A new exotic state of matter, the possibility of whose existence was justified theoretically more than 50 years ago, has been obtained in the laboratory for the first time in history. Created by researchers at Harvard University, the material is called quantum spin liquid, and its further study and use will create a number of new technologies that could have a major impact on the further development of quantum computing and communications.
For any material to have magnetic properties requires that the spin of the electrons of that material's atoms be aligned in the same direction. Somewhat different types of magnetism can be observed when the rotation of electrons in a material alternates, like the cells of a checkerboard, nevertheless such materials still possess exotic magnetic properties due to the ordering of electron spins.
In 1973, the American physicist Philip Anderson hypothesized the possibility of the existence of a state of matter called quantum spin liquid, which does not obey the rules described above. Such a liquid arises when matter cools to a state where it has not yet become a solid and the electrons do not occupy a strictly defined position and, as a consequence, do not align their spins in the same direction. Instead, electron spins are in constant motion, they all become entangled with each other to form a very complex single quantum state.
To create a quantum spin liquid, Harvard researchers used a so-called quantum simulator, a kind of primitive quantum computer focused on solving only one single problem. The core of this simulator consists of 219 atoms arranged in the nodes of an optical trap grid created with laser beams. In addition, the light from additional lasers can be used to control each of the atoms by changing the direction of its electron spin.
Scientists arranged atoms in the trap in the form of a lattice, in the medium of which each of the atoms has two nearest neighbours. A pair of electrons can stabilise and align the values of their spins, but the presence of an electron from the third neighbouring atom destroys the balance, creating what scientists call a "broken magnet", a magnet that is unable to stabilise itself.
And as a result, all these atoms have formed some quantum spin liquid, which has several useful quantum properties. The first one is that the atoms of the liquid are in an entangled state, they can affect each other even at a large distance, which can be used to carry out teleportation of quantum information. The second property is that all liquid atoms are in a superposition state, i.e. their electrons can rotate in two directions at once. Both of these properties are major "quirks" of quantum mechanics that are used today to create quantum computers.
"We are now working to create the first topological quantum bit, a new type of cubit, based on the resulting quantum spin liquid. For this, at the very least, we will need technologies that allow us to control, write and read information from such qubits," the researchers write, "Thus, after obtaining the first liquid samples, a huge field for further research has opened before us."
