464 research outputs found

    Direct measurement of coating thermal noise in the AEI 10m prototype

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    A thermal noise interferometer for the characterization of thermal noise in high reflectivity mirrors has been commissioned and first direct measurements of coating thermal noise have been performed. This serves as an important step in the improvement of current and future gravitational wave detectors

    Laser Technologies for Applications in Quantum Information Science

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    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

    Development of a sensor for microvibrations measurement in the AlbaSat CubeSat mission

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    openMicrovibrations on spacecraft represent an issue for payloads requiring high pointing accuracy and/or stability over time, and they might represent a particular concern for CubeSats and small satellites that, usually, are not equipped with very-high performance attitude control systems. Hence, collecting reliable measures of the vibration spectra during the operations of a CubeSat represents a significant research activity. This thesis presents the development of a sensor, configured as a payload within the AlbaSat mission, capable of accurately measuring the microvibrations in space, with particular focus on those produced by the Momentum Exchange Devices (MED), i.e., Reaction or Momentum Wheels, that represent one of the most important microvibrations sources. The thesis takes place in the framework of the AlbaSat mission. AlbaSat is a 2U CubeSat developed by a student team of the University of Padova under the “Fly Your Satellite! – Design Booster” programme promoted by the European Space Agency (ESA). The mission has four different objectives: (1) to collect measurements of the space debris environment in-situ, (2) to measure the microvibrations on board the CubeSat, (3) to precisely determine the position of the satellite through laser ranging and (4) to investigate alternative systems for possible Satellite Quantum Communication applications on nanosatellites. The requirements for the correct sizing of the sensor and the chosen physical and functional architecture are defined and presented in the thesis. A meticulous schedule for functional tests is finally outlined, aimed at verifying the correct functionality of the microvibration sensor. These tests serve as a starting point for the future development of the payload.Microvibrations on spacecraft represent an issue for payloads requiring high pointing accuracy and/or stability over time, and they might represent a particular concern for CubeSats and small satellites that, usually, are not equipped with very-high performance attitude control systems. Hence, collecting reliable measures of the vibration spectra during the operations of a CubeSat represents a significant research activity. This thesis presents the development of a sensor, configured as a payload within the AlbaSat mission, capable of accurately measuring the microvibrations in space, with particular focus on those produced by the Momentum Exchange Devices (MED), i.e., Reaction or Momentum Wheels, that represent one of the most important microvibrations sources. The thesis takes place in the framework of the AlbaSat mission. AlbaSat is a 2U CubeSat developed by a student team of the University of Padova under the “Fly Your Satellite! – Design Booster” programme promoted by the European Space Agency (ESA). The mission has four different objectives: (1) to collect measurements of the space debris environment in-situ, (2) to measure the microvibrations on board the CubeSat, (3) to precisely determine the position of the satellite through laser ranging and (4) to investigate alternative systems for possible Satellite Quantum Communication applications on nanosatellites. The requirements for the correct sizing of the sensor and the chosen physical and functional architecture are defined and presented in the thesis. A meticulous schedule for functional tests is finally outlined, aimed at verifying the correct functionality of the microvibration sensor. These tests serve as a starting point for the future development of the payload

    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

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    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

    Superconducting Circuit Architectures Based on Waveguide Quantum Electrodynamics

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    Quantum science and technology provides new possibilities in processing information, simulating novel materials, and answering fundamental questions beyond the reach of classical methods. Realizing these goals relies on the advancement of physical platforms, among which superconducting circuits have been one of the leading candidates offering complete control and read-out over individual qubits and the potential to scale up. However, most circuit-based multi-qubit architectures only include nearest-neighbor (NN) coupling between qubits, which limits the efficient implementation of low-overhead quantum error correction and access to a wide range of physical models using analog quantum simulation. This challenge can be overcome by introducing non-local degrees of freedom. For example, photons in a shared channel between qubits can mediate long-range qubit-qubit coupling arising from light-matter interaction. In addition, constructing a scalable architecture requires this channel to be intrinsically extensible, in which case a one-dimensional waveguide is an ideal structure providing the extensible direction as well as strong light-matter interaction. In this thesis, we explore superconducting circuit architectures based on light-matter interactions in waveguide quantum electrodynamics (QED) systems. These architectures in return allow us to study light-matter interaction, demonstrating strong coupling in the open environment of a waveguide by employing sub-radiant states resulting from collective effects. We further engineer the waveguide dispersion to enter the topological photonics regime, exploring interactions between qubits that are mediated by photons with topological properties. Finally, towards the goals of quantum information processing and simulation, we settle into a multi-qubit architecture where the photon-mediated interaction between qubits exhibits tunable range and strength. We use this multi-qubit architecture to construct a lattice with tunable connectivity for strongly interacting microwave photons, synthesizing a quantum many-body model to explore chaotic dynamics. The architectures in this thesis introduce scalable beyond-NN coupling between superconducting qubits, opening the door to the exploration of many-body physics with long-range coupling and efficient implementation of quantum information processing protocols.</p

    Advances in performance and automation of a single ytterbium ion optical clock

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    While the SI second is currently defined in terms of a microwave transition frequency in caesium, atomic clocks based on an optical transition are currently outperforming caesium clocks by up to two orders of magnitude. In order to fully exploit the potential accuracy achievable by optical clocks, the SI second needs to be redefined in terms of an optical frequency standard. The ¹⁷¹Yb⁺ ion is an excellent candidate thanks to the extremely narrow linewidth of its electric octupole (E3) transition and its particular insensitivity to external perturbations. This thesis is focused on the ytterbium ion optical clock at the National Physical Laboratory (NPL), consisting of a single ¹⁷¹Yb⁺ ion trapped in a radio frequency (RF) Paul trap and probed by ultrastable 467-nm light to excite the E3 transition. Improved measurement methods were developed for the evaluation of several systematic frequency shifts. In particular, the electric quadrupole shift, which used to be the leading source of uncertainty, can now be directly measured with an accuracy in the low parts in 10¹⁸. A great focus was put on the automation of several aspects of the experiment. Because all optical clocks generally require a lot of maintenance and attention during their operation, many experimental routines were automated in order to minimise the requirement for human intervention. Furthermore, the analysis of almost all systematic shifts was automated, requiring minimal manual input so that shifts could be evaluated on the fly. Finally, a generalised framework was developed for the automatic evaluation of the absolute frequency of the optical clock via the International Atomic Time (TAI). In order to increase the confidence in the level of performance of the ytterbium ion optical clock, international clock comparison campaigns are regularly carried out. Between 2019 and 2022, several results were produced: two absolute frequency measurements via TAI with an uncertainty at the 1 × 10⁻¹⁵ level; two local frequency ratio measurements between ¹⁷¹Yb⁺ (E3) and ⁸⁷Sr with an uncertainty in the low parts in 10¹⁷; three uncertainty budgets at the parts in 10¹⁸ level; and one measurement of the ratio of the octupole and quadrupole optical clock transitions in ¹⁷¹Yb⁺ with an uncertainty of 1.5 × 10⁻¹⁶. All of these results are shown to be consistent with each other and in good agreement with the literature. Furthermore, a prototype optically-steered time scale was successfully demonstrated for the first time at NPL with the contribution of both the ¹⁷¹Yb⁺ and ⁸⁷Sr optical clocks.Open Acces

    2023- The Twenty-seventh Annual Symposium of Student Scholars

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    The full program book from the Twenty-seventh Annual Symposium of Student Scholars, held on April 18-21, 2023. Includes abstracts from the presentations and posters.https://digitalcommons.kennesaw.edu/sssprograms/1027/thumbnail.jp

    Production and performance of silicon pixel modules with planar sensors for the ATLAS ITk upgrade

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