TRapped ENSembles of Circular RYdBErg atoms for quantum simulation

Project Information

TRENSCRYBE

Grant agreement ID: 786919

DOI

10.3030/786919

Project closed

EC signature date 15 May 2018

Start date 1 November 2018

End date 31 October 2023

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 2 240 000,00

EU contribution

€ 2 240 000,00

Coordinated by

CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE CNRS
France

Periodic Reporting for period 4 - TRENSCRYBE (TRapped ENSembles of Circular RYdBErg atoms for quantum simulation)

Reporting period: 2023-05-01 to 2023-10-31

Summary of the context and overall objectives of the project

TRENSCRYBE proposes a new concept for a quantum simulator of spin systems based on laser-trapped "circular Rydberg atoms". It aims at an in-depth understanding of many-body physics of importance for fundamental issues (quantum transport, quantum phase transitions) and for applications to engineering of new quantum materials. A quantum simulator, as originally proposed by Feynman, aims at synthetizing a quantum system with the same properties as an existing material but with an increased degree of control of physical parameters and offering an experimental access to microscopic observables such as the detailed quantum state of each individual particle. As exact numerical simulations are beyond the reach of classical computers as soon as the system contains more than a few tens of particles, one expects quantum simulators to be a promising alternative route for exploring many-body quantum phenomena.

Moreover, a quantum simulator could also be used to efficiently solve a general class of optimization problems, that can be formulated as the determination of the ground-state of a complex many-body system with tunable interactions. As such, a quantum simulator appears as a realistic and promising route for the development of quantum technologies with an important societal impact.

Our objective consists in performing quantum simulations based on a collection of laser-trapped "circular Rydberg atoms". Rydberg atoms have one of their valence electrons promoted to a highly excited state, close to the ionization limit. Quantum simulators based on the manipulation of up to about 256 laser-accessible low-angular-momentum Rydberg atoms already operate. However, the timescale of these experiments is limited to a few microseconds only, due to the finite radiative lifetime of low-angular-momentum Rydberg states. Instead, Rydberg atoms with maximal angular momentum, so called "circular atoms", whose lifetime of tens of millisecond could be used to extend the range of simulation timescales from microseconds to hundreds of microseconds.

At the end of the project, we achieved the construction of a Rydberg atom quantum simulator involving up to 20 individually trapped circular Rydberg atoms of rubidium. In parallel we developed two other projects aiming on the long term at overcoming the limits of the present rubidium platform. The first project aims at further increasing the accessible timescale of quantum simulations by increasing the lifetime of circular atoms from tens of milliseconds to more than one minute by using a spontaneous emission inhibition structure.
The second project consists in the construction of a second circular atom-based quantum simulation platform using strontium, which is a two valence electrons atom. Once one valence electron is promoted to a circular state, the second one can still be optically excited offering new possibilities for trapping, cooling or manipulating quantum superpositions of circular states. In particular, the possibility to cool down the initial motional state of an atom once it is in a circular state and the perspective of an optical detection of individual circular atoms are of particular interest for circular atom-based quantum simulators. At the end of the project, we have implemented preliminary experiments on circular sates of strontium using a fast atomic beam. A cryogenic version of the experiment involving trapped ultracold circular strontium was designed and is presently in construction.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The rubidium platform project stated by the preparation of ultracold circular Rydberg atoms of rubidium. The circular-atom preparation is directly performed in a 4K cryogenic environment, protecting atoms from room-temperature blackbody radiation, which would reduce drastically the circular atom lifetime. We prepared the ultracold circular Rydberg atoms from a 10 µK cloud of laser-cooled ground-state atoms. We also performed the first demonstration of laser trapping of circular Rydberg atoms. In these experiments the trap was a macroscopic laser beam and many circular atoms were trapped in the same beam.
We then started the construction of a completely new Rydberg atom tweezer experiment for trapping individual atoms. We then demonstrated the trapping off up to 20 circular atoms in individual traps of microscopic size, which can form arbitrary lattices in 2D. The dipole-dipole interactions between the atoms were then fully characterized and the apparatus is ready for performing first simulations using circular atoms.

A second rubidium setup was also constructed in order investigate the possibility to further increase the lifetime of circular atoms from tens of milliseconds to more than one minute by using a spontaneous emission inhibition structure cooled down at cryogenic temperature. As a first step, a tenfold increase of the circular atom lifetime was observed using a spontaneous emission inhibition structure placed in a simpler room-temperature setup. A cryogenic version of the setup is under construction with the objective of manipulating interacting circular atoms with a lifetime above one minute.


During the TRENSCRYBE project, we also realized that using circular Rydberg atoms of alkaline-earth atoms would be of great interest. We have thus started a new experiment aiming at the study of cold circular Rydberg atoms of Strontium. As a first step, we successfully prepared circular Rydberg states of Strontium in an atomic-beam experiment. We then performed an experiment for measuring the stability of the circular states under resonant illumination of the atomic core and observed negligible autoionization at the experimentally accessible timescale of our atomic beam experiment. We then took advantage of this robustness with respect to core excitation to demonstrate laser slowing of a thermal circular atoms beam using the resonant radiation pressure exerted on the ionic core. We also observed that the coherence of a superposition of two circular sates is marginally affected by the interaction with the slowing laser. This is an important result opening the way to laser-cooling the motional sate of trapped circular atoms during a quantum simulation. We finally observed the weak quadrupole coupling between the circular states and the ionic core metastable 4d state. This coupling opens the way to a selective optical detection of a circular state with a given principal quantum number by encoding this number onto the state of the ionic core.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The results presented above are beyond the state-of-the-art. Preparation and optical trapping of ultracold circular Rydberg atoms over their radiative lifetime time scale had not been demonstrated before. For low-angular-momentum Rydberg states, early experiments have demonstrated laser- and electric-field trapping. Recently, optical tweezers for low-angular momentum Rydberg states have been reported opening interesting perspectives for quantum simulation. However, the short lifetime of these levels and their high photoionization rate intrinsically limits the trapping to a few hundreds of microseconds. Circular states have an intrinsic radiative lifetime in the range of 30 ms, which can be further increased by inhibition of spontaneous emission. The implementation of this feature is part of TRENSCRYBE. In addition to the experiment mentioned above, we have also built a room-temperature experiment for a first demonstration of spontaneous-emission inhibition in a less demanding environment as compared to the cryogenic one that we plan to implement in the next step.

Concerning Strontium, preparation of circular atoms of this alkaline-earth element is a "première" and the observation of insensitivity to autoionization is a very promising feature. We are now constructing a new setup for preparing and trapping laser-cooled Strontium Rydberg atom in a cryogenic atom tweezer setup. On the long term this system will combine two of the most advanced systems considered for quantum simulation and quantum computation: individually trapped Rydberg atoms together with a trapped ion at the center of the circular Rydberg level orbit. This opens new perspectives for large atom number and long timescale quantum simulations.

Artist view of trapped circular Rydberg atoms