Research

Towards the quantum internet

Connecting quantum devices to exploit their full potential is the next step in establishing useful applications of quantum technologies and making them accessible to a wide audience. Building such a quantum internet requires the development of new protocols, for example for entanglement distillation, certification and distribution of quantum states. We approach these issues not only from a fundamental perspective, but also consider practical limitations - such as decoherence, noise and imperfections - and analyze both their effects and ways to minimize them.

 

Our research interests include (see below for more details):

  • Entanglement-based quantum networks: we develop concepts and protocols for quantum networks that use entanglement as a central resource and investigate their properties.
  • Quantum sensor networks: We investigate distributed sensor networks that use entanglement for more precise measurement and reduction of noise, and optimize their properties across scales - from single ion traps to global networks.
  • Measurement-based quantum computations: We investigate computational approaches with multipartite entangled resource states and focus on high-dimensional systems, resource-efficient protocols, and error-limiting strategies.

 

We are also concerned with teacher education, and concepts to teach quantum physics in high school (available in German): AG Lehramtsstudium

Current Topics of Interest

Quantum Communication an Quantum Networks

Connecting quantum devices to harness their full power is the next step to establish useful applications of quantum technologies. This can happen over short and medium distances, e.g. to connect quantum computers or quantum sensors, or over long distances, with the ultimate goal to develop a quantum internet spanning the whole planet. Such a quantum internet does not only promise secure communication, but also makes quantum applications broadly accessible.

We develop protocols and methods to realize such networks, where establishing, distributing and utilizing multipartite entangled states is of central importance. To this aim, we design and investigate protocols for entanglement purification, entanglement certification and state distribution for different entangled resource states. We tackle these questions not only from a fundamental perspective, but also take practical problems and limitations – decoherence, noise and imperfections – into account, and study their influence and means to mitigate them. Our approach is focused on so-called entanglement-based quantum networks, where pre-established entanglement serves as a resource to perform network tasks and fulfill network requests. We are also interested in the design of such networks from a conceptual perspective, where we propose stack models and protocols beyond the physical layer. Furthermore, we pursue an approach to make quantum networks genuine quantum, by allowing for a quantum control plane with the possibility to perform tasks in coherent superposition – which may offer new and unexplored possibilities.

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Quantum Sensor Networks

Measuring quantities is at the heart of all Natural Sciences, but is also of central importance for technological applications. Using quantum systems for this task promises a vastly more efficient use of available resources, where a quadratic improvement in achievable precision is possible – the so-called Heisenberg limit. However, the influence of noise and imperfections threatens this quantum advantage, and it is hence relevant to investigate the effect of imperfections, and find ways to mitigate and overcome noise.

We are interested in the development of sensing protocols for different tasks, where we study optimal resource states and protocols, as well as noise effects and ways to overcome them. Of particular relevance are quantum sensor networks, where multiple sensors at different positions are combined to form a sensor network that is capable to directly sense spatially correlated quantities – e.g. field gradients or a signal from a specific source. Such sensor network can be of small scale, e.g. multiple ions in a single ion trap, but also of global scale where sensors may be located at different locations several (thousand) kilometers apart. We have found schemes to make such sensor networks sensitive only to particular signals solely by choosing proper entangled states, while being insensitive to signals with a different spatial correlation – and hence also to noise of this kind. Multipartite entangled states are of central importance in this respect, and we aim to identify suitable states, find their optimal usage and ways to generate, maintain and utilize them.

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