The quantum limit for electrical amplifiers: Can we reach it?

Any scientific instrument, including an electrical amplifier, necessarily adds noise in the process of performing a measurement. As might be expected from knowledge of Heisenberg's uncertainty principle, quantum mechanics sets strict limits on how little noise a measurement can add. There is a great deal of current interest in performing measurements at the quantum limit on such systems as qubits and nanomechanical resonators. Here we introduce the notion of quantum limited electrical measurement, and discuss recent progress made toward this goal.