In the recent years, integrated electrical circuits involving superconducting electrodes have attracted a tremendous interest both in the scientific and industrial communities. These nanometer-scale devices exhibit various quantum behavior like quantized energy levels or quantum entanglement, which makes them an excellent candidate for the physical implementation of a scalable quantum computer.
The basic element of quantum computers is the quantum bit (qubit), which represents a two-level system in analogy to a classical bit. In superconducting circuits, the qubits are built up from the so-called Josephson junctions, which consist of superconductor-normal metal-superconductor sequences. The non-linear Josephson junction element, when integrated in a closed loop (see figure above), is highly sensitive to small changes in the external magnetic field passing through the loop. When the magnetic field is finely tuned, the quantized energy levels can be smoothly transformed, which is an inevitable requirement for initializing a quantum computer. We use a nanometer-size wire in the close proximity of the superconducting loop to produce magnetic field and consequently tune the qubit energies. In our measurement setup, the small applied current (~10 mA) through this wire, supplied by the Yokogawa GS200 Precision DC Voltage/Current Source produces the magnetic field to initialize our quantum bits.
Dr. Andras Gyenis
Postdoctoral Research Associate
Department of Electrical Engineering