Unidirectional single-photon generation via matched zero-index metamaterials

We propose a scheme which can generate a highly directional single photon with almost 100% efficiency. Therefore we can get a useful single photon when it is required. An initial excited atom is placed inside a special Fabry-Pérot cavity whose walls consist of left-handed and zero-index metamaterials. The left-handed slabs work as a closed shell to avoid dissipation of the emitted photon, while the outer zero-index metamaterial slabs act as a special shutter which is transparent only for normal incidence, so that the photon emitted by the atom can only escape out of the cavity unidirectionally. Furthermore, we design the cavity with currently available metamaterials made of two-dimensional dielectric photonic crystals, and simulate the radiative field of an electric dipole to confirm our prediction. Differently from the previous proposal of single-photon sources which demanded complicated structure design and subtle mode analysis, our scheme is simple and robust for atomic position. This work has promising applications for quantum communication and optical quantum computing.

Figure 1

The geometric optical path of the radiative field emitted by an atom (short black arrow) in the cavity made of LHMs and ZIMs.

Figure 2

(a) The radiated electric field distribution in the $x\text{−}z$ plane, (b) the far-field radiative pattern, and (c) the angular spectrum of the decay rate when the atom is in the cavity with parameters ${\varepsilon }_1={\mu }_1=-1,{\varepsilon }_{L2}={\mu }_{L2}={\varepsilon }_2={\mu }_2=0.1,d_1=2{\lambda }_0,d_{L2}=d_2=\lambda$. (d) The decay rate as function of the index of ZIM with the definition ${\varepsilon }_2={\mu }_2={\varepsilon }_{L2}={\mu }_{L2}=n$.

Figure 3

The atomic radiated electric field distribution in the asymmetric structure. The left slab is replaced by PMC with ${\varepsilon }_{L2}=1,{\mu }_{L2}=-50$. (a) The atom is located at ${\mathit{r}}_a=(0,0,0)$; (b) the atom is located at ${\mathit{r}}_a=(0,0,-\lambda )$. Other parameters are the same as those in Fig. 2. The inset of (a) is the corresponding far-field radiation pattern.

Figure 4

The field intensity distribution of an oscillating electric dipole located in the cavity made of realistic LHM (enclosed by rectangle) and ZIM which is constructed by a two-dimensional photonic crystal. The detail parameters are presented in the text. The operating wavelength is $\lambda =1.55\mu \mathrm{m}$.