119 research outputs found
DESIGN MODULAR COMMAND AND DATA HANDLING SUBSYSTEM HARDWARE ARCHITECTURES
Over the past few years, On-Board Computing Systems for satellites have been facing a limited level of modularity. Modularity is the ability to reuse and reconstruct the system from a set of predesigned units, with minimal additional engineering effort. CDHS hardware systems currently available have a limited ability to scale with mission needs. This thesis addresses the integration of smaller form factor CDHS modules used for nanosatellites with the larger counterparts that are used for larger missions. In particular, the thesis discusses the interfacing between Modular Computer Systems based on Open Standard commonly used in large spacecrafts and PC/104 used for nanosatellites. It also aims to create a set of layers that would represent a hardware library of COTS-like modules. At the beginning, a review of related and previous work has been done to identify the gaps in previous studies and understand more about Modular Computer Systems based on Open Standard commonly used in large spacecrafts, such as cPCI Serial Space and SpaceVPX. Next, the design requirements have been set to achieve this thesis objectives, which included conducting a prestudy of system alternatives before creating a modular CDHS hardware architecture which was later tested. After, the hardware suitable for this architecture based on the specified requirements was chosen and the PCB was designed based on global standards. Later, several functional tests and communication tests were conducted to assess the practicality of the proposed architecture. Finally, thermal vacuum testing was done on one of the architecture’s layers to test its ability to withstand the space environment, with the aim to perform the vibration testing of the full modular architecture in the future. The aim of this thesis has been achieved after going through several tests, comparing between interfaces, and understanding the process of interfacing between different levels of the CDHS. The findings of this study pave the way for future research in the field and offer valuable insights that could contribute to the development of modular architectures for other satellite subsystems
Storing, single photons in broadband vapor cell quantum memories
Single photons are an essential resource for realizing quantum technologies. Together with compatible quantum memories granting control over when a photon arrives, they form a foundational component both of quantum communication and quantum information processing. Quality solid-state single photon sources deliver on the high bandwidths and rates required for scalable quantum technology, but require memories that match these operational parameters. In this thesis, I report on quantum memories based on electromagnetically induced transparency and built in warm rubidium vapor, with such fast and high bandwidth interfaces in mind. I also present work on a heralded single photon source based on parametric downconversion in an optical cavity, operated in a bandwidth regime of a few 100s of megahertz. The systems are characterized on their own and together in a functional interface. As the photon generation process is spontaneous, the memory is implemented as a fully reactive device, capable of storing and retrieving photons in response to an asynchronous external trigger.
The combined system is used to demonstrate the storage and retrieval of single photons in and from the quantum memory. Using polarization selection rules in the Zeeman substructure of the atoms, the read-out noise of the memory is considerably reduced from what is common in ground-state storage schemes in warm vapor. Critically, the quantum signature in the photon number statistics of the retrieved photons is successfully maintained, proving that the emission from the memory is dominated by single photons. We observe a retrieved single-photon state accuracy of for short storage times, which remains throughout the memory lifetime of ns. The end-to-end efficiency of the memory interfaced with the photon source is , which will be further improved in the future by optimizing the operating regime. With its operation bandwidth of MHz, our system opens up new possibilities for single-photon synchronization and local quantum networking experiments at high repetition rates
Heuristics Based Test Overhead Reduction Techniques in VLSI Circuits
The electronic industry has evolved at a mindboggling pace over the last five decades. Moore’s Law [1] has enabled the chip makers to push the limits of the physics to shrink the feature sizes on Silicon (Si) wafers over the years. A constant push for power-performance-area (PPA) optimization has driven the higher transistor density trends. The defect density in advanced process nodes has posed a challenge in achieving sustainable yield. Maintaining a low Defect-per-Million (DPM) target for a product to be viable with stringent Time-to-Market (TTM) has become one of the most important aspects of the chip manufacturing process. Design-for-Test (DFT) plays an instrumental role in enabling low DPM. DFT however impacts the PPA of a chip. This research describes an approach of minimizing the scan test overhead in a chip based on circuit topology heuristics. These heuristics are applied on a full-scan design to convert a subset of the scan flip-flops (SFF) into D flip-flops (DFF). The K Longest Path per Gate (KLPG) [2] automatic test pattern generation (ATPG) algorithm is used to generate tests for robust paths in the circuit. Observability driven multi cycle path generation [3][4] and test are used in this work to minimize coverage loss caused by the SFF conversion process. The presence of memory arrays in a design exacerbates the coverage loss due to the shadow cast by the array on its neighboring logic. A specialized behavioral modeling for the memory array is required to enable test coverage of the shadow logic. This work develops a memory model integrated into the ATPG engine for this purpose. Multiple clock domains pose challenges in the path generation process. The inter-domain clocking relationship and corresponding logic sensitization are modeled in our work to generate synchronous inter-domain paths over multiple clock cycles. Results are demonstrated on ISCAS89 and ITC99 benchmark circuits. Power saving benefit is quantified using an open-source standard-cell library
Time-bin encoding for optical quantum computing
Scalability has been a longstanding issue in implementing large-scale photonic experiments for optical quantum computing. Traditional encodings based on the polarisation or spatial degrees of freedom become extremely resource-demanding when the number of modes becomes large, as the need for many nonclassical sources of light and the number of beam splitters required become unfeasible. Alternatively, time-bin encoding paves the way to overcome some of these limitations, as it only requires a single quantum light source and can be scaled to many temporal modes through judicious choice of pulse sequence and delays. Such an apparatus constitutes an important step toward large-scale experiments with low resource consumption.
This work focuses on the time-bin encoding implementation. First, we assess its feasibility by thoroughly investigating its performance through numerical simulations under realistic conditions. We identify the critical components of the architecture and find that it can achieve performances comparable to state-of-the-art devices. Moreover, we consider two implementation approaches, in fibre and free space, and enumerate their strengths and weaknesses. Subsequently, we delve into the lab to explore these schemes and the key components involved therein. For the fibre case, we report the first implementation of time-bin encoded Gaussian boson sampling and use the samples obtained from the device to search for dense subgraphs of sizes three and four in a 10-node graph.
Finally, we complement the study of the time-bin encoding with two side projects that contribute to the broad spectrum of enabling techniques for quantum information science. First, we demonstrate the ability to perform photon-number resolving measurements with a commercial superconducting nanowire single-photon detector system and apply it to improve the statistics of a heralded single-photon source. Second, we demonstrate that by employing a phase-tunable coherent state, we can fully characterise a multimode Gaussian state through solely the low-order photon statistics.Open Acces
Understanding Quantum Technologies 2022
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October 2021.Comment: 1132 pages, 920 figures, Letter forma
Advanced quantum light sources for quantum networking
All of quantum photonics relies on being able to reliably generate quantum states
encoded in a particular degree of freedom of light. A key piece of technology is
therefore the photon source.
The choice of which degree of freedom to encode information in is an interesting one,
there is no universal best option. The historically common option of polarisation
is straightforward to manipulate and detect, but is restricted to a two dimensional
Hilbert space. More modern choices such as orbital angular momentum and path
encodings have become popular as they are high dimensional and offer greater information capacity per photon. The downside of these options is they are difficult
to integrate into existing communication networks.
Time and frequency are in a unique position of being naturally high dimensional
and compatible with single-mode fibre which makes them compatible with standard telecommunication equipment. The first half of this thesis is about generating time-frequency encoded quantum states in a scalable, lossless and arguably
simpler way than other techniques commonly used to generate time-frequency encoded states. This is done through the process of domain-engineering in parametric
downconversion. This thesis will walk through the basics of nonlinear optics and
particular three-wave mixing before going on to discuss the principles of domain-engineering and how it can be used to manipulate the time-frequency structure of
photon pairs produced in parametric downconversion. The experimental characterisation of a high dimensional frequency-bin entangled source is discussed along
with other potential time-frequency states which could be generated using the same
domain-engineering techniques.
The second half of the thesis is centred around building a bright and low noise
single-photon source at telecommunication wavelengths using a frequency converted
quantum dot. The performance of the source before and after conversion is compared
with the end result that the frequency conversion process does not significantly
alter the single-photon nature of the source. Using the mathematical machinery
developed to describe three-wave mixing, we show how the time-frequency properties
of quantum dots can be improved using frequency conversion.
With a bright and low noise source realised, a demonstration of quantum key distribution is carried out. The range and key rate of this demonstration compare
favourably to to other single-photon sources in the literature. Finally, theoretical
predictions of a decoy state quantum key distribution protocol using this source are
carried out which extends the range by around 100 km compared to the protocol
without decoy states
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