Experimental implementation of encoded logical qubit operations in a perfect quantum error correcting code

Large-scale universal quantum computing requires the implementation of quantum error correction (QEC). While the implementation of QEC has already been demonstrated for quantum memories, reliable quantum computing requires also the application of nontrivial logical gate operations to the encoded qubits. Here, we present examples of such operations by implementing, in addition to the identity operation, the NOT and the Hadamard gate to a logical qubit encoded in a five qubit system that allows correction of arbitrary single qubit errors. We perform quantum process tomography of the encoded gate operations, demonstrate the successful correction of all possible single qubit errors and measure the fidelity of the encoded logical gate operations

Laparoscopic Roux-en-Y Gastric Bypass After Failed Vertical Banded Gastroplasty: a Multicenter Experience with 203 Patients

Background: Vertical banded gastroplasty (VBG) has long been the main restrictive procedure for morbid obesity but has many long-term complications for which conversion to Roux-en-Y gastric bypass (RYGBP) is often considered the best option. Methods: This series regroups patients operated on by three different surgeons in four different centers. All data were collected prospectively, then pooled and analyzed retrospectively. Results: Out of 2,522 RYGBP performed between 1998 and 2010, 538 were reoperations, including 203 laparoscopic RYGBP after VBG. There were 175 women and 28 men. The mean BMI before VBG was 43.2 ± 6.3, and the mean BMI before reoperation was 37.4 ± 8.3. Most patients had more than one indication for reoperation and/or had regained significant weight. There was no conversion to open surgery. A total of 24 patients (11.8%) developed complications, including nine (4.5%) who required reoperation and one death. With a follow-up of 88.9% after 8years, the mean BMI after 1, 3, 5, 7, and 9years was 29.1, 28.8, 28.7, 29.9, and 28.8, respectively. Conclusions: On the basis of this experience, the largest with laparoscopic reoperative RYGBP after failed VBG, we conclude that this procedure can safely be performed in experienced hands, with weight loss results similar to those observed after primary RYGBP. In patients with too difficult an anatomy below the cardia, dividing the esophagus just above the esophago-gastric junction and performing an esophagojejunostomy may be a safe alternative to converting to a Scopinaro-type BPD, obviating the additional long-term risks associated with malabsorptio

Charge degree of freedom and single-spin fluid model in YBa_2Cu_4O_8

We present a 17O nuclear magnetic resonance study in the stoichiometric superconductor YBa_2Cu_4O_8. A double irradiation method enables us to show that, below around 180 K, the spin-lattice relaxation rate of plane oxygen is not only driven by magnetic, but also significantly by quadrupolar fluctuations, i.e. low-frequency charge fluctuations. In the superconducting state, on lowering the temperature, the quadrupolar relaxation diminishes faster than the magnetic one. These findings show that, with the opening of the pseudo spin gap, a charge degree of freedom of mainly oxygen character is present in the electronic low-energy excitation spectrum.Comment: 4 pages, 3 figures, REVTE

I.V. MIDAZOLAM AS AN INDUCTION AGENT FOR ANAESTHESIA: A STUDY IN VOLUNTEERS

The central nervous and cardiovascular effects of midazolam 0.15 mg kg−1 were studied in 20 healthy, unpremedicated volunteers (10 male and 10 female). No important side-effects were noted and the venous tolerance to midazolam was excellent. Three minutes after injection mean systolic arterial pressure decreased from 121±(SEM) 2 mm Hg to 115±(SEM) 2 mm Hg and diastolic pressure from 78±2 to 70±2 mm Hg (P <0.05), and these effects persisted for at least 20 mm. Heart rate increased from 77±4 beat mm−1 to 90±3 and 88±3 beat mm−1 1 and 3 mm after the injection (P <0.05). Anterograde amnesia (40±3 min duration) and drowsiness (lasting 128±23 mm) were observed in all subjects. Loss of the eyelash reflex and apnoea were observed more often in the male group than in the female subjects. Midazolam 0.15 mg kg−1 was not sufficient to induce anaesthesia reliably in healthy unpretnedicated volunteer

Spatial characterization of the magnetic field profile of a probe tip used in magnetic resonance force microscopy

We have developed the experimental approach to characterize spatial distribution of the magnetic field produced by cantilever tips used in magnetic resonance force microscopy (MRFM). We performed MRFM measurements on a well characterized diphenyl-picrylhydrazyl (DPPH) film and mapped the 3D field profile produced by a Nd2Fe14B probe tip. Using our technique field profiles of arbitrarily shaped probe magnets can be imaged.Comment: 10 pages, 5 figure

A suggested search for 207Pb nuclear Schiff moment in PbTiO3 ferroelectric

We suggest two types of experiments, NMR and macroscopic magnetometry, with solid PbTiO3 to search for the nuclear Schiff moment of 207Pb. Both kinds of experiments promise substantial improvement over the presently achieved sensitivities. Statistical considerations show that the improvement of the current sensitivity can be up to 10 orders of magnitude for the magnetometry experiment and up to 6 orders of magnitude for the NMR experiment. Such significant enhancement is due to the strong internal electric field of the ferroelectric, as well as due to the possibility to cool the nuclear-spin subsystem in the compound down to nanokelvin temperatures.Comment: 4 pages; revised sensitivity estimate for NMR experimen

Equilibrium properties of the mixed state in superconducting niobium in a transverse magnetic field: Experiment and theoretical model

Equilibrium magnetic properties of the mixed state in type-II superconductors were measured with high purity bulk and film niobium samples in parallel and perpendicular magnetic fields using dc magnetometry and scanning Hall-probe microscopy. Equilibrium magnetization data for the perpendicular geometry were obtained for the first time. It was found that none of the existing theories is consistent with these new data. To address this problem, a theoretical model is developed and experimentally validated. The new model describes the mixed state in an averaged limit, i.e. %without detailing the samples' magnetic structure and therefore ignoring interactions between vortices. It is quantitatively consistent with the data obtained in a perpendicular field and provides new insights on properties of vortices. % and the entire mixed state. At low values of the Ginzburg-Landau parameter, the model converts to that of Peierls and London for the intermediate state in type-I superconductors. It is shown that description of the vortex matter in superconductors in terms of a 2D gas is more appropriate than the frequently used crystal- and glass-like scenarios.Comment: 8 pages, 9 figure

Quantum information processing using strongly-dipolar coupled nuclear spins

Dipolar coupled homonuclear spins present challenging, yet useful systems for quantum information processing. In such systems, eigenbasis of the system Hamiltonian is the appropriate computational basis and coherent control can be achieved by specially designed strongly modulating pulses. In this letter we describe the first experimental implementation of the quantum algorithm for numerical gradient estimation on the eigenbasis of a four spin system.Comment: 5 pages, 5 figures, Accepted in PR