4,189 research outputs found

    Edge-emitting mode-locked quantum dot lasers

    Get PDF
    Edge-emitting mode-locked quantum-dot (QD) lasers are compact, highly efficient sources for the generation of picosecond and femtosecond pulses and/or broad frequency combs. They provide direct electrical control and footprints down to few millimeters. Their broad gain bandwidths (up to 50 nm) for ground to ground state transitions as discussed below, with potential for increase to more than 200 nm by overlapping ground and excited state band transitions) allow for wavelength-tuning and generation of pico- and femtosecond laser pulses over a broad wavelength range. In the last two decades, mode-locked QD laser have become promising tools for low-power applications in ultrafast photonics. In this article, we review the development and the state-of-the-art of edge-emitting mode-locked QD lasers. We start with a brief introduction on QD active media and their uses in lasers, amplifiers, and saturable absorbers. We further discuss the basic principles of mode-locking in QD lasers, including theory of nonlinear phenomena in QD waveguides, ultrafast carrier dynamics, and mode-locking methods. Different types of mode-locked QD laser systems, such as monolithic one- and two-section devices, external-cavity setups, two-wavelength operation, and master-oscillator power-amplifier systems, are discussed and compared. After presenting the recent trends and results in the field of mode-locked QD lasers, we briefly discuss the application areas

    Laser Technologies for Applications in Quantum Information Science

    Get PDF
    Scientific progress in experimental physics is inevitably dependent on continuing advances in the underlying technologies. Laser technologies enable controlled coherent and dissipative atom-light interactions and micro-optical technologies allow for the implementation of versatile optical systems not accessible with standard optics. This thesis reports on important advances in both technologies with targeted applications ranging from Rydberg-state mediated quantum simulation and computation with individual atoms in arrays of optical tweezers to high-resolution spectroscopy of highly-charged ions. A wide range of advances in laser technologies are reported: The long-term stability and maintainability of external-cavity diode laser systems is improved significantly by introducing a mechanically adjustable lens mount. Tapered-amplifier modules based on a similar lens mount are developed. The diode laser systems are complemented by digital controllers for laser frequency and intensity stabilisation. The controllers offer a bandwidth of up to 1.25 MHz and a noise performance set by the commercial STEMlab platform. In addition, shot-noise limited photodetectors optimised for intensity stabilisation and Pound-Drever-Hall frequency stabilisation as well as a fiber based detector for beat notes in the MHz-regime are developed. The capabilities of the presented techniques are demonstrated by analysing the performance of a laser system used for laser cooling of Rb85 at a wavelength of 780 nm. A reference laser system is stabilised to a spectroscopic reference provided by modulation transfer spectroscopy. This spectroscopy scheme is analysed finding optimal operation at high modulation indices. A suitable signal is generated with a compact and cost-efficient module. A scheme for laser offset-frequency stabilisation based on an optical phase-locked loop is realised. All frequency locks derived from the reference laser system offer a Lorentzian linewidth of 60 kHz (FWHM) in combination with a long-term stability of 130 kHz peak-to-peak within 10 days. Intensity stabilisation based on acousto-optic modulators in combination with the digital controller allows for real-time intensity control on microsecond time scales complemented by a sample and hold feature with a response time of 150 ns. High demands on the spectral properties of the laser systems are put forward for the coherent excitation of quantum states. In this thesis, the performance of active frequency stabilisation is enhanced by introducing a novel current modulation technique for diode lasers. A flat response from DC to 100 MHz and a phase lag below 90° up to 25 MHz are achieved extending the bandwidth available for laserfrequency stabilisation. Applying this technique in combination with a fast proportional-derivative controller, two laser fields with a relative phase noise of 42 mrad for driving rubidium ground state transitions are realised. A laser system for coherent Rydberg excitation via a two-photon scheme provides light at 780 nm and at 480 nm via frequency-doubling from 960 nm. An output power of 0.6 W at 480 nm from a single-mode optical fiber is obtained . The frequencies of both laser systems are stabilised to a high-finesse reference cavity resulting in a linewidth of 1.02 kHz (FWHM) at 960 nm. Numerical simulations quantify the effect of the finite linewidth on the coherence of Rydberg Rabi-oscillations. A laser system similar to the 480 nm Rydberg system is developed for spectroscopy on highly charged bismuth. Advanced optical technologies are also at the heart of the micro-optical generation of tweezer arrays that offer unprecedented scalability of the system size. By using an optimised lens system in combination with an automatic evaluation routine, a tweezer array with several thousand sites and trap waists below 1 μm is demonstrated. A similar performance is achieved with a microlens array produced in an additive manufacturing process. The microlens design is optimised for the manufacturing process. Furthermore, scattering rates in dipole traps due to suppressed resonant light are analysed proving the feasibility of dipole trap generation using tapered amplifier systems

    Fully on-chip photonic turnkey quantum source for entangled qubit/qudit state generation

    Get PDF
    Integrated photonics has recently become a leading platform for the realization and processing of optical entangled quantum states in compact, robust and scalable chip formats, with applications in long-distance quantum-secured communication, quantum-accelerated information processing and nonclassical metrology. However, the quantum light sources developed so far have relied on external bulky excitation lasers, making them impractical prototype devices that are not reproducible, hindering their scalability and transfer out of the laboratory into real-world applications. Here we demonstrate a fully integrated quantum light source that overcomes these challenges through the integration of a laser cavity, a highly efficient tunable noise suppression filter (>55 dB) exploiting the Vernier effect, and a nonlinear microring for entangled photon-pair generation through spontaneous four-wave mixing. The hybrid quantum source employs an electrically pumped InP gain section and a Si3N4 low-loss microring filter system, and demonstrates high performance parameters, that is, pair emission over four resonant modes in the telecom band (bandwidth of ~1 THz) and a remarkable pair detection rate of ~620 Hz at a high coincidence-to-accidental ratio of ~80. The source directly creates high-dimensional frequency-bin entangled quantum states (qubits/qudits), as verified by quantum interference measurements with visibilities up to 96% (violating Bell’s inequality) and by density matrix reconstruction through state tomography, showing fidelities of up to 99%. Our approach, leveraging a hybrid photonic platform, enables scalable, commercially viable, low-cost, compact, lightweight and field-deployable entangled quantum sources, quintessential for practical, out-of-laboratory applications such as in quantum processors and quantum satellite communications systems

    RF Wireless Power and Data Transfer : Experiment-driven Analysis and Waveform Design

    Get PDF
    The brisk deployment of the fifth generation (5G) mobile technology across the globe has accelerated the adoption of Internet of Things (IoT) networks. While 5G provides the necessary bandwidth and latency to connect the trillions of IoT sensors to the internet, the challenge of powering such a multitude of sensors with a replenishable energy source remains. Far-field radio frequency (RF) wireless power transfer (WPT) is a promising technology to address this issue. Conventionally, the RF WPT concepts have been deemed inadequate to deliver wireless power due to the undeniably huge over-the-air propagation losses. Nonetheless, the radical decline in the energy requirement of simple sensing and computing devices over the last few decades has rekindled the interest in RF WPT as a feasible solution for wireless power delivery to IoT sensors. The primary goal in any RF WPT system is to maximize the harvested direct current (DC) power from the minuscule incident RF power. As a result, optimizing the receiver power efficiency is pivotal for an RF WPT system. On similar lines, it is essential to minimize the power losses at the transmitter in order to achieve a sustainable and economically viable RF WPT system. In this regard, this thesis explores the system-level study of an RF WPT system using a digital radio transmitter for applications where alternative analog transmit circuits are impractical. A prototype test-bed comprising low-cost software-defined radio (SDR) transmitter and an off-the-shelf RF energy-harvesting (EH) receiver is developed to experimentally analyze the impact of clipping and nonlinear amplification at the digital radio transmitter on digital baseband waveform. The use of an SDR allows leveraging the test-bed for the research on RF simultaneous wireless information and power transfer (SWIPT); the true potential of this technology can be realized by utilizing the RF spectrum to transport data and power together. The experimental results indicate that a digital radio severely distorts high peak-to-average power ratio (PAPR) signals, thereby reducing their average output power and rendering them futile for RF WPT. On similar lines, another test-bed is developed to assess the impact of different waveforms, input impedance mismatch, incident RF power, and load on the receiver power efficiency of an RF WPT system. The experimental results provide the foundation and notion to develop a novel mathematical model for an RF EH receiver. The parametric model relates the harvested DC power to the power distribution of the envelope signal of the incident waveform, which is characterized by the amplitude, phase and frequency of the baseband waveform. The novel receiver model is independent of the receiver circuit’s matching network, rectifier configuration, number of diodes, load as well as input frequency. The efficacy of the model in accurately predicting the output DC power for any given power-level distribution is verified experimentally. Since the novel receiver model associates the output DC power to the parameters of the incident waveform, it is further leveraged to design optimal transmit wave-forms for RF WPT and SWIPT. The optimization problem reveals that a constant envelope signal with varying duty cycle is optimal for maximizing the harvested DC power. Consequently, a pulsed RF waveform is optimal for RF WPT, whereas a continuous phase modulated pulsed RF signal is suitable for RF SWIPT. The superior WPT performance of pulsed RF waveforms over multisine signals is demonstrated experimentally. Similarly, the pulsed phase-shift keying (PSK) signals exhibit superior receiver power efficiency than other communication signals. Nonetheless, varying the duty-cycle of pulsed PSK waveform leads to an efficiency—throughput trade-off in RF SWIPT. Finally, the SDR test-bed is used to evaluate the overall end-to-end power efficiency of different digital baseband waveforms through wireless measurements. The results indicate a 4-PSK modulated signal to be suitable for RF WPT considering the overall power efficiency of the system. The corresponding transmitter, channel and receiver power efficiencies are evaluated as well. The results demonstrate the transmitter power efficiency to be lower than the receiver power efficiency

    Microwave-shielded ultracold polar molecules

    Get PDF
    Since the realization of Bose--Einstein condensates and degenerate Fermi gases, ultracold atoms with tunable interactions have become an essential platform for studying quantum many-body phenomena. Notable examples include the realization of BCS--BEC crossover and the simulation of the Bose/Fermi Hubbard model. Ultracold polar molecules could enrich the quantum gas toolbox with their long-range dipole-dipole interaction, which offers not only new opportunities in many-body physics, such as realizing the topological superfluid and the extended Hubbard model, but also applications in quantum chemistry, quantum computation, and precision measurements. However, the large number of internal degrees of freedom of molecules present a significant challenge in both cooling them to quantum degeneracy and controlling their interactions. Unlike atomic gases, a dense molecular sample suffers from fast collisional losses, preventing the implementation of evaporative cooling and the observation of scattering resonances. In this thesis, we describe how we solved the long-standing issue of collisional losses by microwave shielding, created a degenerate Fermi gas of NaK molecules, and discovered a new type of scattering resonances via which we created the first ultracold tetratomic molecules in the 100-nK regime. By synchronizing the rotation of polar molecules with a circularly polarized microwave electric field, we equip the molecular sample with a highly tunable intermolecular potential. This not only stabilizes the gas against inelastic collisions but also enables field-linked scattering resonances for precise control over scattering lengths. At long range, the molecules interact via their induced rotating dipole moments. As they approach each other, their orientations realign to produce a repulsive force, thereby mitigating inelastic collisions at close distances. With an elastic-to-inelastic collision ratio of 500, we have achieved evaporative cooling of the molecular gas down to 21 nK and 0.36 times the Fermi temperature, setting a new record for the coldest polar molecular gas to date. Thanks to the collisional stability of microwave-shielded molecules, we can directly load them into predominantly a single layer of a magic 3D optical lattice, achieving a peak filling fraction of 24%. These ultracold molecules, owing to their long lifetimes in their ground state and their long-range dipolar coupling, provide a unique platform to study quantum magnetism. With the achieved high filling fraction, we are prepared to study non-equilibrium spin dynamics such as rotational synchronization and spin squeezing. We demonstrated that the interaction between microwave-shielded polar molecules is highly tunable via the microwave power, detuning, and polarization. When the interaction potential is deep enough to host field-linked bound states at the collisional threshold, a shape resonance is induced, allowing us to tune the scattering rate by three orders of magnitude. The field-linked resonances enables controls over the scattering length in a similar fashion as Feshbach resonance for ultracold atoms, promising the realization of strongly correlated phases, such as dipolar pp-wave superfluid. It also paves the way to investigate the interplay between short-range and long-range interactions in novel quantum matters, such as exotic supersolid. Moreover, through a field-linked resonance, we associated for the first time weakly bound tetratomic molecules in the 100-nK regime, with a phase space density of 0.04. The transition from a Fermi gas of diatomic molecules to a Bose gas of tetratomic molecules paves the way for dipolar BCS--BEC crossover. With microwave-shielded polar molecules, we have realized a quantum gas featuring highly tunable long-range interactions. The technique is universal to polar molecules with a sufficiently large dipole moment, and thus offers a general strategy for cooling and manipulating polar molecules, and for associating weakly bound ultracold polyatomic molecules. Utilizing the toolbox developed in ultracold atoms, this platform possesses the potential to unlock an entirely new realm of quantum simulation of many-body physics

    Accurate quantum transport modelling and epitaxial structure design of high-speed and high-power In0.53Ga0.47As/AlAs double-barrier resonant tunnelling diodes for 300-GHz oscillator sources

    Get PDF
    Terahertz (THz) wave technology is envisioned as an appealing and conceivable solution in the context of several potential high-impact applications, including sixth generation (6G) and beyond consumer-oriented ultra-broadband multi-gigabit wireless data-links, as well as highresolution imaging, radar, and spectroscopy apparatuses employable in biomedicine, industrial processes, security/defence, and material science. Despite the technological challenges posed by the THz gap, recent scientific advancements suggest the practical viability of THz systems. However, the development of transmitters (Tx) and receivers (Rx) based on compact semiconductor devices operating at THz frequencies is urgently demanded to meet the performance requirements calling from emerging THz applications. Although several are the promising candidates, including high-speed III-V transistors and photo-diodes, resonant tunnelling diode (RTD) technology offers a compact and high performance option in many practical scenarios. However, the main weakness of the technology is currently represented by the low output power capability of RTD THz Tx, which is mainly caused by the underdeveloped and non-optimal device, as well as circuit, design implementation approaches. Indeed, indium phosphide (InP) RTD devices can nowadays deliver only up to around 1 mW of radio-frequency (RF) power at around 300 GHz. In the context of THz wireless data-links, this severely impacts the Tx performance, limiting communication distance and data transfer capabilities which, at the current time, are of the order of few tens of gigabit per second below around 1 m. However, recent research studies suggest that several milliwatt of output power are required to achieve bit-rate capabilities of several tens of gigabits per second and beyond, and to reach several metres of communication distance in common operating conditions. Currently, the shortterm target is set to 5−10 mW of output power at around 300 GHz carrier waves, which would allow bit-rates in excess of 100 Gb/s, as well as wireless communications well above 5 m distance, in first-stage short-range scenarios. In order to reach it, maximisation of the RTD highfrequency RF power capability is of utmost importance. Despite that, reliable epitaxial structure design approaches, as well as accurate physical-based numerical simulation tools, aimed at RF power maximisation in the 300 GHz-band are lacking at the current time. This work aims at proposing practical solutions to address the aforementioned issues. First, a physical-based simulation methodology was developed to accurately and reliably simulate the static current-voltage (IV ) characteristic of indium gallium arsenide/aluminium arsenide (In-GaAs/AlAs) double-barrier RTD devices. The approach relies on the non-equilibrium Green’s function (NEGF) formalism implemented in Silvaco Atlas technology computer-aided design (TCAD) simulation package, requires low computational budget, and allows to correctly model In0.53Ga0.47As/AlAs RTD devices, which are pseudomorphically-grown on lattice-matched to InP substrates, and are commonly employed in oscillators working at around 300 GHz. By selecting the appropriate physical models, and by retrieving the correct materials parameters, together with a suitable discretisation of the associated heterostructure spatial domain through finite-elements, it is shown, by comparing simulation data with experimental results, that the developed numerical approach can reliably compute several quantities of interest that characterise the DC IV curve negative differential resistance (NDR) region, including peak current, peak voltage, and voltage swing, all of which are key parameters in RTD oscillator design. The demonstrated simulation approach was then used to study the impact of epitaxial structure design parameters, including those characterising the double-barrier quantum well, as well as emitter and collector regions, on the electrical properties of the RTD device. In particular, a comprehensive simulation analysis was conducted, and the retrieved output trends discussed based on the heterostructure band diagram, transmission coefficient energy spectrum, charge distribution, and DC current-density voltage (JV) curve. General design guidelines aimed at enhancing the RTD device maximum RF power gain capability are then deduced and discussed. To validate the proposed epitaxial design approach, an In0.53Ga0.47As/AlAs double-barrier RTD epitaxial structure providing several milliwatt of RF power was designed by employing the developed simulation methodology, and experimentally-investigated through the microfabrication of RTD devices and subsequent high-frequency characterisation up to 110 GHz. The analysis, which included fabrication optimisation, reveals an expected RF power performance of up to around 5 mW and 10 mW at 300 GHz for 25 μm2 and 49 μm2-large RTD devices, respectively, which is up to five times higher compared to the current state-of-the-art. Finally, in order to prove the practical employability of the proposed RTDs in oscillator circuits realised employing low-cost photo-lithography, both coplanar waveguide and microstrip inductive stubs are designed through a full three-dimensional electromagnetic simulation analysis. In summary, this work makes and important contribution to the rapidly evolving field of THz RTD technology, and demonstrates the practical feasibility of 300-GHz high-power RTD devices realisation, which will underpin the future development of Tx systems capable of the power levels required in the forthcoming THz applications

    Developing a Microwave Quantum Memory with Rare-Earth Doped Crystals

    Get PDF
    Rare-earth doped crystals have attracted a significant amount of attention for use in quantum systems. Available, long-lived, optical and microwave transitions has lead to proposals for quantum transduction and quantum memories, both of which are important in building large scale quantum networks. Ensembles of rare-earth spins can be coupled to superconducting resonators, and high coupling strengths (with cooperativity > 1) readily achievable. While such systems have been constructed, a useful quantum memory which exploits highly coherent transitions has not yet been developed in the microwave domain. In this thesis we couple high-Q superconducting resonators to Yb doped YSO. The spin system of Yb:YSO is explored and the main causes of decoherence are outlined, these are found to be instantaneous diffusion and spectral diffusion. In the process of this, new techniques are developed to determine decoherence sources, where nuclear spins within the YSO crystal are found to limit coherence. Two different regimes are explored to increase the coherence time. Using optimal field orientations and high magnetic field magnitudes, the coherence time is extended to (6±2) ms. While the zero field clock transition is used, along with isotopic purification, to reach the same time ((6±1) ms). Using these techniques to increase coherence, the foundations for a microwave quantum memory with Yb:YSO are laid. Cooperativities > 1 are measured for three different Yb spin systems, this allows for these spin systems to be used in memory protocols and reach unit efficiency. New pulse sequences using adiabatic fast passage are developed to provide control over the spin ensemble and for memory protocols. Finally, we use the knowledge from all of these studies to propose a system which would form the basis of an efficient, long-lived microwave quantum memory using FIB-milled Yb:YSO

    Degaussing Procedure and Performance Enhancement by Low-Frequency Shaking of a 3-Layer Magnetically Shielded Room

    Full text link
    We report on the performance of a Magnetically Shielded Room (MSR) intended for next level 3^3He/129^{129}Xe co-magnetometer experiments which require improved magnetic conditions. The MSR consists of three layers of Mu-metal with a thickness of 3 mm each, and one additional highly conductive copper-coated aluminum layer with a thickness of 10 mm. It has a cubical shape with an walk-in interior volume with an edge length of 2560 mm. An optimized degaussing (magnetic equilibration) procedure using a frequency sweep with constant amplitude followed by an exponential decay of the amplitude will be presented. The procedure for the whole MSR takes 21 minutes and measurements of the residual magnetic field at the center of the MSR show that ∣B∣<1|B|<1 nT can be reached reliably. The chosen degaussing procedure will be motivated by online hysteresis measurements of the assembled MSR and by Eddy current simulations showing that saturation at the center of the Mu-metal layer is reached. Shielding Factors can be improved by a factor ≈4\approx 4 in all directions by low frequency (0.2 Hz), low current (1 A) shaking of the outermost Mu-metal layer.Comment: 13 pages. The following article has been submitted to Review of Scientific Instrument

    Beam scanning by liquid-crystal biasing in a modified SIW structure

    Get PDF
    A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium

    Projeto e integração de um sistema de amostragem de tensão e de corrente para aplicações em sistemas de medição de grandezas elétricas

    Get PDF
    This work describes an integrated analog-to-digital interface for electric energy measurement, implemented on 0.35μm CMOS process. In this system, voltages and currents are sampled and converted to digital values for later processing. It has been used the switched capacitor technique on the sampling and conversion circuits, instead of the analogue conventional techniques, thus reducing the circuit size and achieving a higher precision. The developed system has two input channels and can reach 10 bits of resolution at a sampling rate of 61600 words per second. Nevertheless, the system can be expanded up to 12 channels, so that at 7600 samples per second it can reach 369000 words per second. The circuit takes an area of 5.2 mm2, including pads. The system is an improvement compared to all others since it has a built-in anti-aliasing filter and expandable acquisition channels that are simultaneously sampled. Additionally, it can be implemented on a digital process, along with the digital circuitry. Therefore, the system presents a much lower sampling cost compared to the traditional systems, since it can be manufactured on a digital process and thus the whole system can be totally integrated.Este trabalho apresenta o projeto de um sistema de interfaceamento analógico/digital para aplicações em medida de energia elétrica, integrado em tecnologia CMOS de 0,35μm, onde grandezas como tensão e corrente são amostradas e convertidas em códigos digitais, para posterior processamento digital. A utilização de técnicas de capacitores chaveados nos circuitos de amostragem e de conversão, em substituição às técnicas analógicas convencionais, permite a redução do tamanho dos circuitos e a obtenção de sistemas mais precisos. O sistema desenvolvido possui dois canais de entrada e atinge uma resolução de dez bits, a uma taxa de conversão de 61600 palavras por segundo. Entretanto, pode ser expandido para até 12 canais de entrada, com uma taxa de amostragem de 7600 amostras por segundo, o que resulta em uma taxa de conversão de 369000 palavras por segundo. O circuito ocupa uma área de 5,2 mm2, incluindo os pads. Além de ser uma inovação em relação aos sistemas tradicionais de amostragem, devido ao fato de já possuir o filtro anti-aliasing integrado, canais de aquisição expansíveis e amostrados simultaneamente, além da possibilidade de integração no mesmo die dos circuitos de processamento digital, o circuito permite a obtenção de amostras com custos extremamente menores que os tradicionais, uma vez que a tecnologia de fabricação e as topologias utilizadas permitem a implementação de um sistema compacto e preciso
    • …
    corecore