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Laboratory for Physical Sciences
8050 Greenmead Drive
College Park, MD 20740
Phone: (301) 935-6400
Fax: (301) 935-6723

Located adjacent to the University of Maryland's College Park Campus, the Laboratory for Physical Sciences is a unique facility where university and federal government personnel collaborate on research in advanced communication and computer technologies. Faculty, post-doctoral scientists, and students from the UMCP Departments of Physics, Electrical and Computer Engineering, and Materials and Nuclear Engineering all conduct research in LPS laboratories in the areas listed above.

Quantum Computing with a Cooper-Pair Box

Our group is studying quantum mechanical effects in superconducting circuits at very low temperatures (T~10 mK). The circuits that we are studying consist of a small superconducting island separated by a superconducting reservoir through two ultra-small tunnel junctions or Josephson junctions (see below figure). The number of Cooper pairs on the island of the device can be coherently controlled by modulating the voltage on a gate electrode that is capacitively coupled to the island of the device. Since charging effects in the devices that we are studying are relatively large with respect to both temperature and the Josephson energy these devices are called a superconducting charge qubit or Cooper-pair box.

SEM micrograph of typical Cooper-pair device

In our research, we are working to determine the limitations of a Cooper-pair box for quantum computing research. We have studied non-equilibrium quasiparticle effects (which prevent reliable initialization of the qubit) performed detailed spectroscopic measurements of the first excited state, and detailed lifetime measurements of the first excited state.