Quantum Triangles


A friend once told me that all that physicists ever measure is either a sine wave or a straight line. Nothing proves him wrong better than this piece of data we obtained by measuring on a semiconductor nanowire device (Ge/Si nanowires). These double-triangles represent a charge stability diagram of a double quantum dot. Charge stability actually happens in between the triangles, where current is zero (blue), and the number of charges on each of the two quantum dots is fixed. We don’t know how many charges are there on each dot but it is few tens. In the triangular regions, charges move because they have enough energy to jump from one quantum dot into the other and out into the lead that takes them to our ammeter. Inside the triangles, we get a glimpse of quantum energy levels, orbital and spin, of the particles trapped in quantum dots – those energy levels are the stripes of the triangles. The axes of the graphs are voltages on remote electrodes located 10 nanometers away from the nanowire, voltages on these electrodes (gates) are used to change the capacitive energy of the quantum dots.