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

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

Hybrid quantum repeater based on dispersive CQED interactions between matter qubits and bright coherent light

We describe a system for long-distance distribution of quantum entanglement, in which coherent light with large average photon number interacts dispersively with single, far-detuned atoms or semiconductor impurities in optical cavities. Entanglement is heralded by homodyne detection using a second bright light pulse for phase reference. The use of bright pulses leads to a high success probability for the generation of entanglement, at the cost of a lower initial fidelity. This fidelity may be boosted by entanglement purification techniques, implemented with the same physical resources. The need for more purification steps is well compensated for by the increased probability of success when compared to heralded entanglement schemes using single photons or weak coherent pulses with realistic detectors. The principle cause of the lower initial fidelity is fiber loss; however, spontaneous decay and cavity losses during the dispersive atom/cavity interactions can also impair performance. We show that these effects may be minimized for emitter-cavity systems in the weak-coupling regime as long as the resonant Purcell factor is larger than one, the cavity is over-coupled, and the optical pulses are sufficiently long. We support this claim with numerical, semiclassical calculations using parameters for three realistic systems: optically bright donor-bound impurities such as 19-F:ZnSe with a moderate-Q microcavity, the optically dim 31-P:Si system with a high-Q microcavity, and trapped ions in large but very high-Q cavities.Comment: Please consult the published version, where assorted typos are corrected. It is freely available at http://stacks.iop.org/1367-2630/8/18

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

Sfp1 and Rtg3 reciprocally modulate carbon source-conditional stress adaptation in the pathogenic yeast Candida albicans

Acknowledgements We thank Aaron Mitchell, Dominique Sanglard and Suzanne Noble for their generosity in providing mutant collections, and Linghuo Jiang for generously providing strains. We also thank Susan Budge for her support and excellent technical assistance. We also thank the qPCR Facility in the Institute of Medical Sciences, and particularly Fiona Saunders for her great advice and help. SLK was supported by a PhD scholarship from the University of Aberdeen. AJPB was supported by the UK Biotechnology and Biological Research Council (BB/F00513X/1; BB/K017365/1), by the European Research Council (STRIFE Advanced Grant; ERC-2009-AdG-249793), and by the UK Medical Research Council (MR/M026663/1). AJPB and CAM were also supported by the Wellcome Trust (088858; 097377), and by the MRC Centre for Medical Mycology and the University of Aberdeen (MR/N006364/1).Peer reviewedPublisher PD

Weak nonlinearities: A new route to optical quantum computation

Quantum information processing (QIP) offers the promise of being able to do things that we cannot do with conventional technology. Here we present a new route for distributed optical QIP, based on generalized quantum non-demolition measurements, providing a unified approach for quantum communication and computing. Interactions between photons are generated using weak non-linearities and intense laser fields--the use of such fields provides for robust distribution of quantum information. Our approach requires only a practical set of resources, and it uses these very efficiently. Thus it promises to be extremely useful for the first quantum technologies, based on scarce resources. Furthermore, in the longer term this approach provides both options and scalability for efficient many-qubit QIP.Comment: 7 Pages, 4 Figure

Quantum Computation by Communication

We present a new approach to scalable quantum computing--a ``qubus computer''--which realises qubit measurement and quantum gates through interacting qubits with a quantum communication bus mode. The qubits could be ``static'' matter qubits or ``flying'' optical qubits, but the scheme we focus on here is particularly suited to matter qubits. There is no requirement for direct interaction between the qubits. Universal two-qubit quantum gates may be effected by schemes which involve measurement of the bus mode, or by schemes where the bus disentangles automatically and no measurement is needed. In effect, the approach integrates together qubit degrees of freedom for computation with quantum continuous variables for communication and interaction.Comment: final published versio