Probing Many-body Localization with a Programmable Superconducting Quantum Processor

In many-body localized (MBL) systems, entanglement propagates throughout the system despite the absence of transport. Early experiments have relied on population measurements to indirectly probe these entanglement dynamics. However, because the entanglement results from phase relationships between localized orbitals, it is more naturally probed with phase sensitive algorithms and measurement. In this thesis, we use an array of nearest neighbor coupled superconducting qubits to introduce phase sensitive protocols to the experimental study of MBL systems. We establish that system is MBL by demonstrating disorder induced ergodicity breaking and the presence of effective nonlocal interactions. We then use density matrix reconstructions to observe the hallmark slow growth of entanglement and provide a site-resolved spatial and temporal map of the developing entanglement. We also inspect the capacity of the MBL phase to preserve quantum correlations by observing the decay of distillable entanglement when Bell pair embedded in an MBL environment and dephased by remote excitation. In superconducting quantum processors, such as that used in the MBL study above, dissipation leads to computational errors and must be minimized. To that end, we also describe coherence engineering experiments in terms of the low power internal quality factor Qi of coplanar waveguide (CPW) resonators, a figure of merit characterizing dissipation in the quantum computing regime. We investigate titanium nitride as a superconducting base metal for quantum circuits. By optimizing the deposition conditions, we achieve a record low-power Qi in CPW resonators. We also characterize the dielectric loss due to flux trapping hole arrays. Since flux traps are commonly used to prevent magnetic vortex formation and dielectric loss is a limiting dissipation mechanism, it is important to estimate the contribution of flux traps to the dielectric dissipation budget. We find that for reasonable hole patterns the dielectric loss can be small while preventing vortex formation

Outcomes and risk score for distal pancreatectomy with celiac axis resection (DP-CAR) : an international multicenter analysis

Background: Distal pancreatectomy with celiac axis resection (DP-CAR) is a treatment option for selected patients with pancreatic cancer involving the celiac axis. A recent multicenter European study reported a 90-day mortality rate of 16%, highlighting the importance of patient selection. The authors constructed a risk score to predict 90-day mortality and assessed oncologic outcomes. Methods: This multicenter retrospective cohort study investigated patients undergoing DP-CAR at 20 European centers from 12 countries (model design 2000-2016) and three very-high-volume international centers in the United States and Japan (model validation 2004-2017). The area under receiver operator curve (AUC) and calibration plots were used for validation of the 90-day mortality risk model. Secondary outcomes included resection margin status, adjuvant therapy, and survival. Results: For 191 DP-CAR patients, the 90-day mortality rate was 5.5% (95 confidence interval [CI], 2.2-11%) at 5 high-volume (1 DP-CAR/year) and 18% (95 CI, 9-30%) at 18 low-volume DP-CAR centers (P=0.015). A risk score with age, sex, body mass index (BMI), American Society of Anesthesiologists (ASA) score, multivisceral resection, open versus minimally invasive surgery, and low- versus high-volume center performed well in both the design and validation cohorts (AUC, 0.79 vs 0.74; P=0.642). For 174 patients with pancreatic ductal adenocarcinoma, the R0 resection rate was 60%, neoadjuvant and adjuvant therapies were applied for respectively 69% and 67% of the patients, and the median overall survival period was 19months (95 CI, 15-25months). Conclusions: When performed for selected patients at high-volume centers, DP-CAR is associated with acceptable 90-day mortality and overall survival. The authors propose a 90-day mortality risk score to improve patient selection and outcomes, with DP-CAR volume as the dominant predictor

Suppressing quantum errors by scaling a surface code logical qubit

Practical quantum computing will require error rates that are well below what is achievable with physical qubits. Quantum error correction offers a path to algorithmically-relevant error rates by encoding logical qubits within many physical qubits, where increasing the number of physical qubits enhances protection against physical errors. However, introducing more qubits also increases the number of error sources, so the density of errors must be sufficiently low in order for logical performance to improve with increasing code size. Here, we report the measurement of logical qubit performance scaling across multiple code sizes, and demonstrate that our system of superconducting qubits has sufficient performance to overcome the additional errors from increasing qubit number. We find our distance-5 surface code logical qubit modestly outperforms an ensemble of distance-3 logical qubits on average, both in terms of logical error probability over 25 cycles and logical error per cycle ($2.914\%\pm 0.016\%$ compared to $3.028\%\pm 0.023\%$). To investigate damaging, low-probability error sources, we run a distance-25 repetition code and observe a $1.7\times10^{-6}$ logical error per round floor set by a single high-energy event ($1.6\times10^{-7}$ when excluding this event). We are able to accurately model our experiment, and from this model we can extract error budgets that highlight the biggest challenges for future systems. These results mark the first experimental demonstration where quantum error correction begins to improve performance with increasing qubit number, illuminating the path to reaching the logical error rates required for computation.Comment: Main text: 6 pages, 4 figures. v2: Update author list, references, Fig. S12, Table I

Non-Abelian braiding of graph vertices in a superconducting processor

Indistinguishability of particles is a fundamental principle of quantum mechanics. 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. However, in two spatial dimensions, an intriguing possibility exists: braiding of non-Abelian anyons causes rotations in a space of topologically degenerate wavefunctions. 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, 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. While efforts on conventional solid-state platforms typically involve Hamiltonian dynamics of quasi-particles, superconducting quantum processors allow for directly manipulating the many-body wavefunction via unitary gates. Building on predictions that stabilizer codes can host projective non-Abelian Ising anyons, we implement a generalized stabilizer code and unitary protocol 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 employing the anyons for quantum computation and utilize 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 toward fault-tolerant quantum computing

Probing Many-body Localization with a Programmable Superconducting Quantum Processor

In many-body localized (MBL) systems, entanglement propagates throughout the system despite the absence of transport. Early experiments have relied on population measurements to indirectly probe these entanglement dynamics. However, because the entanglement results from phase relationships between localized orbitals, it is more naturally probed with phase sensitive algorithms and measurement. In this thesis, we use an array of nearest neighbor coupled superconducting qubits to introduce phase sensitive protocols to the experimental study of MBL systems. We establish that system is MBL by demonstrating disorder induced ergodicity breaking and the presence of effective nonlocal interactions. We then use density matrix reconstructions to observe the hallmark slow growth of entanglement and provide a site-resolved spatial and temporal map of the developing entanglement. We also inspect the capacity of the MBL phase to preserve quantum correlations by observing the decay of distillable entanglement when Bell pair embedded in an MBL environment and dephased by remote excitation. In superconducting quantum processors, such as that used in the MBL study above, dissipation leads to computational errors and must be minimized. To that end, we also describe coherence engineering experiments in terms of the low power internal quality factor Qi of coplanar waveguide (CPW) resonators, a figure of merit characterizing dissipation in the quantum computing regime. We investigate titanium nitride as a superconducting base metal for quantum circuits. By optimizing the deposition conditions, we achieve a record low-power Qi in CPW resonators. We also characterize the dielectric loss due to flux trapping hole arrays. Since flux traps are commonly used to prevent magnetic vortex formation and dielectric loss is a limiting dissipation mechanism, it is important to estimate the contribution of flux traps to the dielectric dissipation budget. We find that for reasonable hole patterns the dielectric loss can be small while preventing vortex formation

Induction of ADAM10 by RT drives fibrosis, resistance, and EMT in pancreatic cancer.

Stromal fibrosis activates pro-survival and pro-epithelial-to-mesenchymal transition (EMT) pathways in pancreatic ductal adenocarcinoma (PDAC). In patient tumors treated with neoadjuvant stereotactic body radiation therapy (SBRT), we found upregulation of fibrosis, extracellular matrix (ECM), and EMT gene signatures, which can drive therapeutic resistance and tumor invasion. Molecular, functional, and translational analysis identified two cell surface proteins, A disintegrin and metalloprotease 10 (ADAM10) and ephrinB2, as drivers of fibrosis and tumor progression after RT. RT resulted in increased ADAM10 expression in tumor cells, leading to cleavage of ephrinB2, which was also detected in plasma. Pharmacologic or genetic targeting of ADAM10 decreased RT-induced fibrosis and tissue tension, tumor cell migration, and invasion, sensitizing orthotopic tumors to radiation killing and prolonging mouse survival. Inhibition of ADAM10 and genetic ablation of ephrinB2 in fibroblasts reduced the metastatic potential of tumor cells after RT. Stimulation of tumor cells with EphrinB2 FC-protein reversed the reduction in tumor cell invasion with ADAM10 ablation. These findings represent a model of PDAC adaptation that explains resistance and metastasis after radiation therapy and identifies a targetable pathway to enhance RT efficacy