We have theoretically demonstrated the influence of qubit entanglement induced by the detunings among two qubits and surface plasmons in a hybrid qubits-metallic nanoparticle system. Enhancement appears when metallic nanoparticle is placed between qubits.
We theoretically investigate a general scheme for determining quantum entanglement of two detuned quantum dots (QDs) mediated by plasmon nanoparticle for weakly driven dissipative systems. By adiabatically eliminating the field operators, an effective model is proposed to find the underlying mechanism for this determination. Two specific hybrid systems composed of two QDs and a metallic nanoparticle (MNP) are considered. In the QD-MNP-QD system, the concurrence maxima generated by the detunings are several times larger than those in the resonance condition because of the robust superposition between the two separated entangled states. However, in the MNP-QD-QD system, the detunings generally reduce entanglement because the dipole-dipole interaction strongly suppresses the superposition of the entangled states. Moreover, the plateau of large concurrence exists for a broad range of parameters in both cases. The scheme is robust to dissipative systems and paves the way to improve entanglement in quantum information devices at the nanoscale.
We study the generation of entanglement between two distant qubits mediated by the surface plasmons of a metallic waveguide. We show that a V-shaped channel milled in a flat metallic surface is much more efficient for this purpose than a metallic cylinder. The role of the misalignments of the dipole moments of the qubits, an aspect of great importance for experimental implementations, is also studied. A careful analysis of the quantum dynamics of the system by means of a master equation shows that two-qubit entanglement generation is essentially due to the dissipative part of the effective qubit-qubit coupling provided by the surface plasmons. The influence of a coherent external pumping, needed to achieve a steady-state entanglement, is discussed. Finally, we pay attention to the question of how to get information experimentally on the degree of entanglement achieved in the system.
A key to achieving quantum computing is the qubit-entanglement. Nevertheless, real-life qubits cannot be isolated from the environment completely. As a result, the entanglement between qubits decoheres via their interaction with the environment. Therefore, it is essential to understand how the qubit-entanglement changes over time. In this work, we study the entanglement between qubits when placed in a bulk of dielectric material embedded with a nanosized metal particle. Most importantly, we focus on the effects of the unavoidable localized surface plasmons induced at the surface of the metal particle. We discuss how the distance between the metal particles affects the entanglement of the qubits and how various entangled states are affected by the localized surface plasmons.
Abstract We demonstrate the impact of detunings on quantum discord between two qubits in a hybrid system composed of two quantum emitters (QEs) and a resonant Ag nanoparticle (AgNP). The dynamics and steady-state quantum discord in weak- and strong-driving regimes are both investigated. In these regimes, the existence of detunings between QEs can enhance quantum discord because of the superposition of entangled states. By the aid of the strong localized field of the AgNP, quantum discord of two QEs is effectively improved. Our protocol aims to not only complete the dynamics model of cavity-based quantum discord, but also pave a way to on-chip quantum information devices.
The theoretical method to study strong coupling between an ensemble of quantum emitters (QEs) and surface plasmons excited by the nanoparticle cluster has been presented by using a rigorous first-principles electromagnetic Green's tensor technique. We have demonstrated that multi-qubit entanglements for two-level QEs can be produced at different coupling resonance frequencies, when they locate in the hot spots of the metallic nanoparticle cluster. The duration of quantum beats for such an entanglement can reach two orders longer than that for the entanglement in a photonic cavity. The phenomenon originates from collective coupling resonance excitation of the cluster. At the frequency of single scattering resonance, the entanglement cannot be produced although the single QE spontaneous decay rate is very big.