Entanglement distribution for a practical quantum-dot-based quantum processor architecture

We propose a quantum dot (QD) architecture for enabling universal quantum information processing. Quantum registers, consisting of arrays of vertically stacked self-assembled semiconductor QDs, are connected by chains of in-plane self-assembled dots. We propose an entanglement distributor, a device for producing and distributing maximally entangled qubits on demand, communicated through in-plane dot chains. This enables the transmission of entanglement to spatially separated register stacks, providing a resource for the realization of a sizeable quantum processor built from coupled register stacks of practical size. Our entanglement distributor could be integrated into many of the present proposals for self-assembled QD-based quantum computation (QC). Our device exploits the properties of simple, relatively short, spin-chains and does not require microcavities. Utilizing the properties of self-assembled QDs, after distribution the entanglement can be mapped into relatively long-lived spin qubits and purified, providing a flexible, distributed, off-line resource. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft

Quantum-enhanced capture of photons using optical ratchet states

Natural and artificial light harvesting systems often operate in a regime where the flux of photons is relatively low. Besides absorbing as many photons as possible it is therefore paramount to prevent excitons from annihilation via photon re-emission until they have undergone an irreversible energy conversion process. Taking inspiration from photosynthetic antenna structures, we here consider ring-like systems and introduce a class of states we call ratchets: excited states capable of absorbing but not emitting light. This allows our antennae to absorb further photons whilst retaining the excitations from those that have already been captured. Simulations for a ring of four sites reveal a peak power enhancement by up to a factor of 35 under ambient conditions owing to a combination of ratcheting and the prevention of emission through dark-state population. In the slow extraction limit the achievable power enhancement due to ratcheting alone exceeds 20%.Comment: major revision with improved model (all data and figures updated

Superabsorption of light via quantum engineering

Almost 60 years ago Dicke introduced the term superradiance to describe a signature quantum effect: N atoms can collectively emit light at a rate proportional to N^2. Even for moderate N this represents a significant increase over the prediction of classical physics, and the effect has found applications ranging from probing exciton delocalisation in biological systems, to developing a new class of laser, and even in astrophysics. Structures that super-radiate must also have enhanced absorption, but the former always dominates in natural systems. Here we show that modern quantum control techniques can overcome this restriction. Our theory establishes that superabsorption can be achieved and sustained in certain simple nanostructures, by trapping the system in a highly excited state while extracting energy into a non-radiative channel. The effect offers the prospect of a new class of quantum nanotechnology, capable of absorbing light many times faster than is currently possible; potential applications of this effect include light harvesting and photon detection. An array of quantum dots or a porphyrin ring could provide an implementation to demonstrate this effect

Coherent exciton dynamics in a dissipative environment maintained by an off-resonant vibrational mode

This work was supported by the Leverhulme Trust (RPG-080) and the EPSRC (EP/G03673X/1).The interplay between an open quantum system and its environment can lead to both coherent and incoherent behavior. We explore the extent to which strong coupling to a single bosonic mode can alter the coherence properties of a two-level system in a structured environment. This mode is treated exactly, with the rest of the environment comprising a Markovian bath of bosonic modes. The strength of the coupling between the two-level system and the single mode is varied for a variety of forms for the bath spectral density in order to assess whether the coherent dynamics of the two-level system are modified. We find a clear renormalization of the site population oscillation frequency that causes an altered interaction with the bath. This leads to enhanced or reduced coherent behavior of the two-level system, depending on the form of the spectral density function. We present an intuitive interpretation, based on an analytical model, to explain the behavior.Publisher PDFPeer reviewe

Th1 versus Th17: Are T cell cytokines relevant in multiple sclerosis?

AbstractOur understanding of the pathophysiology of multiple sclerosis (MS) has evolved significantly over the past two decades as the fields of immunology and neurobiology provide new avenues of exploration into the cause and mechanism of the disease. It has been known for decades that T cells have different cytokine phenotypes, yet the cytokine phenotype of pathogenic T cells in MS is still an area of debate. In EAE, it appears that IFNγ and IL-17, produced by Th1 and Th17 cells respectively, are not the critical factor that determines T cell encephalitogenicity. However, there are molecules such as IL-23, T-bet and STAT4, that appear to be critical, yet it is unclear whether all these molecules contribute to a common, yet undefined pathway, or act in a synergistic manner which culminates in encephalitogenicity has still to be determined. Therefore, the focus of research on effector T cells in MS should focus on pathways upstream of the cytokines that define Th1 and Th17 cells, since downstream products, such as IFNγ and IL-17, probably are not critical determinants of whether an effector T cells is capable of trafficking to the CNS and inducing inflammatory demyelination

Deflation Troughs, Water, and Prehistoric Occupation on the Margins of the South Texas Sand Sheet

Within the South Texas Plains, the area broadly defined by the Rio Grande to the south and the Nueces River to the north, a distance of ca. 175 km, evidence of open human occupation is remarkably abundant. Because it is predominantly a region of loose, sandy soils and active and relict sand dunes where wind processes dominate, the area is known as the South Texas Sand Sheet (STSS). There is no running water within the STSS and all streams are ephemeral. Existing drainage systems are small, localized, and not integrated, carrying water for a few days and up to two weeks after the passage of a storm. The lack of running water makes human occupation on this semi-arid area even more remarkable. The STSS and the adjacent wind deflated areas have hundreds of small and shallow elongated deflation troughs. Most of these poorly drained swales retain seasonal fresh water that sustain high moisture plants and are ephemeral wetlands; a small percentage of them hold water year round. As a result, the long history of human occupation of the STSS was possible due to the presence of the deflation troughs. This study explores the connection between human occupation of the STSS and deflation troughs at four previously unreported archeological sites in northern Hidalgo County using a combination of intensive archeological and geological survey, oral history, GIS technology, and existing soil maps

Deflation Troughs, Water, and Prehistoric Occupation on the Margins of the South Texas Sand Sheet

Within the South Texas Plains, the area broadly defined by the Rio Grande to the south and the Nueces River to the north, a distance of ca. 175 km, evidence of open human occupation is remarkably abundant. Because it is predominantly a region of loose, sandy soils and active and relict sand dunes where wind processes dominate, the area is known as the South Texas Sand Sheet (STSS). There is no running water within the STSS and all streams are ephemeral. Existing drainage systems are small, localized, and not integrated, carrying water for a few days and up to two weeks after the passage of a storm. The lack of running water makes human occupation on this semi-arid area even more remarkable. The STSS and the adjacent wind deflated areas have hundreds of small and shallow elongated deflation troughs. Most of these poorly drained swales retain seasonal fresh water that sustain high moisture plants and are ephemeral wetlands; a small percentage of them hold water year round. As a result, the long history of human occupation of the STSS was possible due to the presence of the deflation troughs. This study explores the connection between human occupation of the STSS and deflation troughs at four previously unreported archeological sites in northern Hidalgo County using a combination of intensive archeological and geological survey, oral history, GIS technology, and existing soil maps

Antimycobacterial immune responses in HIV-infected children starting antiretroviral therapy in Lusaka, Zambia

Background: Children infected with HIV are at risk of developing tuberculosis (TB). Antiretroviral therapy has been linked to improved immune responses to TB. The objectives of the study were to determine the magnitude and quality of immune reconstitution in HIV-infected children receiving antiretroviral therapy (ART) and to determine pathogen-specific immune reconstitution to Mycobacterium tuberculosis.Methods: A total of 59 children of age 9 months to 5 years initiating ART with a history of BCG vaccination from Matero Reference Clinic in Lusaka were enrolled in a prospective cohort study. Demographic and clinical data were collected using questionnaires. Blood samples were drawn before starting ART, at 3 months and 6 months for measurement of T cell subsets and PPD stimulation for intracellular cytokine staining.Results: After 6 months of ART, the median CD4 T cell percentage increased from 9.4% at baseline to 25.9% (p < 0.001). Total CD8 T cell percentage decreased from 42.8% pre-ART to 36.5% after 6 months of ART (p = 0.010). However, naïve CD8 T cells increased within the same period (p = 0.038). Both activated CD4 and CD8 T cells decreased after 6 months of ART (p < 0.001). On the other hand, both central memory CD4 and CD8 T cells increased after 6 months of ART (p = 0.029 and 0.021, respectively), while effector memory CD8 T cells decreased (p=0.006). After 3 months of ART, CD4 T cells expressing IFN-ã decreased (p = 0.033) but after 6 months of ART the percentage increased to pre-ART levels.Conclusion: ART has a positive impact on HIV infected children, likely reducing the risk of tuberculosis as evidenced by the increases in CD4 T cells critical to an effective immune response against TB. Before starting ART, anti-mycobacterial immune responses seem to be primarily driven by effector memory T cells while after ART by central memory T cells. Therefore, central memory T cells appear to be the primary cells in restoring specific immune responses. These findings have valuable implications for TB vaccine development strategies in HIV-infected children

Use of Patterns for Knowledge Management in the Ceramic Tile Design Chain

Knowledge Management (KM) is a complex objective, especially in the instance of extended enterprises consisting of SMEs, and critical in new product design and development (NPD). The use of patterns is essential to get KM in collaborative NPD processes. This paper presents the use of patterns adopted in the CE-TILE project to standardize information and knowledge in collaborative work. The different types of patterns and models established for the knowledge capture, formalization and configuration are also described

Universal quantum computation using the discrete time quantum walk

A proof that continuous time quantum walks are universal for quantum computation, using unweighted graphs of low degree, has recently been presented by Childs [PRL 102 180501 (2009)]. We present a version based instead on the discrete time quantum walk. We show the discrete time quantum walk is able to implement the same universal gate set and thus both discrete and continuous time quantum walks are computational primitives. Additionally we give a set of components on which the discrete time quantum walk provides perfect state transfer.Comment: 9 pages, 10 figures. Updated after referee comments - Section V expanded and minor changes to other parts of the tex