State tomography of capacitively shunted phase qubits with high fidelity

We introduce a new design concept for superconducting quantum bits (qubits) in which we explicitly separate the capacitive element from the Josephson tunnel junction for improved qubit performance. The number of two-level systems (TLS) that couple to the qubit is thereby reduced by an order of magnitude and the measurement fidelity improves to 90%. This improved design enables the first demonstration of quantum state tomography with superconducting qubits using single shot measurements.Comment: submitted to PR

Transformed Dissipation in Superconducting Quantum Circuits

Superconducting quantum circuits must be designed carefully to avoid dissipation from coupling to external control circuitry. Here we introduce the concept of current transformation to quantify coupling to the environment. We test this theory with an experimentally-determined impedance transformation of $\sim 10^5$ and find quantitative agreement better than a factor of 2 between this transformation and the reduced lifetime of a phase qubit coupled to a tunable transformer. Higher-order corrections from quantum fluctuations are also calculated with this theory, but found not to limit the qubit lifetime. We also illustrate how this simple connection between current and impedance transformation can be used to rule out dissipation sources in experimental qubit systems.Comment: 4 pages, 4 figure

The introduction of the bow and arrow in the Argentine Andes (29-34º S): A preliminary metric approximation

The study size patterns in projectile points (n=39) from six sites in the Argentine Andes (29-34° S) associated with 17 radiocarbon dates with medians spanning 3080-470 cal. BP. In the northern part of our study area (29° S), one site has domestic llama (Lama glama) bones as early as 5800 cal. BP. In the central and southern part of the study area (32 and 34° S), clear evidence for pastoralism, horticulture, and potentially agriculture is no earlier than 1500 cal. BP. Our study area extends to 34° S, which is the southern limit of pastoral and food-producing societies in South America. In our study area, it is unknown if the bow was adopted early, as in the central Andes, or late and used alongside spears, as in Patagonia. This is the region?s first attempt to metrically distinguish arrows and darts, which is based on shoulder or maximum width, following Shott. The northern sector located at 29° S includes the earliest arrow point, slightly after 3080 cal. BP. This suggests a rapid spread of this technology from the central Andes 16-26° S, where early arrows are dated ~3500-3000 cal. BP. However, at 32 and 34° S, arrows are not clearly present until 1280 cal. BP. For 1280-400 cal. BP (European contact), 96% of points were identified as arrows, suggesting the bow and arrow replaced spear-based weapon systems. A single late dart from 34° S may reflect a late use of this space by hunter-gatherers. The predominance of arrows beginning at 1280 cal. BP is associated with broader changes such as demographic growth, reduced mobility, low-level food production, and herding economies, following similar trends in other regions.Fil: Castro, Silvina Celeste. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza; Argentina. Universidad Nacional de Cuyo. Facultad de Ciencias Exactas y Naturales. Laboratorio de Paleoecología Humana; ArgentinaFil: Yebra, Lucía Gabriela. Universidad Nacional de Cuyo. Facultad de Ciencias Exactas y Naturales. Laboratorio de Paleoecología Humana; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza; ArgentinaFil: Marsh, Erik Johnson. Universidad Nacional de Cuyo. Facultad de Ciencias Exactas y Naturales. Laboratorio de Paleoecología Humana; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza; ArgentinaFil: Cortegoso, Valeria. Universidad Nacional de Cuyo. Facultad de Ciencias Exactas y Naturales. Laboratorio de Paleoecología Humana; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza; ArgentinaFil: Lucero Ferreyra, Gustavo Fernando. Universidad Nacional de Cuyo. Facultad de Ciencias Exactas y Naturales. Laboratorio de Paleoecología Humana; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza; Argentin

Microwave Dielectric Loss at Single Photon Energies and milliKelvin Temperatures

The microwave performance of amorphous dielectric materials at very low temperatures and very low excitation strengths displays significant excess loss. Here, we present the loss tangents of some common amorphous and crystalline dielectrics, measured at low temperatures (T < 100 mK) with near single-photon excitation energies, using both coplanar waveguide (CPW) and lumped LC resonators. The loss can be understood using a two-level state (TLS) defect model. A circuit analysis of the half-wavelength resonators we used is outlined, and the energy dissipation of such a resonator on a multilayered dielectric substrate is considered theoretically.Comment: 4 pages, 3 figures, submitted to Applied Physics Letter

Improving the Coherence Time of Superconducting Coplanar Resonators

The quality factor and energy decay time of superconducting resonators have been measured as a function of material, geometry, and magnetic field. Once the dissipation of trapped magnetic vortices is minimized, we identify surface two-level states (TLS) as an important decay mechanism. A wide gap between the center conductor and the ground plane, as well as use of the superconductor Re instead of Al, are shown to decrease loss. We also demonstrate that classical measurements of resonator quality factor at low excitation power are consistent with single-photon decay time measured using qubit-resonator swap experiments.Comment: 3 pages, 4 figures for the main paper; total 5 pages, 6 figures including supplementary material. Submitted to Applied Physics Letter

Social security for seafarers globally

Background: The social security protection is one of the essential elements of decent work. The issue is complexand no previous epidemiological studies of the coverage among the seafarers have yet been performed.Aim: The aim was to overcome the gap of knowledge to promote the further discussion and plan the implementationof the social security for all the seafarers.Materials and methods: The seafarers completed a short questionnaire concerning their knowledge abouttheir social security status.Results: The significant disparities in the social security coverage were pointed out among the nationalities.Especially it is worth mentioning that more than half of the respondents believe they are economicallyuncovered for disability from an injury on board and from a work-related disease.Conclusions: The results confirm the ILO (Convention No. 143) statements that the significant part of theseafarers comes from the poorer countries without the substantial social security systems. The solutionssuggested are to implement the minimum requirements as recommended by the ILO 2006 Convention, tosurvey the implementation and — in the long term — to struggle for a global social equality

Energy decay and frequency shift of a superconducting qubit from non-equilibrium quasiparticles

Quasiparticles are an important decoherence mechanism in superconducting qubits, and can be described with a complex admittance that is a generalization of the Mattis-Bardeen theory. By injecting non-equilibrium quasiparticles with a tunnel junction, we verify qualitatively the expected change of the decay rate and frequency in a phase qubit. With their relative change in agreement to within 4% of prediction, the theory can be reliably used to infer quasiparticle density. We describe how settling of the decay rate may allow determination of whether qubit energy relaxation is limited by non-equilibrium quasiparticles.Comment: Main paper: 4 pages, 3 figures, 1 table. Supplementary material: 8 pages, 3 figure

Reduced phase error through optimized control of a superconducting qubit

Minimizing phase and other errors in experimental quantum gates allows higher fidelity quantum processing. To quantify and correct for phase errors in particular, we have developed a new experimental metrology --- amplified phase error (APE) pulses --- that amplifies and helps identify phase errors in general multi-level qubit architectures. In order to correct for both phase and amplitude errors specific to virtual transitions and leakage outside of the qubit manifold, we implement "half derivative" an experimental simplification of derivative reduction by adiabatic gate (DRAG) control theory. The phase errors are lowered by about a factor of five using this method to $\sim 1.6^{\circ}$ per gate, and can be tuned to zero. Leakage outside the qubit manifold, to the qubit $|2\rangle$ state, is also reduced to $\sim 10^{-4}$ for $20\%$ faster gates.Comment: 4 pages, 4 figures with 2 page supplementa

Deterministic entanglement of photons in two superconducting microwave resonators

Quantum entanglement, one of the defining features of quantum mechanics, has been demonstrated in a variety of nonlinear spin-like systems. Quantum entanglement in linear systems has proven significantly more challenging, as the intrinsic energy level degeneracy associated with linearity makes quantum control more difficult. Here we demonstrate the quantum entanglement of photon states in two independent linear microwave resonators, creating N-photon NOON states as a benchmark demonstration. We use a superconducting quantum circuit that includes Josephson qubits to control and measure the two resonators, and we completely characterize the entangled states with bipartite Wigner tomography. These results demonstrate a significant advance in the quantum control of linear resonators in superconducting circuits.Comment: 11 pages, 11 figures, and 3 tables including supplementary materia