Transport spectroscopy of low disorder silicon tunnel barriers with and without Sb implants.

We present transport measurements of silicon MOS split gate structures with and without Sb implants. We observe classical point contact (PC) behavior that is free of any pronounced unintentional resonances at liquid He temperatures. The implanted device has resonances superposed on the PC transport indicative of transport through the Sb donors. We fit the differential conductance to a rectangular tunnel barrier model with a linear barrier height dependence on source-drain voltage and non-linear dependence on gate bias. Effects such as Fowler-Nordheim (FN) tunneling and image charge barrier lowering (ICBL) are considered. Barrier heights and widths are estimated for the entire range of relevant biases. The barrier heights at the locations of some of the resonances for the implanted tunnel barrier are between 15-20 meV, which are consistent with transport through shallow partially hybridized Sb donors. The dependence of width and barrier height on gate voltage is found to be linear over a wide range of gate bias in the split gate geometry but deviates considerably when the barrier becomes large and is not described completely by standard 1D models such as FN or ICBL effects.

Electronically controlled optical beam-steering by an active phased array of metallic nanoantennas.

An optical phased array of nanoantenna fabricated in a CMOS compatible silicon photonics process is presented. The optical phased array is fed by low loss silicon waveguides with integrated ohmic thermo-optic phase shifters capable of 2π phase shift with ∼ 15 mW of applied electrical power. By controlling the electrical power to the individual integrated phase shifters fixed wavelength steering of the beam emitted normal to the surface of the wafer of 8° is demonstrated for 1 × 8 phased arrays with periods of both 6 and 9 µm.

Demonstration of polarization-independent resonant subwavelength grating filter arrays.

We demonstrate a two-dimensional (2D) polarization-independent resonant subwavelength grating (RSG) in a filter array. RSGs, also called guided mode resonant filters, are traditionally one-dimensional gratings; however, this leads to TE and TM resonances at different wavelengths and with different spectral shape. A 2D grating can remove the polarization dependence at normal incidence, while maintaining the desirable RSG properties of high reflectivity, narrow passband, and low sidebands without ripple. We designed and fabricated 2D gratings with near-identical responses for both polarizations at normal incidence in the telecommunication band. Ninety percent reflectivity is achieved at the resonant wavelengths.

Single-Shot Readout Performance of Two Heterojunction-Bipolar-Transistor Amplification Circuits at Millikelvin Temperatures.

High-fidelity single-shot readout of spin qubits requires distinguishing states much faster than the T1 time of the spin state. One approach to improving readout fidelity and bandwidth (BW) is cryogenic amplification, where the signal from the qubit is amplified before noise sources are introduced and room-temperature amplifiers can operate at lower gain and higher BW. We compare the performance of two cryogenic amplification circuits: a current-biased heterojunction bipolar transistor circuit (CB-HBT), and an AC-coupled HBT circuit (AC-HBT). Both circuits are mounted on the mixing-chamber stage of a dilution refrigerator and are connected to silicon metal oxide semiconductor (Si-MOS) quantum dot devices on a printed circuit board (PCB). The power dissipated by the CB-HBT ranges from 0.1 to 1 µW whereas the power of the AC-HBT ranges from 1 to 20 µW. Referred to the input, the noise spectral density is low for both circuits, in the 15 to 30 fA/[Formula: see text] range. The charge sensitivity for the CB-HBT and AC-HBT is 330 µe/[Formula: see text] and 400 µe/[Formula: see text], respectively. For the single-shot readout performed, less than 10 µs is required for both circuits to achieve bit error rates below 10-3, which is a putative threshold for quantum error correction.

Ion implantation for deterministic single atom devices.

We demonstrate a capability of deterministic doping at the single atom level using a combination of direct write focused ion beam and solid-state ion detectors. The focused ion beam system can position a single ion to within 35 nm of a targeted location and the detection system is sensitive to single low energy heavy ions. This platform can be used to deterministically fabricate single atom devices in materials where the nanostructure and ion detectors can be integrated, including donor-based qubits in Si and color centers in diamond.

Transplantation of an osteoarthrotendinous allograft with autogenous soft-tissue coverage for thumb reconstruction.

A fresh-frozen thumb osteoarthrotendinous allograft and autogenous coverage were used to reconstruct a thumb. Immunosuppressants were not used. The components of the composite allograft are present and functioning 1 year post-operatively. Host cells have replaced and are replacing bone and tendinous structures. The "survival" of this osteoarthrotendinous allograft may have important implications in the treatment of patients with previous digital amputations, congenital absence of digits, and amputated digits that have failed replantation or are not replantable because of severely damaged vessels.

Distal, dorsal superior extremity plasty.

Multiple deep wrinkles and redundant skin over the dorsal hand, wrist, and forearm develop and become of cosmetic importance to some patients as they age. Distal, dorsal superior extremity plasty was performed in selected patients by excising redundant skin and wrinkles from the dorsal hands, wrists, and forearms. The area of skin to be excised is elliptical, with the long axis of the ellipse centered over the wrinkles on the dorsal wrist. The amount of skin to be excised (i.e., the short axis of the ellipse) is determined by grasping the dorsal wrist skin, hence advancing the dorsal forearm and hand skin, while the patient flexes the wrist. This maneuver is performed to avoid excessive excision of dorsal wrist skin, which would cause decreased wrist flexion. The surgical procedure is performed with use of magnification to avoid sensory nerve injury. A relatively large volume of lidocaine is injected subcutaneously to increase the distance between the skin and nerves and therefore decrease the risk of nerve injury. The skin edges are undermined for 1 to 1(1/2) cm, and the wound is closed in two layers. The wrist is splinted in 30 to 45 degrees of extension to decrease wound tension. The procedure produces long-lasting, good to excellent cosmetic improvement and patient satisfaction. The dorsal wrist, hand, and forearm appear smoother and more youthful, and scars are relatively inconspicuous. Potential significant complications include injury to the superficial branch of the radial nerve and dorsal branch of the ulnar nerve, wound dehiscence, and decreased range of motion of the wrist. Use of magnification, a bloodless field, injection of a relatively large volume of local anesthetic (10 to 12 cc), knowledge of regional anatomy, and careful surgical technique decrease the risk of nerve injury. Avoidance of injury to the superficial sensory branches of the radial and ulnar nerves is absolutely necessary for patient satisfaction. Avoidance of injury to the wound edges with good surgical technique, postoperative immobilization with the wrist in an extended position, and subsequent advancement of the wrist to a neutral position for several weeks decrease the risk of wound dehiscence. Avoidance of excessive skin excision and prolonged wrist immobilization lowers the risk of decreasing range of motion. There have been no complications in patients who underwent this procedure.

Cosmetic treatment of shagreen patches in selected patients with tuberous sclerosis.

Patients with mild forms of tuberous sclerosis may request cosmetic treatment of skin hamartomas. Treatment may consist of planning of an elevated shagreen patch with a Reese dermatome and/or laser treatment of facial angiofibromas. These precise patients, i.e., patients with a forme fruste of tuberous sclerosis, are more likely to have pulmonary involvement than patients with the usual complete disease form. A chest x-ray should be obtained in these patients to rule out pulmonary involvement. Half the patients with pulmonary involvement of tuberous sclerosis die an avoidable death from spontaneous pneumothoraces. Positive-pressure ventilation during anesthesia in these patients should be avoided or monitored closely.

Treatment of complex postoperative lumbosacral wounds in nonparalyzed patients.

Postoperative infections after back operations can produce complex wounds with myonecrosis, deep dead space, and exposed orthopedic hardware, bone, and dura. Three ambulatory patients with complex postoperative back wounds that resulted from infections were treated successfully with antibiotics, debridement, irrigation, and closure of deep dead space with a superior gluteal muscle flap. Several surgical maneuvers can be performed to increase the length of the superior gluteal muscle flap. The inferior portion of the gluteus maximus was left intact to preserve gluteus maximus function. All three patients obtained healed wounds. The exposed A.O. plating system was not removed. There has not been any recurrence of infections. The superior gluteal muscle flap is a reasonable flap to fill deep dead space in the low back and has some advantages over free flaps.

Strong coupling in the sub-wavelength limit using metamaterial nanocavities.

The interaction between cavity modes and optical transitions leads to new coupled light-matter states in which the energy is periodically exchanged between the matter states and the optical mode. Here we present experimental evidence of optical strong coupling between modes of individual sub-wavelength metamaterial nanocavities and engineered optical transitions in semiconductor heterostructures. We show that this behaviour is generic by extending the results from the mid-infrared (~10 µm) to the near-infrared (~1.5 µm). Using mid-infrared structures, we demonstrate that the light-matter coupling occurs at the single resonator level and with extremely small interaction volumes. We calculate a mode volume of 4.9 × 10(-4) (λ/n)(3) from which we infer that only ~2,400 electrons per resonator participate in this energy exchange process.