Quantum synthesis of arbitrary unitary operators

Nature provides us with a restricted set of microscopic interactions. The question is whether we can synthesize out of these fundamental interactions an arbitrary unitary operator. In this paper we present a constructive algorithm for realization of any unitary operator which acts on a (truncated) Hilbert space of a single bosonic mode. In particular, we consider a physical implementation of unitary transformations acting on 1-dimensional vibrational states of a trapped ion. As an example we present an algorithm which realizes the discrete Fourier transform.Comment: 6 RevTeX pages with 3 figures, submitted to Phys.Rev.A, see also http://nic.savba.sk/sav/inst/fyzi/qo

Generalized quantum measurements and local realism

The structure of a local hidden variable model for experiments involving sequences of measurements rigorously is analyzed. Constraints imposed by local realism on the conditional probabilities of the outcomes of such measurement schemes are explicitly derived. The violation of local realism in the case of ``hidden nonlocality'' is illustrated by an operational example.Comment: Revtex, 12 pages; Some modifications of introduction has been made; a note stating that part of results had been obtained earlier by other authors, has been added; one postscript figure available at request from [email protected]

Vorhersage effektiver Makroporen durch Regenwurmabundanz und abiotische Umweltvariablen

Regenwürmer erzeugen Bioporen und erhöhen somit die Makroporosität von Böden. Dies kann zu präferenziellem Fließen führen und somit den vertikalen Wasser- und Stofftransport erhöhen. Das Vorkommen hydraulisch effektiver Bioporen variiert jedoch zeitlich und räumlich ebenso wie die Aktivität verschiedener Regenwurmarten. Das Ziel dieser im Rahmen der DFG Forschergruppe CAOS geförderten Studie war es, das Vorkommen effektiver Bioporen über die Abundanz relevanter Regenwurmarten und raumzeitliche Muster verschiedener abiotischer Umweltvariablen vorherzusagen. An sechs Standorten im luxemburgischen Wollefsbach-Einzugsgebiet wurden zu sechs Terminen innerhalb eines Jahres Infiltrationsversuche mit Brilliant Blue in fünffacher Wiederholung durchgeführt. In den Bodentiefen 3, 10 und 30 cm wurde die Anzahl der blau gefärbten, hydraulisch effektiven Bioporen bestimmt. Diese wurden in drei Größenklassen eingeteilt (Durchmesser: <2, 2–6, >6 mm). Zusätzlich wurden jeweils die Abundanzen aller gefundenen Regenwurmarten bestimmt. Mittels generalisierter linearer Modelle haben wir den Einfluss von Regenwurmabundanzen und verschiedenen abiotischen Umweltvariablen auf die Anzahl effektiver Bioporen untersucht. Die wichtigsten Variablen waren die Abundanzen von Lumbricus terrestris und Aporrectodea longa, Zeitreihen der Bodenfeuchte, der Luftfeuchte und des Niederschlags sowie die räumlichen Verteilungen der Landnutzung, der Hangneigung und des topographischen Feuchteindex. Die Eignung einzelner Variablen zur Vorhersage sowie die Güte der Modelle (erklärte Devianz: 5-50 %; Spearman Korrelation: 0,24-0,67) variierten erheblich zwischen den Bodentiefen und Größenklassen der vorhergesagten Bioporen. Die resultierenden Zeitreihen der Anzahl effektiver Bioporen und ihre räumlichen Verteilungen im Einzugsgebiet stellen eine wertvolle Basis für die Parametrisierung bodenhydrologischer Modelle dar. Darüber hinaus zeigen unsere Ergebnisse, wie wichtig die Berücksichtigung der zeitlichen Dynamik hydraulischer Konnektivität von Bioporen ist

All Optical Cellular Quantum Computer having Ancilla Bits for Operations in Each Cell

A quantum cellular network with a qubit and ancilla bits in each cell is proposed. The whole circuit works only with the help of external optical pulse sequences. In the operation, some of the ancilla bits are activated, and autonomous single- and two-qubit operations are made. In the sleep mode of a cell, the decoherence of the qubit is negligibly small. Since only two cells at most are active at once, the coherence can be maintained for a sufficiently long time for practical purposes. A device structure using a quantum dot array with possible operation and measurement schemes is also proposed.Comment: 14 pages, 5 figures RevTeX ;a single sentense is modified for the clarit

Violations of local realism by two entangled quNits are stronger than for two qubits

Tests of local realism vs quantum mechanics based on Bell's inequality employ two entangled qubits. We investigate the general case of two entangled quNits, i.e. quantum systems defined in an N-dimensional Hilbert space. Via a numerical linear optimization method we show that violations of local realism are stronger for two maximally entangled quNits (N=3,4,...,9), than for two qubits and that they increase with N. The two quNit measurements can be experimentally realized using entangled photons and unbiased multiport beamsplitters.Comment: 5 pages, 2 pictures, LaTex, two columns; No changes in the result

Generalized measurements by linear elements

I give a first characterization of the class of generalized measurements that can be exactly realized on a pair of qudits encoded in indistinguishable particles, by using only linear elements and particle detectors. Two immediate results follow from this characterization. (i) The Schmidt number of each POVM element cannot exceed the number of initial particles. This rules out any possibility of performing perfect Bell-measurements for qudits. (ii) The maximum probability of performing a generalized incomplete Bell-measurement is 1/2.Comment: 4 pages. Submitted to Phys. Rev.

Gaussian quantum marginal problem

The quantum marginal problem asks what local spectra are consistent with a given spectrum of a joint state of a composite quantum system. This setting, also referred to as the question of the compatibility of local spectra, has several applications in quantum information theory. Here, we introduce the analogue of this statement for Gaussian states for any number of modes, and solve it in generality, for pure and mixed states, both concerning necessary and sufficient conditions. Formally, our result can be viewed as an analogue of the Sing-Thompson Theorem (respectively Horn's Lemma), characterizing the relationship between main diagonal elements and singular values of a complex matrix: We find necessary and sufficient conditions for vectors (d1, ..., dn) and (c1, ..., cn) to be the symplectic eigenvalues and symplectic main diagonal elements of a strictly positive real matrix, respectively. More physically speaking, this result determines what local temperatures or entropies are consistent with a pure or mixed Gaussian state of several modes. We find that this result implies a solution to the problem of sharing of entanglement in pure Gaussian states and allows for estimating the global entropy of non-Gaussian states based on local measurements. Implications to the actual preparation of multi-mode continuous-variable entangled states are discussed. We compare the findings with the marginal problem for qubits, the solution of which for pure states has a strikingly similar and in fact simple form.Comment: 18 pages, 1 figure, material added, references updated, except from figure identical with version to appear in Commun. Math. Phy

Improved diagnostics targeting c-MET in non-small cell lung cancer: expression, amplification and activation?

Background: Several c-MET targeting inhibitory molecules have already shown promising results in the treatment of patients with Non-small Cell Lung Cancer (NSCLC). Combination of EGFR-and c-MET-specific molecules may overcome EGFR tyrosine kinase inhibitor (TKI) resistance. The aim of this study was to allow for the identification of patients who might benefit from TKI treatments targeting MET and to narrow in on the diagnostic assessment of MET. Methods: 222 tumor tissues of patients with NSCLC were analyzed concerning c-MET expression and activation in terms of phosphorylation (Y1234/1235 and Y1349) using a microarray format employing immunohistochemistry (IHC). Furthermore, protein expression and MET activation was correlated with the amplification status by Fluorescence in Situ Hybridization (FISH). Results: Correlation was observed between phosphorylation of c-MET at Y1234/1235 and Y1349 (spearman correlation coefficient r(s) = 0.41;p 0.05). c-MET gene amplification was detected in eight of 214 patients (3.7 %). No significant association was observed between c-MET amplification, c-MET protein expression and phosphorylation. Conclusion: Our data indicate, that neither expression of c-MET nor the gene amplification status might be the best way to select patients for MET targeting therapies, since no correlation with the activation status of MET was observed. We propose to take into account analyzing the phosphorylation status of MET by IHC to select patients for MET targeting therapies. Signaling of the receptor and the activation of downstream molecules might be more crucial for the benefit of therapeutics targeting MET receptor tyrosine kinases than expression levels alone

Implementing universal multi-qubit quantum logic gates in three and four-spin systems at room temperature

In this paper, we present the experimental realization of multi-qubit gates $$ in macroscopic ensemble of three-qubit and four-qubit molecules. Instead of depending heavily on the two-bit universal gate, which served as the basic quantum operation in quantum computing, we use pulses of well-defined frequency and length that simultaneously apply to all qubits in a quantum register. It appears that this method is experimentally convenient when this procedure is extended to more qubits on some quantum computation, and it can also be used in other physical systems.Comment: 5 Pages, 2 Figure