Universal logic with encoded spin qubits in silicon.

Quantum computation features known examples of hardware acceleration for certain problems, but is challenging to realize because of its susceptibility to small errors from noise or imperfect control. The principles of fault tolerance may enable computational acceleration with imperfect hardware, but they place strict requirements on the character and correlation of errors1. For many qubit technologies2-21, some challenges to achieving fault tolerance can be traced to correlated errors arising from the need to control qubits by injecting microwave energy matching qubit resonances. Here we demonstrate an alternative approach to quantum computation that uses energy-degenerate encoded qubit states controlled by nearest-neighbour contact interactions that partially swap the spin states of electrons with those of their neighbours. Calibrated sequences of such partial swaps, implemented using only voltage pulses, allow universal quantum control while bypassing microwave-associated correlated error sources1,22-28. We use an array of six 28Si/SiGe quantum dots, built using a platform that is capable of extending in two dimensions following processes used in conventional microelectronics29. We quantify the operational fidelity of universal control of two encoded qubits using interleaved randomized benchmarking30, finding a fidelity of 96.3% ± 0.7% for encoded controlled NOT operations and 99.3% ± 0.5% for encoded SWAP. The quantum coherence offered by enriched silicon5-9,16,18,20,22,27,29,31-37, the all-electrical and low-crosstalk-control of partial swap operations1,22-28 and the configurable insensitivity of our encoding to certain error sources28,33,34,38 all combine to offer a strong pathway towards scalable fault tolerance and computational advantage.

Endocrine Tumor Board: Ten Years' Experience of a Multidisciplinary Clinical Working Conference.

INTRODUCTION: Advances in specialized medical areas and updated clinical guidelines show a need for a focused approach for patients with specific disorders. OBJECTIVE: To describe a multidisciplinary tumor board for patients with endocrine tumors. METHODS: We established an endocrine tumor board at a large health maintenance organization and studied cases presented between September 2007 and August 2017. To resolve diagnostic and/or therapeutic questions, a multidisciplinary team of specialists discussed patients' clinical presentations. Cases were broken down into diagnostic categories, demographic characteristics (age, sex), and need for repeated presentations to the board. RESULTS: We included 608 patients: 401 female (66%) and 207 male (34%). Ages ranged from teens to more than 90 years, with the peak decade 50 to 59 years (26%). Although most patients needed only 1 presentation to the board, 151 (25%) required representation, for a total of 853 presentations. The diagnoses reflected the workup status with tumor identification and localization at the initial case presentation. Diagnoses included thyroid cancer (234 patients, 38.4%), adrenal mass (165 patients, 27.1%), primary hyperparathyroidism (120 patients, 19.7%), thyroid nodule (95 patients, 15.6%), and extrathyroidal mass (23 patients, 3.8%). Other diagnoses composed the remaining 14.6%. Tumor board attendees overwhelmingly supported the meetings' benefits, with all clinicians reporting frequently changing patient management because of the meetings. CONCLUSION: Patients with endocrine tumors may benefit from a specialized approach to care. A multidisciplinary tumor board can focus discussions efficiently, provide a forum to advance care, apply endocrine-related clinical guidelines, and lead to recommendations that clinicians often employed.

Isotopically enhanced triple-quantum-dot qubit.

Like modern microprocessors today, future processors of quantum information may be implemented using all-electrical control of silicon-based devices. A semiconductor spin qubit may be controlled without the use of magnetic fields by using three electrons in three tunnel-coupled quantum dots. Triple dots have previously been implemented in GaAs, but this material suffers from intrinsic nuclear magnetic noise. Reduction of this noise is possible by fabricating devices using isotopically purified silicon. We demonstrate universal coherent control of a triple-quantum-dot qubit implemented in an isotopically enhanced Si/SiGe heterostructure. Composite pulses are used to implement spin-echo type sequences, and differential charge sensing enables single-shot state readout. These experiments demonstrate sufficient control with sufficiently low noise to enable the long pulse sequences required for exchange-only two-qubit logic and randomized benchmarking.

First bite syndrome caused by adenoid cystic carcinoma of the submandibular gland.

First bite syndrome is a well-described sequelae of parapharyngeal space surgery, thought to result from sympathetic denervation of the parotid gland. We describe a case of first bite syndrome caused by an adenoid cystic carcinoma of the submandibular gland. The tumor was not clinically or radiographically apparent until 18 months after initial presentation despite repeated imaging. In patients with first bite syndrome and no surgical history, there must be high suspicion for a malignancy, which may be occult on presentation. The submandibular gland should be considered as a possible site of a lesion.

Near-optimal dynamical decoupling of a qubit.

We present a near-optimal quantum dynamical decoupling scheme that eliminates general decoherence of a qubit to order n using O(n2) pulses, an exponential decrease in pulses over all previous decoupling methods. Numerical simulations of a qubit coupled to a spin bath demonstrate the superior performance of the new pulse sequences.

High fidelity quantum gates via dynamical decoupling.

Realizing the theoretical promise of quantum computers will require overcoming decoherence. Here we demonstrate numerically that high fidelity quantum gates are possible within a framework of quantum dynamical decoupling. Orders of magnitude improvement in the fidelities of a universal set of quantum gates, relative to unprotected evolution, is achieved over a broad range of system-environment coupling strengths, using recursively constructed (concatenated) dynamical decoupling pulse sequences.

Phase I study of stereotactic radiosurgery in patients with locally advanced pancreatic cancer.

PURPOSE: To determine the feasibility and toxicity of delivering stereotactic radiosurgery to patients with locally advanced pancreatic cancer. METHODS AND MATERIALS: Patients with Eastern Cooperative Oncology Group performance status < or=2 and locally advanced pancreatic cancer were enrolled on this Phase I dose escalation study. Patients received a single fraction of radiosurgery consisting of either 15 Gy, 20 Gy, or 25 Gy to the primary tumor. Acute gastrointestinal toxicity was scored according to the Radiation Therapy Oncology Group criteria. Response to treatment was determined by serial high-resolution computed tomography scanning. RESULTS: Fifteen patients were treated at 3 dose levels (3 patients received 15 Gy, 5 patients received 20 Gy, and 7 patients received 25 Gy). At these doses, no Grade 3 or higher acute gastrointestinal toxicity was observed. This trial was stopped before any dose-limiting toxicity was reached, because the clinical objective of local control was achieved in all 6 evaluable patients treated at 25 Gy. CONCLUSIONS: It is feasible to deliver stereotactic radiosurgery to patients with locally advanced pancreatic cancer. The recommended dose to achieve local control without significant acute gastrointestinal toxicity is 25 Gy.