Photonic Quantum Simulations

The main objective of this project is to build a photonic quantum simulator that is capable of exploring new physical phenomena in quantum chemistry, solid-state physics and other physical systems. The motivation for this is to use the particular advantage of photons, the single particle quantum control and tunable measurement-induced interaction, to address unsolved problems in the complex world of quantum physics. This will be achieved by developing new techniques for the generation and manipulation of multi-photon entanglement. The main idea is to combine new photon sources, synchronization systems, integrated optical circuits and in particular high-efficiency detectors to break the ground for unimagined quantum control of ten or more individual photons. In the long run, these photon states will be entangled in path and polarization, which provides access to hyper-entangled states of up to 20 qubits. These multi-qubit states will be not only of relevance for studying novel quantum states in previously inaccessible parameter regime, but also for the implementation of new protocols in quantum computing. The results of these experiments will open up new and exciting prospects for photonic quantum computers.

The Photonic Quantum Simulation project led to the development of new photonic quantum technology that allowed to investigate new architectures and concepts for quantum computers and to realize quantum simulations of other quantum systems. This START project enabled the development of a new generation of bright multi-photon sources that generate multi-photon states at wavelengths for which losses in fibres and integrated optics is minimal. The efficient detection of these photons became possible by developing and optimizing high-efficient single-photon detectors based on superconducting technology. This, together with customized integrated waveguides for processing single photons was essential for the scientific results of this project.More than two dozen peer-reviewed publications resulted out of this project. Of particular broad interest was our demonstration of a new feature for quantum computers, namely the privacy-preserving data processing. Our demonstrated blind quantum computer enabled a delegated quantum computation for which the clients input, software and outcome remains private. Another milestone demonstration was the so-called Boson Sampling computation, a resource-efficient quantum computer architecture that relies only on the propagation of many single photons in complex, but passive interferometric networks. Of high impact was also the demonstration of an entirely new scheme for quantum computers that exploits the superposition of different orders of quantum computer circuits. We could show that such schemes allow for computational speed-ups with respect to standard quantum computer schemes using fixed orders of quantum computer circuits.Our quantum photonics setup allowed also for the quantum simulation of two interacting spins and the fundamental investigation of quantum discord as resource for quantum information tasks, as well as to experimentally benchmark values for more complex extensions of standard quantum mechanics.The results of this project contributed significantly to the implementations of new applications for single photons and the development of quantum photonics technology.