An analytical decomposition protocol for optimal implementation of two-qubit entangling gates

This paper addresses the question how to implement a desired two-qubit gate U using a given tunable two-qubit entangling interaction H_int. We present a general method which is based on the K_1 A K_2 decomposition of unitary matrices in SU(4) to calculate analytically the smallest number of two-qubit gates U_int [based on H_int] and single-qubit rotations, and the explicit sequence of these operations that are required to implement U. We illustrate our protocol by calculating the implementation of (1) the transformation from standard basis to Bell basis, (2) the CNOT gate, and (3) the quantum Fourier transform for two kinds of interaction - Heisenberg exchange interaction and quantum inductive coupling - and discuss the relevance of our results for solid-state qubits.Comment: 16 pages, published versio

Synthesis and viscosity behavior of poly(γ-p-biphenylmethyl-L-glutamate) in benzene/dichloroacetic acid mixtures, a comparison with poly(γ-benzyl-L-glutamate)

The synthesis of poly(γ-p-biphenylmethyl-L-glutamate), PBPLG, (poly{L-imino-1-[2-(4-biphenylylmethoxycarbonyl)ethyl]-2-oxoethylene}), (1d) is described. The viscosity behavior of this polymer in benzene/dichloroacetic acid mixtures (c=0,2.10 -3 - 1,4.10 -3 g/cm3) at 25°CC is investigated. The results are compared with measurements on poly(γ-benzyl-L-glutamate), PBLG, (poly[L-imino-1-(2-benzyloxycarbonylethyl)-2-oxoethylene]), (1c) under the same conditions. A transition from a rigid hydrogen bonded helix to a random solvated coil occurs in two stages for both: PBPLG (first stage 0-55%, second stage 55-100% dichloroacetic acid) and PBLG (first stage 0-70%, second stage 70-100% dichloroacetic acid). \ud Therefore, the introduction of a p-phenyl substituent in PBLG leads to a less stable helix in benzene/dichloroacetic acid mixtures. \ud The stability and viscosity behavior of PBLG in benzene/dichloroacetic acid mixtures (c=0,2.10 - 3 - 1,4.10 - 3g/cm3) is quite similar to the behavior of PBLG in m-cresol/dichloroacetic acid mixtures (c=1,0.10 - 3 - 4,0.10 - 3 g/cm3)

High-pressure study of the non-Fermi liquid material U_2Pt_2In

The effect of hydrostatic pressure (p<= 1.8 GPa) on the non-Fermi liquid state of U_2Pt_2In is investigated by electrical resistivity measurements in the temperature interval 0.3-300 K. The experiments were carried out on single-crystals with the current along (I||c) and perpendicular (I||a) to the tetragonal axis. The pressure effect is strongly current-direction dependent. For I||a we observe a rapid recovery of the Fermi-liquid T^2-term with pressure. The low-temperature resistivity can be analysed satisfactorily within the magnetotransport theory of Rosch, which provides strong evidence for the location of U_2Pt_2In at an antiferromagnetic quantum critical point. For I||c the resistivity increases under pressure, indicating the enhancement of an additional scattering mechanism. In addition, we have measured the pressure dependence of the antiferromagnetic ordering temperature (T_N= 37.6 K) of the related compound U_2Pd_2In. A simple Doniach-type diagram for U_2Pt_2In and U_2Pd_2In under pressure is presented.Comment: 21 pages (including 5 figures); pdf forma

Ordered magnetic and quadrupolar states under hydrostatic pressure in orthorhombic PrCu2

We report magnetic susceptibility and electrical resistivity measurements on single-crystalline PrCu2 under hydrostatic pressure, up to 2 GPa, which pressure range covers the pressure-induced Van Vleck paramagnet-to-antiferromagnet transition at 1.2 GPa. The measured anisotropy in the susceptibility shows that in the pressure-induced magnetic state the ordered 4f-moments lie in the ac-plane. We propose that remarkable pressure effects on the susceptibility and resistivity are due to changes in the quadrupolar state of O22 and/or O20 under pressure. We present a simple analysis in terms of the singlet-singlet model.Comment: 14 pages, 9 figures submitted to Phys. Rev.

Might EPR particles communicate through a wormhole?

We consider the two-particle wave function of an Einstein-Podolsky-Rosen system, given by a two dimensional relativistic scalar field model. The Bohm-de Broglie interpretation is applied and the quantum potential is viewed as modifying the Minkowski geometry. In this way an effective metric, which is analogous to a black hole metric in some limited region, is obtained in one case and a particular metric with singularities appears in the other case, opening the possibility, following Holland, of interpreting the EPR correlations as being originated by an effective wormhole geometry, through which the physical signals can propagate.Comment: Corrected version, to appears in EP

Predicting work performance through selection interview ratings and psychological assessment.

The aim of the study was to establish whether selection interviews used in conjunction with psychological assessments of personality traits and cognitive functioning contribute to predicting work performance. The sample consisted of 102 managers who were appointed recently in a retail organisation. The independent variables were selection interview ratings obtained on the basis of structured competency-based interview schedules by interviewing panels, five broad dimensions of personality defined by the Five Factor Model as measured by the 15 Factor Questionnaire (15FQ+), and cognitive processing variables (current level of work, potential level of work, and 12 processing competencies) measured by the Cognitive Process Profile (CPP). Work performance was measured through annual performance ratings that focused on measurable outputs of performance objectives. Only two predictor variables correlated statistically significantly with the criterion variable, namely interview ratings (r = 0.31) and CPP Verbal Abstraction (r = 0.34). Following multiple regression, only these variables contributed significantly to predicting work performance, but only 17.8% of the variance of the criterion was accounted for

Genetic erosion in crops: concept, research results and challenges

The loss of variation in crops clue to the modernization of agriculture has been described as genetic erosion The current paper discusses the different views that exist on the concept of genetic erosion in crops Genetic erosion of cultivated diversity is reflected in a modernization bottleneck in the diversity levels that occurred during the history of the crop Two stages in this bottleneck are recognized the initial replacement of landraces by modern cultivars, and further trends in diversity as a consequence of modern breeding practices Genetic erosion may occur at three levels of integration crop, variety and allele The different approaches in the recent literature to measure genetic erosion in crops are reviewed. Genetic erosion as reflected in a reduction of allelic evenness and richness appears to be the most useful definition, but has to be viewed in conjunction with events at variety level According to the reviewed literature, the most likely scenario of diversity trends during modernization is the following a reduction in diversity clue to the replacement of landraces by modern cultivars, but no further reduction after this replacement has been complete

Superconductivity under pressure in the Dirac semimetal PdTe2

The Dirac semimetal PdTe$_2$ was recently reported to be a type-I superconductor ($T_c =$1.64 K, $\mu_0 H_c (0) = 13.6$ mT) with unusual superconductivity of the surface sheath. We here report a high-pressure study, $p \leq 2.5$ GPa, of the superconducting phase diagram extracted from ac-susceptibility and transport measurements on single crystalline samples. $T_c (p)$ shows a pronounced non-monotonous variation with a maximum $T_c =$1.91 K around 0.91 GPa, followed by a gradual decrease to 1.27 K at 2.5 GPa. The critical field of bulk superconductivity in the limit $T \rightarrow 0$, $H_c(0,p)$, follows a similar trend and consequently the $H_c(T,p)$-curves under pressure collapse on a single curve: $H_c(T,p)=H_c(0,p)[1-(T/T_c(p))^2]$. Surface superconductivity is robust under pressure as demonstrated by the large superconducting screening signal that persists for applied dc-fields $H_a > H_c$. Surprisingly, for $p \geq 1.41$ GPa the superconducting transition temperature at the surface $T_c^S$ is larger than $T_c$ of the bulk. Therefore surface superconductivity may possibly have a non-trivial nature and is connected to the topological surface states detected by ARPES. We compare the measured pressure variation of $T_c$ with recent results from band structure calculations and discuss the importance of a Van Hove singularity.Comment: manuscript 9 pages with 8 figures + supplemental material 3 pages with 6 figure

Evidence for a Quantum Hall Insulator in an InGaAs/InP Heterostructure

We study the quantum critical behavior of the plateau-insulator (PI) transition in a low mobility InGaAs/InP heterostructure. By reversing the direction of the magnetic field (B) we find an averaged Hall resistance \rho_xy which remains quantized at the plateau value h/e^2 throughout the PI transition. We extract a critical exponent \kappa'= 0.57 +/- 0.02 for the PI transition which is slightly different from (and possibly more accurate than) the established value 0.42 +/- 0.04 as previously obtained from the plateau-plateau (PP) transitions.Comment: 3pages, 2 figures; submitted to EP2DS-14 conference proceeding