105 research outputs found
How state preparation can affect a quantum experiment: Quantum process tomography for open systems
We study the effects of preparation of input states in a quantum tomography
experiment. We show that maps arising from a quantum process tomography
experiment (called process maps) differ from the well know dynamical maps. The
difference between the two is due to the preparation procedure that is
necessary for any quantum experiment. We study two preparation procedures,
stochastic preparation and preparation by measurements. The stochastic
preparation procedure yields process maps that are linear, while the
preparations using von Neumann measurements lead to non-linear processes, and
can only be consistently described by a bi-linear process map. A new process
tomography recipe is derived for preparation by measurement for qubits. The
difference between the two methods is analyzed in terms of a quantum process
tomography experiment. A verification protocol is proposed to differentiate
between linear processes and bi-linear processes. We also emphasize the
preparation procedure will have a non-trivial effect for any quantum experiment
in which the system of interest interacts with its environment.Comment: 13 pages, no figures, submitted to Phys. Rev.
Self-paced reaching after stroke: a quantitative assessment of longitudinal and directional sensitivity using the H-Man planar robot for upper limb neurorehabilitation
Technology aided measures offer a sensitive, accurate and time-efficient approach for the assessment of sensorimotor function after neurological insult compared to standard clinical assessments. This study investigated the sensitivity of robotic measures to capture differences in planar reaching movements as a function of neurological status (stroke, healthy), direction (front, ipsilateral, contralateral), movement segment (outbound, inbound), and time (baseline, post-training, 2-week follow-up) using a planar, two-degrees of freedom, robotic-manipulator (H-Man). Twelve chronic stroke (age: 55 ± 10.0 years, 5 female, 7 male, time since stroke: 11.2 ± 6.0 months) and nine aged-matched healthy participants (age: 53 ± 4.3 years, 5 female, 4 male) participated in this study. Both healthy and stroke participants performed planar reaching movements in contralateral, ipsilateral and front directions with the H-Man, and the robotic measures, spectral arc length (SAL), normalized time to peak velocities (TpeakN), and root-mean square error (RMSE) were evaluated. Healthy participants went through a one-off session of assessment to investigate the baseline. Stroke participants completed a 2-week intensive robotic training plus standard arm therapy (8 × 90 min sessions). Motor function for stroke participants was evaluated prior to training (baseline, week-0), immediately following training (post-training, week-2), and 2-weeks after training (follow-up, week-4) using robotic assessment and the clinical measures Fugl-Meyer Assessment (FMA), Activity-Research-Arm Test (ARAT), and grip-strength. Robotic assessments were able to capture differences due to neurological status, movement direction, and movement segment. Movements performed by stroke participants were less-smooth, featured longer TpeakN, and larger RMSE values, compared to healthy controls. Significant movement direction differences were observed, with improved reaching performance for the front, compared to ipsilateral and contralateral movement directions. There were group differences depending on movement segment. Outbound reaching movements were smoother and featured longer TpeakN values than inbound movements for control participants, whereas SAL, TpeakN, and RMSE values were similar regardless of movement segment for stroke patients. Significant change in performance was observed between initial and post-assessments using H-Man in stroke participants, compared to conventional scales which showed no significant difference. Results of the study indicate the potential of H-Man as a sensitive tool for tracking changes in performance compared to ordinal scales (i.e., FM, ARAT)
Completely Positive Maps and Classical Correlations
We expand the set of initial states of a system and its environment that are
known to guarantee completely positive reduced dynamics for the system when the
combined state evolves unitarily. We characterize the correlations in the
initial state in terms of its quantum discord [H. Ollivier and W. H. Zurek,
Phys. Rev. Lett. 88, 017901 (2001)]. We prove that initial states that have
only classical correlations lead to completely positive reduced dynamics. The
induced maps can be not completely positive when quantum correlations
including, but not limited to, entanglement are present. We outline the
implications of our results to quantum process tomography experiments.Comment: 4 pages, 1 figur
Comparing the effect of CTG+STan with CTG alone on emergency Cesarean section rate : STan Australian Randomized controlled Trial (START)
The authors would like to thank the women and their babies for participating. We would like to thank all the staff at the WCH, in particular Priya Umampathysivam, Denise Cheetham and Cecilia Heitmann for their assistance in recruitment of participants for START. We would also like to thank the members of the DSMC, Diogo Ayres-de-Campos, Scott Morris and Katherine Lee, for their oversight of START and the Clinical Information Service (CIS) team at the WCH for the comparative hospital dataPeer reviewedPublisher PD
Operational approach to open dynamics and quantifying initial correlations
A central aim of physics is to describe the dynamics of physical systems.
Schrodinger's equation does this for isolated quantum systems. Describing the
time evolution of a quantum system that interacts with its environment, in its
most general form, has proved to be difficult because the dynamics is dependent
on the state of the environment and the correlations with it. For discrete
processes, such as quantum gates or chemical reactions, quantum process
tomography provides the complete description of the dynamics, provided that the
initial states of the system and the environment are independent of each other.
However, many physical systems are correlated with the environment at the
beginning of the experiment. Here, we give a prescription of quantum process
tomography that yields the complete description of the dynamics of the system
even when the initial correlations are present. Surprisingly, our method also
gives quantitative expressions for the initial correlation.Comment: Completely re-written for clarity of presentation. 15 pages and 2
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