Quantum theory as plausible reasoning applied to data obtained by robust experiments.

We review recent work that employs the framework of logical inference to establish a bridge between data gathered through experiments and their objective description in terms of human-made concepts. It is shown that logical inference applied to experiments for which the observed events are independent and for which the frequency distribution of these events is robust with respect to small changes of the conditions under which the experiments are carried out yields, without introducing any concept of quantum theory, the quantum theoretical description in terms of the Schrödinger or the Pauli equation, the Stern-Gerlach or Einstein-Podolsky-Rosen-Bohm experiments. The extraordinary descriptive power of quantum theory then follows from the fact that it is plausible reasoning, that is common sense, applied to reproducible and robust experimental data.

Experimental protection of quantum coherence by using a phase-tunable image drive.

The protection of quantum coherence is essential for building a practical quantum computer able to manipulate, store and read quantum information with a high degree of fidelity. Recently, it has been proposed to increase the operation time of a qubit by means of strong pulses to achieve a dynamical decoupling of the qubit from its environment. We propose and demonstrate a simple and highly efficient alternative route based on Floquet modes, which increases the Rabi decay time ([Formula: see text]) in a number of materials with different spin Hamiltonians and environments. We demonstrate the regime [Formula: see text] with [Formula: see text] the relaxation time, thus providing a route for spin qubits and spin ensembles to be used in quantum information processing and storage.

Charge diffusion in the one-dimensional Hubbard model.

We study the real-time and real-space dynamics of charge in the one-dimensional Hubbard model in the limit of high temperatures. To this end, we prepare pure initial states with sharply peaked density profiles and calculate the time evolution of these nonequilibrium states, by using numerical forward-propagation approaches to chains as long as 20 sites. For a class of typical states, we find excellent agreement with linear-response theory and unveil the existence of remarkably clean charge diffusion in the regime of strong particle-particle interactions. We additionally demonstrate that, in the half-filling sector, this diffusive behavior does not depend on certain details of our initial conditions, i.e., it occurs for five different realizations with random and nonrandom internal degrees of freedom, single and double occupation of the central site, and displacement of spin-up and spin-down particles.

Relaxation, thermalization, and Markovian dynamics of two spins coupled to a spin bath.

It is shown that by fitting a Markovian quantum master equation to the numerical solution of the time-dependent Schrödinger equation of a system of two spin-1/2 particles interacting with a bath of up to 34 spin-1/2 particles, the former can describe the dynamics of the two-spin system rather well. The fitting procedure that yields this Markovian quantum master equation accounts for all non-Markovian effects in as much the general structure of this equation allows and yields a description that is incompatible with the Lindblad equation.

Image transfer by cascaded stack of photonic crystal and air layers.

We demonstrate image transfer by a cascaded stack consisting of two and three triangular-lattice photonic crystal slabs separated by air. The quality of the image transfered by the stack is sensitive to the air/photonic crystal interface termination and the frequency. Depending on the frequency and the surface termination, the image can be transfered by the stack with very little deterioration of the resolution, that is the resolution of the final image is approximately the same as the resolution of the image formed behind one single photonic crystal slab.

Dynamics of open quantum spin systems: An assessment of the quantum master equation approach.

Data of the numerical solution of the time-dependent Schrödinger equation of a system containing one spin-1/2 particle interacting with a bath of up to 32 spin-1/2 particles is used to construct a Markovian quantum master equation describing the dynamics of the system spin. The procedure of obtaining this quantum master equation, which takes the form of a Bloch equation with time-independent coefficients, accounts for all non-Markovian effects inasmuch the general structure of the quantum master equation allows. Our simulation results show that, with a few rather exotic exceptions, the Bloch-type equation with time-independent coefficients provides a simple and accurate description of the dynamics of a spin-1/2 particle in contact with a thermal bath. A calculation of the coefficients that appear in the Redfield master equation in the Markovian limit shows that this perturbatively derived equation quantitatively differs from the numerically estimated Markovian master equation, the results of which agree very well with the solution of the time-dependent Schrödinger equation.

Eigenstate thermalization hypothesis and quantum Jarzynski relation for pure initial states.

Since the first suggestion of the Jarzynski equality many derivations of this equality have been presented in both the classical and the quantum context. While the approaches and settings differ greatly from one another, they all appear to rely on the condition that the initial state is a thermal Gibbs state. Here, we present an investigation of work distributions in driven isolated quantum systems, starting from pure states that are close to energy eigenstates of the initial Hamiltonian. We find that, for the nonintegrable quantum ladder studied, the Jarzynski equality is fulfilled to a good accuracy.

Decoherence by a chaotic many-spin bath.

We numerically investigate decoherence of a two-spin system (central system) by a bath of many spins 1/2. By carefully adjusting parameters, the dynamical regime of the bath has been varied from quantum chaos to regular, while all other dynamical characteristics have been kept practically intact. We explicitly demonstrate that for a many-body quantum bath, the onset of quantum chaos leads to significantly faster and stronger decoherence compared to an equivalent non-chaotic bath. Moreover, the non-diagonal elements of the system's density matrix, the linear entropy, and the fidelity of the central system decay differently for chaotic and non-chaotic baths. Therefore, knowledge of the basic parameters of the bath (strength of the system-bath interaction, and the bath's spectral density of states) is not always sufficient, and much finer details of the bath's dynamics can strongly affect the decoherence process.

A Jones matrix formalism for simulating three-dimensional polarized light imaging of brain tissue.

The neuroimaging technique three-dimensional polarized light imaging (3D-PLI) provides a high-resolution reconstruction of nerve fibres in human post-mortem brains. The orientations of the fibres are derived from birefringence measurements of histological brain sections assuming that the nerve fibres­consisting of an axon and a surrounding myelin sheath­are uniaxial birefringent and that the measured optic axis is oriented in the direction of the nerve fibres (macroscopic model). Although experimental studies support this assumption, the molecular structure of the myelin sheath suggests that the birefringence of a nerve fibre can be described more precisely by multiple optic axes oriented radially around the fibre axis (microscopic model). In this paper, we compare the use of the macroscopic and the microscopic model for simulating 3D-PLI by means of the Jones matrix formalism. The simulations show that the macroscopic model ensures a reliable estimation of the fibre orientations as long as the polarimeter does not resolve structures smaller than the diameter of single fibres. In the case of fibre bundles, polarimeters with even higher resolutions can be used without losing reliability. When taking the myelin density into account, the derived fibre orientations are considerably improved.

Right-to-left flow through a patent foramen ovale in acute right ventricular infarction. Two case reports and a proposal for management.

Right-to-left shunting through a foramen ovale complicating acute right ventricular infarction and resulting in severe arterial hypoxemia has been described eight times before. Treatment strategies have often aimed at reducing the shunt. Four patients died. Less attention has been paid to attempts at revascularization and, despite a high incidence of atrioventricular conduction disturbances, to temporary dual-chamber pacing. We describe herein two patients with postcardiac surgical right ventricular infarction complicated by severe right-to-left interatrial shunting. Treatment strategy was aimed at improving right ventricular function, and right-to-left shunting ceased. All efforts should be directed at treating right ventricular dysfunction, which is the cause of the clinical picture, and not at reducing the shunt, which is a secondary phenomenon.

Biventricular assist for severe acute rheumatic pancarditis.

Severe heart failure in acute rheumatic myocarditis is rare. It may be rapidly reversible with treatment, so maximal medical treatment and, if necessary, mechanical support should be given before heart transplantation is considered.

Computer simulation of time-gated transillumination and reflection of biological tissues and tissuelike phantoms.

A simulation technique is employed to explore the possibility of locating millimeter-sized objects, immersed in turbid media, from time-gated measurements of the transmitted or reflected light. The simulation results for tissuelike phantoms are compared to experimental transillumination data and excellent agreement is found. Simulations of time-gated reflection experiments show that it is possible to detect objects of 1 mm diameter. This may open new possibilities for medical diagnosis of breast cancer in an early stage.

Liver rupture after cardiopulmonary resuscitation in a patient receiving thrombolytic therapy.

A patient with an acute myocardial infarction had to be resuscitated due to recurring ventricular fibrillation. After stabilisation, she received thrombolytic treatment with anistreplase. Fourteen hours later, clinical signs of hemoperitoneum developed and the diagnosis of liver rupture was made. After abdominal surgery and coronary revascularisation, the subsequent clinical course was uncomplicated. The literature on liver trauma after CPR as well as thrombolysis in association with CPR is reviewed. This observation suggests that there are no convincing arguments to withhold thrombolytic therapy in acute myocardial infarction after CPR in the absence of gross trauma. We stress that a high degree of clinical alertness is necessary to diagnose this life-threatening condition because of its frequent subacute evolution in patients that are per se hemodynamically unstable.

Importance of volume factors in dialysis related hypertension.

OBJECTIVE: To evaluate the relation between total body water and dialysis related hypertension. PATIENTS AND METHODS: Thirty stable chronic hemodialysis patients were studied. Twenty-four-hour ambulatory blood pressure on the day before dialysis, blood pressure before and after dialysis, weight gain, ultrafiltration and total body water were determined. Total body water was measured by body impedance analysis and expressed as percentage of dry weight (TBW %). Ambulatory blood pressure recordings were defined as hypertensive when the blood pressure load (% of readings above 140/90 mmHg) was more than 40%. RESULTS AND CONCLUSION: Patients, classified as normotensive (n = 11) or hypertensive (n = 19), based on 24-hour blood pressure measurements, had significantly different TBW % (54.7 +/- 5.3 vs. 58.9 +/- 4.6%, p = 0.046). Ambulatory blood pressure and postdialysis blood pressure, but not predialysis blood pressure, were significantly correlated with TBW %. Acute volume changes, as reflected by interdialytic weight gain and ultrafiltration did not correlate with TBW %. These changes correlated weakly with predialysis blood pressure. Multivariate analysis showed that only TBW % and antihypertensive medication had an independent influence on 24-hour blood pressure measurements. We conclude that 24-hour blood pressure and blood pressure after dialysis are better related to total body water than blood pressure before dialysis, which was however weakly related to the acute volume overload, induced by interdialytic weight gain. We hypothesize that this could be the result of a more important chronic volume overload leading to an increase in systemic vascular resistance. On the contrary the acute but less important changes in extracellular volume between dialyses cause no hypertension after dialysis and no sustained hypertension over 24 hours, but only in some cases a temporary increase in the blood pressure just before dialysis. This volume overload can be easily determined by measurement of total body water by bioelectrical impedance analysis.

Quantum Monte Carlo method for attractive Coulomb potentials.

Starting from an exact lower bound on the imaginary-time propagator, we present a path-integral quantum Monte Carlo method that can handle singular attractive potentials. We illustrate the basic ideas of this quantum Monte Carlo algorithm by simulating the ground state of hydrogen and helium.

Efficient scheme for numerical simulations of the spin-bath decoherence.

We demonstrate that the Chebyshev expansion method is a very efficient numerical tool for studying spin-bath decoherence of quantum systems. We consider two typical problems arising in studying decoherence of quantum systems consisting of a few coupled spins: (i) determining the pointer states of the system and (ii) determining the temporal decay of quantum oscillations. As our results demonstrate, for determining the pointer states, the Chebyshev-based scheme is at least a factor of 8 faster than existing algorithms based on the Suzuki-Trotter decomposition. For problems of the second type, the Chebyshev-based approach is 3-4 times faster than the Suzuki-Trotter-based schemes. This conclusion holds qualitatively for a wide spectrum of systems, with different spin baths and different Hamiltonians.

Morphological image analysis of quantum motion in billiards.

Morphological image analysis is applied to the time evolution of the probability distribution of a quantum particle moving in two- and three-dimensional billiards. It is shown that the time-averaged Euler characteristic of the probability distribution provides a well defined quantity to distinguish between classically integrable and nonintegrable billiards. In three dimensions the time-averaged mean breadth of the probability distribution may also be used for this purpose.

One-step finite-difference time-domain algorithm to solve the Maxwell equations.

We present a one-step algorithm to solve the time-dependent Maxwell equations for systems with spatially varying permittivity and permeability. We compare the results of this algorithm with those obtained from the Yee algorithm and from unconditionally stable algorithms. We demonstrate that for a range of applications the one-step algorithm may be orders of magnitude more efficient than multiple time-step, finite-difference time-domain algorithms. We discuss both the virtues and limitations of this one-step approach.

Higher-order unconditionally stable algorithms to solve the time-dependent Maxwell equations.

For the recently introduced algorithms to solve the time-dependent Maxwell equations [J. S. Kole, M. T. Figge, and H. De Raedt, Phys. Rev. E 64, 066705 (2001)], we construct a variable grid implementation and an improved spatial discretization implementation that preserve the exceptional property of the algorithms to be unconditionally stable by construction. We find that the performance and accuracy of the corresponding algorithms are significant and illustrate their practical relevance by simulating various physical model systems.