Valley Splitting in Silicon from the Interference Pattern of Quantum Oscillations.

We determine the energy splitting of the conduction-band valleys in two-dimensional electrons confined in silicon metal oxide semiconductor Hall-bar transistors. These silicon metal oxide semiconductor Hall bars are made by advanced semiconductor manufacturing on 300 mm silicon wafers and support a two-dimensional electron gas of high quality with a maximum mobility of 17.6×10^{3} cm^{2}/Vs and minimum percolation density of 3.45×10^{10} cm^{-2}. Because of the low disorder, we observe beatings in the Shubnikov-de Haas oscillations that arise from the energy splitting of the two low-lying conduction band valleys. From the analysis of the oscillations beating patterns up to T=1.7 K, we estimate a maximum valley splitting of ΔE_{VS}=8.2 meV at a density of 6.8×10^{12} cm^{-2}. Furthermore, the valley splitting increases with density at a rate consistent with theoretical predictions for a near-ideal semiconductor-oxide interface.

Universal quantum logic in hot silicon qubits.

Quantum computation requires many qubits that can be coherently controlled and coupled to each other1. Qubits that are defined using lithographic techniques have been suggested to enable the development of scalable quantum systems because they can be implemented using semiconductor fabrication technology2-5. However, leading solid-state approaches function only at temperatures below 100 millikelvin, where cooling power is extremely limited, and this severely affects the prospects of practical quantum computation. Recent studies of electron spins in silicon have made progress towards a platform that can be operated at higher temperatures by demonstrating long spin lifetimes6, gate-based spin readout7 and coherent single-spin control8. However, a high-temperature two-qubit logic gate has not yet been demonstrated. Here we show that silicon quantum dots can have sufficient thermal robustness to enable the execution of a universal gate set at temperatures greater than one kelvin. We obtain single-qubit control via electron spin resonance and readout using Pauli spin blockade. In addition, we show individual coherent control of two qubits and measure single-qubit fidelities of up to 99.3 per cent. We demonstrate the tunability of the exchange interaction between the two spins from 0.5 to 18 megahertz and use it to execute coherent two-qubit controlled rotations. The demonstration of 'hot' and universal quantum logic in a semiconductor platform paves the way for quantum integrated circuits that host both the quantum hardware and its control circuitry on the same chip, providing a scalable approach towards practical quantum information processing.

Tunable Coupling and Isolation of Single Electrons in Silicon Metal-Oxide-Semiconductor Quantum Dots.

Extremely long coherence times, excellent single-qubit gate fidelities, and two-qubit logic have been demonstrated with silicon metal-oxide-semiconductor spin qubits, making it one of the leading platforms for quantum information processing. Despite this, a long-standing challenge in this system has been the demonstration of tunable tunnel coupling between single electrons. Here we overcome this hurdle with gate-defined quantum dots and show couplings that can be tuned on and off for quantum operations. We use charge sensing to discriminate between the (2,0) and (1,1) charge states of a double quantum dot and show excellent charge sensitivity. We demonstrate tunable coupling up to 13 GHz, obtained by fitting charge polarization lines, and tunable tunnel rates down to <1 Hz, deduced from the random telegraph signal. The demonstration of tunable coupling between single electrons in a silicon metal-oxide-semiconductor device provides significant scope for high-fidelity two-qubit logic toward quantum information processing with standard manufacturing.

Spin Lifetime and Charge Noise in Hot Silicon Quantum Dot Qubits.

We investigate the magnetic field and temperature dependence of the single-electron spin lifetime in silicon quantum dots and find a lifetime of 2.8 ms at a temperature of 1.1 K. We develop a model based on spin-valley mixing and find that Johnson noise and two-phonon processes limit relaxation at low and high temperature, respectively. We also investigate the effect of temperature on charge noise and find a linear dependence up to 4 K. These results contribute to the understanding of relaxation in silicon quantum dots and are promising for qubit operation at elevated temperatures.

The influence of early surface thromboreactivity on long-term arterial graft patency.

The influence of early graft surface thromboreactivity on long-term arterial polyester (Dacron) graft patency was investigated with separate ex vivo and in vivo animal models. First, parallel, flow-regulated external aortocaval fistulae were created in five pigs with use of paired 8 mm X 35 cm crimped, warp-knitted, low-profile filamentous velour Dacron tubes: one tube preclotted with autologous blood, the other autoclaved after being soaked in human albumin. Autologous radiolabeled platelets, red cells, and radiolabeled human fibrinogen were injected at initiation of graft flow, with timed graft samples submitted for isotope gamma well-counting. Flow surface accumulation of radiolabeled blood elements was greater on the preclotted graft limb at-all time intervals studied, greatest after 5 minutes of flow initiation with RBC accumulation on the preclotted limb 5.19 +/- 0.84 (x +/- S.E.), platelet accumulation 5.57 +/- 1.00, and fibrinogen accumulation 1.82 +/- 0.14 times greater than that on the albumin-treated limb. Second, bilateral iliofemoral artery bypass grafts were placed in 12 mongrel dogs using 6 mm X 10 cm externally supported, noncrimped, warp-knitted, low-profile filamentous Dacron tubes. Before implant in each dog, one graft limb was clotted with autologous blood and the other was autoclaved after being soaked in 25% human albumin. Fresh autologous radiolabeled platelets were injected after wound closure in seven of these dogs. Postimplant graft imaging at 24 and 72 hours showed radiolabeled platelet accumulation to be 1.43 +/- 0.21 and 2.05 +/- 0.18 times greater on the preclotted graft limb. Six of 12 preclotted graft limbs and 7 of 12 albumin-treated graft limbs were patent when animals were killed 5 to 6 months after implant (not significant). Heat-denatured albumin-coated Dacron surfaces have a reduced early thromboreactivity but do not appear to greatly potentiate long-term arterial graft patency.

Heat-denatured albumin-coated Dacron vascular grafts: physical characteristics and in vivo performance.

Dacron fabrics with a wide range of porosities were autoclaved for 3 minutes after being soaked in serum, 5% albumin, or 25% albumin. Porosity of compound Dacron grafts made with 25% albumin was less than 1 ml/min/cm2 regardless of the fabric base, whereas porosity of grafts made with serum or 5% albumin was proportional to the porosity of the base fabric. Porosity of the compound grafts remained stable for more than 48 hours and to pressure greater than 450 mm Hg, if the grafts were kept moist. Tubes of Marlex mesh coated with heat-denatured albumin, implanted as infrarenal aortic replacements in dogs, showed complete albumin absorption by 3 weeks. However, perigraft tissue reaction and graft incorporation were minimal and extensive false aneurysm formation resulted. Knitted filamentous Dacron 6 mm tubes coated with heat-denatured albumin were implanted as iliofemoral bypass grafts in 12 dogs, with blood-preclotted knitted filamentous Dacron grafts implanted as contralateral control grafts. Comparison of the albumin-coated grafts with the blood-preclotted control grafts showed no differences in healing or patency at 4 to 6 months. Heat-denatured 25% albumin forms a strong and hemostatic coating regardless of fabric base. Albumin-Dacron compound grafts are easily and rapidly made in the operating room, handle well, and are suitable for large and medium-sized arterial replacements without changes in healing or patency. Because of slow tissue incorporation, however, albumin-coated knitted Dacron grafts should be avoided in patients who require long-term anticoagulation therapy.

The value of computed tomography in staging bronchogenic carcinoma: a changing role for mediastinoscopy.

Forty-one patients underwent operative staging for bronchogenic carcinoma following computed tomography of the mediastinum between August, 1982, and March, 1984. Twenty-seven patients were classified as Stage I preoperatively; in 2 of them, positive mediastinal nodes were found at thoracotomy. For the 14 patients in whom positive nodes had been identified by computed tomographic (CT) scanning, staging was unchanged as a result of the findings at mediastinoscopy or thoracotomy or both. In this series, computed tomography had a sensitivity of 89%, a specificity of 100%, and an overall accuracy rate of 95%. We conclude that mediastinoscopy is not needed in patients without evidence of mediastinal nodal enlargement by CT scan; when performed, it should be guided toward those nodes identified as positive.

Transseptal control of the difficult aortic annulus.

Successful control of the aortic root in extensive erosive endocarditis, with or without mycotic ventricular septal defect, frequently depends on secure prosthetic fixation to the interventricular septum. We describe transseptal suture fixation of aortic root prostheses through a pulmonary infundibular approach and recommend its early use to avoid difficult, often injurious, attempts at septal suture from within the left ventricular outflow tract.

Late Mycobacterium chelonei bioprosthetic valve endocarditis: activation of implanted contaminant?

Mycobacterium chelonei contamination of the Hancock porcine heart valve prosthesis occurred in a few lots manufactured between October, 1975, and August, 1976. The unimplanted valves were recalled, but a number of valves in their cohort had already been implanted. This report describes a patient with Mycobacterium chelonei endocarditis of a Hancock bioprosthetic heart valve belonging to this cohort that occurred three years after implantation. We are aware of four similar instances of mycobacterial endocarditis and believe that these latent infections originated either from surgical inoculation or from implantation of a contaminated valve prosthesis. Other Hancock valves manufactured between October, 1975, and August, 1976, may harbor latent M. chelonei. We believe early valve replacement with aggressive combination antibacterial and antituberculosis therapy is essential for control of atypical mycobacterial valve endocarditis.

Intrathoracic application of the latissimus dorsi musculocutaneous flap.

The intrathoracic technique, application, and merits of the latissimus dorsi musculocutaneous flap are presented by the single-stage repair of a presumed postirradiation tracheoesophageal fistula. This etiology, if indeed true, has not been demonstrated, nor has this extension to the flap's many possible uses been previously described.

Veterans Administration Cooperative Study on Bowel Preparation for Elective Colorectal Operations: impact of oral antibiotic regimen on colonic flora, wound irrigation cultures and bacteriology of septic complications.

A ten hospital cooperative study comparing prophylactic oral neomycin and erythromycin base versus placebo demonstrated clinical efficacy of the antibiotics in preventing septic complications following elective colon operations. The present report concerns microbiological studies accomplished during this trial. Cultures of colon contents during surgery showed the antibiotic prep reduced concentrations of both aerobes and anaerobes by approximately 10(5) bacteria/ml. Virtually all major bacterial components of the normal flora were affected. Wound irrigation specimens at the time of closure failed to predict subsequent wound infection, but significantly fewer antibiotic recipients had positive irrigation cultures. Postoperative stool specimens showed that the oral antibiotics did not cause an emergence in resistant forms. Bacteriological studies of postoperative infections indicated that most postoperative infections involved a mixed aerobic-anaerobic flora, and that Bacteroides fragilis accounted for six of eight episodes of bacteremia.

Mesenchymal hamartoma of the liver.

A surgically treated case of a mesenchymal hamartoma, a rare, benign liver tumor of infants and occasionally children, is reported. The clinical picture is characterized by marked, usually rapid abdominal enlargement. If untreated, the tumor may compromise other organ systems, resulting in death. The treatment is surgical removal. The tumor is characterized by proliferation of collagenous connective tissue, immature mesenchyme, and multiple cysts or pseudocysts of varying sizes. The origin of the tumor has not yet been definitely determined. Ultrasonography combined with radionuclide scanning was useful in establishing a working, preoperative diagnosis.

Preoperative oral antibiotics reduce septic complications of colon operations: results of prospective, randomized, double-blind clinical study.

The effectiveness of short-term, low-dose, preoperative oral administration of neomycin and erythromycin base combined with vigorous purgation in reducing the incidence of wound infections and other septic complications of elective colon and rectal operations has been studied in a prospective, randomized, double-blind, clinical trial. One hundred and sixteen patients completed the study; all received mechanical preparation; 56 received neomycin-erythromycin base while 60 received an identical appearing placebo. The two patient groups were comparable in age distribution, clinical diagnoses, associated systemic diseases, types of operation performed and similar clinical features. The overall rate of directly related septic complications was 43 per cent in the placebo group and 9% in the group receiving neomycin and erythromycin base. The wound infection rates were 35% in placebo and 9% in antibiotic treated patients. Oral administration of neomycin and erythromycin base together with vigorous mechanical cleansing reduces the risk of septic complications after elective colo-rectal operations.

Glucocorticoid therapy in children. Effect on somatomedin secretion.

Glucocorticoids cause growth retardation in children. We have studied the effect of these hormones on serum somatomedin (Sm) levels in seven children with nephrosis. Intravenous administration of methylprednisolone sodium succinate, 2.2 mg/kg, causes a rapid fall in serum Sm activity. The activity remains suppressed during continuous therapy, but returns toward normal when medication is omitted during the course of alternate-day therapy. We conclude that one reason for growth retardation secondary to continuous glucocorticoid therapy is suppression of Sm generation. A direct effect of these hormones on the cartilage cell or induction of an Sm inhibitor cannot be excluded by the reported experiments.

Bacteriology of the gut and its clinical implications.

The bacteriology of the gastrointestinal tract is rapidly changing in laboratory techniques and clinical correlations. The flora is found to be very complex, predominantly anaerobic, and importantly dependent on diet. An etiologic role for colon bacteria in colon cancer is suggested by correlations between epidemiologic data and prevalent dietary patterns and stool culture findings. Cultures from aspiration pneumonia, subphrenic abscess, and other intra-abdominal sepsis all yield anaerobes, and for best results antibiotic therapy should combat them as well as aerobes.