TWO-PHOTON INTERFERENCE USING BACKGROUND-FREE FREQUENCY CONVERSION OF SINGLE PHOTONS FROM A SEMICONDUCTOR QUANTUM DOT
S. Ates, Imad H. Agha, A. Gulinatti, I. Rech, M. T. Rakher, A. Badolato, and K. Srinivasan
Photons are considered as ideal carriers of quantum information in future communication technologies. The information encoded in a single photon can be carried over long distances due to the weak interaction with their environment. Among several material systems, self-assembled semiconductor quantum dots (QDs) have generated a great interest as potentially bright and stable solid-state single photon sources. Recent progress on advanced nanofabrication techniques enabled a controlled growth of high quality QDs, which can be integrated in different semiconductor nanophotonic structures, thus providing a suitable test bed for fundamental investigations in the field of quantum optics. However, due to the self-assembly nature of their growth process, each QD has a small variation in size/composition and therefore emits photons at slightly different frequencies. Here, we show that quantum frequency conversion (QFC) can be used to make these different photons indistinguishable by changing their frequencies to a common frequency.
Quantum frequency conversion process requires a nonlinear crystal and two input beams, which are a single-photon beam and a much stronger pump beam. The output of the nonlinear crystal results single photons at a converted frequency that is the sum of the two input frequencies. In our experiments, we use two different transitions of a single InAs QD around 980 nm as input single-photon beams and two corresponding pump beams around 1550 nm, which are merged on periodically-poled lithium niobate waveguide. The conversion process yields a single frequency peak at 600 nm as an output, which is a converted signal composed of both input QD transitions. Performing photon correlation and two-photon interference experiments on the output signal show that the quantum nature of the input single photons is conserved during the conversion process as well as identical photons are achieved . The ability to erase spectral distinguishability in solid-state quantum emitters, as shown here, can be a valuable tool in the development of scalable, chip-based photonic quantum information devices.