Tunable degree of second order coherence for radiation of plasmonic structure excited by single photon source

Currently, a substantial progress has been achieved in creating nano-sized sources of coherent radiation. Radiation sources for quantum information transmission lines in addition to high temporal coherency must also have a... [ view full abstract ]

Currently, a substantial progress has been achieved in creating nano-sized sources of coherent radiation. Radiation sources for quantum information transmission lines in addition to high temporal coherency must also have a desirable correlation function of the second order (g²). Usually, single-photon sources (SPS) are required. To increase the speed of SPSs, single molecules, NV centers or quantum dots interacting with plasmonic structures are used. However, in such systems, due to the Purcell effect, the g²(0) function of radiation is modified. Thus, it is necessary to create sources with required g²(0) and the high radiation rate.

We suppose that SPS is a two-level system (TLS) and choose the one mode of the plasmonic structure interacting with TLS. To find the statistical properties of radiation and the radiation rate of the SPS coupled with plasmonic structure we use the Lindblad master equation formalism. The SPS is excited by incoherent continuous pumping. Both components of the system are surrounded by the medium with non-zero temperature.

We consider the g²(0) function of electromagnetic field emitted by plasmonic structure which is excited by SPS, and show that it strongly depends both on Rabi constant of interaction and temperature of surrounding medium. In the case of high temperature, at low pumping rates of the SPS, the second order correlation function, g²(0), equals two as it takes place for black-body radiation (see Fig. 1). However, in the opposite case, when Rabi constant is much larger than temperature, the g²(0) function equals zero as for radiation of a  single TLS, Fig. 1. 

We show that the reason of such behavior is non-linear dependence of Rabi-splitting on the occupation number of plasmonic mode. At high pumping rates in both cases the g²(0) function tends to unity as in laser above threshold (Fig. 1). Note that the single-photon regime in this system is available at room temperature and the radiation rate of the system greatly exceeds the radiation rate of a single SPS due to Purcell effect (Purcell factor can reach 10³), which is of great interest for the applications in sphere of quantum information processing.