12,755 research outputs found
Extracting high fidelity quantum computer hardware from random systems
An overview of current status and prospects of the development of quantum
computer hardware based on inorganic crystals doped with rare-earth ions is
presented. Major parts of the experimental work in this area has been done in
two places, Canberra, Australia and Lund, Sweden, and the present description
follows more closely the Lund work. Techniques will be described that include
optimal filtering of the initially inhomogeneously broadened profile down to
well separated and narrow ensembles, as well as the use of advanced
pulse-shaping in order to achieve robust arbitrary single-qubit operations with
fidelities above 90%, as characterized by quantum state tomography. It is
expected that full scalability of these systems will require the ability to
determine the state of single rare-earth ions. It has been proposed that this
can be done using special readout ions doped into the crystal and an update is
given on the work to find and characterize such ions. Finally, a few aspects on
the possibilities for remote entanglement of ions in separate
rare-earth-ion-doped crystals are considered.Comment: 19 pages, 9 figures. Written for The Proceedings of the
Nobelsymposium on qubits for future quantum computers, Gothenburg, May-0
Composite Dipolar Recoupling: Anisotropy Compensated Coherence Transfer in Solid-State NMR
The efficiency of dipole-dipole coupling driven coherence transfer
experiments in solid-state NMR spectroscopy of powder samples is limited by
dispersion of the orientation of the internuclear vectors relative to the
external magnetic field. Here we introduce general design principles and
resulting pulse sequences that approach full polarization transfer efficiency
for all crystallite orientations in a powder in magic-angle-spinning
experiments. The methods compensate for the defocusing of coherence due to
orientation dependent dipolar coupling interactions and inhomogeneous
radio-frequency fields. The compensation scheme is very simple to implement as
a scaffold (comb) of compensating pulses in which the pulse sequence to be
improved may be inserted. The degree of compensation can be adjusted and should
be balanced as a compromise between efficiency and length of the overall pulse
sequence. We show by numerical and experimental data that the presented
compensation protocol significantly improves the efficiency of known dipolar
recoupling solid-state NMR experiment
States prepared by decay
We consider the time evolution of a discrete state embedded in a continuum.
Results from scattering theory can be utilized to solve the initial value
problem and discuss the system as a model of wave packet preparation. Extensive
use is made of the analytic properties of the propagators, and simple model
systems are evaluated to illustrate the argument. We verify the exponential
appearence of the continuum state and its propagation as a localized wave
packet.Comment: 22 pages, Latex2.09, 6 Postscript figures embedded using psfig, see
also http://www.physics.helsinki.fi/~kasuomin/ To appear in a Special Issue
of Journal of Modern Optics (1997
A non-destructive view with X-rays into the strain state of bronze axes.
In this paper we present a new approach using highly surface sensitive X-ray diffraction methods for archaeometrical investigation highlighted on the Neolithic Axe of Ahneby. Applying the sin2Κ-method with a scintillation detector and a MAXIM camera setup, both usually applied for material strain analysis on modern metal fabrics. We can distinguish between different production states of bronze axes: Cast, forged and tempered. The method can be applied as a local probe of some 100th of Όm2 or integrative on a square centimeter surface area. We applied established synchrotron radiation based methods of material strain mapping and diffraction on a Neolithic bronze axe as well as replicated material for noninvasive analysis. The main goal of the described investigations was to identify the effects upon the bronze objects of post cast surface treatment with stone tools and of heat treatment
Multiple-spin coherence transfer in linear Ising spin chains and beyond: numerically-optimized pulses and experiments
We study multiple-spin coherence transfers in linear Ising spin chains with
nearest neighbor couplings. These constitute a model for efficient information
transfers in future quantum computing devices and for many multi-dimensional
experiments for the assignment of complex spectra in nuclear magnetic resonance
spectroscopy. We complement prior analytic techniques for multiple-spin
coherence transfers with a systematic numerical study where we obtain strong
evidence that a certain analytically-motivated family of restricted controls is
sufficient for time-optimality. In the case of a linear three-spin system,
additional evidence suggests that prior analytic pulse sequences using this
family of restricted controls are time-optimal even for arbitrary local
controls. In addition, we compare the pulse sequences for linear Ising spin
chains to pulse sequences for more realistic spin systems with additional
long-range couplings between non-adjacent spins. We experimentally implement
the derived pulse sequences in three and four spin systems and demonstrate that
they are applicable in realistic settings under relaxation and experimental
imperfections-in particular-by deriving broadband pulse sequences which are
robust with respect to frequency offsets.Comment: 11 page
Peer mentorship and positive effects on student mentor and mentee retention and academic success
This study examined how the introduction of peer mentorship in an undergraduate health and social welfare programme at a large northern university affected student learning. Using an ethnographic case study approach, the study draws upon data collected from a small group of mentors and their mentees over a period of one academic year using interviews, reflective journals, assessment and course evaluation data.
Analysis of the data collected identified a number of key findings: peer mentorship improves assessment performance for both mentee and mentor; reduces stress and anxiety, enhances participation and engagement in the academic community, and adds value to student outcomes
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