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As astounding as it may still seem to many, Bell’s theorems do not prove nonlocality. Non separable multipartite objects exist classically, meaning with local physics, the statistical state measurement of which violates the famous inequalities. Alleviating the almost century old confusion, the correct laws of statistics and logic pinpoint the true oddity of quantum objects: duality. As it is shown in the first part of this short essay, duality plus conservation laws allow the violation of Bell’s inequalities for any spatio-temporal separation. To dig deeper into particle dualism, in the second part, a class of models is proposed as a working framework. It encompasses some chaotic excitable reaction-diffusion systems, whose generalized susceptibilities make them compatible with quantized fields and excitations, of any desired symmetry group including the renormalization semigroup. Particles are supposed topological in nature. Bohr-Sommerfeld quantization takes place thanks to topological invariants stemming from densely dispersed defects generated by a multifractal background. Entanglement phenomenology arises because latent variables exist that are carried away, along with the moving particles that have interacted, and by which correlations are preserved. Conservation is assumed to be born in the phase, just as momentum is for instance. In other words, all known phenomena in physics are deterministic, classical and real, in the sense that information does propagate locally and experiments conducted statistically do hide latent variables. [ABSTRACT FROM AUTHOR]

Quantum coherence and quantum steering are extremely useful resources for quantum information technology. Based on the correlation between quantum coherence and quantum steering, the steered quantum coherence (SQC) is formed, which is a new quantum correlation measurement method. In this paper, the SQC is applied to explore the dynamic evolution of quantum correlation in non-Markovian systems and it is also compared with typical quantum entanglement (QE). The results show that same as the QE, the SQC can also measure the quantum correlation of quantum system. Further research shows that there are obvious differences between the two measurement methods: on the one hand, in the process of non-Markovian dynamics evolution, death and rebirth occur for QE, but not for SQC, which indicates that SQC is more robust than QE; on the other hand, the superposition effect of the channel is not conducive to maintaining the QE of the system, but it is beneficial to maintaining the SQC. [ABSTRACT FROM AUTHOR]

Quantum nonlocality is a very important quantum resource. Different types of quantum correlation can present the quantum nonlocality in varying degrees. In this paper, we investigate the dynamic evolution of steered quantum coherence (SQC) for a system of interacting qubits in contact with various models of the environment, and emphatically compare the robustness of SQC and quantum entanglement (QE). The results show that from the given initially state, due to the decoherence effect, both SQC and QE evolve with time in the form of oscillation. In the process of dynamic evolution, the QE will appear death and rebirth for all different decay modes. Differently, the SQC will not emerge the sudden death or the dark and bright, which shows a stronger robustness than QE. Moreover, we find that, under the long-term limit condition, the SQC will approach the steady value in different decay modes, which provides a reliable resource foundation for the completion of quantum information processing. [ABSTRACT FROM AUTHOR]

Neural networks are becoming ubiquitous in various areas of physics as a successful machine learning (ML) technique for addressing different tasks. Based on ML technique, we propose and experimentally demonstrate an efficient method for state reconstruction of the widely used Sagnac polarization-entangled photon source. By properly modeling the target states, a multi-output fully connected neural network is well trained using only six of the sixteen measurement bases in standard tomography technique, and hence our method reduces the resource consumption without loss of accuracy. We demonstrate the ability of the neural network to predict state parameters with a high precision by using both simulated and experimental data. Explicitly, the mean absolute error for all the parameters is below 0.05 for the simulated data and a mean fidelity of 0.99 is achieved for experimentally generated states. Our method could be generalized to estimate other kinds of states, as well as other quantum information tasks. [ABSTRACT FROM AUTHOR]

Bell non-locality and steering are archetypal characteristics of quantum mechanics that mark a significant departure from conventional classical notions. They basically refer to the presence of quantum correlations between separated systems which violate a non-local inequality, the violation otherwise is not possible if we restrict ourselves only to classical correlations. In view of the importance of such unique correlations, one may be interested to generate more states exhibiting non-locality starting from a few, a protocol which is termed as broadcasting. However, in the present submission, we show using universal Buzek–Hillary (BH) quantum cloning machine that, if one restricts to broadcasting through local quantum cloning, then such non-locality cannot be broadcasted. Our study is done in the purview of the Bell-CHSH inequality and the CJWR [E G Cavalcanti et al, Phys. Rev. A80, 032112 (2009)] steering inequality. It is observed that when the number of measurement settings is greater than 6, some of the output states are steerable after the application of local optimal BH cloners. We found that, under some restrictions, if the Werner and Bell diagonal states are subjected to such procedures, then the resultant state is rendered unsteerable. We extended this study to three qubit systems and found that genuine tripartite non-locality cannot be broadcasted using universal BH local quantum cloners, when the Svetlichny's inequality was considered. For two qubit systems, we considered 10 5 simulated general local unitaries over Werner and Bell-diagonal states and found that for none of these states, broadcasting on non-locality and 3-steerability is possible. [ABSTRACT FROM AUTHOR]

The remote state preparation (RSP) plays an important role in quantum information processing. In this study we present a scheme, where an eight-qubit entangled state is used as the quantum channel to prepare the four-qubit entangled state in a bidirectional manner. In this scheme, two distant parties, Alice and Bob are not only senders but also receivers, and Alice wants to assist Bob in remotely preparing a known four-qubit state, while Bob wants to assist Alice in remotely preparing a four-qubit state, respectively. We show that our scheme is deterministic, meaning that the bidirectional remote state preparation can have a 100% overall success probability. [ABSTRACT FROM AUTHOR]

An extended non-local field equations characterised by modified dispersion relations have been constructed based on non-local differential and hyperdifferential quantum operators. The dispersion relations obtained are found to be comparable to those obtained within the framework of unified theories and the covariant Kempf–Mangano algebra but free from tachyons. For the case of neutral meson, the upper limit of the characteristic length scale was found to be very close to the nuclear radius obtained from the study of β + -decay energy from finite-sized nuclei. [ABSTRACT FROM AUTHOR]

In this paper, a joint remote state preparation scheme for an arbitrary single-qutrit state is proposed. First, we introduce how to remotely prepare an arbitrary single-qutrit state in the ideal environment with the form of the density operator. Then we investigate the effects of four typical types of 3D Pauli-like noises corresponding to the Weyl operators: the trit-flip, the t-phase-flip, the trit-phase-flip and the t-depolarising in the ideal environment. For each type of noise, we calculate and analyse the results of fidelity. The results show that when the trit-flip, the trit-phase-flip and the t-depolarising noises are considered, the fidelity is related to the noise factor and all the coefficients of the target state. However, when the t-phase-flip noise is considered, the fidelity is only related to the noise factor and the amplitude coefficients of the target state. [ABSTRACT FROM AUTHOR]

Quantum dialogue (QD) enables two communication parties to directly exchange secret messages simultaneously. In conventional QD protocols, photons need to transmit in the quantum channel for two rounds. In this paper, we propose a one-step QD protocol based on the hyperentanglement. With the help of the non-local hyperentanglement-assisted Bell state measurement (BSM), the photons only need to transmit in the quantum channel once. We prove that our one-step QD protocol is secure in theory and numerically simulate its secret message capacity under practical experimental condition. Compared with previous QD protocols, the one-step QD protocol can effectively simplify the experiment operations and reduce the message loss caused by the photon transmission loss. Meanwhile, the non-local hyperentanglement-assisted BSM has a success probability of 100% and is feasible with linear optical elements. Moreover, combined with the hyperentanglement heralded amplification and purification, our protocol is possible to realize long-distance one-step QD. [ABSTRACT FROM AUTHOR]

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

Recently, Pan proposed a semi-quantum dialogue scheme with Bell entangled states Pan (Int. J. Theor. Phys. 59, 1364-1371, 2020). Here we re-examin the security of it and discover a security vulnerability in the original scheme. Eavesdropper Eve may utilize double controlled-not operation attack to obtain Bob’s secret without being detected. Finally, we give an improvement of the semi-quantum dialogue protocol and prove its security. We sincerely hope the researchers pay enough attention to double controlled-not operation attack hidden in semi-quantum cryptography protocols and design truly secure semi-quantum protocols. [ABSTRACT FROM AUTHOR]

In entanglement theory, the long-standing distillability problem asks whether the two-copy 4 × 4 Werner states are distillable under local operations and classical communications. We report the partial solution to the problem when the involved 4 × 4 matrices A and B, respectively, have one and three nonzero entries. As a corollary, the problem is solved when A and B have at most four nonzero entries. Our result presents the latest progress on the problem. [ABSTRACT FROM AUTHOR]

We develop an approach using coherent states and path integral to investigate the dynamics of entanglement in a simple two-dimensional non-commutative harmonic oscillator. We start by employing a Bopp shift to convert the Hamiltonian describing the system into a commutative equivalent one. This allows us to construct coherent states and calculate the propagator in standard way. By deriving the explicit expression of the time-dependent coherent states and considering its connection with the number states, we provide exact results for evaluating the degree of entanglement between the ground state and any excited state through the purity function. The interesting emerging result is that, as long as the non-commutativity parameter is non-zero, our system exhibits the phenomenon of collapse and revival of entanglement. [ABSTRACT FROM AUTHOR]

Special fermionic systems entered the realm of quantum chemistry in the seventies in the work of Borland and Dennis in the form of a toy model. This work was leading to a detailed study of the N-representability problem by Klyachko. The topic then has been reconsidered in the light of entanglement theory boiling down to the notion of entanglement polytopes. Recently building on certain properties of such special fermionic systems, a connection between the coupled cluster method and entanglement has been established. In this paper we show that precisely such a special class of systems also provides an interesting physical realization for structures related to the Lie algebras of exceptional groups. This result draws such exotic symmetry structures under the umbrella of entangled systems of physical relevance. [ABSTRACT FROM AUTHOR]

Deformed Jaynes–Cummings model (JCM) has a physical importance in quantum optics. Hence, we investigated the nonlinear JCM including the intensity-dependent coupling constant and the additional Kerr term. The cavity was assumed to be in thermal equilibrium with a heat reservoir at temperature T. Using the generators of a closed algebra which reduces to the su(1, 1) and Heisenberg–Weyl algebras at limiting cases, and considering the total excitation number as a constant of motion, the total Hilbert space decomposes into two subspaces. So the eigenvalues and the corresponding eigenvectors were obtained. We derived the thermal density matrix and analysed the fidelity and thermal entanglement using negativity measure. Furthermore, we studied the Berry phase of the nonlinear atom–field system and explored the influence of nonlinearity on the quantum phase transition (QPT) point and entanglement. It is found that the deformation parameter can strongly affect the fidelity, negativity and QPT point. [ABSTRACT FROM AUTHOR]

By using the complete solution of the Milburn equation (beyond the Lindblad form that it is generally used) that describes intrinsic decoherence, we studied the decaying dynamics of a displaced harmonic oscillator. We calculated the expectation values of position quadrature and the number operator in the initial coherent and squeezed states. [ABSTRACT FROM AUTHOR]

Sequential sharing of nonlocal correlation is inherently related to its application. We address the question as to how many observers can share the nonlocal advantage of quantum coherence (NAQC) in a (d × d)-dimensional state, where d is a prime or a power of a prime. We first analyze the trade-off between disturbance and information gain of the general d-dimensional unsharp measurements. Then in a scenario where multiple Alices perform unsharp measurements on one party of the state sequentially and independently and a single Bob measures coherence of the conditional states on the other party, we show that at most one Alice can demonstrate NAQC with Bob. This limit holds even when considering the weak measurements with optimal pointer states. These results may shed light on the interplay between nonlocal correlations and quantum measurements on high-dimensional systems and the hierarchy of different quantum correlations. [ABSTRACT FROM AUTHOR]

Identification of quantum phase transitions has been a long standing issue in quantum systems. In this work, we study the renormalization of Wigner–Yanase skew information in XY spin chain and compare its relation with cost of energy quantum correlation near the critical point. This study is presented by implementing the quantum renormalization group (RG) technique. We apply the (RG) method to examine existing phase transition in XY spin chain by using the cost of energy quantum correlations and Wigner–Yanase skew information. We demonstrate that cost of energy quantum can provide crucial information about quantum phase transitions as well as quantum correlations. [ABSTRACT FROM AUTHOR]

A salient merit of processing quantum information is the ability of simultaneously working with both bit zero and bit one. The basic unit of quantum information, the so-called qubit, is a superposition of two orthogonal (or near-orthogonal) quantum states which can be realised on distinct physical platforms. At present, no unique qubit encoding exists that is superior to all the other ones. Different labs are implementing their most convenient technique for encoding the qubit and so the network of labs becomes heterogeneous. In this paper, we consider two types of qubit encodings, one is the single-rail qubit in terms of discrete-variable (DV) states 0 and 1 which are respectively the vacuum and the single-photon state and the other is the coherent-state qubit in terms of continuous-variable (CV) states α and - α which are coherent states with equal amplitudes but opposite phases. We devise linear-optics schemes to teleport one type of qubit to the other type. More than that, our teleportation schemes are designed so that two kinds of controllers, one is capable of manipulating single-rail qubits (DV controller) while the other coherent-state ones (CV controller), are able to simultaneously supervise the tasks in both directions. We first propose a quantum circuit to prepare a relevant four-party pure entangled state serving as a quantum channel between the four participants: two teleporters and two controllers. We then detail the hybrid controlled teleportation protocols taking into account the dissipation effect caused by the presence of losses in the environment surrounding the participants. [ABSTRACT FROM AUTHOR]

In this paper, the concept of nested multilevel entanglement is studied and formulated in terms of Matryoshka states. The generation of Matryoshka quantum resource states, which contain nested entanglement patterns, based on an anisotropic XY spin–spin interaction-based model has been proposed. Other classes of nested entanglement, such as in Matryoshka generalised GHZ states and Matryoshka Q-GHZ states, are studied. Generation, characterisation and application of a genuinely entangled seven-qubit resource state close to being a Matryoshka Q-GHZ states is explored, with theoretical schemes for quantum teleportation of arbitrary one-, two- and three-qubits states, bidirectional teleportation of arbitrary two-qubit states and probabilistic circular controlled teleportation proposed for the state. Fractal network protocols, surface codes and graph states as well as generation of arbitrary entangled states at remote locations are also discussed, to highlight the importance of this class of quantum states. [ABSTRACT FROM AUTHOR]

This review, of the understanding of quantum mechanics, is broad in scope, and aims to reflect enough of the literature to be representative of the current state of the subject. To enhance clarity, the main findings are presented in the form of a coherent synthesis of the reviewed sources. The review highlights core characteristics of quantum mechanics. One is statistical balance in the collective response of an ensemble of identically prepared systems, to differing measurement types. Another is that states are mathematical terms prescribing probability aspects of future events, relating to an ensemble of systems, in various situations. These characteristics then yield helpful insights on entanglement, measurement, and widely-discussed experiments and analyses. The review concludes by considering how these insights are supported, illustrated and developed by some specific approaches to understanding quantum mechanics. The review uses non-mathematical language precisely (terms defined) and rigorously (consistent meanings), and uses only such language. A theory more descriptive of independent reality than is quantum mechanics may yet be possible. One step in the pursuit of such a theory is to reach greater consensus on how to understand quantum mechanics. This review aims to contribute to achieving that greater consensus, and so to that pursuit.

We uncover new behaviors of the transmission of information by three quantum channels in superposition of causal orders subject to some level of noise. We find that the transmission can exhibit three different behaviors as the level of noise is varied. This multifold behavior can be explained by the different equivalence classes of quantum switch matrices related to specific combinations of causal orders. We classify these matrices using their characteristic polynomials and matrix invariants, and we calculate analytical expressions for the Holevo information in three representative cases. Our results are a step forward to understand and harness quantum control of causal orders with different levels of noise. We also study the Holevo information as function of a continuous order parameter and analyze transitions at integer values. [ABSTRACT FROM AUTHOR]

We quantify the entanglement and its variations via generalized concurrence, Meyer–Wallach measure and its generalizations. Then we investigate the interactions between qubits on complete graphs, tree graphs, chain graphs and loop graphs with 3 to 8 qubits. It is observed that the amount of all entanglement measures in tree graph in the first group of considered graphs, are equal. The complete equivalent graph is equal and the entanglement measures for these graphs change altering the number of qubits. Furthermore, it can be seen that the entanglement measures are increased augmenting the number of qubits in the chain graph and loop graph. The entanglement of loop graphs is equal to or greater than the entanglement of chain graphs assuming the same number of qubits. Also there is a significant relation between entanglement, number of qubits, and interactions between qubits for the second group of considered graphs. As the number of interactions (presented by edges) increases between the qubits, the entanglements increase in these states. It is shown that the employed entanglement measures reveal the different values changing the number of qubits (vertices). [ABSTRACT FROM AUTHOR]

We study the entanglement and the Bell nonlocality of a coupled two-qubit system, in which each qubit is coupled with one individual environment. We study how the nonequilibrium environments (with different temperatures or chemical potentials) influence the entanglement and the Bell nonlocality. The nonequilibrium environments can have constructive effects on the entanglement and the Bell nonlocality. Nonequilibrium thermodynamic cost can sustain the thermal energy or particle current and enhance the entanglement and the Bell nonlocality. However, the nonequilibrium conditions (characterized by the temperature differences or the thermodynamic cost quantified by the entropy production rates) which give the maximal violation of the Bell inequalities are different from the nonequilibrium conditions which give the maximal entanglement. When the Bell inequality has asymmetric observables (between Alice and Bob), for example the I 3322 inequality, such asymmetry can also be reflected from the effects under the nonequilibrium environments. The spatial asymmetric two-qubit system coupled with nonequilibrium bosonic environments shows the thermal rectification effect, which can be witnessed by the Bell nonlocality. Different spatial asymmetric factors can be linearly cancelled with each other in the thermal rectification effect, which is also reflected on the changes of the entanglement and the Bell nonlocality. Our study demonstrates that the nonequilibrium environments are both valuable for the entanglement and Bell nonlocality resources, based on different optimal nonequilibrium conditions though. [ABSTRACT FROM AUTHOR]

The entangled qudits of three-level trapped ion and two phonons (in coherent state) in Λ configuration forming a Hilbert space of 12-D are investigated. The quantum entropy is analyzed "such as an elaborated measure" in trapped ion-coherent state system. Four values of Lamb-Dicke parameter (LDP), η = 0.005 , 0.07 , 0.08 and 0.09 are probed for deep Lamb-Dick regime. We elucidate that as η is increased, sudden death of entangled state in the trapped ion-coherent state system is decreased or vice versa. By this way, sudden birth of entangled state can be tuned by LDP. All graphs in this study are plotted with aid of the Wolfram Mathematica 9. [ABSTRACT FROM AUTHOR]

We investigate the entanglement of the ground state in the quantum cyclic graphs whose nodes are considered as quantum harmonic oscillators. To this end, the Schmidt numbers and entanglement entropy between two arbitrary partitions with equal nodes of a cyclic graphs, are calculated. For that, the local operation is used to build singular value decomposition of potential matrix of cyclic graphs. Then the maximum value of entanglement entropy among all bipartite cyclic graphs is obtained. [ABSTRACT FROM AUTHOR]

We analyse the entanglement of the light produced by a three-level laser whose cavity contains a parametric amplifier, with the cavity mode driven by the coherent light and coupled to a squeezed vacuum reservoir. Employing stochastic differential equations associated with the normal ordering resulted from the pertinent master equation, the quadrature variances and entanglement of the two-mode light are obtained and photon statistics of the two-light modes is discussed. It is found that the three-level laser generates squeezed light under certain conditions, with maximum intracavity squeezing being 89.7% below the coherent state level. We also show that the parametric amplifier enhances the mean photon number and photon number correlation. [ABSTRACT FROM AUTHOR]

The 4-qubit unextendible product bases (UPBs) has been recently studied by [Johnston, J. Phys. A: Math. Theor. 47 (2014) 424034]. Based on this study we show that there is only one UPB of size 6 and six UPBs of size 9 in H = C 2 ⊗ C 2 ⊗ C 4 , three UPBs of size 9 in K = C 4 ⊗ C 4 , and no UPB of size 7 in H and K . Furthermore we construct a new family of 4-qubit positive-partial-transpose (PPT) entangled states of rank seven, and show that they are also PPT entangled states in H and K , respectively. We analytically derive a geometric measure of a special PPT entangled states. [ABSTRACT FROM AUTHOR]

We propose an optimal protocol for remotely preparing a four-qubit entangled state. In this protocol, a sender and two potential receivers share a ten-qubit entangled state. The sender performs a two-qubit state measurement based on the information of the quantum state that needs to be prepared. According to the measurement results of the sender, any potential receiver can obtain the quantum state that the sender needs to prepare by using the corresponding unitary transformation. [ABSTRACT FROM AUTHOR]

We propose a scheme of controlled teleportation of an arbitrary three-qubit state by using a five-qubit cluster state. In our scheme, the sender Alice performs five sets of single-qubit measurements and the controller Charlie needs only take a single-qubit measurement. The receiver Bob can reconstruct the arbitrary three-qubit state by performing the single-qubit unitary operations and a controlled-NOT operation if he obtains the help of the controller. We show that the efficiency in this scheme approaches 100% [ABSTRACT FROM AUTHOR]

Polarized light passing through twisted wave plates shows entangled state of both SAM and OAM. The polarization matrix and the polarized state are constructed on OAM sphere for l = 1 where m varies between l, 0, − l. The twisted birefringent matrix develops the twisted quarter- and half-wave plates which in turn identify various retarders. The variable circular and linear retarders (VCR and VLR) are studied here from the viewpoint of quantum processing of entangled states. Interestingly, the geometric phase in association with the gain of OAM has been studied here for the phase shifter of an antenna array. [ABSTRACT FROM AUTHOR]

It is shown that there is no remote action with polarization measurements of photons in singlet state. A model is presented introducing a hidden parameter which determines the polarizer output. This model is able to explain the polarization measurement results with entangled photons. It is not ruled out by Bell’s Theorem.

The general class, Λ, of Bell hidden variables is composed of two subclasses ΛR and ΛN such that ΛR⋃ΛN = Λ and ΛR∩ ΛN = {}. The class ΛN is very large and contains random variables whose domain is the continuum, the reals. There are an uncountable infinite number of reals. Every instance of a real random variable is unique. The probability of two instances being equal is zero, exactly zero. ΛN induces sample independence. All correlations are context dependent but not in the usual sense. There is no “spooky action at a distance”. Random variables, belonging to ΛN, are independent from one experiment to the next. The existence of the class ΛN makes it impossible to derive any of the standard Bell inequalities used to define quantum entanglement.

An historical overview and detailed explication of a critical analysis of what has become known as Bell’s Theorem to the effect that, it should be impossible to extend Quantum Theory with the addition of local, real variables so as to obtain a version free of the ambiguous and preternatural features of the currently accepted interpretations is presented. The central point on which this critical analysis, due originally to Edwin Jaynes, is that Bell incorrectly applied probabilistic formulas involving conditional probabilities. In addition, mathematical technicalities that have complicated the understanding of the logical or mathematical setting in which current theory and experimentation are embedded, are discussed. Finally, some historical speculations on the sociological environment, in particular misleading aspects, in which recent generations of physicists lived and worked are mentioned.

In this note we compare the views of Bohr (known as the Copenhagen interpretation of quantum mechanics) with the views of Bell: complementarity versus nonlocality.

Local realism is in conflict with special quantum Bell-type models. Recently, several experiments have demonstrated violation of local realism if we trust their setup assuming special relativity valid. In this paper we question the assumption of relativity, point out not commented anomalies and show that the experiments have not closed objectivity loophole because clonability of the result has not been demonstrated. We propose several improvements in further experimental tests of local realism make the violation more convincing.

Recent Einstein-Podolsky-Rosen-Bohm experiments [M. Giustina et al. Phys. Rev. Lett. 115, 250401 (2015); L. K. Shalm et al. Phys. Rev. Lett. 115, 250402 (2015)] that claim to be loophole free are scrutinized. The combination of a digital computer and discrete-event simulation is used to construct a minimal but faithful model of the most perfected realization of these laboratory experiments. In contrast to prior simulations, all photon selections are strictly made, as they are in the actual experiments, at the local station and no other “post-selection” is involved. The simulation results demonstrate that a manifestly non-quantum model that identifies photons in the same local manner as in these experiments can produce correlations that are in excellent agreement with those of the quantum theoretical description of the corresponding thought experiment, in conflict with Bell’s theorem which states that this is impossible. The failure of Bell’s theorem is possible because of our recognition of the photon identification loophole. Such identification measurement-procedures are necessarily included in all actual experiments but are not included in the theory of Bell and his followers.

This paper argues that quantum nonlocality (QNL) has not been rigorously proven, despite the existence of recent Einstein-Podolsky-Rosen-Bohm (EPRB) experiments that are claimed to be ‘loophole-free’. First, readers are alerted to rhetorical arguments, which are unfortunately often appealed to in the QNL debate, to empower readers to identify and reject such arguments. Second, logical problems in QNL proofs are described and exemplified by a discussion of the projection postulate problem. Third, experimental issues are described and exemplified by a discussion of the postselection problem. The paper concludes that QNL has not been proven and that locality cannot be excluded.

In this paper, we study a model of two two-level atoms interacting with a quantum field. An analytical solution is obtained which is used to study the information entropy of the system. It is shown that the nonlinear term plays a significant role in the behaviour of the minimum uncertainty (MU) compared with the concurrence (C). Our extensive study of information entropy of atoms–field interaction demonstrates that using the coupling strength between the atoms and the field as a controller parameter, one can control the dynamics of the system by increasing the lower bound of the entropic uncertainty relation or decreasing the entanglement. [ABSTRACT FROM AUTHOR]

By repeated trials, one can determine the fairness of a classical coin with a confidence which grows with the number of trials. A quantum coin can be in a superposition of heads and tails and its state is most generally a density matrix. Given a string of qubits representing a series of trials, one can measure them individually and determine the state with a certain confidence. We show that there is an improved strategy which measures the qubits after entangling them, which leads to a greater confidence. This strategy is demonstrated on the simulation facility of IBM quantum computers. [ABSTRACT FROM AUTHOR]

In this paper, we put forward a scheme to realise joint remote state preparation (JRSP) of an arbitrary eight-qubit cluster-type state with two non-maximally entangled Greenberger–Horne–Zeilinger (GHZ) states in a recursive manner. The senders begin by helping the remote receiver to construct one intermediate state which is related to the target state closely. Then, the receiver introduces auxiliary qubits and applies appropriate local operations to obtain the target eight-qubit cluster-type state. It is shown that one new GHZ channel can be distributed among three participants with a certain probability if the initial attempt fails. Moreover, compared with the previous protocols, in our scheme both quantum resources and classical communications are considerably reduced. [ABSTRACT FROM AUTHOR]

We have studied the case in which one mode of the light field in the two-mode squeezed vacuum state evolves in a diffusion channel. By virtue of thermo-entangled state representation and the technique of integration within an ordered product, the evolution formula of the field density operator is given. Its non-classical properties, such as squeezing effect, antibunching effect, the violation of Cauchy–Schwartze inequality and the entanglement property between two modes, are studied. The influences of the squeezing parameter and the dissipation time on the non-classical properties are discussed. The results obtained by the numerical method show that its non-classical properties are all weakened with the dissipation. On the other hand, its squeezing effect and the entanglement property between two modes are strengthened, but its antibunching effect and the violation of Cauchy–Schwartze inequality are weakened with the increase of the squeezing parameter. [ABSTRACT FROM AUTHOR]

Quantum privacy query (QPQ) is a cryptographic application that protects the privacy of both users and databases while querying the database secretly. In most existing QPQ protocols, the protection of user privacy can only be cheat-sensitive. Cheat-sensitive means that Bob will be found later with a certain probability if he tries to get the address queried by Alice. On the premise of cheat-sensitive, although Alice can discover Bob's malicious behavior after a query (transaction), the secret information of Alice was leaked in the completed query, which is likely to be a fatal blow to Alice. Or, to prevent Bob's malicious behavior, Alice executes one or more additional queries to test Bob's honesty. However, to bypass Alice's honesty test, Bob can also provide several honest queries before performing dishonest queries. Therefore, cheat-sensitive should not be the ultimate goal of user privacy protection in QPQ. In this paper, we propose a two-way QKD-based QPQ protocol with better user privacy protection than cheat-sensitive based on order rearrangement of qubits. The proposed QPQ protocol can resist the Trojan horse attack even without wavelength filter and photon number splitter equipped with auxiliary monitoring detectors. [ABSTRACT FROM AUTHOR]

We propose a scheme of controlled cyclic quantum teleportation of an arbitrary two-qubit entangled state by using a ten-qubit entangled state. In our scheme, Alice can teleport an arbitrary two-qubit entangled state to Bob, Bob can teleport an arbitrary two-qubit entangled state to Charlie and at the same time Charlie can teleport an arbitrary two-qubit entangled state to Alice with the help of the controller David. [ABSTRACT FROM AUTHOR]