Approaching Transform-Limited Line Widths in Telecom-Wavelength Transitions of Ungated Quantum Dots

Highly coherent quantum emitters operating in the telecommunication C-band (1530–1565 nm), where ultralow-loss fibers and photonic circuits are available, are crucial to the development of scalable quantum technologies. In this work, we report on a modified Stranski–Krastanov growth scheme using chemical beam epitaxy to enable the generation of high-quality InAs/InP quantum dots, characterized by near-transform-limited line widths (Γ TL ). We demonstrate the growth of highly symmetric quantum dots with aspect ratios >0.8 and densities ranging from 2 to 22 μm –2 . Optical characterization of these sources reveal fine-structure splittings down to 25 ± 4 μeV and a single-photon purity of g (2) (0) = 0.012 ± 0.007, confirming the quality of these dots. Further, using an etalon to measure the line width, in combination with rigorous modeling, we find an upper-bound to the mean, low-power line widths of only 12.2 ± 6.7 Γ TL and, in the best case, 2.8 ± 1.9 Γ TL . These results represent a significant step in the development of telecom-wavelength quantum light sources, which are essential for complex quantum networks and devices.