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Quantized Conductance

This quantized conductance Immersion focuses on a simple and robust transport-based quantum mechanics experiment. It can be easily employed in a sophomore modern physics lab (or higher) and is best understood using 1-dimensional infinite well-shaped potentials. It is a direct demonstration of the wave nature of matter and that quantization emerges due to confinement at the nano- or atomic scale.

The effect emerges as a gold wire is stretched slowly until it breaks. Due to the ductile nature of the wire, it will elongate and get extremely narrow (down to one atom) before it breaks. Because that corresponds to a diameter less than the de Broglie wavelength, quantization emerges as step-wise change in electrical conductance of the wire. A D-size battery is used to apply a voltage across the wire in series with a 100kΩ resistor and the voltage across the wire is measured using a voltmeter (i.e. a NI DAQ unit).

In the first day, we will: 1) prepare gold wires glued to a thin, elastic stainless steel sheets and let the glue harden overnight; 2) assemble the mechanical setup that will be used to measure the conductance of the gold wire while repeatedly breaking and reconnecting the wire; and 3) get an introduction to LabVIEW and ‘build’ a simple LabVIEW program to collect the conductance data of the wires.

In the second day, we will: 1) complete the preparation of the gold wires by creating a partial cut in each of them and 2) conduct the main experimental collection and analysis of data using the LabVIEW program. The third day will be for exploring the use of a piezo-crystal to break and reconnect the wire and to finalize the data collection and analysis.

  The cost of the experimental setup is as follows:

  1. Headless micrometer: $64
  2. Gold wire: $100
  3. DAQ Unit (NI USB-6009): $279 (48k samples/sec)
  4. Machine shop materials, springy steel sheet, miscellaneous: $80

for a total cost of about $523.

   The manual for this Immersion, along with an equipment list can be found at:  QC Manual