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In the present work, a novel approach was proposed to optimize the teleportation cost in Distributed Quantum Circuits (DQCs) by applying a new approach. To overcome the difficulty with keeping a large number of qubits next to each other, DQCs, as a well-known solution, have always been employed. In a distributed quantum system, qubits are transferred from a subsystem to another subsystem by a quantum protocol such as teleportation. First, we proposed a heuristic approach through which we could replace the equivalent circuits in the initial quantum circuit. Then, we used a genetic algorithm to partition the placement of qubits so that the number of teleportations could be optimized for the communications of a DQC. Finally, results showed that the proposed approach could impressively work.

In this paper, we use exact matrix diagonalization to research property of the many-body localization (MBL) in the disordered Heisenberg XXX model with periodic driving. We get the periodic time-dependent external field by trigonometric function, which is added to periodically drive this model. It is demonstrated that the fidelity of eigenstate is able to capture quantum criticality underlying many-body physics (Zhou et al. Phys. Rev. Lett. 100, 080601, 2008, Zhou and Barjaktarevi J. Phys. A: Math. Theor. 41, 412001 2008), which can be used to characterize the many-body localization transition in this closed spin system (Zanardi and Paunkovic Phys. Rev. E 74, 031123, 2006). We obtain the fidelity for high-energy many-body eigenstates, namely, the excited state fidelity, which shows the phase transition of periodically driven Heisenberg XXX chain with different disordered external field strengths and different system sizes. It is demonstrated that when Heisenberg XXX system is in a very small disorder, periodic driving can cause the occurrence of a transition from ergodic phase to MBL phase. In contrast to the HS model which has global two-body interaction, which we have studied recently with the same situation, there is no MBL phase transition when we drive the HS model in ergodic phase with periodic driving. It also shows that for the strong disordered Heisenberg XXX system, there will exist a critical driving period Tc, when driving period T is higher than Tc, the system will undergo a transition from localized phase to ergodic phase and the MBL phase will be broken. Furthermore, we discover that the size of the system and the strength of disorder will affect the critical point of driving period and the magnitude of the phase change. For the same system, the critical point increases as the strength of disorder increases. We also explore the non-disorder system of HS model with the same driving to explore the properties of MBL, it shows that under periodic driving, the non-disordered HS system has the quantum phase transition rather than MBL phase transition. This illustrates the important role of disorder on MBL.

We propose a bidirectional controlled teleportation scheme using two pairs of Bell states as quantum channels. This solution uses Charlie as the controlled party. After two Bell state measurements, while Alice sends any single particle state to Bob, Bob can also send any single particle state to Alice, thus successfully completing the bidirectional controlled teleportation. Our plan is also compared with several other protocols from five aspects to illustrate that the plan has certain advantages. This makes our scheme relatively simpler and easier to implement and more maneuverable.

We explore quantum multi-parameter estimation, based on quantum Fisher information matrix (QFIM), in an extended anisotropic XY spin chain associated with non-trivial topological characterization driven by varying system parameters (i.e., magnetic field λ, the anisotropic of the nearest-neighbor interaction γ, the next-nearest-neighbor interaction α and its anisotropy δ). The results show that QFIM can provide us a useful tool to detect the topological critical points in this model. Furthermore, we find that the behavior of QFIM associated with variance of estimators are driving parameters dependent at different topological quantum phase transition points. Meanwhile, the choice of estimators $\hat {\theta }$ also take a prominent role on the behavior of QFIM.

Quantum image scaling is an important branch of quantum image processing and has been extensively studied in recent years. A quantum image scaling algorithm based on bilinear interpolation is proposed in this paper. This algorithm can scale the image of any floating point number scale. Quantum arithmetics for floating point numbers are proposed, and quantum algorithms for quantum image scaling up and down are presented. Moreover, the quantum circuits of quantum image scaling are designed and their network complexity is analyzed. With the results of simulation experiment on the classical computer MATLAB software, it is demonstrated that the proposed quantum image scaling algorithms have the good effect.

The analog multicolor optomechanically induced transparency (OMIT) of distant optomechanical system is studied. The two charged mechanical oscillators couple to each other via Coulomb interaction, and the atomic ensemble is introduced into the hybrid system. We focus on the width of OMIT windows which is manipulated by some interference effects of the system components. The research shows that five transparency windows can be observed from the output field at the probe frequency. In the absence of some internal interactions, the number of transparent windows will reduce. Furthermore, the width and the number of the transparent windows are affected by the coupling strength between the optical mode and the mechanical mode, between the optical mode and atoms and the Rabi frequency, between the two optical modes, as well as the Coulomb coupling between the two charged oscillators. It is feasible for our approach to manipulate multiple optomechanically induced transparency, which provides potential applications in quantum information processing and quantum net works.

In this paper, we study cyclic codes over a finite non-chain ring $\mathbb {F}_{p^{m}}+v\mathbb {F}_{p^{m}}$ with v2 = 1 and find new and better quantum error-correcting codes than previously known quantum error correcting codes over $\mathbb {F}_{p^{m}}$ . Therewith, we characterize the LCD codes and obtain many new LCD codes. Also, we prove that the Gray map of an LCD code of length n over $\mathbb {F}_{p^{m}}+v\mathbb {F}_{p^{m}}$ is an LCD code of length 2n over $\mathbb {F}_{p^{m}}$ .

Quantum enhancement of the optical behavior for V −type open atomic system is examined analytically. With consideration of the system which contain N number of atoms, it is derived that the evolution of the atomic variable evolution with respect to time. At steady state, the optical properties of the system have been analyzed. The phase between the upper doublet levels is influencing the optical parameters change in the system. It is observed that for small values of the phase between the upper doublet energy states, the better refractive index of the atomic medium. The refractive index gets the peak value near to the resonance frequency of the probe field. The properties of the re-emitted light from ensemble of three-level atoms have been analyzed in details. In this regard, it is observed that the height of the power spectrum increased while the number of atoms are large in the sample.

Different from traditional signature schemes, the paper gives a novel protocol which uses quantum logic gates to perform operations on quantum states, and it realizes the quantum state representation of two classical information and uses mixed entangled states to measure information. The binary measurement results of the protocol are converted into blocks of a certain length, and these blocks are encrypted by quantum Fourier transform and transmitted through N-dimensional quantum states. In the proposed protocol, the quantum channel uses N-dimensional quantum states, which is more efficient than the currently proposed two-dimensional information carrier channel protocol. The security analysis of this article shows that the program is anti-counterfeit, undeniable and blind. In addition, compared with other existing efficiency analysis schemes, this scheme has higher signature efficiency.

We study the effect of unentangled states with nonzero discord on Quantum Stackelberg duopoly game (QSD). We show that the initial state parameter and quantum discord will cause remarkable change in the Nash equilibrium of the QSD game and the profits of the two players. We also find that under certain conditions there is a ‘specific point’ of the initial state parameter and quantum discord. The two players have the same moves and payoffs at the ‘specific point’. The QSD game can switch between the first-mover advantage game and the follower-mover advantage game when the initial state parameter and quantum discord varies from the left-hand-side regime of the ‘specific point’ to the right-hand-side regime.

In this paper, we investigate the entanglement of a quantum system containing two subsystems characterized by the angular momenta j1 and j2, in the framework of the superposition of spin coherent states. We formulate the measure of the entanglement in terms of the amplitudes of the spin coherent states as well as their spins j1 and j2. We extend this investigation to rank-two bipartite mixed states involving spin-j coherent states by using a simplified expression of concurrence. We show that the bipartite entanglement of mixed states is strongly dependent on the spin ji of each subsystem and the probabilities associated with it.

We study the interatomic energy and force of two ground-state atoms in interaction with the fluctuating quantum massless scalar field in vacuum with two different approaches, i.e. the stationary perturbation theory and the DDC formalism [the formalism proposed by Dalibard, Dupont-Roc and Cohen-Tannoudji]. With the DDC formalism, we calculate the interatomic energy in terms of the contributions of vacuum fluctuations and the contributions of the atomic radiation reaction. We find that, in the near region, the contributions of vacuum fluctuations is less important than the contributions of the atomic radiation reaction, and as a result, the interatomic force is attractive and proportional to L− 3. While in the far zone, the contributions of vacuum fluctuations and those of the atomic radiation reaction become equally important, and the interatomic force is attractive and proportional to L− 4. The interatomic energy and force derived with these two different approaches are accurately the same. We comment that the two different approaches deal with the interatomic interaction from different perspectives and have their own advantages.

Private set intersection(PSI) allows two parties to get all common elements of their private sets without leaking any information about their sets. In this paper, we present a novel PSI protocol which is based on quantum Fourier transform. Correctness analysis shows that our protocol can get the result correctly. And the security of our protocol is also analyzed, it can resist most of outside attacks, such as Trojan horse attack, intercept-resend attack, entanglement-and-measure attack, man-in-the-middle attack and so on. And it also can overcome participant attacks.

The exploration of quantum entanglement in multipartite quantum systems is of great significance to the study of quantum entanglement, maximally multi-qubit entangled state is one of the research objects. Recently, Che et al. presented a recurrence relation of multi-qubit state. According to this inspiration, we present the recurrence relation of maximally multi-qubit pure states of N-qubits for N = 6, 7, 8. Further, some new forms of the seven- and eight-qubit maximally entangled states are found with the recurrence relation.

Hardy’s paradox can demonstrate the conflict between quantum mechanics and local realism. Experimental testing of Hardy’s paradox has been carried out, but it involved only a few qubits. We propose a simple but novel approach to verify the generalized Hardy’s paradox and Hardy’s inequality using quantum programming. By designing scalable quantum circuits, we write quantum programs in Q# and corresponding classical controls in C# using Visual Studio. Our quantum simulation results are consistent with the original theoretical values; moreover, they can be easily extended to multiqubit systems. This provides an effective means for investigating multipartite entanglement question using quantum programming.

Quantum coherence, coming from quantum superposition, occupies a significant position in the field of physics. We put forward a lower bound of the robustness of multilevel coherence mathematically by optimizing the coherence witnesses via semi-definite programming, which can be direct and easy to evaluate and experimentally accessible. A numerical example is supplemented to illustrate the efficiency of the presented bound.

We consider entangled state production utilizing a full optomechanical arrangement, based on which we create entanglement between two far three-level V-type atoms using a quantum repeater protocol. At first, we consider eight identical atoms (1; 2;...; 8), while adjacent pairs (i; i + 1) with i = 1; 3; 5; 7 have been prepared in entangled states and the atoms 1, 8 are the two target atoms. The three-level atoms (1,2,3,4) and (5,6,7,8) distinctly become entangled with the system including optical and mechanical modes by performing the interaction in optomechanical cavities between atoms (2,3) and (6,7), respectively. Then, by operating appropriate measurements, instead of Bell state measurement which is a hard task in practical works, the entangled states of atoms (1,4) and (5,8) are achieved. Next, via interacting atoms (4,5) of the pairs (1,4) and (5,8) and operating proper measurement, the entangled state of target atoms (1,8) is obtained. In the continuation, entropy and success probability of the produced entangled state are then evaluated. It is observed that the time period of entropy is increased by increasing the mechanical frequency and by decreasing optomechanical coupling strength to the field modes. Also, in most cases, the maximum of success probability is increased by decreasing G and via decreasing.

Recently, Lang suggested a quantum private comparison (QPC) without classical computation (Int J Theor Phys, 59(2020)2984). Lang claimed that this QPC protocol is secure against both the participant attack and the outside attack. It is pointed out in this paper that the third party (TP) can totally obtain the private binary sequences of two communicants by launching a special measurement attack; and moreover, an outside attacker can make this protocol fail by launching the disturbance attack. The corresponding methods are further put forward to overcome these drawbacks.

We propose a new scheme to strengthen the performance of the discrete-modulated continuous-variable measurement-device-independent quantum key distribution (DM-CV-MDI-QKD) protocol by introducing a quantum scissors (QS) operation to Bob’s side. According to the equivalent one-way scheme of the protocol, we further investigate the success probability of the QS operation, and analyze the security of the DM-CV-MDI-QKD equipped with this operation in the asymptotic case. Simulation results show that the QS operation can indeed effectively improve the performance of the existing protocol, and compared with the scheme without QS operation, our proposed scheme has a higher secret key rate and a longer secure transmission distance.

Entanglement-assisted quantum maximum distance separable (MDS) codes form a significant class of quantum codes. By using constacyclic codes, we construct some new classes of q-ary entanglement-assisted quantum error-correcting MDS codes. Most of these codes are new in the sense that their parameters are not covered by the codes available in the literature.

With entanglement-assisted (EA) formalism, arbitrary classical linear codes are allowed to transform into EAQECCs by using pre-shared entanglement between the sender and the receiver. In this paper, based on classical cyclic MDS codes by exploiting pre-shared maximally entangled states, we construct two families of $q$-ary entanglement-assisted quantum MDS codes $[[\frac{q^{2}+1}{a},\frac{q^{2}+1}{a}-2(d-1)+c,d;c]]$, where q is a prime power in the form of $am+l$, and $a=(l^2+1)$ or $a=\frac{(l^2+1)}{5}$. We show that all of $q$-ary EAQMDS have minimum distance upper limit much larger than the known quantum MDS (QMDS) codes of the same length. Most of these $q$-ary EAQMDS codes are new in the sense that their parameters are not covered by the codes available in the literature., arXiv admin note: substantial text overlap with arXiv:1803.04168, arXiv:1912.12031

Quantum correlations are physical resources for quantum information processing. The nonlocal advantage of quantum coherence (NAQC) is a kind of quantum correlation which is stronger than entanglement. We report here methods for enhancing thermal NAQC in the two-site, triangular, and tetrahedral lattices. It is found that for all the considered cases, the NAQC can be noticeably enhanced by introducing the Dzyaloshinsky-Moriya (DM) interaction to two spins and tune the anisotropy of the spin-spin coupling. Besides, the critical temperature below which the thermal NAQC exists can also be noticeably enhanced by introducing the DM interaction. Hence, our results provide a way to achieve NAQC for quantum tasks based on spin lattices.

Quantum secret sharing (QSS) protocols are designed to allow a secret message to be divided into several shadows, and the secret can be reconstructed cooperatively. Motivated by the eight quantum entangled (EQE) state, a tripartite verifiable QSS scheme is proposed. It involves three agents, in four phases, i.e., shadow distribution phase, eavesdropping detection phase, measurement and secret sharing phase, verification and secret recover phase. The protocol can not only share and recover the secret correctly, but also verify whether there are dishonest participants in communication. In addition, the protocol is extended to a multiparty quantum secret sharing scheme by utilizing the unitary operations. Security analysis shows that the proposed schemes achieve the fundamental security requirements against the external and internal attackers with the aid of the quantum decoy states. It is shown that the efficiency in classical and quantum transmission is higher than the other protocols.

In this paper, we construct a general Bell inequality for the graph state. Firstly, we show that the Bell inequality is maximally violated by graph state corresponding to some given graph. In addition, we obtain the classical bound and maximal quantum violation of Bell inequality are N + |n(i)|− 1 and $N+(\sqrt {2}-1)(|n(i)|+1)$ , respectively. Furthermore, the classical bound and maximal quantum violation of Bell inequality are dependent on the choice of the vertex for most graphs expect for complete graph.

A tripartite quantum operation sharing protocol is proposed by utilizing a five-qubit absolutely maximally entangled (AME) state presented by Helwig et al. (Phys. Rev. A 86, 052335 (2012). The security of the proposed protocol is analyzed and ensured. The essential role of the state in this quantum task is explained. The protocol determinacy and the sharer asymmetry are identified. The experimental feasibility of the proposed protocol is discussed and confirmed. Moreover, the protocol is compared with Peng’s tripartite protocol using a six-qubit AME state [Quantum Inf Process 14, 4255 (2015)] and its distinct advantages of consuming less quantum resources, degrading the intensity of necessary operations, and owning the higher intrinsic efficiency, are revealed.

We present a novel scheme for deterministically realizing remote preparation of three-dimensional quantum states in a controlled manner. In this scheme, to link the three legitimate parties, generalized Einstein-Podolsky-Rosen (EPR) states, generalized Greenberger-Horne-Zeilinger (GHZ) states or their combinations are employed to product the shared quantum resources. Then to complete the deterministic controlled remote state preparation (DCRSP) in a three-dimensional system, some suitable sets of mutually orthogonal quantum states are hired as the measuring bases. It is shown that, after performing projective measurements under the proper measuring bases, the remote preparation of two-qutrit equatorial states can be successfully realized under control of a third party with unit successful probability.

As an important topic of quantum cryptography, quantum voting has attracted more and more attention in recent years. In this paper, we propose a quantum voting scheme based on a new set of orthogonal product states. Since different particles in the same orthogonal product state are transmitted separately, the security of the vote message in the scheme can be protected. The availability and security analysis show that the scheme satisfies the basic properties of voting can resist known quantum attacks. Furthermore, our scheme solves the problem of difficult preparation of entangled states in actual situations and improves the practicability of voting scheme. We hoped that our research will provide new ideas for the further study of quantum voting.

We present a novel scheme of cyclic remote state preparation via a six-qubit entangled state as the quantum channel. By introducing three auxiliary particles and using feedforward measurement strategy, Alice can remotely prepare an arbitrary single-qubit quantum state for Bob, Bob can remotely prepare an arbitrary single-qubit quantum state on Charlie’s site and Charlie can also remotely prepare an arbitrary single-qubit quantum state for Alice. It is pointed out that the cyclic remote preparation in the opposite direction can be perfectly achieved by changing the quantum channel. Furthermore, we generalize the above scheme to systems having N observers, so that cyclic remote state preparation can be realized in quantum information networks with N observers in different directions by changing quantum channels.

We present a theoretical study on quantum breathers in a XXZ Heisenberg ferromagnet with the single-ion uniaxial anisotropy on a two-dimensional hexangular lattice. In our work, the full quantum and the semiclassical cases are considered, respectively. For the full quantum case, we find that some isolated two-magnon bands can exist below the free magnon band. Physically, each isolated two-magnon band correspond to a two-magnon bound state, which is the simplest quantum breather state. For the semiclassical case, the analytical form of the discrete breather solution with a line localized structure is obtained by adopting the Glauber’s coherent-state representation. Furthermore, the influence of the anisotropy on the properties of quantum breathers is discussed in detail.

Recently, Cui and Guo (Quantum Inform. Process. 18, 182, 2019) gave some quantum testing algorithms of multi-output Boolean functions, one of them was for resiliency testing. However, through the algorithm, we cannot get the probability distribution of a Boolean function. Improving the algorithm there, we present quantum algorithms for this problem. Under the condition of non-resiliency, we obtain not only the conclusion that the function F(x) is statistically dependent of which t variables but also the distance of the probability distribution from the uniform distribution.

In this work, we give an analytical derivation of the reduced density matrix between two qubits in a cavity field, which is described by the quantum Rabi model. Using the coherent state method and the generalized hypergeometric functions, we find a complete solution of the 4-by-4 reduced density matrix for each eigen energy by taking the partial trace over the cavity field states. Four kinds of measurements used to describe the quantum entanglement and quantum correlation between the two qubits, i.e., the concurrence, quantum discord, steerable weight, and robustness of coherence, are calculated for the ground state and excited states. For both the weak coupling ( $g\rightarrow 0$ ) and deep-strong coupling ( $g\rightarrow \infty $ ) regimes, quantum entanglement and quantum correlation between the two qubits are vanishing. An appropriate coupling in the deep strong coupling regime between the qubits and the cavity field is required if one wants to establish quantum entanglement between the qubits.

We provide a characterization of multipartite systems constraints in terms of quantum correlations. By using the Hamming weight of the binary vectors associated with the subsystems, we give the α th power of monogamy and β th power of polygamy inequalities for general quantum correlations. Using concurrence as an application, one gets tighter inequalities than the existing ones for some classes of quantum states. Detailed examples are presented.

In this paper, a multi-party quantum private comparison (MQPC) scheme is suggested based on entanglement swapping of Bell entangled states within d-level quantum system, which can accomplish the equality comparison of secret binary sequences from n users via one execution of scheme. Detailed security analysis shows that both the outside attack and the participant attack are ineffective. The suggested scheme needn't establish a private key among n users beforehand through the quantum key distribution (QKD) method to encrypt the secret binary sequences. Compared with previous MQPC scheme based on d-level Cat states and d-level Bell entangled states, the suggested scheme has distinct advantages on quantum resource, quantum measurement of third party (TP) and qubit efficiency., 8 pages, 1 figure, 1 table

Importance of quantum entanglement has been demonstrated in various applications. Usually, separability of a bipartite state is defined by its algebraic structure, i.e. a convex combination of product states. But it seems to be hard to check separability (equivalently, entanglement) of a state from its algebraic structure. In this note, we give some characterizations of separability of bipartite states based on POVM measurements. For bipartite pure states, we prove the separability, Bell locality, unsteerability and classical correlation are the same. As a consequence, every entangled pure bipartite state is always Bell nonlocal, steerable and quantum correlated.

Based on quantum renormalization group (QRG) method, we investigated quantum coherence and quantum phase transition (QPT) in XXZ chain and XY chain, respectively. The results show that both the geometric quantum coherence and entropic coherecne can accurately indicate the QPT at critical point after enough iteration steps. Moreover, the increasing anisotropy parameter destroys the coherence in the XXZ chain, while enhances it in the XY chain. In addition, focused on the XXZ chain we analyzed the nonanalytic phenomena and scaling behaviors with different theoretical exponents in detail.

The number of qubits involved in a quantum system increases as the quantum computation is being progressed. Restrictions in monolithic quantum computing systems capacity can be overcome by utilizing the distributed circuits. For the implementation of global gates (two-quibt gates whose control and target qubits belong to different partitions), it is required that one qubit be teleported to the other partition. Teleportation is a costly protocol (it requires sharing entanglement between two partitions), and the number of teleportations required for implement a given distributed circuit is called teleportation cost. It is desirable to distribute a quantum computation in such a way that the teleportation cost is reduced. A previous work has presented a way to optimize distributed quantum circuits in terms of teleportation cost for a predetermined partitioning. In this research, Shore circuit to factor number 15 synthesized in the single-qubit and CNOT gates is provided. After that, the circuit partitioning with the minimal cost of communication is presented.

In this paper, a quantum payment protocol based on a special set of local indistinguishable orthogonal product states (X-LIOP) is proposed. In the presented protocol, the purchase information is encoded as a sequence of X-LIOP states. With our security analysis, it can be seen that our protocol satisfies the requirements of blindness, unforgeability and undeniability. Specially, the blindness means the purchase information is only known to the buyer and the seller, while the others (including the bank) cannot obtain the purchase information by any means. Once the buyer and seller wants to forge or deny information, they will be found by a trusted third party. Furthermore, since the non-entangled states are applied in our protocol, the protocol can be easily implemented in practice.

Quantum state sharing (QSS) plays significant role in transmitting quantum secret information. However, in practical quantum communication situation, quantum information transmission is inevitably affected by the noisy environment. In this paper, we investigate the influence of correlated noise on QSS. We first present a QSS scheme and construct a noisy QSS. Subsequently, the fidelity of the scheme is discussed. It is found that there are different behaviors of fidelity in Markovian regime and non-Markovian regime. Furthermore, a method is proposed to steer the performance of the noisy QSS scheme with filtering operator.

Quantum degenerate systems can be simulated by the classical resonant oscillators in the means of quantum-classical mapping theory. In this work, we show the classical version of shortcuts to adiabaticity-transitionless quantum driving (TQD) for the non-Abelian quantum systems by averaging the quantum version. The non-Abelian geometric angle corresponding to the quantum Wilczek-Zee phase is given and the non-Abelian angle gauge potential is just the opposite of the third term of TQD Hamiltonian or the averaging of Wilczek-Zee gauge potential. An example of Hamiltonian with two degenerate subspaces is employed to illustrate the classical non-Abelian dynamics, geometric angle and shortcuts to adiabaticity. This provides a promising platform to simulate the quantum shortcut or for quantum computation and quantum information processing.

A novel practical quantum secure direct communication (QSDC) protocol is constructed by utilizing the evolution law of atom via cavity QED. It transmits the atoms from one communicant to the other communicant in a two-step manner. It adopts two-atom product states as the initial quantum resource and the decoy atom technique to guarantee the security against the outside attack. It only needs single-atom measurements, and neither the quantum entanglement swapping nor the unitary operations.

Motivated by the existing circuit model of quantum convolutional neural network, a new quantum convolutional neural network circuit model is devised, which is combined with quantum chaotic map to construct a symmetric cryptosystem. Quantum chaotic map produces key stream for encryption and decryption. The cryptosystem simulates the basic process of communication. Theoretical analysis manifests that the cryptosystem is effective. Additionally, simulation experiments based on MNIST data set show that the cryptosystem is secure. Furthermore, the proposed cryptosystem can be applied not only for image data, but for text data. Therefore, the grid data can be encrypted by utilizing the cryptosystem.

We investigate the dynamical behaviors of quantum-memory-assisted entropic uncertainty relation (QMA-EUR) and quantum correlation (both quantum entanglement and quantum discord) for a two-qubit system coupled to a spin environment by a z–x-type interaction. Our purpose is to find out how the QMA-EUR and quantum correlations are affected by the pre-designed factors of the environment, including initial spin environmental states and the coupling constants. The numerical results show that the initial environmental state has significant effect on the dynamics of quantum correlations of the central spin system. We find that the environment should be prepared in a block entangled state with Bell state. This option is beneficial to reducing entropic uncertainty and inhibits the damping of quantum correlation. We also find that the high frequency particles in a spin bath can significantly enhance the robustness of quantum correlation of the system.

A comparative study of quantum properties associated with coherent correlations between the modes of light generated by a nondegenerate parametric down-conversion process is presented. Particularly, the degree of nonclassicality that can be quantified by logarithmic negativity and quantum discord is compared, and a striking similar tendency is observed. In the same manner, a comparison of the quadrature variance, the smallest eigenvalue of the symplectic matrix and Einstein-Podolsky-Rosen (EPR) steering is made whereby a significant similarity is witnessed. The highest degree of quantum features of the radiation is in general manifested near threshold, whereas the quantifying measure related to the smallest eigenvalue of the symplectic matrix is found to capture a better degree of quantumness. Since each criterion renders only sufficient condition, it is hoped that witnessing consistent outcome across different criteria enhances the chance for experimental verification and practical application.

In this paper, a linear generalized uncertainty principle (GUP), which suggests a minimum measurable length and a maximal measurable momentum, is used in analyzing COW experiment and Einstein-Bohr’s a photon box experiment. Based in these experiments a modified Schwarzschild metric was obtained in order to calculate a quantum corrections in Schwarzschild black hole thermodynamics and tunneling probability. It was found that GUP placed restrictions on the minimum mass, size and temperature of the black hole, indicating that there was a black hole remnant after the completion of the evaporation process. The resulting values of minimum mass and size of the black hole are identical to that values predicted by quadratic GUP, which points out that the two models are equivalence in Planck scale measurements.

We study the usefulness of the broken-line-type decoherence in quantum Hash functions based on discrete-time quantum walks on a cycle. We first observe that the time-evolution of probability distribution of quantum walks on a cycle is of high sensitivity to such broken-line-type decoherence, increasing with the number of steps in the walk. Based on this observation, we further propose a quantum Hash function based on the broken-line quantum walk on a cycle. Numerical simulation and performance analyses show that decoherence can be useful to improve the performances of quantum hash functions such as better diffusion and confusion, better collision resistance and more uniform distribution of hash values in the hash space. Moreover, our results promote the practical use of quantum-walk-based hash functions in realistic situations.

In this paper, we propose a mutual authenticated quantum key agreement scheme based on three-particle entangled states, which can achieve both completely secure and more efficient. In our scheme, the pre-shared keys are classical bit strings between the semi-honest server (SHS) and the client (Alice or Bob), so they are kept and use to authenticate each other easily. More important, by the SHS’s helping with three-particle entangled states, SHS and Alice/Bob can authenticate each other, and at the same time anyone else cannot get the session key between Alice and Bob even for SHS. The proposed scheme has the properties of completeness, information theoretic security, non-repudiation and unforgeability. Its information-theoretic security is ensured by quantum indistinguishability mechanics. Compared with the related works, our proposed scheme can increase efficiency factors η1 and η2 to 50% and 80% respectively in one communication round.

Quantum key agreement (QKA) and quantum search algorithm (QSA) are two important branches in quantum topic. The former asks all participants to negotiate the agreement key equally, and none of them can fully determine the agreement key. The latter is used to provide an acceleration in searching the marked item in an unsorted database. To date, several QKA schemes based on either BB84 or entangled states have been proposed, the QKA protocol based on QSA is rare, only exists one multi-party QKA (MQKA) protocol based on QSA. In this paper, on the basis of the properties of Grover’s QSA, the first two-party quantum key agreement protocol based on quantum search algorithm known as Grover’s algorithm is proposed. The participants transmit a two-particle quantum state sequence directly by inserting decoy photons randomly. The initial-prepared two-particle quantum states are easy to be prepared with current technology. Moreover, there is no swapping entanglement technology used in this protocol, it only needs unitary operations and single-particle measurements. Compared with the existing two-party QKA protocol, the proposed QKA protocol is more efficient. In addition, the security analysis shows that the proposed protocol is secure against both external attacks and internal ones. Finally, the proposed protocol is generated to MQKA protocol based on quantum search algorithm.

We investigate the dynamical behaviors of quantum-memory-assisted (QMA) entropic uncertainty for the central two-qubit system coupled to the N-site spin XY chain environment with z-component Dzyaloshinsky-Moriya (DM) interaction and external magnetic field, asymmetrically. The results show that the dynamics of QMA entropic uncertainty for a pair of Pauli observables are oscillatory and ascending gradually with evolution time, which is anti-correlated to the entanglement of the two-qubit system. We also find that QMA entropic uncertainty exhibits sudden change phenomena near the critical point of quantum phase transform both in the case of weak and strong coupling regimes, which can act as a new witness of the critical point of quantum phase transition. Meanwhile, the DM interactions of the spin chain environment have non-equivalent effects on the QMA entropic uncertainty when the external magnetic field strength is far from the critical point. Furthermore, the asymmetricallity of the qubit-environment couplings has slightly effects on QMA entropic uncertainty in the case of strong coupling regime of the two-qubit system. While, in the weak coupling regime of the two-qubit system, QMA entropic uncertainty is very sensitive to the asymmetricallity of qubit-environment couplings. Finally, the larger the number of spin sites of the environment, the more quickly the QMA entropic uncertainty increases to the maximal value both in the weak and strong coupling regimes of the two-qubit system.

Recently, Chen et al. [Int. J. Theor. Phys. 59, 1402–1412 (2020)] proposed a theoretical scheme for controlled quantum teleportation (CQT) of a Bell state by using seven-qubit entangled state as a quantum channel. In this comment, it is shown that the consumption of both the quantum and classical resources used by Chen et al. is excessively high because the actual task of CQT of a Bell state via seven-qubit entangled state can be reduced to the CQT of an arbitrary single-qubit state via three-qubit GHZ state. Hence, in this work, an improved scheme for CQT has been presented. We have also shown that the CQT of certain class of N-qubit entangled state can also be realized successfully by using a three-qubit GHZ state as the quantum channel. The intrinsic efficiency of the present communication scheme is very large as compared to that proposed by Chen et al.

We investigate the dynamics of quantum coherence of a system consisting of two interacting atoms coupling with a common cavity which is filled with a nonlinear Kerr-like medium, in the presence of intrinsic decoherence. It is shown that the stationary quantum coherence can arise in the system as the time approach to infinite. In particular, the amount of stationary quantum coherence can be enhanced by adjusting the Kerr interaction and dipole-dipole interaction. Furthermore, we also explore the influence of Kerr interaction and dipole-dipole interaction on the transfer of quantum information by a witness of the trace distance and find that the transferred information and stationary quantum information can be controlled by the Kerr interaction and dipole-dipole interaction.