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Laterally coupled distributed feedback lasers using high-density InAs quantum dots-in-a-well (DWELL) active region demonstrate a nominal wavelength of 1310 nm, a linewidth as small as 68 kHz, and a linewidth-power product of 100 kHz-mW.
InGaAs/InGaAsP strained quantum well buried heterostructure and distributed feedback lasers emitting at wavelengths as long as 2.06 micrometers with low internal loss and threshold currents have been demonstrated for the first time. The room and high temperature characteristics and the threshold gain are discussed.
It is noted that the phenomenon of entanglement is not a prerogative of quantum systems, but also occurs in other, non-classical systems such as quantum-classical hybrids, and covers the concept of entanglement as a special type of global constraint imposed upon a broad class of dynamical systems. Application of hybrid systems for physics of life, as well as for quantum-inspired computing, has been outlined. In representing the Schroedinger equation in the Madelung form, there is feedback from the Liouville equation to the Hamilton-Jacobi equation in the form of the quantum potential. Preserving the same topology, the innovators replaced the quantum potential with other types of feedback, and investigated the property of these hybrid systems. A function of probability density has been introduced. Non-locality associated with a global geometrical constraint that leads to an entanglement effect was demonstrated. Despite such a quantum like characteristic, the hybrid can be of classical scale and all the measurements can be performed classically. This new emergence of entanglement sheds light on the concept of non-locality in physics.
Paramagnetic-salt low-temperature thermometer incorporates improved superconducting magnetic-flux pump, multiple superconducting quantum interference devices as magnetometers, and feedback stabilization of magnetic flux. Requires much smaller initial magnetizing currents and provides improved temperature resolution via suppression of drift in magnetic induction.
The index change near a quantum transition is shown to cause significant feedback into a gain medium. Criteria are given for the onset of self-lasing in an extended material. The distortion of a reflected pulse is also considered.
The index change near a quantum transition is shown to cause significant feedback into a gain medium. Criteria are given for the onset of self-lasing in an extended material. The distortion of a reflected pulse is also considered.
A program of research is dedicated to development of a mathematical formalism that could provide, among other things, means by which living systems could be distinguished from non-living ones. A major issue that arises in this research is the following question: What invariants of mathematical models of the physics of systems are (1) characteristic of the behaviors of intelligent living systems and (2) do not depend on specific features of material compositions heretofore considered to be characteristic of life? This research at earlier stages has been reported, albeit from different perspectives, in numerous previous NASA Tech Briefs articles. To recapitulate: One of the main underlying ideas is to extend the application of physical first principles to the behaviors of living systems. Mathematical models of motor dynamics are used to simulate the observable physical behaviors of systems or objects of interest, and models of mental dynamics are used to represent the evolution of the corresponding knowledge bases. For a given system, the knowledge base is modeled in the form of probability distributions and the mental dynamics is represented by models of the evolution of the probability densities or, equivalently, models of flows of information. At the time of reporting the information for this article, the focus of this research was upon the following aspects of the formalism: Intelligence is considered to be a means by which a living system preserves itself and improves its ability to survive and is further considered to manifest itself in feedback from the mental dynamics to the motor dynamics. Because of the feedback from the mental dynamics, the motor dynamics attains quantum-like properties: The trajectory of the physical aspect of the system in the space of dynamical variables splits into a family of different trajectories, and each of those trajectories can be chosen with a probability prescribed by the mental dynamics. From a slightly different perspective, the mechanism of decision-making is feedback from the mental dynamics to the motor dynamics, and this mechanism provides a quantum-like collapse of a random motion into an appropriate deterministic state, such that entropy undergoes a pronounced decrease. The existence of this mechanism is considered to be an invariant of intelligent behavior of living systems, regardless of the origins and material compositions of the systems.
Central to the advancement of both satellite and in-situ science are improvements in continuous-wave and pulsed infrared laser systems coupled with integrated miniaturized optics and electronics, allowing for the use of powerful, single-mode light sources aboard both satellite and unmanned aerial vehicle platforms. There is a technological gap in supplying adequate laser sources to address the mid-infrared spectral window for spectroscopic characterization of important atmospheric gases. For high-power applications between 2 to 3 micron, commercial laser technologies are unsuitable because of limitations in output power. For instance, existing InP-based laser systems developed for fiber-based telecommunications cannot be extended to wavelengths longer than 2 micron. For emission wavelengths shorter than 3 micron, intersubband devices, such as infrared quantum cascade lasers, become inefficient due to band-offset limitations. To date, successfully demonstrated singlemode GaSb-based laser diodes emitting between 2 and 3 micron have employed lossy metal Bragg gratings for distributed- feedback coupling, which limits output power due to optical absorption. By optimizing both the quantum well design and the grating fabrication process, index-coupled distributed-feedback 2.65-micron lasers capable of emitting in excess of 25 mW at room temperature have been demonstrated. Specifically, lasers at 3,777/cm (2.65 micron) have been realized to interact with strong absorption lines of HDO and other isotopologues of H2O. With minor modifications of the optical cavity and quantum well designs, lasers can be fabricated at any wavelength within the 2-to-3-micron spectral window with similar performance. At the time of this reporting, lasers with this output power and wavelength accuracy are not commercially available. Monolithic ridge-waveguide GaSb lasers were fabricated that utilize secondorder lateral Bragg gratings to generate single-mode emission from InGaAsSb/ AlInGaAsSb multi-quantum well structures. The device fabrication utilizes etched index-coupled gratings in the top AlGaAsSb cladding of the laser chip along the ridge waveguide, whereas commercial lasers that emit close to this wavelength include loss-coupled metal gratings that limit the output power of the laser. Semiconductor-laser-based spectrometers can be used to replace gas sensors currently used in industry and government. With the availability of high-power laser sources at mid-infrared wavelengths, sensors can target strong fundamental gas absorption lines to maximize instrument sensitivity.
We show that a model, recently introduced for quantum nondemolition measurements of a quantum observable, can be adapted to obtain a measurement scheme which is able to slow down the destruction of macroscopic coherence due to the measurement apparatus.
We look at time evolution of a physical system from the point of view of dynamical control theory. Normally we solve motion equation with a given external potential and we obtain time evolution. Standard examples are the trajectories in classical mechanics or the wave functions in Quantum Mechanics. In the control theory, we have the configurational variables of a physical system, we choose a velocity field and with a suited strategy we force the physical system to have a well defined evolution. The evolution of the system is the 'premium' that the controller receives if he has adopted the right strategy. The strategy is given by well suited laboratory devices. The control mechanisms are in many cases non linear; it is necessary, namely, a feedback mechanism to retain in time the selected evolution. Our aim is to introduce a scheme to obtain Quantum wave packets by control theory. The program is to choose the characteristics of a packet, that is, the equation of evolution for its centre and a controlled dispersion, and to give a building scheme from some initial state (for example a solution of stationary Schroedinger equation). It seems natural in this view to use stochastic approach to Quantum Mechanics, that is, Stochastic Mechanics [S.M.]. It is a quantization scheme different from ordinary ones only formally. This approach introduces in quantum theory the whole mathematical apparatus of stochastic control theory. Stochastic Mechanics, in our view, is more intuitive when we want to study all the classical-like problems. We apply our scheme to build two classes of quantum packets both derived generalizing some properties of coherent states.
Techniques for mass production of tunneling electrodes developed from silicon-micromachining, lithographic patterning, and related microfabrication processes. Tunneling electrodes named because electrons travel between them by quantum-mechanical tunneling; tunneling electrodes integral parts of tunneling transducer/sensors, which act in conjunction with feedback circuitry to stabilize tunneling currents by maintaining electrode separations of order of 10 Angstrom. Essential parts of scanning tunneling microscopes and related instruments, and used as force and position transducers in novel microscopic accelerometers and infrared detectors.
We present new CMOS photodiode imager pixel with ultra-low read noise through on-chip suppression of reset noise via column-based feedback circuitry. The noise reduction is achieved without introducing any image lag, and with insignificant reduction in quantum efficiency and full well.
A series of displacement transducers have been demonstrated which are based on the detection of electrons that quantum-mechanically tunnel across a narrow gap between electrodes.
We demonstrate GaSb-based laterally-coupled distributed-feedback type-I cascade diode lasers emitting near 2.9 µm as potential sources for OH measurements. The laser heterostructures consist of two GaInAsSb quantum well stages in series separated by GaSb/AlSb/InAs tunnel junction and InAs/AlSb electron injectors. Single-mode emission is generated using second order lateral Bragg grating etched alongside narrow ridge waveguides. The lasers were fabricated into 2-mm-long devices, solder-mounted epi-up on copper submounts, and operate at room temperature. With an anti-reflection coating at the emission facet, the lasers exhibit a typical current threshold of 110 mA at 20 °C and emit more than 14 mW of output power. The Bragg wavelength temperature tuning rate was 0.29 nm/°C.
Recent work [1] has proposed a compact fermion-to-qubit mapping for the Fermi-Hubbard model (FHM), potentially lowering the overhead needed to simulate such a system on quantum hardware. In prior work [2], we numerically investigated how well a quantum annealer could prepare ground states of the FHM encoded using the resource-efficient mapping. In order to compare these results to gate-model systems, we turn to a QAOA-style approach and replace the annealing schedule with both Trotterizations thereof and also more general Hamiltonian-variational ansatze based on the terms of the mapped FH Hamiltonian. We investigate the achievable ground state fidelities of these gate sequences, consider various optimizations of the ansatze structure, and offer resource estimations of the optimized QAOA protocols for near-term hardware.
proposed instrument, intended mainly for use as a magnetometer, would include an optoelectronic oscillator (OEO) stabilized by an atomic cell that could play the role of a magnetically tunable microwave filter. The microwave frequency would vary with the magnetic field in the cell, thereby providing an indication of the magnetic field. The proposed magnetometer would offer a combination of high accuracy and high sensitivity, characterized by flux densities of less than a picotesla. In comparison with prior magnetometers, the proposed magnetometer could, in principle, be constructed as a compact, lightweight instrument: It could fit into a package of about 10 by 10 by 10 cm and would have a mass <0.5 kg. As described in several prior NASA Tech Briefs articles, an OEO is a hybrid of photonic and electronic components that generates highly spectrally pure microwave radiation, and optical radiation modulated by the microwave radiation, through direct conversion between laser light and microwave radiation in an optoelectronic feedback loop. As used here, "atomic cell" signifies a cell containing a vapor, the constituent atoms of which can be made to undergo transitions between quantum states, denoted hyperfine levels, when excited by light in a suitable wavelength range. The laser light must be in this range. The energy difference between the hyperfine levels defines the microwave frequency. In the proposed instrument (see figure), light from a laser would be introduced into an electro-optical modulator (EOM). Amplitude-modulated light from the exit port of the EOM would pass through a fiber-optic splitter having two output branches. The light in one branch would be sent through an atomic cell to a photodiode. The light in the other branch would constitute the microwave-modulated optical output. Part of the light leaving the atomic cell could also be used to stabilize the laser at a frequency in the vicinity of the desired hyperfine or other quantum transition. The microwave signal from the output of the photodiode would be amplified (if necessary, as explained below) and fed back into the EOM. This system would oscillate if the amplification in the closed loop exceeded the linear absorption of the loop. The microwave amplifier may be unnecessary to sustain stable oscillations, depending on the power of the laser radiation at the photodetector and on particular features of the modulator and optical delay line.
Efficient mid-IR interband cascade (IC) lasers are developed based on 111-V semiconductor materials to cover wavelength range from 2.7 to 5.6 (mu)m. These IC lasers reuse injected electrons in cascade stages for photon generation with high quantum efficiency to achieve high output powers. Also, IC lasers have low threshold current density with very efficient use of applied voltage, resulting in reduced power consumptions. Single-mode distributed feedback lasers have been made, and integrated into aircraft and balloon instrument which made measurements of CH4 and HCI. In this work, the characteristics of IC lasers and their recent development are reviewed.
Unprecedented stability of frequency in superconducting, triple-cavity ruby maser oscillator achieved by incorporation of amplitude-control subsystem. New design enhances ultra-stable measurements of time by reducing fluctuations to 2 X 10 to negative 19th power routinely, and to as little as 10 to negative 20th power in exceptional cases. Currents induced in superconducting pickup coil by changes in magnetic field in ruby. Currents from coil fed to superconducting quantum-interference device (SQUID) magnetometer, output used to generate control signal for electronically variable attenuator. Attenuator varies pump-signal amplitude in response to magnetic-field fluctuations in ruby. Very high feedback-loop gain used for sensitivity of control and adequate compensation of fluctuations.