operation. This is an encouraging step towards an experimental demonstration of quantum algorithmic supremacy. In this paper, we will review sampling problems and the arguments that have been used to deduce when sampling problems are hard for classical computers to simulate. Two classes of quantum sampling problems that demonstrate the supremacy of quantum algorithms are BosonSampling and IQP Sampling. We will present the details of these classes and recent experimental progress towards demonstrating quantum supremacy in BosonSampling.Comment: Survey paper first submitted for publication in October 2016. 10 pages, 4 figures, 1 tabl