A new platform for quantum technologies using nanophotonics (Conference Presentation)

Point-like defects in wide-bandgap materials are at the heart of a broad range of emerging applications including quantum information processing and metrology [1]. A well-known example is the nitrogen-vacancy (NV) defect in diamond, which can be used as a solid-state qubit to perform elaborate quantum information protocols [2] and highly sensitive magnetic field sensing [3]. These results motivate the search of new defects in other wide-bandgap materials, which would offer an expanded range of functionalities compared to NV defects in diamond. In that context, hexagonal boron nitride (hBN) appears as an appealing material. First, it has a 6-eV bandgap, which is ideally suited to host optically active defects with energy levels deeply buried between the valence band and the conduction band. Second, hBN is an electrical insulator with a two-dimensional (2D) honeycomb structure, which is a key element of Van der Waals heterostructures. Such "artificial" materials are currently attracting a great interest owing to their unique mechanical, electrical and optical properties [4]. Combining these properties with individual quantum systems would likely open new perspectives in quantum technologies. In this talk, I will report on the optical detection of individual defects hosted in a high-purity hBN crystal. Stable single photon emission is demonstrated under ambient conditions by means of photon correlation measurements [5]. A detailed analysis of the photophysical properties of the defect reveals a highly efficient radiative transition, leading to one of the brightest single photon source reported to date from a bulk, unpatterned, material. These results make a bridge between the physics of 2D materials and quantum technologies, and pave the way towards applications of van der Waals heterostructures in photonic-based quantum information science, metrology and optoelectronics.

The last five years have witnessed dramatic advances in realization of quantum emitters (QEs) in one dimensional carbon nanotubes and two dimensional layered semiconductors. These novel QEs offer exciting opportunities for not only storing, processing and transducing of quantum information but also sensing physical phenomena beyond classical detection limits. Realization of these opportunities also present multiple challenges including: (1) realizing room temperature, telecommunication wavelength operation; (2) controlling fundamental as well as quantum optical properties such as QE emission wavelengths, linewidths, polarization, coherent times, single photon purity and indistinguishability; (3) deterministic placement and integration of QEs into photonic, plasmonic, and mangnonic platforms for quantum sensing and transduction applications. Here in this talk I will present recent efforts toward meeting these challenges. In 1D carbon nanotubes, we recently demonstrated that chemical binding configuration of covalent quantum defects can be controlled through the spin multiplicity of photoexcited intermediates. This enable us to control the emission wavelength of QEs by creating previously inaccessible chemical configuration. In 2D semiconductor, we have successfully created the telecommunication wavelength quantum emitters by local strain engineering of MoTe2. We have also realized chiral quantum emitters via exploit of magnetic proximity interaction between quantum emitters of WSe2 monolayer and localized magnetization crated in NiPS3 anti-ferromagnetic insulator by nanoscale stain engineering.

The Jaynes–Cummings Model (JCM) has been at the forefront of modern physics as one of the simplest, yet intricately nonlinear, models of light–matter interaction. Focusing on the omnipresence of the JCM across a range of disciplines, this significantly updated and comprehensive review conveys to the reader the fundamental generality of its formalism, looking at a wide range of applications in specific physical systems and across disciplines including atomic physics, quantum optics, solid-state physics and quantum information sciences. An ideal reference for researchers in quantum physics and quantum optics, the book also comprises an accessible introduction for students engaged with non-equilibrium quantum phase transitions, quantum computing and simulation, quantum many-body physics, cavity, circuit and waveguide quantum electrodynamics. Part of <a href="https://iopscience.iop.org/bookListInfo/iop-series-in-quantum-technology#series">IOP Series in Quantum Technology</a>. Key features • Collects JCM physics and applications scattered across literature and different applications. • The exposition guides the reader through a rich and appealing landscape interlacing quantum optics and condensed-matter physics. • All chapters discuss theory and experiment, linked historically to the development of the various directions stemming from JC physics. This is accompanied by a thorough list of references to the key publications. • The presentation is kept concise, while continuous text is interspersed with various illustrations and an economical use of mathematical expressions.

The Nobel Prizes in Physics (2022) and Chemistry (2023) heralded the recognition of quantum information science and the synthesis of quantum dots (QDs), respectively. This acknowledgment has propelled colloidal QDs and perovskite nanocrystals to the forefront of quantum technologies. Their distinct emission properties, facilitating the efficient generation of both single photons and photon pairs, render them particularly captivating. Moreover, their adaptability to diverse structures, ranging from traditional electronics to nanopatterned frameworks, underscores their pivotal role in shaping quantum technologies. Despite notable strides in synthesis, certain properties require refinement for enhanced applicability in quantum information, encompassing emission brightness, stability, single-photon indistinguishability, and entanglement fidelity of photon pairs. Here we offer an overview of recent achievements in plasmon-exciton quantum emitters (QEs) based on luminescent semiconductor nanocrystals. Emphasizing the utilization of the light-matter coupling phenomenon, we explore how this interaction enables the manipulation of quantum properties without altering the chemical structure of the emitters. This approach addresses critical aspects for quantum information applications, offering precise control over emission rate, intensity, and energy. The development of these hybrid systems represents a significant stride forward, demonstrating their potential to overcome existing challenges and advance the integration of QEs into cutting-edge quantum technology applications.

Quantum emitters such as quantum dots, defects in diamond or in silicon have emerged as efficient single-photon sources that are progressively exploited in quantum technologies. In 2019, it was shown that the emitted single-photon states often include coherence with the vacuum component. Here we investigate how such photon-number coherence alters quantum interference experiments that are routinely implemented both for characterizing or exploiting the generated photons. We show that it strongly modifies intensity correlation measurements in a Hong–Ou–Mandel experiment and leads to errors in indistinguishability estimations. It also results in additional entanglement when performing partial measurements. We illustrate the impact on quantum protocols by evidencing modifications in heralding efficiency and fidelity of two-qubit gates.

We demonstrate the monolithic integration of an on-demand quantum emitter in the form of a single self-assembled InGaAs quantum dot with an air clad, free standing directional coupler acting as a beam-splitter for anti-bunched light.

Quantum technologies such as quantum sensing, quantum imaging, quantum communications, and quantum computing rely on the ability to actively manipulate the quantum state of light and matter. Quantum emitters, such as color centers trapped in solids, are a useful platform for the realization of elementary building blocks (qubits) of quantum information systems. In particular, the modular nature of such solid-state devices opens up the possibility to connect them into quantum networks and create nonclassical states of light shared among many qubits. The function of a quantum network relies on efficient and controllable interactions among individual qubits. In this context, we present a scheme where optically active qubits of differing excitation energies are mutually coupled via a dispersive interaction with a shared mode of an optical cavity. This generally off-resonant interaction is prohibitive of direct exchange of information among the qubits. However, we propose a scheme in which by acoustically modulating the qubit excitation energies it is, in fact, possible to tune to resonance a preselected pair of qubits and thus open a communication channel between them. This method potentially enables fast (approximately nanoseconds) and parallelizable on-demand control of a large number of physical qubits. We develop an analytical and a numerical theoretical model demonstrating this principle and suggest feasible experimental scenarios to test the theoretical predictions.

The Symmetries of Quantum and Classical Information. The Ressurected “Ether" of Quantum Information

Developing quantum systems which are robust against noise are of prime importance to the realisation of quantum technologies. Without fault tolerance, we will never be able to preserve delicate quantum states for macroscopic time scales, a necessary requirement in the construction of scalable quantum computer. Topologically ordered models offer very beautiful mechanisms for preserving quantum states. In such models, quantum information is encoded globally over a degenerate topological Hilbert space which offers a natural robustness against local environmental noise. Remarkably, topological order is present in certain realistic condensed-matter systems. This provides a platform for accessing topological order in a laboratory. Moreover, considering condensed-matter systems enables us to combine topological features with other physical effects to enhance their behaviour. In this Thesis we study the physics of topologically ordered lattice models with defects. We seek practical applications of lattice defects for the realisation of a fault-tolerant quantum computer. The first result we present shows that anyonic data of point-like lattice defects, called twists, can be found by measuring the entanglement of the ground state of the host system. The data we learn relates to the capacity of a twist defect to perform quantum computational tasks. The second result in this Thesis concerns the dynamics of the qudit toric code model with line-like defects coupled to a thermal bath. We show we can entropically inspire fragile glassy dynamics in the system. Such dynamics qualitatively improve the coherence times of quantum information encoded in the ground state of the lattice. A novel way of achieving fault-tolerant quantum computation is by producing and manipulating twist defects of topologically ordered systems. In many ways, this paradigm of topological quantum computation is analogous to quantum computation using anyons. The first area of study in this Thesis extends the analogy between anyons and twists. Specifically, we show that the anyonic data of twists in Kitaev’s toric code model can be extracted

We review the national projects on quantum information science and technology in Japan over the past 30 years. The main funding agencies for this field have been the Japan Science and Technology Agency, the National Institute of Information and Communications Technology, the Japan Society for the Promotion of Science, and the Cabinet Office of the Government of Japan. The total investment in the quantum information science and technology field from these funding agencies for the past 15 years amounts to US$250 million. A similar amount of investment has been put in parallel by industry. As a result, new science frontiers have been created, and some service prototypes, such as quantum key distribution systems and coherent Ising machines, have been delivered to user premises. Recently, Japan has launched new initiatives to advance quantum information science and technology to the next phase, and to make full use of them for the resolution of societal problems.

Quantum emitters are widely used in quantum networks, quantum information processing, and quantum sensing due to their excellent optical properties. Compared with Stokes excitation, quantum emitters under anti-Stokes excitation exhibit better performance. In addition to laser cooling and nanoscale thermometry, anti-Stokes excitation can improve the coherence of single-photon sources for advanced quantum technologies. In this review, we follow the recent advances in phonon-assisted upconversion photoluminescence of quantum emitters and discuss the upconversion mechanisms, applications, and prospects for quantum emitters with anti-Stokes excitation.

Quantum science and technology is a rapidly growing field that harnesses the unique properties of quantum mechanics. The manipulation of quantum systems has led to unprecedented development in secure quantum communication, simulation, computing, sensing and metrology. Despite the significance of these technologies, the existing literature lacks a comprehensive understanding of how they can address various challenges faced by Africa. We address this gap by using systematic literature review methods and draw insights from diverse perspectives to present an overview of the current state of quantum science and technology in Africa. Furthermore, we explore how the full adoption and implementation of quantum technologies can contribute to achieving the United Nations Sustainable Development Goals 1-4, 10, 13, and 17. We analyze the data from literature review and insights from African quantum experts, which we synthesize into a cohesive summary. This review underscores that, with appropriate efforts, quantum technologies can significantly promote social, economic, and environmental sustainability in Africa. This review goes beyond the present literature to offer a conceptual framework, theoretical insights and practical recommendations. This study is particularly timely, coinciding with the 2025 International Year of Quantum Science and Technology, which recognizes 100 years since the initial development of quantum mechanics.

Quantum error correction plays a vital role in the Quantum information process. Nowadays, the research has been increased in quantum technology and is being applied in various applications like secure communications, finance, machine learning, drug analysis and etc. But the quantum information process is difficult compared to the classical due to the challenges in quantum technology like no-cloning theorem, decoherence, and the difficulty in quantum states measurement. Thus the error rate is high and it is not possible to build a quantum computer without an error detection and correction mechanism. In this paper, we are discussing various error correction methods and proposing a novel encoding method for quantum error correction.

We report room-temperature observations of CuZn-VS quantum emitters in individual ZnS:Cu nanocrystals (NCs). Using time-gated imaging, we isolate the distinct ∼3-μs-long, red photoluminescence (PL) emission of CuZn-VS defects, enabling their precise identification and statistical characterization. The emitters exhibit distinct blinking and photon antibunching, consistent with individual NCs containing two to four CuZn-VS defects. The quantum emitters' PL spectra show a pronounced blue shift compared to NC dispersions, likely due to photochemical and charging effects. Emission polarization measurements of quantum emitters are consistent with a σ-character optical dipole transition and the symmetry of the CuZn-VS defect. These observations motivate further investigation of CuZn-VS defects in ZnS NCs for use in quantum technologies.

Integration of chip-scale quantum technology was the main aim of this study. First, the recent progress on silicon-based photonic integrated circuits is surveyed, and then it is shown that silicon integrated quantum photonics can be considered a compelling platform for the future of quantum technologies. Among subsections of quantum technology, quantum emitters were selected as the object, and different quantum emitters such as quantum dots, 2D materials, and carbon nanotubes are introduced. Later on, the most recent progress is highlighted to provide an extensive overview of the development of chip-scale quantum emitters. It seems that the next step towards the practical application of quantum emitters is to generate position-controlled quantum light sources. Among developed processes, it can be recognized that droplet–epitaxial QD growth has a promising future for the preparation of chip-scale quantum emitters.