Widely Tunable Single-Photon Source from a Carbon Nanotube in the Purcell Regime

The narrow emission of a single carbon nanotube at low temperature is coupled to the optical mode of a fiber microcavity using the built-in spatial and spectral matching brought by this flexible geometry. A thorough cw and time-resolved investigation of the very same emitter both in free space and in cavity shows an efficient funneling of the emission into the cavity mode together with a strong emission enhancement corresponding to a Purcell factor of up to 5. At the same time, the emitted photons retain a strong sub-Poissonian statistics. By exploiting the cavity feeding effect on the phonon wings, we locked the emission of the nanotube at the cavity resonance frequency, which allowed us to tune the frequency over a 4 THz band while keeping an almost perfect antibunching. By choosing the nanotube diameter appropriately, this study paves the way to the development of carbon-based tunable single-photon sources in the telecom bands.

Figure 1

(a), (b) Sketch of the experimental setup showing the versatile micro-PL or scanning cavity microscope. DBR stands for Distributed Bragg Reflector.

Figure 2

(a) 2D plot of the emission spectrum of a nanotube embedded in the fiber microcavity. The color scale encodes the emission intensity while the horizontal axis corresponds to the wavelength and the vertical one to the cavity length. The green dashed line corresponds to the ZPL wavelength, while the light blue one corresponds to the resonant cavity length. (b) Emission spectrum ($\text{photon}·{\mathrm{GHz}}^{-1}{\mathrm{s}}^{-1}$) of the nanotube when the cavity is tuned in resonance with its ZPL [horizontal cut of (a) along the blue dashed line]. (c) Free-space luminescence spectrum of the same nanotube. (d) Integrated count rate as a function of the mode volume when the cavity length is increased by steps of $\lambda /2$.

Figure 3

Time-resolved photoluminescence of a nanotube in free space (blue line) or coupled to a resonant cavity (red line). Response of the detector (dashed line). The free-space transient was convoluted with the empty cavity response (not shown) in order to account for the photon storage time in the cavity. Inset: Saturation measurement of the same nanotube measured in free space under pulsed excitation.

Figure 4

Intensity correlation measurements of a nanotube resonantly coupled to a fiber cavity obtained in a Hanbury Brown–Twiss setup under pulsed excitation. The missing peak at time 0 [$g^{(2)}(0)=0.03$] shows that high-quality single photons are emitted by the nanotube. The signal between the first and second peaks corresponds to detector artifacts (afterpulses). Right inset: Same measurements for a detuning of the cavity corresponding to an emission of the phonon side wings. Left inset: Output of the cavity for several detunings. The corresponding intensity correlations are displayed in the main panel and in the right inset according to the color code of the arrows.