# Fundamental Physics

New, emerging technologies will be based on quantum mechanics. Examples are quantum sensors, quantum metrology, quantum computing, quantum communication, quantum cryptography, and quantum materials. The basis of quantum metrology are atomic clocks which are nowadays approaching a stability of 10-19. This means that a difference in height of 1 mm will lead to a measurable gravitational redshift which is one of the major predictions of Einstein's General Relativity.

Accordingly, in order to understand such devices and to use such devices, it is mandatory to consider the fundamental theories of quantum mechanics and General Relativity. As examples, atomic clocks are based on quantum mechanics and their use in space for positioning or on ground for geodesy require the full understanding of all special and general relativistic effects. Also the introduction of the International Atomic Time TAI is possible only taking all special and general relativistic effects into account. There are more examples of that kind which range from satellite geodesy and navigation to climate and ocean sciences.

It is obvious that new, in particular space-based technologies require a thorough understanding regarding their underlying quantum and general relativistic principles. In particular, quantum communication is one of the major activities we are planning to do within the GOC. Beside the discussion of fundamental theoretical aspects we are also planning experimental studies of the performance of quantum communication in various environments and constellations.

- Ultrakalte Atome und Atom-interferometrie in Schwerelosigkeit (QUANTUS, PRIMUS)
- Bester Test der gravitativen Rot-verschiebung mit Galileo (RelaGal, GREAT)
- Modellierung von Satelliten und payload (Pioneer, Galileo, MICROSCOPE, GRACE)
- Bester Test des Äquivalenzprinzips mittels Satelliten (MICROSCOPE)
- Theoretische Beschreibung von Uhren in Satelliten