Manipulating atoms for a better macroscopic world
An optical lattice forms at the intersection of superposing laser beams. The resulting specific spatial pattern can trap neutral atoms that cool and bundle together in locations that resemble a crystal lattice. These atoms may then be set in motion in a form called quantum tunnelling, where a particle is able to tunnel through an obstacle it could not classically surmount. Ultra-cold atoms in optical lattices present as ideal test beds for models of condensed matter. One such example is high-temperature superconductivity, seen in materials with a superconducting transition temperature (Tc) above -243.2 degrees Celsius. Research in this area in recent years has seen ultra-cold quantum gases evolve into a tool for many-body solid state and quantum physics. The use of laser beams allows for many relevant parameters (such as lattice depth and spacing) to be controlled. The possibility of detecting and manipulating individual atoms on their lattice sites offers the potential to conceive a whole new generation of experiments in the fields of quantum information and simulation. The 'Ultracold quantum gases in optical lattices with single site addressability' (Addressing) project proposed to use a specially designed lens system to observe and manipulate density, spin structure and correlations at the scale of a lattice site. The EU-funded project designed and implemented a novel experimental set-up capable of resolving and addressing single lattice sites. First, researchers focused on assembling and testing the vacuum setup, producing ultra-cold atomic samples and developing and testing a high-resolution, custom-made imaging system. The latter facilitated the achievement of a major milestone at the interface between cold atoms and condensed matter, i.e. single-atom–resolved imaging of a strongly correlated quantum many-body system. This was realised by imaging a so-called Mott insulating state in optical lattices where atoms, thanks to quantum mechanical repulsion acting on them, are ordered in states of well-defined occupation numbers. Resulting images clearly showed each individual atom, making it possible, for the first time, to observe individual defects that form as a result of the sample's finite temperature. Being able to reliably determine temperature in optical lattices is critical for advancing other elusive quantum phases of great importance. This development opens the way to manipulating the state of individual atoms in an optical lattice, and could provide the basis for a quantum computation architecture with up to hundreds of individually addressable qubits (units of quantum information). Addressing's outcomes offer many possibilities for studying equilibrium phenomena in order to observe how a system evolves.