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Quantum entanglement as a fundamental resource of quantum information processing is at the heart of emerging applications, including quantum cryptography, quantum communication and quantum computation. One of the promising physical realizations is solid-state quantum entanglement achieved with quantum dots (QDs) in the visible frequency range. The long-distance entanglement is necessary to transmit information through a long distance. For this purpose, the correlation between two distant qubits must be mediated by virtual bosons, for example, photons. However, it has attracted intensive interests that this mediation can be done by the surface plasmon instead of by the photons from its similar property to the light propagation in conventional dielectric optical components. The plasmonic nanowaveguide confines light to subwavelength dimension with propagating surface plasmon below diffraction limit and strongly interacts with the quantum emitters located near it. To explore scattering of single plasmon and entanglement of qubits, the three main approaches are used in the waveguide QED: the real space formalism, the input-output formalism and the master equation approaches.
There have been considerable investigations widely discussed about the entanglement of two qubits coupled to a plasmonic nanowaveguide with the real space formalism. The previous works on the entanglement of qubits in plasmonic nanowaveguide system focused on two-qubit system. Meanwhile, it is already demonstrated that multi-particle entanglement is much more efficient than two-particle entanglement and the simplest three-particle entanglement will play a pivotal role in quantum information processing. In the recent research concerned with multi-qubit waveguide system, the bipartite entanglement has not been considered but only the pairwise entanglement.
We theoretically investigated the properties of not only the pairwise entanglement but also the bipartite entanglement of three non-equally separated QDs mediated by a plasmonic nanowaveguide system by using the concurrence as an entanglement measure and the real space formalism. We focused on calculating the pairwise concurrence between two QDs and the bipartite concurrence for three QDs in the nanosystem and analyzed the influence of several physical parameters on the entanglement. It was demonstrated that high concurrences of pairwise and bipartite entangled states for three QDs are obtained in wide range of the separation distances between the QDs. Moreover, the switching between maximally entangled state and unentangled state become feasible by properly modulating the frequency detuning of the QDs from the plasmon field, the separation distances between the QDs, the QD-waveguide coupling strength, the group velocity of surface plasmon and so on.
The nanosystem proposed here can have potential application in the realization of quantum device to control the three-particle entanglement which is widely used in quantum communication and quantum computation.
The article with our research results entitled "Pairwise and Bipartite Entanglements of Three Non-Equally Separated Quantum Dots in Plasmonic Nanowaveguide System" (https://doi.org/10.1007/s11468-021-01406-9) was published in the Journal "Plasmonics" of the Publishing Company "Springer".
