### Cottrell College Science Awards - 2014

## Characterization of Inductive Superconducting Nanowires as a Building Block for Quantum Circuits

Daniel F. Santavicca, assistant professor of physics at the University of North Florida, is attemptingt to develop quantum circuits using high-inductance superconducting nanowires.

“Nano” refers to the very small – a nanometer is equal to one-billionth of a meter. A high-inductance nanowire, then, is a very small wire in which a slight change in the current of electrons flowing through it readily creates (induces) a specific corresponding voltage (electrical pressure).

Quantum electronics, a promising branch of technology, is based upon the effects of the dual wave-like and particle-like interactions of energy and matter at the subatomic level.

Studying quantum effects in tiny bits of matter requires minimizing the tendency of energy to dissipate, a phenomenon exacerbated by the motion of molecules (heat) through which the energy flows. Hence superconductors, which are chilled to near absolute zero, provide a stable platform for the study of quantum electronics, Santavicca pointed out.

Santavicca’s research centers on the fact that electrons (tiny charged particles that also have mass) moving through any type of wire (current), whether large or small, must overcome a certain amount of inertia. In superconducting nanowires, this inertial energy serves as an “inductance,” that quality of a current which resists change. Specifically, this phenomenon is termed kinetic inductance.

An important property of kinetic inductance in superconductors is that if the current fluctuates, the inductance changes can be measured.

Meanwhile, electrical circuits – in this case, the nanowire -- also have a quality of resistance or acceptance of current known as “impedance.” In superconductors through which a direct electrical current flows, resistance is zero, and thus the nanowire’s impedance is essentially the same as the current’s kinetic inductance.

Furthermore, this inductance/impedance is “nonlinear,” meaning the system’s output is not directly proportional to its input. In other words, the fluctuations in output vary in ways that are more noticeable than if the system were “linear,” that is, if the output were directly proportional to the input.

“And nonlinear impedance is the basis for many practical electronic devices such as amplifiers, mixers, and oscillators,” Santavicca noted, perhaps hinting at the varieties of quantum electronic devices he may one day hope to create.