Sweet Grandmother’s Spatula! After pulling out your fresh cookies from the oven and taking your first taste you notice that in creating your cookie dough, you accidentally mixed up the sugar and salt. Now your dreams of enjoying that oh so sweet sugar cookie have been dashed away and you are left with a confectionary calamity. However, all is not lost…. your seemingly imperfect dough with salty defects can be fixed to result in the masterpiece of baked goods. Thus I present to you, the challenge of baking the chocolate chip and sea salt cookie. When balanced correctly, these two flavours can enhance each other to create complex layers of pure deliciousness.
Now you may be asking yourself, what does this have to do with quantum mechanics? Picture your salty cookie, full of defects within its dough, seemingly useless. However, if you add the right amount of chocolate chips in places as accurately as possible, you will achieve the right balance of flavour and achieve the perfect chocolate chip and sea salt cookie, a true baking delicacy. Likewise, in experiment, we begin with a crystal that contains lattice defects with quantum properties. In the general scheme of things, the goal is to add other materials within or near the substrate in as precise a location and concentration as possible so that we may enhance, control and measure these defects.
When people talk about physics, and in particular the human side of it, the ‘doing’ physics, they will usually point out that there exist two main forms of physicists. There are experimentalists, who spend their days gathering data in labs or tinkering with huge particle accelerators. These physicists, although rarely actually wearing white lab coats – at least in my experience – seem to be the closest to the pop culture stereotype of a scientist: wedding a strong analytical spirit to a practical, do-it-yourself mindset and a work ethic that often borders on obsession. They form the majority of physics practitioners and often speak with mild disdain about the ‘other’ type of physicist: the theorist. Theorists differ from experimentalist in that they mostly do, well, theory. Their days are usually not spent tinkering with equipment or analysing data but rather studying literature and diving into the complicated mathematics needed to describe modern physics. They often eschew the practical in favour of a generalist, axiomatic mindset; using as few assumptions as possible to describe the largest possible piece of the physical puzzle.
Throughout history these two strands of physics were usually not distinct professions but merely reflected the interests of a singular physicist. Even Newton, the prototype of a theoretical physicist, regularly performed experiments using prisms and even built one of the earliest reflecting telescopes. In my understanding of the history of physics these two strands of physicist started splitting into true professions in the late 19th century and early 20th century in response to the ever growing complexity of physics. Over time they grew further apart until the present day where among many theorists it is considered a point of pride to have never performed any experiments at all. Entire careers can be wholly devoted to the understanding of ‘physical theories’ that are decades away from being subjected to experimental verification. On the other hand, as the scale and complexity of experiments has grown, many experimentalists find themselves spending most of their time not doing physics but the cutting edge engineering work necessary to perform modern experiments to begin with. This has lead both groups to develop language and practices which differ immensely and can lead to almost Babylonic misunderstandings in the occasions where theorists and experimentalists do meet.