Quantum Computer – How it works
Post By Saksham Garg on 09-August-2015
As you might recall, a qubit was related to the spin of the electron. Researchers have been using the outermost electron of a single phosphorus atom as a qubit, embedded in a silicon crystal.
To measure the spin of the outermost electron of the phosphorus atom, a very strong magnetic field has to be applied. Enter: Superconductors. Once we apply this field, we know the electron will be in spin down or the lowest energy state. But at room temperature it might have enough thermal energy to bounce from spin up to spin down and so on, making any measurement useless. So it needs to be super cooled, that is to a few hundredths above absolute zero. This ensures the electron will be in the spin down (or 0) position.
Now if you want to write information on the qubit, you can put it in spin up state by hitting it with a pulse of microwave. But the pulse needs to be of a very specific frequency in order to excite the electron. This frequency depends on the magnetic field that the electron is in. For a particular value of magnetic field, there is a resonance frequency which and only which brings the electron to spin up state. Thus you can picture the electron as a radio, which works only at a particular frequency. A quantum superposition is created with a phase between them, thus recording data.
What about reading out the information? You remember that lonely phosphorus atom in the transistor? If the outermost electron on that atom is in spin up state, it’ll have enough energy to jump into the transistor, leaving a small positive charge on the phosphorus atom.
It’s like the transistor has been switched more on. Because of this we see a small pulse of current, indicating the electron was in spin up state.
In this graph, the spikes show we encountered a spin up electron and hence the pulse of current. The other region shows no current and hence is a spin down electron.