An innovative platform for quantum simulation

The electronic properties of condensed matter are often determined by an intricate competition between kinetic energy that aims to superimpose and delocalize electronic wave functions through the crystal lattice, and to locate electron-electron interactions. In contrast, the gas phase is characterized by closely located valence electrons around the nuclei of ionic atoms in discrete quantum states with well-defined energies. As an exotic hybrid of the two situations, one may wonder what state of matter is created when a gas of isolated atoms is suddenly excited to a state where the electron wave functions overlap spatially, as in a solid.

However, such an exotic phase of matter has so far been impossible to create in principle. Here, Professor Kenji Ohmori, Institute of Molecular Science, Japan National Institutes of Natural Sciences, and his co-workers have noticed such an exotic hybrid with overlapping electron wave (Rydberg) overlapping functions created coherently in just 10 picoseconds by ultra-fast laser excitation on an artificial microcrystal of ultra-cold atoms. The degree of spatial overlap is actively adjusted with a precision and accuracy of nearly 50 nanometers. Exquisite, long-lived control of this exotic metal-like quantum gas, decaying in nanoseconds, opens up a whole new regime of many-body physics to simulate ultrafast, many-body electron dynamics dominated by Coulomb interactions.

The experiment was performed with a set of 30,000 gas phase rubidium atoms. It was cooled to a temperature below 10 millionth of 1 Kelvin above an absolute zero temperature by laser / evaporative cooling. Those ultra-cold atoms in the energetically lowest quantum state, called the Bose-Einstein condensate, are loaded into a cubic network of optical traps formed by counterpropagation laser beams, resulting in an artificial microcrystal consisting of 30,000 atoms, the closest The distance between neighbors is 0.5 microns. This microcrystal with a size of a few tens of micrometers was irradiated with an ultrashort laser pulse whose pulse width was 10 pico-seconds. Then it was observed that an electron confined in each of the neighboring atoms was excited towards its giant electronic orbital (Rydberg orbital), so that they spatially overlapped each other. The degree of overlap was exquisitely controlled with a precision and accuracy of nearly 50 nanometers by changing the frequency of the laser that selects the orbital.

When the orbitals of these loosely bonded electrons overlap and the atoms begin to share their orbitals, they enter a new regime of metal-like quantum gas. Professor Ohmori and his coworkers have created a metal-like quantum gas for the first time. This phase of exotic matter is expected to be an innovative platform for ultrafast quantum simulation of electron dynamics of many bodies dominated by Coulomb interactions that would enhance our understanding of the physical properties of matter, including superconductivity and magnetism, and could contribute to disruptive innovation in the development of new functional Materials.

The study is published in Physical Review Letters.

Provided by the National Institutes of Natural Sciences