 Random news from the Archive Two bits of information - in one atom
09.09.2020
The Dutch scientists managed to create a system of one iron atom on a substrate, in which it is possible to control the orbital momentum of an atom and the excitation of its spin states independently of each other.
To control the system, the researchers used the needle of a scanning tunneling microscope, when interacting with an atom, its orbital momentum was reversed without excitation of spin states. Under such conditions, the atom has two degrees of freedom associated with a magnetic field, which in the future can be used to create particularly capacious information storage systems with a recording density of two bits per atom.
Reducing the size of a single bit to the scale of an atom would make it possible to fit huge amounts of data into extremely small media. Potentially, such systems can be created using the magnetic field-controlled spins of individual atoms S - the vector sums of their own angular momenta of the elementary particles included in their composition. It is spin states that are chosen as bits in such systems, because the orbital momentum of each atom L (its angular momentum as a whole) in real samples is suppressed due to the combination of spin-orbit interaction and the crystal field.
But even in the case when L of an atom in such a system is not equal to zero, the spin-orbit interaction leads to the coupling of L and S into a superposition, in which only the total angular momentum of the system L + S is preserved, and independent excitations of L and S are impossible. To store information in the orbital state of an atom, in turn, you need to be able to store L and be able to control it without affecting the spin states. Then the spin and orbital states can play the role of zeros and ones, and the atom itself could act as an information carrier in the amount of two bits, each of which corresponds to one degree of freedom of the system (one bit per spin and orbital momentum).
Just such a system of one atom, in which it is possible to independently excite spin and orbital states, was created by Rasa Rejali from the Delft University of Technology. To do this, the physicist and colleagues placed a single iron atom over a magnetically neutral nitrogen atom in a Cu2N substrate, thereby obtaining a system with practically free orbital momentum and spin. The needle of a scanning electron microscope allowed physicists to study the atom and manipulate it.
The proposed method for independently changing the orbital and spin states of a single atom is still far from practical implementation. Nevertheless, the similarity of the nature of spin and orbital states gives hope that in the future the orbital momentum of atoms can be controlled as simply as it is now - spins. In this case, information carriers can become quite real, in which each atom will act as not one, but two bits, which will further increase the potential maximum data recording density.
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