Quasiparticle engineering and entanglement propagation in a quantum many-body system.

The key to explaining and controlling a range of quantum phenomena is to study how information propagates around many-body systems. Quantum dynamics can be described by particle-like carriers of information that emerge in the collective behaviour of the underlying system, the so-called quasiparticles. These elementary excitations are predicted to distribute quantum information in a fashion determined by the system's interactions. Here we report quasiparticle dynamics observed in a quantum many-body system of trapped atomic ions. First, we observe the entanglement distributed by quasiparticles as they trace out light-cone-like wavefronts. Second, using the ability to tune the interaction range in our system, we observe information propagation in an experimental regime where the effective-light-cone picture does not apply. Our results will enable experimental studies of a range of quantum phenomena, including transport, thermalization, localization and entanglement growth, and represent a first step towards a new quantum-optic regime of engineered quasiparticles with tunable nonlinear interactions.

Dynamical Topological Transitions in the Massive Schwinger Model with a θ Term.

Aiming at a better understanding of anomalous and topological effects in gauge theories out of equilibrium, we study the real-time dynamics of a prototype model for CP violation, the massive Schwinger model with a θ term. We identify dynamical quantum phase transitions between different topological sectors that appear after sufficiently strong quenches of the θ parameter. Moreover, we establish a general dynamical topological order parameter, which can be accessed through fermion two-point correlators and, importantly, which can be applied for interacting theories. Enabled by this result, we show that the topological transitions persist beyond the weak-coupling regime. Finally, these effects can be observed with tabletop experiments based on existing cold-atom, superconducting-qubit, and trapped-ion technology. Our Letter thus presents a significant step towards quantum simulating topological and anomalous real-time phenomena relevant to nuclear and high-energy physics.

Revealing Quantum Statistics with a Pair of Distant Atoms.

Quantum statistics have a profound impact on the properties of systems composed of identical particles. At the most elementary level, Bose and Fermi quantum statistics differ in the exchange phase, either 0 or π, which the wave function acquires when two identical particles are exchanged. In this Letter, we demonstrate that the exchange phase can be directly probed with a pair of massive particles by physically exchanging their positions. We present two protocols where the particles always remain spatially well separated, thus ensuring that the exchange contribution to their interaction energy is negligible and that the detected signal can only be attributed to the exchange symmetry of the wave function. We discuss possible implementations with a pair of trapped atoms or ions.

Direct Observation of Dynamical Quantum Phase Transitions in an Interacting Many-Body System.

The theory of phase transitions represents a central concept for the characterization of equilibrium matter. In this work we study experimentally an extension of this theory to the nonequilibrium dynamical regime termed dynamical quantum phase transitions (DQPTs). We investigate and measure DQPTs in a string of ions simulating interacting transverse-field Ising models. During the nonequilibrium dynamics induced by a quantum quench we show for strings of up to 10 ions the direct detection of DQPTs by revealing nonanalytic behavior in time. Moreover, we provide a link between DQPTs and the dynamics of other quantities such as the magnetization, and we establish a connection between DQPTs and entanglement production.

Spectroscopy of Interacting Quasiparticles in Trapped Ions.

The static and dynamic properties of many-body quantum systems are often well described by collective excitations, known as quasiparticles. Engineered quantum systems offer the opportunity to study such emergent phenomena in a precisely controlled and otherwise inaccessible way. We present a spectroscopic technique to study artificial quantum matter and use it for characterizing quasiparticles in a many-body system of trapped atomic ions. Our approach is to excite combinations of the system's fundamental quasiparticle eigenmodes, given by delocalized spin waves. By observing the dynamical response to superpositions of such eigenmodes, we extract the system dispersion relation, magnetic order, and even detect signatures of quasiparticle interactions. Our technique is not limited to trapped ions, and it is suitable for verifying quantum simulators by tuning them into regimes where the collective excitations have a simple form.

Constrained dynamics via the Zeno effect in quantum simulation: implementing non-Abelian lattice gauge theories with cold atoms.

We show how engineered classical noise can be used to generate constrained Hamiltonian dynamics in atomic quantum simulators of many-body systems, taking advantage of the continuous Zeno effect. After discussing the general theoretical framework, we focus on applications in the context of lattice gauge theories, where imposing exotic, quasilocal constraints is usually challenging. We demonstrate the effectiveness of the scheme for both Abelian and non-Abelian gauge theories, and discuss how engineering dissipative constraints substitutes complicated, nonlocal interaction patterns by global coupling to laser fields.

Spread of correlations in long-range interacting quantum systems.

The nonequilibrium response of a quantum many-body system defines its fundamental transport properties and how initially localized quantum information spreads. However, for long-range-interacting quantum systems little is known. We address this issue by analyzing a local quantum quench in the long-range Ising model in a transverse field, where interactions decay as a variable power law with distance ∝r(-α), α>0. Using complementary numerical and analytical techniques, we identify three dynamical regimes: short-range-like with an emerging light cone for α>2, weakly long range for 1<α<2 without a clear light cone but with a finite propagation speed of almost all excitations, and fully nonlocal for α<1 with instantaneous transmission of correlations. This last regime breaks generalized Lieb-Robinson bounds and thus locality. Numerical calculation of the entanglement spectrum demonstrates that the usual picture of propagating quasiparticles remains valid, allowing an intuitive interpretation of our findings via divergences of quasiparticle velocities. Our results may be tested in state-of-the-art trapped-ion experiments.

Tunable gauge potential for neutral and spinless particles in driven optical lattices.

We present a universal method to create a tunable, artificial vector gauge potential for neutral particles trapped in an optical lattice. The necessary Peierls phase of the hopping parameters between neighboring lattice sites is generated by applying a suitable periodic inertial force such that the method does not rely on any internal structure of the particles. We experimentally demonstrate the realization of such artificial potentials, which generate ground-state superfluids at arbitrary nonzero quasimomentum. We furthermore investigate possible implementations of this scheme to create tunable magnetic fluxes, going towards model systems for strong-field physics.

[Nonaneurysmal vascular pressure lesions of the cranial nerves (author's transl)]. / Nichtaneurysmatische gefässbedingte Druckläsionen von Hirnnerven

Four cases of facial spasm and 1 case of oculomotor paresis are described. The source of the disorder in all 5 cases is mostlikely not an aneurysm of the vessels of the base of the brain. The literature is discussed and thereby it is shown that mechanical disturbances of other cranial nerves (II, V, VI, IX, XII) can be caused by similar vascular (nonaneurysmal) abnormalities.

[Advantages in the use of teflon-catheter cannulas, compared with needles, for direct carotid angiography (author's transl)]. / Vorteile bei der Verwendung von Teflon-Katheterkanülen gegenüber Punktionsnadeln bei der direkten Karotisangiographie

A method for direct carotid puncture, using a Teflon-catheter cannula, is described. The complication rate of this method is compared with the usual technique using a rigid cannula. The significant advantage of using the Teflon-cannula consists in: 1. In the absence of sub-intimal contrast injection and 2. The possibility of selectively demonstrating the internal or external arteries from the common carotid.

[Anastomoses between the vertebral and external occipital arteries in occlusion of the external carotid and vertebral arteries (author's transl)]. / Anastomosen zwischen der A. vertebralis und der A. occipitalis externa bei Verschlüssen der A. carotis externa bzw. A. vertebralis

Five cases of anastomose formation between the external carotid and the vertebral arteries are reported. In 2 cases occlusion of the vertebral artery in the upper section of the cervical spine were present. In 2 further cases there were occlusions of the external carotid artery. In only a single case did angiographic examination show no pathological change. From these observations it is concluded that, when the formation of such collaterals is established, occlusions and important part-occlusions of the large cervical vessels should be sought.

[Paradoxical embolism with preferential localisation to the cerebral vessels]. / Paradoxe Embolic mit bevorzugter Streuung id die Hirnge FE

Massive paradoxical embolism with cerebral symptoms developed at 30 hours after abdominal hysterectomy in a 53-year-old woman. An essential condition for the occurrence of paradoxical embolism is an increased pressure in the lesser circulation; the most frequent cause is massive pulmonary embolism which, however, may take a relatively mild course if there is adequate right to left shunting. The absence of clinical signs of pulmonary embolism does not exclude systemic venous thrombosis as the site or origin of peripheral arterial emboli.

[Results of angiographic investigations in basilar artery insufficiency (author's transl)]. / Ergebnisse angiographischer Untersuchungen bei Basilarisinsuffizienz

Angiographies were performed in 75 selected patients with basilar artery insufficiency. In only one case was there an indication for vascular surgery to the vertebral artery, and in two cases for an uncoforaminectomy, whereas in 13 cases prophylactic desobliteration of the internal carotid artery was performed. Thus vascular surgical consequences of angiography of the supraaortic vessels in basilar insufficiency are minimal. However, personal observations and reports in the literature indicate that the indications for surgery to the vertebral artery or the cervical spine will increase if functional investigations can be performed in various positions of the cervical spine by means of selective catheter angiography.

[The value of xerotomography in the radiologic diagnosis of chronic cervical myelopathy (author's transl)]. / Die Wertigkeit der Xerotomographie bei der Röntgendiagnostik der chronischen zervikalen Myelopathie.

Report on experience with radiologic diagnosis of 13 patients with chronic cervical myelopathy, who were examined at our clinic within 6 months. The various neuroradiologic findings are described and evaluated as to their causal importance. If plain radiograms show a spinal canal of normal diameter and where there are no multiple osteochondrotic changes, examinations with positive contrast media are most suitable. Air myelograms should be used when the advantages of xerotomography can be made use of.

[Doppler ultrasonic diagnosis of the subclavian-steal syndrome (author's transl)]. / Doppler-sonographische Funktionsuntersuchung bei Subclavia-Anzapfsyndrom

It is possible to perform percutaneous Doppler ultrasonic flow measurements in the vertebral artery below its curvature over the atlas. Criteria supporting the subclavian-steal syndrome are (I) red side, (2) slowing of blood flow in the vertebral artery after compression of the axillary artery on the same side, and (3) delayed pulse in the axillary artery of the diseased compared with the normal side.

Application of xeroradiography for pneumencephalography.

The feasibility of xerotomography with pneumencephalography is demonstrated. One of the advantages of a xerotomogram is that it reduces the lack of sharpness caused by tomography. The wide recording latitude of a xerotomogram makes a more detailed evaluation of the bone structure and the outlines of the soft tissue possible when these are contrasted be means of air. The characteristic edge effect of a xerogram also facilitates better detection of the small structures which are less well discerible on a film tomogram.

[The significance of cranial computerized tomography for diagnosis and therapy of inflammatory diseases of the brain and meninges in children (author's transl)]. / Die Bedeutung der kranialen Computertomographie für die Diagnostik und Therapie entzündlicher Erkrankungen des ZNS im Kindesalter.

The significance of cranial computerized tomography (CCT) for the diagnosis and therapy of inflammatory diseases of the central nervous system in children is discussed in connection with five characteristic case studies. CCT is shown to be superior to classical neuroradiological approaches, and to allow important diagnostic insights: 1. the early recognition of diffuse brain edema and the resulting possibility of an early begin of therapy--2. the pathological expansions of the cerebral ventricles of various etiology before a pathological enlargement of the head can be detected, and the size of the ventricles after neurosurgical therapy can be measured--3. the early recognition of space-occupying inflammatory complications.

[Fibromuscular dysplasia of the internal carotid and intracerebral arteries (author's transl)]. / Fibromuskuläre Dysplasie der Corotis interna und der intrazerebralen Gefässe

Fibromuscular dysplasia was found in six patients (four women over 50 years, a 20-year-old man and a five-year-old girl). Angiography (in five cases performed because of a cerebrovascular accident) gave the typical appearance of "knotted string" changes in the large and medium sized arteries. With marked localized arterial narrowing treatment is surgical. Conservative treatment remains sympotomatic because the cause of the disease is still unknown. Even surgical treatment brings only sympotomatic relief and, because of the slowly progressive nature, is indicated only when there are neurological signs.

[Main signs of neurologic disease during pregnancy (author's transl)]. / Leitsymptome neurologischer Erkrankungen in der Schwangerschaft

The most important neurologic diseases which may start during pregnancy are described. On the basis of clinical, easily discovered, signs the essential differential diagnosis and specific diagnostic techniques (electromyography, electroneurography, angiography, computotumography) and their indications are outlined. In some detail prognosis and indications for common diseases (epilepsy, M.S.) are discussed. Treatment of those diseases is especially considered in which emergency drug therapy may be needed.

Planigraphic measurement of angiograms and pneumencephalograms in the diagnosis of hydrocephalus.

Instead of the usual descriptive criteria commonly adopted for angiographic assessment of hydrostatic hydrocephalus, planimetric measuring methods were tried out. It was shown that the surface area under the anterior cerebral artery (pericallosal) as measured in the lateral angiogram increases proportionally to the volume of the cella media. A high degree of conformity was shown between the clinical and descriptive neurological findings and the planimetrically obtainable values.