Formation of robust bound states of interacting microwave photons.

Systems of correlated particles appear in many fields of modern science and represent some of the most intractable computational problems in nature. The computational challenge in these systems arises when interactions become comparable to other energy scales, which makes the state of each particle depend on all other particles1. The lack of general solutions for the three-body problem and acceptable theory for strongly correlated electrons shows that our understanding of correlated systems fades when the particle number or the interaction strength increases. One of the hallmarks of interacting systems is the formation of multiparticle bound states2-9. Here we develop a high-fidelity parameterizable fSim gate and implement the periodic quantum circuit of the spin-½ XXZ model in a ring of 24 superconducting qubits. We study the propagation of these excitations and observe their bound nature for up to five photons. We devise a phase-sensitive method for constructing the few-body spectrum of the bound states and extract their pseudo-charge by introducing a synthetic flux. By introducing interactions between the ring and additional qubits, we observe an unexpected resilience of the bound states to integrability breaking. This finding goes against the idea that bound states in non-integrable systems are unstable when their energies overlap with the continuum spectrum. Our work provides experimental evidence for bound states of interacting photons and discovers their stability beyond the integrability limit.

Correlated charge noise and relaxation errors in superconducting qubits.

The central challenge in building a quantum computer is error correction. Unlike classical bits, which are susceptible to only one type of error, quantum bits (qubits) are susceptible to two types of error, corresponding to flips of the qubit state about the X and Z directions. Although the Heisenberg uncertainty principle precludes simultaneous monitoring of X- and Z-flips on a single qubit, it is possible to encode quantum information in large arrays of entangled qubits that enable accurate monitoring of all errors in the system, provided that the error rate is low1. Another crucial requirement is that errors cannot be correlated. Here we characterize a superconducting multiqubit circuit and find that charge noise in the chip is highly correlated on a length scale over 600 micrometres; moreover, discrete charge jumps are accompanied by a strong transient reduction of qubit energy relaxation time across the millimetre-scale chip. The resulting correlated errors are explained in terms of the charging event and phonon-mediated quasiparticle generation associated with absorption of γ-rays and cosmic-ray muons in the qubit substrate. Robust quantum error correction will require the development of mitigation strategies to protect multiqubit arrays from correlated errors due to particle impacts.

A phase I dose-escalation and dose-expansion study of brontictuzumab in subjects with selected solid tumors.

Background: Brontictuzumab is a monoclonal antibody that targets Notch1 and inhibits pathway activation. The purpose of this first-in-human study was to determine the maximum tolerated dose (MTD), safety, pharmacokinetics, immunogenicity and preliminary efficacy of brontictuzumab in patients with solid tumors. Patients and methods: Subjects with selected refractory solid tumors were eligible. Brontictuzumab was administered intravenously at various dose levels and schedule during dose escalation, and at 1.5 mg/kg every 3 weeks (Q3W) during expansion. Evidence of Notch1 pathway activation as determined by an immunohistochemistry assay was required for entry in the expansion cohort. Adverse events were graded according to the NCI-CTCAE v 4.03. Efficacy was assessed by RECIST 1.1. Results: Forty-eight subjects enrolled (33 in dose escalation and 15 in the expansion phase). The MTD was 1.5 mg/kg Q3W. Dose-limiting toxicities were grade 3 diarrhea in two subjects and grade 3 fatigue in one subject. The most common drug-related adverse events of any grade were diarrhea (71%), fatigue (44%), nausea (40%), vomiting (21%), and AST increase (21%). Brontictuzumab exhibited nonlinear pharmacokinetics with dose-dependent terminal half-life ranging 1-4 days. Clinical benefit was seen in 6 of 36 (17%) assessable subjects: 2 had unconfirmed partial response (PR) and 4 subjects had prolonged (≥ 6 months) disease stabilization (SD). Both PRs and three prolonged SD occurred in adenoid cystic carcinoma (ACC) subjects with evidence of Notch1 pathway activation. Pharmacodynamic effects of brontictuzumab were seen in patients' blood and tumor. Conclusion: Brontictuzumab was well tolerated at the MTD. The main toxicity was diarrhea, an on-target effect of Notch1 inhibition. An efficacy signal was noted in subjects with ACC and Notch1 pathway activation. ClinicalTrials.gov identifier: NCT01778439.

Stable quantum-correlated many-body states through engineered dissipation.

Engineered dissipative reservoirs have the potential to steer many-body quantum systems toward correlated steady states useful for quantum simulation of high-temperature superconductivity or quantum magnetism. Using up to 49 superconducting qubits, we prepared low-energy states of the transverse-field Ising model through coupling to dissipative auxiliary qubits. In one dimension, we observed long-range quantum correlations and a ground-state fidelity of 0.86 for 18 qubits at the critical point. In two dimensions, we found mutual information that extends beyond nearest neighbors. Lastly, by coupling the system to auxiliaries emulating reservoirs with different chemical potentials, we explored transport in the quantum Heisenberg model. Our results establish engineered dissipation as a scalable alternative to unitary evolution for preparing entangled many-body states on noisy quantum processors.

Quantum bath suppression in a superconducting circuit by immersion cooling.

Quantum circuits interact with the environment via several temperature-dependent degrees of freedom. Multiple experiments to-date have shown that most properties of superconducting devices appear to plateau out at T ≈ 50 mK - far above the refrigerator base temperature. This is for example reflected in the thermal state population of qubits, in excess numbers of quasiparticles, and polarisation of surface spins - factors contributing to reduced coherence. We demonstrate how to remove this thermal constraint by operating a circuit immersed in liquid 3He. This allows to efficiently cool the decohering environment of a superconducting resonator, and we see a continuous change in measured physical quantities down to previously unexplored sub-mK temperatures. The 3He acts as a heat sink which increases the energy relaxation rate of the quantum bath coupled to the circuit a thousand times, yet the suppressed bath does not introduce additional circuit losses or noise. Such quantum bath suppression can reduce decoherence in quantum circuits and opens a route for both thermal and coherence management in quantum processors.

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.

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.

Two-level systems in superconducting quantum devices due to trapped quasiparticles.

A major issue for the implementation of large-scale superconducting quantum circuits is the interaction with interfacial two-level system (TLS) defects that lead to qubit parameter fluctuations and relaxation. Another major challenge comes from nonequilibrium quasiparticles (QPs) that result in qubit relaxation and dephasing. Here, we reveal a previously unexplored decoherence mechanism in the form of a new type of TLS originating from trapped QPs, which can induce qubit relaxation. Using spectral, temporal, thermal, and magnetic field mapping of TLS-induced fluctuations in frequency tunable resonators, we identify a highly coherent subset of the general TLS population with a low reconfiguration temperature ∼300 mK and a nonuniform density of states. These properties can be understood if the TLS are formed by QPs trapped in shallow subgap states formed by spatial fluctutations of the superconducting order parameter. This implies that even very rare QP bursts will affect coherence over exponentially long time scales.

Suppression of low-frequency charge noise in superconducting resonators by surface spin desorption.

Noise and decoherence due to spurious two-level systems located at material interfaces are long-standing issues for solid-state quantum devices. Efforts to mitigate the effects of two-level systems have been hampered by a lack of knowledge about their chemical and physical nature. Here, by combining dielectric loss, frequency noise and on-chip electron spin resonance measurements in superconducting resonators, we demonstrate that desorption of surface spins is accompanied by an almost tenfold reduction in the charge-induced frequency noise in the resonators. These measurements provide experimental evidence that simultaneously reveals the chemical signatures of adsorbed magnetic moments and highlights their role in generating charge noise in solid-state quantum devices.

April 2001: a 70 year old woman with recurrent meningioma.

The April Case of the Month (COM). The contributors report a case of a 70 year-old woman with recurrent meningiomas, one of which showed rhabdoid and lipomatous differentiation. Histopathological study of the first and second previous resections showed only typical meningothelial meningioma. On the third craniotomy, a new tumor specimen showed an admixture of classic meningothelial meningioma with lipomatous and rhabdoid foci. Immunohistochemical studies showed diffuse reactivity for epithelial membrane antigen and vimentin, as well as focal positivity for desmin and smooth muscle actin in the areas with rhabdoid features and S100 protein in the lipomatous foci. The presence of these three different and concomitant histological patterns only in the third surgical resection might support a metaplastic origin and, also, corroborates the concept that rhabdoid features are suggestive of an aggressive behavior.

Mammary epithelioid myofibroblastoma arising in bilateral gynecomastia: case report with immunohistochemical profile.

Myofibroblastoma of the breast is a rare benign neoplasm, which has rarely been reported in association with gynecomastia. We report a case of a 25-year-old male patient with an epithelioid myofibroblastoma arising in a context of bilateral gynecomastia. The lesion was composed of nests and cords of epithelioid cells, with round to oval nuclei, granular chromatin, and distinct nucleoli dispersed in a myxoid to collagenous stroma with marked vascular proliferation. Immunohistochemical profile showed diffuse positivity for vimentin and focal immunoreactivity for desmin, whereas cytokeratins (CAM5.2 and AE1/AE3), EMA, alpha smooth muscle actin, actin HHF35, CEA, S100, factor VIII, neuron-specific enolase, CD31, and CD34 were all negative. We emphasize that this diagnosis is difficult to establish, owing to the rarity of this variant and clinical presentation.

Pleomorphic xanthoastrocytoma: report of a case diagnosed by intraoperative cytopathological examination.

The authors present an unusual case of a 13-yr-old boy with a 3-mo history of seizures. A CT scan showed a contrast-enhancing mass located in the left temporal lobe. The patient underwent a stereotatic-guided craniotomy; intraoperative cytological diagnosis was performed by the smear technique, showing a pleomorphic xanthoastrocytoma. The tumor was totally resected. Definitive diagnosis was established by examination of paraffin-embedded material. Six months after the surgical intervention, the patient is doing well, with no radiological evidence of recurrence. The cytological differential diagnosis of giant cell lesions of the central nervous system is emphasized.

[Medulloblastomas: clinical, epidemiological and pathological findings in 28 cases]. / Meduloblastomas: achados clínicos, epidemiológicos e anátomo-patológicos de 28 casos.

We report the clinical, epidemiological and pathological findings of 28 patients with medulloblastoma: 22 were male; age ranged from 1 to 50 years, with a mean of 15 years. The most frequent symptoms and signs were headache (64%) and vomiting (64%). Only one patient showed a desmoplastic medulloblastoma variant, the others showed classical medulloblastomas. Regarding treatment, most patients were submitted to total resection (n=10) or partial tumorectomy (n=7). A low rate of tumoral recurrence was observed, occurring in 21% of the patients (n=6) after 4 years of follow-up. Chemotherapy seemed to contribute to a lower recurrence rate amongst our patients. Our findings are similar to those reported in literature, thus helping to understand the biological behavior of this type of tumor.

[Haemangioblastomas: clinical, epidemiological and pathological findings in 14 cases]. / Hemangioblastomas: achados clínicos, epidemiológicos e anatomopatológicos em 14 casos.

We report the clinical, epidemiological and pathological findings of 14 patients with haemangioblastoma. Sixty-four percent occurred in males, with ages ranging from 16 to 60 years, with an average of 34, 4 years. Most of the tumours were confined to the cerebellum (n=9). The most frequent symptoms were headache (n=7) and dizziness (n=7), with a mean duration of 70 days. Von Hippel-Lindau syndrome (vHL) was diagnosed in 3 patients. Eleven patients were submitted to total surgical removal and in 3 the tumour was partially resected. A relapse rate of 28% in 3 years of follow-up was found. The patients with vHL showed recurrence in 66% of the cases. These findings corroborate those in current medical literature, showing an increased morbidity of this tumor when associated with vHL.

[Neurocysticercosis: a clinical and pathological study of 27 necropsied cases]. / Neurocisticercose: estudo clínico e patológico de 27 casos de necrópsia.

Neurocysticercosis is the most frequent and widespread neuroparasitosis of the human being. The development of brain and leptomeningeal lesions, with subsequent symptoms, are mainly related with the immune status of the host, and to the number and evolutional phase of the parasites. We present the pathological findings in 27 necropsies of patients with neurocysticercosis, which accounted for 3.1% of the necropsies. 77% of the patients were male and the age ranged from 18 to 85 years. In 26% there was previous history of alcoholism. Clinicopathological study showed that 50% of the cases were classified as asymptomatic form, 11% epileptic form, 11% intraventricular form and 11% combined form. 33% of the patients presented seizures as a factor of aggravation of the clinical picture. There was a single cysticercus in 60% of the cases, the cellulosae form present in 82% and the racemous form in 7% of the cases; the remaining 11% had both forms present. In 30% of the patients the cause of death was directly related with the presence of the cysticercus in the central nervous system. Our findings confirm the high morbidity of this disease.

[Craniopharyngioma: clinical, epidemiological and pathological findings in 25 cases]. / Craniofaringiomas. Achados clínicos, epidemiológicos e anatomopatológicos de 25 casos.

We report the clinical and pathological findings of 25 cases of craniopharyngiomas. Fourteen patients were males and 11 were females. The ages ranged between 3 and 64 years, with a mean of 30.52 years. The symptoms reflected the growth and topography of the tumours; visual disorders (72%), headache (68%), vomits (40%) and papilledema (24%) were the most frequent symptoms. Twelve cases were suprasellar; 10 tumours arose from sellar region, from which 8 presented suprasellar extension; frontal lobe (n = 2) and ponto cererebellar angle (n = 1) were also affected. Eleven patients undergone total resection of the tumor and 14 were submitted to partial resection, from which 1 received adjuvant chemotherapy. The overall recurrence rate was 48%. Eight recurrences were observed in the patients submitted to partial resection and 4 in which total resection were performed. These results are similar with the literature, corroborating to the extension of residual tumour after the surgical resection as the main prognostic factor for this neoplasm.

[True neurogenic outlet syndrome: report of 2 cases]. / Síndrome do desfiladeiro torácico tipo neurogênico verdadeiro. Relato de dois casos.

True neurogenic thoracic outlet syndrome is caused by compression of the lower trunk of the brachial plexus usually by a cervical rib, fibrous band or an elongated transverse process of C7. We describe two cases of female patients (23 and 19 years old) with pain in the right superior limb and progressive muscular weakness and atrophy of the intrinsic muscles of hand. Electrodiagnostic studies showed reduced amplitude of compound muscle action potential of median nerve and decreased amplitude of ulnar sensory nerve action potential. Motor and sensory nerve conduction velocities were normal in both patients. Needle electromyography were findings compatible with chronic denervation in the intrinsic muscles of the right hand of both patients. Radiological investigation showed cervical ribs in one case and elongated transverse process of C7 in the other. A discussion about the clinical and electrophysiological features and the treatment of the syndrome was performed.

Evidence for interacting two-level systems from the 1/f noise of a superconducting resonator.

The performance of a great variety of electronic devices--ranging from semiconductor transistors to superconducting qubits--is hampered by low-frequency noise with spectra proportional to 1/f. The ubiquity and negative impact of 1/f noise has motivated intensive research into its cause, and it is now believed to originate from a bath of fluctuating two-level defect states (TLSs) embedded in the material. This phenomenon is commonly described by the long-established standard tunnelling model (STM) of independent TLS. A key prediction of STM is that the noise should vanish at low temperatures. Here we report measurements on superconducting microresonators over previously unattainable, very long time scales that show an increase in 1/f noise at low temperatures and low microwave power, contrary to the STM. We propose a new generalised tunnelling model that includes significant interaction between multiple TLSs, which fully describes these observations, as well as recent studies of individual TLS lifetimes in superconducting qubits.