Quantum simulations with circular Rydberg atoms
Recent publications
♦ Laser Trapping of circular Rydberg atoms
R. Cortiñas, M. Favier, B. Ravon, P. Méhaignerie, Y. Machu, J.M. Raimond, C. Sayrin and M. Brune
arXiv:02316 (2019)
♦ Towards quantum simulation with circular Rydberg atoms
T.L. Nguyen, J.M. Raimond, C. Sayrin, R. Cortiñas, T. CantatMoltrecht, F. Assemat, I. Dotsenko, S. Gleyzes, S. Haroche, G. Roux, T. Jolicœur and M. Brune
Phys. Rev. X 8, 011032 (2018)
PEOPLE
Permanents: Clément Sayrin, Michel Brune, JeanMichel Raimond, Serge Haroche
PhDs: Rodrigo Cortiñas, Brice Ravon, Paul Méhaignerie, Yohann Machu
Postdoc: Maxime Favier
Quantum simulations with circular Rydberg atoms
Thanks to their large electric polarizabilities, Rydberg atoms interact very strongly through dipoledipole interactions. At a few micrometres distance, this interaction can be still as big as several MHz. The socalled dipole blockade is one of the most striking consequences of this interaction strength: the presence of a Rydberg atom prevents the excitation of a subsequent Rydberg atom in its immediate proximity.
Rydberg atoms, which can be laserexcited from alkali atoms in their ground states, and which are longlived (several 100µs lifetime), are thus ideal candidates for the study of spinspin interactions in dense systems. In particular, they can be used to realise a quantum simulator of condensedmatter systems.
In our group, we prepare a gas of Rydberg atoms in the vicinity of a superconducting atomchip. Rydberg atoms are excited from a gas of lasercooled Rubidium87 atoms, initially trapped in a magnetic trap created by the atomchip. Our work focuses on the realisation of a quantum simulator that exploits the unique properties of circular Rydberg atoms. They can be efficiently lasertrapped in spontaneous emissioninhibiting structure, thereby reaching lifetimes on the order of a minute! This should enable, e.g., the study of the dynamics of condensedmatter systems over extremely long times (about \(10^410^5\) interaction cycles), their response to quenches or their thermalisation properties.
LATEST NEWS

A new doctor!11/01/2018After 4 year of hard work, Tigrane has successfully defended his PhD thesis! He is now a doctor of the ENS. Congratulations!
EVENTS
Tigrane’s PhD Defence
11/01/2018
Tigrane has successfully defended his PhD thesis entitled Interacting Rydberg Atoms : from Dense Clouds of Rydberg Atoms to Quantum Simulation with Circular Atoms in front of a jury composed of Robin Kaiser, Leticia Tarruell, Jérôme Tignon and Matthias Weidemüller, and his supervisors Michel Brune and Clément Sayrin.
We wish him all the best for his future research activities!
Here are some pictures of this important event for the team!
RESEARCH
Towards quantum simulation with circular Rydberg atoms
Publications
♦ Towards quantum simulation with circular Rydberg atoms
T.L. Nguyen, J.M. Raimond, C. Sayrin, R. Cortinas, T. CantatMoltrecht, F. Assemat, I. Dotsenko, S. Gleyzes, S. Haroche, G. Roux, T. Jolicoeur, M. Brune
Phys. Rev. X 8, 011032 (2018)
Supplementary Materials
Towards quantum simulation with circular Rydberg atoms
The main objective of quantum simulation is an indepth understanding of manybody physics. It is important for fundamental issues (quantum phase transitions, transport, . . . ) and for the development of innovative materials. Analytic approaches to manybody systems are limited and the huge size of their Hilbert space makes numerical simulations on classical computers intractable. A quantum simulator avoids these limitations by transcribing the system of interest into another, with the same dynamics but with interaction parameters under control and with experimental access to all relevant observables. Quantum simulation of spin systems is being explored with a large variety of experimental systems. Some of the most advanced ones rely on trapped ion systems, superconducting circuits, trapped ultracold ground state atoms or even atoms excited to low angular momentum Rydberg levels.
We propose a new paradigm for quantum simulation of spin1/2 arrays providing unprecedented flexibility and allowing one to explore domains beyond the reach of other platforms. It is based on lasertrapped circular Rydberg atoms.
The intrinsic lifetime of circular Rydberg atoms lies in the msrange. This very long lifetime stems from the fact that a circular Rydberg atoms \( nC\rangle\) can only decay to the \( (n1)C\rangle\) circular Rydberg level by the emission of a microwave photon of wavelength \(\lambda\). By placing a circular Rydberg atom in a planeparallel condenser of size \(d\leq\lambda/2\), spontaneous emission can be efficiently inhibited and the lifetime of the circular level increased by several orders of magnitude.
In addition, while photoionisation is a severe limitation for laser trapping of lowangular momentum Rydberg levels, circular Rydberg levels do not photoionise. The combination of a LaguerreGaussian beam (lateral confinement) and of two crossed Gaussian beams (longitudinal confinement) then realise a very efficient trap for the lowfield seeking circular Rydberg levels. Trapping lifetimes in the minute range are realistic with stateoftheart techniques.
Finally, using an innovative approach, namely a van der Waals variant of the evaporative cooling method, ultracold defectfree circular atom chains containing several tens of atoms can be prepared. A chain of about 40 atoms can be deterministically prepared using this method. Its lifetime is on the range of seconds! This method also leads to the individual detection of arbitrary spin observables and, thus, to the measurement of spinspin correlation functions.
The proposed simulator realises an XXZ spin1/2 Hamiltonian with nearestneighbor couplings ranging from a few to tens of kHz. The simulated Hamiltonian takes the general form
\( H/h = \frac{\Delta}{2}\sum_{i=1}^N \sigma_i^z + \frac{\Omega_0}{2}\sum_{i=1}^N \sigma_i^x + J_z \sum_{i=1}^{N1} \sigma_i^z \sigma_{i+1}^z + J \sum_{i=1}^{N1} \sigma_i^x \sigma_{i+1}^x + \sigma_i^y \sigma_{i+1}^y. \)
All the model parameters can be tuned at will, making a large range of simulations accessible. In particular, by a mere tuning of an electric and a magnetic field, the ratio \(J_z/J\) can be tuned from 3 to 3. The accessible phase diagram is extremely rich. The typical interaction time, \(1/4J\), is on the order of \(15\mu\mathrm{s}\). The system evolution can thus be followed over \(10^4\) to \(10^5\) interaction cycles, long enough to be relevant for groundstate adiabatic preparation and for the study of thermalization, disorder or Floquet time crystals. This platform presents unrivaled features for quantum simulation.
Dipole blockade and microwave spectroscopy
Publications
♦ Microwaves Probe Dipole Blockade and van der Waals Forces in a Cold Rydberg Gas
R. Teixeira, C. HermannAvigliano, T.L. Nguyen, T. CantatMoltrecht, J.M. Raimond, S. Haroche, S. Gleyzes, M. Brune
Phys. Rev. Lett. 115, 013001 (2015)
Supplementary Materials
Dipole blockade and microwave spectroscopy
Because of their strong electric polarizability, Rydberg atoms interact very strongly through dipoledipole interaction. During a resonant laser excitation of Rydberg levels in a dense atomic cloud, the strength of the interaction leads to the socalled dipole blockade effect [Lukin et al. (2001)]: every Rydberg atoms is surrounded by a blockade sphere into which no other Rydberg atom can be excited. At saturation, the distance between the Rydberg atoms then corresponds to the radius of this sphere, the socalled blockade radius. However, when the laser excitation is detuned from resonance, the dipole interaction can facilitate the excitation of a Rydberg atom at a distance called facilitation radius from an initial Rydberg seed. The value of the facilitation radius is controlled via the detuning of the excitation light.
In our experiments, we have been recently able to demonstrate that the relative distance between Rydberg atoms excited in a cold gas of atoms, trapped in the vicinity of our atomchip, can be controlled via the detuning of the excitation laser. Using microwave spectroscopy, we have measured directly the interaction energy distribution of the Rydberg gas, from which we can deduce the Rydberg atoms spatial distribution. By recording the time evolution of the interaction energy distribution, we have also observed the dynamics of the Rydberg gas, which expands due to the strong repulsive interaction between the atoms. In particular, we have been able to observe the breakdown of the frozen gas approximation, few µs only after the preparation of the Rydberg gas.