Resonator/zero-Qubit architecture for superconducting qubits

We analyze the performance of the Resonator/zero-Qubit (RezQu) architecture in which the qubits are complemented with memory resonators and coupled via a resonator bus. Separating the stored information from the rest of the processing circuit by at least two coupling steps and the zero qubit state results in a significant increase of the ON/OFF ratio and the reduction of the idling error. Assuming no decoherence, we calculate such idling error, as well as the errors for the MOVE operation and tunneling measurement, and show that the RezQu architecture can provide high fidelity performance required for medium-scale quantum information processing.Comment: 11 pages, 5 figure

Assessing Laws and Legal Authorities for Obesity Prevention and Control

This is the first paper in a two part series on the laws and legal authorities for obesity prevention and control, which resulted from the National Summit on Legal Preparedness for Obesity Prevention and Control in 2008. In this paper, the authors apply the “laws and legal authorities” component of the Centers for Disease Control and Prevention (CDC) legal framework on public health legal preparedness to demonstrate the essential role that law can play in the fight against obesity. Their analysis identified numerous laws and policies in the three vital domains of healthy lifestyles, healthy places, and healthy societies. For example, in terms of healthy lifestyles, governments can impact nutrition through: food subsidies, taxation, and bans; food marketing strategies; and nutritional labeling and education. With regard to healthy places, state and local governments can apply zoning laws and policy decisions to change the environment to encourage healthy eating and physical activity. Governments can promote healthy societies through laws and legal authorities that affect the ability to address obesity from a social perspective (such as antidiscrimination law, health care insurance and benefit design, school and day care for children, and surveillance). This paper describes instances of how current laws and legal authorities affect the public health goal of preventing obesity in both positive and negative ways. It also highlights the progressive use of laws at every level of government (i.e., federal, state, and local) and the interaction of these laws as they relate to obesity prevention and control. In addition, general gaps in the use of law for obesity prevention and control are identified for attention and action. (These gaps serve as the basis for the companion paper, which delineates options for policymakers, practitioners, and other key stakeholders in the improvement of laws and legal authorities for obesity prevention and control.

Analysis of measurement errors for a superconducting phase qubit

We analyze several mechanisms leading to errors in a course of measurement of a superconducting flux-biased phase qubit. Insufficiently long measurement pulse may lead to nonadiabatic transitions between qubit states $|1>$ and $|0>$, before tunneling through a reduced barrier is supposed to distinguish the qubit states. Finite (though large) ratio of tunneling rates for these states leads to incomplete discrimination between $|1>$ and $|0>$. Insufficiently fast energy relaxation after the tunneling of state $|1>$ may cause the repopulation of the quantum well in which only the state $|0>$ is supposed to remain. We analyze these types of measurement errors using analytical approaches as well as numerical solution of the time-dependent Schr\"{o}dinger equation.Comment: 14 pages, 14 figure

Inflationary spectra and partially decohered distributions

It is generally expected that decoherence processes will erase the quantum properties of the inflationary primordial spectra. However, given the weakness of gravitational interactions, one might end up with a distribution which is only partially decohered. Below a certain critical change, we show that the inflationary distribution retains quantum properties. We identify four of these: a squeezed spread in some direction of phase space, non-vanishing off-diagonal matrix elements, and two properties used in quantum optics called non-$P$-representability and non-separability. The last two are necessary conditions to violate Bell's inequalities. The critical value above which all these properties are lost is associated to the `grain' of coherent states. The corresponding value of the entropy is equal to half the maximal (thermal) value. Moreover it coincides with the entropy of the effective distribution obtained by neglecting the decaying modes. By considering backreaction effects, we also provide an upper bound for this entropy at the onset of the adiabatic era.Comment: 42 pages, 9 figures; 1 ref. adde

Emergence of Oscillons in an Expanding Background

We consider a (1+1) dimensional scalar field theory that supports oscillons, which are localized, oscillatory, stable solutions to nonlinear equations of motion. We study this theory in an expanding background and show that oscillons now lose energy, but at a rate that is exponentially small when the expansion rate is slow. We also show numerically that a universe that starts with (almost) thermal initial conditions will cool to a final state where a significant fraction of the energy of the universe -- on the order of 50% -- is stored in oscillons. If this phenomenon persists in realistic models, oscillons may have cosmological consequences.Comment: 13 pages, 4 .eps figures, uses RevTeX4; v2: clarified details of expansion, added reference

Bound and resonance states of the nonlinear Schroedinger equation in simple model systems

The stationary nonlinear Schroedinger equation, or Gross-Pitaevskii equation, is studied for the cases of a single delta potential and a delta-shell potential. These model systems allow analytical solutions, and thus provide useful insight into the features of stationary bound, scattering and resonance states of the nonlinear Schroedinger equation. For the single delta potential, the influence of the potential strength and the nonlinearity is studied as well as the transition from bound to scattering states. Furthermore, the properties of resonance states for a repulsive delta-shell potential are discussed.Comment: 19 pages, 10 figure

P.A.M. Dirac and the Discovery of Quantum Mechanics

Dirac's contributions to the discovery of non-relativistic quantum mechanics and quantum electrodynamics, prior to his discovery of the relativistic wave equation, are described

Nonlocal Electrodynamics of Rotating Systems

The nonlocal electrodynamics of uniformly rotating systems is presented and its predictions are discussed. In this case, due to paucity of experimental data, the nonlocal theory cannot be directly confronted with observation at present. The approach adopted here is therefore based on the correspondence principle: the nonrelativistic quantum physics of electrons in circular "orbits" is studied. The helicity dependence of the photoeffect from the circular states of atomic hydrogen is explored as well as the resonant absorption of a photon by an electron in a circular "orbit" about a uniform magnetic field. Qualitative agreement of the predictions of the classical nonlocal electrodynamics with quantum-mechanical results is demonstrated in the correspondence regime.Comment: 23 pages, no figures, submitted for publicatio

Cooling Torsional Nanomechanical Vibration by Spin-Orbit Interactions

We propose and study a spin-orbit interaction based mechanism to actively cool down the torsional vibration of a nanomechanical resonator made by semiconductor materials. We show that the spin-orbit interactions of electrons can induce a coherent coupling between the electron spins and the torsional modes of nanomechanical vibration. This coherent coupling leads to an active cooling for the torsional modes via the dynamical thermalization of the resonator and the spin ensemble.Comment: 4 pages, 3 figure

Signatures of High-Intensity Compton Scattering

We review known and discuss new signatures of high-intensity Compton scattering assuming a scenario where a high-power laser is brought into collision with an electron beam. At high intensities one expects to see a substantial red-shift of the usual kinematic Compton edge of the photon spectrum caused by the large, intensity dependent, effective mass of the electrons within the laser beam. Emission rates acquire their global maximum at this edge while neighbouring smaller peaks signal higher harmonics. In addition, we find that the notion of the centre-of-mass frame for a given harmonic becomes intensity dependent. Tuning the intensity then effectively amounts to changing the frame of reference, going continuously from inverse to ordinary Compton scattering with the centre-of-mass kinematics defining the transition point between the two.Comment: 25 pages, 16 .eps figure