Abstract We studied the entangling power of two pure global noises, i.e. amplitude damping noise and classic noise. The entangling power of the two-qubit amplitude damping global noise periodically oscillates with time. Additionally, the entangling power of two-qubit global classical noise increases exponentially with time. The maximum entangling power of both of them exceeds that of the perfect entanglers. Based on this, we propose the conditions for generating a maximally entangled state with global noise acting on a two-qubit separable state. Only if the two-qubit composite system, which is initially in one of those product states: 1 2 ( | 0 ⟩ ± | 1 ⟩ ) ⊗ 1 2 ( | 0 ⟩ ± | 1 ⟩ ) , | 10 ⟩ and | 01 ⟩ suffers an amplitude damping global noise, can we prepare this system in the maximally entangled state by appropriately controlling the evolution time of amplitude damping. Finally, we investigate the disentanglement of the maximum entangled Bell state using these two types of global noise. The two global noises cannot completely disentangle the Bell states Φ ± . Under the influence of amplitude damping global noise, the entanglement of Bell state Ψ + undergoes a cyclical variation, alternating between disappearance and recovery to reach maximum entanglement within one period. The entanglement of either Bell state Ψ + or Ψ − is completely independent of global classical noise. The entanglement of Bell state Ψ − is also robust against amplitude damping global noise.
Abstract We studied the entangling power of two pure global noises, i.e. amplitude damping noise and classic noise. The entangling power of the two-qubit amplitude damping global noise periodically oscillates with time. Additionally, the entangling power of two-qubit global classical noise increases exponentially with time. The maximum entangling power of both of them exceeds that of the perfect entanglers. Based on this, we propose the conditions for generating a maximally entangled state with global noise acting on a two-qubit separable state. Only if the two-qubit composite system, which is initially in one of those product states: 1 2 ( | 0 ⟩ ± | 1 ⟩ ) ⊗ 1 2 ( | 0 ⟩ ± | 1 ⟩ ) , | 10 ⟩ and | 01 ⟩ suffers an amplitude damping global noise, can we prepare this system in the maximally entangled state by appropriately controlling the evolution time of amplitude damping. Finally, we investigate the disentanglement of the maximum entangled Bell state using these two types of global noise. The two global noises cannot completely disentangle the Bell states Φ ± . Under the influence of amplitude damping global noise, the entanglement of Bell state Ψ + undergoes a cyclical variation, alternating between disappearance and recovery to reach maximum entanglement within one period. The entanglement of either Bell state Ψ + or Ψ − is completely independent of global classical noise. The entanglement of Bell state Ψ − is also robust against amplitude damping global noise.
Abstract We investigate the entanglement swapping under phase damping global noise and amplitude damping global noise. The two qubits the intermediate user holds during the entanglement swapping process first suffer from a global noise before the Bell measurement is carried out. Based on this assumption, the influence of global phase damping noise and global amplitude damping noise on the output entanglement of entanglement swapping is investigated, respectively. Our findings imply that the output entanglement is completely independent of the phase damping global noise and determined by the input entanglement when entanglement swapping is performed in a global phase damping noise environment. In addition, when entanglement swapping is executed in an amplitude damping environment, the output entanglement oscillates periodically with time, and the output entanglement may disappear at some points and reappear at others. In this case, we need not only to improve the input entanglement but also to control the evolution time of the amplitude damping global noise to ensure the optimal output entanglement. Our findings may help experimentalists to avoid and utilize environmental noise in entanglement swapping.
We systematically characterize quantum entanglement in all sixteen combinations of two-qubit Bell states across three operational regimes: pure superposition, noiseless mixing, and asymmetric mixing of one noisy and one pure Bell state. For pure superpositions, we calculate the von Neumann entropy and show that entanglement depends critically on the relative phase phi between superposed states. For mixed states, we use concurrence C under three physically motivated decoherence channels. The Depolarizing (DP) and Phase Damping (PD) channels are modeled as global, collective operations on the two-qubit Hilbert space, while Amplitude Damping (AD) is treated as independent local decay on each qubit, reflecting the asymmetric, energy-dissipating nature of spontaneous emission. A central and counterintuitive result is that increasing noise can raise concurrence in specific parameter regimes across all three channels. We further map the boundary between mathematical entanglement (C > 0) and operational quantum non-locality using the Horodecki criterion, finding this boundary to be strongly channel-dependent. Under Phase Damping, the Bell-local entanglement regime vanishes entirely for identical and same-bases mixtures, meaning any surviving entanglement guarantees a CHSH violation. Under Depolarizing noise, a large Bell-local region requires mixing probability r > 1/sqrt(2) to recover non-locality at maximum noise. For Amplitude Damping, certain mixtures exhibit a non-monotonic Horodecki parameter M(T): concurrence decreases monotonically with noise, yet the capacity for CHSH violation is lost at intermediate noise levels and restored at high noise, as maximal damping repurifies the noisy branch. These results provide a unified analytical reference for entanglement and non-locality management across Bell-state combinations and decoherence channels relevant to NISQ architectures.
Abstract We investigate the Bell nonlocality dynamics of bipartite quantum systems under three distinct types of global decoherence environments: global amplitude damping noise, globally correlated classical noise, and global phase-damping noise. By combining numerical optimization techniques over Bell inequalities—specifically the Clauser–Horne–Shimony–Holt inequality—and describing the global noise-evolution process of a two-qubit system with the Kraus operator formalism, we systematically characterize the evolution of quantum nonlocality in a two-qubit system. Our results demonstrate that, under a global amplitude damping noise environment, precise temporal modulation of the amplitude damping channel enables the composite system to retain maximal Bell-nonlocal correlations in its final state. In contrast, globally correlated classical noise fields induce exponential suppression of Bell inequality violations. Remarkably, the systems subjected to global phase-damping noise exhibit pronounced robustness to nonlocality. These findings highlight the critical role of global noise in nonlocality dynamics.
We analytically characterize entanglement generation by two paradigmatic coherently controlled quantum processes, the quantum switch and time-flip. Retaining rather than measuring or discarding the control, we treat the control and target as the bipartite system and assume pure product inputs, so that any output entanglement reflects the entangling capability of the process. For the switch of qubit unitaries, we derive exact expressions for entanglement, together with a geometric characterization and a coherence-entanglement conservation relation. We then extend our analysis to binary random unitary, Pauli, amplitude damping, and generalized amplitude damping channels. We prove that switch of channels commuting under composition cannot entangle a separable input. Yet maximal entanglement is possible even with dissipation, e.g., an entanglement-breaking damping channel switched with a bit-flip can transform a product input into a maximally entangled state. For two generalized amplitude damping channels, a common stationary state prevents entanglement, while different stationary populations can enable it. We present an analogous study for the time-flip of unitary and binary random unitary channels. Our findings provide a systematic analysis of how much entanglement can be generated by coherent control of channel order or input-output direction.
We propose a scheme to enhance entanglement from amplitude damping or correlated amplitude damping decoherence. We show that entanglement sudden death time can be prolonged by the initial single-qubit operation combined with local filtering operation. For the amplitude damping channel case, we give the optimal single-qubit operation for arbitrary pure state [Formula: see text]. For the correlated amplitude damping channel case, we find that single-qubit operation on the initial state can not only enhance the final entanglement but also avoid entanglement sudden death. Compared to the previous schemes, the optimal operations and local filtering operations used in our scheme are independent with the decay parameters of the environment.
Quantum correlations between two or more different degrees of freedom of the same particle is sometimes referred to as intraparticle entanglement. In this work, we study these intra-particle correlations between two different degrees of freedom under various decoherence channels viz. amplitude damping, depolarising and phase damping channels. We observe a unique feature of the amplitude damping channel, wherein entanglement is shown to arise starting from separable states. In case of non maximally entangled input states, in addition to entanglement sudden death, the creation of entanglement is also observed, having an asymptotic decay over a long time. These counter-intuitive behaviours arise due to the subtle interplay of channel and input state parameters, and are not seen for interparticle entanglement without consideration of non-Markovian noise. It is also not observed for maximally entangled input states. Furthermore, investigation of entanglement evolution in phase damping and depolarizing channels shows its robustness against decoherence as compared to interparticle entanglement.