Genetic correlations in mutation processes

We study the role of phylogenetic trees on correlations in mutation processes. Generally, correlations decay exponentially with the generation number. We find that two distinct regimes of behavior exist. For mutation rates smaller than a critical rate, the underlying tree morphology is almost irrelevant, while mutation rates higher than this critical rate lead to strong tree-dependent correlations. We show analytically that identical critical behavior underlies all multiple point correlations. This behavior generally characterizes branching processes undergoing mutation.     

Bell-type inequalities to detect true n-body nonseparability

We analyze the structure of correlations among more than two quantum systems. We introduce a classification of correlations based on the concept of nonseparability, which is different a priori from the concept of entanglement. Generalizing a result of Svetlichny [Phys. Rev. D 35, 3066 (1987)] on three-particle correlations, we find an inequality for n-particle correlations that holds under the most general separability condition and that is violated by some quantum-mechanical states.     

Increasing complexity with quantum physics

We argue that complex systems science and the rules of quantum physics are intricately related. We discuss a range of quantum phenomena, such as cryptography, computation and quantum phases, and the rules responsible for their complexity. We identify correlations as a central concept connecting quantum information and complex systems science. We present two examples for the power of correlations: using quantum resources to simulate the correlations of a stochastic process and to implement a classically impossible computational task.     

Detecting Quantum Dissonance and Discord in Exact Dynamics of qubit Systems

In this paper, we evaluate the quantum and classical correlations in exact dynamics of qubit systems interacting with a common dephasing environment. We show the existence of a sharp transition between the classical and quantum loss of correlations during the time evolution. We show that it is possible to exploit a large class of initial states in different tasks of quantum information and processing without any perturbation of the correlations from the environment noisy for large time intervals. On the other hand, we include the dynamics of a new kind of correlation so-called quantum dissonance, which contains the rest of the nonclassical correlations. We show that the quantum dissonance can be considered as an indicator to expect the behavior of the dynamics of classical and quantum correlations in composite open quantum systems.     

Critical point estimation and long-range behavior in the one-dimensional XY model using thermal quantum and total correlations

We investigate the thermal quantum and total correlations in the anisotropic XY spin chain in transverse field. While we adopt concurrence and geometric quantum discord to measure quantum correlations, we use measurement-induced non-locality and an alternative quantity defined in terms of Wigner–Yanase information to quantify total correlations. We show that the ability of these measures to estimate the critical point at finite temperature strongly depend on the anisotropy parameter of the Hamiltonian. We also identify a correlation measure which detects the factorized ground state in this model. Furthermore, we study the effect of temperature on long-range correlations.     

Positive current correlations associated with super-Poissonian shot noise

We report on shot noise cross spectrum measurements in a beam splitter configuration. Electrons tunneling through potential barriers are incident on a beam splitter and scattered into two separate channels. Such a partition process introduces correlations between the fluctuations of the two currents. Our work has confirmed that the generally expected negative correlations resulted from sub-Poissonian electron sources. More interestingly, positive cross correlations associated with barriers exhibiting super-Poissonian shot noise have also been observed. We have found that both positive and negative correlations can be related to the noise properties of the electron source.     

Energy transfer and correlation dynamics in a three-quasi-spin-pigment system

In this paper, the effects of quantum and classical correlations on the excitation energy transfer in a three-quasi-spin-pigment system are investigated. We first study the dependence of the energy transfer efficiency on various initial correlations of the donor pigments, and find that the initial concurrence is crucial to the efficiency no matter whether the initial states are pure or mixed. We then demonstrate the dynamics of correlations of the system and observe the appearance of sudden death of quantum correlations in the donor pigments. The relation between the energy transfer efficiency and the dynamics of correlations in the donor pigments is also discussed.     

Maximally nonlocal and monogamous quantum correlations

We introduce a version of the chained Bell inequality for an arbitrary number of measurement outcomes and use it to give a simple proof that the maximally entangled state of two d-dimensional quantum systems has no local component. That is, if we write its quantum correlations as a mixture of local correlations and general (not necessarily quantum) correlations, the coefficient of the local correlations must be zero. This suggests an experimental program to obtain as good an upper bound as possible on the fraction of local states and provides a lower bound on the amount of classical communication needed to simulate a maximally entangled state in dxd dimensions. We also prove that the quantum correlations violating the inequality are monogamous among nonsignaling correlations and, hence, can be used for quantum key distribution secure against postquantum (but nonsignaling) eavesdroppers.     

Robustness of quantum correlations against decoherence

We study dynamics of nonclassical correlations by exactly solving a model consisting of two atomic qubits with spontaneous emission. We find that the nonclassical correlations defined by different measures give different qualitative characterizations of those correlations. The relative behaviors of those correlation measures are presented explicitly for various quantum states in the two-qubit atomic system. In particular, we find that the robustness of quantum correlations can be greatly enhanced by performing appropriate local unitary operations on the initial state of the system.     

Correlated emission of hadrons from recombination of correlated partons

We discuss different sources of hadron correlations in relativistic heavy ion collisions. We show that correlations among partons in a quasithermal medium can lead to the correlated emission of hadrons by quark recombination and argue that this mechanism offers a plausible explanation for the dihadron correlations in the few GeV/c momentum range observed in Au+Au collisions at the BNL Relativistic Heavy Ion Collider.     

Observable Correlations in Two-Qubit States

The total correlations in a bipartite quantum state are well quantified by the quantum mutual information, the amount of which is not necessarily fully extractable by local measurements. The observable correlations are the maximal correlations that can be extracted via local measurements, and have an intuitive interpretation as a measure of classical correlations. We evaluate the observable correlations for generic two-qubit states and obtain analytical expressions in some particular cases. The intricate and subtle relationships among the total, quantum and classical correlations are illustrated in terms of observable correlations. In the course, we also disprove an intuitive conjecture of Lindblad which states that the classical correlations account for at least half of the total correlations, or equivalently, correlations are more classical than quantum.     

Jet–jet and hadron–jet correlations in hadro- and electroproduction

We discuss, in the framework of perturbative QCD at next to leading order, two related observables which are usually considered to provide tests of the BFKL dynamics: jet–jet correlations at Tevatron energies and forward particle–jet correlations at HERA. In the first case we study the rapidity gap dependence of the azimuthal correlations and find slightly too strong correlations at large gap. In the second case we discuss the cross section as well as the azimuthal correlations over a rapidity gap range of 5 units. We find that the requirement of a forward particle imposes strong kinematical constraints which distort the distributions, notably at small rapidity gaps. We also show that the decorrelation is stronger in electroproduction than in hadron–hadron collisions. Unfortunately data are not yet available for comparison.     

Non-linear and quantum optics of a type II OPO containing a birefringent element

We describe theoretically the quantum properties of a type-II Optical Parametric Oscillator containing a birefringent plate which induces a linear coupling between the orthogonally polarized signal and idler beams and results in phase locking between these two beams. As in a standard OPO, the signal and idler waves show large quantum correlations which can be measured experimentally due to the phase locking between the two beams. We study the influence of the waveplate on the various criteria characterizing quantum correlations. We show in particular that the quantum correlations can be maximized by using optimized quadratures.     

Two-qubit correlations via a periodic plasmonic nanostructure

We theoretically investigate the generation of quantum correlations by using two distant qubits in free space or mediated by a plasmonic nanostructure. We report both entanglement of formation as well as quantum discord and classical correlations. We have found that for proper initial state of the two-qubit system and distance between the two qubits we can produce quantum correlations taking significant value for a relatively large time interval so that it can be useful in quantum information and computation processes.     

Correlation effects in disordered metallic photonic crystal slabs

We analyze the influence of correlations on the optical properties of disordered metallic photonic crystal slabs experimentally and theoretically. Different disorder models with different nearest-neighbor correlations are considered. We present a theory that allows us to quantitatively calculate the optical properties of the different samples. We find that different kinds of correlations produce characteristic spectral features such as peak reduction and inhomogeneous broadening. These features are caused by reduced excitation efficiencies and the excitation of multiple resonances.     

The effect of coulomb correlations on the nonequilibrium charge redistribution tuned by the tunneling current

We demonstrate that the tunneling current flowing through a system with Coulomb correlations leads to a charge redistribution between the different localized states. A simple model consisting of two electron levels is analyzed by means of the Heisenberg equations of motion taking correlations of electron filling numbers in localized states into account exactly in all orders. We consider various relations between the Coulomb interaction and localized electron energies. Sudden jumps of the electron density at each level in a certain range of the applied bias are found. We find that for some parameter range, inverse occupation in the two-level system appears due to Coulomb correlations. It is also shown that Coulomb correlations lead to the appearance of negative tunneling conductivity at a certain relation between the values of tunneling rates from the two electron levels.     

Chiral Magnetic Effect and Chiral Phase Transition

We study the influence of the chiral phase transition on the chiral magnetic effect. The azimuthal charge-particle correlations as functions of the temperature are calculated. It is found that there is a pronounced cusp in the correlations as the temperature reaches its critical value for the QCD phase transition. It is predicted that there will be a drastic suppression of the charge-particle correlations as the collision energy in RHIC decreases to below a critical value. We show then the azimuthal charge-particle correlations can be the signal to identify the occurrence of the QCD phase transitions in RHIC energy scan experiments.     

Information-theoretic approach to the problem of detection of genuine multipartite classical correlations

We examine the problem of detection of genuine multipartite classical correlations. We first show that genuine multipartite classical correlations cannot be reliably detected by analyzing the multipartite covariances, and then we introduce an information-theoretic approach to the problem of detection of such correlations.