We describe a simple, inexpensive, and robust undergraduate lab experiment that demonstrates the emergence of quantized conductance as a macroscopic gold wire is broken and unbroken. The experiment utilizes a mechanically controlled break junction and demonstrates how conductance quantization can be used to understand the importance of quantum mechanics at the nanoscale. Such an experiment can be integrated into the curriculum of a course on nanoscale science or contemporary physics at the junior and senior levels.

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