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By inserting index perturbations at certain positions along a semiconductor Fabry–Perot laser cavity the threshold gain for one or several of the longitudinal cavity modes can be selectively lowered to facilitate, e.g., single-mo...
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By inserting index perturbations at certain positions along a semiconductor Fabry–Perot laser cavity the threshold gain for one or several of the longitudinal cavity modes can be selectively lowered to facilitate, e.g., single-mode or two-color operation. Previous design methods were limited to a fairly small number of perturbations, leading to only weakly perturbed cavities and thus a limited freedom in tailoring the spectral properties of the laser. In our approach we fully account for all multiple-reflection events and use a search space that permits any distribution of the locations and lengths of the perturbations. We are therefore able to design cavities with almost arbitrary spectral properties with very low threshold gain values for, e.g., the lasing modes of a two-color cavity. Constraining the design by reducing the geometrical freedom, which can be used to increase the smallest feature size to simplify fabrication, we seamlessly approach the weakly perturbed regime while maintaining much of the freedom for spectral engineering.
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We study a superconducting charge qubit coupled to an intensive electromagnetic field and probe changes in the resonance frequency of the formed dressed states. At large driving strengths, exceeding the qubit energy-level splittin...
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We study a superconducting charge qubit coupled to an intensive electromagnetic field and probe changes in the resonance frequency of the formed dressed states. At large driving strengths, exceeding the qubit energy-level splitting, this reveals the well known Landau-Zener-Stueckelberg interference structure of a longitudinally driven two-level system. For even stronger drives, we observe a significant change in the Landau-Zener-Stiickelberg pattern and contrast. We attribute this to photon-assisted quasiparticle tunneling in the qubit. This results in the recovery of the qubit parity, eliminating effects of quasiparticle poisoning, and leads to an enhanced interferometric response. The interference pattern becomes robust to quasiparticle poisoning and has a good potential for accurate charge sensing.
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We demonstrate a planar superconducting microwave resonator intended for use in applications requiring strong magnetic fields and high quality factors. In perpendicular magnetic fields of 20 mT, the niobium resonators maintain a q...
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We demonstrate a planar superconducting microwave resonator intended for use in applications requiring strong magnetic fields and high quality factors. In perpendicular magnetic fields of 20 mT, the niobium resonators maintain a quality factor above 25 000 over a wide range of applied powers, down to single photon population. In parallel field, the same quality factor is observed above 160 mT, the field required for coupling to free spins at a typical operating frequency of 5 GHz. We attribute the increased performance to the current branching in the fractal design. We demonstrate that our device can be used for spectroscopy by measuring the dissipation from a pico-mole of molecular spins.
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A new fabrication process is presented for epitaxial transfer of InP-based heterostructure barrier varactor diodes, as high-frequency varactor multipliers, onto low-dielectric borosilicate glass substrate, employing anodic bonding...
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A new fabrication process is presented for epitaxial transfer of InP-based heterostructure barrier varactor diodes, as high-frequency varactor multipliers, onto low-dielectric borosilicate glass substrate, employing anodic bonding. The fabricated diodes on the new host substrate display symmetric electrical characteristics with only minor differences compared to those of the reference devices on the original InP substrate.
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We demonstrate Electro Wetting-On-Dielectric (EWOD) transport and SQUID gradiometcr detection of magnetic nanoparticles (MNPs) suspended in a 2 ul de-ionized water droplet. This proof-of-concept methodology constitutes the first d...
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We demonstrate Electro Wetting-On-Dielectric (EWOD) transport and SQUID gradiometcr detection of magnetic nanoparticles (MNPs) suspended in a 2 ul de-ionized water droplet. This proof-of-concept methodology constitutes the first development step towards a highly sensitive magnetic immunoassay platform with SQUID readout and droplet-based sample handling. Magnetic AC-suscepllbility measurements were performed on MNPs with a hydrodynamic diameter of 100 nm using a high-Tc dc Superconducting Quantum Interference Device (SQUID) gradiometer as detector. We observed that the signal amplitude per unit volume is 2.5 times higher for a 2 μl sample droplet compared to a 30 ul sample volume.
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Inversion and depletion regions generally form at the interfaces between doped leads (cladding layers) and the active region of polar heterostructures like AIN/GaN and other nitride compounds. The band bending in the depletion reg...
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Inversion and depletion regions generally form at the interfaces between doped leads (cladding layers) and the active region of polar heterostructures like AIN/GaN and other nitride compounds. The band bending in the depletion region sets up a barrier that may seriously impede perpendicular electronic transport. This may ruin the performance of devices such as quantum-cascade lasers and resonant-tunneling diodes. Here we introduce the concepts of polarization balance and polarization-balanced designs: A structure is polarization balanced when the applied bias match the voltage drop arising from spontaneous and piezeolectric fields. Devices designed to operate at this bias have polarization-balanced designs. These concepts offer a systematic approach to avoid the formation of depletion regions. As a test case, we consider the design of AIN/GaN double-barrier structures with Al_xGa_(1-x)N leads. To guide our efforts, we derive a simple relation between the intrinsic voltage drop arising from polar effects, average alloy composition of the active region, and the alloy concentration of the leads. Polarization-balanced designs secure good filling of the ground state for unbiased structures, while for biased structures with efficient emptying of the active region they remove the depletion barriers.
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Spectrally engineered semiconductor Fabry-Perot laser resonators are designed to enhance the optical feedback for selected longitudinal modes, which thereby require less gain for lasing. This is achieved by introducing refractive ...
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Spectrally engineered semiconductor Fabry-Perot laser resonators are designed to enhance the optical feedback for selected longitudinal modes, which thereby require less gain for lasing. This is achieved by introducing refractive index perturbations along the length of the resonator. However, the physical realization of these resonators is a challenge because of very narrow tolerances; in particular the need for precise positioning of the end facets of the resonator in relation to the perturbations, and the excess propagation loss associated with the perturbations, has been a major concern. We report on a method to achieve high-quality end facet mirrors enabling precise positioning relative to the perturbations, the latter which are realized as lateral corrugations of the waveguide. Measurements show that the mirror quality is comparable to that of cleaved mirrors and that the additional loss introduced by the perturbations adds approx< 10 cm~(-1) to the overall propagation loss, provided that the perturbations are densely enough spaced along the resonator. This implies that the number of perturbations should be large, which is beneficial for the realization of strongly perturbed resonators enabling the most flexible engineering of the spectral properties of the laser.
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The emission wavelength of a GalnNAs quantum well (QW) laser was adjusted to 1310 nm. the zero dispersion wavelength of optical fibre, by an appropriate choice of QW composition and thickness and N concentration in the barriers. A...
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The emission wavelength of a GalnNAs quantum well (QW) laser was adjusted to 1310 nm. the zero dispersion wavelength of optical fibre, by an appropriate choice of QW composition and thickness and N concentration in the barriers. A triple QW design was employed to enable the use of a short cavity with a small photon lifetime while having sufficient differential gain for a large modulation bandwidth. High speed, ridge waveguide lasers fabricated from high quality material grown by molecular beam epitaxy exhibited a damped modulation response with a bandwidth of 13 GHz.
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We have embedded an artificial atom, a superconducting transition qubit, in a ID open space and investigated the scattering properties of an incident microwave coherent state. By studying the statistics of the reflected and transm...
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We have embedded an artificial atom, a superconducting transition qubit, in a ID open space and investigated the scattering properties of an incident microwave coherent state. By studying the statistics of the reflected and transmitted fields, we demonstrate that the scattered states can be nonclassical. In particular, by measuring the second-order correlation function, g~((2)) we show photon antibunching in the reflected field and superbunching in the transmitted field. We also compare the elastically and inelastically scattered fields using both phase-sensitive and phase-insensitive measurements.
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We present measurements of the ac response of a single-electron box (SEB). We apply a radio frequency signal with a Frequency larger than the tunneling rate and drive the system out of equilibrium. We observe much more dissipation...
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We present measurements of the ac response of a single-electron box (SEB). We apply a radio frequency signal with a Frequency larger than the tunneling rate and drive the system out of equilibrium. We observe much more dissipation in the SEB then one would expect from a simple circuit model, We can explain this in terms of a mechanism that we call the Sisyphus resistance. The Sisyphus resistance has a strong gate dependence which can be used for electrometery applications.
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