Two-photon interference in the telecom C-band after frequency conversion of photons from remote quantum emitters

Abstract

Efficient fiber-based long-distance quantum communication via quantum repeaters relies on deterministic single-photon sources at telecom wavelengths, with the potential to exploit the existing world-wide infrastructures. For upscaling the experimental complexity in quantum networking, two-photon interference (TPI) of remote non-classical emitters in the low-loss telecom bands is of utmost importance. With respect to TPI of distinct emitters, several experiments have been conducted, e.g., using trapped atoms [1], ions [2], NV-centers [3, 4], SiV-centers [5], organic molecules[6] and semiconductor quantum dots (QDs) [7][8][9][10][11][12][13][14]; however, the spectral range was far from the highly desirable telecom C-band. Here, we report on TPI at 1550 nm between down-converted single photons from remote QDs [15], demonstrating quantum frequency conversion [16][17][18] as precise and stable mechanism to erase the frequency difference between independent emitters. On resonance, a TPI-visibility of (29 ± 3) % has been observed, being only limited by spectral diffusion processes of the individual QDs [19,20]. Up to 2-km of additional fiber channel has been introduced in both or individual signal paths with no influence on TPI-visibility, proving negligible photon wave-packet distortion. The present experiment is conducted within a local fiber network covering several rooms between two floors of the building. Our studies pave the way to establish long-distance entanglement distribution between remote solid-state emitters including interfaces with various quantum hybrid systems [21][22][23][24].

Controllable Delay and Polarization Routing of Single Photons

“…There, the particular delay would not be required, but rather the difference of the spectra of the two circular polarization components. Pinning the emission frequency to a universal reference is an important feature in the implementation of quantum networks, where multiple distinct sources need to be used (and matched in frequency) …”

Advanced Technologies for Quantum Photonic Devices Based on Epitaxial Quantum Dots

“…As a result, the two single photons that were initially nondegenerate in the 980 nm band became degenerate in the 600 nm band, and nonclassical two‐photon interference was observed . Recently, a similar experiment was carried out for two InAs/GaAs QDs in the 900 nm band; but instead of upconversion, they were downconverted to the same wavelength in telecom band (1550 nm) using a 2157 nm pump . This is particularly meaningful for long‐distance quantum communication, since fibers have the lowest transmission loss in the telecom band and a vast body of infrastructures exists in this spectral window …”

Spectral noise in frequency conversion from the visible to the telecommunication C-band

“…Other QFC experiments based on DFG have been performed of input photons in the deep red or near-infrared range [15,[21][22][23][24][25], with the target in a telecom band, which are closely related to the experiments discussed here. However, in terms of the noise mechanism these experiments are different.…”

“…In some cases the pump was spectrally close to the target wavelength [21,23], such that Raman noise induced by the pump was the dominant source of noise. In other experiments the pump had a wavelength well above the target wavelength [15,22,24,25], which strongly suppresses the SPDC noise. Similarly Esfandyarpour et al demonstrated a cascaded, two-stage DFG conversion of 650 nm photons to the telecom C-band using a pump at 2.2 µm [26].…”