In the field of quantum information and quantum computing, entanglement plays an essential role. Entanglement preservation is an important issue as realistic quantum systems are affected by decoherence and entanglement losses due to the interaction with their environment. For example, in spite of an exponential decay of a single qubit, the entanglement between two qubits may completely disappear at a finite time; a phenomenon known as “entanglement sudden death” . Recently, interest has been given in cases that qubits can be strongly coupled to plasmonic nanostructures, like, for example, an one-dimensional plasmonic waveguide  or a two-dimensional lattice of metal-coated dielectric nanoparticles . In such systems the strong interaction with the surface plasmons leads to significant entanglement between the two qubits. Here, we consider the interaction of two initially entangled qubits interacting individually with a two-dimensional lattice of metal-coated dielectric nanoparticles. We consider two cases for the qubits, a pair of regular two-level systems and a pair of V-type systems where one transition is the qubit and the other level acts as an umbrella level . We consider the entanglement dynamics for different initial conditions of the qubits. The specific plasmonic nanostructure leads to strongly modified spontaneous emission rates of individual quantum systems (strong suppression in certain cases) and, in addition, to strongly anisotropic Purcell effect for orthogonal dipoles, that in turn can be used for simulating quantum interference in spontaneous emission . We use these effects for significantly prolonging entanglement dynamics near the plasmonic nanostructure in both cases, in comparison to the cases that the qubits are in free space.
1. T. Yu and J. H. Eberly, Phys. Rev. Lett. 93, 140404 (2004).
2. A. Gonzalez-Tudela, D. Martin-Cano, E. Moreno, L. Martin-Moreno, C. Tejedor, and F. J. Garcia-Vidal, Phys. Rev. Lett. 106, 020501 (2011).
3. N. Iliopoulos, A. F. Terzis, V. Yannopapas, and E. Paspalakis, Ann. Phys. 365, 38 (2016).
4. S. Das and G. S. Agarwal, Phys. Rev. A 81, 052341 (2010).
5. V. Yannopapas, E. Paspalakis, and N. V. Vitanov, Phys. Rev. Lett. 103, 063602 (2009).
We study theoretically the phenomenon of four-wave mixing in intersubband transitions of a symmetric double
quantum well structure. In the theoretical model we consider two quantum well subbands that are coupled by
a strong pump electromagnetic field and a weak probe electromagnetic field, taking into account the effects of
electron-electron interactions. For the description of the system dynamics we use the density matrix equations
obtained from the effective nonlinear Bloch equations. These equations are solved numerically for a realistic
semiconductor quantum well structure GaAs/AlGaAs. We show that the four-wave mixing spectrum can be
significantly dependent on the frequency and the intensity of the pump field and on electron sheet density.
We analyze the steady state and transient properties of the polarization and of the electronic population in a triple semiconductor quantum well structure with tunneling induced interference. We first derive the dark states of the system and show that this structure can lead to double dark states. Then, we show that under the dark state conditions the system can exhibit tunneling induced transparency, slow light, transient gain without inversion and coherent population trapping. The dynamics of the polarization and of the electronic population, as well as the total trapped electronic population in the system, are found to be depended on which dark state condition is satisfied.