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Excess micromotion can be a substantial source of errors in trapped-ion based quantum processors and clocks due to the sensitivity of the internal states of the ion to external fields and motion. This problem can be fixed by compensating background electric fields in order to position ions at the RF node and minimize their driven micromotion. Here we describe techniques for compensating ion chains in scalable surface ion traps. These traps are capable of cancelling stray electric fields with fine spatial resolution in order to compensate multiple closely spaced ions due to their large number of relatively small control electrodes. We demonstrate a technique that compensates an ion chain to better than 5 V/m and within 0.1 degrees of chain rotation. [ABSTRACT FROM AUTHOR]

Quantum physics is intrinsically probabilistic, where the Born rule yields the probabilities associated with a state that deterministically evolves. The entropy of a quantum state quantifies the amount of randomness (or information loss) of such a state. The degrees of freedom of a quantum state are position and spin. We focus on the spin degree of freedom and elucidate the spin-entropy. Then, we present some of its properties and show how entanglement increases spin-entropy. A dynamic model for the time evolution of spin-entropy concludes the paper. [ABSTRACT FROM AUTHOR]

Within the quantum field theory approach and using the technique of Bogoliubov transformations, the von Neumann boson-antiboson pair creation quantum entanglement entropy is studied in the context of the noncommutative Bianchi I universe. The investigations have shown that the behavior of entanglement entropy is strongly influenced by the choice of the noncommutativity θ parameter, k ⊥ -frequency modes and the structure of the curved spacetime. Moreover, the relationship between thermodynamics, Bose–Einstein condensation and quantum entanglement is also discussed. [ABSTRACT FROM AUTHOR]

Kinetic theory provides modeling of open quantum systems subject to Markovian noise via the Wigner–Fokker–Planck equation, which is an alternate of the Lindblad master equation setting, having the advantage of great physical intuition as it is the quantum equivalent of the classical phase space description. We perform a numerical inspection of the Wehrl entropy for the benchmark problem of a harmonic potential, since the existence of a steady state and its analytical formula have been proven theoretically in this case. When there is friction in the noise terms, no theoretical results on the monotonicity of absolute entropy are available. We provide numerical results of the time evolution of the entropy in the case with friction using a stochastic (Euler–Maruyama-based Monte Carlo) numerical solver. For all the chosen initial conditions studied (all of them Gaussian states), up to the inherent numerical error of the method, one cannot disregard the possibility of monotonic behavior even in the case under study, where the noise includes friction terms. [ABSTRACT FROM AUTHOR]

In this study, a novel technique for the quantum splitting of multi-qubit gates is presented. This brings innumerable advantages for the analysis of quantum circuits, the design of simulators, and back-ends, which are fundamentally needed in quantum computing development environments. This technique can be applied to any gate that involves two or more qubits, facilitating its treatment during its application in configurations of the Greenberger-Horne-Zeilinger (GHZ) type for more than two entangled photons, or protocols where CNOT or Toffoli gates connect qubits that are not close, which implies the intensive use of SWAP gates. The study is completed with the application of the new technique to quantum teleportation, quantum secret sharing, and entanglement swapping. [ABSTRACT FROM AUTHOR]

This article delves into the intricate interplay between quantum information, black hole dynamics, and spacetime emergence. We explore the fundamental phenomenon of quantum entanglement, which challenges traditional distance boundary concepts. The AdS/CFT correspondence is examined, revealing a profound connection between gravitational theories and quantum fields. It also emphasizes the holographic nature of our universe. The enigmatic nature of black holes is investigated, particularly their impact on locality and information preservation. We delve into the intricacies of black hole evaporation, a process guided by entangled qubits, shedding light on information’s dynamic nature. Using the concept of the thermofield double, we track the profound link between quantum information and cosmos geometry. Our exploration concludes by charting potential future research directions to unravel the complex symphony underlying our universe’s fabric. [ABSTRACT FROM AUTHOR]

The shape complexity of a particle confined in the circular quantum well with an external homogeneous perpendicular magnetic field is investigated. First, the Shannon entropy and the averaging electron probability density, as well as the shape complexities in the position and momentum spaces for several quantum states, are computed and discussed. The quantum confinement effect on the shape complexity of this system is extensively explored. Then, the influence of the magnetic field on the shape complexities of the particle confined in the circular quantum well is discussed. It is demonstrated that the shape complexity exhibits scaled invariance under the influence of the magnetic field. However, when the radius of the quantum well is fixed, the shape complexity of the given quantum state changes with the magnetic field strength. Results suggest that the shape complexity of a particle confined in the quantum well can be changed by varying both the strength of the magnetic field and the size of the well. This study has some practical applications in quantum information measurement of the confined particle and can guide future researches for the disorder characteristics of confined particle in semiconductor quantum dots. [ABSTRACT FROM AUTHOR]

Quantum‐information storage and retrieval in an optimized manner are of significance to information processing with composite systems. In this paper, an effective scheme is proposed for performing rapid information storage and retrieval between microwave photons and a nitrogen‐vacancy electron spin via shortcuts to adiabaticity. A qutrit of composite photon‐spin system interacts with two classical drivings. By modifying two original Rabi drivings, instead of directly adding an auxiliary counter‐diabatic interaction, information storage and retrieval can be rapidly performed with the optimized shortcut dynamics. Benefited from the shorter duration time, the shortcut‐based operation is more insensitive to decoherence effects than that of adiabatic counterpart. This strategy provides a promising avenue toward fast and robust information processing with solid‐state hybrid systems. [ABSTRACT FROM AUTHOR]

When studying the geometry of quantum states, it is acknowledged that mixed states can be distinguished by infinitely many metrics. Unfortunately, this freedom causes metric-dependent interpretations of physically significant geometric quantities such as the complexity and volume of quantum states. In this paper, we present an insightful discussion on the differences between the Bures and the Sjöqvist metrics inside a Bloch sphere. First, we begin with a formal comparative analysis between the two metrics by critically discussing three alternative interpretations for each metric. Second, we explicitly illustrate the distinct behaviors of the geodesic paths on each one of the two metric manifolds. Third, we compare the finite distances between an initial state and the final mixed state when calculated with the two metrics. Interestingly, in analogy with what happens when studying the topological aspects of real Euclidean spaces equipped with distinct metric functions (for instance, the usual Euclidean metric and the taxicab metric), we observe that the relative ranking based on the concept of a finite distance between mixed quantum states is not preserved when comparing distances determined with the Bures and the Sjöqvist metrics. Finally, we conclude with a brief discussion on the consequences of this violation of a metric-based relative ranking on the concept of the complexity and volume of mixed quantum states. [ABSTRACT FROM AUTHOR]

Today, we are already using several-component devices and systems based on the technologies developed during the first quantum revolution. Examples include microchips for servers, laptops and smartphones, medical imaging devices, LED, lasers, etc. Now, a second quantum revolution is progressing fast, exploiting technological advances for the ability to engineer and manipulate other quantum phenomena such as superposition, entanglement and measurement. As a matter of fact, there is an impressive increase in research and development activities, innovation, public and private investments in a new wave of quantum services and applications. In this scenario, quantum information and communication technologies (QICTs) can be defined as a set of technological components, devices, systems and methods for elaborating, storing and transmitting/sharing quantum information. This paper addresses the challenges and opportunities enabling the rise of QICTs. In order to provide a concrete example, the paper describes an overview of the European project EQUO (European Quantum ecOsystems) dealing with ongoing innovation activities in the QICT avenue; in fact, EQUO aims at developing and demonstrating the feasibility of QKD (quantum key distribution) networks and their related integration in current telecommunications infrastructures towards the quantum internet. [ABSTRACT FROM AUTHOR]

Controlled quantum teleportation (CQT), which is regarded as the prelude and backbone for a genuine quantum internet, reveals the cooperation, supervision, and control relationship among the sender, receiver, and controller in the quantum network within the simplest unit. Compared with low-dimensional counterparts, high-dimensional CQT can exhibit larger information transmission capacity and higher superiority of the controller's authority. In this article, we report a proof-of-principle experimental realization of three-dimensional (3D) CQT with a fidelity of 97.4% ± 0.2%. To reduce the complexity of the circuit, we simulate a standard 4-qutrit CQT protocol in a 9×9-dimensional two-photon system with high-quality operations. The corresponding control powers are 48.1% ± 0.2% for teleporting a qutrit and 52.8% ± 0.3% for teleporting a qubit in the experiment, which are both higher than the theoretical value of control power in 2-dimensional CQT protocol (33%). The results fully demonstrate the advantages of high-dimensional multi-partite entangled networks and provide new avenues for constructing complex quantum networks. [ABSTRACT FROM AUTHOR]

We present a formalization of several fundamental notions and results from Quantum Information theory in the proof assistant Isabelle/HOL, including density matrices and projective measurements, along with the proof that the local hidden-variable hypothesis advocated by Einstein to model quantum mechanics cannot hold. The proof of the latter result is based on the so-called CHSH inequality, and it is the violation of this inequality that was experimentally evidenced by Aspect, who earned the Nobel Prize in 2022 for his work. We also formalize various results related to the violation of the CHSH inequality, such as Tsirelson’s bound, which quantifies the amount to which this inequality can be violated in a quantum setting. [ABSTRACT FROM AUTHOR]

We study the properties of postselective transformations of quantum states, that is, transformations for which some classical results are declared "successful" while the rest are discarded. We demonstrate that for every postselective transformation there exists a distinguished orthonormal basis for which the transformation reduces to probabilistic blocking of the basis states followed by a deterministic transformation. We also describe a generalization of an arbitrary postselective transformation that corresponds to its partial version with a given success probability. [ABSTRACT FROM AUTHOR]

Metasurfaces have recently opened up applications in the quantum regime, including quantum tomography and the generation of quantum entangled states. With their capability to store a vast amount of information by utilizing the various geometric degrees of freedom of nanostructures, metasurfaces are expected to be useful for processing quantum information. Here, we propose and experimentally demonstrate a programmable metasurface capable of performing quantum algorithms using both classical and quantum light with single photons. Our approach encodes multiple programmable quantum algorithms and operations, such as Grover's search algorithm and the quantum Fourier transform, onto the same metalens array on a metasurface. A spatial light modulator selectively excites different sets of metalenses to carry out the quantum algorithms, while the interference patterns captured by a single-photon camera are used to extract information about the output state at the selected output directions. Our programmable quantum metasurface approach holds promising potential as a cost-effective means of miniaturizing components for quantum computing and information processing. [ABSTRACT FROM AUTHOR]

As an important part of strategic emerging industries, the new-generation information technology plays a major leading role in the overall and long-term development of the economy and society. The new-generation information technology industry is also the cornerstone for cultivating new quality productivity, and is an important starting point for opening up new fields and tracks for development and for shaping new momentum and advantages. Based on the implications of the new-generation information technology industry, this study sorts out the global development trend of the new-generation information technology industry, summarizes the current status and development trend of the industry in China, and analyzes the opportunities and challenges faced by the industry. Moreover, focusing on the requirements of high-quality development of the new-generation information technology industry, the study proposes the following countermeasures and suggestions: (1) improving the integrated strategic system and capabilities while adhering to a system engineering thinking; (2) strengthening the research of key core technologies to strengthen the basic capacity of the industry; (3) promoting the integrated and clustered development of industries, highlighting enterprises as the main body; (4) constructing an open innovation ecosystem based on scenario-driven innovation; and (5) promoting the coordinated development of production, education, research, application, and funds to cultivate a high-level talent team.

When studying the geometry of quantum states, it is acknowledged that mixed states can be distinguished by infinitely many metrics. Unfortunately, this freedom causes metric-dependent interpretations of physically significant geometric quantities such as the complexity and volume of quantum states. In this paper, we present an insightful discussion on the differences between the Bures and the Sjöqvist metrics inside a Bloch sphere. First, we begin with a formal comparative analysis between the two metrics by critically discussing three alternative interpretations for each metric. Second, we explicitly illustrate the distinct behaviors of the geodesic paths on each one of the two metric manifolds. Third, we compare the finite distances between an initial state and the final mixed state when calculated with the two metrics. Interestingly, in analogy with what happens when studying the topological aspects of real Euclidean spaces equipped with distinct metric functions (for instance, the usual Euclidean metric and the taxicab metric), we observe that the relative ranking based on the concept of a finite distance between mixed quantum states is not preserved when comparing distances determined with the Bures and the Sjöqvist metrics. Finally, we conclude with a brief discussion on the consequences of this violation of a metric-based relative ranking on the concept of the complexity and volume of mixed quantum states.

Today, we are already using several-component devices and systems based on the technologies developed during the first quantum revolution. Examples include microchips for servers, laptops and smartphones, medical imaging devices, LED, lasers, etc. Now, a second quantum revolution is progressing fast, exploiting technological advances for the ability to engineer and manipulate other quantum phenomena such as superposition, entanglement and measurement. As a matter of fact, there is an impressive increase in research and development activities, innovation, public and private investments in a new wave of quantum services and applications. In this scenario, quantum information and communication technologies (QICTs) can be defined as a set of technological components, devices, systems and methods for elaborating, storing and transmitting/sharing quantum information. This paper addresses the challenges and opportunities enabling the rise of QICTs. In order to provide a concrete example, the paper describes an overview of the European project EQUO (European Quantum ecOsystems) dealing with ongoing innovation activities in the QICT avenue; in fact, EQUO aims at developing and demonstrating the feasibility of QKD (quantum key distribution) networks and their related integration in current telecommunications infrastructures towards the quantum internet.

Abstract The quantum internet is a cutting‐edge paradigm that uses the unique characteristics of quantum technology to radically alter communication networks. This new network type is expected to collaborate with 6G networks, creating a synergy that will fundamentally alter how we communicate, engage, and trade information. The improved security, increased speed, and increased network capacity of the quantum internet will lead to the emergence of a broad variety of new applications and services. The current state of quantum technology and its integration with 6G networks are summarised in this study, with an emphasis on the key challenges and untapped possibilities. The main goal is to get knowledge about how the quantum internet might impact communication in the future and alter several economic and societal sectors.

Abstract The authors devised a protocol that allows two parties, who may malfunction or intentionally convey incorrect information in communication through a quantum channel, to verify each other's measurements and agree on each other's results. This has particular relevance in a modified version of the quantum coin flipping game. The key innovation of the authors’ work includes the new design of a quantum coin that excludes any advantage of cheating, by which the long‐standing problem of the fair design of the game is, affirmatively, solved. Furthermore, the analysis is extended to N‐parties communicating with each other, where multiple solutions for the verification of each player's measurement is proposed. The results in the N‐party scenario could have particular relevance for the implementation of future quantum networks, where verification of quantum information is a necessity.

The rapid development of quantum information has brought new opportunities and challenges to modern information technologies. As one of the popular research directions in the field of quantum information, quantum networks aim to utilize the fundamental properties of quantum mechanics to achieve long-distance (secure) communications or provide computational capabilities superior to classical computing networks through distributed computing. The study of quantum networks holds great significance in advancing the practicality of quantum information. To gain a comprehensive understanding of the development trajectory of quantum networks, this study categorizes quantum networks into three types: quantum cryptography, quantum cloud computing, and quantum teleportation networks, based on different application scenarios and technical approaches. It provides comprehensive reviews of both domestic and international research progress and the challenges faced in each aspect. Furthermore, in conjunction with the practical implementation of quantum networks, the key technologies that need to be overcome in the development of quantum network systems, involving link establishment, information transmission, networking protocols, and physical hardware, are summarized. Overall, the development of quantum networks is still in the primary stage. At this stage, actively addressing challenges and seizing opportunities are of great significance to enhance the technological prowess of China. Therefore, to promote the development of quantum network systems in China, suggestions are proposed from three aspects: strengthening investment in the research and development of fundamental hardware infrastructure, attaching importance to the theoretical research of quantum networks, and enhancing interdisciplinary research and talent cultivation.

There is increasing interest in the study of chiral degrees of freedom occurring in matter and in electromagnetic fields. Opportunities in quantum sciences will likely exploit two main areas that are the focus of this Review: (1) recent observations of the chiral-induced spin selectivity (CISS) effect in chiral molecules and engineered nanomaterials and (2) rapidly evolving nanophotonic strategies designed to amplify chiral light-matter interactions. On the one hand, the CISS effect underpins the observation that charge transport through nanoscopic chiral structures favors a particular electronic spin orientation, resulting in large room-temperature spin polarizations. Observations of the CISS effect suggest opportunities for spin control and for the design and fabrication of room-temperature quantum devices from the bottom up, with atomic-scale precision and molecular modularity. On the other hand, chiral-optical effects that depend on both spin- and orbital-angular momentum of photons could offer key advantages in all-optical and quantum information technologies. In particular, amplification of these chiral light-matter interactions using rationally designed plasmonic and dielectric nanomaterials provide approaches to manipulate light intensity, polarization, and phase in confined nanoscale geometries. Any technology that relies on optimal charge transport, or optical control and readout, including quantum devices for logic, sensing, and storage, may benefit from chiral quantum properties. These properties can be theoretically and experimentally investigated from a quantum information perspective, which has not yet been fully developed. There are uncharted implications for the quantum sciences once chiral couplings can be engineered to control the storage, transduction, and manipulation of quantum information. This forward-looking Review provides a survey of the experimental and theoretical fundamentals of chiral-influenced quantum effects and presents a vision for their possible future roles in enabling room-temperature quantum technologies.

A composable design scheme is presented for the development of hybrid quantum/classical algorithms and workflows for applications of quantum simulation. The proposed object-oriented approach is based on constructing an expressive set of common data structures and methods that enables programming of a broad variety of complex hybrid quantum simulation applications. The abstract core of the scheme is distilled from the analysis of the current quantum simulation algorithms. Subsequently, it allows synthesis of new hybrid algorithms and workflows via the extension, specialisation, and dynamic customisation of the abstract core classes defined by the proposed design. The design scheme is implemented using the hardware-agnostic programming language QCOR into the QuaSiMo library. To validate the implementation, the authors test and show its utility on commercial quantum processors from IBM and Rigetti, running some prototypical quantum simulations.

Abstract Quantum key distribution (QKD) holds the potential to establish secure keys over long distances. The distance of point-to-point QKD secure key distribution is primarily impeded by the transmission loss inherent to the channel. In the quest to realize a large-scale quantum network, increasing the QKD distance under current technology is of great research interest. Here we adopt the 3-intensity sending-or-not-sending twin-field QKD (TF-QKD) protocol with the actively-odd-parity-pairing method. The experiment demonstrates the feasibility of secure QKD over a 1002 km fibre channel considering the finite size effect. The secure key rate is 3.11 × 10 − 12 $3.11\times 10^{-12}$ per pulse at this distance. Furthermore, by optimizing parameters for shorter fiber distances, we conducted performance tests on key distribution for fiber lengths ranging from 202 km to 505 km. Notably, the secure key rate for the 202 km, the normal distance between major cities, reached 111.74 kbps.

In this work we study five Grover’s algorithm modifications, where each iteration is constructed by two generalized Householder reflections, against inaccuracies in the phases. By using semi-empirical methods, we investigate various characteristics of the dependence between the probability to find solution and the phase errors. The first of them is the robustness of the probability to errors in the phase. The second one is how quickly the probability falls beyond the stability interval. And finally, the average success rate of the algorithm when the parameters are in the range of the highly robust interval. Two of the modifications require usage of the same Grover operator each iteration and in the other three it differs. Those semi-empirical methods give us the tool to make prediction of the quantum algorithm modifications’ overall behavior and compare them for even larger register size.

Excess micromotion can be a substantial source of errors in trapped-ion based quantum processors and clocks due to the sensitivity of the internal states of the ion to external fields and motion. This problem can be fixed by compensating background electric fields in order to position ions at the RF node and minimize their driven micromotion. Here we describe techniques for compensating ion chains in scalable surface ion traps. These traps are capable of cancelling stray electric fields with fine spatial resolution in order to compensate multiple closely spaced ions due to their large number of relatively small control electrodes. We demonstrate a technique that compensates an ion chain to better than 5 V/m and within 0.1 degrees of chain rotation.

The nonadiabatic holonomic quantum computation based on the geometric phase is robust against the built-in noise and decoherence. In this work, we theoretically propose a scheme to realize nonadiabatic holonomic quantum gates in a surface electron system, which is a promising two-dimensional platform for quantum computation. The holonomic gate is realized by a three-level structure that combines the Rydberg states and spin states via an inhomogeneous magnetic field. After a cyclic evolution, the computation bases pick up different geometric phases and thus perform a holonomic gate. Only the electron with spin up experiences the holonomic gate, while the electron with spin down is decoupled from the state-selective driving fields. The arbitrary controlled-U gate encoded on the Rydberg states and spin states can then be realized. The fidelity of the output state exceeds 0.99 with experimentally achievable parameters. [ABSTRACT FROM AUTHOR]

The universality of classical thermodynamics rests on the central limit theorem, due to which, measurements of thermal fluctuations are unable to reveal detailed information regarding the microscopic structure of a macroscopic body. When small systems are considered and fluctuations become important, thermodynamic quantities can be understood in the context of classical stochastic mechanics. A fundamental assumption behind thermodynamics is therefore that of coarse graining, which stems from a substantial lack of control over all degrees of freedom. However, when quantum systems are concerned, one claims a high level of control. As a consequence, information theory plays a major role in the identification of thermodynamic functions. Here, drawing from the concept of gauge symmetry—essential in all modern physical theories—we put forward a new possible intermediate route. Working within the realm of quantum thermodynamics, we explicitly construct physically motivated gauge transformations which encode a gentle variant of coarse graining behind thermodynamics. As a first application of this new framework, we reinterpret quantum work and heat, as well as the role of quantum coherence. [ABSTRACT FROM AUTHOR]

Consider the n! different unitary matrices that permute nd-dimensional quantum systems. If d ≥ n then they are linearly independent. This paper discusses a sense in which they are approximately orthogonal (with respect to the Hilbert–Schmidt inner product, ⟨ A , B ⟩ = tr A † B / tr I ) if d ≫ n 2 , or, in a different sense, if d ≫ n . Previous work had shown pairwise approximate orthogonality of these matrices, but here we show a more collective statement, quantified in terms of the operator norm distance of the Gram matrix to the identity matrix. This simple point has several applications in quantum information and random matrix theory: (1) showing that random maximally entangled states resemble fully random states, (2) showing that Boson sampling output probabilities resemble those from Gaussian matrices, (3) improving the Eggeling–Werner scheme for multipartite data hiding, (4) proving that the product test of Harrow–Montanaro cannot be performed using LOCC without a large number of copies of the state to be tested, (5) proving that the purity of a quantum state also cannot be efficiently tested using LOCC, and (6, published separately with Brandão and Horodecki) helping prove that poly-size random quantum circuits are poly-designs. [ABSTRACT FROM AUTHOR]

Entanglement witnesses (EWs) are a fundamental tool for the detection of entanglement. We investigate the inertia of bipartite EWs constructed by the partial transpose of NPT states. Furthermore, we find out most of the inertia of the partial transpose of the two-qutrit bipartite NPT states. As an application, we extend our results to high-dimensional states. [ABSTRACT FROM AUTHOR]

Spin network (SN) systems can be used to achieve quantum state transfer with high fidelity and to generate entanglement. A new approach to design spin‐chain‐based spin network systems, for short‐range quantum information processing and phase‐sensing, has been proposed recently in Advanced Quantum Technologies. In this paper, the scalability of such systems is investigated, by designing larger SN systems that can be used for longer‐range quantum information tasks, such as connecting together quantum processors. Furthermore, more complex SN designs, which can produce different types of entangled states, are presented. Simulations of disorder effects show that even such larger SN systems are robust against realistic levels of disorder. [ABSTRACT FROM AUTHOR]

This work presents a comprehensive exploration of the entanglement and graph connectivity properties of Graph States (GSs). Qubit entanglement in Pseudo Graph States (PGSs) is quantified using the Entanglement Distance (ED), a recently introduced measure of bipartite entanglement. In addition, a new approach is proposed for probing the underlying graph connectivity of genuine GSs, using Pauli matrix quantum correlators. These findings also reveal interesting implications for measurement processes, demonstrating the equivalence of some projective measurements. Finally, the emphasis is placed on the simplicity of data analysis in this framework. This work contributes to a deeper understanding of the entanglement and connectivity properties of GSs, offering valuable information for quantum information processing and quantum computing applications. The famous stabiliser formalism, which is the typically preferred framework for the study of this type of states, is not used in this work; on the contrary, this approach is based exclusively on the concepts of expectation values, quantum correlations, and projective measurement, which have the advantage of being very intuitive and fundamental tools of quantum theory. [ABSTRACT FROM AUTHOR]

Controlled interaction between localized and delocalized solid-state spin systems offers a compelling platform for on-chip quantum information processing with quantum spintronics. Hybrid quantum systems (HQSs) of localized nitrogen-vacancy (NV) centers in diamond and delocalized magnon modes in ferrimagnets—systems with naturally commensurate energies—have recently attracted significant attention, especially for interconnecting isolated spin qubits at length-scales far beyond those set by the dipolar coupling. However, despite extensive theoretical efforts, there is a lack of experimental characterization of the magnon-mediated interaction between NV centers, which is necessary to develop such hybrid quantum architectures. Here, we experimentally determine the magnon-mediated NV–NV coupling from the magnon-induced self-energy of NV centers. Our results are quantitatively consistent with a model in which the NV center is coupled to magnons by dipolar interactions. This work provides a versatile tool to characterize HQSs in the absence of strong coupling, informing future efforts to engineer entangled solid-state systems. [ABSTRACT FROM AUTHOR]

In this paper, we consider an extension of the previously proposed algebraic model and study the constraints of non-Abelian superselection rules on the transfer quantum information, taking into account conjugate endomorphism. The procedure of averaging (over the group ) projectors to the basic states of coherent orthogonal subspaces into which the space of two three-level systems decomposes is considered. Main attention is paid to the superselection structure of the algebra of observables defined by the Cuntz algebra (field algebra) containing as a pointwise fixed subalgebra with respect to the action of the gauge group . As an application of the model, we consider the encoding of information using a three-level system and show that information can be transmitted only by those states whose projectors belong to the algebra of observables. These projectors commute with the elements of the representation of the group , and therefore, allow the recipient to restore the obtained information. [ABSTRACT FROM AUTHOR]

The research paper introduces a novel approach to multi‐party quantum key distribution using variational quantum eigensolvers (VQEs). The protocol aims to establish secure communication among multiple parties in a quantum network. The paper outlines a comprehensive framework incorporating quantum state preparation, VQE‐based key generation, error correction, and privacy amplification circuits. Mathematical formulations guide the design of quantum gates, variational parameters, and error correction codes. The protocol utilizes quantum entanglement, VQE optimization, and classical operations for error correction and secure key extraction. The paper's experimental focus involves implementing the proposed protocol on a quantum computer, analyzing security metrics such as mutual information and min‐entropy, and simulating circuit outcomes. [ABSTRACT FROM AUTHOR]

Since the 1980s, researchers have taken giant steps in understanding how to use quantum mechanics for solving real problems—for example, making a computer that works according to the laws of quantum mechanics. In recent decades, researchers have tried to develop a platform for quantum information and computation that can be integrated into digital and telecom technologies without the need of a cryogenic environment. The current status of research in the field of quantum integrated photonics will be reviewed. A review of the most common integrated photonic platforms will be given, together with the main achievements and results in the last decade. [ABSTRACT FROM AUTHOR]

Single-photon emitters in hexagonal boron nitride have been extensively studied recently. Although unambiguous identification of the emitters is still under intense research, carbon-related defects are believed to play a vital role for the emitter producing zero-phonon lines in the range of 1.6–2.2 eV. In this study, we systematically investigate two configurations of carbon-vacancy defects, VNCB and CNVB, by means of density functional theory calculations. We calculated the reaction barrier energies from one defect to the other to determine relative stability. We find that the barrier energies are charge dependent, and CNVB could easily transform to VNCB in neutral- and positive-charge states while it is stable when negatively charged. Formation energy calculations show that the VNCB is the dominant defect over CNVB. However, neither VNCB nor CNVB has suitable fluorescence spectra that could reproduce the observed ones. Our results indicate that the origin of the 1.6-to2.2-eV emitters should be other carbon-related configurations. [ABSTRACT FROM AUTHOR]

Color centers in diamonds attract significant scientific attention due to their unique photophysical properties. This mini review covers some of the most promising applications of diamonds with color centers, such as biological imaging, sensing, and quantum information processing. [ABSTRACT FROM AUTHOR]

Training of Quantum Neural Networks can be affected by barren plateaus—flat areas in the landscape of the cost function, which impede the model optimisation. While there exist methods of dealing with barren plateaus, they could reduce the model's effective dimension—the measure of its capacity to learn. This paper therefore reports an investigation of four barren plateaus countermeasures, i.e. restricting the model's circuit depth and relying on the local cost function; layer-by-layer circuit pre-training; relying on the circuit block structure to support its initialisation; as well as, model creation without any constraints. Several experiments were conducted to analyse the impact of each countermeasure on the model training, its subsequent ability to generalise and its effective dimension. The results reveal which of the approaches enhances or impedes the quantum model's capacity to learn, which gives more predictable learning outcomes, and which is more sensitive to training data. Finally, the paper provides some recommendations on how to utilise the effective dimension measurements to assist quantum model development. [ABSTRACT FROM AUTHOR]