The entanglement beam splitter: a quantum-dot spin in a double-sided optical microcavity

We propose an entanglement beam splitter (EBS) using a quantum-dot spin in a double-sided optical microcavity. In contrast to the conventional optical beam splitter, the EBS can directly split a photon-spin product state into two constituent entangled states via transmission and reflection with high fidelity and high efficiency (up to 100 percent). This device is based on giant optical circular birefringence induced by a single spin as a result of cavity quantum electrodynamics and the spin selection rule of trion transition (Pauli blocking). The EBS is robust and it is immune to the fine structure splitting in a realistic quantum dot. This quantum device can be used for deterministically creating photon-spin, photon-photon and spin-spin entanglement as well as a single-shot quantum non-demolition measurement of a single spin. Therefore, the EBS can find wide applications in quantum information science and technology.Comment: 7 pages, 5 figure

On being oneself: a comparison of Heidegger and Buber on personal identity

The question is posed, what does it mean to be oneself? It is argued that to look for an answer in the psycho-physical characteristics of the individual himself does not take account of man's restless refusal to be content with what he is. The starting point of the inquiry is that an understanding of what makes man himself must take account of the 'beyond' in terms of which he seeks to define himself. It is this preliminary assumption which explains how Heidegger and Buber come to be considered together, for both philosophers share the view that man is an ec-static being, one who 'stands out' from himself in some way. However, it is precisely when Heidegger and Buber are juxtaposed that the problem of the thesis is set, for their views seem mutually exclusive. In Heidegger's understanding a. man is only himself when he steps forth towards his own possibility of non¬ existence. In contrast for Buber it is the relation of love which enables a person to be himself. The purpose of the comparison is to attempt to face the reality of death for each person with its effect on identity, and also the reality of the love of another person freeing one to be oneself.The argument is presented that man's relation with man as Buber presents it requires a radical reconstruction of Heidegger's analysis of existence. It is suggested that through the reality of love which resists the world 'as it is', including the power of death, the boundaries of existence need to be redefined. If love is accepted as an ontological phenomenon, then its appearance does not seem to be explicable within Heidegger's ontology of Being-towards-death. It is noted, on the other hand, that if it is possible to build an alternative ontology on love, the final possibility of death cannot be sidestepped. It is here that Heidegger can be used to strengthen Buber's notion of relation, for Buber seems to ignore the finitude of man, and the threat it poses to the 'I-Thou' relation as an ontological category.In the final section of the thesis, it is argued that the phenomenon of love cannot have its roots in this dying world. It is suggested that an explanation of the reality of love and its power to create personal Being requires an eschatological perspective. Only from such a perspective, with its refusal to accept death as a condition of man being himself, can an alternative ontology to Heidegger's be found.The conclusion reached is that the concept of God is implicit in the view of selfhood developed in the thesis. In accordance with that conclusion, in the final chapter some theological implications of a relational view of the self are outlined. In particular, the question is asked whether Persons-in-Trinity can be viewed as the ultimate resource for personhood. Pinally, requirements for a Christological anthropology consistent with a relational selfhood, are considered

Giant optical Faraday rotation induced by a single electron spin in a quantum dot: Applications to entangling remote spins via a single photon

We propose a quantum non-demolition method - giant Faraday rotation - to detect a single electron spin in a quantum dot inside a microcavity where negatively-charged exciton strongly couples to the cavity mode. Left- and right-circularly polarized light reflected from the cavity feels different phase shifts due to cavity quantum electrodynamics and the optical spin selection rule. This yields giant and tunable Faraday rotation which can be easily detected experimentally. Based on this spin-detection technique, a scalable scheme to create an arbitrary amount of entanglement between two or more remote spins via a single photon is proposed.Comment: 5 pages, 3 figure

Efficient optical quantum information processing

Quantum information offers the promise of being able to perform certain communication and computation tasks that cannot be done with conventional information technology (IT). Optical Quantum Information Processing (QIP) holds particular appeal, since it offers the prospect of communicating and computing with the same type of qubit. Linear optical techniques have been shown to be scalable, but the corresponding quantum computing circuits need many auxiliary resources. Here we present an alternative approach to optical QIP, based on the use of weak cross-Kerr nonlinearities and homodyne measurements. We show how this approach provides the fundamental building blocks for highly efficient non-absorbing single photon number resolving detectors, two qubit parity detectors, Bell state measurements and finally near deterministic control-not (CNOT) gates. These are essential QIP devicesComment: Accepted to the Journal of optics B special issue on optical quantum computation; References update

Single photon quantum non-demolition in the presence of inhomogeneous broadening

Electromagnetically induced transparency (EIT) has been often proposed for generating nonlinear optical effects at the single photon level; in particular, as a means to effect a quantum non-demolition measurement of a single photon field. Previous treatments have usually considered homogeneously broadened samples, but realisations in any medium will have to contend with inhomogeneous broadening. Here we reappraise an earlier scheme [Munro \textit{et al.} Phys. Rev. A \textbf{71}, 033819 (2005)] with respect to inhomogeneities and show an alternative mode of operation that is preferred in an inhomogeneous environment. We further show the implications of these results on a potential implementation in diamond containing nitrogen-vacancy colour centres. Our modelling shows that single mode waveguide structures of length $200 \mu\mathrm{m}$ in single-crystal diamond containing a dilute ensemble of NV$^-$ of only 200 centres are sufficient for quantum non-demolition measurements using EIT-based weak nonlinear interactions.Comment: 21 pages, 9 figures (some in colour) at low resolution for arXiv purpose

The efficiencies of generating cluster states with weak non-linearities

We propose a scalable approach to building cluster states of matter qubits using coherent states of light. Recent work on the subject relies on the use of single photonic qubits in the measurement process. These schemes can be made robust to detector loss, spontaneous emission and cavity mismatching but as a consequence the overhead costs grow rapidly, in particular when considering single photon loss. In contrast, our approach uses continuous variables and highly efficient homodyne measurements. We present a two-qubit scheme, with a simple bucket measurement system yielding an entangling operation with success probability 1/2. Then we extend this to a three-qubit interaction, increasing this probability to 3/4. We discuss the important issues of the overhead cost and the time scaling. This leads to a "no-measurement" approach to building cluster states, making use of geometric phases in phase space.Comment: 21 pages, to appear in special issue of New J. Phys. on "Measurement-Based Quantum Information Processing

Layer by layer generation of cluster states

Cluster states can be used to perform measurement-based quantum computation. The cluster state is a useful resource, because once it has been generated only local operations and measurements are needed to perform universal quantum computation. In this paper, we explore techniques for quickly and deterministically building a cluster state. In particular we consider generating cluster states on a qubus quantum computer, a computational architecture which uses a continuous variable ancilla to generate interactions between qubits. We explore several techniques for building the cluster, with the number of operations required depending on whether we allow the ability to destroy previously created controlled-phase links between qubits. In the case where we can not destroy these links, we show how to create an n x m cluster using just 3nm -2n -3m/2 + 3 operations. This gives more than a factor of 2 saving over a naive method. Further savings can be obtained if we include the ability to destroy links, in which case we only need (8nm-4n-4m-8)/3 operations. Unfortunately the latter scheme is more complicated so choosing the correct order to interact the qubits is considerably more difficult. A half way scheme, that keeps a modular generation but saves additional operations over never destroying links requires only 3nm-2n-2m+4 operations. The first scheme and the last scheme are the most practical for building a cluster state because they split up the generation into the repetition of simple sections.Comment: 16 pages, 11 figure

Decoy Effects in Choice Experiments and Contingent Valuation: Asymmetric Dominance

While a dominated choice involves a situation in which one option clearly dominates another on all relevant dimensions, an asymmetrically dominated choice typically arises where at least two options do not dominate each other and one (but not both) of those options does dominate a third option. We demonstrate that the introduction of such an asymmetrically dominated option can have a significant impact upon choices between non-dominated options within the same choice set for non-market goods. Furthermore, we show that this effect can then translate into significant impacts upon subsequent valuations for those non-dominated options.Preprinthttp://www.grips.ac.jp/list/jp/facultyinfo/munro_alistair