Towards Quantum Simulation with Circular Rydberg Atoms
T. L. Nguyen, J. M. Raimond, C. Sayrin, Rodrigo G. Cortiñas, Tigrane Cantat-Moltrecht, F. Assémat, I. Dotsenko, S. Gleyzes, S. Haroche, Guillaume Roux, Th. Jolicœur, M. Brune
Quantum simulation can provide insight into physical systems that are too complex for traditional computing techniques. A new proposal describes how a quantum simulator could be realized using laser-trapped circular Rydberg atoms, whose long lifetimes and stability are beneficial for simulations lasting up to seconds.
Summary form only given. Quantum simulation offers a highly promising way to understand large correlated quantum systems, and many experimental platforms are now being developed. Rydberg atoms are specially appealing thanks to their strong and short-range dipole-dipole interaction and to their long lifetime. Low-angular momentum Rydberg atoms have been successfully used recently to realize early quantum simulators. These experiments suffer, however, from the limited (despite long) lifetime of these levels and the fact that they cannot be efficiently trapped [1, 2].Here, we propose to use circular Rydberg atoms, i.e., Rydberg atoms with maximum angular momentum, to realize a quantum simulator: A chain of circular atoms is laser trapped inside a spontaneous emission inhibiting structure. A defect-free chain of 40 atoms could be prepared. It is expected to live several seconds inside the inhibition structure. Given the strong interaction frequencies between nearby Rydberg atoms, such a system would, thus, allow us to observe the dynamics of the spin chain over several 10 4 interaction cycles. In addition, the solid state Hamiltonian that would be simulated is fully tuneable experimentally. The proposed circular atoms quantum simulator should therefore open the way towards the simulations of systems and of their dynamics beyond the grasp of classical computation.
Summary form only given. Condensed-matter systems are interesting and important to understand, for fundamental science as well as towards more applied objectives in the development of new materials for instance. Unfortunately, these many-body quantum systems are difficult to study: both the theoretical approach and the numerical simulation are proving impossible to carry out to relevant system sizes. Quantum simulation proposes to mimic those out-of-reach systems with more controllable and accessible quantum systems. Rydberg atoms gained renewed interest in the last decades thanks to their very high polarizability, allowing for strong and tunable short-range interactions. They constitute an interesting candidate for a quantum simulation platform. However, low angular momentum Rydberg states have limited, despite relatively long, lifetimes which limit the scope of such a quantum simulator. Moreover, low-l Rydberg states cannot be efficiently laser-trapped. In order to overcome these limitations, we propose to use circular Rydberg states, i.e., of maximum angular momentum. Circular Rydberg states exhibit much longer lifetimes, and can be trapped using laser light. By placing the circular Rydberg atoms inside a spontaneous emission-inhibiting capacitor, we hope to achieve the deterministic preparation of a 1D-chain of 40 atoms, with a collective lifetime of over 2 seconds. With expected exchange energies in the 10-100 kHz range, this would provide a platform capable of simulating quantum many-body physics up to 105exchange times. The first step towards the experimental realization of such a quantum simulator is the demonstration of the laser-trapping of circular Rydberg atoms. To this end, we use a Laguerre-Gauss hollow beam at 1064 nm, imposing a ponderomotive potential on the nearly-free electron of the Rydberg atoms. I will present our latest experimental results of light-trapping of circular Rydberg atoms.
Physics
Quantum simulation can map challenging problems in complex materials onto better defined ones in simpler, easier-to-manipulate systems. Physical implementations range from trapped ions to superconducting qubits, each having distinct strengths and weaknesses. Nguyen et al. propose a quantum simulator that seems to combine many of the best features of the existing simulators in one system, while being within current experimental reach. The simulator is based on circular Rydberg atoms—with a highly excited electron orbiting the nucleus along a roughly circular path—where the atoms can be trapped by laser light, can be read out one by one, and have very long lifetimes. The interactions between such atoms would make it possible to simulate some of the most challenging problems in many-body physics.
Phys. Rev. X 8 , 011032 (2018).
Rydberg atoms are remarkable tools for quantum simulation and computation. They are the focus of an intense experimental activity, mainly based on low-angular-momentum Rydberg states. Unfortunately, atomic motion and levels lifetime limit the experimental timescale to about 100 μs. Here, we demonstrate two-dimensional laser trapping of long-lived circular Rydberg states for up to 10 ms. Our method is very general and opens many opportunities for quantum technologies with Rydberg atoms. The 10 ms trapping time corresponds to thousands of interaction cycles in a circular-state-based quantum simulator. It is also promising for quantum metrology and quantum information with Rydberg atoms, by bringing atom-field interaction times into unprecedented regimes.
We propose a new paradigm for quantum simulation of spin-1/2 arrays, providing unprecedented flexibility and allowing one to explore domains that remain unexplored, based on laser-trapped circular Rydberg atoms. The long intrinsic atomic lifetimes, combined with the inhibition of their microwave spontaneous emission and their negligible photoionisation, make operation in the minute range realistic. The proposed simulator realizes an XXZ spin-1/2 Hamiltonian, with nearest-neighbour couplings ranging from a few to tens of kilohertz. All the model parameters can be dynamically tuned at will, making a large range of simulations accessible. Thus, the system evolution can be followed long enough to be relevant for ground-state adiabatic preparation and for the study of thermalization and disorder. In this thesis, as a first step towards the implementation of this quantum simulation scheme, we (i) demonstrate the preparation of cold circular Rydberg states in a 4,2 K cryogenic environment with optical access out of a cold atom cloud. Their lifetime reveals an effective microwave black-body temperature of 11±2 K. We (ii) assess the single qubit coherence time (268±5 μs) and lifetime (3,7±0,1 ms), and, finally, we (iii) demonstrate the laser trapping of circular Rydberg atoms to prove their negligible photoionisation at the timescale of 10 ms.
We propose a novel platform for the realisation of quantum simulations of spin arrays, providing unprecedented flexibility and allowing one to explore regimes beyond the reach of other platforms. It is based on laser-trapped circular Rydberg levels. The strong van der Waals interaction between the atoms emulates a spin-1/2 XXZ Hamiltonian. All its parameters are experimentally and dynamically tunable over a wide range. A spontaneous-emission inhibiting structure extends the lifetime of individual laser-trapped circular Rydberg atoms to the minute range. Quantum simulations over more than 104 interaction cycles are thus within reach. This enables the observation of adiabatic evolutions through quantum phase transitions, of sudden quenches, and fast modulations of the interaction parameters. After I present the key features of this simulator, I will focus on our latest experimental results regarding the preparation and manipulation of laser-cooled circular Rydberg atoms in the vicinity of an atomchip in an optical-access 4K-cryostat. Lifetime measurements reveal a below-10K microwave blackbody temperature, while Ramsey interferometry shows coherence times solely limited by magnetic field noise. I will finally present our latest results on laser-trapping of circular Rydberg atoms, a decisive step towards the realisation of the proposed quantum simulator.