Physical Foundations of IT Security

Current Research Projects

Completed Research Projects

Photon source for Integrated Quantum processors (PiQ)


We analyse the improvement potentials of the photon source of DLR OS and QuiX Quantum’s photonic quantum processor in order to further improve their respective technologies and thus extend technological advances. In this way, we are making an important contribution to developing core technologies for realising the first scalable, integrated optical quantum computer in Germany and Europe overall.

In this project, we are tuning sources for single photonic quantum bits at DLR for use in a commercial photonic processor. The sources at DLR are based on a phenomenon in which photons from a laser are converted into a pair of entangled photons in a special crystal. The source parameters of the photon source and the fast electronic control are tuned to allow scalability of the approach. The goal is an analysis of improvement potentials of the two key components photon source and photonic quantum processor, which will enable further improvement of the respective technologies and thus extend technology advances.


The scaling potential of photonic quantum computing platforms is extremely promising and has already produced several recent high-profile demonstrations. However, in order to exploit the full potential of this technology in the future, it is crucial to first have suitable components such as high-performance quantum processors and efficient photon sources. In this project, our main focus is to link the development and functionality of the photon sources developed at DLR with DLR QCI contract partner QuiX Quantum’s quantum processors and to test their integration. Overall, this project is an important step towards the realisation of a scalable, powerful and efficient photonic quantum computer. It provides an opportunity to develop and test innovative technologies that can form the basis for future advances in quantum computing.


Individual photons, as the fundamental units of light, can carry quantum information in the form of photonic states. Such a photonic state can then represent a single quantum bit in a photonic quantum computer. For such a quantum computer to function, it is first important that a sufficiently large number of photons can be generated simultaneously and that they are indistinguishable from each other. Subsequently, these photons must be fed into a photonic circuit and processed further. So far, however, no photon sources exist that meet all the requirements for photonic quantum computers. Such sources are still the subject of basic research at DLR. This project addresses the adaptation of sources researched at DLR for use in photonic quantum computers, in particular by testing the interaction of photon sources developed at DLR with a commercial photonic processor from QuiX Quantum.

Funded by: BMWK through the QC-I of the DLR
Partners: QuiX Quantum GmbH

High performance light sources for quantum communication (MIHQU)


Quantum communication is an important building block for the future security of digital infrastructures in our society. In quantum communication, the exchange of cryptographic keys is based on fundamental physical laws, which means that security, in contrast to currently used encryption, remains fundamentally guaranteed. This also applies to attacks by novel, previously unknown algorithms or by powerful quantum computers. For successful realization, it is necessary in research to further improve quantum encryption algorithms and core components, for example sources for light quanta, the so-called photons, and to find efficient ways of implementation.


The goal of the project "Microintegrated High Performance Sources for Quantum Communication (MIHQU)" is the miniaturization of sources for photons. In addition, the operation of these is to be simplified, their resilience to external influences increased and at the same time their reproducible industrial production established. To this end, the researchers want to adapt the design of the sources and optimize the associated manufacturing methods. They also want to significantly increase the photon generation rates and ensure compatibility with so-called quantum memories. To do this, the researchers are exploiting a phenomenon in which photons from a laser are converted into a pair of entangled photons in a special crystal. In particular, they are investigating whether specially processed crystals and certain crystal geometries are particularly suitable for meeting the requirements for storage in quantum memories or for the simultaneous generation of photons at frequencies throughout the low-loss telecommunications frequency range. At the same time, the researchers are working to make the developed system very compact and robust to enable multiple application and commercialization scenarios.


The proposed entangled photon sources will allow operation at room temperature and offer great flexibility in terms of spectral characteristics, making them ideal for use in existing fiber optic networks. In addition, the design approach used will enable reproducible and cost-effective industrial fabrication. Thus, the overall cost in quantum communications can be reduced. This is a necessary step for the successful transition of the source into various commercial applications. The researchers are thus making an important contribution to the quantum communications industry and beyond. This helps to ensure Germany's technological sovereignty in this field in the future.

Funded by: BMBF
Partners: TU Berlin, HU Berlin, Aixemtec GmbH, son-x GmbH, qutools GmbH

Processing of single photons from DBT molecules in a fast ladder 87Rb quantum memory (DBT-FLAME)

Photonics is among the most promising platforms for realizing quantum information processing. In general, four major ingredients are required for realizing these applications: photon sources that generate non-classical light, passive linear optical circuits for high fidelity processing, active devices for routing and manipulation of photonic states in real time, and efficient single photon detectors. Photon detectors and passive processors are nowadays well developed, and a huge community is investigating single photon sources. However, the real-time routing and manipulation of single photons is still challenging and rarely addressed. For further progress in optical quantum information processing this is arguably one of today’s biggest roadblocks that will be tackled by this project. The overarching goal of this project is to develop an atomic vapor-based quantum memory for the storage and read-out as well as for processing of single photons emitted by DBT molecules. This key building block in quantum photonics enables the routing and processing of indistinguishable photons from organic molecules. The underlying technological approach is to combine the efficient and on- demand photon generation in organic molecules with quantum memories implemented in warm atomic vapor. The photon source is realized by coupling a DBT molecule to an optical antenna and collection of the photons emitted at 780 nm by using a cryogenic microscope. The memory follows a fast ladder EIT scheme on the D2-line in warm Rb vapor. In our consortium two groups join their complementary technological and experimental expertise, which is quantum optics with atomic systems and quantum nano photonics with organic molecules in an ideal way to ensure the success of the project.

Funded by: DFG
Partner: Andreas Schell, Universität Linz

Optical Systems for Classical and Quantum Computing for Machine Learning in Orbit (OMLO)

Machine learning (ML) is now the principal approach to processing complex sensor data (such as image and video data). The standard method for this is the use of artificial neural networks simulated on binary computer architectures. This creates the need for ever-increasing computing power, which can be served on the ground in part by specialized digital hardware such as graphics cards, tensor-flow processors, etc. For data processing in orbit, these possibilities are only available to a limited extent, since the special requirements for energy consumption and radiation hardness are generally not met. Data transfer to the ground and processing there is also difficult to realize due to the immense amounts of data. Therefore, high-performance computers for on-board data processing would be desirable. Optical systems for classical and quantum computing have a high potential to fill this gap and enable ML and other complex computations even in space environments. This would result in a technological leap in the field of space science. 

Funded by: BMWK

Projektpartner: Enrico Stoll, TU Berlin


Quantum token based on alkali metals and Xenon (Q-ToRX)

Quantum communication is an important building block for the future security of digital infrastructures. In quantum communication, the exchange of cryptographic keys is based on fundamental physical laws that ensure security even in the event of attacks by quantum computers. In addition to secure data transmission, quantum communication also offers new ways to securely authenticate users of digital systems and store private data on a network. So-called quantum tokens could ensure all of this in the future. Analogous to today's security tokens such as bank cards, transponders or transaction numbers, quantum tokens are conceivable as an authentication solution using quantum physical properties. On the way to their realization, it is important for research to further improve important key parameters of quantum physical systems, such as quantum memories, and to find efficient application possibilities.

In order to make quantum communication methods usable, e.g. for the secure authentication of system users by means of quantum tokens, a long-term stable and transportable quantum memory is needed. The aim of the project "Quantum tokens based on alkali metals and xenon (Q-ToRX)" is therefore to extend the storage time of quantum information in quantum memories at room temperature to the range of hours. Gas cells containing xenon and alkali atoms are used for this purpose. Research will be conducted on how to combine the long storage time of xenon with the efficient optical interface of alkalis. In parallel, the robustness and technological simplicity of the system used will be further developed in a multidimensional approach.

The storage of light quanta as carriers of quantum information in warm atomic gases is of particular interest, since neither complex cooling mechanisms nor large magnetic fields are required. This makes such quantum memories ideal for field applications. The results of the project are also highly relevant for a variety of current research areas where the storage of quantum information is required, for example in quantum encryption.

Funded by: BMBF

Project partner: Physikalisch-Technische Bundesanstalt, Leibniz Universität Hannover


Photonic Integrated Quantum Computer (QPIC-1)

Quantum computers have the potential to perform complex computations much more efficiently than classical computers by specifically exploiting the remarkable properties of quantum physics. The expected speed advantage is so substantial that problems become computable that are considered unsolvable with classical computers. However, in order to solve problems from practical applications, systems must be developed that can work with a considerably larger number of quantum bits, so-called qubits, than previous prototypes.

The goal of this project is the development of a novel platform for a quantum computer using single light particles, so-called photons, as qubits. For this purpose, novel sources are to be developed that generate quantum light, as well as integrated photonic circuits in which the information processing takes place.

The processor reads out the generated so-called cluster state, which consists of a large number of entangled photons and thus qubits, one after the other, i.e. qubit by qubit. Thus, it is possible to work with a much larger number of qubits than can be addressed by the processor simultaneously. This project therefore forms the basis for scalable photonic quantum computers that can operate with thousands of qubits, making quantum computing practical for real-world applications. The results achieved in this project will be protected by patents and subsequently exploited commercially, thus securing Germany a leading role in this emerging technology.

Funded by: BMBF

Project partner: TU München, University of Paderborn, HU Berlin, Ferdinand-Braun-Institute, Universität des Saarlandes, FU Berlin, Q.Ant GmbH,


Heterogenous quantum systems for single photon delay and pulse shaping (HQ.Sys)

Photonic quantum technology is an exciting field in science and technology. Potential applications include secure quantum communication, quantum computing and on the long-term the Quantum Internet. These have in common that information is encoded in single photons acting as flying qubits. Importantly, these flying qubits need to be efficiently interfaced with stationary qubits to implement quantum memories and quantum gates. The overarching goal of this project is to develop and test a quantum memory for the storage and retrieval as well as for the efficient spectral/temporal waveform manipulation of single quantum dot photons. Our project realizes for the first time a heterogeneous quantum interface between semiconductor quantum dots and a quantum memory realized in alkaline atoms. This key building block in quantum nanophotonics enables the generation of almost perfectly indistinguishable photons and near unity entanglement swapping fidelity in quantum repeater protocols. At the same time, we envision that quantum information can be encoded into the temporal envelope and phase of the single photons allowing for high capacity quantum information transfer with large alphabet. The underlying technological approach is to combine the efficient and on-demand photon generation in semiconductor quantum dots with quantum memories implemented in warm atomic vapor. The source is realized deterministically by in-situ electron beam lithography of single-QD CBR devices. Here, the advanced in- situ EBL nanotechnology platform guarantees the fabrication of QD quantum light source with well-controlled emission wavelength and high photon extraction efficiency. The memory follows a fast ladder EIT scheme in warm Cs vapor.

Funded by: DFG

Projektpartner: Prof. Dr. Stephan Reitzenstein, TU Berlin 

Hybrid photonic computing in delay-coupled non-linear systems with memory (HyPCom)

In recent years, artificial intelligence (AI) as a groundbreaking innovation has developed into a driver of digitization and autonomous systems in all areas of life. This has created great potential for mastering global challenges, such as environmental, resource and climate protection, as well as the security and performance of communication and IT systems. The current progress of AI, especially in the field of machine learning, is based on the exponential increase in hardware performance and its use for processing large amounts of data. However, despite the famous nature of Moore’s Law, the overall increase in hardware performance has slowed down in recent years, as for example measured by transistor-density. This motivates research into other approaches. Reservoir computing is one such promising novel paradigm, which has emerged in analogue neuromorphic computing. It shows great potential to overturn the digital transistor-hegemony and explore novel computational mechanisms and substrates for artificial intelligence. In a joint theoretical and experimental effort, this project aims at realizing non- linear optical networks with reconfigurable topology, enabled by combining feedback-coupled optical amplifiers with coherent optical memories. The potential of these systems for neuro-inspired information processing in the reservoir computing approach is explored.

Funded by: DFG

Project partner: Prof. Dr. Kathy Lüdge, TU Ilmenau



Building a Photonic Processor for Energy-Efficient AI

Classical digital computer architectures are visibly approaching their technological and physical limits. Thus, there is a growing interest in developing post-digital computing approaches to overcome these limitations. Besides quantum computers, approaches that emulate neuromorphic processes represent a very promising alternative because they mimic the massively parallel, energy-efficient computations carried out by the human brain. Such computations constitute the building blocks of the pattern recognition algorithms underpinning the success of machine learning and artificial intelligence (AI). Optically integrated systems promise 2–3 orders of magnitude higher energy efficiency compared to today's electronic approaches [Pen18]. Among others, post-digital computer concepts will enable numerous new applications for AI in places like data centers or security systems, as well as autonomous vehicles, drones and satellites – any area where massive amounts of computations need to be done but is limited by power and time. 

In this project we will realize machine learning with optical neural networks in free-space bulk optics. That is, we want to use light to power machine learning, instead of electrons, due to the potential advantages that a light-based neural network system has over one that utilizes conventional GPU chips.

[Hue19] T.W. Hughes, M. Minkov, Y. Shi, and S. Fan, ”Training of photonic neural networks through in situ backpropagation and gradient measurement,” Optica 5, 864 (2018)

[Pen18] H.-T. Peng et al. “Neuromorphic Photonic Integrated Circuits” IEEE JSTQE, 2018


Funded through HEIBRiDS.

Project partner: Prof. Guillermo Gallego, Technische Universität Berlin

Completed Research Projects

Quantum Memories for Secure Communication in Tomorrow‘s Society (QuMSeC)

Photonic quantum memories are so far missing key components for the second quantum revolution and enable a plethora of novel applications. For example, quantum networks promise provable security in communication and also the possibility for connecting quantum computers and simulators for calculations on distributed machines.

We focus on the one hand on the development of non-classical light sources and quantum memories for single photons. On the other hand, security-relevant applications of these key components in the emerging quantum technologies are explored. Most prominent, quantum secured communication and optical computation in the quantum and classical regime are in the research focus. At the beginning of the PhD work, a quantum memory for single photons in alkaline vapor at room temperature is built and optimized with respect to noise, efficiency, bandwidth and storage time. Special remark is on using components suitable for future airborne and space missions. Later, the memory is tested in applications.

Funded by: INNOspace Masters, BMWi through DLR.

Project partner: Dr. Markus Krutzik, FBH/HU Berlin

Escape Challenge Quantum Technologies (EsCQuTe)

Quantum technologies will fundamentally change our world. Their potential should be made tangible and understandable for many people. Therefore, we develop a live escape game, which challenges the players to collaboratively solve exciting puzzles. The players are immersed in a world where second generation quantum technologies are already being applied. In a playful way, the visitors are motivated to deal with the remarkable properties of quantum mechanics.

Funded by: BMBF

Project partner: Dr. Robert Richter