Measurement of an integral of a classical field with a single quantum particle

A method for measuring an integral of a classical field via local interaction of a single quantum particle in a superposition of 2^N states is presented. The method is as efficient as a quantum method with N qubits passing through the field one at a time and it is exponentially better than any known classical method that uses N bits passing through the field one at a time. A related method for searching a string with a quantum particle is proposed.Comment: 3 page

Sinais climáticos em anéis de crescimento de Cedrela fissilis em diferentes tipologias de florestas ombrófilas do Sul do Brasil.

Os anéis de crescimento de Cedrela fissilis foram analisados em duas unidades fitogeográficas do estado do Paraná, em áreas de Florestas Ombrófilas Densa e Mista, litoral e planalto, no domínio da Floresta Atlântica, buscando encontrar sinais climáticos nas séries radiais temporais de anéis de crescimento. As áreas não apresentam estação seca bem definida, com precipitações bem distribuídas ao longo do ano. Na área do litoral, as temperaturas são altas e constantes durante todo o ano, enquanto que na área do planalto as temperaturas são mais amenas, ocorrendo considerável variação durante o ano. Nas duas áreas foram coletadas 3-4 amostras radiais dos indivíduos selecionados, sendo 15 no litoral e 21 no planalto. Os anéis de crescimento foram marcados, mensurados, submetidos ao controle de qualidade por meio do programa COFECHA® e as cronologias foram geradas utilizando o programa ARSTAN®. Sinais climáticos nas séries foram identificados utilizando-se Correlações de Pearson. As séries analisadas provenientes da área de planalto apresentaram melhores correlações com as variáveis temperatura e precipitação, sendo identificados sinais climáticos, enquanto que as séries do litoral não puderam ser datadas com total acurácia. É atribuída a hipótese da competição, principalmente por luz, para explicar a dificuldade na datação dos indivíduos do litoral

The Structure of Graphene on Graphene/C60/Cu Interfaces: A Molecular Dynamics Study

Two experimental studies reported the spontaneous formation of amorphous and crystalline structures of C60 intercalated between graphene and a substrate. They observed interesting phenomena ranging from reaction between C60 molecules under graphene to graphene sagging between the molecules and control of strain in graphene. Motivated by these works, we performed fully atomistic reactive molecular dynamics simulations to study the formation and thermal stability of graphene wrinkles as well as graphene attachment to and detachment from the substrate when graphene is laid over a previously distributed array of C60 molecules on a copper substrate at different values of temperature. As graphene compresses the C60 molecules against the substrate, and graphene attachment to the substrate between C60s ("C60s" stands for plural of C60) depends on the height of graphene wrinkles, configurations with both frozen and non-frozen C60s structures were investigated in order to verify the experimental result of stable sagged graphene when the distance between C60s is about 4 nm and height of graphene wrinkles is about 0.8 nm. Below the distance of 4 nm between C60s, graphene becomes locally suspended and less strained. We show that this happens when C60s are allowed to deform under the compressive action of graphene. If we keep the C60s frozen, spontaneous "blanketing" of graphene happens only when the distance between them are equal or above 7 nm. Both above results for the existence of stable sagged graphene for C60 distances of 4 or 7 nm are shown to agree with a mechanical model relating the rigidity of graphene to the energy of graphene-substrate adhesion. In particular, this study might help the development of 2D confined nanoreactors that are considered in literature to be the next advanced step on chemical reactions.Comment: 7 pages, 4 figure

A simple proof that anomalous weak values require coherence

The quantum mechanical weak value $A_w=\left\langle \phi|A|\psi \right \rangle / \left\langle \phi | \psi \right\rangle$ of an observable $A$ is a measurable quantity associated with an observable $A$ and pre- and post-selected states $\vert\psi \rangle, \vert \phi \rangle$. Much has been discussed about the meaning and metrological uses of anomalous weak values, lying outside of the range of eigenvalues of $A$. We present a simple proof that anomalous weak values require that the (possibly mixed) pre- and post- selection states have coherence in the eigenbasis of $A$. We also present conditions under which anomalous $A_w$ are witnesses of generalized contextuality, dispensing with the operational weak measurement set-up.Comment: 6 pages, 2 figure

Geometries for universal quantum computation with matchgates

Matchgates are a group of two-qubit gates associated with free fermions. They are classically simulatable if restricted to act between nearest neighbors on a one-dimensional chain, but become universal for quantum computation with longer-range interactions. We describe various alternative geometries with nearest-neighbor interactions that result in universal quantum computation with matchgates only, including subtle departures from the chain. Our results pave the way for new quantum computer architectures that rely solely on the simple interactions associated with matchgates.Comment: 6 pages, 4 figures. Updated version includes an appendix extending one of the result