Super Quantum Discord Research Articles

Exploring the impact of weak measurements on exciton–exciton interactions

In our study of super quantum discord between two excitonic qubits inside a coupled semiconductor quantum dots system, our primary focus is to uncover the impact of weak measurement on its quantum characteristics. To achieve this, we analyze how varying the measurement strength x, affects this super quantum correlation in the presence of thermal effects. Additionally, we assess the effect of this variation on the system’s evolution against its associated quantum parameters; external electric fields, exciton–exciton dipole interaction energy and Förster interaction. Our findings indicate that adjusting x to smaller values effectively enhances the super quantum correlation, making weak measurements act as a catalyst. This adjustment ensures its robustness against thermal effects while preserving the non-classical attributes of the system. Furthermore, our study unveils that the effect of weak measurements on this latter surpasses the quantum effects associated with the system. Indeed, manipulating the parameter x allows the weak measurement to function as a versatile tool for modulating quantum characteristics and controlling exciton–exciton interactions within the coupled semiconductor quantum dots system.

On super quantum discord for high-dimensional bipartite state

On super quantum discord for high-dimensional bipartite state

Simulating the effect of weak measurements by a phase damping channel and determining different measures of bipartite correlations in nuclear magnetic resonance

Quantum discord is a measure based on local projective measurements which captures quantum correlations that may not be fully captured by entanglement. A change in the measurement process, achieved by replacing rank-one projectors with a weak positive operator-valued measure (POVM), allows one to define weak variants of quantum discord. In this work, we experimentally simulate the effect of a weak POVM on a nuclear magnetic resonance quantum information processor. The two-qubit system under investigation is part of a three-qubit system, where one of the qubits is used as an ancillary to implement the phase damping channel. The strength of the weak POVM is controlled by varying the strength of the phase damping channel. We experimentally observed two weak variants of quantum discord namely, super quantum discord and weak quantum discord, in two-qubit Werner and Bell-diagonal states. The resultant dynamics of the states is investigated as a function of the measurement strength.

Dynamics of quantum correlations for different types of noisy channels

The effect of noise channels (amplitude damping, phase damping, depolarizing and phase flip) on the behaviors of quantum correlations such as quantum discord (QD), super quantum discord (SQD) within an atom-field interaction with environments are investigated. Generation and preservation of the quantum entanglement between the qubit and field have played an important role for both fundamental quantum theories and experiments. This topic motivates us to explore the role of noise channels on quantum correlations in the Jaynes–Cummings model. Our analytical results show that the entanglement and quantum correlation dynamics is strongly related to the decoherenc strength and type of noisy channel. One purpose of this work is to answer the following question: is it possible the effects of noise channels on entangled states lead to birth of entanglement and quantum correlations or do they just have a destructive effects? We show that, the noise of all above channels do not lead to a sudden vanishing of quantum correlations. But the noise of phase flip channel reproduces initial quantum correlations. Furthermore, we find that entanglement and QD are more fragile to environmental noises than the SQD. For this reason, it seems that our results can be beneficial to deeply understanding the weak measurement and quantum correlation in quantum information resource.

Super dense coding in one-axis twisting model

We study thermal dense coding in a two-spin model under an external magnetic eld. Its depen-dencies on magnetic eld, strength of the spin squeezing and temperature are presented in detail.Our main goal now is to study how we can increase the thermal dense coding capacity in the presenceof magnetic eld, strength of the spin squeezing and temperature. It shows that the dense codingtend to valid value by setting the value of the input quantum correlations. Our most importantmotive for this study is to examine the relationship between the thermal properties of super quan-tum discord (SQD) and dense coding. The results show that the thermal properties of the SQD onour channel enable us to determine when and under what conditions the system is suitable for validdense coding. Our proposals could be lead to that this scheme is efficient for quantum informationprocessing.

热环境下超量子失协的动力学特性

热环境下超量子失协的动力学特性

Super-quantum discord in ferromagnetic and antiferromagnetic materials

Super-quantum discord is an extension of the quantum discord concept where weak measurements are made instead of projective measurements. We study the temperature behavior of the super-quantum discord for two real magnetic materials. We extract information about super-quantum discord from the magnetic susceptibility data for iron nitrosyl complexes $\mathrm{ Fe_2(SC_3 H_5N_2)_2(NO)_4}$ and binuclear Cu(II) acetate complex $\mathrm{[Cu_2 L(OAc)]\cdot 6 H_2O}$, where $\mathrm{ L}$ is a ligand that allows us to compare the super-quantum discord with the standard one. The dependence of the super-quantum discord on the parameter describing weak measurements is studied. Obtained difference between super-quantum and quantum discords confirms the detection of additional quantum correlations that are usually destroyed during projective measurements. The use of the approach allows to predict quantitatively in advance the advantages of use of weak measurements versus projective one for quantum technologies in real settings where quantum discord is used as resource. This can be relevant particularly in macroscopic quantum systems where weak measurements can be used to extract information about the system.

The pairwise quantum correlations for teleported state via a symmetric multi-qubit system

We study the pairwise quantum correlations for teleported state via a symmetric multi-qubitsystem. In the other words, the proposed model is considered as a quantum channel. Using thequantum discord, super quantum discord and concurrence to quantify quantum correlations forteleported state, some analytical and numerical results are presented. Moreover, we compare thedynamical evolutions of quantum correlations and fidelity versus measurement strength and thenumber of qubit channel for teleported state via symmetric multi-qubit model. Our main goalnow is to study how we can increase the quantum correlations and the fidelity of the teleportedstate in the presence of decoherence. The results show that, measurement strength and thenumber of qubit can control the quantum information obtained through the quantum channel.Therefore, measurement strength can be a good option for measuring exchanged information inthe teleportation process. In addition to, quantum correlations can provide an effective role inquantum teleportation

Measurement-based quantum correlation in mixed-state quantum metrology

Entanglement is crucial for realizing quantum advantages in metrology. However, entanglement has been outcast by discord in order to capture the worst-case sensitivity in quantum metrology to estimate an unknown parameter. In contrast to traditional measures—namely entanglement and discord—there exist noncommutativity-based quantum correlation measures induced by local von Neumann measurements. Such correlations are more comprehensive than entanglement and discord in quantum information processing. In this paper, we investigate the metrological resourcefulness of measurement-based quantum correlations (MbQCs). We provide a lower bound on the minimum precision of the estimation in terms of the MbQC. We show that the MbQC is more resourceful in quantum metrology than entanglement and super quantum discord. For any non-product state, the MbQC gives a metrological insight into the sensitivity of a mixed state toward perturbation caused by a local von Neumann measurement.

Dynamics of super quantum discord and optimal dense coding in quantum channels

Quantum discord (QD), super quantum discord (SQD) and optimal dense coding at entangled states of three types of quantum channels, are investigated. The used models include: two-qubit spin squeezing, the two-qubit Heisenberg XYZ model with decoherency and the Jaynes–Cummings model. In the first two models the quantum correlations and the optimal dense coding capacity are calculated in terms of channel parameters, system initial conditions and decoherency rate. It has been found that valid dense coding can exist, although there is no trace of entanglement in the quantum channel. In contrast, despite the presence of entanglement states in the system, there may be no dense coding capacity. We investigate the effects of cavity Fock states on quantum correlations and optimal dense coding in the Jaynes–Cummings model. Cavity Fock states are found to be effective for quantum correlations and optimal dense coding. The common result of all three models is that the dynamic properties of SQD on our channel enable us to determine when and under what conditions the system is suitable for dense coding capacity.

Thermal Quantum Discord and Super Quantum Discord Teleportation Via a Two-Qubit Spin-Squeezing Model

We study thermal quantum correlations (quantum discord and super quantum discord) in a two-spin model in an external magnetic field and obtain relations between them and entanglement. We study their dependence on the magnetic field, the strength of the spin squeezing, and the temperature in detail. One interesting result is that when the entanglement suddenly disappears, quantum correlations still survive. We study thermal quantum teleportation in the framework of this model. The main goal is investigating the possibility of increasing the thermal quantum correlations of a teleported state in the presence of a magnetic field, strength of the spin squeezing, and temperature. We note that teleportation of quantum discord and super quantum discord can be realized over a larger temperature range than teleportation of entanglement. Our results show that quantum discord and super quantum discord can be a suitable measure for controlling quantum teleportation with fidelity. Moreover, the presence of entangled states is unnecessary for the exchange of quantum information.

Thermal quantum discord and super quantum discord teleportation via a two-qubit spin-squeezing model

Изучаются термальные квантовые корреляции (квантовый дискорд и квантовый супердискорд) в двухспиновой модели во внешнем магнитном поле, получены соотношения между ними и запутанностью. Подробно изучена их зависимость от магнитного поля, от силы спинового сжатия и температуры. Одним из интересных результатов является то, что при внезапном исчезновении запутанности квантовые корреляции все же выживают. Изучена термальная квантовая телепортация в рамках упомянутой модели. Основной целью является изучение возможности увеличить термальные квантовые корреляции телепортированного состояния при наличии магнитного поля, силы спинового сжатия и температуры. Отмечено, что телепортация квантового дискорда и квантового супердискорда осуществима на большем интервале температур, чем телепортация запутанности. Наши результаты показывают, что наряду с надежностью квантовый дискорд и квантовый супердискорд могут быть подходящими мерами контроля квантовой телепортации. Кроме того, для обмена квантовой информацией необязательно наличие запутанных состояний.

Super-quantum correlation for SU(2) invariant state in $$4\otimes 2$$ 4 ⊗ 2 system

We analytically evaluate the weak one-way deficit and super-quantum discord for a system composed of spin-3/2 and spin-1/2 subsystems possessing SU(2) symmetry. We also make a comparative study of the relationships among the quantum discord, one-way deficit, weak one-way deficit, and super-quantum discord for the SU(2) invariant state. It is shown that super-quantum discord via weak measurement is greater than that via von Neumann measurement. But weak one-way deficit is less than the one-way deficit. As a result, weak measurement do not always reveal more quantumness.

Dynamics super quantum discord and quantum discord teleportation in the Jaynes–Cummings model

The aim of this paper is investigation on dynamics of super quantum discord (SQD) and quantum discord (QD) teleportation in the Jaynes–Cummings model. In order to teleport one and two qubit states, a scheme is proposed for quantum channel where is induced from an atom-field interaction. The initial state of the atom is its excited state while the state of field starts in a coherent one. The model reveals that the dynamics of quantum correlations depends crucially on atom-field initial conditions and the field parameters can be utilized as control parameters for optimal teleportation. Interestingly, we find that QD teleportation and SQD teleportation are not always zero when the entanglement falls to zero for a teleported state. This result clearly illustrates that in some cases we can only get a truly quantum teleportation by QD and SQD if we use a suitable field parameters and initial state, which have no entanglement. The results reveal that QD and SQD for teleported states are much robuster than entanglement in the process of communication. According to the results, the proposed scheme can greatly reduce the cost of quantum communication. We also obtain that the behaviour of the QD and SQD teleportation are similar to average fidelity. So, QD and SQD can be used to analyse teleported state as average fidelity.

Super quantum discord for general two qubit X states

The exact solutions of the super quantum discord are derived for general two qubit X states in terms of a one-variable function. Several exact solutions of the super quantum discord are given for the general X-state over nontrivial regions of a seven dimensional manifold. It is shown that the super quantum discord of the X state may increase or decreases under the phase damping channel.

Nonclassical Correlations in a Three-Mode Continuous-Variable System

We investigate a standard measure of quantum discord for tripartite coherent states of the Greenberger–Horne–Zeilinger (GHZ) type. Furthermore, we check the monotonicity of a superquantum discord according to weak quantum measurements. We accomplish our study by manipulating the amount of quantum information lost during the perturbation of the quantum system and controlling the measurement strength. In addition, we calculate the entanglement of the system under study. Finally we compare the behavior of the three correlations.

Super One-Way Information Deficit for A Two-Parameter Class of States In 2 ⊗ D Quantum Systems

So far, the super one-way deficit in weak measurement has been calculated explicitly only for a limited set of two-qubit quantum states and expressions for more general states are not known. In this paper, we extend the previous studies to 2 ⊗ d quantum systems and derive an analytical expression for a two-parameter class of states for d ≥ 3. We compare quantum discord and super one-way deficit for qubit-qutrit systems. We find that super one-way deficit is smaller than the quantum discord. On the other hand, by tuning the weak measurement continuously to the projective measurement, both super one-way deficit and quantum discord converge to the same value.

Super quantum discord for a class of X-states with weak measurements

So far, super quantum discord has been calculated explicitly only for Bell-diagonal states and expressions for more general quantum states are not known. In this paper, we derive explicit expressions for super quantum discord for a larger class of two-qubit states, namely, a 4-parameter family of X-states. We observe that, weak measurements obtain more quantumness of correlations than strong measurements. As an application, the dynamic behavior of the super quantum discord under decoherence channel is investigated. We find that, the super quantum discord decreases monotonically as a function of the measurement strength parameter.

Super-quantum discord with weak measurement in circuit QED

Super-quantum discord (SQD) with weak measurement is regarded as a kind of quantum correlation in quantum information processing. We investigate the dynamical evolution of SQD under weak measurement in circuit quantum electrodynamics (circuit QED). The results indicate that in the correlated dephasing decay channel, the SQD monotonously tends to a stable value depending on the purity of initial quantum state, and the freezing phenomenon occurs. In the correlated instantaneous decay channel, however, not only the detuning sudden change but also the freezing phenomenon appear, and the freezing stable value is unrelated to the purity of the initial quantum state. The results reveal that the dynamical behavior of SQD entirely differs from the quantum discord, and it could become one important resource of quantum information.

Dynamics of Super Quantum Correlations and Quantum Correlations for a System of Three Qubits

The dynamics of quantum discord for two qubits independently interacting with dephasing reservoirs have been studied recently. The authors [Phys. Rev. A 88 (2013) 034304] found that for some Bell-diagonal states (BDS) which interact with their environments the calculation of quantum discord could experience a sudden transition in its dynamics, this phenomenon is known as the sudden change. Here in the present paper, we analyze the dynamics of normal quantum discord and super quantum discord for tripartite Bell-diagonal states independently interacting with dephasing reservoirs. Then, we find that basis change does not necessary mean sudden change of quantum correlations.