Decoherence of flux qubits due to 1/f flux noise

We have investigated decoherence in Josephson-junction flux qubits. Based on the measurements of decoherence at various bias conditions, we discriminate contributions of different noise sources. In particular, we present a Gaussian decay function of the echo signal as evidence of dephasing due to $1/f$ flux noise whose spectral density is evaluated to be about $(10^{-6} \Phi_0)^2$/Hz at 1 Hz. We also demonstrate that at an optimal bias condition where the noise sources are well decoupled the coherence observed in the echo measurement is mainly limited by energy relaxation of the qubit.Comment: 4 pages, error in Fig.4 corrected, to appear in PR

Fatty acid and triacylglycerol compositions of milk thistle seeds growing wild in Tunisia (Silybum marianum L.)

The milk thistle plant grows in many regions in Tunisia; however, there is no literature regarding their oil composition. In this study, oil content, fatty acids and triacylglycerols compositions of milk thistle seeds growing wild in Tunisia were determined. The oil content was 30.5%, thus milk thistle seeds could be exploited as natural new source of oil. Among the fatty acids, linoleic acid had the highest percentage (59.98%) followed by oleic acid (21.26%) and palmitic acid (12.74%). The extracted oil from milk thistle seeds is rich in polyunsaturated fatty acids (60.37%). Various molecular species of TAGs were detected and the major forms were LLL (22.30%), OLL (20.40%), PLL (17.31%), POL (14.30%), and OOL (7.90%). It can be concluded that milk thistle seed oil has a characteristic TAG pattern as compared with these elucidated for olive oil and soybean oil

Cambios en la composición de esteroles del aceite de cardo mariano (Silybium marianum L.) durante la maduración de la semilla

In this study, the total lipid content and sterol compositions were determined during the development of milk thistle seeds. The oil content increased to a maximum value of 36±1.7% and then declined to reach a value of 30.5±0.9% at full maturity. The sterol content of milk thistle seeds was affected by the ripening degree of the seeds. At the early stages of seed maturation, Δ7-stigmastenol was the most abundant sterol followed by β-sitosterol. However, at full maturity, β-sitosterol was the most predominant sterol (46.50±0.8%). As the seed developed, campesterol and stigmasterol amounts increased, while Δ7-avenasterol content decreased. It can be concluded that milk thistle seed oil has a characteristic sterol pattern comparable to the ones elucidated for olive oil and corn oil. The extracted oil from milk thistle seeds is rich in phytosterols and could be used in food preparation and human nutrition.En este estudio se determinaron la composición de lípidos totales y esteroles durante el desarrollo de semillas de cardo mariano. El contenido de aceite incrementó a un valor máximo de 36±1,7% y posteriormente disminuyó hasta alcanzar un valor de 30,5±0,9% cuando la maduración fue completa. El contenido de esteroles de las semillas de cardo mariano se ve afectado por el grado de maduración de las semillas. En las primeras etapas de la maduración de las semillas el Δ7-estigmastenol fué el esterol más abundante, seguido de β-sitosterol. Sin embargo en plena madurez, β-sitosterol fue el esterol predominante (46,50±0,8%). A medida que las semillas se desarrollan las cantidades de campesterol y estigmasterol aumentan, mientras que el contenido Δ7-avenasterol disminuye. Se puede concluir que el aceite de semillas de cardo mariano tiene un patrón característico de esteroles en comparación con lo especificado para los aceites de oliva y de maíz. El aceite extraído de las semillas del cardo mariano es rica en fitoesteroles y podría ser utilizado en la preparación de alimentos y en nutrición humana

Microwave saturation of the Rydberg states of electrons on helium

We present measurements of the resonant microwave excitation of the Rydberg energy levels of surface state electrons on superfluid helium. The temperature dependent linewidth agrees well with theoretical predictions and is very small below 300 mK. Absorption saturation and power broadening were observed as the fraction of electrons in the first excited state was increased to 0.49, close to the thermal excitation limit of 0.5. The Rabi frequency was determined as a function of microwave power. The high values of the ratio of the Rabi frequency to linewidth confirm this system as an excellent candidate for creating qubits.Comment: 4 pages, 4 figure

Bioactive Lipids, Antibacterial, Hypoglycaemic, and Antioxidant Potentials of Immature and Mature Vicia faba L. Seeds Cultivated in Tunisia

Both the immature and mature Vicia faba L. seeds are used for human consumption. However, there is a lack of information on the phytochemical composition and the potent biological properties of the immature seeds. The aim of the present study was to establish the profile of bioactive lipids as well as the antibacterial, antioxidant, and α-amylase and α-glucosidase inhibitory capacities of the immature and mature Vicia faba L. seeds. The studied petroleum ether extracts contain different bioactive compounds such as β-sitosterol, lupeol, β-amyrin, α-tocopherol, and γ-tocopherol. The extracts of the immature seeds exhibited higher antioxidant and antibacterial activities than those of mature ones. All tested extracts exerted higher inhibition on α-glucosidase than α-amylase. The immature seeds appeared as promising sources of natural antioxidants, antibacterial compounds, and α-amylase and α-glucosidase inhibitors. Thus, the immature Vicia faba L. seeds have a great potential as functional foods providing health beneficial properties

Interqubit coupling mediated by a high-excitation-energy quantum object

We consider a system composed of two qubits and a high-excitation-energy quantum object used to mediate coupling between the qubits. We treat the entire system quantum mechanically and analyze the properties of the eigenvalues and eigenstates of the total Hamiltonian. After reproducing well-known results concerning the leading term in the mediated coupling, we obtain an expression for the residual coupling between the qubits in the off state. We also analyze the entanglement between the three objects, i.e. the two qubits and the coupler, in the eigenstates of the total Hamiltonian. Although we focus on the application of our results to the recently realized parametric-coupling scheme with two qubits, we also discuss extensions of our results to harmonic-oscillator couplers, couplers that are near resonance with the qubits and multi-qubit systems. In particular, we find that certain errors that are absent for a two-qubit system arise when dealing with multi-qubit systems.Comment: 15 pages (two-column

Microwave microscopy applied to EMC problem: Visualisation of electromagnetic field in the vicinity of electronic circuit and effect of nanomaterial coating

This proposal is devoted to a collaborative approach dealing with microwave microscopy experiments. The application is dedicated to an electromagnetic field cartography above circuits and the influence of nanometric material layer deposition on the circuits. The first application is associated to a microstrip ring resonator. The results match with the simulated fields. The second application is focused on the effects of a dielectric layer deposited on the circuit and its impact in terms of electromagnetic propagation

Direct Measurement of the System-Environment Coupling as a Tool For Understanding Decoherence and Dynamical Decoupling

Decoherence is a major obstacle to any practical implementation of quantum information processing. One of the leading strategies to reduce decoherence is dynamical decoupling --- the use of an external field to average out the effect of the environment. The decoherence rate under any control field can be calculated if the spectrum of the coupling to the environment is known. We present a direct measurement of the bath coupling spectrum in an ensemble of optically trapped ultracold atoms, by applying a spectrally narrow-band control field. The measured spectrum follows a Lorentzian shape at low frequencies, but exhibits non-monotonic features at higher frequencies due to the oscillatory motion of the atoms in the trap. These features agree with our analytical models and numerical Monte-Carlo simulations of the collisional bath. From the inferred bath-coupling spectrum, we predict the performance of well-known dynamical decoupling sequences: CPMG, UDD and CDD. We then apply these sequences in experiment and compare the results to predictions, finding good agreement in the weak-coupling limit. Thus, our work establishes experimentally the validity of the overlap integral formalism, and is an important step towards the implementation of an optimal dynamical decoupling sequence for a given measured bath spectrum.Comment: 9 pages, 6 figure