Loss tolerance in one-way quantum computation via counterfactual error correction

We introduce a scheme for fault tolerantly dealing with losses (or other "leakage" errors) in cluster state computation that can tolerate up to 50% qubit loss. This is achieved passively using an adaptive strategy of measurement - no coherent measurements or coherent correction is required. Since the scheme relies on inferring information about what would have been the outcome of a measurement had one been able to carry it out, we call this "counterfactual" error correction.Comment: Published version - much revised and with a new title. Here we now focus solely on the general aspects of the protocol - a much expanded and improved discussion of its application in linear optical quantum computation can now be found in quant-ph/070204

Loss tolerant linear optical quantum memory by measurement-based quantum computing

We give a scheme for loss tolerantly building a linear optical quantum memory which itself is tolerant to qubit loss. We use the encoding recently introduced in Varnava et al 2006 Phys. Rev. Lett. 97 120501, and give a method for efficiently achieving this. The entire approach resides within the 'one-way' model for quantum computing (Raussendorf and Briegel 2001 Phys. Rev. Lett. 86 5188–91; Raussendorf et al 2003 Phys. Rev. A 68 022312). Our results suggest that it is possible to build a loss tolerant quantum memory, such that if the requirement is to keep the data stored over arbitrarily long times then this is possible with only polynomially increasing resources and logarithmically increasing individual photon life-times

How good must single photon sources and detectors be for efficient linear optical quantum computation?

We present a scheme for linear optical quantum computation (LOQC) which is highly robust to imperfect single photon sources and inefficient detectors. In particular we show that if the product of the detector efficiency with the source efficiency is greater than 2/3, then efficient LOQC is possible. This threshold is many orders of magnitude more relaxed than those which could be inferred by application of standard results in fault tolerance. The result is achieved within the cluster state paradigm for quantum computation.Comment: New version contains an Added Appendi

Recreating rural Britain and maintaining Britishness in the Mediterranean: the Troodos Hill Station in early British Cyprus

Britain occupied Cyprus in 1878 for strategic reasons, but while these reasons were being questioned, it was decided to establish a hill station. This was the one thing that the British could agree on, namely that they wanted a space safe enough to protect them from the harsh summer, unhealthy towns and marshy plains of Cyprus. The Troodos Hill Station became the summer capital of the Cyprus Colonial Government within a year of the occupation of Cyprus. At Troodos, the officers of the civil and military establishments, expatriates and travellers, spent the sultry summer months. This paper will explore the original and changing role of the hill station and situate it within the colonial structure and imaginary. I will contend that it was vital in creating and maintaining British identity, namely the rural life of country Britain. It was only at the isolated confines of Troodos that the British could recreate the social and cultural setting of home, because it was only there where they could disengage from the social, political and cultural conditions of the cities. Thus, it comes as no surprise that the Cyprus Government had a protective attitude to its position there against the demands of the military authorities for land rights.Nicosia, Cypru

Maintaining Britishness in a setting of their own design: the Troodos Hill Station in Cyprus during the early British occupation

Britain occupied Cyprus by virtue of the Anglo-Turkish Convention of 4 June 1878, which ceded the occupation and administration (but not sovereignty) to Britain. The Lord Beaconsfield Government planned to convert Cyprus into a place of arms. The architects of this policy saw Cyprus as ideal for stationing troops, and sent there a 10,000 strong army of occupation. They saw Famagusta Harbour as the perfect naval and commercial station in the eastern Mediterranean. But within months of the occupation, uncertainties developed over the military and naval value of Cyprus. The decision to build the Troodos Hill Station stood in stark contrast to the uncertainties over the military and naval value of the island, and the uncertainties over whether to act as if Cyprus was a British or Ottoman territory.Melbourne, VI

Can students\u27 concept of learning influence their learning outcomes?

This paper aims to readdress the lack of empirical data concerning university learning and in particular the dynamics students’ conceptions of learning may have on students’ learning outcomes. This paper is written at a time when the EU commission for Higher Education (HE) through the Bologna Process declaration has put into action, since 1999, a series of reforms needed to make European Higher Education compatible, efficient and competitive for students and academics alike. One of the reforms was the development of learning outcomes in the form of the European Credit Transfer and Accumulation System (ECTS). As part of the process the European universities require to identify and describe the learning outcomes a student is supposed to achieve, in a particular course. The learning outcomes are, now, expected to be clearly specified in all the university course syllabuses. The main argument stated within this paper is that the design of effective learning outcomes, such as the ECTS, especially for curriculum development, cannot be successfully achieved in the absence of the students’ own experience of how they conceive learning to be, including the methods (approaches) they use for learning. Thus, the first aim of this investigation is to analyse the students’ conceptions of learning and the second aim is to examine, through prior research evidence, the effects these conceptions may have on learning approaches and specifically on learning outcomes. Drawing on a 2007 study of Cypriot students’ conceptions of learning, this paper discusses the possibility of a relation between these issues and outlines the importance of taking them into consideration when exploring learning outcomes, curriculum and syllabus design and the professional development of faculty.DOI: 10.18870/hlrc.v2i2.2

Historicising Australian Deportation of 'Suspect' and 'Undesirable' Migrant Communities

The overall aim of the paper is to present evidence on the factors underpinning historical deportation cases, by exploring the reasons, explanations and patterns related to deportation in Australia. The purpose is to consider whether these historical factors are antecedent to current forms of deportation occurring in Australia, and to bring to the fore potential recurring patterns. Deportation is currently conceptualised by border criminologists as a punitive tool of discipline and control, within the realm of penal powers. Some of this work on the ‘deportation regime’ asserts that certain migrants, or groups of migrants, are undesirable: their identity, (not)belonging and punishment have become inherently intertwined, and their mobility has become politicised and criminalised. This article theorises that deportation has been used in Australia, now and in the past, to expel individuals who are viewed as detrimental to the ‘health’ of the host society. The ‘deportation categories’ demonstrate that migrants’ desirability has historically been a temporary condition, shifting over time in line with the state’s requirements. They also demonstrate the historical regime of criminalisation of undesirable others enacted through Australia’s border control regime

Quantum dot-based Entangled-Light Emitting Diodes (E-LED) for quantum relays

Sources of entangled pairs of photons can be used for encoding signals in quantum-encrypted communications, allowing a sender, Alice, and a receiver, Bob, to exchange keys without the possibility of eavesdropping. In fact, any quantum information system would require single and entangled photons to serve as qubits. For this purpose, semiconductor quantum dots (QD) have been extensively studied for their ability to produce entangled light and function as single photon sources. The quality of such sources is evaluated based on three criteria: high efficiency, small multi-photon probability, and quantum indistinguishability. In this work, a simple quantum dot-based LED (E-LED) was used as a quantum light source for on-demand emission, indicating the potential for use as quantum information devices. Limitations of the device include the fine-structure splitting of the quantum dot excitons, their coherence lengths and charge carrier interactions in the structure. The quantum dot-based light emitting diode was initially shown to operate in pulsed mode under AC bias frequencies of up to several hundreds of MHz, without compromising the quality of emission. In a Hong-ou-Mandel interference type experiment, the quantum dot photons were shown to interfere with dissimilar photons from a laser, achieving high two-photon interference (TPI) visibilities. Quantum entanglement from a QD photon pair was also measured in pulsed mode, where the QD-based entangled-LED (E-LED) was electrically injected at a frequency of 203 MHz. After verifying indistinguishability and good entanglement properties from the QD photons under the above conditions, a quantum relay over 1km of fibre was demonstrated, using input qubits from a laser source. The average relay fidelity was high enough to allow for error correction for this BB84-type scheme. To improve the properties of the QD emission, an E-LED was developed based on droplet epitaxy (D-E) QDs, using a different QD growth technique. The relevant chapter outlines the process of QD growth and finally demonstration of quantum entanglement from an electrically injected diode, yielding improvements compared to previous E-LED devices. For the same reason, an alternative method of E-LED operation based on resonant two-photon excitation of the QD was explored. Analysis of Rabi oscillations in a quantum dot with a bound exciton state demonstrated coupling of the ground state and the biexciton state by the external oscillating field of a laser, therefore allowing the transition between the two states. The results include a considerable improvement in the coherence length of the QD emission, which is crucial for future quantum network applications. We believe that extending this research can find application in quantum cryptography and in realising the interface of a quantum network, based on semiconductor nanotechnology