arXiv subjects

H. Wang

Publications and source records attributed to H. Wang.

At least 361 records · Page 20Linked to original sources

arXiv2011

Phase qubits fabricated with trilayer junctions

We have developed a novel Josephson junction geometry with minimal volume of lossy isolation dielectric, being suitable for higher quality trilayer junctions implemented in qubits. The junctions are based on in-situ deposited trilayers with thermal tunnel oxide, have micron-sized areas and a low subgap current. In qubit spectroscopy only a few avoided level crossings are observed, and the measured relaxation time of $T_1\approx400\;\rm{nsec}$ is in good agreement with the usual phase qubit decay time, indicating low loss due to the additional isolation dielectric.

cond-mat.supr-con↗

arXiv2011

Mean Interplanetary Magnetic Field Measurement Using the ARGO-YBJ Experiment

The sun blocks cosmic ray particles from outside the solar system, forming a detectable shadow in the sky map of cosmic rays detected by the ARGO-YBJ experiment in Tibet. Because the cosmic ray particles are positive charged, the magnetic field between the sun and the earth deflects them from straight trajectories and results in a shift of the shadow from the true location of the sun. Here we show that the shift measures the intensity of the field which is transported by the solar wind from the sun to the earth.

astro-ph.SR↗

arXiv2011

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.

cond-mat.supr-con↗

arXiv2010

Wirebond crosstalk and cavity modes in large chip mounts for superconducting qubits

We analyze the performance of a microwave chip mount that uses wirebonds to connect the chip and mount grounds. A simple impedance ladder model predicts that transmission crosstalk between two feedlines falls off exponentially with distance at low frequencies, but rises to near unity above a resonance frequency set by the chip to ground capacitance. Using SPICE simulations and experimental measurements of a scale model, the basic predictions of the ladder model were verified. In particular, by decreasing the capacitance between the chip and box grounds, the resonance frequency increased and transmission decreased. This model then influenced the design of a new mount that improved the isolation to -65 dB at 6 GHz, even though the chip dimensions were increased to 1 cm by 1 cm, 3 times as large as our previous devices. We measured a coplanar resonator in this mount as preparation for larger qubit chips, and were able to identify cavity, slotline, and resonator modes.

cond-mat.supr-con↗

arXiv2010

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.

quant-ph↗

arXiv2010

Spectral Perturbation and Reconstructability of Complex Networks

In recent years, many network perturbation techniques, such as topological perturbations and service perturbations, were employed to study and improve the robustness of complex networks. However, there is no general way to evaluate the network robustness. In this paper, we propose a new global measure for a network, the reconstructability coefficient θ, defined as the maximum number of eigenvalues that can be removed, subject to the condition that the adjacency matrix can be reconstructed exactly. Our main finding is that a linear scaling law, E[θ]=aN, seems universal, in that it holds for all networks that we have studied.

cond-mat.stat-mech↗

arXiv2010

Demonstration of a Tuneable Coupler for Superconducting Qubits Using Coherent, Time Domain, Two-Qubit Operations

A major challenge in the field of quantum computing is the construction of scalable qubit coupling architectures. Here, we demonstrate a novel tuneable coupling circuit that allows superconducting qubits to be coupled over long distances. We show that the inter-qubit coupling strength can be arbitrarily tuned over nanosecond timescales within a sequence that mimics actual use in an algorithm. The coupler has a measured on/off ratio of 1000. The design is self-contained and physically separate from the qubits, allowing the coupler to be used as a module to connect a variety of elements such as qubits, resonators, amplifiers, and readout circuitry over long distances. Such design flexibility is likely to be essential for a scalable quantum computer.

quant-ph↗

arXiv2010

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.

quant-ph↗

arXiv2010

Quantum process tomography of two-qubit controlled-Z and controlled-NOT gates using superconducting phase qubits

We experimentally demonstrate quantum process tomography of controlled-Z and controlled-NOT gates using capacitively-coupled superconducting phase qubits. These gates are realized by using the $|2\rangle$ state of the phase qubit. We obtain a process fidelity of 0.70 for the controlled-phase and 0.56 for the controlled-NOT gate, with the loss of fidelity mostly due to single-qubit decoherence. The controlled-Z gate is also used to demonstrate a two-qubit Deutsch-Jozsa algorithm with a single function query.

cond-mat.mes-hall↗

arXiv2010

Production of high purity TeO2 single crystals for the study of neutrinoless double beta decay

High purity TeO2 crystals are produced to be used for the search for the neutrinoless double beta decay of 130Te. Dedicated production lines for raw material synthesis, crystal growth and surface processing were built compliant with radio-purity constraints specific to rare event physics experiments. High sensitivity measurements of radio-isotope concentrations in raw materials, reactants, consumables, ancillaries and intermediary products used for TeO2 crystals production are reported. Production and certification protocols are presented and resulting ready-to-use TeO2 crystals are described.

cond-mat.mtrl-sci↗

arXiv2010

Exploring the "Island of Inversion" by in-beam gamma-ray spectroscopy of the neutron-rich sodium isotopes 31,32,33Na

The structure of the neutron rich sodium isotopes 31,32,33Na was investigated by means of in-beam gammaray spectroscopy following one-neutron knockout and inelastic scattering of radioactive beams provided by the RIKEN Radioactive Ion Beam Factory. The secondary beams were selected and separated by the fragment separator BigRIPS and incident at ~240 meV/u on a natural carbon (secondary) target, which was surrounded by the DALI2 array to detect coincident de-excitation gammarays. Scattered particles were identified by the spectrometer ZeroDegree. In 31Na, a new decay gammaray was observed in coincidence with the known (5/2+)-> 3/2(+) transition, while for 32,33Na excited states are reported for the first time. From a comparison to state-of-the-art shell model calculations it is concluded that the newly observed excited state in 31Na belongs to a rotational band formed by a 2p2h intruder configuration within the "Island of Inversion".

nucl-ex↗

arXiv2010

Generation of Three-Qubit Entangled States using Superconducting Phase Qubits

Entanglement is one of the key resources required for quantum computation, so experimentally creating and measuring entangled states is of crucial importance in the various physical implementations of a quantum computer. In superconducting qubits, two-qubit entangled states have been demonstrated and used to show violations of Bell's Inequality and to implement simple quantum algorithms. Unlike the two-qubit case, however, where all maximally-entangled two-qubit states are equivalent up to local changes of basis, three qubits can be entangled in two fundamentally different ways, typified by the states $|\mathrm{GHZ}> = (|000> + |111>)/\sqrt{2}$ and $|\mathrm{W}> = (|001> + |010> + |100>)/\sqrt{3}$. Here we demonstrate the operation of three coupled superconducting phase qubits and use them to create and measure $|\mathrm{GHZ}>$ and $|\mathrm{W}>$ states. The states are fully characterized using quantum state tomography and are shown to satisfy entanglement witnesses, confirming that they are indeed examples of three-qubit entanglement and are not separable into mixtures of two-qubit entanglement.

cond-mat.supr-con↗

arXiv2010

On Temporal Variations of the Multi-TeV Cosmic Ray Anisotropy using the Tibet III Air Shower Array

We analyze the large-scale two-dimensional sidereal anisotropy of multi-TeV cosmic rays by Tibet Air Shower Array, with the data taken from 1999 November to 2008 December. To explore temporal variations of the anisotropy, the data set is divided into nine intervals, each in a time span of about one year. The sidereal anisotropy of magnitude about 0.1% appears fairly stable from year to year over the entire observation period of nine years. This indicates that the anisotropy of TeV Galactic cosmic rays remains insensitive to solar activities since the observation period covers more than a half of the 23rd solar cycle.

astro-ph.HE↗

arXiv2009

Observation of TeV Gamma Rays from the Fermi Bright Galactic Sources with the Tibet Air Shower Array

Using the Tibet-III air shower array, we search for TeV gamma-rays from 27 potential Galactic sources in the early list of bright sources obtained by the Fermi Large Area Telescope at energies above 100 MeV. Among them, we observe 7 sources instead of the expected 0.61 sources at a significance of 2 sigma or more excess. The chance probability from Poisson statistics would be estimated to be 3.8 x 10^-6. If the excess distribution observed by the Tibet-III array has a density gradient toward the Galactic plane, the expected number of sources may be enhanced in chance association. Then, the chance probability rises slightly, to 1.2 x 10^-5, based on a simple Monte Carlo simulation. These low chance probabilities clearly show that the Fermi bright Galactic sources have statistically significant correlations with TeV gamma-ray excesses. We also find that all 7 sources are associated with pulsars, and 6 of them are coincident with sources detected by the Milagro experiment at a significance of 3 sigma or more at the representative energy of 35 TeV. The significance maps observed by the Tibet-III air shower array around the Fermi sources, which are coincident with the Milagro >=3sigma sources, are consistent with the Milagro observations. This is the first result of the northern sky survey of the Fermi bright Galactic sources in the TeV region.

astro-ph.HE↗

arXiv2009

Constraints on Inelastic Dark Matter Signal using ZEPLIN-II Results

There has been an increasing interest on the concept of Inelastic Dark Matter (iDM) - motivated in part by some recent data. We describe the constraints on iDM from the results of the two phase dark matter detector ZEPLIN-II, which has demonstrated strong background discrimination capabilities (>98%). Using previously published estimates of the ZEPLIN-II residual background, the iDM limits presented here exclude a significantly larger iDM parameter space than the limits derived without background subtraction. Moreover, assuming standard xenon quenching factor (qXe) of 0.19, our ZEPLIN-II limits strongly suggest the exclusion of iDM signal claims at >99% C.L., for Weakly Interacting Massive Particles (WIMPs) masses >100 GeV.

astro-ph.CO↗

arXiv2009

Decoherence Dynamics of Complex Photon States in a Superconducting Circuit

Quantum states inevitably decay with time into a probabilistic mixture of classical states, due to their interaction with the environment and measurement instrumentation. We present the first measurement of the decoherence dynamics of complex photon states in a condensed-matter system. By controllably preparing a number of distinct, quantum-superposed photon states in a superconducting microwave resonator, we show that the subsequent decay dynamics can be quantitatively described by taking into account only two distinct decay channels, energy relaxation and dephasing. Our ability to prepare specific initial quantum states allows us to measure the evolution of specific elements in the quantum density matrix, in a very detailed manner that can be compared with theory.

cond-mat.mes-hall↗

arXiv2009

Large-scale sidereal anisotropy of multi-TeV galactic cosmic rays and the heliosphere

We develop a model anisotropy best-fitting to the two-dimensional sky-map of multi-TeV galactic cosmic ray (GCR) intensity observed with the Tibet III air shower (AS) array. By incorporating a pair of intensity excesses in the hydrogen deflection plane (HDP) suggested by Gurnett et al., together with the uni-directional and bi-directional flows for reproducing the observed global feature, this model successfully reproduces the observed sky-map including the "skewed" feature of the excess intensity from the heliotail direction, whose physical origin has long remained unknown. These additional excesses are modeled by a pair of the northern and southern Gaussian distributions, each placed ~50 degree away from the heliotail direction. The amplitude of the southern excess is as large as ~0.2 %, more than twice the amplitude of the northern excess. This implies that the Tibet AS experiment discovered for the first time a clear evidence of the significant modulation of GCR intensity in the heliotail and the asymmetric heliosphere.

astro-ph.GA↗

arXiv2009

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.

cond-mat.mes-hall↗