Stabilized cat qubits that possess biased noise channel with bit-flip errors exponentially smaller than phase-flip errors. Together with a set of bias-preserving (BP) gates, cat qubits are a promising candidate for realizing hardware efficient quantum error correction and fault-tolerant quantum computing. Compared to dissipatively stabilized cat qubits, the Kerr cat qubits can in principle support faster gate operations with higher gate fidelity, benefiting from the large energy gap that protects the code space. However, the leakage of the Kerr cats can increase the minor type of errors and compromise the noise bias. Both the fast implementation of gates and the interaction with environment can lead to such detrimental leakage if no sophisticated controls are applied. In this work, we introduce new fine-control techniques to overcome the above obstacles for Kerr cat qubits. To suppress the gate leakage, we use the derivative-based transition suppression technique to design derivative-based controls for the Kerr BP gates. We show that the fine-controlled gates can simultaneously have high gate fidelity and high noise bias and when applied to concatenated quantum error correction, can not only improve the logical error rate but also reduce resource overhead. To suppress the environment-induced leakage, we introduce colored single-photon dissipation, which can continuously cool the Kerr cats and suppress the minor errors while not enhancing the major errors.
μWe report the demonstration of multi-spectral quantum dots-in-a-well infrared photo-detectors through the coupling of
incident light to resonant modes of surface plasmons. The integration of a surface plasmon assisted cavity with the detector
results in shifting the peak wavelength of absorption of the detector to that of the resonant wavelength of the cavity. The
cavity consists of a square lattice structure with square holes in it. A wavelength tuning of 8.5 to 9 μm was observed,
by changing the pitch of the fabricated pattern forming the cavity. Polarization sensitive detectors can be fabricated by
breaking the symmetry of the lattice. This is achieved by stretching the lattice constants along the x and y directions. A
DWELL detector with resonant frequency at 6.8 μm where the response of the 0 ° polarization is twice as strong as the 90°
polarization is reported. This technique, in principle, is detector agnostic and shows promise in fabrication of multi-spectral
focal plane arrays (FPA).
We report Quantum Dot Infrared Detectors (QDIP) where light coupling to the self assembled quantum dots
is achieved through plasmons occurring at the metal-semiconductor interface. The detector structure consists
of an asymmetric InAs/InGaAs/GaAs dots-in-a-well (DWELL) structure and a thick layer of GaAs sandwiched
between two highly doped n-GaAs contact layers, grown on a semi-insulating GaAs substrate. The aperture of
the detector is covered with a thin metallic layer which along with the dielectric layer confines light in the vertical
direction. Sub-wavelength two-dimensional periodic patterns etched in the metallic layer covering the aperture
of the detector and the active region creates a micro-cavity that concentrate light in the active region leading
to intersubband transitions between states in the dot and the ones in the well. The sidewalls of the detector
were also covered with metal to ensure that there is no leakage of light into the active region other than through
the metal covered aperture. An enhanced spectral response when compared to the normal DWELL detector
is obtained despite the absence of any aperture in the detector. The spectral response measurements show
that the Long Wave InfraRed (LWIR) region is enhanced when compared to the Mid Wave InfraRed (MWIR)
region. This may be due to coupling of light into the active region by plasmons that are excited at the metal-semiconductor
interface. The patterned metal-dielectric layers act as an optical resonator thereby enhancing the
coupling efficiency of light into the active region at the specified frequency. The concept of plasmon-assisted
coupling is in principle technology agnostic and can be easily integrated into present day infrared sensors.
In this paper we report the use of a photonic crystal resonant cavity to increase the quantum efficiency, detectivity (D*) and the background limited infrared photodetector (BLIP) temperature of a quantum dot detector. The photonic crystal is incorporated in InAs/InGaAs/GaAs dots-in-well (DWELL) detector using Electron beam lithography. From calibrated blackbody measurements, the conversion efficiency of the detector with the photonic crystal (DWELL-PC) is found to be 58.5% at -2.5 V while the control DWELL detectors have quantum efficiency of 7.6% at the same bias. We observed no significant reduction in the dark current of the photonic crystal devices compared to the normal structure. The generation-recombination limited D* at 77K with a 300K F1.7 background, is estimated to be 6 x 1010 cmHz1/2/W at -3V bias for the DWELL-PC which is a factor of 20 higher than that of the control sample. We also observed a 20% increase in the BLIP temperature for the DWELL-PCs.
We describe the realization of Quantum Cascade photonic-crystal microlasers. Photonic and electronic bandstructure
engineering are combined to create a novel Quantum Cascade microcavity laser source. A high-index
contrast two-dimensional photonic crystal forms a micro-resonator that provides feedback for laser action and
diffracts light vertically from the surface of the semiconductor chip. A top metallic contact is used to form
both a conductive path for current injection as well as to provide vertical optical confinement to the active
region through a bound surface plasmon state at the metal-semiconductor interface. The device is miniaturized
compared to standard Quantum Cascade technology, and the emission properties can in principle be engineered
by design of the photonic crystal lattice. The combination of size reduction, vertical emission, and lithographic
tailorability of the emission properties enabled by the use of a high-index contrast photonic crystal resonant
cavity makes possible a number of active sensing applications in the mid- and far-infrared. In addition, the use
of electrical pumping in these devices opens up another dimension of control for fundamental studies of photonic
crystal and surface plasmon structures in linear, non-linear, and near-field optics.
Optically thin dielectric slabs, in which a fully etched through two-dimensional patterning is applied, can be used to form high-Q optical cavities with modal volumes approaching the theoretical limit of a cubic half-wavelength. A cavity design strategy based upon simple group theoretical techniques is presented in which emphasis is placed upon a momentum space description of the resonant modes. It is shown that photonic crystal laser cavities can be designed with a particular wavelength, polarization, and radiation pattern using these methods.
Optically thin dielectric slabs, in which a fully etched through two-dimensional patterning is applied, can be used to form high-Q optical cavities with modal volumes approaching the theoretical limit of a cubic half-wavelength. A cavity design strategy based upon simple group theoretical techniques is presented in which emphasis is placed upon a momentum space description of the resonant modes. It is shown that photonic crystal laser cavities can be designed with a particular wavelength, polarization, and radiation pattern using these methods.
We present the detailed analysis of the spontaneous emission coupling factor of the micro cavity based on a 2D photonic crystal in an optically thin dielectric slab. We investigate the maximum (beta) value that can be achieved with this micro cavity and discuss its dependence on the quantum well position, as well as on the pumping area diameter. The analysis is performed using the general method for the (beta) factor calculation that we developed. The method is based on the classical model for atomic transitions in a semiconductor active medium. Finite difference time domain method is used to solve the electromagnetic fields of the system and calculate the total radiated energy, as well as the energy radiated into the mode of interest.
Ridge waveguide, edge-emitting single quantum well GaAs lasers with an integrated gating electrode have been fabricated. These devices integrate a MESFET structure with the laser PN junction so that the SBD (Schottky barrier diode) depletion layer can be used for transverse current confinement in the laser. Device fabrication was very simple requiring only an anisotropic etch for waveguide definition followed by a single self-aligned contact deposition step. The Schottky barrier depletion layers on either side of the ridge waveguide act to confine free carriers. This structure allows for separation of the optical and electrical confinement in the transverse direction without requiring complex fabrication. The device demonstrated modulation of the pulsed lasing threshold with gate control voltage on a 30 micron wide ridge. Above threshold, increasing power output with increasing gate voltage was demonstrated with negligible gate current. The multimode lasing spectrum showed that the increased power output occurred for all modes with no shift in the mode wavelengths to within the resolution of the measurement system.
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