Revival Of Entanglement Research Articles

Dynamics of the homogeneous two-qubit XXZ central spin model with the spin bath prepared in superpositions of symmetric Dicke states

We obtain exact dynamics of a two-qubit central spin model (CSM) consisting of two interacting qubits homogeneously coupled to a spin bath via the $XXZ$-type coupling, with the bath initially prepared in linear superpositions of the symmetric Dicke states. Using the interaction picture Hamiltonian with respect to the non-spin-flipping part of the model, we derive a sequence of equations of motion within each magnetization sector satisfied by the probability amplitudes of the time-evolved state. These equations of motion admit analytical solutions for the single-qubit CSM in which one of the two central qubits decouples from the rest of the system. Based on this, we provide a quantitative interpretation to the observed collapse-revival phenomena in the single-qubit Rabi oscillations when the bath is prepared in the spin coherent state. We then study the disentanglement and coherence dynamics of two initially entangled noninteracting qubits when the two qubits interact with individual baths or with a common bath. For individual baths the coherent dynamics is found to positively correlated to the single-qubit purity dynamics, and entanglement sudden disappearance and revivals are observed in both cases. The entanglement creation of two initially separable qubits coupled to a common bath is also studied and collapse and revival behaviors in the entanglement dynamics are observed. Choosing the equally weighted state and the $W$-class states as the bath initial states, we finally study the dynamics of entanglement between two individual bath spins and demonstrate the entanglement sharing mechanism in such a system.

Entanglement revivals as a probe of scrambling in finite quantum systems

The entanglement evolution after a quantum quench became one of the tools to distinguish integrable versus chaotic (non-integrable) quantum many-body dynamics. Following this line of thoughts, here we propose that the revivals in the entanglement entropy provide a finite-size diagnostic benchmark for the purpose. Indeed, integrable models display periodic revivals manifested in a dip in the block entanglement entropy in a finite system. On the other hand, in chaotic systems, initial correlations get dispersed in the global degrees of freedom (information scrambling) and such a dip is suppressed. We show that while for integrable systems the height of the dip of the entanglement of an interval of fixed length decays as a power law with the total system size, upon breaking integrability a much faster decay is observed, signalling strong scrambling. Our results are checked by exact numerical techniques in free-fermion and free-boson theories, and by time-dependent density matrix renormalisation group in interacting integrable and chaotic models.

Non-Markovian entanglement transfer to distant atoms in a coupled superconducting resonator**Project supported by the Fundamental Research Funds for the Central Universities, China (Grant No. 2018MS056) and the National Natural Science Foundation of China (Grant Nos. 11605055 and 11974108).

We investigate the non-Markovian effects on the entanglement transfer to the distant non-interacting atom qubits, which are embedded in a coupled superconducting resonator. The master equation governing the dynamics of the system is derived by the non-Markovian quantum state diffusion (NMQSD) method. Based on the solution, we show that the memory effect of the environment can lead to higher entanglement revival and make the entanglement last for a longer time. That is to say, the non-Markovian environment can enhance the entanglement transfer. It is also found that the maximum entanglement transferred to distant atoms can be modified by appropriately selecting the frequency of the modulated inter-cavity coupling. Moreover, with the initial anti-correlated state, the entanglement between the cavity fields can be almost completely transferred to the separated atoms. Lastly, we show that the memory effect has a significant impact on the generation of entanglement from the initial non-entangled states.

Collapses and revivals of entanglement in phase space in an optomechanical cavity

We analyse the dynamics of an optomechanical cavity considering two modes of the electromagnetic field and a mechanical resonator. As a result of this interaction, the initial non-entangled state evolves into a final entangled state. In this work, we use the function to observe the behavior of the system in the phase space, finding that such entanglement is a function of time showing collapses and revivals. To carry out this analysis, we use the generalization of the single-party function towards three-party systems and we ascertain that the entanglement perfectly maps into the function because it becomes non-separable too. To prove that the Q function accurately certifies entanglement, we compare its behaviour with the plots of the van Loock inequalities. Additionally, as the optomechanical systems were proposed to carry out quantum information tasks, we investigate the kind of phase gate that is produced when we keep the Kerr term that arises in the evolution operator.

Dynamics of entanglement in a two-qubit system subjected to the joint relaxation and dephasing classical noises

We address the entanglement dynamics of two initially entangled non-interacting qubits subjected to the independent sources of classical noises. As classical noises, we consider different configurations of two important classical noises, i.e., static noise and random telegraph noise. Previous studies have focused on the local classical noises acting in the same directions and producing the same relaxation or dephasing dynamics on the qubits. Here, however, we focus on the local classical noises acting in perpendicular directions and producing pure relaxation and dephasing dynamics on the first and second qubits, respectively. This leads to considerably different dynamics of entanglement compared to the one of previous studies. When the qubits are both locally coupled to either the random telegraph noises in the weak coupling regimes or the static noises, we find that there occurs only the entanglement sudden-death effect, while for other configurations the entanglement sudden death may be followed by the revival of entanglement.

Trends of information backflow in disordered spin chains

We investigate the trends of information backflow associated with the dynamics of a sub-part of a disordered spin-1/2 transverse field Heisenberg chain for different regimes of the Hamiltonian. Towards this aim, the decay profile of bipartite entanglement shared between a probe-qubit and a system-qubit (sub-part) of the chain is monitored in time. A clear shift in the trends of the decay profiles of the bipartite entanglement from monotonic in the low-disorder limit to non-monotonic in the moderately large disorder limit occurs due to strong information backflow from the environment (complementary part) to the system-qubit. A connection between environmental interruption caused by the information backflow and the disorder strength is established by examining the entanglement revival frequencies. The growth patterns of the revival frequencies in the localized phase plays an instrumental role to effectively distinguish an interacting system (many-body localized) from its non-interacting (Anderson localized) counterpart.

Entanglement dynamics for quantum emitters strongly coupled with molybdenum disulfide nanodisks

We study the dynamics of entanglement for a composite two-qubit system, where each qubit is close to a molybdenum disulfide nanodisk, by combining quantum dynamics and classical electromagnetic calculations. We assume that each qubit interacts locally with its own photonic environment and its free-space decay time is in the picosecond regime. We observe non-Markovian entanglement dynamics indicating strong light-matter interaction between the qubits and the photonic reservoirs. We investigate the entanglement dynamics using entanglement of formation as a measure of entanglement by varying the initial state of the composite system, which always remains an extended Werner-like state, the transition frequency and the orientation of the transition dipole moment of each qubit, the radius of the molybdenum disulfide nanodisk, and the distance of a qubit from its corresponding nanodisk. For several values of the above parameters, we observe interesting phenomena during the time evolution of entanglement of formation, such as entanglement sudden death, revival of entanglement and entanglement trapping. • The entanglement dynamics of two initially entangled quantum emitters next to MoS 2 nanodisks is analyzed. • The results are obtained by combining quantum dynamics calculations with electromagnetic calculations. • Non-Markovian entanglement dynamics is obtained. • Entanglement sudden death, revival of entanglement and entanglement trapping are found for different system parameters. • The effects of the electric dipole orientation of the quantum emitter are also analyzed.

The effects of Dzyaloshinskii–Moriya interaction on entanglement dynamics of a spin chain in a non-Markovian regime

We study the dynamics of entanglement in a one-dimensional spin-1/2 XX model with three-spin interaction (TSI) and Dzyaloshinskii–Moriya (DM) interaction. The revival of the quantum entanglement is an indication of non-Markovian dynamics, which is observed in the system with TSI interaction. Results of the research show that in the system with both TSI and Heisenberg interaction, there is a critical value in which a dynamical phase transition from the Markovian to the non-Markovian regime. The dynamic behavior of the correlation in the system with XX Heisenberg and DM interaction is non-Markovian in αc. In the system with TSI and DM interaction, in D≥J′, DM interaction reinforces the non-Markovian behavior of the correlation introduced by TSI interaction. Moreover, the results show that in system with TSI, XX Heisenberg, and DM interaction, if D=αc, the non-Markovian behavior of the system is improved.

Dynamic Evolution of Open Spin Chain in Markovian Environment

There have been numerous researches on spin chain while most are gathered in the thermal entanglement or the intrinsic decoherence of spin chain, and only few papers investigate the spin chain under dephasing channel. Thus the dynamics of open spin chain in thermal noises is desiderated to research. In this paper, the entanglement dynamics induced by 2-qubit anisotropy Heisenberg model that each qubit coupled with reservoir is investigated. The corresponding master equation is analytically solved by the new Ket-Bra Entangled State (KBES) method with computer; The evolution of entanglement is also analyzed in detail when initial state is described by Extended Wenger-Like(EWL) state. It’s found that the spin coupling can lead to the revival of entanglement; Besides the fluctuation frequency show a positive correlation with the coupling coefficient. The most distinguished discovery is that the system still keep part entangled even for time tend to infinity, which imply that people can inhibit the disentanglement process by internal interaction of system.

Manipulating entanglement sudden death in two coupled two-level atoms interacting off-resonance with a radiation field: an exact treatment.

We study a model of two coupled two-level atoms (qubits) interacting off-resonance (at non-zero detuning) with a single mode radiation field. This system is of special interest in the field of quantum information processing (QIP) and can be realized in electron spin states in quantum dots or Rydberg atoms in optical cavities and superconducting qubits in linear resonators. We present an exact analytical solution for the time evolution of the system starting from any initial state. Utilizing this solution, we show how the entanglement sudden death (ESD), which represents a major threat to QIP, can be efficiently controlled by tuning atom-atom coupling and non-zero detuning. We demonstrate that while one of these two system parameters may not separately affect the ESD, combining the two can be very effective, as in the case of an initial correlated Bell state. However in other cases, such as a W-like initial state, they may have a competing impacts on ESD. Moreover, their combined effect can be used to create ESD in the system, as in the case of an anti-correlated initial Bell state. A clear synchronization between the population inversion collapse-revival pattern and the entanglement dynamics is observed at all system parameter combinations. Nevertheless, only for initial states that may evolve to ESD, the population inversion revival oscillations, where exchange of energy between the atoms and the field takes place, temporally coincide with the entanglement revival peaks, whereas the population collapse periods match the ESD intervals. The variation of the radiation field intensity has a clear impact on the duration of the ESD at any combination of the other system parameters.

Revival of Quantum Interference by Modulating the Biphotons.

The possibility to manipulate the wave packets of single photons or biphotons has enriched quantum optics and quantum information science, with examples ranging from faithful quantum-state mapping and high-efficiency quantum memory to the purification of single photons. Here we demonstrate another fascinating use of wave packet manipulation on restoring quantum interference. By modulating the photons' temporal wave packet, we observe the revival of postselected entanglement that would otherwise be degraded or lost due to poor quantum interference. Our study shows that the amount of the restored entanglement is only limited by the forms of modulation and can achieve full recovery if the modulation function is properly designed. Our work has potential applications in long-distance quantum communication and linear optical quantum computation, particularly for quantum repeaters and large cluster states.

Macroscopic entanglement in optomechanical system induced by non-Markovian environment.

In this paper, the non-Markovian dynamics of an optomechanical system is analyzed by using the non-Markovian quantum state diffusion (NMQSD) method. An exact solution is obtained for the system composed of a Fabry-Pérot (F-P) cavity with two movable mirrors without the linearization of the Hamiltonian. Based on the solution, we find that the memory effect of the non-Markovian environment can be used to generate macroscopic entanglement between two mirrors. In order to achieve the maximum entanglement generation, the non-Markovian properties of the environment have to be chosen carefully depending on the properties of the system. Then, we also show that the coherence (superposition) in the initial state may produce entanglement in the evolution. At last, we show the entanglement sudden death and revival significantly depend on the strength of the memory effect, and the entanglement revival can be only observed in non-Markovian case. Our treatment, as an example, paves a way to exactly solve a large category of optomechanical systems without the linearization of the Hamiltonian.

Entanglement dynamics for circularly accelerated two-level atoms coupled with electromagnetic vacuum fluctuations

We investigate, in the framework of open quantum systems, the entanglement dynamics of two circularly accelerated two-level atoms with the same centripetal acceleration interacting with a bath of fluctuating electromagnetic fields in the Minkowski vacuum. We assume that the two atoms rotate synchronically with their separation perpendicular to the rotating plane, and study the entanglement degradation, creation, revival, and enhancement by solving the Markovian master equation. In contrast to the scalar-field case, the entanglement dynamics is crucially dependent on the atomic polarizations in the sense that the polarization directions may affect the entanglement decay rate, and may determine the occurrences of entanglement creation, revival and enhancement. Compared with the uniformly accelerated case and the thermal case, the decay rate of entanglement for circularly accelerated atoms is larger, while the revival and enhancement rates are smaller.

Quantum correlations in quantum emitters strongly coupled with metallic nanoparticles

We study the dynamics of two initially entangled qubits prepared in an extended Werner-like state, where each one interacts locally with a spherical metallic nanoparticle. We combine quantum dynamics beyond the rotating-wave approximation with classical electromagnetic calculations in order to compute the time evolution of quantum discord and entanglement using entanglement of formation. We present results for qubits either quantum dots or J-aggregates and compare the evolution of quantum discord and entanglement of formation. We find interesting phenomena such as entanglement sudden death, periodic entanglement revival, entanglement oscillations and entanglement trapping by varying the initial state or the distance of each qubit to the corresponding nanoparticle.

Schemes to avoid entanglement sudden death of decohering two qubit system

We investigate the entanglement dynamics of two interacting qubits in a common vacuum environment. The inevitable environment interaction leads to entanglement sudden death (ESD) in a two qubit entangled system. The entanglement dynamics can be modified by the use of local unitary operations (quantum gates), applied on the system during its evolution. We show that these operations not only delays or avoids the ESD but also advances the entanglement revival with an enhanced entanglement depending on the time of operation. We have analytically found out different time windows for switching with different quantum gates so that the ESD can be completely avoided in the subsequent evolution of the system. Our result offers practical applications in the field of quantum information processing where the entanglement is a necessary resource.

Dynamic Properties for BEC in an Optical Cavity with Atom-Photon Nonlinear Interaction

In this paper we investigate the dynamics of physical properties of the system introduced in Dimer et al. (Phys. Rev. A 75, 013804, 2007) and Zhao et al. (Phys. Rev. A 90, 023622, 2014) consisting of an ensemble of four-level atoms in Bose-Einstein condensate (BEC) state and a single-mode quantized field in which nonlinear interaction is taken into account. In fact, we start with a four-level atom and then explain how this model can be reduced to an effective two-level one via the adiabatic elimination. Also, our presentation is free of any classical approximation and so it is fully quantized. In this regard, we introduce the dynamical Hamiltonian of the system in terms of angular momentum operators and use the Dicke model to achieve the state of atomic sub-system. After obtaining the analytical solution of the state vector associated with the quantized BEC-field system, various physical properties such as atomic population inversion, quantum statistics of the field, squeezing in atomic and field subsystems as well as the degree of entanglement between the “BEC atoms” and the “photons” are numerically evaluated. It is shown that, the nonlinear interaction and other involved parameters in the presented model can dramatically affect the dynamics of the system. The collapse-revival phenomenon in the population inversion, Mandel parameter and atomic squeezing is a superb feature of the system which can be controlled by tuning the chosen parameters. Meanwhile, we propose an efficient way for the generation of sub-Poissonian and squeezed fields as well as squeezed atoms via nonlinear interaction of quantized filed with atomic BEC. In addition, it is found that, after the onset of interaction the system is always entangled. Altogether, under particular conditions, the approximated sudden death and then revival of entanglement can be observed.

Photoinduced entanglement in a magnonic Floquet topological insulator

When irradiated via high frequency circularly polarized light, the stroboscopic dynamics in a Heisenberg spin system on a honeycomb lattice develops a next nearest neighbor (NNN) Dzyaloshinskii-Moriya (DM) type term\cite{owerre}, making it a magnonic Floquet topological insulator. We investigate the entanglement generation and its evolution on such systems - particularly an irradiated ferromagnetic XXZ spin-$\frac{1}{2}$ model in a honeycomb lattice as the system parameters are optically tuned. In the high frequency limit, we compute the lowest quasi-energy state entanglement in terms of the concurrence between nearest neighbor (NN) and NNN pair of spins and witness the entanglement transitions occurring there. For the easy axis scenario, the unirradiated system forms a product state but entanglement grows between the NNN spin pairs beyond some cut-off DM strength. Contrarily in easy planar case, NN and NNN spins remain already entangled in the unirradiated limit. It then goes through an entanglement transition which causes decrease (increase) of the NN (NNN) concurrences down to zero (up to some higher value) at some critical finite DM interaction strength. For a high frequency of irradiation and a suitably chosen anisotropy parameter, we can vary the field strength to witness sudden death and revival of entanglement in the Floquet system. Both exact diagonalization and modified Lanczos techniques are used to obtain the results upto 24 site lattice. We also calculate the thermal entanglement and obtain estimates for the threshold temperatures below which non-zero concurrence can be expected in the system.

Amplitude tuning of steady-state entanglement in strongly driven coupled qubits

In this work we report on a new mechanism to generate dissipative steady state entanglement in two coupled qubits driven by strong periodic ac fields. We show that steady entanglement can be generated at one side of a multiphoton resonance between a non-entangled ground state and an entangled excited state. The degree of entanglement can be tuned as a function of the amplitude of the periodic drive. A rich dynamic behavior with creation, death and revival of entanglement can be observed for certain parameter regimes, accessible in current experimental devices.

Entanglement dynamics for uniformly accelerated two-level atoms in the presence of a reflecting boundary

We study the entanglement dynamics for two uniformly accelerated two-level atoms in interaction with a bath of fluctuating electromagnetic fields in vacuum in the presence of a reflecting boundary. We consider two different alignments of atoms, i.e. parallel and vertical alignments with respect to the boundary. In particular, we focus on the effects of the boundary, and acceleration on the entanglement dynamics, which are closely related to the orientations of polarization. For the parallel case, the initial entanglement of two transversely polarizable atoms very close to the boundary can be preserved as if it were a closed system, while for two vertically polarizable atoms, the concurrence evolves two times as fast as that in the free space. In the presence of a boundary, entanglement revival is possible for two atoms initially in the symmetric state depending on the orientations of the atomic polarizations, which is in sharp contrast to the fact that the concurrence always decays monotonically in the free space. Interestingly, two initially separable atoms, for which entanglement generation can never happen in the free space with any given acceleration and separation, can get entangled in the presence of a boundary if they are aligned parallel to the boundary. The birth time of entanglement can be noticeably advanced or postponed for the parallel two-atom system placed close to the boundary, while the maximal concurrence during evolution can be significantly enhanced when the atoms are vertically aligned. Moreover, two inertial atoms with different polarizations remain separable all the time, while as the acceleration increases, the delayed birth of entanglement happens, and the nonzero concurrence can be enhanced.

Free and bound entanglement dynamics in qutrit systems under Markov and non-Markov classical noise

We investigate in detail the dynamics of decoherence, free and bound entanglements, and the conversion from one to another (quantum state transitions), in a two non-interacting qutrits system initially entangled and subject to independents or a common classical noise. Both Markovian and non-Markovian environments are considered. Furthermore, isotropic and bound entangled states for qutrits systems are considered as initial states. We show the efficiency of the formers over the latters against decoherence, and in preserving quantum entanglement. The loss of coherence increases monotonically with time up to a saturation value depending upon the initial state parameter and is stronger in a collective Markov environment. For the non-Markov regime the presence or absence of entanglement revival and entanglement sudden death phenomena is deduced depending on both the peculiar characteristics of the noise, the physical setup and the initial state of the system. We demonstrate distillability sudden death for conveniently selected parameters in bound entangled states; meanwhile, it is completely absent for isotropic states, where entanglement sudden death is avoided for dynamic noise independently of the noise regime and the physical setup. Our results indicate that distillability sudden death under the Markov/non-Markov noise considered can be avoided depending upon the physical setup.