Dynamics of magnetization at infinite temperature in a Heisenberg spin chain

Understanding universal aspects of quantum dynamics is an unresolved problem in statistical mechanics. In particular, the spin dynamics of the one-dimensional Heisenberg model were conjectured as to belong to the Kardar-Parisi-Zhang (KPZ) universality class based on the scaling of the infinite-temperature spin-spin correlation function. In a chain of 46 superconducting qubits, we studied the probability distribution of the magnetization transferred across the chain's center, [Formula: see text]. The first two moments of [Formula: see text] show superdiffusive behavior, a hallmark of KPZ universality. However, the third and fourth moments ruled out the KPZ conjecture and allow for evaluating other theories. Our results highlight the importance of studying higher moments in determining dynamic universality classes and provide insights into universal behavior in quantum systems.

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.

Non-Abelian braiding of graph vertices in a superconducting processor

Indistinguishability of particles is a fundamental principle of quantum mechanics¹. For all elementary and quasiparticles observed to date-including fermions, bosons and Abelian anyons-this principle guarantees that the braiding of identical particles leaves the system unchanged^2,3. However, in two spatial dimensions, an intriguing possibility exists: braiding of non-Abelian anyons causes rotations in a space of topologically degenerate wavefunctions^4-8. Hence, it can change the observables of the system without violating the principle of indistinguishability. Despite the well-developed mathematical description of non-Abelian anyons and numerous theoretical proposals^9-22, the experimental observation of their exchange statistics has remained elusive for decades. Controllable many-body quantum states generated on quantum processors offer another path for exploring these fundamental phenomena. Whereas efforts on conventional solid-state platforms typically involve Hamiltonian dynamics of quasiparticles, superconducting quantum processors allow for directly manipulating the many-body wavefunction by means of unitary gates. Building on predictions that stabilizer codes can host projective non-Abelian Ising anyons^9,10, we implement a generalized stabilizer code and unitary protocol²³ to create and braid them. This allows us to experimentally verify the fusion rules of the anyons and braid them to realize their statistics. We then study the prospect of using the anyons for quantum computation and use braiding to create an entangled state of anyons encoding three logical qubits. Our work provides new insights about non-Abelian braiding and, through the future inclusion of error correction to achieve topological protection, could open a path towards fault-tolerant quantum computing.

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.

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 ℤ 2 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

[Figure: see text].

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.

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.

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.

Abstract OT3-4-04: InVite: an observational pilot study evaluating the feasibility of genome-wide association studies using self-reported data from patients with metastatic breast cancer treated with bevacizumab

Background: Personalized healthcare tailors treatments to patients and their disease characteristics through the use of genetics and other biomarkers. Genetic differences among individuals may explain variations in drug treatment response, including side effects. With such information physicians could make more informed decisions about drugs and dosing for a given individual, thereby improving patient care. Although there has been some success, to a large extent genetic variation related to drug response remains unexplained.

Bevacizumab, a humanized monoclonal antibody against the angiogenic factor VEGF, has demonstrated activity in patients with metastatic breast cancer (MBC). The InVite study will evaluate the feasibility of performing genomewide association studies using self-reported information collected via an online platform from patients with MBC who have been treated with bevacizumab. Using novel methodology in a convenient, user-friendly, and scientifically rigorous format, InVite ultimately aims to identify potential pharmacogenetic associations in this patient population.

Trial design: InVite is a pilot, non-interventional, observational, web-based, prospective cohort study designed to collect patient-reported safety, efficacy, and genetic data from patients with MBC treated with bevacizumab. Data on demographics, breast cancer disease status, cancer treatment history, bevacizumab-related outcomes, and certain safety events will be collected directly from patients entirely via online surveys. Patients will be asked to complete surveys at the time of enrollment and then every 3 months for 1 year after enrollment. A saliva sample for DNA collection will be gathered using an at-home kit. Evaluations of data quality and collection feasibility will be conducted intermittently. There will be an optional substudy to allow for blood sample collection for DNA analysis.

Eligibility criteria: ≥18 years of age, residing in the US, locally recurrent breast cancer or MBC, currently being or having been treated with bevacizumab starting on or before Dec 31, 2011, fluent in English, and access to a computer with an internet connection.

Specific aims: The primary objective is to assess the feasibility of recruiting subjects and collecting biospecimens and self-reported data online. The secondary objective is to characterize the patient population. Exploratory objectives include analyzing potential associations between genetic polymorphisms and 1) bevacizumab-induced hypertension, the most common bevacizumab-related adverse event, and 2) patient-reported time-to-progression.

Statistical methods: Baseline demographics, clinical and treatment characteristics of enrolled patients will be summarized. Each polymorphism genotyped will be tested for association with the defined endpoint using appropriate statistical modeling.

Present and target accrual: Accrual as of May 23, 2012 is 82 patients. Target accrual is 1000 patients.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr OT3-4-04.

Lymphatic vessel density is not associated with lymph node metastasis or survival in non-small cell lung carcinoma (NSCLC)

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Background: Angiogenesis is accepted as being essential for tumors to grow and metastasize to distant sites. Lymphatic metastasis is also an important means of tumor spread. Vascular endothelial growth factor C (VEGF-C) plays and important role in lymphangiogenesis and activates VEGFR (VEGF receptor)-3. Numerous studies suggest that tumor expression of VEGF-C is a significant prognostic factor in NSCLC. In non-small cell lung carcinoma (NSCLC), the relationship of lymphangiogenesis with lymph node metastasis and patient prognosis is unknown. Methods: A retrospective analysis of 78 patients who were diagnosed with NSCLC from 1987 to 2004 were analyzed for lymphatic vascular density (LVD). LVD was measured by use of D2–40 monoclonal antibody staining. Survival was assessed and Mantel-Cox and Wilcoxon signed rank tests were used for statistical analysis. Results: Intratumoral and peritumoral LVD was significantly higher than in the uninvolved adjacent lung, but showed no significant association with lymph node status at the time of tumor resection. Variables which appeared to affect survival in our study were the presence of lymph node metastasis (median survival 1,425 vs absence 467 days, p=0.002). The presence of VEGF staining inversely affected median survival (present 757 vs absent 1,944 days, p= 0.014). LVD ≤ 53 events per field 895 days vs >53 median survival 1,302 days, p+0.867. Survival appeared to not be affected by LVD. Conclusions: These data suggest that although lymphangiogenesis occurs in association with NSCLC, it may not be an important factor in lymph node metastasis or in survival. In fact, there is a suggestion that the number of lymphatics that a patient inherently has appears to be more important than lymphangiogenesis when it comes to the development of lymph node metastasis.

No significant financial relationships to disclose.

Molecular correlates (EGFR status) and plasma VEGF levels associated with a phase II study of bevacizumab plus erlotinib (BE) for patients with recurrent ovarian cancer (OC) and fallopian tube (FT) cancer

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Background: The epidermal growth factor receptor (EGFR) and vascular endothelial growth factor (VEGF) are commonly over- expressed in OC and may correlate with poor prognosis. EGFR mutations, although rare, have recently been reported in ovarian cancer. We examined these factors for prognostic value in the setting of treatment with BE. Results of a phase II trial of BE in recurrent OC pts have previously been reported; there were 1 CR and 1 PR among 13 patients. The trial was closed to accrual due to 2 bowel perforations. Methods: Pretreatment plasma VEGF, urine VEGF, and serum VEGFR2 levels are available on 9, 8, and 8 pts to date. VEGF levels were determined using an ELISA (R& D Systems, Minneapolis, MN). Tumor from 8 pts: 1(CR), 1 (PR), 5 (SD), 1 (PD) was available for immunohistochemical analysis for EGFR. Genomic DNA was successfully isolated from 6 paraffin embedded tumor specimens. EGFR exons 18 to 21 were amplified by PCR using primary and secondary PCR primer pairs. PCR products were purified and submitted for DNA sequencing against forward and reverse primers (analyzed with Sequencher). Results: Mean baseline plasma VEGF level was 107.6 pg/ml (range, 52–198 pg/ml). For analysis, we combined CR+PR+SD versus PD. Wilcoxon rank-sum test was used to compare baseline plasma VEGF levels, urine VEGF and serum VEGFR2 between the two response groups. There were no significant differences between response and baseline VEGF levels (p=0.39), urine VEGF (p=0.56), and VEGFR2 (p=0.56) respectively. The pt with prolonged CR (18 mos) had the highest baseline VEGF level. Cox proportional hazards regression models was used to look at the association between overall survival (OS) and VEGF levels. There was no significant relationship between (OS) and baseline plasma VEGF (p= 0.38), urine VEGF (p=0.33) or serum VEGFR2 (p=0.63) respectively. No EGFR mutations were found in exon 19 (n=4) or exon 21 (n=6). EGFR expression is being evaluated. Conclusions: Our results indicate that there were no significant relationship between response or OS and baseline VEGF or VEGFR2 levels in our treated pts. The study was supported by NCI Grant N01-CM-17102.

[Table: see text]

Expression of protein kinase C beta (PKCß) as a prognostic marker in non-small cell lung cancer (NSCLC) and mesothelioma

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Background: The protein kinase C (PKC) family of serine-threonine protein kinases has been shown to be involved in tumor cell growth, survival, and progression. Tumor-induced angiogenesis requires activation of PKCs, particularly PKCβ, through vascular endothelial growth factor (VEGF) pathways. PKCβ-2 appears to be a major down-stream signaling protein for the VEGFR. This makes PKCβ an attractive target in treatment of malignancies, including lung cancer. Methods: 135 tumor samples (111 Non-small cell lung cancer tissues (52 adenocarcinomas (AC), 34 large cell (LC), 25 squamous cell carcinoma (SCC)) and 24 mesotheliomas (MT)) arranged in tumor microarrays (TMAs) were subject to immunohistochemical staining of PKCβ-1 and PKCβ-2. Results were analyzed manually and scored for intensity (1+, 2+, 3+). Clinical information was available for the AC, LC, and SCC group. Survival curves were generated and median survival between groups was compared utilizing the Log-rank methodology. Results: In NSCLC the expression of PKCβ1 was negative in 1% (1/107), 1+ in 14% (15/107), 2+ in 43% (46/107), 3+ in 42% (45/107); PKCβ2 immunostaining was negative in 28.4% (29/102), 1+ in 12.7% (13/102), 3+ in 23.6% (24/102) and 3+ in 35.3% (36/102). Median survival was superior for patients who expressed PKCβ1 (2+ or 3+) as compared to non-expressors (median survival 1258 days versus 124 days, p<0.001). There was no difference in median survival in patients whose tumors expressed PKCβ2 and those that did not express it. In mesothelioma, staining for PKCβ1 was negative in 0, 1+ in 0, 2+ in 8.3% (2/24) and 3+ in 91.7% (22/24). For PKCβ2, tissues stained negative in 56.5% (13/23), 1+ in 21.8% (5/23), 2+ in 8.7% (2/23), 3+ in 13% (3/23). Median survival was superior for patients whose tumors did not express PKC-beta 2 (0 or 1+) as compared to expressors (median survival 604 days versus 103 days, p<0.001). Conclusions: PKCβ is expressed in NSCLC and mesothelioma. PKCβ1 expression is a favorable prognostic factor in NSCLC, whereas expression of PKCβ2 is an adverse prognostic factor in mesothelioma. Therapeutic targeting of this molecule would be useful for the future.

No significant financial relationships to disclose.

Decoherence and 1/f noise in Josephson qubits

We propose and study a model of dephasing due to an environment of bistable fluctuators. We apply our analysis to the decoherence of Josephson qubits, induced by background charges present in the substrate, which are also responsible for the 1/f noise. The discrete nature of the environment leads to a number of new features which are mostly pronounced for slowly moving charges. Far away from the degeneracy this model for the dephasing is solved exactly.