Quantum Valley Lower Saxony (QVLS) sees itself as a connecting body that brings together scientific expertise in the field of quantum technologies, industry and politics in order to establish a network for the research and transfer of quantum technologies in Lower Saxony.
In addition to the Physikalisch-Technische Bundesanstalt Braunschweig and the Technische Universität Braunschweig, Leibniz Universität Hannover is also one of the scientific partners working intensively on various quantum technology topics.
Among other things, this is being done in the QVLS-Q1 research project, which aims to develop a quantum computer with 50 qubits by the end of 2025. This quantum computer is to be based on ion trap technology, which is seen as particularly promising for continuously scaling up systems.
On the way to the quantum computer in the QVLS-Q1 research project
The development of functional quantum computers is considered a key technology for the future and is therefore the focus of international research and development. The principles of quantum mechanics are used to process information, which should enable quantum computers to solve complex problems particularly efficiently. This includes, for example, simulations of material or molecular properties, which are of great importance in physics, chemistry and pharmacy. In this context, breakthroughs are expected in the development of new drugs, for example.
In connection with the development of a quantum computer as part of QVLS-Q1, the Institute of Microproduction Technology (IMPT) is involved in three sub-projects. These are the sub-projects T2.4 Atom chips, T3.1 Hybrid integration and T3.3 Vacuum technology.
In sub-project T3.1, the IMPT is working on concepts for integrating the core component of the quantum computer, the ion trap chip, into the overall structure. This integration includes the mechanical fixation and electrical contacting of the ion trap chip as well as the positioning of components that are necessary for operation near the chip surface or the back of the chip. Subprojects T2.4 and T3.3, on the other hand, are not directly associated with the development of the ion trap, but include other aspects of the structure and the utilisation of quantum technological effects.
Researchers at the IMPT develop multifunctional atom chips
Subproject T2.4 deals with multifunctional atom chips, which are used for quantum gravimetric experiments. High-precision measurements of gravitational fields are made in these experiments. On the one hand, the measurements can be used to detect underground raw materials or water deposits, for example, and on the other hand they can help to clarify physical theories thanks to the precise measured values.
n atomic interferometers, the wave nature of matter described in quantum mechanics is utilised for measurements. Atoms are caught in a so-called magneto-optical trap, cooled down and converted into a macroscopic quantum state, the Bose-Einstein condensate. Using lasers, the atoms are split into two different gravitational paths and brought together again in a similar way to an interferometer. The wave nature of the reunification leads to the formation of interference patterns, which react very sensitively to changes in the gravitational field.
To realise and miniaturise the magneto-optical trap, the IMPT has been researching the production and further development of these atom chips for years, as they form the heart of the traps.
The chips are constructed in several layers and consist of a silicon substrate with etched conductor structures, insulation layers, filled gold conductor tracks and an optical coating. A total of two chips are joined together on a ceramic carrier that dissipates heat and carries wires for other necessary magnetic fields. The components are installed in a vacuum chamber using a copper holder and conventional vacuum flanges.
This is where sub-project T2.4 comes in, as the miniaturisation of the overall structure is the designated goal. To this end, the chips are to be considered as part of the outer wall of the vacuum chamber. In this way, many components are no longer located inside the vacuum chamber (ceramic, copper holder, vacuum flange) so that it can become significantly smaller. This reduces the amount of pumping technology required, which is a major advantage. As a result, the overall design is lighter, easier to handle and also requires less energy due to the lower pumping capacity.
This is realised by encapsulating the atom chips in a glass cell. The joint between the atom chip and the glass cell must be particularly tight in order to maintain the vacuum. It has already been possible to produce mechanically very stable joints, so that the focus of future investigations will be on the tightness of the joints.
Miniaturised atomic sources: Which elements are best suited?
With the QVLS T3.3 sub-project, the IMPT is also involved in the development of miniaturised atom sources for various quantum technology systems. The atom source enables the precise generation of vapour phase atoms of a specific type of atom and is one of the core components for quantum systems based on ultracold atoms. It is particularly important to control the mass flow of the atoms and guarantee the purity of the vapour phase atoms in order to increase the efficiency of laser cooling and laser trapping of these atoms.
Depending on the application, various elements can be used as atom types. The electronic transitions of the elements are particularly important here. These determine which wavelength of the laser is required for cooling the atoms and for operating the quantum system. Alkali metals such as rubidium, alkaline earth metals such as strontium or calcium and many other elements are used here. Strontium is particularly suitable for highly stable and accurate atomic clocks, among other things. Atomic clocks are particularly important in communication and navigation. Modern mobile communications with a signal frequency of 3.84 GHz must be stable over 24 hours. The relative deviation of the clock must therefore be better than 3*10-12. The requirements for satellite navigation are even higher. Here, a time difference of 10 ns corresponds to a location error of around 3 metres and deviations of less than 10-14 are required.
There is also a continuous focus on miniaturising the entire assembly platform in order to make the technologies ready for mobile applications, such as on board aircraft or satellites. This includes both physically reducing the volume of the atomic sources and integrating them into compact and portable quantum applications. These developments open up new applications that have so far remained untapped due to technical limitations.
The core element of the atom source is a micro-engineered heater made of glass or silicon. This enables targeted heating of the material to be vaporised. The heating region is thermally decoupled from the rest of the substrate by thin bridge structures in order to increase the efficiency of the heating process.
Most of the relevant elements, such as rubidium or strontium, oxidise immediately on contact with air. The entire production and integration process must therefore take place in an oxygen-free atmosphere. This begins with the preparation of the materials, continues with the filling of the reservoir and ends with the integration into the vacuum chamber of the quantum systems. A specific opening mechanism was developed for simple integration, which protects the rubidium in an inert atmosphere. Only after integration into the quantum system and the creation of an ultra-high vacuum is the source opened by an electrical pulse. Such precautions are necessary to ensure the chemical purity and effectiveness of the atomic source. These are necessary for consistent and reproducible function in quantum technology applications.
Quantum technology in Lower Saxony: Interdisciplinary cooperation
In conclusion, it can be said that the QVLS-Q1 project is not only significantly advancing technological development in the field of quantum computers in Lower Saxony, but is also an example of successful interdisciplinary collaboration between science, industry and politics. The participation of Leibniz University Hannover and its partners in such ambitious projects lays the foundation for innovative applications in various sectors and strengthens Germany’s position in the global competition for quantum technologies. Overall, QVLS-Q1 forms a bridge between basic research and practical application, which could lead to significant advances in many scientific and industrial fields in the long term.