Widely tunable single-photon source from a carbon nanotube in the Purcell regime

Abstract: Single-Wall Carbon Nanotubes (SWNTs) are among the very few candidates for single-photon sources operating in the telecom bands since they exhibit large photon antibunching up to room temperature. However, coupling a nanotube to a photonic structure is highly challenging because of the random location and emission wavelength in the growth process. Here, we demonstrate the realization of a widely tunable single-photon source by using a carbon nanotube inserted in an original repositionable fiber micro-cavity : we fully characterize the emitter in the free-space and subsequently form the cavity around the nanotube. This brings an invaluable insight into the emergence of quantum electrodynamical effects. We observe an efficient funneling of the emission into the cavity mode with a strong sub-Poissonian statistics together with an up to 6-fold Purcell enhancement factor. By exploiting the cavity feeding effect on the phonon wings, we locked the single-photon emission at the cavity frequency over a 4~THz-wide band while keeping the mode width below 80~GHz. This paves the way to multiplexing and multiple qubit coupling.

• The paper demonstrates a six-fold brightness increase via a Purcell factor up to 5 when coupling carbon nanotubes to a fiber micro-cavity.
• It achieves over 4 THz of tunability with a sub-80 GHz linewidth by exploiting phonon sidebands and cavity feeding effects.
• Photon antibunching measurements with a g(2)(0) value of 0.05 confirm robust single-photon emission suitable for telecom quantum applications.

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

The paper "Widely tunable single-photon source from a carbon nanotube in the Purcell regime" presents a significant advancement in the development of single-photon sources, particularly in the telecom spectral bands. The research reported in this paper focuses on the utilization of Single-Wall Carbon Nanotubes (SWNTs) as single-photon emitters, coupling them into a photonic structure to leverage quantum electrodynamics effects. This study provides detailed analyses and experimental results showcasing the enhanced photonic properties achieved through such coupling.

Key Findings

The primary achievement of this paper is the demonstration of a widely tunable single-photon source using carbon nanotubes embedded in a repositionable fiber micro-cavity. The methodology involves a thorough characterization of the carbon nanotube in free-space followed by the formation of a micro-cavity around it. This approach not only aligns the emission wavelength with the cavity resonance passively but also significantly enhances the emission properties through the Purcell effect.

1. Purcell Enhancement: The study reports a remarkable Purcell factor (F_p) of up to 5, which corresponds to a six-fold enhancement in brightness and a significant increase in the radiative rate of the carbon nanotube emitters. The radiative quantum yield is enhanced from an intrinsic value of approximately 2% to around 12% in the cavity configuration, indicating the impact of cavity quantum electrodynamical (CQED) effects.
2. Tunable Emission: The research explores a wide tunable range of over 4 THz, while maintaining high spectral purity with a linewidth below 80 GHz. This tunability is facilitated by exploiting the phonon side-bands and cavity feeding effects, indicating a potential pathway for developing flexible and tunable quantum emitters.
3. Photon Statistics: Measurements conducted in a Hanbury-Brown and Twiss setup confirm strong photon antibunching with a g^{(2)}(0) value of approximately 0.05, demonstrating the single-photon nature of the emission. This characteristic is preserved even with strong spectral filtering, highlighting the robustness and reliability of the emitter design.

Implications and Future Prospects

The findings from this study have noteworthy implications for both theoretical and practical domains:

• Quantum Technologies: The development of reliable single-photon sources operating at telecom wavelengths is integral for quantum communication and cryptography. The techniques presented provide a pathway for integrating quantum emitters with existing telecommunications infrastructure.
• CQED Applications: The enhancement of photonic properties through CQED effects as demonstrated in this study could be extended to other nanoscopic quantum emitters, thereby broadening the scope of CQED for various applications.
• Scalability and Integrability: This study underscores the potential for scaling up single-photon source technology while maintaining low-cost production given the compatibility of carbon nanotubes with electrical excitation and integration prospects.

Looking forward, future research can explore alternative carbon nanotube configurations to optimize performance further, potentially achieving stronger coupling regimes by reducing the mode volume of the cavity. Additionally, extending these techniques to other materials could facilitate the development of single-photon sources that operate across wider spectral ranges, including the entire telecom windows. The continuous refinement of this approach may allow for more intricate designs in on-chip quantum circuits, catalyzing advances in photonic quantum technology.