Scaling up quantum computing hardware is hindered by the narrow operating margins of current quantum components. Here, we introduce a composite qubit and gate scheme that achieves wide margins by use of transistor-like nonlinearities to suppress the effects of both ambient noise and control signal imperfections. This is accomplished by adiabatic deformation of subsystem codes based on anti-commuting two-body interactions. We focus on a resource-effcient variation that exploits biased noise and preserves bias under gate operation. As a proof of concept, we present simulations of a superconducting circuit that demonstrates core elements of the approach and discuss the challenges of experimental implementation.

We present design and simulation of a Josephson parametric amplifier with bandwidth exceeding 1.6 GHz, and with high saturation power approaching -90 dBm at a gain of 22.8 dB. An improvement by a factor of roughly 50 in bandwidth over the state of the art is achieved by using well-established impedance matching techniques. An improvement by a factor of roughly 100 in saturation power over the state of the art is achieved by implementing the Josephson nonlinear element as an array of rf-SQUIDs with a total of 40 junctions. WRSpice simulations of the circuit are in excellent agreement with the calculated gain and saturation characteristics.

A simple protocol based on low-weight Pauli Hamiltonians is introduced for performing quantum gates that are robust to control noise. Gates are implemented by an adiabatic sequence of single-qubit fields and two-qubit interactions with a single ancillary qubit, whereas related techniques require three-qubit interactions, perturbation gadgets, higher dimensional subsystems, and/or more ancilla qubits. Low-weight interactions and low qubit overhead open a viable path to experimental investigation, while operation in a degenerate ground space allows for physical qubit designs that are immune to energy relaxation. Simulations indicate that two-qubit gate error due to control noise can be as low as 10^-5, for realizable coupling strengths and time-scales, with low-frequency noise that is as high as 15

We report high power operation of a vertical external-cavity surface-emitting laser (VECSEL) operating around 1180 nm. The gain chip of the VECSEL comprises 10 strain-compensated GaInAs/GaAs quantum wells in a top-emitting configuration. A maximum output power of 23 W was achieved with a mount temperature of about 0 ‡C, and 20.5 W with the mount temperature of about 12 °C. By introducing a birefringent filter inside the laser cavity we demonstrate a tuning range of 67 nm. The gain chip was also used to construct a VECSEL for single-frequency operation. In this configuration, a maximum output power of about 11 W was recorded.

Optically pumped semiconductor lasers in conjunction with intra-cavity frequency conversion and tuning elements offer high continuous-wave power, narrow linewidth, and broad tunability. As a result, they are well suited to precision spectroscopic applications. We describe the development and testing of optically pumped semiconductor lasers operating at fundamental wavelengths of 1119 and 1178 nm. The fourth and second harmonic wavelengths are resonant with transitions in Mg II and Na I, respectively. We demonstrate continuously tunable, single-frequency lasers with watt-level average power at 1119, 1178, and 589 nm.

We report on the development of an optically-pumped vertical external-cavity surface-emitting laser emitting near 1120 nm using strain compensated quantum wells. The development is motivated by the need to achieve narrow linewidth emission at ~280 nm via fourth harmonic generation, which is required to cool Mg+ ions. The gain mirror had a top-emitting geometry, was grown by molecular beam epitaxy and comprised GaInAs/GaAs quantum wells strain compensated by GaAsP layers; the strain compensation was instrumental for achieving a dislocation free epitaxial structure without dark lines. We demonstrate VECSEL operation at a fundamental wavelength close to 1118 nm with a linewidth of less than 300 kHz. Using a lithium triborate crystal we achieved frequency doubling to ~559 nm with an output power of 1.1W.

This paper presents the development and narrow-linewidth characteristics of an optically-pumped vertical external-cavity surface-emitting laser emitting light near 1120 nm. The laser development is motivated by the need to achieve narrow-linewidth, frequency-stable laser emission near 280 nm for cooling of Mg+ ions. The laser is capable of emitting similar to 0.8 W at 1118.542 nm in a less than 300 kHz linewidth.

We demonstrate a semiconductor disk laser emitting ~0.8 W close to 1120 nm with a short-term linewidth <300 kHz without active stabilization. The disk laser gain mirror used strain compensated GaInAs quantum wells.

We report a study investigating the power scaling properties of a single gain chip GaInNAs/GaAs semiconductor disk laser emitting around 1180 nm. The power scaling was done by varying the pump spot diameter between 320 mu m and 460 mu m. The emission efficiency was assessed for output coupling ratios between 0.1% and 3%. A maximum output power of 11 W was achieved with a 1.5 % output coupling ratio and a pump spot diameter of 390 mu m. The heat from the active region was extracted by an intracavity diamond heat spreader attached to a water-cooled copper mount.

High resolution imaging of unresolved targets is achieved using a combination of digital range compression and tomography principles. Image reconstruction of a meter sized target at 22.4 km range with 15 cm resolution is reported.

We demonstrate a dilute nitride (GaInAsN) based gain mirror capable of meeting the wavelength and linewidth requirements for laser guide stars. The mirror was grown by molecular beam epitaxy on a GaAs(100) substrate. The heat generated during laser operation was extracted from the active region with a wedged intracavity CVD diamond. An intracavity birefringent filter was employed for wavelength selection and a YAG etalon for linewidth narrowing. The laser radiation was intra-cavity frequency doubled to achieve emission at 589 nm. The frequency-doubled semiconductor disk laser emitted a narrow linewidth beam (~20 MHz) at 589 nm. In a free-running mode, the laser emitted more than 6W of yellow-orange light with a maximum conversion efficiency of 15.5%.

We demonstrate > 2 W of 589 nm output from an intra cavity frequency doubled optically pumped GaInNAs/GaAs laser. Single longitudinal mode operation with linewidths < 50 MHz are shown. Output powers are currently limited by available pump power and spot size.

A scalable, multiplexed ion trap for quantum information processing is fabricated and tested. The trap design and fabrication process are optimized for scalability to small trap size and large numbers of interconnected traps, and for integration of control electronics and optics. Multiple traps with similar designs are tested with 111Cd+, 25Mg+, and 88Sr+ ions at room temperature and with 88Sr+ at 6 K, with respective ion lifetimes of 90 s, 300 ± 30 s, 56 ± 6 s, and 4.5 ± 1.1 hours. The motional heating rate for 25Mg+ at room temperature and a trap frequency of 1.6 MHz is measured to be 7 ± 3 quanta per millisecond. For 88Sr+ at 6 K and 540 kHz the heating rate is measured to be 220 ± 30 quanta per second.

We cool a 7 kHz cantilever from room temperature to 45 K by capacitively coupling it to a driven rf resonant circuit. Cooling results from the capacitive force, phase shifted relative to the cantilever motion.

Recent theoretical advances have identified several computational algorithms that can be implemented utilizing quantum information processing (QIP), which gives an exponential speedup over the corresponding (known) algorithms on conventional computers. QIP makes use of the counter-intuitive properties of quantum mechanics, such as entanglement and the superposition principle. Unfortunately it has so far been impossible to build a practical QIP system that outperforms conventional computers. Atomic ions confined in an array of interconnected traps represent a potentially scalable approach to QIP. All basic requirements have been experimentally demonstrated in one and two qubit experiments. The remaining task is to scale the system to many qubits while minimizing and correcting errors in the system. While this requires extremely challenging technological improvements, no fundamental roadblocks are currently foreseen.

We have measured motional heating rates of trapped atomic ions, a factor that can influence multi-ion quantum logic gate fidelities. Two simplified techniques were developed for this purpose: one relies on Raman sideband detection implemented with a single laser source, while the second is even simpler and is based on time-resolved fluorescence detection during Doppler recooling. We applied these methods to determine heating rates in a microfrabricated surface-electrode trap made of gold on fused quartz, which traps ions 40 mu m above its surface. Heating rates obtained from the two techniques were found to be in reasonable agreement. In addition, the trap gives rise to a heating rate of 300 +/- 30 s(-1) for a motional frequency of 5.25 MHz, substantially below the trend observed in other traps.