Due to their excellent optical properties, such as fast emission rates and nearly transform-limited linewidth, semiconductor quantum dots are promising for applications in photonic quantum technologies and for testing fundamental quantum-optical predictions. This talk addresses the dynamics of generating non-classical light from resonantly driven quantum systems. Specifically, the fundamental limits of the single-photon purity and photon indistinguishability for resonantly driven two-level systems and three-level ladder systems will be discussed, as well as the origin of antibunching under weak cw excitation. [1] A. Fischer, et al., Nature Physics 13, 649-654 (2017). [2] Hanschke et al., npj Quantum Information 4, 43 (2018). [3] Schöll et al., arXiv:2006.05476 (2020). [4] Hanschke et al., arXiv:2005.11800 (2020).

Integrated photonic devices fabricated by femtosecond lasers exhibit numerous advantages regarding stability, robustness, and miniaturization. In particular in the field of quantum photonics they provide an excellent testbed for exploring novel physical effects that may play a significant role in innovative applications.

In this presentation, I will discuss three recently explored phenomena implemented in laser-written integrated photonic devices: Photonic Boson sampling as an inherent quantum computation task, the observation of non-Hermitian PT-symmetric quantum optics as an extension of common Hermitian quantum optics, and three-dimensional quantum walks on complex graphs exploring higher-dimensional physics.

This talk aims to provide a general introduction to the physics of quantum dots and an overview of recent exciting developments in the field of semiconductor quantum optics with quantum dots (QDs). Semiconductor QDs have been identified as promising hardware for implementing the basic building blocks of novel quantum technologies, such as quantum computing, quantum communication, quantum metrology and quantum sensing. This is because individual charge carriers in QDs can be generated, manipulated, and coherently controlled. Moreover, miniaturized and integrated solutions with existing semiconductor technology are foreseeable. The topics addressed in this tutorial are two-photon interference with remote QDs, quantum dots emitting in the telecom O- and C-bands and quantum dots embedded in photonic integrated circuits.

Individual quantum systems are extremely sensitive sensors e.g. for magnetic fields. The strength of such quantum sensors is to harness quantum mechanics for ultimate sensitivity and versatility while simultaneously atomically small quantum systems boost spatial resolution in imaging. We employ point defects in diamond crystals, so called color centers, as nanoscale sensors. Electrons bound to such defects provide highly controllable spins and create bright luminescence that enables us to use even individual color centers. Applications of the sensors include e.g. material science where magnetic nanostructures are characterized to life science were currents in living organisms are detected. 

Superconducting circuits are ideally suited for studying quantum phenomena at the macroscopic scale. Since complex circuits, containing a few tens to a few hundreds of elements, can be designed, fabricated, and operated with relative ease, they are one of the prime contenders for realizing quantum computers. Now academic and industrial labs work on realizing universal fault-tolerant quantum computaters as well as on implementing algorithms on noisy intermediate-scale quantum (NISQ) hardware. Building systems, which can address commercially relevant computational problems, however, still requires significant conceptual and technological progress. In this talk, I will begin by introducing the quantum physics of superconducting circuits [1] which underlies the hardware used in superconducting quantum processors. I will then present our recent progress [2] towards realizing quantum error correction in superconducting circuits. Finally, I will discuss the challenges on the route toward large-scale quantum processors based on superconducting circuits. [1] A. Blais et al., arXiv:2005.12667 (2020) [2] C. K. Andersen et al., Nature Physics 16, 875–880 (2020)