Search

With the rapid development of quantum computing technology, the traditional cryptosystem will face a significant threat. It is an urgent security issue to study the security impact of quantum computing on classical cryptosystems and provide reliable cryptographic primitives for the post-quantum era. A powerful way to solve this problem is to quantize the classical cryptanalysis tools and use the improved versions for cryptanalysis. In this paper, we propose a quantum Zero-correlation analysis algorithm based on the Bernstein–Vazirani and Grover algorithms. It can find zero-correlation linear hulls for Feistel and SPN structures. We prove the correctness of the algorithm and analyze its complexity. Compared with the classical algorithms, the proposed quantum algorithm has significant advantages when the number of encryption rounds of block ciphers is large. Moreover, compared with the existing quantum Zero-correlation linear analysis, the proposed algorithm is more efficient and does not depend on the algebraic characteristics of the target cipher, which makes the algorithm has more flexible application scenarios. With the development of quantum computers, we discuss the threat of quantum cryptanalysis algorithms to classical security. [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 walks are referred to as quantum analogs to random walks in mathematics. They have been studied as quantum algorithms in quantum information for quantum computers. There are two types of quantum walks. One is the discrete-time quantum walk and the other is the continuous-time quantum walk. We study a continuous-time quantum walk on the half line and challenge to find a limit theorem for it in this paper. As a result, approximate behavior of the quantum walker is revealed after the system of quantum walk gets updated in long time. [ABSTRACT FROM AUTHOR]

Here, we propose the use of the majorization-based indicator for quantum computation complexity introduced in Vallejos et al. (Phys. Rev. A 104:012602, 2021) as a tool to benchmark the complexity within reach of quantum processors, when taking into account hardware and noise constraints. By considering specific qubit systems and native gate sets of currently available technologies, we numerically simulate the operation of various quantum processors in the presence of typical types of noise. We characterize their complexity for different native gate sets, qubit connectivity, and increasing number of gates. We identify and assess quantum complexity by comparing the performance of each device against benchmark lines provided by randomized Clifford circuits and Haar-random pure states. In this way, we are able to specify, for each specific processor, the number of native quantum gates which are necessary, on average, for achieving those levels of complexity. Moving toward real implementations, our results validate the use of the majorization-based indicator in the presence of noise. We determine how much noise one quantum processor can admit while maintaining high levels of complexity. Our benchmarking procedure can thus be used to set target levels for noise in quantum processors, while taking into account their physical constraints. [ABSTRACT FROM AUTHOR]

Quantum computing is a new discipline combining quantum mechanics and computer science, which is expected to solve technical problems that are difficult for classical computers to solve efficiently. At present, quantum algorithms and hardware continue to develop at a high speed, but due to the serious constraints of quantum devices, such as the limited numbers of qubits and circuit depth, the fault-tolerant quantum computing will not be available in the near future. Variational quantum algorithms(VQAs) using classical optimizers to train parameterized quantum circuits have emerged as the main strategy to address these constraints. However, VQAs still have many challenges, such as trainability, hardware noise, expressibility and entangling capability. The fundamental concepts and applications of VQAs are reviewed. Then, strategies are introduced to overcome the challenges of VQAs and the importance of further researching VQAs is highlighted. [ABSTRACT FROM AUTHOR]

Facial expressions bring human interactions to life with nonverbal cues that convey hues of emotions, feelings, and cultural intent. Analyzing these expressions is essential in the age of digital transformation. Traditional approaches to real-time facial expression analysis have limitations in capturing the complexity of these expressions and consume enormous computational power. The promising computing capacity of quantum computers is poised to solve current problems and set new standards by meeting growing demands. We have created a hybrid model that leverages the capabilities of the classical and quantum domains. The proposed model uses a quantum distance-based classifier along with classical artificial neural networks to perform real-time facial expression analysis and classification. Based on a thorough review of the literature, this novel and comprehensive work is, to the best of our knowledge, one of the few that addresses eight different emotions in the quantum domain. The implementation of a novel quantum error correction method has improved the accuracy of this hybrid model. Our model was trained on the CK+ facial expression database. To ensure fairness of the study, we tested our model on the largest facial expression database, AffectNet-8, and compared the performance with state-of-the-art models. Our model accuracy is 10.83% higher than that of the state-of-the-art models. From a holistic perspective, our proposed novel hybrid model appears to have universal value for all kinds of real-time image analysis and classification problems. As we move forward, we planned to focus on quantum neural networks for image processing and facial expression analysis. [ABSTRACT FROM AUTHOR]

Secure multiparty computation (SMC) provides collaboration among multiple parties, ensuring the confidentiality of their private information. However, classical SMC implementations encounter significant security and efficiency challenges. Resorting to the entangled Greenberger–Horne–Zeilinger (GHZ) state, we propose a quantum-based two-party protocol to compute binary Boolean functions, with the help of a third party. We exploit a technique in which a random Z-phase rotation on the GHZ state is performed to achieve higher security. The security and complexity analyses demonstrate the feasibility and improved security of our scheme compared to other SMC Boolean function computation methods. Additionally, we implemented the proposed protocol on the IBM QisKit and found consistent outcomes that validate the protocol's correctness. [ABSTRACT FROM AUTHOR]

To share images securely in the network, this paper proposes a multiparty sharing of quantum images scheme based on the basic theory of quantum state sharing. According to the number of qubits within the shared quantum image and involved participants, the product state of a certain number of maximal entanglement GHZ state with specific qubits has been chosen to act as quantum channel. To achieve the process of quantum image sharing, the dealer Alice performs local unitary operations of the Controlled-NOT gate and Hadamard gate as well as single-qubit measurement operation, and other assistant participants perform single-qubit measurement operation. On basis of Alice's and other participants' measurement results, the assigned participant can reconstruct the shared quantum image on his local qubits via performing local unitary operations. Since all participants in present scheme only need perform the single-qubit measurement operations, it makes the present scheme more realizable than former similar schemes. The comparisons illustrate that the present scheme possesses higher qubit efficiency. Security analysis proves that the present scheme is immune to the intercept-resend and entangled probe attacks of a third party. [ABSTRACT FROM AUTHOR]

Quantum computing has made many important achievements in the field of cryptanalysis. However, due to the limitations of current physical system and technology, the realization of large-scale universal quantum computers is a long way off. Currently, small-scale quantum computers are easier to implement than large-scale universal quantum computers. Distributed quantum computing proposes an implementation architecture, which attempts to break down large-scale tasks into many sub-tasks distributed across multiple small-scale quantum computers. How to use small-scale quantum computers with fewer qubits and shallower quantum depths to complete large-scale tasks and improve the success rate of attacking symmetric cryptosystems is our concern. In this paper, we propose a distributed exact Simon's algorithm, apply it to achieve quantum key recovery attacks on single-permutation-based pseudorandom cryptographic schemes with classical birthday bound security, and estimate the quantum resources of quantum circuits. Furthermore, we combine distributed exact Grover's algorithm and distributed exact Simon's algorithm to achieve quantum key recovery attacks on two-permutation-based pseudorandom cryptographic schemes with classical beyond birthday bound security and estimate the corresponding quantum resources. Our results show that (1) our algorithms are exact which means that the theoretical success probability of attacking pseudorandom cryptographic schemes is 100%; (2) the depth of circuit is in polynomial time which means that the theoretical depth of attacking symmetric cryptosystems is exponentially accelerated relative to the previous results; (3) the qubits of circuit don't increase significantly. Our work is of great importance. It could lead to the rapid realization of effective quantum attacks against symmetric cryptosystems on small-scale quantum computers. [ABSTRACT FROM AUTHOR]

Quantum error mitigation is becoming increasingly crucial. We have reformulated the expression of the Pauli channel, termed as the Z-mixed-state expression of the Pauli channel (ZMSEPC). Based on this expression, we have studied the changes of measurement expectation values after composing multiple Pauli channels and proposed related theorems. Afterward, we proposed a method called quantum error mitigation based on the Z-mixed-state expression of the Pauli channel (QEM-ZMSEPC) that can mitigate both quantum gate noise and quantum measurement noise, which offers a lower complexity compared to traditional measurement error mitigation methods. We have conducted experiments for the QEM-ZMSEPC method on classical computers and real quantum computers. The results demonstrate that compared to zero noise extrapolation method, QEM-ZMSEPC has superior error mitigation effects. Furthermore, our experimental results demonstrate the potential of the QEM-ZMSEPC combining other error mitigation techniques such as Pauli twirling. These positive results imply the significance of QEM-ZMSEPC. [ABSTRACT FROM AUTHOR]

This work introduces the use of a variational quantum circuit in order to perform unitary decomposition of a quantum operator. By use of classical optimization techniques and exploiting correlations and entanglement, the variational quantum circuit is able to translate a wide range of quantum algorithms, including the Toffoli gate and random unitary. A case study is also presented, where this decomposition is used to decompose a unitary matrix arise from a classification task. [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]

We explore the relationship between entropy and quantum measurements and present a variational algorithm for preparing statistical ensembles on quantum computers using mid-circuit measurements. This algorithm optimizes both the entropy and variational parameters describing the state to obtain the minimum free energy of quantum systems in thermal equilibrium with some external heat bath. We demonstrate our algorithm on IBM-Q Lagos. [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]

The foundation of this research is the quantum implementation of two hashing algorithms, namely Secure Hash Algorithm (SHA1) and Message Digest (MD5). Quantum cryptography is a challenging topic in network security for future networks. Quantum cryptography is an outgrowth of two broad topics—cryptology and cryptanalysis. In this paper, SHA1 and MD5 algorithms are designed and implemented for quantum computers. The main aim is to study and investigate the time requirement to build a hash and the bit rate at which a hash value is sent through. In this paper, a comprehensive analysis of these two algorithms is performed. Experiments have been done to compare and contrast the performances of the classical and proposed algorithms. In the experiment, it was found that the total time of execution of quantum SHA1 and quantum MD5 is much higher than the classical SHA1 and MD5. During quantum MD5 execution, it is observed that the time doubles when the number of chunks is increased from 1 to 2. Another experimental observation is that the execution time of the implemented algorithms depends upon the processor's speed. [ABSTRACT FROM AUTHOR]

Variational quantum circuits are one of the promising ways to exploit the advantages of quantum computing in the noisy intermediate-scale quantum technology era. The design of the quantum circuit architecture might greatly affect the performance capability of the quantum algorithms. The quantum architecture search is the process of automatically designing quantum circuit architecture, aiming at finding the optimal quantum circuit composition architecture by the algorithm for a given task, so that the algorithm can learn to design the circuit architecture. Compared to manual design, quantum architecture search algorithms are more effective in finding quantum circuits with better performance capabilities. In this paper, based on the deep reinforcement learning, we propose an approach for quantum circuit architecture search. The sampling of the circuit architecture is learnt through reinforcement learning-based controller. Layer-based search is also used to accelerate the computational efficiency of the search algorithm. Applying to data classification tasks, we show that the method can search for quantum circuit architectures with better accuracies. Moreover, the circuit has a smaller number of quantum gates and parameters. [ABSTRACT FROM AUTHOR]

It is known that Mermin–Peres-like proofs of quantum contextuality can furnish non-local games with a guaranteed quantum strategy, when classically no such guarantee can exist. This phenomenon, also called quantum pseudo-telepathy, has been studied in the case of the so-called Mermin magic square game. In this paper, we review in detail two different ways of implementing on a quantum computer such a game and propose a new Doily game based on the geometry of 2-qubit Pauli group. We show that the quantumness of these games is almost revealed when we play them on the IBM Quantum Experience; however, the inherent noise in the available quantum machines prevents a full demonstration of the non-classical aspects. [ABSTRACT FROM AUTHOR]

One of the main important features of the noisy intermediate-scale quantum (NISQ) era is the correct evaluation and consideration of errors. In this paper, we analyse the main sources of errors in current (IBM) quantum computers and we present a useful tool (TED-qc) designed to facilitate the total error probability expected for any quantum circuit. We propose this total error probability as the best way to estimate a lower bound for the fidelity in the NISQ era, avoiding the necessity of comparing the quantum calculations with any classical one. In order to contrast the robustness of our tool we compute the total error probability that may occur in three different quantum models: 1) the Ising model, 2) the Quantum-Phase Estimation (QPE), and 3) the Grover's algorithm. For each model, the main quantities of interest are computed and benchmarked against the reference simulator's results as a function of the error probability for a representative and statistically significant sample size. The analysis is satisfactory in more than the 99 % of the cases. In addition, we study how error mitigation techniques are able to eliminate the noise induced during the measurement. These results have been calculated for the IBM quantum computers, but both the tool and the analysis can be easily extended to any other quantum computer. [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]

The no-quantum broadcasting theorem which is a weaker version of the nocloning theorem restricts us from broadcasting completely unknown quantum information to multiple users. However, if the sender is aware of the quantum information (state) to be broadcasted, then the above restriction disappears and the task reduces to a multiparty remote state preparation. Without recognizing this fact, several schemes for broadcasting of known quantum states have been proposed in the recent past and erroneously/misleadingly referred to as protocols for quantum broadcasting (e.g., Yu et al. in Quant Inf Process 16(2):41, 2017 presented a technically correct scheme for multiparty remote state preparation which can at best be referred to as broadcasting of known quantum states, but referred to it as a scheme for quantum broadcasting). Here, we elaborate on the relation between the protocols of remote state preparation and those of broadcasting of known quantum information and show that it is possible to broadcast known quantum information to multiple receivers in deterministic as well as probabilistic manner with optimal resources. Further, the effect of noise on such schemes, and some new facets (like joint broadcasting) of such schemes have been discussed. A proof of principle realization of the proposed optimal scheme using an IBM quantum computer is also reported. Possibilities of generalizations of the so-called broadcasting schemes and potential applications are also discussed with appropriate importance. [ABSTRACT FROM AUTHOR]

The quantum convolutional neural networks (QCNNs) are emerging as a promising solution for image classification problems on near-term quantum devices. While QCNNs have shown encouraging results in binary classification tasks, their effectiveness in more complex multiclass classification tasks remains to be fully understood. In this study, we propose three distinct QCNN architectures, each inspired by the configuration of two-qubit entangling blocks available in quantum hardware. These QCNNs are designed based on different sliding modes of quantum filters. We investigate the impact of quantum filter structure, filter arrangement and parameter sharing among filters on the performance of QCNNs in multiclass classification. Our findings indicate that the specific structure of the quantum filter significantly affects the models' performance. Moreover, we observed that unsharring parameters and more complex filter arrangements can significantly enhance the performance of QCNNs. These results contribute to the development of powerful quantum classifiers for multiclass image classification. [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]

Grover's algorithm has been widely used for quantum key search to attack block ciphers with a quadratic speedup as compared to classical brute-force attacks and also used for evaluating the post-quantum security of block ciphers against quantum computer attack. But, this quantum key search on block ciphers has a high quantum circuit depth and AES-128 is still secure against such attack. In this paper, we introduce a method called the depth–measurement trade-off method that reduces the overall quantum circuit depth of quantum key search to attack block ciphers by increasing the number of measurements of the circuit. This method is to introduce dummy keys in the quantum circuit as part of the correct key. This will reduce both quantum circuit resource and quantum circuit depth. Based on this technique, the quantum circuit depth of AES-128 is less than 2 64 , while NIST suggested circuit depth should be greater than MAXDEPTH, which is 2 40 , 2 64 and 2 96 in order to resist the respective attacks. In addition, we also simulated the depth–measurement trade-off method on the reduced SIMON block cipher algorithm as a proof of concept. Furthermore, we also apply the depth–measurement technique on various block ciphers, for example AES, PRESENT, SIMON, GIFT, SPECK, RECTANGLE, LowMC, KNOT, PIPO, etc. [ABSTRACT FROM AUTHOR]

Landauer's bound is applicable to irreversible quantum operations. In this study, we showcased that the Doppler temperature manifests the existence of Landauer's bound, which does not block a spin from (irreversibly) flipping with a tiny amount of energy via quantum tunneling. Verified by a spin–spin magnetic interaction experiment, this (energy) amount was determined to be only 1.25 times the theoretical value of Landauer's bound. Based on Heisenberg's principle, we defined information from a measuring perspective: one bit of information corresponds to the smallest error when quantifying the product of the measured energy uncertainty ( Δ E ) and the measured time duration ( Δ t ). We then illustrate an optically manipulated, spin-encoded, near-Landauer-bound, near-Heisenberg-limit quantum computer that encompasses this new definition of information. This study may represent the last piece of the puzzle in understanding both quantum Landauer erasure and Heisenberg's quantum limit since a single spin is the smallest information carrier. [ABSTRACT FROM AUTHOR]

In this paper, we present some new key-recovery attacks on Misty L-KF, Misty R-KF, and generalized Feistel schemes. Firstly, we propose a new 5-round distinguisher on Misty L-KF structure. Based on our new distinguisher attack, we propose a new 6-round Demiric–Selçuk meet-in-the-middle attack (DS-MITM attack) against Misty L-KF structure. Secondly, we extend our classical DS-MITM attack to a new quantum DS-MITM attack on Misty L-KF structure by using the quantum claw finding algorithm. In addition, we apply the above method to attack Misty R-KF and generalized Feistel schemes. To sum up, we construct our classical key-recovery attacks on the 6-round Misty L-KF structure and Misty R-KF structure with O (2 3 n / 4) time and O (2 n / 2) memory cost. By using a quantum computer, our new quantum key-recovery attacks on the 6-round Misty L-KF structures and Misty R-KF structures can be constructed with O ~ (2 n / 2) time and O (2 n / 2) memory cost. Furthermore, we can construct our new quantum (5 d - 4) -round key-recovery attacks on the d-branch contracting Feistels with O ~ (2 (d - 1) n / d) time and O (2 (d - 1) n / d) memory cost. In the end, we can construct our new quantum (4 d - 3) -round and (5 d - 4) -round key-recovery attacks on the two types of d-branch expanding Feistels with O ~ (2 (d - 1) n / d) time and O (2 (d - 1) n / d) memory cost. [ABSTRACT FROM AUTHOR]

This article explores the critical aspect of error mitigation within quantum systems, particularly its significance in enabling secure qutrit distribution via Cleve's protocol. Initially, it investigates quantum secret sharing utilizing a (k, n) threshold scheme, demonstrating its cryptographic robustness in securely disseminating secrets among multiple parties. Subsequently, a comprehensive analysis is conducted to elucidate the nuanced impact of bit-flip, phase-flip, and depolarization errors on quantum data integrity, highlighting the necessity for tailored error mitigation strategies. Within the context of a Quantum Neural Q Network (QNQN), error correction techniques are applied to classification outcomes, showcasing their efficacy in rectifying states uniformly despite initial errors. This underscores the critical importance of error mitigation in preserving data accuracy and integrity in quantum computations and secure qutrit distribution methodologies, particularly within the framework of Cleve's protocol. [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]

Quantum multidimensional scaling is a quantum dimensionality reduction algorithm. Its complex quantum circuit design structure and excessive qubits consumption make it difficult to run on the current quantum computers. In order to solve this problem, this paper proposes the variational quantum multidimensional scaling algorithm based on the variational quantum algorithm. Utilizing the parallel advantages of quantum computing to quickly compute low-dimensional embeddings of high-dimensional data, the variational quantum multidimensional scaling algorithm can provide lower time complexity; compared with the non-variational quantum multidimensional scaling algorithm, the variational quantum multidimensional scaling algorithm provides a simpler quantum circuit. In the noisy intermediate scale quantum era, the algorithm can run on a quantum computer. In addition, the article finally implemented the variational quantum multidimensional scaling algorithm on the Qiskit framework, proving the correctness of the algorithm. [ABSTRACT FROM AUTHOR]

This paper promotes reinforcement machine learning for route-finding tasks in quantum communication networks, where, due to the non-additivity of quantum errors, classical graph path or tree-finding algorithms cannot be used. We propose using a proximal policy optimization algorithm capable of finding routes in teleportation-based quantum networks. This algorithm is benchmarked against the Monte Carlo search. The topology of our network resembles the proposed 6 G topology and analyzed that quantum errors correspond to typical errors in realistic quantum channels. [ABSTRACT FROM AUTHOR]

Classical encryption protocols that are currently used to secure the internet and transmission control protocol/internet protocol (TCP/IP) protocols will be subjected to high risks with the development and expansion of quantum computers with high processing power. Therefore, in recent years, secure quantum communication has been suggested as an alternative solution. Quantum secure communications based on quantum keys in fiber optics have high potential in modern communications. However, for designing a quantum key distribution (QKD) network, there will be widespread issues and problems that must be resolved in a way to establish secure and reliable communication between the two communication nodes in the network. Therefore, in this paper, for the first time, a seven-layer reference model called QTCP/IP is proposed in the partially trusted-node-based QKD-secured optical networks. In the proposed model, the layers are divided by functional independence, and each has protocols that specify its performance. In addition, the QTCP/IP model provides a practical solution for secure communication in current networks by being compatible with the TCP/IP model. Furthermore, in this proposed model, a QKD service is supplied, which provides quantum keys to the end users and the applications on demand to establish timely security requirements. Moreover in this reference model, a dynamic routing algorithm is proposed for transferring quantum keys. Our work has the potential to become a reference standard for a practical QKD network. [ABSTRACT FROM AUTHOR]

The emergence of quantum computers is having an impact on almost every field of engineering. Electrical drives, in particular, can benefit from the power of quantum computing. This paper presents a quantum version of the pulse-width modulation (PWM) algorithm, which is used widely to control electrical motors. The proposed algorithm is implemented using a real number comparator, which is novel to the authors' knowledge. Unlike other quantum comparators in the literature, which provide quantum versions of binary-based comparators, the suggested comparator compares real numbers ranging from 0 to 100%, making it more usable in practice for many industrial applications, particularly control. When applied to DC motor speed control, the quantum PWM controller achieved similar speed precision to the classical version, but with lower energy consumption and less switching. It could therefore significantly increase the lifetime of power devices while achieving similar control performance at lower energy consumption. [ABSTRACT FROM AUTHOR]

Quantum abstract detecting systems (QADS) provide a common framework to address detection problems in quantum computers. A particular QADS family, that of combinatorial QADS, has been proved to be useful for decision problems on eigenvalues or phase estimation methods. In this paper, we consider functional QADS, which not only have interesting theoretical properties (intrinsic detection ability, relation to the QFT), but also yield improved decision and phase estimation methods, as compared to combinatorial QADS. A first insight into the comparison with other phase estimation methods also shows promising results. [ABSTRACT FROM AUTHOR]

Portfolio optimization plays a central role in finance to obtain optimal portfolio allocations that aim to achieve certain investment goals. Portfolio optimization also provides a rich area to study the application of quantum computers to obtain advantages over classical computers. In a multi-period setting, we give a sampling version of an existing classical online portfolio optimization algorithm by Helmbold et al., for which we in turn develop a quantum version. The quantum advantage is achieved by using techniques such as quantum state preparation, inner product estimation and multi-sampling. Our quantum algorithm provides a quadratic speedup in the time complexity, in terms of n, where n is the number of assets in the portfolio. The transaction cost of both of our classical and quantum algorithms is independent of n which is especially useful for practical applications with a large number of assets. [ABSTRACT FROM AUTHOR]

Proposed by Hillery et al., Quantum Secret Sharing (QSS) is a technique used to break a quantum secret into multiple pieces (called Shares), such that any proper subset of the pieces does not reveal any information about the original secret. The secret can be reconstructed only when all of the pieces are combined together. However, most of the QSS protocols assume that the shares are untampered, hence fail to regenerate the original secret if some of the shares are damaged due to several reasons like cheating participants, eavesdropping, etc. In order to tackle this practical challenge, Resilient Quantum Secret Sharing (RQSS) protocols are required. In this paper, we propose an RQSS protocol that uses Quantum Error Correcting Codes (QECC) for share generation and secret reconstruction. Our protocol generates n shares of a m-qubit quantum secret, owned by the dealer, and distributes it among nparticipants; moreover, it can regenerate the original secret even if k < n shares are damaged. To the best of our knowledge, no such generalized protocol exists in the available literature. [ABSTRACT FROM AUTHOR]

The security of most quantum signatures cannot be proved with security model under chosen-message attack. No formal proof can prove that their security is fully dependent on the basic quantum theory. Based on the orthogonal quantum state and key-controlled quantum hash function, an arbitrated quantum signature is proposed. In this scheme, the signatory produces the quantum signature by quantum-encrypting the output of key-controlled quantum hash function. The signature verification is performed by decrypting the signed message and comparing the decrypted message with the output of the key-controlled quantum hash function. The security of the proposed scheme depends on the indistinguishability of the unknown quantum sequence. Its unforgeability can be formally proved with security model under chosen-message attack. Therefore, its security can be supported by the formal proof. On the other hand, in the proposed scheme, no entangled state is used. It also has better qubit efficiency as well. [ABSTRACT FROM AUTHOR]

Using the recent ability of quantum computers to initialize quantum states rapidly with high fidelity, we use a function operating on a discrete set to create a simple class of quantum channels. Fixed points and periodic orbits, that are present in the function, generate fixed points and periodic orbits in the associated quantum channel. Phenomenology such as periodic doubling is visible in a 6 qubit dephasing channel constructed from a truncated version of the logistic map. Using disjoint subsets, discrete function-generated channels can be constructed that preserve coherence within subspaces. Error correction procedures can be in this class as syndrome detection uses an initialized quantum register. A possible application for function-generated channels is in hybrid classical/quantum algorithms. We illustrate how these channels can aid in carrying out classical computations involving iteration of non-invertible functions on a quantum computer with the Euclidean algorithm for finding the greatest common divisor of two integers. [ABSTRACT FROM AUTHOR]

We propose a circuit optimization algorithm that facilitates the implementation of various applications on noise intermediate-scale quantum (NISQ) devices. The algorithm is hardware-independent and reduces the overall circuit cost of Hamiltonian simulation, particularly by minimizing the number of CNOT gates. Our approach employs a sub-circuit synthesis scheme for intermediate representation and proposes the practical template matching algorithm (TM) for gate elimination to minimize CNOT counts. This algorithm demonstrates low complexity and enhances the circuit performance of Hamiltonian simulations. In our simulations, we benchmarked different algorithms across various Hamiltonian models to quantify and compare the benefits of our approach. Compared with advanced generic compilers and specific quantum compilers, the results obtained from simulating our algorithm show an average reduction of 1.5 × (up to 2.56 × ) in CNOT counts, and 1.4 × (up to 3.1 × ) in circuit depth. This improvement further advances the practical application of Hamiltonian simulation in the NISQ era. [ABSTRACT FROM AUTHOR]

In recent years, quantum algorithms have emerged as a groundbreaking approach toward solving complex computational problems, particularly in physical modeling and artificial intelligence. This study introduces a novel quantum algorithm termed the duality game, tailored for addressing challenges in body dynamics modeling. The practicality and efficacy of the proposed algorithm are elucidated through three distinct data scenarios: (1) approximation of classical von Bertalanffy growth in the presence of random noise (simulated), (2) personalized tumor burden modeling leveraging a small dataset, and (3) modeling of COVID-19 population growth employing big data analytics. The algorithm's performance in these scenarios underscores its potential for practical applications at a large scale. Moreover, the findings foster optimism regarding the algorithm's promise in the burgeoning field of physical-based quantum artificial intelligence (quantum AI). Through the duality game, a pathway is delineated for addressing real-world problems in body dynamics, opening avenues for further research and development in quantum AI, aimed at harnessing quantum computational advantages for solving intricate physical modeling problems. [ABSTRACT FROM AUTHOR]

In recent years, quantum Boltzmann methods have gained more and more interest as they might provide a viable path toward solving fluid dynamics problems on quantum computers once this emerging compute technology has matured and fault-tolerant many-qubit systems become available. The major challenge in developing a start-to-end quantum algorithm for the Boltzmann equation consists in encoding relevant data efficiently in quantum bits (qubits) and formulating the streaming, collision and reflection steps as one comprehensive unitary operation. The current literature on quantum Boltzmann methods mostly proposes data encodings and quantum primitives for individual phases of the pipeline, assuming that they can be combined to a full algorithm. In this paper, we disprove this assumption by showing that for encodings commonly discussed in the literature, either the collision or the streaming step cannot be unitary. Building on this landmark result, we propose a novel encoding in which the number of qubits used to encode the velocity depends on the number of time steps one wishes to simulate, with the upper bound depending on the total number of grid points. In light of the non-unitarity result established for existing encodings, our encoding method is to the best of our knowledge the only one currently known that can be used for a start-to-end quantum Boltzmann solver where both the collision and the streaming step are implemented as a unitary operation. [ABSTRACT FROM AUTHOR]

We propose a quantum circuit that implements a delayed-choice quantum eraser via bipartite entanglement with the extension that the degree of entanglement between the two paired quantons is adjustable. This provides a broader setting to test complementarity relations between interference visibility and which-way distinguishability in the scenario that the which-way information is obtained through entanglement without direct contact with the quantum state for interference. The visibility-distinguishability relations are investigated from three perspectives that differ in how the which-way information is taken into consideration. These complementarity relations can be understood in terms of entropic uncertainty relations in the information-theoretic framework and the triality relation that incorporates single-particle and bipartite properties. We then perform experiments on the quantum computers provided by the IBM Quantum platform to verify the theoretical predictions. We also apply the delay gate to delay the measurement of the which-way information to affirm that the measurement can be made truly in the "delayed-choice" manner. [ABSTRACT FROM AUTHOR]

We present a number of new physical systems that may be addressed using methods of time dependent transformation. A recap of results available for two-state systems is given, with particular emphasis on the AC Stark effect. We give some results that are not well known, including the full solution for a two state system in a static electric field with arbitrary direction. Connection with established theorems in time optimal quantum control is given, and a full discussion outlines some advanced results in matrix calculus. In particular, we derive a set of matrix gates relevant to quantum information theory and computation using time optimal unitary operators, and define the hyperbolic equivalent of the quantum brachistochrone problem. [ABSTRACT FROM AUTHOR]

The introduction of quantum walk into quantum teleportation offers a new formation of entanglement between the position space and the coin space using a conditional shift operator. By considering discrete time quantum walks on the cycles, controlled quantum teleportation schemes which can teleport multiple qubits in the multi-dimensional Hilbert spaces are put forward. We also present a decoherence analysis of the proposed protocols in different environments containing dephasing, dissipative and noisy channels using Lindblad operators under the effect of Markovian and non-Markovian regimes. [ABSTRACT FROM AUTHOR]

In the noisy intermediate-scale quantum (NISQ) era, the computing power displayed by quantum computing hardware may be more advantageous than classical computers, but the emergence of the barren plateau (BP) has hindered quantum computing power and cannot solve large-scale problems. This summary analyzes the phenomenon of the BP in the quantum neural network that is rapidly developing in the NISQ era. This article will review the research status of the BP problem in the quantum neural network (QNN) in the past five years from the analysis of the source of the BP, the current stage solution, and the future research direction. First of all, the source of the BP was briefly explained and then classified the BP solution from different perspectives, including quantum embedding in QNN, ansatz parameter selection and structural design, and optimization algorithms. Finally, the BP problem in the QNN is summarized, and the research direction for solving problems in the future is made. [ABSTRACT FROM AUTHOR]

Timetable scheduling is a combinatorial optimization problem that presents formidable challenges for classical computers. This paper introduces a pioneering methodology for addressing the high-speed train timetabling problem through quantum computing. Initially, a comprehensive binary integer programming model, grounded in the space–time network, is proposed (M1). To manage the intricacy of model M1, a knapsack problem reformulation is employed to establish a simplified binary integer programming model (M2). Both M1 and M2 are subsequently converted into quadratic unconstrained binary optimization (QUBO) models to harness the potential of quantum computing. Several techniques, including the Gurobi solver, simulated annealing, and the coherent Ising machine (CIM) quantum simulator, are deployed to solve the model across four distinct scenarios of varying complexity. The findings indicate that CIM quantum simulator outperforms the simulated annealing method in terms of solution quality for medium-scale problems. [ABSTRACT FROM AUTHOR]

In recent years, blockchain technology has been established as a solution to a spectrum of issues associated with conventional financial systems, including but not limited to high transaction costs, slow processing times, and lack of transparency, leading to the proliferation of various digital assets and cryptocurrencies that are finding new use cases such as tokenization of real-world assets, access control systems, records management, etc. However, a significant impediment that has emerged is the need for interoperability between incompatible decentralized networks, which has thwarted the ability to exchange digital assets across these networks efficiently and securely. In this paper, the authors propose a novel quantum blockchain-enabled exchange protocol model (QBEEP) for the secure exchange of digital assets between various stakeholders on different decentralized networks, harnessing the potential of quantum computing, homomorphic encryption, and distributed ledgers. QBEEP is designed to be highly secure and transparent, ensuring stakeholders can trust the transaction's outcome. Furthermore, it addresses several challenges posed by quantum computing, including the susceptibility of traditional cryptographic systems to attacks by quantum computers. The authors use quantum key distribution and quantum-resistant cryptographic algorithms to ensure that the proposed model is secure against attacks by classical and quantum computers. The authors demonstrate the feasibility and effectiveness of QBEEP through simulation experiments, and the results show that the protocol is highly secure and efficient, with low overhead and fast execution time. The authors also compare QBEEP to existing solutions and show that it outperforms them in terms of security and efficiency. The proposed protocol provides a promising solution for the growing need for secure and efficient decentralized exchange platforms in the emerging digital economy. [ABSTRACT FROM AUTHOR]

Authentication is a security function that ensures the system's proper security by identifying and verifying users. Despite the advantages of quantum computers, it is still difficult to enforce authentication on behalf of multiple quantum channel users without the involvement of a third party because present protocols only consider two parties involved in communication. Scalability becomes an issue as the number of parties engaged in the quantum network increases. In addition, an eavesdropper may disguise herself among numerous participants and take advantage of the circumstances to gather information. The authentication method should be used throughout the quantum data exchange process to ensure that the parties participating in the protocol are who they claim to be. The suggested protocol's implementation has been tested using a simulation written in Python. This research aims to propose a protocol for multiparty authentication procedures without the assistance of a third party. The result of the proposed protocol is expected to be a simple and reliable quantum experiment. Importantly, this protocol can establish an environment that is more secure in terms of authentication and allows numerous parties to communicate freely and openly. [ABSTRACT FROM AUTHOR]

In the race for quantum computing supremacy, the key factor lies in maximizing the number of stable qubits by far, as each additional qubit doubles the computing power. Namely, it makes sense various ecosystems of organizations and developers gravitate toward these extraordinarily expensive supercomputers. Concurrently, the drive to democratize quantum computing has given rise to cloud-based operating systems built upon classical models. However, a growing demand forecast underscores the need for executing an infinite stream of near-real-time quantum tasks accessible via the cloud. This vacancy represents a potential boundary between quantum and classical operating systems. To address this, a refinement method called XIRAC-Q is introduced, which harnesses the principles of information theory for optimization. By maximizing the entropy toleration of the system, our approach enhances overall performance, particularly as the number of processes and tasks approaches infinity. Unlike the limited literature that has explored information theory principles solely for task priority alignment in classical computers, yielding limited advantage, our work integrates information theory and entropy in the design cycle of quantum operating system infrastructure. This paper highlights the novel advantages offered by the proposed paradigm, encompassing improved performance, scalability, and adaptability, which are thoroughly explained and explored. [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]

In recent years, there has been a growing interest in the potential of quantum computing for enhancing the security and efficiency of blockchain technology. While quantum blockchain protocols offer improved security over their classical counterparts, implementing such protocols on present-day quantum computers poses difficulties due to the limited number of qubits and quantum gates and the significant effects of noise. In this paper, we propose a set of improvements for implementing a quantum blockchain protocol based on hypergraphs that aim to reduce the required resources and operations and increase noise tolerance. Specifically, we focus on enhancing the state-of-the-art quantum circuits that underpin the quantum blockchain by optimizing the so-called T-count and T-depth, which represent the number of quantum gates and the circuit depth, respectively. Our proposed implementations also leverage proven error detection and correction codes to improve noise tolerance. To evaluate the effectiveness of our proposed improvements, we tested them on real quantum devices. Our results demonstrate a significant reduction in the T-count and T-depth. Overall, our proposed improvements provide a promising direction for the practical implementation of quantum blockchain protocols on current quantum computers and lay a foundation for further research in this area. [ABSTRACT FROM AUTHOR]

Due to Grover's algorithm, any exhaustive search attack of block ciphers can achieve a quadratic speed-up. To implement Grover's exhaustive search and accurately estimate the required resources, one needs to implement the target ciphers as quantum circuits. Recently, there has been increasing interest in quantum circuits implementing lightweight ciphers. In this paper, we present the quantum implementations and resource estimates of the lightweight ciphers LBlock and LiCi. We optimize the quantum circuit implementations in the number of gates, require qubits and the circuit depth, and simulate the quantum circuits on ProjectQ. Furthermore, based on the quantum implementations, we analyze the resources required for exhaustive key search attacks of LBlock and LiCi with Grover's algorithm. Finally, we compare the resources for implementing LBlock and LiCi with those of other lightweight ciphers. [ABSTRACT FROM AUTHOR]