Noise-resilient edge modes on a chain of superconducting qubits.

Inherent symmetry of a quantum system may protect its otherwise fragile states. Leveraging such protection requires testing its robustness against uncontrolled environmental interactions. Using 47 superconducting qubits, we implement the one-dimensional kicked Ising model, which exhibits nonlocal Majorana edge modes (MEMs) with [Formula: see text] parity symmetry. We find that any multiqubit Pauli operator overlapping with the MEMs exhibits a uniform late-time decay rate comparable to single-qubit relaxation rates, irrespective of its size or composition. This characteristic allows us to accurately reconstruct the exponentially localized spatial profiles of the MEMs. Furthermore, the MEMs are found to be resilient against certain symmetry-breaking noise owing to a prethermalization mechanism. Our work elucidates the complex interplay between noise and symmetry-protected edge modes in a solid-state environment.

Learning Curve for Flow Diversion of Posterior Circulation Aneurysms: A Long-Term International Multicenter Cohort Study.

BACKGROUND AND PURPOSE: Flow diversion has gradually become a standard treatment for intracranial aneurysms of the anterior circulation. Recently, the off-label use of the flow diverters to treat posterior circulation aneurysms has also increased despite initial concerns of rupture and the suboptimal results. This study aimed to explore the change in complication rates and treatment outcomes across time for posterior circulation aneurysms treated using flow diversion and to further evaluate the mechanisms and variables that could potentially explain the change and outcomes. MATERIALS AND METHODS: A retrospective review using a standardized data set at multiple international academic institutions was performed to identify patients with ruptured and unruptured posterior circulation aneurysms treated with flow diversion during a decade spanning January 2011 to January 2020. This period was then categorized into 4 intervals. RESULTS: A total of 378 procedures were performed during the study period. Across time, there was an increasing tendency to treat more vertebral artery and fewer large vertebrobasilar aneurysms (P = .05). Moreover, interventionalists have been increasingly using fewer overlapping flow diverters per aneurysm (P = .07). There was a trend toward a decrease in the rate of thromboembolic complications from 15.8% in 2011-13 to 8.9% in 2018-19 (P = .34). CONCLUSIONS: This multicenter experience revealed a trend toward treating fewer basilar aneurysms, smaller aneurysms, and increased usage of a single flow diverter, leading to a decrease in the rate of thromboembolic and hemorrhagic complications.

Realizing topologically ordered states on a quantum processor.

The discovery of topological order has revised the understanding of quantum matter and provided the theoretical foundation for many quantum error­correcting codes. Realizing topologically ordered states has proven to be challenging in both condensed matter and synthetic quantum systems. We prepared the ground state of the toric code Hamiltonian using an efficient quantum circuit on a superconducting quantum processor. We measured a topological entanglement entropy near the expected value of ­ln2 and simulated anyon interferometry to extract the braiding statistics of the emergent excitations. Furthermore, we investigated key aspects of the surface code, including logical state injection and the decay of the nonlocal order parameter. Our results demonstrate the potential for quantum processors to provide insights into topological quantum matter and quantum error correction.

Accurately computing the electronic properties of a quantum ring.

A promising approach to study condensed-matter systems is to simulate them on an engineered quantum platform1-4. However, the accuracy needed to outperform classical methods has not been achieved so far. Here, using 18 superconducting qubits, we provide an experimental blueprint for an accurate condensed-matter simulator and demonstrate how to investigate fundamental electronic properties. We benchmark the underlying method by reconstructing the single-particle band structure of a one-dimensional wire. We demonstrate nearly complete mitigation of decoherence and readout errors, and measure the energy eigenvalues of this wire with an error of approximately 0.01 rad, whereas typical energy scales are of the order of 1 rad. Insight into the fidelity of this algorithm is gained by highlighting the robust properties of a Fourier transform, including the ability to resolve eigenenergies with a statistical uncertainty of 10-4 rad. We also synthesize magnetic flux and disordered local potentials, which are two key tenets of a condensed-matter system. When sweeping the magnetic flux we observe avoided level crossings in the spectrum, providing a detailed fingerprint of the spatial distribution of local disorder. By combining these methods we reconstruct electronic properties of the eigenstates, observing persistent currents and a strong suppression of conductance with added disorder. Our work describes an accurate method for quantum simulation5,6 and paves the way to study new quantum materials with superconducting qubits.

Demonstrating a Continuous Set of Two-Qubit Gates for Near-Term Quantum Algorithms.

Quantum algorithms offer a dramatic speedup for computational problems in material science and chemistry. However, any near-term realizations of these algorithms will need to be optimized to fit within the finite resources offered by existing noisy hardware. Here, taking advantage of the adjustable coupling of gmon qubits, we demonstrate a continuous two-qubit gate set that can provide a threefold reduction in circuit depth as compared to a standard decomposition. We implement two gate families: an imaginary swap-like (iSWAP-like) gate to attain an arbitrary swap angle, θ, and a controlled-phase gate that generates an arbitrary conditional phase, ϕ. Using one of each of these gates, we can perform an arbitrary two-qubit gate within the excitation-preserving subspace allowing for a complete implementation of the so-called Fermionic simulation (fSim) gate set. We benchmark the fidelity of the iSWAP-like and controlled-phase gate families as well as 525 other fSim gates spread evenly across the entire fSim(θ,ϕ) parameter space, achieving a purity-limited average two-qubit Pauli error of 3.8×10^{-3} per fSim gate.

Risk of Branch Occlusion and Ischemic Complications with the Pipeline Embolization Device in the Treatment of Posterior Circulation Aneurysms.

BACKGROUND AND PURPOSE: Flow diversion with the Pipeline Embolization Device is increasingly used for endovascular treatment of intracranial aneurysms due to high reported obliteration rates and low associated morbidity. While obliteration of covered branches in the anterior circulation is generally asymptomatic, this has not been studied within the posterior circulation. The aim of this study was to evaluate the association between branch coverage and occlusion, as well as associated ischemic events in a cohort of patients with posterior circulation aneurysms treated with the Pipeline Embolization Device. MATERIALS AND METHODS: A retrospective review of prospectively maintained databases at 8 academic institutions from 2009 to 2016 was performed to identify patients with posterior circulation aneurysms treated with the Pipeline Embolization Device. Branch coverage following placement was evaluated, including the posterior inferior cerebellar artery, anterior inferior cerebellar artery, superior cerebellar artery, and posterior cerebral artery. If the Pipeline Embolization Device crossed the ostia of the contralateral vertebral artery, its long-term patency was assessed as well. RESULTS: A cohort of 129 consecutive patients underwent treatment of 131 posterior circulation aneurysms with the Pipeline Embolization Device. Adjunctive coiling was used in 40 (31.0%) procedures. One or more branches were covered in 103 (79.8%) procedures. At a median follow-up of 11 months, 11% were occluded, most frequently the vertebral artery (34.8%). Branch obliteration was most common among asymptomatic aneurysms (P < .001). Ischemic complications occurred in 29 (22.5%) procedures. On multivariable analysis, there was no significant difference in ischemic complications in cases in which a branch was covered (P = .24) or occluded (P = .16). CONCLUSIONS: There was a low occlusion incidence in end arteries following branch coverage at last follow-up. The incidence was higher in the posterior cerebral artery and vertebral artery where collateral supply is high. Branch occlusion was not associated with a significant increase in ischemic complications.

Predictors of Incomplete Occlusion following Pipeline Embolization of Intracranial Aneurysms: Is It Less Effective in Older Patients?

BACKGROUND AND PURPOSE: Flow diversion with the Pipeline Embolization Device (PED) for the treatment of intracranial aneurysms is associated with a high rate of aneurysm occlusion. However, clinical and radiographic predictors of incomplete aneurysm occlusion are poorly defined. In this study, predictors of incomplete occlusion at last angiographic follow-up after PED treatment were assessed. MATERIALS AND METHODS: A retrospective analysis of consecutive aneurysms treated with the PED between 2009 and 2016, at 3 academic institutions in the United States, was performed. Cases with angiographic follow-up were selected to evaluate factors predictive of incomplete aneurysm occlusion at last follow-up. RESULTS: We identified 465 aneurysms treated with the PED; 380 (81.7%) aneurysms (329 procedures; median age, 58 years; female/male ratio, 4.8:1) had angiographic follow-up, and were included. Complete occlusion (100%) was achieved in 78.2% of aneurysms. Near-complete (90%-99%) and partial (<90%) occlusion were collectively achieved in 21.8% of aneurysms and defined as incomplete occlusion. Of aneurysms followed for at least 12 months (211 of 380), complete occlusion was achieved in 83.9%. Older age (older than 70 years), nonsmoking status, aneurysm location within the posterior communicating artery or posterior circulation, greater aneurysm maximal diameter (≥21 mm), and shorter follow-up time (<12 months) were significantly associated with incomplete aneurysm occlusion at last angiographic follow-up on univariable analysis. However, on multivariable logistic regression, only age, smoking status, and duration of follow-up were independently associated with occlusion status. CONCLUSIONS: Complete occlusion following PED treatment of intracranial aneurysms can be influenced by several factors related to the patient, aneurysm, and treatment. Of these factors, older age (older than 70 years) and nonsmoking status were independent predictors of incomplete occlusion. While the physiologic explanation for these findings remains unknown, identification of factors predictive of incomplete aneurysm occlusion following PED placement can assist in patient selection and counseling and might provide insight into the biologic factors affecting endothelialization.

Treatment of Tandem Internal Carotid Artery Aneurysms Using a Single Pipeline Embolization Device: Evaluation of Safety and Efficacy.

BACKGROUND AND PURPOSE: Tandem aneurysms are defined as multiple aneurysms located in close proximity on the same parent vessel. Endovascular treatment of these aneurysms has rarely been reported. Our aim was to evaluate the safety and efficacy of a single Pipeline Embolization Device for the treatment of tandem aneurysms of the internal carotid artery. MATERIALS AND METHODS: A retrospective analysis of consecutive aneurysms treated with the Pipeline Embolization Device between 2009 and 2016 at 3 institutions in the United States was performed. Cases included aneurysms of the ICA treated with a single Pipeline Embolization Device, and they were divided into tandem versus solitary. Angiographic and clinical outcomes were compared. RESULTS: The solitary group (median age, 58 years) underwent 184 Pipeline Embolization Device procedures for 184 aneurysms. The tandem group (median age, 50.5 years) underwent 34 procedures for 78 aneurysms. Aneurysms were primarily located along the paraophthalmic segment of the ICA in both the single and tandem groups (72.3% versus 78.2%, respectively, P = .53). The median maximal diameters in the solitary and tandem groups were 6.2 and 6.7 mm, respectively. Complete occlusion on the last angiographic follow-up was achieved in 75.1% of aneurysms in the single compared with 88.6%% in the tandem group (P = .06). Symptomatic thromboembolic complications were encountered in 2.7% and 8.8% of procedures in the single and tandem groups, respectively (P = .08). CONCLUSIONS: Tandem aneurysms of the ICA can be treated with a single Pipeline Embolization Device with high rates of complete occlusion. While there appeared to be a trend toward higher thromboembolic complication rates, this did not reach statistical significance.

Intraluminal septation of the basilar artery: incidence and potential clinical significance.

Variations in the cerebrovascular tree can increase surgical or interventional morbidity. To date, only scant comments are to be found in the literature regarding intraluminal variations of the basilar artery. To further elucidate such anatomy, a cadaveric study was performed. One hundred and fifty human brains were evaluated for the present study. The basilar artery was identified in each and sectioned longitudinally to observe for the presence of intraluminal septa. One specimen (0.67%) was identified that harbored an intraluminal septum of the basilar artery. This wall was within the proximal basilar artery and measured 3 mm by 1.5 mm. No specimen was found to have other anomalies of the basilar artery and in the single specimen with an intraluminal septum no signs of intracranial pathology were seen. Although seemingly rare, septation of the basilar artery can be found. Knowledge of such an intraluminal vascular variation may be important during invasive and minimally invasive procedures.

Effects of intraventricular infusion of vascular endothelial growth factor on cerebral blood flow, edema, and infarct volume.

BACKGROUND: Therapeutic cerebral angiogenesis, utilizing angiogenic factors to enhance collateral vessel formation within the central nervous system, is a potential method for cerebral revascularization. A prior dose-response study determined that intracerebroventricular infusion of vascular endothelial growth factor (VEGF) increases vascular density with minimal associated brain edema at a concentration of 5 microg/ml. The purpose of this study was to assess effects of intracerebroventricular infusion of VEGF (5 microg/ml) on cerebral blood flow, infarct volume, and brain edema after ischemia. METHODS: Recombinant human VEGF(165) was infused into the right lateral ventricle of rats with an osmotic minipump at a rate of 1 microl/hr for 7 days. Control animals received vehicle only. Ischemia was produced by transient (2 hours) middle cerebral artery occlusion (MCAO). After MCAO, cerebral blood flow was determined with the indicator fractionation technique: infarct volume was assessed with 2,3,5-triphenlytetrazolium chloride staining, and brain edema was determined by measuring brain water content. FINDINGS: Cerebral blood flow was not significantly different in animals treated with VEGF compared to controls. There was a significant reduction in total infarct volume after temporary MCAO in VEGF-treated animals compared to controls (163+/-37 mm(3) vs. 309+/-54 mm(3), P<0.05). Brain water content after transient MCAO was also significantly reduced in VEGF-treated animals compared to controls (80.9+/-0.7% vs. 83.3+/-0.6%, P<0.05). INTERPRETATION: Intracerebroventricular infusion of VEGF(165) (5 microg/ml) decreases infarct volume and brain edema after temporary MCAO without a significant increase in cerebral blood flow. These results indicate that VEGF may have a direct neuroprotective effect in cerebral ischemia.

Persistent autoregulatory disturbance after angioplasty for cerebral vasospasm. A case report.

SUMMARY: Hyperdynamic therapy, consisting of hypervolemia, haemodilution, and hypertension, is an established treatment for cerebral vasospasm following subarachnoid haemorrhage. Angioplasty has emerged as an additional, effective treatment for symptomatic vasospasm. Loss of autoregulation, however, can occur despite effective angioplasty, underscoring the need for treatment with hyperdynamic therapy in combination with angioplasty. A 43-year-old woman underwent endovascular coiling of a ruptured left posterior communicating artery aneurysm. The patient went on to develop symptomatic vasospasm and was treated with hyperdynamic therapy and angioplasty. Autoregulation was assessed with xenon CT cerebral blood flow (CBF) measurement. An initial CBF study was obtained when the patient received dopamine and dobutamine infusions to maintain systolic blood pressure at 160 mmHg. The vasopressor drips were then temporarily held for twenty minutes, allowing the patient's systolic blood pressure to drop to 140 mmHg, and a repeat CBF study was obtained. Several days after angioplasty, CBF decreased significantly when the patient was taken off vasopressors, indicating impaired autoregulation. Hyperdynamic therapy was continued, and another CBF study one week later showed a return of autoregulation and normalization of CBF without induced hypertension. Autoregulation is disturbed during vasospasm. Although angioplasty can improve large artery blood flow during vasospasm, hyperdynamic therapy is also needed to maintain cerebral perfusion, particularly in the face of impaired autoregulation. Quantitative CBF measurement permits the maintenance of optimal CBF and monitoring of response to therapy.

Cerebral salt wasting syndrome.

There is significant evidence to show that many patients with hyponatremia and intracranial disease who were previously diagnosed with SIADH actually have CSW. The critical difference between SIADH and CSW is that CSW involves renal salt loss leading to hyponatremia and volume loss, whereas SIADH is a euvolemic or hypervolemic condition. Attention to volume status in patients with hyponatremia is essential. The primary treatment for CSW is water and salt replacement. The mechanisms underlying CSW are not understood but may involve ANP or other natriuretic factors and direct neural influence on renal function. Future investigation is needed to better define the incidence of CSW in patients with intracranial disease, identify other disorders that can lead to CSW, and elucidate the mechanisms underlying this syndrome.

Effect of hematocrit on calculation of cerebral blood flow and lambda in xenon CT.

Knowledge of the patient's hematocrit is necessary for calculation of cerebral blood flow (CBF) with xenon CT, and is a potential source of error. This study quantifies the effect of hematocrit on the calculation of CBF and lambda, and determines if the magnitude of the effect is dependent on actual CBF or lambda. The effect of hematocrit was measured empirically using software employing the numerical calculation method. CBF and lambda were found to be inversely related to hematocrit. The percent error produced by an inaccurate hematocrit is greater for lower actual CBF values.

Metastatic adenocarcinoma to the brain mimicking hemorrhage: case report.

BACKGROUND: Computerized tomography (CT) of metastatic adenocarcinoma to the brain usually shows low-to-moderate attenuation. However, mucinous adenomas may appear with high attenuation, mimicking hemorrhage. CASE DESCRIPTION: A 68-year-old man with a history of metastatic esophageal adenocarcinoma presented to the emergency room complaining of a chronic, progressive right occipital headache. A head CT demonstrated a moderate-to-high attenuation, homogenous mass in the right cerebellar hemisphere consistent with an intracerebral hemorrhage. There was no frank calcification in the mass by CT criteria. An emergent posterior fossa craniectomy revealed nonhemorrhagic metastatic mucinous adenocarcinoma. CONCLUSION: Moderate-to-high attenuation, noncalcified brain masses should raise the possibility of mucin-containing neoplasm.

Adenoid cystic carcinoma metastatic to the dura: report of two cases.

Adenoid cystic carcinoma (ACC) originating in the salivary and lacrimal glands usually spreads to the intracranial space by following cranial nerves into the cavernous sinus, temporal bone and cerebellopontine angle. We present two cases in which ACC metastasized extensively to the dura, suggesting that ACC has an affinity for the dura. Case 1, a 43-year-old man, was operated on 12 years earlier for invasive ACC of the right palate. He experienced recurrence of the tumor in the left cavernous sinus and sella, and extensive involvement of the dura of both right and left temporal fossae. Case 2, a 33-year-old woman, had spread of ACC to the right convexity dura and tentorium after undergoing a resection of a left-sided ACC tumor of the lacrimal gland two years earlier. Both patients underwent multiple resections and radiation treatment. Extensive, multifocal, bilateral spread of ACC to the dura in both cases indicates that ACC has an affinity for the dura.

Abducens nerve palsy after radiofrequency rhizolysis for trigeminal neuralgia: case report.

OBJECTIVE AND IMPORTANCE: Abducens nerve palsy is a rare and reversible complication associated with percutaneous radiofrequency trigeminal rhizolysis. CLINICAL PRESENTATION: An 86-year-old man developed an abducens nerve palsy immediately after undergoing percutaneous radiofrequency trigeminal rhizolysis for severe trigeminal neuralgia involving all three divisions of the trigeminal nerve. The palsy resolved spontaneously after 2 months. CONCLUSION: This case, in combination with previous reports, suggests that cases of transient sixth nerve palsy associated with percutaneous radiofrequency trigeminal rhizolysis for trigeminal neuralgia are more likely to occur in elderly patients with ophthalmic division involvement.

Collimating cylindrical diffractive lenses: rigorous electromagnetic analysis and scalar approximation.

Practical collimating diffractive cylindrical lenses of 2, 4, 8, and 16 discrete levels are analyzed with a sequential application of the two-region formulation of the rigorous electromagnetic boundary-element method (BEM). A Gaussian beam of TE or TM polarization is incident upon the finite-thickness lens. F/4, F/2, and F/1.4 lenses are analyzed and near-field electric-field patterns are presented. The near-field wave-front quality is quantified by its mean-square deviation from a planar wave front. This deviation is found to be less than 0.05 free-space wavelengths. The far-field intensity patterns are determined and compared with the ones predicted by the approximate Fraunhofer scalar diffraction analysis. The diffraction efficiencies determined with the rigorous BEM are found to be generally lower than those obtained with the scalar approximation. For comparison, the performance characteristics of the corresponding continuous Fresnel (continuous profile within a zone but discontinuous at zone boundaries) and continuous refractive lenses are determined by the use of both the BEM and the scalar approximation. The diffraction efficiency of the continuous Fresnel lens is found to be similar to that of the 16-level diffractive lens but less than that of the continuous refractive lens. It is shown that the validity of the scalar approximation deteriorates as the lens f-number decreases.

Effects of fabrication errors on the performance of cylindrical diffractive lenses: rigorous boundary-element method and scalar approximation.

The effects of fabrication errors on the performance of collimating finite-thickness cylindrical diffractive lenses with eight discrete levels are investigated with a rigorous boundary-element method and a scalar approach. The photolithographic fabrication errors considered are mask alignment errors, exposure errors (that result in linewidth errors), and etch-depth errors. A cylindrical Gaussian beam of TE or TM polarization is incident upon the resulting lenses. Lenses of F/4, F/2, and F/1.4 are examined. The diffraction efficiencies of the lenses with fabrication errors are generally lower than the error-free lenses with the most severe performance degradation occurring for mask misalignment and exposure errors.

Indomethacin in the management of elevated intracranial pressure: a review.

Elevated intracranial pressure occurs frequently in patients with severe head injury. A number of studies in recent years suggest that indomethacin may be useful in the management of elevated intracranial pressure. Indomethacin acts primarily by reducing cerebral blood flow and decreasing cerebral edema following head injury. This review summarizes the basic and clinical studies of the effects of indomethacin on cerebral blood flow, brain edema, and intracranial pressure. The pharmacology of indomethacin, and issues for future investigation in the use of indomethacin in severe head injury, are discussed.

Cerebral salt wasting syndrome: a review.

Hyponatremia is frequently seen in neurosurgical patients and is often attributed to inappropriate secretion of antidiuretic hormone. A number of studies in recent years have shown that hyponatremia in many patients with intracranial disease may actually be caused by cerebral salt wasting, in which a renal loss of sodium leads to hyponatremia and a decrease in extracellular fluid volume. The appropriate treatment of cerebral salt wasting fluid and salt replacement, is opposite from the usual treatment of hyponatremia caused by inappropriate secretion of antidiuretic hormone. This review summarizes the evidence in favor of cerebral salt wasting in patients with intracranial disease, examines the possible mechanisms responsible for this phenomenon, and discusses methods for diagnosis and treatment.