In February 2022, Junyong Yan published a research paper titled “Double-Pulse Generation of Indistinguishable Single Photons with Optically Controlled Polarization” in Nano Letters.
Single-photon sources (SPSs) play a key role in linear optical quantum computing and solid-state quantum networks. So far semiconductor self-assembled quantum dots, as “artificial atoms” with high stability and easy integration into high-quality factor microcavites, have been demonstrated to be used to produce high-purity indistinguishable single photons under pulsed resonance excitation. However, traditional pulsed resonance fluorescence techniques usually require polarization filtering in order to extract single-photon signals from excitation pulses, but due to the lack of active control technology for generating single-photon polarization states, this filtering technique will lead to at least 50% loss of brightness of SPS devices, which directly reduces the scalability of SPSs.
In this work, we demonstrates a double-pulse excitation(DPE) scheme that is easy to filter out excitation laser and can generate single-photon sequences with optically controlled polarization. We demonstrated that the DPE scheme not only does not sacrifice the single-photon purity and indistinguishability of single photons, but also can exceed the 50% limitation of device brightness. This scheme is realized by exciting the quantum dot to the biexciton state and subsequently driving the quantum dot to an exciton eigenstate. By combining with a magnetic fi eld, we demonstrated the generation of photons with optically controlled polarization (the degree of polarization is 101(2)%), laser-neutral exciton detuning up to 0.81 meV, high single-photon purity (99.6(1)%), and indistinguishability (85(4)%). Laser pulses can be blocked using polarization and spectral fi ltering. Our work makes an important step toward indistinguishable SPSs with near-unity collection efficiency.