Abstract By assuming a general pure state and a mixed Werner state as two initial states, we investigate the time evolution of entropic uncertainty bound in the presence of quantum memory for a two-qubit system interacting with an XY spin chain regarded as an environment constrained to carry the energy current. We obtain an explicit relationship between the entropic uncertainty bound and decoherence factor, and analytically study the dynamical process of entropic uncertainty bound for both weak and strong-coupling cases in two initial states. Our results reveal that the evolution of entropic uncertainty bound depends not only on the energy current, the system-environment couplings and the anisotropy parameter but also on the size of the environmental XY spin chain. Interestingly, we find that the entropic uncertainty bound can be suppressed by reducing the energy current on the environmental spin chain in a weak-coupling region, however, it has no sensitivity to the energy current in a strong-coupling region.
Abstract By assuming a general pure state and a mixed Werner state as two initial states, we investigate the time evolution of entropic uncertainty bound in the presence of quantum memory for a two-qubit system interacting with an XY spin chain regarded as an environment constrained to carry the energy current. We obtain an explicit relationship between the entropic uncertainty bound and decoherence factor, and analytically study the dynamical process of entropic uncertainty bound for both weak and strong-coupling cases in two initial states. Our results reveal that the evolution of entropic uncertainty bound depends not only on the energy current, the system-environment couplings and the anisotropy parameter but also on the size of the environmental XY spin chain. Interestingly, we find that the entropic uncertainty bound can be suppressed by reducing the energy current on the environmental spin chain in a weak-coupling region, however, it has no sensitivity to the energy current in a strong-coupling region.
We investigate the entanglement dynamics of a two-qubit system which interacts with a Heisenberg XY spin chain constrained to carry an energy current. We show an explicit connection between the decoherence factor and entanglement, and numerically and analytically study the dynamical process of entanglement in both weak- and strong-coupling cases for two initial states, the general pure state and the mixed Werner state. We provide results that the entanglement evolution depends not only on the energy current, the anisotropy parameter and the system-environment couplings but also on the size of degrees of freedom of environment. In particular, our results imply that entanglement will be strongly suppressed by the introduction of energy current on the environmental spin chain in the weak-coupling region while it is not sensitive to the energy current in the strong-coupling region. We also observe the sudden death of entanglement in the system and show how the energy current affects the phenomenon.
Abstract The precision of measurements for two incompatible observables in a physical system can be improved with the assistance of quantum memory. In this paper, we investigate the quantum-memory-assisted entropic uncertainty relation for a spin-1 Heisenberg model in the presence of external magnetic fields, the systemic quantum entanglement (characterized by the negativity) is analyzed as contrast. Our results show that for the XY spin chain in thermal equilibrium, the entropic uncertainty can be reduced by reinforcing the coupling between the two particles or decreasing the temperature of the environment. At zero-temperature, the strong magnetic field can result in the growth of the entropic uncertainty. Moreover, in the Ising case, the variation trends of the uncertainty are relied on the choices of anisotropic parameters. Taking the influence of intrinsic decoherence into account, we find that the strong coupling accelerates the inflation of the uncertainty over time, whereas the high magnetic field contributes to its reduction during the temporal evolution. Furthermore, we also verify that the evolution behavior of the entropic uncertainty is roughly anti-correlated with that of the entanglement in the whole dynamical process. Our results could offer new insights into quantum precision measurement for the high spin solid-state systems.
Abstract The uncertainty principle is an inherent characteristic of quantum mechanics. This principle can be formulated in various forms. Fundamentally, this principle can be expressed in terms of the standard deviation of the measured observables. In quantum information theory, the preferred mathematical quantity to express the entropic uncertainty relation is Shannon’s entropy. In this work, we consider the generalized entropic uncertainty relation in which there is an additional particle as a quantum memory. Alice measures on her particle A and Bob, with memory particle B , predicts Alice’s measurement outcomes. It has a wide range of applications, for example, entanglement witnessing and quantum key distribution. We study the effects of the environment on the entropic uncertainty lower bound in the presence of weak measurement and measurement reversal. The dynamical model that is intended in this work is as follows: first the weak measurement is performed, second, the decoherence affects the system and finally the measurement reversal is performed on the quantum system. Here, we consider the generalized amplitude damping channel and depolarizing channel as environmental noises. We will show that in the presence of weak measurement and measurement reversal, despite the presence of environmental factors, the entropic uncertainty lower bound drops to an optimal minimum value. In fact, weak measurement and measurement reversal enhance the quantum correlation between the subsystems A and B , and thus the uncertainty of Bob regarding Alice’s measurement outcomes reduces. Based on the entropic uncertainty relation, one can also show that the weak measurement and measurement reversal can preserve the quantum secret key rate lower bound from decoherence.
Abstract Based on a simple cavity‐engineered architecture, the dynamics of quantum memory–assisted entropic uncertainty relation (QMA‐EUR) for two qubits initially prepared in a generic Werner state is investigated. The effects of cavity decay rate, qubit–cavity couplings, and cavity–cavity couplings on the uncertainty are explored. It is found that the damped oscillation of uncertainty can be induced by the increase of two types of coupling strengths mentioned above. It is demonstrated that the maximum value of uncertainty is closely related to the purity of the initial state. The uncertainty can be either increased or decreased, depending on the threshold value of coupling strength between the two cavities. Finally, in agreement with a recent observation, an asynchronous relation between uncertainty and mixedness is found during the initial time evolution.
Abstract Recently, Ming et al (Quantum Inf Process 17 267, 2018) have investigated the entropic uncertainty relation in the presence of quantum memory (EUR-QM) and quantum coherence in a thermal regime for a two-spin chain under the effect of Dzyaloshinskii–Moriya (DM) interaction. Here, we study thermal quantum coherence and EUR-QM for a three-spin chain in Ising model under the effect of different directions of DM interaction. Our results confirm the results for the two-qubit case. Increasing temperature can reduce the quantum coherence but oppositely the uncertainty will grow. We show that the coupling parameter and DM interaction have constructive effects on quantum coherence and they reduce uncertainty in measurement results of incompatible observables, and especially the y -direction of DM interaction has a better influence on decreasing the uncertainty than the x and z directions. Unfortunately, the effect of the third spin acts destructively on the uncertainty and its bound, as well as the quantum coherence between the first two spins. Notably, an explicit relationship between quantum coherence and the uncertainty lower bound is found.
Abstract In this study, the quantum-memory assisted entropic uncertainty (QM-EU) and entanglement dynamics of the two-qubit Heisenberg XXX chain have been explored in the presence of intrinsic decoherence. The effect of the x-component of Dzyaloshinskii-Moriya (DM) and Kaplan-Shekhtman-Entin-Wohlman-Aharony (KSEA) interactions has been considered. The generation and preservation of quantum memory and entanglement have been examined for various values of the DM, KSEA, spin-spin, and spin coupling strengths. The uncertainty negatively affects the entanglement and both have anti-correlation. The absence and presence of intrinsic decoherence prevail in differing impacts on the dynamics of the system. In the first case, prolonged entanglement preservation, uncertainty suppression, and oscillatory dynamics have been observed. Moreover, in order to achieve the best-prolonged entanglement preservation and relative reduction of the entropic uncertainty, we have analyzed several parameter settings. We find that the effects of raising the DM, KSEA, and spin-spin interaction individually and simultaneously are different. The individual and simultaneous increase of the DM, KSEA, and spin-spin interaction parameters control the degree of entanglement, entropic uncertainty, and primarily the dynamics of the system.