The possibility that one party steers their partner is discussed for a driven two-qubit system, where it is assumed that either one or both of them is driving via an exponential pulse. It is shown that the maximum and minimum degrees of steerability and the survival amount of quantum correlation depend on the initial-state settings and the pulsing strength. If only one party is driven, the long-lived steerability is observed at long pulsing time and high strength. However, if both parties are driven, then the steerability's behavior depends on the difference between the strengths of the pulses.
The possibility that one party steers their partner is discussed for a driven two-qubit system, where it is assumed that either one or both of them is driving via an exponential pulse. It is shown that the maximum and minimum degrees of steerability and the survival amount of quantum correlation depend on the initial-state settings and the pulsing strength. If only one party is driven, the long-lived steerability is observed at long pulsing time and high strength. However, if both parties are driven, then the steerability's behavior depends on the difference between the strengths of the pulses.
Abstract Einstein–Podolsky–Rosen steering refers to the quantum phenomenon whereby the state of a system held by one party can be ‘steered’ into different states at the will of another, distant, party by performing different local measurements. Although steering has been demonstrated in a number of experiments involving qubits, the question of which two-qubit states are steerable remains an open theoretical problem. Here, we derive a necessary condition for any two-qubit state to be steerable when the steering party suffers from a given probability of qubit loss. Our main result finds application in one-way steering demonstrations that rely upon loss. Specifically, we apply it to a recent experiment on one-way steering with projective measurements and POVMs, reported by Wollmann et al (2016 Phys. Rev. Lett. 116 160403).
The entanglement of different classes of initially entangled qubit pair is investigated in the presence of short laser pulses of rectangular and exponential shapes with either one or both qubits are excited. For the rectangular pulse, the detuning parameter protects the entanglement from degradation and controls its upper and lower bounds. We show that the upper bounds of entanglement decrease if both particles are excited, but the lower bounds are much better if only one particle is excited. The phenomena of entanglement degradation, sudden-death and -birth are shown for small initial time. Long-lived entanglement behavior, but with a variable degree, appears in the presence of rectangular pulse. However, in the case of the exponential pulse one obtains an invariably long-lived entanglement. For the combined case (rectangular + exponential), we show that one can generate a long-lived entanglement with small variable by increasing the strength of the rectangular pulse area and decreasing the Rabi-frequency of the exponential pulse.
The entanglement of different classes of initially entangled qubit pair is investigated in the presence of short laser pulses of rectangular and exponential shapes with either one or both qubits are excited. For the rectangular pulse, the detuning parameter protects the entanglement from degradation and controls its upper and lower bounds. We show that the upper bounds of entanglement decrease if both particles are excited, but the lower bounds are much better if only one particle is excited. The phenomena of entanglement degradation, sudden-death and -birth are shown for small initial time. Long-lived entanglement behavior, but with a variable degree, appears in the presence of rectangular pulse. However, in the case of the exponential pulse one obtains an invariably long-lived entanglement. For the combined case (rectangular + exponential), we show that one can generate a long-lived entanglement with small variable by increasing the strength of the rectangular pulse area and decreasing the Rabi-frequency of the exponential pulse.
In this work, there are two parties, Alice on Earth and Bob on the satellite, which initially share an entangled state, and some open problems, which emerge during quantum steering that Alice remotely steers Bob, are investigated. Our analytical results indicate that all entangled pure states and maximally entangled evolution states (EESs) are steerable, and not every entangled evolution state is steerable and some steerable states are only locally correlated. Besides, quantum steering from Alice to Bob experiences a "sudden death" with increasing decoherence strength. However, shortly after that, quantum steering experiences a recovery with the increase of decoherence strength in bit flip (BF) and phase flip (PF) channels. Interestingly, while they initially share an entangled pure state, all EESs are steerable and obey Bell nonlocality in PF and phase damping channels. In BF channels, all steerable states can violate Bell-CHSH inequality, but some EESs are unable to be employed to realize steering. However, when they initially share an entangled mixed state, the outcome is different from that of the pure state. Furthermore, the steerability of entangled mixed states is weaker than that of entangled pure states. Thereby, decoherence can induce the degradation of quantum steering, and the steerability of state is associated with the interaction between quantum systems and reservoirs.
Phenomena that slip beyond the grasp of our classical intuition reveal uniquely quantum effects that deepen our understanding of the physical world and enable advances in information processing, particularly in quantum communication and computation. One such phenomenon is quantum steering, whereby measurements performed by one party influence the conditional states of another when the two share an entangled quantum system. If the observed correlations cannot be explained by a local hidden state model, the state is said to be steerable. In this work, we investigate the typicality of this behavior: given a generic two-qubit state and m Haar-random projective measurements, what is the probability of observing steering? We derive analytical expressions for the steering probability PS of Werner states in two- and three-setting scenarios, the latter restricted to coplanar projective measurements on the Bloch sphere. For larger numbers of settings and various random states ensembles, we perform numerical analyses showing that PS increases systematically with the number of measurements and substantially exceeds the corresponding probabilities associated with Bell nonlocality. Our results demonstrate that random states with minimal environmental coupling exhibit a high probability of steering for finite m and approach genuine typicality, PS=100%, as the number of settings increases. We provide a detailed characterization of PS across different state ensembles and specific families, including Bell-diagonal and Werner states, identifying those with the greatest non-classical potential and highlighting their relevance for protocols in which steering serves as a key resource.
Einstein-Podolsky-Rosen steering describes a quantum correlation in addition to entanglement and Bell nonlocality. However, conceptually different from entanglement and Bell nonlocality, quantum steering has an asymmetric definition. Motivated by the asymmetric definition of quantum steering, we study the steerability of two interacting qubits, which have asymmetric energy levels, coupled with asymmetric environments. The asymmetric (nonequilibrium) environments are two environments with different temperatures or chemical potentials. The Bloch-Redfield equation is applied to study the dynamics of two qubits and its long-time behavior. In our study, the steady-state steerability is determined by an experimentally friendly steering criteria, which demonstrates steering through the entanglement detection. Our results show that the steady states of two asymmetric qubits have the advantage for one direction of steering, compared to the symmetric setup. We also provide analytical results on the minimal coupling strength between the two qubits in order to be steerable. The asymmetric steerability is collectively determined by the nature of the two qubits and the influence from equilibrium or nonequilibrium environments. Nonequilibrium environments with the cost of nonzero entropy production can enhance the steerability in one direction. We also show the strict hierarchy of entanglement, steering, and Bell nonlocality of the nonequilibrium steady states, which shows a richer structure of steering than entanglement and Bell nonlocality.