Observe super-exchange interactions in cold atomic systems and optical networks

German and American physicists have for the first time observed the super-exchange interaction between atomic spins in an optical network. Super-exchange interaction is a mechanism of magnetic production of a wide range of materials, including high-temperature superconducting materials. And the team believes that this technique helps elucidate the mechanism of the electronic properties and magnetic properties of these materials.

Superexchange interaction (SE) is a type of interaction that often occurs between the spins of electrons in crystal materials. Unlike other interchange interactions that occur when electrons are close enough so that their wavefunctions overlap, SE does not require the overlap of the wavefunction. Instead, this interaction is based on the principle of electronic hopping (virtual hopping) from one position to another in a lattice. This is a quantum mechanical process whereby electrons can tunnel through separate neighborhoods and participate in that neighboring location, and only allow that electron or electronically in the vicinity. Close to jumping back to the old position after a while. The possibilities that can occur here are governed by the relative orientation of the electrons' spins. As a result, both hyper-exchange interaction causes the spins of electrons to be in a parallel or anti-parallel direction, depending exactly on the composition of the material.

Ten thousand double potential wells

Recently, the research team of Immanuel Bloch (Johannes Guttenberg University, Germany) and colleagues at Harvard University, and Boston University (USA) observed super-interactions in an optical network of integers. Rubidium super cold. The team crossed a laser beam to create 10,000 identical double potential wells, each containing two atoms and arranged in a straight line to create a one-dimensional optical network (figure).

Figure 1. One-way dual-optical optical network model.

With the network model set up so that each pair of atoms will have spins pointing in opposite directions - creating a configuration of antiferromagnetic materials. The laser beam is then adjusted to reduce the potential barrier between the pairs of atoms, allowing the electrons to tunnel between the wells and thereby increasing the super-exchange interaction. And then, the reaction of the atom's spin with this change is noted. When they were unable to observe each individual atom, they could measure the effect by averaging the left and right directions of the spin of each double well.

Spin fluctuations

The team observed that the spins vibrate from the back to the front between the wells. For example, if the atom on the left of the well starts to spin up, the right one is spin down, then after a time of about 25 ms, the left well will hold the spin down state and the right side becomes spin up . The group asserts that this observation is entirely consistent with what is described in the theory of super-exchange interactions between atomic pairs. Bloch and colleagues also changed the hyper-exchange link from antiferromagnetic (actually called the double exchange) that has parallel spins, by raising the dimension of a double well. compared to other positions.

Figure 2. Model of super-exchange interaction in supercooled atoms.

Bloch told Physicsworld.com that his team hopes to expand the technique to create a two-dimensional optical network to allow a wider range of complex magnetic systems, including interactions. ferromagnetism in one direction and ferromagnet in another direction. Optical networks can also be used to study the properties of some high-temperature superconductors, known to have magnetic properties related to super-exchange interactions. These materials contain overlapping two-dimensional layers, and therefore a two-dimensional optical network will be useful to understand interactions that bring superconductivity. Bloch also believes that it is possible to fine-tune super-exchange interactions between atoms in the optical network to create logical elements for quantum computers.

(See details of the work just published in ScienceExpress ).

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According to Physicsworld.com & Science, Vietnam Physics