Science Daily August 30, 2023
Recently, there has been significant interest in rare earth ions, in particular Er3+ for its telecom band optical transition that allows long-distance transmission in optical fibres. However, the development of repeater nodes based on rare earth ions has been hampered by optical spectral diffusion, precluding indistinguishable single-photon generation. Researchers at Princeton University implanted Er3+ into CaWO4 to realize significantly reduced optical spectral diffusion. For shallow implanted ions coupled to nanophotonic cavities with large Purcell factor, they observed single-scan optical linewidths of 150 kHz and long-term spectral diffusion of 63 kHz, both close to the Purcell-enhanced radiative linewidth of 21 kHz. This enabled the observation of Hong–Ou–Mandel interference between successively emitted photons with a visibility of V = 80(4)%, measured after a 36 km delay line. They also observed spin relaxation times T1,s = 3.7 s and T2,s > 200 μs, with the latter limited by paramagnetic impurities in the crystal instead of nuclear spins. According to the researchers this represents a notable step towards the construction of telecom band quantum repeater networks with single Er3+ ions…read more. TECHNICAL ARTICLEÂ
Generation of indistinguishable photons. Credit: Nature volume 620, pages977–981 (2023)Â