Death Of Entanglement Research Articles

Robustness of interferometric power to sudden death

In this paper, we study the dissipative dynamics of interferometric power as a discord-like measure in Markovian environments such as dephasing, depolarizing, and generalized amplitude damping. Moreover, we compare the dynamics of interferometric power and entanglement by choosing the proper initial conditions. Our study shows that interferometric power decays asymptotically in all cases where the sudden death of entanglement appears. Therefore, quantum metrology based on interferometric power is more robust than entanglement.

Dynamics of entanglement of qubits in the three-qubit Tavis — Cummings model with dipole-dipole interaction

The article studies the dynamics of pairwise entanglement of three qubits, two of which are trapped in a resonator and interact with a single-mode ideal resonator through single-photon transitions, and the third qubit is outside the resonator. This takes into account the dipole-dipole coupling between the isolated qubit and the qubit in the resonator. We have found a solution to the quantum nonstationary Schrodinger equation for the total wave function of the system for the initial separable and biseparable states of qubits and the thermal initial state of the resonator field. Using these solutions, the criterion of entanglement of qubit pairs - negativity is calculated. The results of numerical simulation of the negativity criterion have shown that the including of a small dipole-dipole coupling between an isolated and one of the trapped qubits can lead to significant entanglement of qubit pairs for all initial states. There is a transition of entanglement from one pair of atoms to other pairs of atoms during the evolution of the system. It is also shown that for some separable and biseparable states, the dipole-dipole interaction can suppress the effect of sudden death of entanglement

Quantum simulation of entanglement dynamics in a quantum processor

We implement a five-qubit protocol in IBM quantum processors to study entanglement dynamics in a two qubit system in the presence of a simulated environment. Specifically, two qubits represent the main system, while another two qubits serve as the environment. Additionally, we employ an auxiliary qubit to estimate the quantum entanglement. Specifically, we observe the sudden death and sudden birth of entanglement for different inital conditions that were simultaneously implemented on the IBM 127-qubit quantum processor ibm _brisbane. We obtain the quantum entanglement evolution of the main system qubits and the environment qubits averaging over N = 10 independent experiments in the same quantum device. Our experimental data shows the entanglement and disentanglement signatures in system and enviroment qubits, where the noisy nature of current quantum processors produce a shift on times signaling sudden death or sudden birth of entanglement. This work takes relevance showing the usefulness of current noisy quantum devices to test fundamental concepts in quantum information.

Dynamics of a two-qubit Tavis-Cummings model in the presence of an Ising-type interaction between qubits

In this paper, we investigated the dynamics of entanglement of two qubits interacting non-resonantly with the thermal field of a one-mode lossless resonator, taking into account the Ising-type direct interaction between qubits. Based on the exact solution of the quantum Liouville equation, we found the density matrix of the system under consideration. With its help, the reduced qubit-qubit density matrix was calculated and the entanglement criteriоn of the two-qubit system, Pres-Horodeсki parameter, was found. It was shown that for the resonance model and separable initial states of qubits, the direct interaction of qubits leads to a significant increase in the maximum degree of their entanglement. It was also found that for the nonresonant interaction between qubits and field, the increase of the maximum degree of entanglement of qubits is much greater than that due to direct interaction. For the original entangled Bell-type state of the qubits, the direct interaction was found to lead to the vanishing of the effect of the sudden death of entanglement in the case of a resonant qubit-field interaction and, conversely, to an increase in this effect for a nonresonant interaction.

Enhancing sideband cooling by initial photon-phonon correlation

We propose an optimized sideband cooling protocol for an optomechanical system coupled to a mechanical non-Markovian reservoir, considering the presence of initial system correlations. By incorporating the effect of initial correlations in the Heisenberg equations, we derive a more stringent dependence on the initial conditions and time-dependent evolution of the phonon numbers. Our findings demonstrate that considering the initial correlations can significantly reduce the number of phonons during the cooling process. Moreover, by adjusting the strength and phase of the initial correlation, the ground-state cooling process can be accelerated. We observe a characterization of this cooling optimization process that resembles the phenomenon of entanglement death and revival. This work provides a promising platform for effectively manipulating phonons and facilitating quantum information processing in optomechanical systems.

Entangled states dynamics of moving two-level atoms in a thermal field bath

We consider a two-level atom that follows a wordline of constant velocity, while interacting with a massless scalar field in a thermal state through: (i) an Unruh–DeWitt (UDW) coupling, and (ii) a coupling that involves the time derivative of the field. We treat the atom as an open quantum system, with the field playing the role of the environment, and employ a master equation to describe its time evolution. We study the dynamics of entanglement between the moving atom and a (auxiliary) qubit at rest and isolated from the thermal field. We find that in the case of the standard UDW coupling and for high temperatures of the environment the decay of entanglement is delayed due to the atom’s motion. Instead, in the derivative coupling case, the atom’s motion always causes the rapid death of entanglement.

Dynamics of atom-atom entanglement in two-atom model with degenerate two-photon raman transitions

The exact dynamics of a model consisting of two two-level atoms interacting with the electromagnetic field mode of an ideal resonator through degenerate Raman transitions are found for coherent and thermal field states. The exact solution is used to calculate atom-atom negativity. It is shown that for separable initial states of atoms, their interaction with the resonator field does not lead to the occurrence of atom-atom entanglement. It was found that for the Bell initial states of atoms in the case of a coherent resonator field, the effect of sudden death of entanglement takes place for large average values of the number of photons in the resonator, while in case of thermal noise, this effect is absent for any intensities of the resonator field.

Modulations of superradiance and quantum entanglement of quantum emitters in terahertz frequency

We study the superradiance and entanglement phenomena between two quantum emitters (QEs) operating at terahertz frequencies, facilitated by the presence of a topological insulator bismuth selenide (Bi2Se3). Controlled by the hyperbolic phonon polaritons and electron surface state in the terahertz frequency range, the interaction between QEs is significantly enhanced both within and outside the hyperbolic bands. Moreover, the entanglement between two QEs through Bi2Se3 is studied in detail. Certain initial entanglement states undergo sudden death of entanglement when the system is in non-interaction. However, in the cases of moderate or strong interaction, the entanglement can be revive after experiencing the sudden death phenomenon. These findings hold significant implications for controlling the interaction of QEs and their potential applications in the fields of quantum metrology and quantum imaging in the terahertz frequency region.

Enhanced quantum resources via two distant atom-cavity systems under the influence of atomic dissipation

Quantum resources such as entanglement and coherence are the holy grail for modern quantum technologies. Although the unwanted environmental effects tackle quantum information processing tasks, suprisingly these key quantum resources may be protected and even enhanced by the implementation of some special hybrid open quantum systems. Here, we aim to show how a dissipative atom-cavity-system can be accomplished to generate enhanced quantum resources. To do so, we consider a couple of dissipative cavities, where each one contains two effective two-level atoms interacting with a single-mode cavity field. In practical applications, a classical laser field may be applied to drive each atomic subsystem. After driving the system, a Bell-state measurement is performed on the output of the system to quantify the entanglement and coherence. The obtained results reveal that the remote entanglement and coherence between the atoms existing inside the two distant cavities are not only enhanced, but can be stabilized, even under the action of dissipation. In contrast, the local entanglement between two atoms inside each dissipative cavity attenuates due to the presence of unwanted environmental effects. Nevertheless, the local coherence may show the same behavior as the remote coherence. Besides, the system provides the steady state entanglement in various interaction regimes, particularly in the strong atom-cavity coupling and with relatively large detuning. More interestingly, our numerical analyses demonstrate that the system may show a memory effect due to the fact that the death and revival of the entanglement take place during the interaction. Our proposed model may find potential applications for the implementation of long distance quantum networks. In particular, it facilitates the distribution of quantum resources between the nodes of large-scale quantum networks for secure communication.

Birth and death of entanglement between two accelerating Unruh-DeWitt detectors coupled with a scalar field

We study two accelerating Unruh-DeWitt detectors coupled linearly or quadratically with a scalar field, by using an approach different from previous ones. We use Rindler frame, and integrate over the spacetime coordinates before over the momenta. In this way, the divergent problem previously encountered is avoided. We show that entanglement between the detectors can be created by coupling with the field, and is divergent only in the limit that the two detectors coincide in spacetime. For linear coupling, entanglement increases monotonically with the decrease of acceleration, as previously found, while for quadratic coupling, entanglement behaves non-monotonically, as noted for the first time.

Postponing the decay of entanglement and quantum coherence for maximally entangled mixed states under the action of correlated noise channels

We investigate the dynamics of a maximally entangled mixed state (MEMS) under the action of correlated noise channels. The channel acts in a way that its successive uses are correlated. We have studied the MEMS properties, including quantum coherence and entanglement. For partially correlated channels, both the entanglement and coherence of MEMS are found to decay much slower than those of the memoryless channels. Moreover, we observe a freezing effect of coherence for phase damping as well as depolarizing channels and freezing of entanglement for phase-damping channels with perfect memory. For amplitude damping and depolarizing channels, memory helps in either delaying the sudden death of entanglement or slowing the decay rate of coherence. These observations suggest that memory channels perform better than memoryless channels in maintaining the integrity of quantum states and have utility in quantum information processing protocols.

ENTANGLEMENT BETWEEN TWO SUPERCONDUCTING CHARGE
 QUBITS

In this paper, we investigated the dynamics of entanglement of two identical charge qubits with Josephson junctions in the case when one of the qubits is exposed to a microwave field in a coherent or thermal state. We have found the exact solution of the quantum time equation of evolution of the system under consideration for the statistical operator in the case of initial separable and entangled states of qubits. The exact solution for the complete statistical operator is used to calculate the qubit entanglement criterion - concurrence. The results of numerical simulation of the time dependence of the concurrence in the case of the coherent field showed that, with a certain choice of model parameters, the system can realize long-lived entangled states. It is also shown that for the thermal state of the field and the entangled initial state of qubits, the qubits retain a certain degree of entanglement during evolution even in the case of very intensive fields. In this case, for any intensities of thermal noise, there is no effect of the sudden death of entanglement.

The management of Monochorionic Monoamniotic (MCMA) twin pregnancy

HIGHLIGHTS Monochorionic monoamniotic (MCMA) twin pregnancy has a significant risk of perinatal morbidity and mortality, including intrauterine fetal death (IUFD). The risk of prematurity, the risk of death due to MCMA complications, the availability of the NICU, also high costs on preterm care were factors in deciding to terminate the pregnancy. The ideal time to deliver monochorionic twins in order to reduce the risks of cord entanglement, growth discrepancies, and intrauterine fetal death is still a point of controversy. Early diagnosis, intensive antenatal monitoring, patient and family decision would contribute to antenatal mortality reduction. ABSTRACT Objectives: To present the management of monochorionic monoamniotic (MCMA) twin pregnancy. Case Report: Advanced prenatal treatment has improved the prognosis for Monochorionic Monoamniotic (MCMA) pregnancies; however, there is still no agreement on how to handle MCMA twins. The authors report 2 cases of monoamniotic monochorionic twin pregnancies. In the first case, a 30-years-old primi pregnant woman detected MCMA at 14 weeks of gestation; no complications related to MCMA were found; she planned delivery at 32 weeks, but one of the babies died in the womb at 31/32 weeks pregnant, a live baby born by cesarean section. The second case was a 36-year-old pregnant woman, on her third pregnancy, diagnosed with MCMA after 12 weeks of pregnancy, no complications related to MCMA, the baby was born at 32 weeks pregnant, and both babies survived. The management was the same in both cases, but different outcomes were obtained; in case 1, the baby died allegedly due to cord entanglement, which could not be detected during pregnancy.

Sudden death of entanglement with a Hamiltonian ensemble assisted by auxiliary qubits

Sudden death of entanglement with a Hamiltonian ensemble assisted by auxiliary qubits

Fatal entanglements of sea turtles caused by widely deployed weather instruments

Sea turtles have been found to interact with discarded fishing gear, plastic bags, and balloons, among other anthropogenic materials. One infrequently documented interaction is entanglement in scientific research instruments, which presents a unique management and mitigation challenge. This paper highlights two Kemp's ridley sea turtles that stranded ~10 years apart, deceased and entangled in weather balloons in Virginia, USA. The turtles were recovered 11 and 20 days after the balloons were launched from two different facilities along the Virginia coast in 2009 and 2019, respectively. Based on external evaluation and necropsy findings, both animals were assigned a probable cause of death of debris entanglement. This paper seeks to inform other stranding response organizations, as well as stakeholders like manufacturers and users of weather balloons, of the threats these instruments can pose to marine life. With strengthened education, collaboration, and changes in instrument design, future entanglements may be mitigated.

Open quantum system dynamics of X-states: Entanglement sudden death and sudden birth

In this paper, the origin of disentanglement for two specific sub-classes of [Formula: see text]-states namely maximally nonlocal mixed states (MNMSs) and maximally entangled mixed states (MEMSs) is investigated analytically for a physical system consisting of two spatially separated qubits interacting with a common vacuum bath. The phenomena of entanglement sudden death (ESD) and the entanglement sudden birth (ESB) are observed, but the characteristics of ESD and ESB are found to be different for the case of two-photon coherence and single photon coherence states. The role played by initial coherence for the underlying entanglement dynamics is investigated. Further, the entanglement dynamics of MNMSs and MEMSs under different environmental noises namely phase damping, amplitude damping and random telegraph noise (RTN) noise with respect to the decay and revival of entanglement is analyzed. It is observed that the single photon coherence states are more robust against the sudden death of entanglement, indicating the usability of such states in the development of technologies for the practical implementation of quantum information processing tasks.

Interplay of noise, memory and entangling operator in quantum Stackelberg-Bertrand duopoly game

In this work, we make an attempt to understand how noise, memory and entangling operators collectively decide the profit of the firms Here we have studied the quantum version of Stackelberg-Bertrand duopoly game using modified EWL scheme in both correlated and uncorrelated noise channels. When this game is analyzed for amplitude damping channels following interesting results are obtained: Firstly, decoherence in channel 2 effects the profit function of the firms more than that of channel 1. Secondly, in the case of correlated noise memory prevents the death of entanglement at maximum noise. Finally, the profit function of the firms depends upon noise, memory, strategies, and entangling operator in any given game setting.

Analog de Sitter universe in quantum Hall systems with an expanding edge

Expanding edges in quantum Hall systems can become a simulator of quantum 1+1 dimensional expanding universes. In these systems, edge exciations are represented as a chiral scalar field in curved spacetimes. We investigate Hawking radiation and entanglement behavior predicted by this model assuming that the expansion law of the edge region corresponds to a de Sitter universe. As observable quantities for the quantum field, local spatial modes associated with detection regions are introduced using window functions for the field, and their correlations are evaluated. We found impact of Hawking radiation caused by the edge expansion on auto-correlation functions of the local modes, and confirmed that entanglement death due to Hawking radiation occurs. This behavior of entanglement is related to ``quantum to classical transition" in cosmic inflations.

Entanglement recovery in noisy binary quantum information protocols via three-qubit quantum error correction codes

The task of preserving entanglement against noises is of crucial importance for both quantum communication and quantum information transfer. To this aim, quantum error correction (QEC) codes may be employed to compensate, at least partially, the detriments induced by environmental noise that can be modeled as a bit-flip or a phase-flip error channel. In this paper, we investigate the effects of the simple three-qubit QEC codes to restore entanglement and nonlocality in a two-qubit system and consider two practical applications: superdense coding and quantum teleportation. Though the considered three-qubit QEC codes are known to perfectly work in the presence of very small noise, we show that they can avoid the sudden death of entanglement and improve the performance of the addressed protocols also for larger noise amplitudes.

Перепутывание изолированного кубита и кубита в резонаторе со средой Керра

We found the exact solution for a model consisting of two dipole-coupled qubits, one of which is an isolated, and the other interacts with the thermal mode of a cavity with the Kerr medium. The results showed that Kerr nonlinearity may greatly enhance the degree of entanglement induced by a thermal field both for separable and entangled initial states of qubits. We also showed the possibility of the disappearance of the sudden death of entanglement for a model with a Kerr nonlinearity..