High-precision force sensing using a single trapped ion

We introduce quantum sensing schemes for measuring very weak forces with a single trapped ion. They use the spin-motional coupling induced by the laser-ion interaction to transfer the relevant force information to the spin-degree of freedom. Therefore, the force estimation is carried out simply by observing the Ramsey-type oscillations of the ion spin states. Three quantum probes are considered, which are represented by systems obeying the Jaynes-Cummings, quantum Rabi (in 1D) and Jahn-Teller (in 2D) models. By using dynamical decoupling schemes in the Jaynes-Cummings and Jahn-Teller models, our force sensing protocols can be made robust to the spin dephasing caused by the thermal and magnetic field fluctuations. In the quantum-Rabi probe, the residual spin-phonon coupling vanishes, which makes this sensing protocol naturally robust to thermally-induced spin dephasing. We show that the proposed techniques can be used to sense the axial and transverse components of the force with a sensitivity beyond the yN $/\sqrt{\text{Hz}}$ range, i.e. in the xN$/\sqrt{\text{Hz}}$ (xennonewton, $10^{-27}$). The Jahn-Teller protocol, in particular, can be used to implement a two-channel vector spectrum analyzer for measuring ultra-low voltages.Comment: 7 pages, 4 figure

Quenched and first unquenched lattice HQET determination of the Bs-Meson width difference

We present recent results for the prediction of the Bs lifetime difference from lattice Heavy Quark Effective Theory simulations. In order to get a next-to-leading order result we have calculated the matching between QCD and HQET and the two-loop anomalous dimensions in the HQET for all the \Delta B=2 operators, in particular for the operators which enter the width difference. We present results from quenched and, for the first time, from unquenched simulations. We obtain for the Bs lifetime difference, (\Delta\Gamma_Bs/\Gamma_Bs)^{(que.)}=(5.1+/- 1.9+/- 1.7)10^(-2) and (\Delta\Gamma_Bs/\Gamma_Bs)^{(unq.)}=(4.3+/- 2.0+/- 1.9)10^(-2) from the quenched and unquenched simulations respectivelyComment: Lattice 2000 (Heavy Quark Physics), 4 pages, LaTeX. Some misprints corrected. No result change

Multistable alignment states in nematic liquid crystal filled wells

Two distinct, stable alignment states have been observed for a nematic liquid crystal confined in a layer with thickness of 12 μm and in square wells with sides of length between 20 and 80 μm. The director lies in the plane of the layer and line defects occur in two corners of the squares. The positions of the defects determine whether the director orientation is across the diagonal or is parallel to two opposite edges of the square. The device is multistable because both the diagonal and parallel states are stable when rotated by multiples of 90° in plane

Scorzonera sensu lato (Asteraceae, Cichorieae) – taxonomic reassessment in the light of new molecular phylogenetic and carpological analyses

Scorzonera comprises 180–190 species and belongs to the subtribe Scorzonerinae. Its circumscription has long been the subject of debate and available molecular phylogenetic analyses affirmed the polyphyly of Scorzonera in its wide sense. We provide a re-evaluation of Scorzonera and other related genera, based on carpological (including anatomical) and extended molecular phylogenetic analyses. We present, for the first time, a comprehensive sampling, including Scorzonera in its widest sense and all other genera recognised in the Scorzonerinae. We conducted phylogenetic analyses using Maximum Parsimony, Maximum Likelihood and Bayesian analyses, based on sequences of the nuclear ribosomal ITS and of two plastid markers (partial rbcL and matK) and Maximum Parsimony for reconstructing the carpological character states at ancestral nodes. Achene characters, especially related to pericarp anatomy, such as general topography of the tissue types, disposition of the mechanical tissue and direction of its fibres, presence or absence of air cavities, provide, in certain cases, support for the phylogenetic lineages revealed. Confirming the polyphyly of Scorzonera, we propose a revised classification of the subtribe, accepting the genera Scorzonera (including four major clades: Scorzonera s. str., S. purpurea, S. albicaulis and Podospermum), Gelasia, Lipschitzia gen. nov. (for the Scorzonera divaricata clade), Pseudopodospermum, Pterachaenia (also including Scorzonera codringtonii), Ramaliella gen. nov. (for the S. polyclada clade) and Takhtajaniantha. A key to the revised genera and a characterisation of the genera and major clades are provided

Quantum sensors assisted by spontaneous symmetry breaking for detecting very small forces

We propose a quantum-sensing scheme for measuring weak forces based on a symmetry-breaking adiabatic transition in the quantum Rabi model. We show that the system described by the Rabi Hamiltonian can serve as a sensor for extremely weak forces with sensitivity beyond the yoctonewton (yN) per sqrt (Hz) range. We propose an implementation of this sensing protocol using a single trapped ion. A major advantage of our scheme is that the force detection is performed by projective measurement of the population of the spin states at the end of the transition, instead of the far slower phonon number measurement used hitherto

Correlation length in cuprates deduced from the impurity-induced magnetization

We report a new multi-nuclei based NMR method which allows us to image the staggered polarization induced by nonmagnetic Li impurities in underdoped O6.6 and slightly overdoped O7 YBa2Cu3O6+y above T_C. The spatial extension of the polarization xi_imp approximately follows a Curie law, increasing up to six lattice constants at T=80K at O6.6 in the pseudogap regime. Near optimal doping, the staggered magnetization has the same shape, with xi_imp reduced by a factor 2. xi_imp is argued to reveal the intrinsic magnetic correlation length of the pure system. It is found to display a smooth evolution through the pseudogap regime.Comment: 8 latex pages + 8 figures, to appear in Physical Review B, this resubmitted version is twice longer than the previous one : we detail here our method to determine the impurity-induced magnetizatio

Higgsless electroweak symmetry breaking at the LHC

While the Higgs model is the best studied scenario of electroweak symmetry breaking, a number strongly-coupled models exist, predicting new signatures. Recent studies of WW and WZ final states at the ATLAS and CMS experiments are summarized and expected sensitivities are presented within the frameworks of the technicolor straw-man model and the electroweak chiral Lagrangian.Comment: Proceedings for the EPS HEP 2007 conference, Manchester, U.K., on behalf of the ATLAS and CMS Collaboration

Towards Communication-Efficient Quantum Oblivious Key Distribution

Oblivious Transfer, a fundamental problem in the field of secure multi-party computation is defined as follows: A database DB of N bits held by Bob is queried by a user Alice who is interested in the bit DB_b in such a way that (1) Alice learns DB_b and only DB_b and (2) Bob does not learn anything about Alice's choice b. While solutions to this problem in the classical domain rely largely on unproven computational complexity theoretic assumptions, it is also known that perfect solutions that guarantee both database and user privacy are impossible in the quantum domain. Jakobi et al. [Phys. Rev. A, 83(2), 022301, Feb 2011] proposed a protocol for Oblivious Transfer using well known QKD techniques to establish an Oblivious Key to solve this problem. Their solution provided a good degree of database and user privacy (using physical principles like impossibility of perfectly distinguishing non-orthogonal quantum states and the impossibility of superluminal communication) while being loss-resistant and implementable with commercial QKD devices (due to the use of SARG04). However, their Quantum Oblivious Key Distribution (QOKD) protocol requires a communication complexity of O(N log N). Since modern databases can be extremely large, it is important to reduce this communication as much as possible. In this paper, we first suggest a modification of their protocol wherein the number of qubits that need to be exchanged is reduced to O(N). A subsequent generalization reduces the quantum communication complexity even further in such a way that only a few hundred qubits are needed to be transferred even for very large databases.Comment: 7 page