Boundary of Quantum Evolution under Decoherence

Relaxation effects impose fundamental limitations on our ability to coherently control quantum mechanical phenomena. In this letter, we establish physical limits on how closely can a quantum mechanical system be steered to a desired target state in the presence of relaxation. In particular, we explicitly compute the maximum coherence or polarization that can be transferred between coupled nuclear spins in the presence of very general decoherence mechanisms that include cross-correlated relaxation. We give analytical expressions for the control laws (pulse sequences) which achieve these physical limits and provide supporting experimental evidence. Exploitation of cross-correlation effects has recently led to the development of powerful methods in NMR spectroscopy to study very large biomolecules in solution. We demonstrate with experiments that the optimal pulse sequences provide significant gains over these state of the art methods, opening new avenues for spectroscopy of much larger proteins. Surprisingly, in spite of very large relaxation rates, optimal control can transfer coherence without any loss when cross-correlated relaxation rates are tuned to auto-correlated relaxation rates

The specter of accountability

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71611/1/j.1360-0443.1994.tb03346.x.pd

A matter of moral perspective

In the USA, treatment for alcohol and drug problems is provided in both the public and private sectors. But because there is no universal health insurance scheme, access to treatment is severely limited. This unfortunate situation may be a consequence of an historically influential moral perspective on poverty and illness. An alternative perspective is urged.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75191/1/j.1360-0443.1991.tb02620.x.pd

Patterns of ‘balancing between hope and despair’ in the diagnostic phase: a grounded theory study of patients on a gastroenterology ward

Aim: The aim of the study was to learn how patients going through the diagnostic phase experienced and handled their situation. Background: Many studies report about the stressful diagnostic phase; however, none has presented a conceptual theory where the concepts are sufficiently related to each other. The Theory of Preparative Waiting has previously been published as a descriptive grounded theory and describes the experience of a group of gastroenterology patients going through the diagnostic phase. Method: A classical grounded theory design was used, with data derived from 18 in-depth interviews with 15 patients in a gastroenterology ward at a Norwegian University Hospital. Interviews were conducted during 2002–2003. Findings: Participants’ main concern was found to be how they could prepare themselves for the concluding interview and life after diagnosis. The theoretical code of ‘balancing’ had four patterns; controlling pain, rational awaiting, denial, and accepting. These patterns of ‘balancing’ guided how participants used the categories of ‘Preparative Waiting Theory’ ‘seeking and giving information’, ‘interpreting clues’, ‘handling existential threats’ and ‘seeking respite’. Patterns were strategies, so one person could use more than one pattern. Conclusion: The diagnostic phase was a difficult time for the participants and the ‘Preparative Waiting Theory’ can assist nurses in assessing how patients prepare themselves differently for getting a diagnosis. All patients would find it helpful to be followed up by a designated contact person at the ward; however, patients using mostly the patterns of controlling pain and denial would benefit most from such support

Geometric optimal control of the contrast imaging problem in Nuclear Magnetic Resonance

The objective of this article is to introduce the tools to analyze the contrast imaging problem in Nuclear Magnetic Resonance. Optimal trajectories can be selected among extremal solutions of the Pontryagin Maximum Principle applied to this Mayer type optimal problem. Such trajectories are associated to the question of extremizing the transfer time. Hence the optimal problem is reduced to the analysis of the Hamiltonian dynamics related to singular extremals and their optimality status. This is illustrated by using the examples of cerebrospinal fluid / water and grey / white matter of cerebrum.Comment: 30 pages, 13 figur

Being Healthy: a Grounded Theory Study of Help Seeking Behaviour among Chinese Elders living in the UK

The health of older people is a priority in many countries as the world’s population ages. Attitudes towards help seeking behaviours in older people remain a largely unexplored field of research. This is particularly true for older minority groups where the place that they have migrated to presents both cultural and structural challenges. The UK, like other countries,has an increasingly aging Chinese population about who relatively little is known. This study used a qualitative grounded theory design following the approach of Glaser (1978). Qualitative data were collected using semi-structured interviews with 33 Chinese elders who were aged between 60 and 84, using purposive and theoretical sampling approaches. Data were analysed using the constant comparative method until data saturation occurred and a substantive theory was generated. ‘Being healthy’ (the core category) with four interrelated categories: self-management, normalizing/minimizing, access to health services, and being cured form the theory. The theory was generated around the core explanations provided by participants and Chinese elders’ concerns about health issues they face in their daily life. We also present data about how they direct their health-related activities towards meeting their physical and psychological goals of being healthy. Their differential understanding of diseases and a lack of information about health services were potent predictors of non�help seeking and ‘self’ rather than medical management of their illnesses. This study highlights the need for intervention and health support for Chinese elders

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