# Towards Deep Integration of Electronics and Photonics
## 5 More Quasiparticles  
Along with SPPs, there are other quasi-particle excitations which mix light and matter. In general, the polariton quasiparticle, introduced by [PERSON] in 1958 [94], is used to describe the response of matter to light. The polarization field can be quantized and represented as an ensemble of bosons. Depending on the type of matter involved in the interaction, one may distinguish, for example, phonon-polaritons, plasmon-polaritons and exciton-polaritons. A more intense use of quasiparticles and their combinations can be fruitful approach for the deep integration between electronics and photonics.  
Phonons and molecular vibrations play a significant role in many processes in nature. Interaction of electrons and photons with phonons is used a lot in modern technology. For example, the interaction of photons with molecular vibrations lay the ground for Raman scattering, which is widely used in science and industry. Interaction of electrons with molecular vibrations is an important process in biology [95; 96; 97]. It is also implemented in the resonant negative ions mass-spectrometry method to identify substances [98; 99]. Electron-phonon interactions play a significant role in molecular electronics and is highly involved in the charge transport through molecular bridges [100; 101].  
Another example of useful quasiparticles with intriguing properties are exciton-polaritons, which can be formed in semiconductor microcavities. It is demonstrated that exciton-polaritons may condense at room temperatures forming a nonlinear superfluid medium [102]. Along with other types of quantum fluids, exciton-polariton condensates support many exotic excitations, including solitons and quantum vortices [103; 104; 105; 106]. Regarding possible applications, it is already suggested theoretically and is demonstrated experimentally that nonlinear properties of exciton-polariton condensates can be implemented to create quantum simulators [107], capable of solving optimization problems with a large number of degrees of freedom.  
Various quasiparticles may interact with each other forming more complex hybrid states and providing even more possibilities to use them in future electronics. Interaction of exciton-polaritons with molecular vibrations is utilized to create a prototype of a photonic transistor [108]. Another example comes from the field of plasmonic photovoltaics [109], where the solar energy of photons can be converted to electron-hole pairs in a semiconductor via the excitation of a SPP on gold nanorods. This could augment photoconversion processes and improve photon harvesting.  
More experimental and theoretical works on plasmon-exciton interactions are available. In [110] coupling between excitons and SPPs is studied. The dependence of coupling on plasmonic dumping, which depends on the thickness of the plasmonic material, is demonstrated. The formation of a strongly coupled hybrid plasmon-exciton state is shown experimentally by probing the dispersion of the coupled system. The ability to tune the level of hybridization is declared to be promising for potential applications. A theoretical semi analytical model which can be used to describe coupled plasmon-exciton state is developed [111]. It describes the system where a single two-level  
Figure 4: The design of a single-photon transistor. Reproduced from [92] with the permission. SPP modes on a silver nanowire are used to provide a strong coupling between the three-level quantum gate and waveguided photons. The gate works as a single-photon memory device controlled by the external optical field. The transparency of the transistor for the incoming signal depends on the quantum sate of the gate.  
quantum emitter (quantum dot or an impurity center in diamond) is coupled to an arbitrarily shaped metallic nanoparticle (silver nanorod, for instance). The model is useful for understanding and designing plasmonic-excitonic nanostructures, which potentially may find their place in novel electro-optical technologies.