Long-lived qubit from three spin-1/2 atoms

A system of three spin-1/2 atoms allows the construction of a reference-frame-free (RFF) qubit in the subspace with total angular momentum $j=1/2$. The RFF qubit stays coherent perfectly as long as the spins of the three atoms are affected homogeneously. The inhomogeneous evolution of the atoms causes decoherence, but this decoherence can be suppressed efficiently by applying a bias magnetic field of modest strength perpendicular to the plane of the atoms. The resulting lifetime of the RFF qubit can be many days, making RFF qubits of this kind promising candidates for quantum information storage units. Specifically, we examine the situation of three $^6\textrm{Li}$ atoms trapped in a $\textrm{CO}_2$-laser-generated optical lattice and find that, with conservatively estimated parameters, a stored qubit maintains a fidelity of 0.9999 for two hours.Comment: 15 pages, 9 figures; version 2 reports a much improved analysis; version 3 contains more details about the four-atom cas

Quantum Phase Diffusion in a Small Underdamped Josephson Junction

Quantum phase diffusion in a small underdamped Nb/AlO$_x$/Nb junction ($\sim$ 0.4 $\mu$m$^2$) is demonstrated in a wide temperature range of 25-140 mK where macroscopic quantum tunneling (MQT) is the dominant escape mechanism. We propose a two-step transition model to describe the switching process in which the escape rate out of the potential well and the transition rate from phase diffusion to the running state are considered. The transition rate extracted from the experimental switching current distribution follows the predicted Arrhenius law in the thermal regime but is greatly enhanced when MQT becomes dominant.Comment: 4 pages, 4 figures, 1 tabl

Tuning Fermi-surface properties through quantum confinement in metallic meta-lattices: New metals from old atoms

We describe a new class of nanoscale structured metals wherein the effects of quantum confinement are combined with dispersive metallic electronic states to induce modifications to the fundamental low-energy microscopic properties of a three-dimensional metal: the density of states, the distribution of Fermi velocities, and the collective electronic response.Comment: 4 pages, 5 figures, to appear in Phys. Rev. Let

Field Theoretical Description of Quantum Hall Edge Reconstruction

We propose a generalization of the chiral Luttinger liquid theory to allow for a unified description of quantum Hall edges with or without edge reconstruction. Within this description edge reconstruction is found to be a quantum phase transition in the universality class of one-dimensional dilute Bose gas transition, whose critical behavior can be obtained exactly. At principal filling factors $\nu=1/m$, we show the additional edge modes due to edge reconstruction modifies the point contact tunneling exponent in the low energy limit, by a small and non-universal amount.Comment: 4 pages with 1 ps figure embedde

Estimasi Volume Sampah Domestik Dan Rekomendasi Rute Pengangkutan Sampah Berdasarkan Analisis Spasial Di Kota Surakarta

Penelitian ini bertujuan untuk menyusun model estimasi volume sampah domestik dan menentukan rute optimum pengangkutan sampah dari TPS ke TPA di Kota Surakarta. Metode penelitian yang digunakan yaitu metode survey dengan pengambilan data secara sampling (Proportional Random Sampling) dan analisis dilakukan secara kuantitatif dan kualitatif. Dari penelitian ini dihasilkan : a) jumlah rumah mukim hasil dari interpretasi citra Quickbird sebesar 141.049, estimasi jumlah penduduk sebesar 646.732 jiwa, estimasi volume sampah domestik sebesar 2.766.399,91 dm3, dan b) 52 rute optimum pengangkutan sampah dari TPS menuju TPA Mojosongo

Simultaneous reactive dyeing and surface modification of polyamide fabric with TiO₂ precursor finish using a one-step hydrothermal process

In this article, the approach of dyeing polyamide (PA) fabric by using C.I. Reactive Blue 19 dye and simultaneously modifying it with titanium dioxide precursor under hydrothermal conditions is developed. The anthraquinone-based Reactive Blue 19 dye, which is more resistant to biodegradation owing to its fused aromatic structure compared to an azo-based one, is utilized as a model compound in this research to demonstrate the photodegradation effect of TiO₂ on reactive dyes. It is shown that a layer of TiO₂ nanoparticles is homogeneously coated on fiber surfaces and their particle sizes are smaller than those remaining in the residual dyeing liquors. The crystallinity and optical properties of the resultant PA fabrics are changed due to this hydrothermal dyeing process. In comparison with the dyed-only PA fabrics, the PA fabrics dyed and simultaneously modified with anatase TiO₂ nanoparticles exhibit better color fastness against artificial light (xenon) while maintain similar grades of color fastness against washing with soap, wet scrubbing, dry cleaning as well as dry/wet rubbing. While changes in tensile strength, elongation and water absorbency of the resultant PA fabrics were not found, the addition of tetrabutyl titanate in the dyeing liquor is proved to facilitate the reaction of reactive dye with PA fabric and the resultant PA fabric shade. More interestingly, it is noticed that the residual dyeing liquor can be photodegraded after 50 mins of either UV or visible light irradiation, and the dyeing wastewater can thus be released in an eco-friendly manner to the environment

Quantum and classical resonant escapes of a strongly-driven Josephson junction

The properties of phase escape in a dc SQUID at 25 mK, which is well below quantum-to-classical crossover temperature $T_{cr}$, in the presence of strong resonant ac driving have been investigated. The SQUID contains two Nb/Al-AlO$_{x}$/Nb tunnel junctions with Josephson inductance much larger than the loop inductance so it can be viewed as a single junction having adjustable critical current. We find that with increasing microwave power $W$ and at certain frequencies $\nu$ and $\nu$/2, the single primary peak in the switching current distribution, \textrm{which is the result of macroscopic quantum tunneling of the phase across the junction}, first shifts toward lower bias current $I$ and then a resonant peak develops. These results are explained by quantum resonant phase escape involving single and two photons with microwave-suppressed potential barrier. As $W$ further increases, the primary peak gradually disappears and the resonant peak grows into a single one while shifting further to lower $I$. At certain $W$, a second resonant peak appears, which can locate at very low $I$ depending on the value of $\nu$. Analysis based on the classical equation of motion shows that such resonant peak can arise from the resonant escape of the phase particle with extremely large oscillation amplitude resulting from bifurcation of the nonlinear system. Our experimental result and theoretical analysis demonstrate that at $T\ll T_{cr}$, escape of the phase particle could be dominated by classical process, such as dynamical bifurcation of nonlinear systems under strong ac driving.Comment: 10 pages, 9 figures, 1 tabl