33 research outputs found
The Optimal Control Landscape for the Generation of Unitary Transformations with Constrained Dynamics
The reliable and precise generation of quantum unitary transformations is
essential to the realization of a number of fundamental objectives, such as
quantum control and quantum information processing. Prior work has explored the
optimal control problem of generating such unitary transformations as a surface
optimization problem over the quantum control landscape, defined as a metric
for realizing a desired unitary transformation as a function of the control
variables. It was found that under the assumption of non-dissipative and
controllable dynamics, the landscape topology is trap-free, implying that any
reasonable optimization heuristic should be able to identify globally optimal
solutions. The present work is a control landscape analysis incorporating
specific constraints in the Hamiltonian corresponding to certain dynamical
symmetries in the underlying physical system. It is found that the presence of
such symmetries does not destroy the trap-free topology. These findings expand
the class of quantum dynamical systems on which control problems are
intrinsically amenable to solution by optimal control.Comment: Submitted to Journal of Mathematical Physic
Encoding a qubit into multilevel subspaces
We present a formalism for encoding the logical basis of a qubit into
subspaces of multiple physical levels. The need for this multilevel encoding
arises naturally in situations where the speed of quantum operations exceeds
the limits imposed by the addressability of individual energy levels of the
qubit physical system. A basic feature of the multilevel encoding formalism is
the logical equivalence of different physical states and correspondingly, of
different physical transformations. This logical equivalence is a source of a
significant flexibility in designing logical operations, while the multilevel
structure inherently accommodates fast and intense broadband controls thereby
facilitating faster quantum operations. Another important practical advantage
of multilevel encoding is the ability to maintain full quantum-computational
fidelity in the presence of mixing and decoherence within encoding subspaces.
The formalism is developed in detail for single-qubit operations and
generalized for multiple qubits. As an illustrative example, we perform a
simulation of closed-loop optimal control of single-qubit operations for a
model multilevel system, and subsequently apply these operations at finite
temperatures to investigate the effect of decoherence on operational fidelity.Comment: IOPart LaTeX, 2 figures, 31 pages; addition of a numerical simulatio
Defining Natural History: Assessment of the Ability of College Students to Aid in Characterizing Clinical Progression of Niemann-Pick Disease, Type C
Niemann-Pick Disease, type C (NPC) is a fatal, neurodegenerative, lysosomal storage disorder. It is a rare disease with broad phenotypic spectrum and variable age of onset. These issues make it difficult to develop a universally accepted clinical outcome measure to assess urgently needed therapies. To this end, clinical investigators have defined emerging, disease severity scales. The average time from initial symptom to diagnosis is approximately 4 years. Further, some patients may not travel to specialized clinical centers even after diagnosis. We were therefore interested in investigating whether appropriately trained, community-based assessment of patient records could assist in defining disease progression using clinical severity scores. In this study we evolved a secure, step wise process to show that pre-existing medical records may be correctly assessed by non-clinical practitioners trained to quantify disease progression. Sixty-four undergraduate students at the University of Notre Dame were expertly trained in clinical disease assessment and recognition of major and minor symptoms of NPC. Seven clinical records, randomly selected from a total of thirty seven used to establish a leading clinical severity scale, were correctly assessed to show expected characteristics of linear disease progression. Student assessment of two new records donated by NPC families to our study also revealed linear progression of disease, but both showed accelerated disease progression, relative to the current severity scale, especially at the later stages. Together, these data suggest that college students may be trained in assessment of patient records, and thus provide insight into the natural history of a disease
Nonuniversality in the Pinch-Off of Yield Stress Fluids: Role of Nonlocal Rheology
The pinch-off behavior of yield stress fluids is investigated using droplet and liquid-bridge breakup experiments. Contrary to expectations, the neck thinning behavior depends strongly on the way the breakup experiment is carried out. This nonuniversal behavior can be explained through an analysis of the thinning dynamics as well as the shapes of the fluid necks. Recent nonlocal models for the rheology of yield stress fluids are found to be compatible with the results presented
Observation of correlated X-ray scattering at atomic resolution
International audienceTools to study disordered systems with local structural order, such as proteins in solution, remain limited. Such understanding is essential for e.g. rational drug design. Correlated X-ray scattering (CXS) has recently attracted new interest as a way to leverage next-generation light sources to study such disordered matter. The CXS experiment measures angular correlations of the intensity caused by the scattering of X-rays from an ensemble of identical particles, with disordered orientation and position. Averaging over 15 496 snapshot images obtained by exposing a sample of silver nanoparticles in solution to a micro-focused synchrotron radiation beam, we report on experimental efforts to obtain CXS signal from an ensemble in three dimensions. A correlation function was measured at wide angles corresponding to atomic resolution that matches theoretical predictions. These preliminary results suggest that other CXS experiments on disordered ensembles\textemdashsuch as proteins in solution\textemdashmay be feasible in the future