A normal computer(like the one your sitting at right now) work with 1s and 0s to create the data which is shown on your screen. But let’s take it quantum mechanically. What if you had a particle who’s spin represented 1s and 0s? E.g an up spin would be 1 and a down spin would be 0. Then you could have the particle in a uncertain state, a super position, and voila two numbers at the same time, a so called qbit(quantum bit).
Now you might think that we only get the double capacity because we can store two numbers in one atom. But indeterminacy is sweater then that. Say we have two atoms; they are both in a super position and hold two numbers, 1 and 0. Then we have, because of the uncertainty, some probability of the pair together creating: 00, 11, 01 or 10, that is four numbers in two atoms. And they all exist, remember bells theorem, particles doesn’t have determined attributes but they become determined only after measurement so since the particles are in super positions both states exist in the particles, and all the four states exist in the two particle combined. And it gets better, in three atoms we can store 000, 111, 010, 101, 100, 001, 110, 011, eight numbers in three atoms. So now we see an exponential growth which has the formula 2x where x is the number of atoms. As said, we can do this is because the atoms are in uncertain states, instead of being fixed and we just don’t know about them, so both the 1 and the 0 exist and interact parallel. And using only 300 atoms you have a computer, which can store more 1 and 0 then there’s atoms in the entire known universe.
But there are problems, the biggest one involves decoherence. The least interaction causes the atoms to come into a certain state and the computer is ruined. So you have to keep the computer completely sealed of. And more, you can only extract one answer from a preformed calculation, then the calculation gets destroyed, since to extract an answer you have to measure the particle, which will collapse its wave function and therefore destroy its super position.
But it was found that a liquid could work very well as a quantum computer. Then instead of having one particle hold one qbit you would have a whole bunch of particles holding the same qbit. Then you can interact with some of the atoms and some can get destroyed by decoherence, without affecting the computations.
In order to be able to control a quantum computer you have to be able to control the spin of the particles in the liquid. This can be done, if you have a static magnetic field present the particles spin either align itself with the applied field(the particles magnetic north aligns with the fields magnetic north and its south with its south), or not. You can say that if it’s aligned it represents a 0 and if it’s not it represents a 1. Then, using another magnetic field, you can “flip” the particles spins to either align them with the static field or not. Which means that you change the spins so to represent 0s or 1s as you like. But then of course you could turn the not-static field on for just as long time so it doesn’t quite flip the particle in alignment with the statical field or leave it unaligned. But right in the middle, not aligned nor unaligned. Then you have the uncertain 0-and-1 spin which makes a quantum computer a quantum computer.