Optimal control of a leaking qubit

Physical implementations of quantum bits can contain coherent transitions to energetically close non-qubit states. In particular, for anharmonic oscillator systems such as the superconducting phase qubit and the transmon a two-level approximation is insufficient. We apply optimal control theory to the envelope of a resonant Rabi pulse in a qubit in the presence of a single, weakly off-resonant leakage level. The gate error of a spin flip operation reduces by orders of magnitude compared to simple pulse shapes. Near-perfect gates can be achieved for any pulse duration longer than an intrinsic limit given by the nonlinearity. The pulses can be understood as composite sequences that refocus the leakage transition. We also discuss ways to improve the pulse shapes.Comment: 4 pages, 2 figure

Engineering adiabaticity at an avoided crossing with optimal control

We investigate ways to optimize adiabaticity and diabaticity in the Landau-Zener model with non-uniform sweeps. We show how diabaticity can be engineered with a pulse consisting of a linear sweep augmented by an oscillating term. We show that the oscillation leads to jumps in populations whose value can be accurately modeled using a model of multiple, photon-assisted Landau-Zener transitions, which generalizes work by Wubs et al. [New J. Phys. 7, 218 (2005)]. We extend the study on diabaticity using methods derived from optimal control. We also show how to preserve adiabaticity with optimal pulses at limited time, finding a non-uniform quantum speed limit

Ohmic and step noise from a single trapping center hybridized with a Fermi sea

We show that single electron tunneling devices such as the Cooper-pair box or double quantum dot can be sensitive to the zero-point fluctuation of a single trapping center hybridized with a Fermi sea. If the trap energy level is close to the Fermi sea and has line-width \gamma > k_B T, its noise spectrum has an Ohmic Johnson-Nyquist form, whereas for \gamma < k_B T the noise has a Lorentzian form expected from the semiclassical limit. Trap levels above the Fermi level are shown to lead to steps in the noise spectrum that can be used to probe their energetics, allowing the identification of individual trapping centers coupled to the device.Comment: Revised version to appear in Phys. Rev. Let

Stereoscopic Polar Plume Reconstructions from Stereo/Secchi Images

We present stereoscopic reconstructions of the location and inclination of polar plumes of two data sets based on the two simultaneously recorded images taken by the EUVI telescopes in the SECCHI instrument package onboard the \emph{STEREO (Solar TErrestrial RElations Observatory)} spacecraft. The ten plumes investigated show a superradial expansion in the coronal hole in 3D which is consistent with the 2D results. Their deviations from the local meridian planes are rather small with an average of $6.47^{\circ}$. By comparing the reconstructed plumes with a dipole field with its axis along the solar rotation axis, it is found that plumes are inclined more horizontally than the dipole field. The lower the latitude is, the larger is the deviation from the dipole field. The relationship between plumes and bright points has been investigated and they are not always associated. For the first data set, based on the 3D height of plumes and the electron density derived from SUMER/\emph{SOHO} Si {\sc viii} line pair, we found that electron densities along the plumes decrease with height above the solar surface. The temperature obtained from the density scale height is 1.6 to 1.8 times larger than the temperature obtained from Mg {\sc ix} line ratios. We attribute this discrepancy to a deviation of the electron and the ion temperatures. Finally, we have found that the outflow speeds studied in the O {\sc vi} line in the plumes corrected by the angle between the line of sight and the plume orientation are quite small with a maximum of 10 $\mathrm{km s^{-1}}$. It is unlikely that plumes are a dominant contributor to the fast solar wind.Comment: 25 pages, 13 figure

Entangling flux qubits with a bipolar dynamic inductance

We propose a scheme to implement variable coupling between two flux qubits using the screening current response of a dc Superconducting QUantum Interference Device (SQUID). The coupling strength is adjusted by the current bias applied to the SQUID and can be varied continuously from positive to negative values, allowing cancellation of the direct mutual inductance between the qubits. We show that this variable coupling scheme permits efficient realization of universal quantum logic. The same SQUID can be used to determine the flux states of the qubits.Comment: 4 pages, 4 figure

Asthmatic Children: Parental Child-Rearing Attitudes and Family Dynamics

Es wird versucht einige in der Literatur genannten Konzepte über familiendynamische Vorgänge in Familien mit asthmakranken Kindern am Beispiel der elterlichen Erziehungseinstellung empirisch zu überprüfen. Untersucht wurden 68 Kinder mit Asthma bronchiale und deren Eltern sowie 118 gesunde Kontrollkinder und deren Eltern mit einem mehrdimensionalen Fragebogen zur vom Kind perzipierten väterlichen bzw. mütterlichen Erziehungseinstellung sowie mit dem FPI. Die Testdaten sowie psychosoziale und klinische Daten wurden durch multivariate Verfahren statistisch bearbeitet. Die Erziehungsskalen diskriminierten nur die Asthmaväter von den Kontrollvätern, nicht jedoch die Mütter. Dennoch werden die Ergebnisse als zumindest partielle Bestätigung der familiendynamischen Konzepte interpretiert. Das wichtigste Ergebnis der Studie ist, dass die Rolle der Väter in Asthmafamilien und die Vater-Kind-Beziehung bedeutender und differenzierter ist, als bisher angenommen wurde. Die Rolle der Väter kann als extrem konfliktvermeidend, harmonisierend und weiblich-mütterlich charakterisiert werden, was familiendynamisch in Zusammenhang mit einer mangelhaften Geschlechtsrollendifferenzierung der Eltern und dem Problem der Machtausübung der asthmakranken Kinder über ihre Eltern eine besondere Bedeutung erlangt. (DIPF/ Orig.)The study is an attempt to empirically test some concepts concerning dynamic processes in families with asthmatic children by means of the parental child-rearing attitude. 68 children suffering from asthma bronchiale and their parents were compared to 118 healthy children and their parents. We used the FPI and a multidimensional questionnaire concerning the child\u27s perception of the paternal respectively maternal child-rearing attitude. The test scores, psychosocial and clinical data were treated statistically by multivariate procedures. Discriminant analysis revealed child-rearing differences only among the fathers. No differences were found among the mothers of asthmatics and controls. However the results are interpreted at least as a partial verification of the family dynamics. The main results of the study concern the father\u27s role in the family. This part as well as the father-child-relation in families with asthmatic children seem much more significant and differentiated than research has hitherto supposed. The father\u27s role may be characterized as extremely harmonizing, conflict avoiding, and maternal. This role combined with insufficient gender role differentiation of the parents obtains a special significance. This is particularly the case when combined with the asthmatic child\u27s powerful position within the family process. (DIPF/ Orig.