28 Jan Building the smallest compass ever to find the route inside the world of atoms
A compass, it’s useful…
Compasses are ubiquitous tools, you can use them to orient yourself using the Earth magnetic field, they are embedded in your smartphone as well as in many other devices around you and scientists use them to analyse the properties of materials as they act as sensors for magnetic fields.
Though modern compasses devices have reached miniaturized sizes there is always room for improvement, especially with respect to the magnetic sensing on very small scales. In fact measuring magnetic fields gives a lot of information about the molecular structure and the magnetic properties of molecules and atoms.
In this spirit during the last decades, many scientists have worked hard to be able to control and measure the smallest compasses present in nature, namely the spins of electrons and nuclei. In facts elementary particles (as electrons, protons and neutrons) behave in some sense as tiny compasses that orient their needle along an external magnetic field. In such sense, they can be exploited to investigate magnetic properties of atoms and molecules on very small scales.
…if you can play with it!
But how to control and how to read such a tiny object?
It may be useful to recall the Biot-Savart law: a current flowing in a wire produces a magnetic field, which we can use to move our compass. It means that if we are able to build a very tiny wire (about one millionth of meter width) and be able to place it very close to the electron we can control and read its compass if we are gentle and sensitive enough. The good news is: we are able to do it!
Using an advanced nanofabrication technique called electron-beam lithography we can pattern incredibly tiny circuits on top of a material, in this way electron spins can be controlled and measured with very high sensitivity.
Extending the toolbox
Unfortunately, we are not still able to control nuclear spins, and this is because the type of current needed for this latter task should have much lower frequency compared to that used to control electronic spins. Our circuit is designed to support only the current with a frequency suitable for electrons but not for nuclei.
How to accomplish this? The trick is to make the circuit compatible both with the electron spin frequency and the nuclear spin one, for this I implemented a new specific design based on the experience of other scientists in Princeton. Now I am starting the testing of the device and hopefully I will soon be able to play with both electronic and nuclear spins to gain more insight into the microscopic laws of nature.
Here the challenge becomes interesting; in fact, the interplay between nuclear and electronic spins is very useful and can be used for advanced sensing techniques but also for quantum computation. Being able to control both in the same device is of great importance and is the subject of my research.