CORDIS - EU research results

Quantum simulation of strong interaction of light and matter

Periodic Reporting for period 1 - QuSLAM (Quantum simulation of strong interaction of light and matter)

Reporting period: 2019-04-01 to 2020-09-30

Classical computers are limited when trying to solve quantum physics problems that involve many strongly-interacting particles. This is because with every new particle we introduce into the problem, the computation time grows by at least a factor of two. This means that with only 100 particles or more, classical computers need years to solve a problem. The famous, Nobel-prize-winning physicist Richard Feynman suggested using a well-controlled quantum system to simulate the quantum problem of interest, much like a model airplane in a wind tunnel simulates a real airplane. Experimental platforms that achieve this are called quantum simulators.
The objective of this project is to build a new type of quantum simulator using ultracold strontium atoms in optical lattices, standing waves of light that act as a potential for atoms.
These optical lattices cannot be made infinitely large due to laser power limitations and therefore, state-of-the-art quantum simulators are limited to only a few hundred atoms. The optical lattices in this new quantum simulator should be very large and thus enable simulations with tens of thousands of atoms, a particle number 100 times larger than previously possible. These lattices should also be different for different internal states of the atom, i.e. state-dependent, to enable new types of quantum simulations.
The envisioned quantum simulation is of strong light-matter interactions. Atom-light interaction in only well understood in the few-body or weak-interaction regime. Strong interactions of light and matter in a many-body system are not well understood. This quantum simulator could answer these questions and enable better time keeping by enabling better atomic clocks, more robust quantum memories for quantum information, and provide solutions to long-standing quantum-chemistry problems.
To generate very large optical lattices and to get around the technical limitations of available laser sources, a unique build-up cavity was installed in the experiment. An optical cavity is made of two mirrors between which light bounces many times. Because of this circulation of light inside the cavity its intensity can be much higher than the input laser intensity. In our build-up cavity the intensity of the circulating light is between 100 to 1000 times higher (depending on the wavelength) than the input light, making very large lattices possible. These lattices were fully characterized and their size was measured to show that they are the largest and most homogeneous lattices implemented in a quantum simulator experiment to date. The possibility of addressing atoms in a particular position in the lattice was also demonstrated, a capability that is needed for next-generation quantum simulation.
Furthermore, state-dependent lattices for the strontium were implemented. This kind of lattices have different influence on atoms in different internal states, and the extreme version of a state-dependent lattice has no influence on atoms in one state, while trapping atoms in a different state. This so-called tune-out lattice for the ground state in strontium was implemented and its precise wavelength measured with a very high accuracy using a novel method.
Additionally, imaging optics and coils were prepared which will enable the implementation of single-resolution imaging in the near future. This, together with the implemented build-up cavity and the state-dependent lattices will enable the next-generation quantum simulations that are capable of simulating strong light-matter interactions.
The implemented build-up cavity is a unique technological advancement in the field of quantum simulators that considerably goes beyond the state of the art by achieving optical lattices that are a factor of 100 times larger than what was previously possible. This solves the long-standing problem of scalability in the field of quantum simulators that limited system sizes to a few hundred particles. It is thus predicted that a new generation of quantum simulators will use similar build-up cavities. The large increase in system size will enable simulations with new parameter regimes previously unreachable, to explore, for instance, quantum chemistry problems.
Further more, the novel technique which was developed to measure the tune-out wavelength in strontium is more sensitive than previous techniques, has reduced systematics, and is applicable to atoms in excited states, molecules, and trapped ions. The sensitivity of the technique enabled the measurement of the ground-state tune-out wavelength with the highest relative accuracy in any atomic system to date. This will enable new insight into the structure of the strontium atoms and help improve the accuracy of strontium atomic clocks even further.
The assembled build-up cavity
The build-up cavity in vacuum