Why do I need to know about quantum mechanics?

In my last lecture before the Easter break, I spent a bit of time putting the subject matter into a broader context for the students. It was a second year lecture in our short paper on ‘Quantum and Solid State Physics’. The paper is mostly taken by electronic engineering (the majority) and physics students. It’s intended to be a ‘start’ in the subject for the physics students (which will be developed in much more detail in the third year) and simultaneously a lightning education for the engineering students in what they need to know about solid-state physics.

In this paper, we first do a bit of quantum stuff, then develop the solid-state. At this moment in time, towards the end of the quantum section, it’s not really obvious to many of the electronic engineering students why they should learn any of this stuff. It’s all very abstract, and not clear how they would every apply it in their careers. That’s not a good place to be in as a teacher, because students who can’t see the point don’t pay attention, and eventually slink off and do something else with their careers. One of the roles of the teacher is to show them the point of what they are learning. (Incidentally, I think if you the teacher don’t know the point, then you shouldn’t be teaching it, because if you can’t see it your students certainly won’t.)

So, I spent a while (not for the first time) describing how the paper will develop, and how the paper then supports further learning in the next year. From the bottom up, it goes something like this.

Quantum mechanics applies to very small things. Of particular importance here are electrons, since these are what are doing the work in ‘electronics’ (note the name is no co-incidence). In order to understand how electrons interact with other matter, we need, at a lowest level, quantum mechanics. Now, the QM that we do is pretty simple stuff, really only applying to a single particle in simple situations.  But we take our simple, one electron situations, then use what we have learned to help us understand more complicated single electron situations (the hydrogen atom).  From there, we think about how multi-electron atoms will behave. Then we bring in some quantum statistics, and talk about how many atoms will behave together. Finally, this leads on to describing how the all-important semi-conductor (e.g. silicon or germanium and others) will behave.

Once we are at the semiconductor stage it is the purpose becomes more obvious to the students. We can use our semiconductor physics (band theory) to explain why diodes and transistors do the things they do, and, because we understand why, we can start talking about some of the effects that happen when you pile in zillions of transistors close together on a single piece of silicon (a ‘chip’, or integrated circuit). And integrated circuits drive just about everything these days, whether it’s your iPhone, computer, TV or car. This means our engineers aren’t just working with a black-box understanding of a diode or transistor – they have some idea of why it does what it does, which will really help in careers where understanding an electronic circuit is vital.

To get to that point, we need some quantum mechanics. Yes, it’s abstract, and yes it’s very weird, but it is very very useful, for engineers as well as physicists.