Physikalisch-Technische Bundesanstalt

Tasks

The activity of this group is focused on fabrication and measurement of superconducting circuits with Josephson tunnel junctions, which show salient quantum behaviour. These circuits demonstrate remarkable example of applicability of fundamental laws of quantum mechanics to macroscopic solid state systems. Due to inherent macroscopic coherence of the superconducting condensate these metallic circuits are particularly suitable for engineering of the quantum devices. These devices are developed for improving the electrical measuring technique by extending it to detecting weak quantum signals with ultimate resolution and for deepening our knowledge about physics of metallic circuits utilized for realization of quantum electrical standards and quantum information devices.

The pair of quantum-mechanically conjugate variables in these electric circuits are the magnetic flux (or, equivalently, the Josephson phase) and electric charge. Realization of quantum regime simultaneously for both these collective variables is possible due to small self-capacitance of the relatively small tunnel junctions. (The junction capacitance is equivalent to the mass of an effective quantum particle whose coordinate variable is the flux, while momentum is the electric charge.) The technologies for manufacturing such Josephson junctions and the circuits on their basis are available. The main problem in designing the macroscopic quantum circuits is their fast (of the order of a microsecond) decoherence occurring because of coupling of the circuit collective variables to multiple environmental degrees of freedom, which include, for example, fluctuating electromagnetic signals in the control and readout circuits, as well as the degrees of freedom inside the investigated circuit itself. Therefore, the goal of our work is to ultimately improve the coherence property of the circuits and to realize efficient readout of quantum information with minimum back action.

Main tasks of the group are:

• Designing and manufacturing of superconducting circuits operating as controlled quantum two-level systems, i.e. quantum bits, and non-linear quantum oscillators, which have sufficiently long coherence time.
  
  
• Development of the measuring strategy for these circuits including application of both linear and non-linear dispersive measurement technique, single-shot projective measurements and realization of quantum-limited measurements. 

Contact

Head of Working Group		Dr. Ralf Dolata Phone: ++ 49-531-592-2247 E-Mail: Ralf Dolata
Address		Physikalisch-Technische Bundesanstalt AG 2.45 Bundesallee 100 38116 Braunschweig GERMANY