The size of computers is decreasing continuously, and it won’t be late before we reach the smallest possible size. Currently, it requires almost 100,000 atoms to store one bit of memory, which enables us to store around a terabyte of data in one square inch. But recently scientists at IBM pushed this limit to its very edges, they stored a single memory unit ( a binary 1 or 0) in a single atom, which would mean that if this technology can be used in regular computers, we can store almost 1000 times more data in the same space.
To do this, the team used a Holomium atom, on a Magnesium Oxide substrate. The holomium atoms was a comparably large atom, with many unpaired electrons. In contrary to paired electrons in an orbital, whose spins cancel, unpaired electrons contribute to a net atomic spin. It is this spin that they used to store the bits. Since electrons can have two spins, one was assigned the value 1 and the other 0. But spins are chaotically aligned, so how was a memory ‘stored’? Well the IBM team used their own nobel-prize winning 1994 Scanning Tunneling Microscope (STM) to fire a beam of electrons, and thus a current on the Ho-atom. Tunneling is a quantum process, according to this, chaotic quantum jitters or disturbances in the quantum feild around a particle, like electron, enables it to suddenly appear on the other side of a barrier, and thus seem to have ‘tunneled’ through. The STM applies a 150 mV voltage which might seem very low, but at atomic scales is similar to a current equivalent to a lightening strike. This current aligned the magnetic spin of the atom in one stable mode, which either corresponds to a 1 or 0. They thus ‘wrote’ a memory unit on the atom.
In order to read what type of spin does the atom have, a smaller voltage is applied of the orders of 75 mV, which reads the magneto-resistance of the atom. Since the different spins have different conductivities, depending on the resistance, we can know the type of spin in the atom, and thus ‘read’ the memory.
Spins, in contrary to the rotational spins of classical bodies like tops, in quantum mechanics is an inherent property of particles, but shouldn’t be confused with the classical meaning, since particles like electrons lack an internal structure, they cannot rotate in the classical sense. It is really hard to explain spin physically for even a very experienced physicist. To be honest, no one actually knows what it is.
The above reading and writing of memory on a single atom thus shows, in principle, that computers with 1 atom for 1 binary bit can be created. But that is a dream of distant future. Since because of thermal agitation the aligned spins of the electrons of the atom can deviate, and get randomly aligned, thus destroying the memory, methods to increase this energy limit are yet to be found. This experiment was carried out a temperature of 5 Kelvin (~268° Celcius), thus making this a reality at room temperature will take still a lot more research and years. But nevertheless, it has been shown that it is possible, and one day, no matter how distant, we can have such small sized storage units for regular use. To put into better perspective, these revolutionary storage units will allow us to store the complete iTunes library ( almost 35 million songs) in a credit card! Happy Reading!
-The Cosmogasmic Person