School experiment: The quantised conductance
Quantum phenomena can also be observed in everyday phenomena, such as a ‘loose connection’, if you observe closely enough. In its astonishing simplicity, this experiment is an interesting addition to the established, but usually cost-intensive, school experiments on quantum mechanics: Two thin gold wires that are only slightly touching are carefully pulled apart. This requires some skill and a steady hand - but can also be done by the pupils themselves.
Quantum mechanics in loose contact!
Thanks to pioneering experiments in the 1980s, we now know that the resistance and conductance in nanoscopic wires are quantised. The quantum of conductance is 2e^2/h ≈ 1/12906 Ohm and combines two fundamental natural constants: The elementary charge e and Planck's constant h. In order to demonstrate the quantisation of resistance, complex semiconductor heterostructures, temperatures close to absolute zero and, in some cases, high magnetic fields were initially required. In 1985, Klaus von Klitzing was awarded the Nobel Prize in Physics for his discovery of the quantised Hall resistor.
10 years later, Costa-Krämer and co-authors showed that quantised conductance values can also be observed at room temperature with very weakly touching wires. Quantum mechanics in loose contact!
Quantum conductance kit for schools
To mark the International Year of Quantum Science and Technology, a simple circuit has been developed with the kind support of the Wilhelm and Else Heraeus Foundation, which can be used to demonstrate quantised conductance in physics lessons in a simple way. 200 of these circuits will be made available for school lessons, for use in physics clubs or as demonstration experiments for public relations work.
You can already register now to order a ‘quantum conductance kit’. The Wilhelm and Else Heraeus Foundation will generously cover the costs. The delivery (circuit, instructions and accompanying material) is expected to take place at the end of 2024 so that the quantum conductance kit will be available in time for use at your school in the quantum year 2025. In addition to the circuit, an oscilloscope is required to demonstrate the experiment.
Further information
- A demonstration of quantised conductance with the developed circuit and a few simple explanations can be found in this video (you will be redirected to YouTube).
- You can download a more in-depth discussion with a derivation of the quantised conductance in ultra-thin wires adapted for school lessons here.
- From 21 to 25 October 2024, a teacher training course ‘History of Quantum Physics / Quantum Physics in Everyday Life’ will take place at the Physikzentrum Bad Honnef, where the circuit for quantised conductance can also be tried out. Registration is possible here.