Quantum Computer Technology Research Articles

Ask me anything: Michelle Simmons

Michelle Simmons is director of the Centre of Excellence for Quantum Computation and Communication Technology at the University of New South Wales, Australia. A pioneer in atomic-scale silicon devices, she has built the world’s smallest transistor, the narrowest conducting wires, 3D atomic electronics and the first two-qubit silicon gate. In 2018 Simmons was named Australian of the Year.

Colloidal Quantum Dots as Platforms for Quantum Information Science.

Colloidal quantum dots (QDs) are nanoscale semiconductor crystals with surface ligands that enable their dispersion in solvents. Quantum confinement effects facilitate wave function engineering to sculpt the spatial distribution of charge and spin states and thus the energy and dynamics of QD optical transitions. Colloidal QDs can be integrated in devices using solution-based assembly methods to position single QDs and to create ordered QD arrays. Here, we describe the synthesis, assembly, and photophysical properties of colloidal QDs that have captured scientific imagination and have been harnessed in optical applications. We focus especially on the current understanding of their quantum coherent effects and opportunities to exploit QDs as platforms for quantum information science. Freedom in QD design to isolate and control the quantum mechanical properties of charge, spin, and light presents various approaches to create systems with robust, addressable quantum states. We consider the attributes of QDs for optically addressable qubits in emerging quantum computation, sensing, simulation, and communication technologies, e.g., as robust sources of indistinguishable, single photons that can be integrated into photonic structures to amplify, direct, and tune their emission or as hosts for isolated, coherent spin states that can be coupled to light or to other spins in QD arrays.

The Organizational Structure and Operational Logic of an Urban Smart Governance Information Platform: Discussion on the Background of Urban Governance Transformation in China

At present, the Chinese government is trying to resolve various social contradictions, such as people’s ever-growing need for a better life and unbalanced and inadequate development. To do so, urban governance practices including holistic governance, decentralized and interconnected governance, multiple participatory governance, and smart governance have been developed in China. Urban smart governance supported by mobile Internet, the Internet of Things, quantum computing, big data, artificial intelligence, and other information technologies has also entered the field of vision of academics and administrators. However, the research and practice on the integration of organizational structure and smart governance technology for urban governance in China are still insufficient. Hence, this paper proposes the design of the organizational structure of an urban smart governance platform and presents the “1 + N” integrated smart information platform and the “power-sharing linkage, one-center and dual-track” platform construction command system. In this system, the functional module of the information platform for smart urban governance is elaborated. This paper contributes to promoting the modernization of China’s urban governance capacity, which can enhance social equity and social order, promote social democracy and rule of law, and enhance the efficiency of urban governance.

When Molecular Magnetism Meets Supramolecular Chemistry: Multifunctional and Multiresponsive Dicopper(II) Metallacyclophanes as Proof-of-Concept for Single-Molecule Spintronics and Quantum Computing Technologies?

Molecular magnetism has made a long journey, from the fundamental studies on through-ligand electron exchange magnetic interactions in dinuclear metal complexes with extended organic bridges to the more recent exploration of their electron spin transport and quantum coherence properties. Such a field has witnessed a renaissance of dinuclear metallacyclic systems as new experimental and theoretical models for single-molecule spintronics and quantum computing, due to the intercrossing between molecular magnetism and metallosupramolecular chemistry. The present review reports a state-of-the-art overview as well as future perspectives on the use of oxamato-based dicopper(II) metallacyclophanes as promising candidates to make multifunctional and multiresponsive, single-molecule magnetic (nano)devices for the physical implementation of quantum information processing (QIP). They incorporate molecular magnetic couplers, transformers, and wires, controlling and facilitating the spin communication, as well as molecular magnetic rectifiers, transistors, and switches, exhibiting a bistable (ON/OFF) spin behavior under external stimuli (chemical, electronic, or photonic). Special focus is placed on the extensive research work done by Professor Francesc Lloret, an outstanding chemist, excellent teacher, best friend, and colleague, in recognition of his invaluable contributions to molecular magnetism on the occasion of his 65th birthday.

A Speed Test for Ripples in a Quantum System

A re there limits on how fast a can propagate in a system? The answer to this fundamental question has far-reaching consequences for practically any dynamic system we want to use or understand, from media for sending long-distance messages to extended bodies approaching thermal equilibrium. In a pioneering 1972 study, Elliott Lieb and Derek Robinson showed that the speed at which a could travel through a collection of interacting particles always has an upper limit [1]. The existence of the Lieb-Robinson bound, however, assumes that the particles are locally interacting, whereas many forms of complex of interest today involve long-range interactions. In a trio of papers, researchers now establish a bound for many long-range systems as well [2-4]. The findings settle a recent debate over if and when such bounds exist, and they may have implications for the choice of platform for quantum computation and other quantum technologies. You may have raised an eyebrow upon reading that the Lieb-Robinson bound was considered a discovery. After all, special relativity says that the speed of light is the ultimate limit on how fast a signal can travel, and this limit is built into the quantum field theory that describes the interactions between elementary particles. But researchers are also interested in whether an intrinsic limit on the speed of a exists simply by virtue of the way a system's particles interact. This limit determines, for instance, how quickly a jolt to an atom in a solid will influence a distant atom's behavior. When Lieb and Robinson explored this bound, they used a lattice of spins as a generic model of matter on a microscopic scale, where quantum mechanics prevails. The interactions in their model refer, for instance, to the energy cost of two spins pointing in opposite directions. The interactions are also short-ranged because the energy cost falls off exponentially with the distance between two spins, as exp(−x/d). Lieb and Robinson defined their physical effect as a correlation between two distant spins. Consider, for instance, a lattice with all spins initially aligned upwards (Fig. 1). Now imagine flipping one spin at x = 0. It will mainly stir its closest neighbors, which will stir theirs, and so on, and it will take some time t before a spin at a distant point x feels the initial flip. Lieb and Robinson quantified this correlation onset between distant spins with a so-called commutator, a mathematical object involving the quantum spin operator acting at x = 0 and t = 0 and the quantum spin operator acting at x and t. They showed that there is always a velocity v such that the norm of this commutator is negligibly small when x > vt. In modern language, physicists would say the speed of a is bound to an effective light cone (Fig. 1)-akin to the causal light cone of relativity. The slope of this cone is v, and the fact that it's constant means that the bound doesn't speed up or slow down with time.

Quantum Machine Learning: A Patent Review

One of the central problems bottlenecking machine learning research is classical computational power limits. Quantum computing provides a solution, offering more processing power for less electric cost. Quantum Machine Learning (QML) is a research field at the intersection of quantum computing and machine learning technologies, driving the cutting edge in technological innovation. While the legal literature on software patents is rapidly scaling, the research focused on QML patents is noticeably nascent. As such, this Article contributes the first empirical patent survey for QML technologies.

Progress in quantum-dot single photon sources for quantum information technologies: A broad spectrum overview

Semiconductor quantum dots (QDs) of various material systems are being heavily researched for the development of solid state single photon emitters, which are required for optical quantum computing and related technologies such as quantum key distribution and quantum metrology. In this review article, we give a broad spectrum overview of the QD-based single photon emitters developed to date, from the telecommunication bands in the IR to the deep UV.

Observation of a Strongly Enhanced Relaxation Time of an In-situ Tunable Transmon on a Silicon Substrate up to the Purcell Limit Approaching 100 μs

The remarkable advances of quantum computation technology with superconducting qubits based on circuit quantum electrodynamics (QED) architecture have been achieved by improving control, protection and measurement of the quantum states at the same time. At the heart of all these quantum operations, the significant enhancement of the qubit coherence time during the last decades was the key. Even after all these advances, the coherence and relaxation time of superconducting qubits still requires further improvements toward fault-tolerant quantum computation. Here, we report our observation of a strongly enhanced lifetime of an in-situ tunable superconducting transmon qubit on a silicon substrate that is embedded in a three-dimensional copper cavity. We measured a lifetime of the qubit of up to 84 µs, which is the best reported value of an in-situ tunable transmon on a silicon substrate. In our experiment, the in-situ frequency tunability over a broad range enabled the Purcell factor to be controlled continuously by detuning the qubit frequency against the resonator frequency in the strong dispersive regime. The silicon substrate has its own importance because the substrate should be fully compatible with the conventional semiconductor processes so that scalability and multi-chip module capability are guaranteed. In order to control the Purcell factor with another parameter, we displaced the qubit position in the cavity and observed a longer relaxation time with a smaller coupling coefficient. We believe that this systematic study and the control technique of the Purcell effect in the circuit QED design, together with minimizing the microwave photon loss through an improvement of the fabrication, will contribute to the realization of a practical large-scale quantum computer based on superconducting qubit technology.

An Identity-Based Blind Signature Scheme Using Lattice with Provable Security

With the rapid development of quantum computing and quantum information technology, the universal quantum computer will emerge in the near decades with a very high probability and it could break most of the current public key cryptosystems totally. Due to the ability of withstanding the universal quantum computer’s attack, the lattice-based cryptosystems have received lots of attention from both industry and academia. In this paper, we propose an identity-based blind signature scheme using lattice. We also prove that the proposed scheme is provably secure in the random oracle model. The performance analysis shows that the proposed scheme has less mean value of sampling times and smaller signature size than previous schemes. Thus, the proposed scheme is more suitable for practical applications.

Proposing a Novel Method for Increasing Security in the Network Communication

Advances in quantum computer technology are threatening cryptographic systems based on mathematical complexity. As an alternative, quantum cryptography has been proposed and developed. Among the reported quantum cryptography systems, quantum key distribution (QKD) constitutes a symmetric key system that can securely distribute a secret key on a quantum channel. While there have been many studies on confidential communication using QKD, only a few of them address its application to the digital signature. In this paper, we propose a new digital signature method with public parameter and signature key through shared symmetric key from QKD. We also analyze the proposed plan from security.

A review on reversible logic gates

In recent years, reversible logic circuits have applications in the emerging field of digital signal processing, optical information processing, quantum computing and nano technology. Reversibility plays an important role when computations with minimal energy dissipation are considered. The main purpose of designing reversible logic is to decrease the number of reversible gates, garbage outputs, constant inputs, quantum cost, area, power, delay and hardware complexity of the reversible circuits. This paper reveals a comparative review on various reversible logic gates. This paper provides some reversible logic gates, which can be used in designing more complex systems having reversible circuits and can execute more complicated operations using quantum computers. Future digital technology will use reversible logic gates in order to reduce the power consumption and propagation delay as it effectively provides negligible loss of information in the circuit. 
 Keywords: Garbage output, Power dissipation, quantum cost, Reversible Gate, Reversible logic,

Political Organising and Mobilising in the Age of the Fourth Industrial Revolution: A Reflection on the Gauteng Young Communist League of South Africa

What does the Fourth Industrial Revolution (4IR) portend for the future of political organising and mobilising? As “a way of describing the blurring of boundaries between the physical, digital, and biological worlds...a fusion of advances in artificial intelligence, robotics, the Internet of Things, 3D printing, genetic engineering, quantum computing, and other technologies…” (McGinnis, 2018), the 4IR is primarily concerned with the inchoate transformation of the production of goods and services, resulting from the application of a new wave of technological innovations. Definitions such as these cement the narrow idea that the 4IR is principally about industry, when in reality it is a revolution that goes beyond economic activity concerned with the manufacturing of goods and services.

Research on Particle Swarm Optimization Algorithm Based on Quantum Computing Technology

In view of the shortcomings of particle swarm optimization such as premature convergence to local optimization, particle swarm optimization algorithm based on quantum gate and particle swarm optimization algorithm based on quantum behavior are studied in this paper. The first algorithm uses the random observation method of quantum bit coding particles to simulate quantum particle collapse for generating a population and uses the quantum rotating gate to generate a new population. The adaptive mutation operator is used for ensuring the diversity of the population, effectively reducing the impact of local optimization; therefore, the robustness of the algorithm is improved. The second algorithm uses the probability density function of quantum computation to make the particles jump out of the local extreme points and fulfils the global search, which is more suitable for continuous optimization. The results of computational experiments show that both the two particle swarm optimization algorithms based on quantum technology have a good global convergence.

Preface to Topical Papers on the Progress of Photonic Quantum Computer and Pertinent Technologies

Preface to Topical Papers on the Progress of Photonic Quantum Computer and Pertinent Technologies

The Features of the Spacetime

The present paper aims to introduce a new algebra based on the knots and their ability to change dramatically the physical state, when we act on them with the braiding operator. The frame of all this ideas is the topological quantum computing. Nowadays, the quest for a reliable quantum computer technology refers, among others quantum phenomena, to the Quantum Hall Effect. Setting suitable quantum experiments (for instance a super lattice - two dimensional electron system that appears in the hetero structures of two semiconductors) involving exceptionally strong magnetic fields and very low temperatures, the QHE puts into evidence new quasi particles, evolving in 2+1 dimensions space. Such a topological quantum computer will successfully fight against the undesirable interaction between the quantum system and the environment (de-coherence). The knotted quantum world-lines of quasi-particles (anyons) provide the quantum computing physical support. The necessary algebra (which will deal with) is the algebra of the creation and annihilation of the knot's braids when the corresponding braiding operators act.

On the Relationship between Boolean Algebra and Quantum Informatics

The fundamental relationship between quantum physics and discrete mathematics is examined. A method for representing Boolean functions in the form of unitary transformations is described. The question of the connection of Zhegalkin polynomials defining the algebraic normal form of a Boolean function with quantum circuits is considered. It is shown that the quantum information language provides a simple algorithm for constructing the Zhegalkin polynomial based on the truth table. The developed methods and algorithms are generalized to the case of an arbitrary Boolean function with a multibit domain of definition and a multibit set of values, as well as to the case of multivalued ($$k$$-value) logic when $$k = p$$ is a prime number. The developed approach is important for the implementation of quantum computer technologies and is the foundation for the transition from classical computer logic to quantum hardware.

Distributed quantum sensing in a continuous-variable entangled network

Networking plays a ubiquitous role in quantum technology. It is an integral part of quantum communication and has significant potential for upscaling quantum computer technologies that are otherwise not scalable. Recently, it was realized that sensing of multiple spatially distributed parameters may also benefit from an entangled quantum network. Here we experimentally demonstrate how sensing of an averaged phase shift among four distributed nodes benefits from an entangled quantum network. Using a four-mode entangled continuous variable (CV) state, we demonstrate deterministic quantum phase sensing with a precision beyond what is attainable with separable probes. The techniques behind this result can have direct applications in a number of primitives ranging from biological imaging to quantum networks of atomic clocks.

History and Outlook of Quantum Computer Technology

History and Outlook of Quantum Computer Technology

Quantum: A Global Leadership Opportunity for the UK

Abstract Evert Geurtsen is Co-Director for User Engagement of NQIT, the Quantum Computing Technology Hub of the UK Quantum Technologies Programme. He tells ITNOW how the UK National Quantum Technologies Programme and NQIT is an opportunity to turn the UK’s scientifi c excellence into global economic leadership in this new transformative technology

China: Determined to dominate cyberspace and AI

ABSTRACTChina is chasing dominance in emerging artificial intelligence (AI) technologies in both the private and military sectors, as a central part of its effort to be the leading global cyber power. The rise of AI – a subset of cyber as are machine learning, quantum computing, and other new technologies – does not herald a new arms race equivalent to that of the Cold War. Rather, the concern should be on the profound disruption to the existing westernized global order. This piece reviews how the 1990s westernized national creation called cyberspace created so many ubiquitous, embedded vulnerabilities whose easy exploitation directly accelerated the rise of an otherwise impoverished authoritarian and aggressive China. Today no single democracy has the scale and sufficient resources to alone match the foreknowledge and strategic coherence of the newly confident and assertive China. To change current global trends, the small group of consolidated democratic civil societies needs a collective approach to counter China’s growing dominance across all fields of cyberspace. The piece ends describing the Cyber Operational Resilience Alliance (CORA) to provide the public and private scale and collective strategic coherence required to ensure the future wellbeing and security of democracy in an overwhelmingly authoritarian, post-western, cybered world.