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A simple relation is established for the evolution equation of quantum-information-processing protocols such as quantum teleportation, remote state preparation, Bell-inequality violation, and particularly the dynamics of geometric quantum correlation measures. This relation shows that when the system traverses the local quantum channel, various figures of merit of the quantum correlations for different protocols demonstrate a factorization decay behavior for dynamics. We identified the family of quantum states for different kinds of quantum channels under the action of which the relation holds. This relation simplifies the assessment of many quantum tasks. [ABSTRACT FROM AUTHOR]

The effect of a local trace-preserving single-qubit channel on a two-qubit state is investigated in the frame of quantum steering ellipsoids (QSEs). The phenomenon of locally increased quantum discord is visualized in this picture. We strictly prove that a 5-side two-qubit discordant state can be locally prepared from a classical state by a trace-preserving channel on qubit B if and only if its QSE of B is a nonradial line segment. For states with higher-dimensional QSEs, the phenomenon of locally increased quantum correlation generally happens when the shape of the QSE is like a baguette. Based on this observation, we find a class of entangled states whose quantum discord can be increased by the local amplitude-damping channel. Further, we find that the local quantum channel does not increase the size of the QSEs of either qubit A or qubit B, for the needle-shaped QSE states, or for the Bell diagonal states with higher-dimensional QSEs. [ABSTRACT FROM AUTHOR]

We study controllable single-photon transport in a one-dimensional waveguide with a nonlinear dispersion relation coupled to a three-level emitter in a cascade configuration. An extra cavity field is introduced to drive one of the level transitions of the emitter. In the resonance case, when the extra cavity does not contain photons, the input single photon will be reflected; when the cavity contains one photon, the full transmission of the input single photon can be obtained. In the off-resonance case, the single-photon transport can also be controlled by the parameters of the cavity. Therefore, we show that single-photon transport can be controlled by an extra cavity field. [ABSTRACT FROM AUTHOR]

We investigate the fine-grained uncertainty relations for qubit systems by measurements corresponding respectively to two and three spin operators. Then we derive the general bound for a combination of two probabilities of projective measurements in mutually unbiased bases in d-dimensional Hilbert space. All of those uncertainty inequalities can be applied to construct different thermodynamic cycles such that the violation of those inequalities will lead to the violation of the second law of thermodynamics. This reveals the relationship between fine-grained uncertainty and the second law of thermodynamics. [ABSTRACT FROM AUTHOR]

Precise measurement is crucial to science and technology. However, the rule of nature imposes various restrictions on the precision that can be achieved depending on specific methods of measurement. In particular, quantum mechanics poses the ultimate limit on precision which can only be approached but never be violated. Depending on analytic techniques, these bounds may not be unique. Here, in view of prior information, we investigate systematically the precision bounds of the total mean-square error of vector parameter estimation which contains d independent parameters. From quantum Ziv-Zakai error bounds, we derive two kinds of quantum metrological bounds for vector parameter estimation, both of which should be satisfied. By these bounds, we show that a constant advantage can be expected via a simultaneous estimation strategy over the optimal individual estimation strategy, which solves a long-standing problem. A general framework for obtaining the lower bounds in a noisy system is also proposed. [ABSTRACT FROM AUTHOR]

When a probe qubit is coupled to a quantum register that represents a physical system, the probe qubit will exhibit a dynamical response only when it is resonant with a transition in the system. Using this principle, we propose a quantum algorithm for solving discrete mathematical problems based on the circuit model. Our algorithm has favorable scaling properties in solving some discrete mathematical problems. [ABSTRACT FROM AUTHOR]

By using the quantum-memory-assisted entropie uncertainty relation (EUR), we derive a computable tight upper bound for quantum discord, which applies to an arbitrary bipartite state. Detailed examples show that this upper bound is tighter than other known bounds in a wide regime. Furthermore, we show that for any tripartite pure state, the quantum-memory-assisted EUR imposes a constraint on the shareability of quantum correlations among the constituent parties. This conclusion amends the well-accepted result that quantum discord is not monogamous. [ABSTRACT FROM AUTHOR]

We investigate the superadditivity property of quantum-correlating power (QCP), which is the power of generating quantum correlation by a local quantum channel. We prove that, when two local quantum channels are used in parallel, the QCP of the composed channel is no less than the sum of QCP of the two channels. For local channels with zero QCP, the superactivation of QCP is a fairly common effect, and it is proven to exist widely except for the trivial case where both of the channels are completely decohering channels or unitary operators. For general quantum channels, we show that the (not-so-common) additivity of QCP can be observed for the situation where a measuring-and-preparing channel is used together with a completely decohering channel. [ABSTRACT FROM AUTHOR]

We define quantum-correlating power (QCP) of a local quantum channel acting on the left part of a bipartite quantum system as the maximum amount of left quantum correlation that can be created by this channel. We prove that for any local channel, the optimal input state, which corresponds to the maximum quantum correlation in the output state, must be a classical-classical state. Further, the single-qubit channels with maximum QCP can be found in the class of channels which take their optimal input states to rank-two quantum-classical states. A superactivation property of QCP, that is, two zero-QCP channels can constitute a positive-QCP channel, is observed and discussed for single-qubit phase damping channels. The analytic expression for QCP of single-qubit amplitude damping channel is obtained. [ABSTRACT FROM AUTHOR]

We investigate the quantum anomalous Hall effect in a mixture of ultracold neutral bosons and fermions held on a hexagonal optical lattice. In the strong atom-atom interaction limit, composite fermions composed of one fermion with bosons or bosonic holes in the mixture are formed. Such composite fermions have already been generated successfully in experiment [Nat. Phys. 7, 642 (2011)]. Here we predict that this kind of composite fermion may provide a realization of the quantum anomalous Hall effect by tuning the atom-atom interaction or the filling of the bosons in the mixture. We also discuss the corresponding experimental signatures of the quantum anomalous Hall effect in the Bose-Fermi mixture on hexagonal optical lattice. [ABSTRACT FROM AUTHOR]

With the aid of a quantum memory, the uncertainty about the measurement outcomes of two incompatible observables of a quantum system can be reduced. We investigate this measurement uncertainty bound by considering an additional quantum system connected with both the quantum memory and the measured quantum system. We find that the reduction of the uncertainty bound induced by a quantum memory, on the other hand, implies it is increasing for a third participant. We also show that the properties of the uncertainty bound can be viewed from perspectives of both quantum and classical correlations, in particular, that the behavior of the uncertainty bound is a result of competitions of various correlations between different parties. [ABSTRACT FROM AUTHOR]

By exploring the spin-orbit-coupled rotating pseudo-spin-1/2 Bose-Einstein condensates with the stochastic projected Gross-Pitaevskii equations, we prove the existence of the circular-hyperbolic skyrmion, which possesses two extreme values of Sz. The nonequal intraspecies interactions and interspecies interactions cause the two components to be wholly disproportionate when the system reaches the equilibrium state. The circular-hyperbolic skyrmion results from the vortex-dipole structure. For the miscible condensates, the increase of spin-orbit coupling enhances the creation of the circular-hyperbolic skyrmion, and makes them link one after another locally. In particular, the circular-hyperbolic skyrmion even can form a chain when the spin-orbit coupling is only in one direction. For the immiscible condensates, the hyperbolic skyrmion occurs at the center, while the circular-hyperbolic skyrmion occurs at the outskirts of the condensates. The increase of the spin-orbit coupling restricts the creation of the hyperbolic skyrmion and enhances the creation of the circular-hyperbolic skyrmion. [ABSTRACT FROM AUTHOR]

In this paper, we present the concept of the one-way unlocalizable quantum discord and investigate its properties. We provide a polygamy inequality for it in a tripartite pure quantum system of arbitrary dimension. Several tradeoff relations between the one-way unlocalizable quantum discord and other correlations are given. If the von Neumann measurement is made on a part of the system, we give two expressions of the one-way unlocalizable quantum discord in terms of partial distillable entanglement and quantum disturbance. Finally, we also provide a lower bound for bipartite shareability of quantum correlation beyond entanglement in a tripartite system. [ABSTRACT FROM AUTHOR]

Quantum correlation can be created by a local operation from some initially classical states. We prove that the necessary and sufficient condition for a local trace-preserving channel to create quantum correlation is that it is not a commutativity-preserving channel. This condition is valid for arbitrary finite dimension systems. We also derive the explicit form of commutativity-preserving channels. For a qubit, a commutativity-preserving channel is either a completely decohering channel or a mixing channel. For a three-dimensional system (qutrit), a commutativity-preserving channel is either a completely decohering channel or an isotropic channel. [ABSTRACT FROM AUTHOR]

Quantum coherence, incompatibility, and quantum correlations are fundamental features of quantum physics. A unified view of those features is crucial for revealing quantitatively their intrinsic connections. We define the relative quantum coherence of two states as the coherence of one state in the reference basis spanned by the eigenvectors of another one and establish its quantitative connections with the extent of mutual incompatibility of two states. We also show that the proposed relative quantum coherence, which can take any form of measures such as l¹ norm and relative entropy, can be interpreted as or connected to various quantum correlations such as quantum discord, symmetric discord, entanglement of formation, and quantum deficits. Our results reveal conceptual implications and basic connections of quantum coherence, mutual incompatibility, and quantum correlations. [ABSTRACT FROM AUTHOR]

We present a quantum clock synchronization scheme of multiple parties which uses operation as the trigger to start the evolution of the initial state. In comparison, the existing protocols use measurement to start the evolution. We show that our protocol links the problem to a multiple-phase estimation problem, such that we have provided a general framework for the study of quantum clock synchronization. We can use the Fisher information to give the precision of the synchronization, and we explicitly show that the Heisenberg scale of synchronization is achieved in the two-party case. We prove that the measurement-triggered quantum clock synchronization is included in the operation-triggered quantum clock synchronization, so the operation-triggered quantum clock synchronization is, in general, more powerful than measurement-triggered quantum clock synchronization. We show that our protocol is very efficient in synchronizing a clock to the average time of other clocks. [ABSTRACT FROM AUTHOR]

We present the entropie uncertainty relations for multiple measurement settings which demonstrate the uncertainty principle of quantum mechanics. Those uncertainty relations are obtained for both cases with and without the presence of quantum memory, and can be proven by a unified method. Our results recover some well known entropie uncertainty relations for two observables, which show the uncertainties about the outcomes of two incompatible measurements. The bounds of those relations which quantify the extent of the uncertainty take concise forms and are easy to calculate. Those uncertainty relations might play important roles in the foundations of quantum theory. Potential experimental demonstration of those entropie uncertainty relations is discussed. [ABSTRACT FROM AUTHOR]

We investigate the coherence measures induced by fidelity and trace norm, based on the coherence quantification recently proposed by Baumgratz et al. [T. Baumgratz, M. Cramer, and M. B. Plenio, Phys. Rev. Lett. 113, 140401 (2014)]. We show that the fidelity of coherence does not in general satisfy the monotonicity requirement as a measure of coherence under the subselection of the measurement condition. We find that the trace norm of coherence can act as a measure of coherence for qubits and some special class of qutrits with some restrictions on the incoherent operators, while the general case needs to be explored further. [ABSTRACT FROM AUTHOR]

In quantum metrology schemes, one generally needs to prepare m copies of N entangled particles, such as entangled photon states, and then they are detected in a destructive process to estimate an unknown parameter. Here we present an experimental scheme for estimating this parameter by using repeated indirect quantum nondemolition measurements in the setup consisting of a photon in a superconducting cavity (called a photon box). This interaction-based scheme is able to achieve the phase sensitivity scaling as l/N with a Fock state of N photons. Moreover, we only need to prepare one initial //-photon state and it can be used repetitively for m trials of measurements. This scheme is shown to sustain the quantum advantage for a much longer time than the damping time of Fock state and be more robust than the common strategy with exotic entangled states. To overcome the 2π/N periodic error in the estimation of the true parameter, we can employ a cascaded strategy by adding a real-time feedback interferometric layout. [ABSTRACT FROM AUTHOR]

We study the dynamics of classical correlation, quantum discord, and measurement-induced disturbance of Dirac fields in the background of a dilaton black hole. We present an alternative physical interpretation of single mode approximation for Dirac fields in black hole spacetimes. We show that the classical and quantum correlations are degraded as the increase of black hole's dilaton. We find that, comparing to the inertial systems, the quantum correlation measured by the one-side measuring discord is always not symmetric with respect to the measured subsystems, while the measurement-induced disturbance is symmetric. The symmetry of classical correlation and quantum discord is influenced by gravitation produced by the dilaton of the black hole. [ABSTRACT FROM AUTHOR]

In this study, accurate static dipole polarizability and hyperpolarizability are calculated for Al+ ground state 3s² ¹S0 and excited state 3s3p ³PJ with J=0,1,2 . The finite-field computations use energies obtained with the relativistic configuration interaction approach and the relativistic coupled-cluster approach. Excellent agreement with previously recommended values is found for the dipole polarizability of Al+ ground state 3s2 ¹S0 and excited state 3s3p ³P0 as well as the hyperpolarizability of the ground state 3s 2 ¹S0 . The recommended values of the dipole polarizability of the Al+ 3s3p ³P1 and ³P2 and the hyperpolarizability of Al+ 3s3p ³P0, ³P1, and ³P2 are also given. The impacts of the relativity and spin-orbit coupling are elucidated by analyzing the angular momentum dependence of the dipole polarizability and the hyperpolarizability, and comparing the fully and scalar relativistic calculated data. It is shown that the impact of the relativity and spin-orbit coupling are small for the dipole polarizability but become significant for the hyperpolarizability. Finally, the blackbody radiation shifts contributed by the dipole polarizability and hyperpolarizability, respectively, are evaluated for transitions of Al+ 3s 2 ¹S0 to 3s3p ³PJ with J=0,1,2 . [ABSTRACT FROM AUTHOR]

We study the quantum error-correcting codes over mixed alphabets to deal with a more complicated and practical situation in which the physical systems for encoding may have different numbers of energy levels. In particular we investigate their constructions and propose the theory of quantum Singleton bound. Two kinds of code constructions are presented: a projection-based construction for general case and a graphical construction based on a graph-theoretical object composite coding clique dealing with the case of reducible alphabets. We find out some optimal one-error correcting or detecting codes over two alphabets. Our method of composite coding clique also sheds light on constructing standard quantum error-correcting codes, and other families of optimal codes are found. [ABSTRACT FROM AUTHOR]

We present a nondemolition quantum information processing task of probing the information of a class of quantum state. In this task, the information is extracted by some unitary evolution with the introduced probing qubit assisted, but the probed quantum state (density matrix) is undisturbed at any time and independent of the choice of the initial probing state. We give a sufficient and necessary condition on the Hamiltonian that can lead to the successful realization of such a task. We prove that, for any feasible scheme, the probed plus probing system will always stay at a disentangled state with one side's quantum discord absent and the other side's inevitably produced in the probing process. An explicit example is given for the demonstration, which shows that the ratio of quantum discord to the total correlation will have to reduce to zero for the maximal accessible information. In this sense, we say that quantum discord plays a dual role in this case. [ABSTRACT FROM AUTHOR]

The overlap measurement scheme accomplishes the evaluation of the overlap of two input quantum states by only measuring an introduced auxiliary qubit, irrespective of the complexity of the two input states. We find a counterintuitive phenomenon that no quantum dissonance can be found in the process of overlap measurement scheme, even though the auxiliary qubit might be entangled, classically correlated, or even uncorrelated with the two input states based on different types of input states. In principle, this provides an opposite but supplementary example to the remarkable algorithm of the deterministic quantum computation with one qubit in which no entanglement is present but quantum dissonance is necessary. Finally, we consider a simple overlap measurement model to demonstrate the continuous change (including potential sudden death of quantum discord) of the input states from entangled to product states by only adjusting some initial parameters. [ABSTRACT FROM AUTHOR]

Conversions between the ground states in quantum critical systems via entanglement-assisted local operations and classical communications (ELOCC) are studied. We propose an alternative method to reveal the different convertibility by local operations when a quantum phase transition occurs. We have studied the ground-state local convertibility in the one-dimensional transverse field Ising model, XY model and XXZ model. It is found that the ELOCC convertibility suddenly changes at the phase transition points. In the transverse field Ising model the ELOCC convertibility between the first-excited state and the ground state are also distinct for different phases. The relation between the order of quantum phase transitions and the local convertibility is discussed. [ABSTRACT FROM AUTHOR]

Einstein-Podolsky-Rosen (EPR) steering is an intermediate type of quantum nonlocality which sits between entanglement and Bell nonlocality. A set of correlations is Bell nonlocal if it does not admit a local hidden variable (LHV) model, while it is EPR nonlocal if it does not admit a local hidden variable-local hidden state (LHV-LHS) model. It is interesting to know what states can generate EPR-nonlocal correlations in the simplest nontrivial scenario, that is, two projective measurements for each party sharing a two-qubit state. Here we show that a two-qubit state can generate EPR-nonlocal full correlations (excluding marginal statistics) in this scenario if and only if it can generate Bell-nonlocal correlations. If full statistics (including marginal statistics) is taken into account, surprisingly, the same scenario can manifest the simplest one-way steering and the strongest hierarchy between steering and Bell nonlocality. To illustrate these intriguing phenomena in simple setups, several concrete examples are discussed in detail, which facilitates experimental demonstration. In the course of study, we introduce the concept of restricted LHS models and thereby derive a necessary and sufficient semidefinite-programming criterion to determine the steerability of any bipartite state under given measurements. Analytical criteria are further derived in several scenarios of strong theoretical and experimental interest. [ABSTRACT FROM AUTHOR]

We investigate maximally coherent states to provide a refinement in quantifying coherence and give a measure-independent definition of the coherence-preserving operations. A maximally coherent state can be considered a resource to create arbitrary quantum states of the same dimension by merely incoherent operations. We propose that only maximally coherent states should achieve the maximal value for a coherence measure and use this condition as an additional criterion for coherence measures to obtain a refinement in quantifying coherence that excludes invalid and inefficient coherence measures. Under this criterion, we then give a measure-independent definition of the coherence-preserving operations, which play a role in quantifying coherence similar to that played by the local unitary operations in the scenario of studying entanglement. [ABSTRACT FROM AUTHOR]

The problems of genuine multipartite entanglement detection and classification are challenging. We show that a multipartite quantum state is genuine multipartite entangled if the multipartite concurrence is larger than certain quantities given by the number and the dimension of the subsystems. This result also provides a classification of various genuine multipartite entanglements. We present a lower bound of the multipartite concurrence in terms of bipartite concurrences. While various operational approaches are available for providing lower bounds of bipartite concurrences, our results give an effective operational way to detect and classify genuine multipartite entanglement. As applications, genuine multipartite entanglement of tripartite systems is analyzed in detail. [ABSTRACT FROM AUTHOR]

The dipole polarizabilities, dipole hyperpolarizabilities, quadrupole moments, and quadrupole polarizabilities of the 5s² ¹S and 5s5p ³P0 states of In+ and Sr are calculated by using the finite-field method. The electron correlation effect and the basis set convergence are investigated in the relativistic coupled-cluster and configuration interaction calculations in order to obtain polarizabilities of high accuracy. Comparative study of the fully and scalar relativistic calculations reveals the effect of the spin-orbit coupling on the dipole polarizabilities of In+ and Sr. The blackbody-radiation shifts of the clock transition 5s² ¹S0-5.s5 f p ³Po0 due to the dipole polarizabilities, quadrupole polarizabilities, and dipole hyperpolarizabilities are evaluated to be 0.017, 8.33x10-10, and 1.93x10-17 Hz for In+ and 2.09 and 5.82x10-8, and 1.69x10-15 Hz for Sr. The blackbody-radiation shifts from the quadrupole polarizabilities and dipole hyperpolarizabilities are significantly less than that from the dipole polarizabilities and therefore can be safely omitted for the quoted 10-18 uncertainty of the optical frequency standard of In+ and Sr. [ABSTRACT FROM AUTHOR]