The year is 2022. Scientists and engineers inch ever closer to building a practical quantum computer. The excitement in the research community, that we might soon fulfil Feynman’s dream to leverage quantum mechanics in machines capable of exponentially quicker computation, is steadily growing. With promised revolutions in chemistry, condensed matter physics and machine learning, and an expected market of 1.8 billion USD by 2026, quantum computing fights for the spotlight amid international pandemics and climate catastrophe. But the journey ahead is not an easy one. Quantum computers, requiring precise control of extraordinarily delicate quantum systems, are unsurprisingly challenging to engineer and equally difficult to design. A demonstration of quantum advantage through the quantum solving of a practical problem faster than available classical means, remains a research ambition. At the forefront of this research are classical computers: the machines which crunch the numbers in our calculations, which interface with our quantum experiments, and which render this very document. Without them, quantum computation would have remained a fanciful whim on Feynman’s chalkboard. Behind the rapidly growing repertoire of quantum algorithms lies an equally impressive and expanding corpus of classical simulation strategies. This thesis is about utilising first generation quantum computers and predicting their behaviour using classical computers. It develops novel quantum algorithms to perform variational minimisation, Hamiltonian diagonalisation, and approximate circuit recompilation, all intendedly compatible with near-future machines. It also devises classical algorithms for efficiently simulating quantum variational algorithms, emulating quantum computers using high-performance supercomputing facilities, and showcases the author’s efforts in scientific software development. Incidentally, this thesis makes no direct use of current day quantum hardware facilities. We hope to convince the disappointed reader that such an endeavour is presently pointless.
The year is 2022. Scientists and engineers inch ever closer to building a practical quantum computer. The excitement in the research community, that we might soon fulfil Feynman’s dream to leverage quantum mechanics in machines capable of exponentially quicker computation, is steadily growing. With promised revolutions in chemistry, condensed matter physics and machine learning, and an expected market of 1.8 billion USD by 2026, quantum computing fights for the spotlight amid international pandemics and climate catastrophe. But the journey ahead is not an easy one. Quantum computers, requiring precise control of extraordinarily delicate quantum systems, are unsurprisingly challenging to engineer and equally difficult to design. A demonstration of quantum advantage through the quantum solving of a practical problem faster than available classical means, remains a research ambition. At the forefront of this research are classical computers: the machines which crunch the numbers in our calculations, which interface with our quantum experiments, and which render this very document. Without them, quantum computation would have remained a fanciful whim on Feynman’s chalkboard. Behind the rapidly growing repertoire of quantum algorithms lies an equally impressive and expanding corpus of classical simulation strategies. This thesis is about utilising first generation quantum computers and predicting their behaviour using classical computers. It develops novel quantum algorithms to perform variational minimisation, Hamiltonian diagonalisation, and approximate circuit recompilation, all intendedly compatible with near-future machines. It also devises classical algorithms for efficiently simulating quantum variational algorithms, emulating quantum computers using high-performance supercomputing facilities, and showcases the author’s efforts in scientific software development. Incidentally, this thesis makes no direct use of current day quantum hardware facilities. We hope to convince the disappointed reader that such an endeavour is presently pointless.
Quantum computation has teased scientific imagination ever since Richard Feynman dreamed in 1982 of quantum-mechanical computers, which could solve problems that are effectively out of reach of classical computation thanks to their ability to use superposition and entanglement. This critical survey recalls the field’s journey from theoretical advances to present-day engineering challenges, highlighting the yawning gulf between quantum computing’s lofty promises and its actual realizations. By examining three decades of developments, from Shor’s integer factorization and Grover’s search algorithms to recent demonstrations of quantum supremacy, this paper shows how idealized mathematical models interact with the noisy, resource-constrained realities of physical quantum systems. The author presents a literature review through critically analyzing key achievements in quantum computing research.. This paper concludes that quantum advantage will not arise from brute-force universality, but through application specific co-design, combining noise-adjusted algorithms to quantum hardware restrictions whilst mixing classical and quantum processing modes and fundamentally changing the way we think of error correction through the physics of qubits. This shift in paradigm from theoretical maximalism to engineering pragmatism embodies a realistic roadmap for practical quantum computation.
Many important physical and mathematical problems are difficult to solve on classical computers, resulting in difficulty in finding new advanced materials, simulating quantum field theories and solving large combinatorial optimisation tasks. Quantum computers have shown great promise in being able to solve these (and many other) problems faster than their classical counterparts, and therefore should be thoroughly investigated as a significant tool for enabling the acceleration of scientific progress. This work develops methods to tackle several problems across the spectrum of quantum algorithms, providing methods suitable for the near-term hardware, to the future where large fault-tolerant quantum computers exist. Therefore, the works in this thesis range from efficiently making use of limited quantum hardware to taking advantage of hardware benefits (e.g. excess qubits) as quantum computation advances. Covered topics include: an alternative paradigm for the optimisation of variational circuits and quantum neural networks; techniques for improving energy estimation of quantum states through the collection and processing of large amounts of randomised measurement data; the use of entanglement in guiding the automatic discovery of quantum circuits; investigating the role of symmetries in adiabatic state preparation of molecules and the large scale parallelisation of a common fault-tolerant subroutine, potentially producing large runtime speed-ups for the simulation of chemistry on quantum computers. Although there are many challenges remaining from both hardware and algorithms perspectives before the large-scale utility of quantum computers can be demonstrated, the contributions of this work make steps towards the efficient utilisation of quantum hardware that will be available in the coming years.
Quantum computing has emerged as a transformative paradigm, leveraging principles of quantum mechanics to tackle computationally intractable problems. This manuscript explores the potential of quantum computing for solving complex engineering problems—specifically optimization, simulation, and data analysis tasks—using technologies and methodologies available up to 2022. We examine both gate-based and quantum annealing approaches, outline experimental frameworks, and compare performance against classical counterparts. Results from simulated benchmark problems demonstrate promising speedups in select cases, though practical adoption is constrained by hardware limitations such as qubit coherence times and noise. The study concludes by highlighting avenues for integrating hybrid quantum-classical workflows in engineering, along with a discussion of current constraints and future directions. Over the past decade, research efforts have focused on understanding how quantum phenomena like superposition and entanglement can be harnessed to realize computational advantages for specific problem classes. In particular, combinatorial optimization problems—ubiquitous in engineering design and logistics—offer fertile ground for quantum algorithms such as the Quantum Approximate Optimization Algorithm (QAOA) and quantum annealing. Additionally, quantum simulation techniques, including the Variational Quantum Eigensolver (VQE), promise to accelerate the modeling of physical systems at the molecular and materials level, potentially informing the design of next-generation structural and functional materials. Beyond raw algorithmic performance, this paper carefully assesses the end‑to‑end workflow, accounting for overheads in problem encoding, error mitigation, and classical post‑processing. We also present a detailed analysis of resource utilization—quantified by qubit counts, circuit depths, and annealing schedules—highlighting trade‑offs between solution quality and execution time. Ultimately, our findings underscore that, while pure quantum speedups remain rare in 2022, hybrid approaches harnessing both quantum and classical resources can yield practical benefits for small‑to‑medium scale engineering tasks. This expanded evaluation provides a roadmap for researchers and practitioners interested in applying quantum computing to real‑world engineering challenges.
Over the last decade, quantum simulation and computation has progressed from a purely scientific testbed of quantum mechanics to a mature field that is starting to offer new insights into materials, quantum effects, and algorithms that are intractable with even the most state-of-the-art classical computation. Simulating certain quantum Hamiltonians that are theorized to be at the heart of high-Tc superconductivity, topological quantum systems such as the fractional quantum Hall effect or fundamental questions of thermalization quickly exceed the available memory of even the most advanced supercomputers – and in fact all memory in the world – due to the exponential growth of the Hilbert space with system size. As postulated by Feynman himself, the computational system best suited for solving quantum problems is to use a quantum system itself, as it can intrinsically represent the entanglement that is the key resource making quantum computing challenging but also promising. Apart from simulating problems in physics and chemistry, there is also tremendous excitement for quantum computers to provide speedups for general algorithms in optimization at a rate that is exponentially faster than existing classical programming. So far only a small class of algorithms has been actually proven to provide such a speedup, most prominently Shor's algorithm which can factor large prime numbers, and several other search and oracle algorithms. In the last two decades, many experiments using ultracold atoms, ions, or superconducting circuits have focused on analog quantum simulation. Here, a model Hamiltonian that is believed to capture all the relevant physics of the system of study is experimentally realized using different building blocks and interactions but replicating condensed matter effects at an increased scale. This has led to a number of bespoke experiments such as BEC/Fermigass machines, quantum gas microscopes and more exotic setups that are purpose built to study a particular effect. More recently, there has been a shift to develop more universal simulation platforms and optical tweezer arrays have emerged as a leading solution due to their high degree of reconfigurability. Through tremendous improvements in the degree of control and measurement of single qubits, error correction has become a viable route to build a true universal digital quantum computer. Even as we transition into the digital age of quantum simulation, certain classes of problems with additional physics constraints such as Fermionic statistics, gauge fields and lattice gauge theories still incur too large of an overhead to be encoded on these digital simulators. In this thesis, we use a highly degenerate twisted cavity to simulate the effect of a magnetic field on a two-dimensional system of interacting photons to enable realization of states of the quantum Hall effect. We design, build, and commission a new lens based cavity apparatus realizing a lowest Landau level for a mesoscopic number of modes. We demonstrate the integration of highly excited Rydberg atoms to mediate strong interactions and demonstrate photon blockade as well as mean field interactions. As a second application of cavities to quantum information leveraging our newfound comfort with intra-cavity optics, and experience with aberration modeling in resonators, we demonstrate a new class of small waist optical resonators enabled by lens-based cavities and then apply our understanding of optical aberrations in cavities to the development of a new class of cavity array. This Cavity Array Microscope (CAM) realizes a large number of cavities (up to currently 600) using only a fixed number of free space optics and is both scalable with constant overhead as well as compatible with Rydberg atoms. This platform provides a route to highly parallel quantum repeater operation or entanglement generation between atom arrays in the future.
Quantum computing is rapidly evolving as a paradigm that promises to solve complex computational problems far beyond the capabilities of classical systems. This article explores the current challenges facing quantum computation, particularly in algorithm development, error correction, and hardware scalability. The paper also outlines the prospects of next-generation quantum algorithms, especially those applicable to cryptography, optimization, and machine learning. Recent advances in quantum error mitigation and hybrid quantum-classical models are reviewed, emphasizing the transition from theoretical constructs to practical deployment. This study aims to bridge the gap between quantum algorithm research and its implementation, offering insights into the interdisciplinary efforts needed to make quantum advantage a reality.
Unlock the future of quantum technology with this comprehensive guide that bridges the gap between complex quantum theory and real-world applications, giving you the practical edge needed to solve the next generation’s toughest scientific and industrial problems. At its core, quantum computing leverages the principles of quantum mechanics to process information in fundamentally different ways from classical computing. As physical limits constrain the continued scaling of classical technologies, quantum computing offers a fundamentally new pathway toward solving complex problems in science, engineering, and industry. This book is a comprehensive guide designed to bridge the gap between theoretical principles and real-world quantum computing applications. It explores quantum information theory, a cornerstone of quantum computing, to explain how information is encoded, manipulated, and measured in a quantum system. Topics such as quantum gates, circuits, and the Bloch sphere representation are covered in detail, offering readers a solid grounding in the mechanics of quantum operations. With a focus on practical implementation, this book is tailored for students, researchers, and professionals seeking to delve into the transformative world of quantum computing, where the boundaries of classical computation are redefined. Readers will find the book: Uses step-by-step guides and hands-on tutorials for building quantum circuits and running algorithms; Explores core algorithms through detailed walkthroughs of quantum algorithms, including Shor’s, Grover’s, and Quantum Fourier Transform; Provides hands-on learning through exercises, coding challenges, and projects to reinforce practical skills. Audience Academics, researchers, quantum software developers and hardware engineers, data scientists, AI specialists, and security experts focused on the study and implementation of quantum systems and processors.