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The operations of current quantum computers are still significantly affected by decoherence caused by interaction with the environment. In this work, we employ the non-perturbative hierarchical equations of motion (HEOM) method to simulate the operation of model quantum computers and reveal the effects of dissipation on the entangled quantum states and on the performance of well-known quantum algorithms. Multi-qubit entangled states in Shor's factorizing algorithm are first generated and propagated using the HEOM. It is found that the failure of factorization is accompanied by a loss of fidelity and mutual information. An important challenge in using the HEOM to simulate quantum computers in a dissipative environment is how to efficiently treat systems with many qubits. We propose a two-dimensional tensor network scheme for this problem and demonstrate its capability by simulating a one-dimensional random circuit model with 21 qubits. [ABSTRACT FROM AUTHOR]

Quantum information technology offers the potential to realize unprecedented computational resources via secure channels distributing entanglement between quantum computers. Diamond, as a host to optically-accessible spin qubits, is a leading platform to realize quantum memory nodes needed to extend such quantum links. Photonic crystal (PhC) cavities enhance light-matter interaction and are essential for an efficient interface between spins and photons that are used to store and communicate quantum information respectively. Here, we demonstrate one- and two-dimensional PhC cavities fabricated in thin-film diamonds, featuring quality factors (Q) of 1.8 × 105 and 1.6 × 105, respectively, the highest Qs for visible PhC cavities realized in any material. Importantly, our fabrication process is simple and high-yield, based on conventional planar fabrication techniques, in contrast to the previous with complex undercut processes. We also demonstrate fiber-coupled 1D PhC cavities with high photon extraction efficiency, and optical coupling between a single SiV center and such a cavity at 4 K achieving a Purcell factor of 18. The demonstrated photonic platform may fundamentally improve the performance and scalability of quantum nodes and expedite the development of related technologies. Improving the performance and scalability of quantum nodes is of paramount importance to expedite the development of quantum technologies. Here the authors demonstrate fiber-coupled 1D PhC cavities with high photon extraction efficiency, and optical coupling between a single SiV center and such a cavity. [ABSTRACT FROM AUTHOR]

Quantum computing has emerged as a transformative paradigm, with revolutionary potential in numerous fields, including quantum image processing and compression. Applications that depend on large scale image data could benefit greatly from parallelism and quantum entanglement, which would allow images to be encoded and decoded with unprecedented efficiency and data reduction capability. This paper provides a comprehensive overview of the rapidly evolving field of quantum image compression, including its foundational principles, methods, challenges, and potential uses. The paper will also feature a thorough exploration of the fundamental concepts of quantum qubits as image pixels, quantum gates as image transformation tools, quantum image representation, as well as basic quantum compression operations. Our survey shows that work is still sparse on the practical implementation of quantum image compression algorithms on physical quantum computers. Thus, further research is needed in order to attain the full advantage and potential of quantum image compression algorithms on large-scale fault-tolerant quantum computers. [ABSTRACT FROM AUTHOR]

With the rapid advancement of quantum computers in the past few years, there is ongoing development of algorithms aimed at solving problems that are difficult to tackle with classical computers. A pertinent instance of this is the resolution of partial differential equations (PDEs), where a current trend involves the exploration of variational quantum algorithms (VQAs) tailored to efficiently function on the noisy intermediate-scale quantum (NISQ) devices. Recently, VQAs for solving the Poisson equation have been proposed, and these algorithms require highly entangled quantum states or specific types of qubit entanglement to compute the expectation value of the Laplace operator. Implementing such requirements on NISQ devices poses a significant challenge. To overcome this problem, we propose a new method for representing the Laplace operator in the finite difference formulation. Since the quantum circuits introduced for evaluating the expectation value of the Laplace operator through proposed method do not require processes that degrade the fidelity of computation, such as swap operations or generation of highly entangled states, they can be easily implemented on NISQ devices. In the regime of quantum supremacy (the number of qubits is approximately 50), our proposed approach necessitates approximately one-third fewer CNOT operations compared to conventional methods. To assess the effectiveness of the proposed method, we conduct computations for finding the eigenvalues of the Helmholtz equation and solving the Poisson equation on cloud-based quantum hardware. We calculate the fidelity of quantum states required for each method through quantum tomography and also estimate the fidelity in the quantum supremacy regime. We believe that the proposed method can be applied to other PDEs having the Laplace operator and greatly assists in solving them. [ABSTRACT FROM AUTHOR]

Quantum computing is an exciting field that uses quantum principles, such as quantum superposition and entanglement, to tackle complex computational problems. Superconducting quantum circuits, based on Josephson junctions, is one of the most promising physical realizations to achieve the long-term goal of building fault-tolerant quantum computers. The past decade has witnessed the rapid development of this field, where many intermediate-scale multi-qubit experiments emerged to simulate nonequilibrium quantum many-body dynamics that are challenging for classical computers. Here, we review the basic concepts of superconducting quantum simulation and their recent experimental progress in exploring exotic nonequilibrium quantum phenomena emerging in strongly interacting many-body systems, e.g., many-body localization, quantum many-body scars, and discrete time crystals. We further discuss the prospects of quantum simulation experiments to truly solve open problems in nonequilibrium many-body systems. [ABSTRACT FROM AUTHOR]

Software-based remote memory attestation is a method for determining the state of a remote device without relying on secure hardware. In classical computing devices, the method is vulnerable to proxy and authentication attacks, because an infected device has no means of preventing the leak of its cryptographic secrets. In this paper, we demonstrate how these attacks can be mitigated by making use of quantum effects, while remaining within the class of software-based methods. In particular, we make use of entanglement and the inability of an attacker to clone qubits. Our proposed protocol is lightweight and can be implemented by near-term Quantum Computing techniques. The resulting protocol has the unique feature of resisting collusion between two dishonest devices, one of which has unbounded computational resources. [ABSTRACT FROM AUTHOR]

DNA is a complex multi-resolution molecule whose theoretical study is a challenge. Its intrinsic multiscale nature requires chemistry and quantum physics to understand the structure and quantum informatics to explain its operation as a perfect quantum computer. Here, we present theoretical results of DNA that allow a better description of its structure and the operation process in the transmission, coding, and decoding of genetic information. Aromaticity is explained by the oscillatory resonant quantum state of correlated electron and hole pairs due to the quantized molecular vibrational energy acting as an attractive force. The correlated pairs form a supercurrent in the nitrogenous bases in a single band π -molecular orbital (π -MO). The MO wave function (Φ) is assumed to be the linear combination of the n constituent atomic orbitals. The central Hydrogen bond between Adenine (A) and Thymine (T) or Guanine (G) and Cytosine (C) functions like an ideal Josephson Junction. The approach of a Josephson Effect between two superconductors is correctly described, as well as the condensation of the nitrogenous bases to obtain the two entangled quantum states that form the qubit. Combining the quantum state of the composite system with the classical information, RNA polymerase teleports one of the four Bell states. DNA is a perfect quantum computer. [ABSTRACT FROM AUTHOR]

The proposed hierarchical quantum operation sharing scheme cannot solve the supervision problem of the highest power owner. Therefore, with the help of the local operations and classical communication, a novel hierarchical quantum rotation operation sharing scheme with five users is proposed by utilizing a genuine five-qubit entangled state as the quantum channel. In this scheme, both senders can remotely and independently perform rotation operations from the set U on the target quantum state of any two low-level agents or one high-level agent, so that if the high-level agent wants to reconstruct the conceivable state, he needs the help of one low-level agent. Similarly, if the low-level agent wants to reconstruct the conceivable state, he needs the help of all other high-level and low-level agents. Furthermore, the above hierarchical quantum rotation operation sharing scheme with five users is extended to the case of multiple senders and agents by utilizing a m + x + y -qubit entangled state as the quantum channel. Finally, the security analysis shows that this scheme can solve the supervision problem of the highest power owner, prevent him from abusing his power, and resist external eavesdropper attack. [ABSTRACT FROM AUTHOR]

We present a quantum teleportation scheme for single qubits, qutrits, and ququads using maximally entangled pairs of two ququads. Additionally, we demonstrate that, under a specific mapping, single ququad teleportation is equivalent to two-qubit teleportation using generalized Bell states. Furthermore, we establish a dense (superdense) coding scheme for sending four bits of classical information using a single ququad state. We also investigate the efficiency of the single ququad quantum teleportation scheme by studying the fidelity of teleportation when subjected to noise, such as amplitude damping, depolarizing channel, phase damping, and bit flip. Finally, we investigate noise effects in two qubit teleportation and compare its results with the ququad case. We observe that in both cases, adding more noise increases the fidelity of teleportation. Additionally, we show that qubit teleportation is more resilient to noise than ququad teleportation. [ABSTRACT FROM AUTHOR]

Entanglement serves as the resource to empower quantum computing. Recent progress has highlighted its positive impact on learning quantum dynamics, wherein the integration of entanglement into quantum operations or measurements of quantum machine learning (QML) models leads to substantial reductions in training data size, surpassing a specified prediction error threshold. However, an analytical understanding of how the entanglement degree in data affects model performance remains elusive. In this study, we address this knowledge gap by establishing a quantum no-free-lunch (NFL) theorem for learning quantum dynamics using entangled data. Contrary to previous findings, we prove that the impact of entangled data on prediction error exhibits a dual effect, depending on the number of permitted measurements. With a sufficient number of measurements, increasing the entanglement of training data consistently reduces the prediction error or decreases the required size of the training data to achieve the same prediction error. Conversely, when few measurements are allowed, employing highly entangled data could lead to an increased prediction error. The achieved results provide critical guidance for designing advanced QML protocols, especially for those tailored for execution on early-stage quantum computers with limited access to quantum resources. Given that entangled states can store more information than unentangled ones, it would be natural to assume that highly-entangled data would always enhance capabilities of quantum machine learning models. Here, the authors show that this is not the case, in particular when the allowed number of measurements to incoherently learn quantum dynamics is low [ABSTRACT FROM AUTHOR]

We showcase the digital quantum simulation of the action of a Hamiltonian that governs the interaction between a quantum mechanical oscillator and an optical field, generating quantum entanglement between them via gravitational effects. This is achieved by making use of a boson-qubit mapping protocol and a digital gate decomposition that allow us to run the simulations in the quantum computers available in the IBM Quantum platform. We present the obtained results for the fidelity of the experiment in two different quantum computers, after applying error mitigation and post-selection techniques. The achieved results correspond to fidelities over 90%, which indicates that we were able to perform a faithful digital quantum simulation of the interaction and therefore of the generation of quantum entanglement by gravitational means in optomechanical systems. [ABSTRACT FROM AUTHOR]

With the rapid development of computer and internet technology, quantum signature plays an extremely important role in modern secure communication. Quantum homomorphic aggregate signature, as an important guarantee of quantum signature, plays a significant role in reducing storage, communication, and computing costs. This article draws on the idea of quantum multi-party summation and proposes a quantum homomorphic aggregate signature scheme based on quantum Fourier transform. Our scheme uses n-particle entangled states as quantum channels, with different particles of each entangled state sent separately. This ensures secure transmission of signatures and messages with fewer entangled particles during transmission, further improving the efficiency of quantum signatures. Meanwhile, our scheme generates private keys for each participating party by randomly constructing key generation matrixes. Different signers perform quantum Fourier transforms and basis exchange operations on entangled particles based on different messages and private keys to generate signatures. In addition, the aggregator does not need to measure and verify the signature particles after receiving signatures from different signers, and the group addition operation process has additive homomorphism. Security analysis shows that our scheme has unforgeability, non-repudiation, and can resist various attacks such as entanglement measurement attacks, intercept-resend attacks, private key sequence attacks, and internal attacks by aggregator. [ABSTRACT FROM AUTHOR]

Quantum blockchain (QBC) is a novel decentralised concept anticipated to offer an alternative to the classical blockchain to provide transaction security and transparency. The QBC frameworks can offer the most tangible advantage against the security threat posed by quantum computers on the classical blockchain. The proposed scheme offers a new QBC framework in which voting is performed by the Quantum-Secured Yet Another Consensus (QSYAC) algorithm to create a fast decentralised QBC. QSYAC algorithm is also used to ensure the reliability and fault tolerance of the blockchain framework. The classical information and the chaining are provided using a single qubit state and quantum entanglement. The transactions are signed via a cyclic permutation of the computational distinguishability of the quantum states problem, and quantum key distribution protocol is used for secure key sharing. Assuring the security of the key and the blockchain, the suggested model is more effective and safe from potential quantum assaults than earlier systems. [ABSTRACT FROM AUTHOR]

This paper presents an innovative entanglement-based protocol to address the Dining Cryptographers problem, utilizing maximally entangled | G H Z n 〉 tuples as its core. This protocol aims to provide scalability in terms of both the number of cryptographers n and the amount of anonymous information conveyed, represented by the number of qubits m within each quantum register. The protocol supports an arbitrary number of cryptographers n, enabling scalability in both participant count and the volume of anonymous information transmitted. While the original Dining Cryptographers problem focused on a single bit of information—whether a cryptographer paid for dinner—the proposed protocol allows m, the number of qubits in each register, to be any arbitrarily large positive integer. This flexibility allows the transmission of additional information, such as the cost of the dinner or the timing of the arrangement. Another noteworthy aspect of the introduced protocol is its versatility in accommodating both localized and distributed versions of the Dining Cryptographers problem. The localized scenario involves all cryptographers gathering physically at the same location, such as a local restaurant, simultaneously. In contrast, the distributed scenario accommodates cryptographers situated in different places, engaging in a virtual dinner at the same time. Finally, in terms of implementation, the protocol accomplishes uniformity by requiring that all cryptographers utilize identical private quantum circuits. This design establishes a completely modular quantum system where all modules are identical. Furthermore, each private quantum circuit exclusively employs the widely used Hadamard and CNOT quantum gates, facilitating straightforward implementation on contemporary quantum computers. [ABSTRACT FROM AUTHOR]

The evolution of quantum computers has encouraged research into how to handle tasks with significant computation demands in the past few years. Due to the unique advantages of quantum parallelism and entanglement, various types of quantum machine learning (QML) methods, especially variational quantum classifiers (VQCs), have attracted the attention of many researchers and have been developed and evaluated in numerous scenarios. Nevertheless, most of the research on VQCs is still in its early stages. For instance, as a consequence of the mathematical constraints imposed by the properties of quantum states, the majority of research has not fully taken into account the impact of data formats on the performance of VQCs. In this paper, considering a significant number of data in the real world exist in the form of complex numbers, i.e., phasor data in power systems and the result of Fourier transform on image processing, we develop two categories of data encoding methods, including coupling data encoding and splitting data encoding. This paper features the coupling data encoding method to encode complex-valued data in a way of amplitude encoding. By leveraging the property of quantum states living in a complex Hilbert space, the complex-valued data is embedded into the amplitude of quantum states to comprehensively characterize complex-valued information. Optimizers will be utilized to iteratively tune a parameterized ansatz, with the aim of minimizing the value of loss functions defined with respect to the specific classification task. In addition, distinct factors in VQCs have been explored in detail to investigate the performance of VQCs, including data encoding methods, loss functions, and optimizers. The experimental result shows that the proposed data encoding method outperforms other typical encoding methods on a given classification task. Moreover, different loss functions are tested, and the capability of finding the minimum value is evaluated for gradient-free and gradient-based optimizers, which provides valuable insights and guidelines for practical implementations. [ABSTRACT FROM AUTHOR]

Current protocols face limitations due to the small number and single form of transmitted qubits, as well as the complexity involved in preparing quantum channels. To address these limitations and develop a novel and practical protocol, we propose a new symmetric cyclic controlled quantum teleportation protocol, using nineteen-qubit entangled state as the quantum channel. Specifically, Alice, Bob and Charlie cyclically send arbitrary three-qubit states among themselves with the help of the controller David. The specialty of the proposed protocol is the utilization of multiple easy-to-prepare Bell-states and single-qubits within the quantum channel, which effectively minimizes resource consumption. Furthermore, we generalize the protocol with n+1(n≥3) parties by using (6n+1)-qubit entangled state as the quantum channel. This paper briefly analyzes the security of the protocol and compares them with the previous protocols in terms of efficiency. The results show that the present protocol is secure and more efficient. Our scheme has the potential to play a crucial role in facilitating secure quantum communication between quantum nodes in quantum networks. [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]

With gates of a quantum computer designed to encode multi-dimensional vectors, projections of quantum computer states onto specific qubit states can produce kernels of reproducing kernel Hilbert spaces. We show that quantum kernels obtained with a fixed ansatz implementable on current quantum computers can be used for accurate regression models of global potential energy surfaces (PESs) for polyatomic molecules. To obtain accurate regression models, we apply Bayesian optimization to maximize marginal likelihood by varying the parameters of the quantum gates. This yields Gaussian process models with quantum kernels. We illustrate the effect of qubit entanglement in the quantum kernels and explore the generalization performance of quantum Gaussian processes by extrapolating global six-dimensional PESs in the energy domain. [ABSTRACT FROM AUTHOR]

Prime factorization is a procedure of determining the prime factors of a given number N that requires super-polynomial time for conventional digital computers. Peter Shor developed a polynomial-time algorithm for quantum computers. Period finding is the key part of the algorithm, which is accomplished with the help of quantum superposition of states and quantum entanglement. The period finding can be also accomplished using classical wave superposition. In this study, we present experimental data obtained on a multi-port spin wave interferometer made of Y3Fe2(FeO4)3. Number 817 was factorized by a sequence of phase measurements. We also present the results of numerical modeling on the prime factorization of larger numbers 334 597 , 1 172 693 , 3 377 663 , and 9 363 239. The results of numerical modeling reveal significant shortcomings of the period-based approach. The major problems are associated with an inability to predict the period of the modular function, significant overhead over classical digital computers in some cases, and phase accuracy requirements. We argue that the same problems are inherent in classical analog and quantum computers. [ABSTRACT FROM AUTHOR]

Quantum physics has some unique properties, such as quantum entanglement and quantum superposition. Encryption algorithms designed based on quantum physical properties usually have higher security than classical computing. Applying quantum cryptography to data retrieval can realize cloud database encryption of quantum information. We propose a cloud ciphertext retrieval scheme, which combines quantum encryption and quantum search algorithm to ensure the privacy of data while the server completes information retrieval. In this scheme, the data are stored in the form of qubits string and placed in the quantum superposition state. We establish the mapping relationship between classical information and quantum states. Our scheme solves the problem of a large amount of computing and lack of sufficient computing resources at the client, assigns computing tasks to servers with sufficient resources, and ensures the security of information. [ABSTRACT FROM AUTHOR]

This article presents an enable-based bidirectional quantum teleportation protocol, leveraging distributed quantum gates with minimal resource requirements. The proposed protocol establishes a two-qubit entangled state as the quantum channel for the transmission of an unknown qubit message between Alice and Bob, enabling bidirectional teleportation. In traditional bidirectional teleportation protocols, both parties serve as senders and receivers, necessitating the utilization of at least two sets of a two-qubit entangled qubit for the channel (totaling four qubits). Contrarily, our contribution controls the functionality of each side via enabling qubits, enabling the implementation of bidirectional teleportation with a mere two-qubit entangled state. Furthermore, the protocol employs simple Z-basis measurements to implement the appropriate unitary operation for obtaining the teleported message. To validate the functionality of the protocol, the quantum circuit is simulated using the Qiskit library, with simulation results on the qasm simulator confirming its effectiveness. The proposed technique possesses wide-ranging applicability and can be incorporated into diverse protocols that employ Toffoli gates as quantum resources. [ABSTRACT FROM AUTHOR]

This article proposes a benchmark testing set and evaluation system for quantum computers. Our tests do not focus on the topology of quantum computers or the specific implementation details of preparing quantum bits. Instead, we examine the overall performance of quantum computers from the perspective of users. Inspired by traditional computer benchmark tests such as SPECCPU2017, we integrate existing scalable quantum applications and algorithms to generate a testing set that covers algorithms such as search, machine learning, factorization, portfolio optimization, and entanglement state preparation, effectively simulating real workloads. By running the testing set, we can understand the performance of current quantum computers and generate a comprehensive score by combining our evaluation system, which consists of sub-scores of various backend features, including quantum gate error rate, entanglement between quantum bits, cross talk, and connectivity. These sub-scores are calculated based on the program features of the testing cases combined with their running results, where the program features are analyzed through the logical circuits of the testing cases. We incorporate Hellinger fidelity and polarization rescaling into each benchmark to calculate the fidelity of the running results. Through our evaluation system, researchers can be guided toward research directions and understand how far quantum computers are from solving practical problems. [ABSTRACT FROM AUTHOR]

Copulas are mathematical tools for modeling joint probability distributions. In the past 60 years they have become an essential analysis tool on classical computers in various fields. The recent finding that copulas can be expressed as maximally entangled quantum states has revealed a promising approach to practical quantum advantages: performing tasks faster, requiring less memory, or, as we show, yielding better predictions. Studying the scalability of this quantum approach as both the precision and the number of modeled variables increase is crucial for its adoption in real-world applications. In this paper, we successfully apply a Quantum Circuit Born Machine (QCBM) based approach to modeling 3- and 4-variable copulas on trapped ion quantum computers. We study the training of QCBMs with different levels of precision and circuit design on a simulator and a state-of-the-art trapped ion quantum computer. We observe decreased training efficacy due to the increased complexity in parameter optimization as the models scale up. To address this challenge, we introduce an annealing-inspired strategy that dramatically improves the training results. In our end-to-end tests, various configurations of the quantum models make a comparable or better prediction in risk aggregation tasks than the standard classical models. [ABSTRACT FROM AUTHOR]

A Hybrid Quantum Genetic Algorithm with an Adaptive Rotation Angle (HQGAAA) for the 0-1 knapsack problem is presented. This novel proposal uses the Deutsch-Jozsa quantum circuit to generate quantum populations, which synergistically works as haploid recombination and mutation operators taking advantage of quantum entanglement providing exploitative and explorative features to produce new individuals. Furthermore, the created individuals are updated using an adaptive rotation angle operator that helps refine new individuals to converge to the optimal solution. We performed comparative tests with other quantum evolutionary algorithms and the classical genetic algorithm to demonstrate that this proposal performed better with the tested problem. Results showed that quantum algorithms performed similar but better than the classic genetic algorithm regarding accuracy. Moreover, statistic tests demonstrated that our proposal is faster than the other quantum algorithms tested. [ABSTRACT FROM AUTHOR]

In this study, the security implications of utilizing the concept of entanglement in time in the quantum representation of a blockchain data structure are investigated. The analysis reveals that the fundamental idea underlying this representation relies on an uncertain interpretation of experimental results. A different perspective is provided by adopting the Copenhagen interpretation, which explains the observed correlations in the experiment without invoking the concept of entanglement in time. According to this interpretation, the qubits responsible for these correlations are not entangled, posing a challenge to the security foundation of the data structure. The study incorporates theoretical analysis, numerical simulations, and experiments using real quantum hardware. By employing a dedicated circuit for detecting genuine entanglement, the existence of entanglement in the process of generating a quantum blockchain is conclusively excluded. [ABSTRACT FROM AUTHOR]

We introduce a new approach towards generative quantum machine learning significantly reducing the number of hyperparameters and report on a proof-of-principle experiment demonstrating our approach. Our proposal depends on collaboration between the generators and discriminator, thus, we call it quantum synergic generative learning. We present numerical evidence that the synergic approach, in some cases, compares favorably to recently proposed quantum generative adversarial learning. In addition to the results obtained with quantum simulators, we also present experimental results obtained with an actual programmable quantum computer. We investigate how a quantum computer implementing generative learning algorithm could learn the concept of a maximally-entangled state. After completing the learning process, the network is able both to recognize and to generate an entangled state. Our approach can be treated as one possible preliminary step to understanding how the concept of quantum entanglement can be learned and demonstrated by a quantum computer. [ABSTRACT FROM AUTHOR]

The existence of universal quantum computers has been theoretically well established. However, building up a real quantum computer system not only relies on the theory of universality, but also needs methods to satisfy requirements on other features, such as programmability, modularity, scalability, etc. To this end, here we study the recently proposed model of quantum von Neumann architecture by putting it in a practical and broader setting, namely, the hierarchical design of a computer system. We analyze the structures of quantum CPU and quantum control units and draw their connections with computational advantages. We also point out that a recent demonstration of our model would require less than 20 qubits. [ABSTRACT FROM AUTHOR]

In this paper a quantum communication protocol is proposed for the purpose of the exchange of a single qubit and a three-qubit state between two parties. It is a bi-directional teleportation protocol where the two parties have no information about the states they possess. The protocol has a Mentor who initiates the process and by measurement fixes the course of it amongst several possible alternatives. The participants are not initially connected through a single entangled state. It is the action of the Mentor which creates a seven-qubit entanglement amongst the legitimate parties. The role of the Mentor ends thereby. There is a Controller to oversee the process whose action leads to the completion of the protocol. The efficiency of the present protocol is calculated and it is found to be higher than several existing bi-directional protocols. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate the efficacy of the universally robust dynamical decoupling (URDD) sequence to preserve multipartite maximally entangled quantum states on a cloud-based quantum computer via the IBM platform. URDD is a technique that can compensate for experimental errors and simultaneously protect the state against environmental noise. To further improve the performance of the URDD sequence, phase randomization (PR) as well as correlated PR (CPR) techniques are added to the basic URDD sequence. The performance of the URDD sequence is quantified by measuring the entanglement in several noisy entangled states (two-qubit triplet state, three-qubit Greenberger–Horne–Zeilinger (GHZ) state, four-qubit GHZ state and four-qubit cluster state) at several time points. Our experimental results demonstrate that the URDD sequence is successfully able to protect noisy multipartite entangled states and its performance is modestly improved by adding the PR and CPR sequences. [ABSTRACT FROM AUTHOR]

In this paper, the key challenges (loss due to distance, entanglement routing, multi‐commodities) for the coming quantum internet, relying on entanglement of quantum bits (for short, qubits) on top of an existing network, are analyzed. A unifying framework enabling to compare the various entanglement distribution, purification, and routing protocols published so far is presented. With regard to entanglement routing, the introduction of different time windows will be essential in order to cope efficiently with the main challenges like complex route calculation and fidelity estimation on the one hand, actual entanglement route selection and entangled photon generation on the other hand. For a roll‐out on top of existing transmission networks, all the research publications for the last 20 years start to cover pretty well the global scheme. Nevertheless, open questions remain, like the actual advantage of some task execution prior to the online quantum path selection, or the design of algorithms approximating the multi‐commodities flow optimization problem, or the issue of dealing with a processing time not much longer than the qubit life time. [ABSTRACT FROM AUTHOR]

Quantum machine learning (QML) has attracted significant research attention over the last decade. Multiple models have been developed to demonstrate the practical applications of the quantum properties. In this study, we first demonstrate that the previously proposed quanvolutional neural network (QuanvNN) using a randomly generated quantum circuit improves the image classification accuracy of a fully connected neural network against the Modified National Institute of Standards and Technology (MNIST) dataset and the Canadian Institute for Advanced Research 10 class (CIFAR-10) dataset from 92.0% to 93.0% and from 30.5% to 34.9%, respectively. We then propose a new model referred to as a Neural Network with Quantum Entanglement (NNQE) using a strongly entangled quantum circuit combined with Hadamard gates. The new model further improves the image classification accuracy of MNIST and CIFAR-10 to 93.8% and 36.0%, respectively. Unlike other QML methods, the proposed method does not require optimization of the parameters inside the quantum circuits; hence, it requires only limited use of the quantum circuit. Given the small number of qubits and relatively shallow depth of the proposed quantum circuit, the proposed method is well suited for implementation in noisy intermediate-scale quantum computers. While promising results were obtained by the proposed method when applied to the MNIST and CIFAR-10 datasets, a test against a more complicated German Traffic Sign Recognition Benchmark (GTSRB) dataset degraded the image classification accuracy from 82.2% to 73.4%. The exact causes of the performance improvement and degradation are currently an open question, prompting further research on the understanding and design of suitable quantum circuits for image classification neural networks for colored and complex data. [ABSTRACT FROM AUTHOR]

Introduction: In the future, quantum networks will be an important development direction. Quantum networks should be studied considering quantum's unique physical properties. In quantum networks with limited resources, decoherence will lead to qubits loss, which restricts the time that data qubits can be stored in memory before use. To realize the network function, it is very important to transmit data qubits as quickly as possible. In order to ensure timeliness and make use of entanglement resources as much as possible, this paper proposes a concurrent multipath entanglement routing scheme based on segment routing for quantum hybrid networks. Methods: In this scheme, centralized routing is used to calculate the "segments" of quantum relay path, and distributed routing is used to transmit control messages between the "segments". The "concurrent" mechanism is fully adopted in classical messages passing, path nodes BSM (Bell State Measurement) execution and multipath shunt transmission. Conclusion: This scheme has obvious advantages in multipath concurrent transmission, traffic diversion, reducing transmission time and providing redundancy. [ABSTRACT FROM AUTHOR]

The goal of this paper is to further study multi-party multicast quantum communication of arbitrary two-qubit states. We first construct 9-qubit entangled channel by Hadamard gates and controlled-NOT gates and then, propose a new deterministic four-party scheme for multicast-based remote state preparation of two different two-qubit states, where the different arbitrary complex coefficient two-qubit states are transmitted synchronously from one sender to two spatially separated receivers under the control of the supervisor. In order to meet the needs of communication in noisy environment, we propose another three-party scheme for multicast-based remote state preparation of special complex coefficient two-qubit states by using the eight-qubit partially entangled state as the quantum channel. Finally, we discuss the feasibility of physical experiment, the security and the control power of the controller of the presented schemes. [ABSTRACT FROM AUTHOR]

We report the digital quantum simulation of a hamiltonian involved in the generation of quantum entanglement by gravitational means. In particular, we focus on a pair of quantum harmonic oscillators, whose interaction via a quantum gravitational field generates single-mode squeezing in both modes at the same time, a non-standard process in quantum optics. We perform a boson-qubit mapping and a digital gate decomposition specific for IBM quantum devices. We use error mitigation and post-selection to achieve high-fidelity, accessing a parameter regime out of direct experimental reach. [ABSTRACT FROM AUTHOR]

Distributed quantum information processing protocols such as quantum entanglement distillation and quantum state discrimination rely on local operations and classical communications (LOCC). Existing LOCC-based protocols typically assume the availability of ideal, noiseless, communication channels. In this paper, we study the case in which classical communication takes place over noisy channels, and we propose to address the design of LOCC protocols in this setting via the use of quantum machine learning tools. We specifically focus on the important tasks of quantum entanglement distillation and quantum state discrimination, and implement local processing through parameterized quantum circuits (PQCs) that are optimized to maximize the average fidelity and average success probability in the respective tasks, while accounting for communication errors. The introduced approach, Noise Aware-LOCCNet (NA-LOCCNet), is shown to have significant advantages over existing protocols designed for noiseless communications. [ABSTRACT FROM AUTHOR]

We introduce the quantum-house effect, a non-local quantum phenomenon which goes against classical intuition. We show how the effect can be achieved with any bipartite quantum state where neither subsystem is in a pure state. Besides its theoretical description, the quantum-house effect is also demonstrated on SpinQ Gemini, a 2-qubit liquid-state NMR desktop quantum computer. [ABSTRACT FROM AUTHOR]

An arbitrary amount of entanglement shared among nodes of a quantum network might be nondistillable if the nodes lack the information on the entangled Bell pairs they share. Making such a system distillable, which is called the superactivation of bound entanglement (BE), was shown to be possible through systematic quantum teleportation between the nodes, requiring the implementation of controlled-gates scaling with the number of nodes. In this work, we show in two scenarios that the superactivation of BE is possible if nodes implement the proposed local quantum Zeno strategies based on only single qubit rotations and simple threshold measurements. In the first scenario we consider, we obtain a two-qubit distillable entanglement system as in the original superactivation proposal. In the second scenario, we show that superactivation can be achieved among the entire network of eight qubits in five nodes. In addition to obtaining all-particle distillable entanglement, the overall entanglement of the system in terms of the sum of bipartite cuts is increased. We also design a general algorithm with variable greediness for optimizing the QZD evolution tasks. Implementing our algorithm for the second scenario, we show that a significant improvement can be obtained by driving the initial BE system into a maximally entangled state. We believe our work contributes to quantum technologies from both practical and fundamental perspectives bridging nonlocality, bound entanglement and the quantum Zeno dynamics among a quantum network. [ABSTRACT FROM AUTHOR]

We investigated influence of multiwalled carbon nanotubes (CNT) on spectral characteristics of composites “rubber-carbon nanotubes” on the base of butadiene-nitrile rubber at 0–10 % of CNTs. IR reflectance maxima of composites were measured in the spectral area of the rubber CH deformation and valence vibrations. IR absorption spectra of composites “rubber-carbon nanotubes” after vulcanization includes some giant two-polar oscillations. IR absorption spectrum of composites “rubber-carbon nanotubes” at 1 % of CNTs without vulcanization includes the alone two-polar oscillation. Two-photon interference is a result of quantum entanglement of dipole-active vibrations and photon splitting according to Hong-Ou-Mandel (HOM) quantum effect. Two-photon maximal entanglement saturation is called as Bell states. HOM quantum effect is perspective for high-coherent optical quantum computers on composites “rubber-carbon nanotubes”. [ABSTRACT FROM AUTHOR]

Quantum imaging algorithm is modified to reduce the complexity of the quantum circuit. Simplification was done by replacing nonlinear optical elements by linear elements which allow one to obtain conventional quantum entanglement operator. The obtained results show the expected efficiency of data transmission. Quantum error correction is used to improve the quality of image transmission. Modelling of image transmission with classic quantum computer interpreter is suggested. [ABSTRACT FROM AUTHOR]

Quantum communications is a promising technology that will play a fundamental role in the design of future networks. In fact, significant efforts are being undertaken by both the quantum physics and the classical communications communities on developing new architectures, solutions, and practical implementations of quantum communication networks (QCNs). Although these efforts led to various advances in today's technologies, there still exists a non-trivial gap between the research efforts of the two communities on designing and optimizing the performance of QCNs. For instance, most prior works by the classical communications community ignore important quantum physics-based constraints when designing QCNs. For example, many existing works on entanglement distribution do not account for the decoherence of qubits inside quantum memories and, thus, their designs become impractical since they assume an infinite lifetime of quantum states. In this article, we bring forth a novel analysis of the performance of QCNs in a physics-informed manner, by relying on the quantum physics principles that underly the different components of QCNs. The need for the physics-informed approach is then assessed and its fundamental role in designing practical QCNs is analyzed across various open research areas. Moreover, we identify novel physics-informed performance metrics and controls that enable QCNs to leverage the state-of-theart advancements in quantum technologies to enhance their performance. Finally, we analyze multiple pressing challenges and open research directions in QCNs that must be treated using a physics-informed approach to lead practically viable results. Ultimately, this work attempts to bridge the gap between the classical communications and the quantum physics communities in the area of QCNs to foster the development of the future communication networks toward the quantum Internet. [ABSTRACT FROM AUTHOR]

It is well known that physical phenomena may be of great help in computing some difficult problems efficiently. A typical example is prime factorization that may be solved in polynomial time by exploiting quantum entanglement on a quantum computer. There are, however, other types of (non-quantum) physical properties that one may leverage to compute efficiently a wide range of hard problems. In this perspective, we discuss how to employ one such property, memory (time non-locality), in a novel physics-based approach to computation: Memcomputing. In particular, we focus on digital memcomputing machines (DMMs) that are scalable. DMMs can be realized with non-linear dynamical systems with memory. The latter property allows the realization of a new type of Boolean logic, one that is self-organizing. Self-organizing logic gates are “terminal-agnostic,” namely, they do not distinguish between the input and output terminals. When appropriately assembled to represent a given combinatorial/optimization problem, the corresponding self-organizing circuit converges to the equilibrium points that express the solutions of the problem at hand. In doing so, DMMs take advantage of the long-range order that develops during the transient dynamics. This collective dynamical behavior, reminiscent of a phase transition, or even the “edge of chaos,” is mediated by families of classical trajectories (instantons) that connect critical points of increasing stability in the system's phase space. The topological character of the solution search renders DMMs robust against noise and structural disorder. Since DMMs are non-quantum systems described by ordinary differential equations, not only can they be built in hardware with the available technology, they can also be simulated efficiently on modern classical computers. As an example, we will show the polynomial-time solution of the subset-sum problem for the worst cases, and point to other types of hard problems where simulations of DMMs' equations of motion on classical computers have already demonstrated substantial advantages over traditional approaches. We conclude this article by outlining further directions of study. [ABSTRACT FROM AUTHOR]

The dawn of quantum computing brings on a revolution in the way combinatorially complex power system problems such as Unit Commitment are solved. The Unit Commitment problem complexity is expected to increase in the future because of the trend toward the increase of penetration of intermittent renewables. Even though quantum computing has proven effective for solving a host of problems, its applications for power systems’ problems have been rather limited. In this paper, a quantum unit commitment is innovatively formulated and the quantum version of the decomposition and coordination alternate direction method of multipliers (ADMM) is established. The above is achieved by devising quantum algorithms and by exploiting the superposition and entanglement of quantum bits (qubits) for solving subproblems, which are then coordinated through ADMM to obtain feasible solutions. The main contributions of this paper include: 1) the innovative development of a quantum model for Unit Commitment; 2) development of decomposition and coordination-supported framework which paves the way for the utilization of limited quantum resources to potentially solve the large-scale discrete optimization problems; 3) devising the novel quantum distributed unit commitment (QDUC) to solve the problem in a larger scale than currently available quantum computers are capable of solving. The QDUC results are compared with those from its classical counterpart, which validate the efficacy of quantum computing. [ABSTRACT FROM AUTHOR]

Employing the single item search algorithm of N dimensional database it is shown that: First, the entanglement developed between two any-size parts of database space varies periodically during the course of searching. The periodic entanglement of the associated reduced density matrix quantified by several entanglement measures (linear entropy, von Neumann, Renyi), is found to vanish with period O (s q r t (N)) . Second, functions of equal entanglement are shown to vary also with equal period. Both those phenomena, based on size-independent database bi-partition, manifest a general scale invariant property of entanglement in quantum search. Third, measuring the entanglement periodicity via the number of searching steps between successive canceling out, determines N, the database set cardinality, quadratically faster than ordinary counting. An operational setting that includes an Entropy observable and its quantum circuits realization is also provided for implementing fast counting. Rigging the marked item initial probability, either by initial advice or by guessing, improves hyper-quadratically the performance of those phenomena. [ABSTRACT FROM AUTHOR]

Clifford group lies at the core of quantum computation—it underlies quantum error correction, its elements can be used to perform magic state distillation and they form randomized benchmarking protocols, Clifford group is used to study quantum entanglement, and more. The ability to utilize Clifford group elements in practice relies heavily on the efficiency of their circuit-level implementation. Finding short circuits is a hard problem; despite Clifford group being finite, its size grows quickly with the number of qubits n, limiting known optimal implementations to n = 4 qubits. For n = 6, the number of Clifford group elements is about 2.1 × 1023. In this paper, we report a set of algorithms, along with their C++ implementation, that implicitly synthesize optimal circuits for all 6-qubit Clifford group elements by storing a subset of the latter in a database of size 2.1TB (1kB = 1024B). We demonstrate how to extract arbitrary optimal 6-qubit Clifford circuit in 0.0009358 and 0.0006274 s using consumer- and enterprise-grade computers (hardware) respectively, while relying on this database. We use this implementation to establish a new example of quantum advantage by Clifford circuits over CNOT gate circuits and find optimal Clifford 2-designs for up to 4 qubits. [ABSTRACT FROM AUTHOR]