Circular Rydberg atoms, with their long lifetimes and adjustable strong dipolar interactions, are promising candidates for the implementation of quantum simulations in regimes that were previously out of reach. A new quantum simulator paradigm, based on qubits encoded in circular states, would implement an XXZ spin-1/2 Hamiltonian with dynamically adjustable parameters over a wide range of values. This thesis addresses the preliminary steps in constructing such a quantum simulator. First, we present the realization of two-dimensional arrays of optically-trapped circular Rydberg atoms with arbitrary geometries. For this purpose, we prepare arrays of ultra-cold rubidium atoms, individually trapped in optical tweezers. An additional beam with adjustable position allows us to rearrange the atoms within the array to implement the desired geometry in a deterministic manner. We then excite the atoms to the circular state with principal quantum number n=52, while trapping them in hollow beams using the ponderomotive force. These experimental capabilities allowed us to control and characterize, for the first time, the dipolar interactions between circular states, within pairs of individually trapped atoms. We showed the good agreement of these measurements with theoretical expectations and highlighted their dependence on the system's geometry. This experimental study is coupled to an investigation of the motion of the circular atoms within their traps.
Circular Rydberg atoms, with their long lifetimes and adjustable strong dipolar interactions, are promising candidates for the implementation of quantum simulations in regimes that were previously out of reach. A new quantum simulator paradigm, based on qubits encoded in circular states, would implement an XXZ spin-1/2 Hamiltonian with dynamically adjustable parameters over a wide range of values. This thesis addresses the preliminary steps in constructing such a quantum simulator. First, we present the realization of two-dimensional arrays of optically-trapped circular Rydberg atoms with arbitrary geometries. For this purpose, we prepare arrays of ultra-cold rubidium atoms, individually trapped in optical tweezers. An additional beam with adjustable position allows us to rearrange the atoms within the array to implement the desired geometry in a deterministic manner. We then excite the atoms to the circular state with principal quantum number n=52, while trapping them in hollow beams using the ponderomotive force. These experimental capabilities allowed us to control and characterize, for the first time, the dipolar interactions between circular states, within pairs of individually trapped atoms. We showed the good agreement of these measurements with theoretical expectations and highlighted their dependence on the system's geometry. This experimental study is coupled to an investigation of the motion of the circular atoms within their traps.
Quantum simulation offers interesting perspectives for the understanding of complex systems that are out of reach for numerical approaches. In this line, a new quantum simulation platform has recently been proposed. A spin-1/2 XXZ hamiltonian is thus realized in which the parameters can be controlled over a large range. The spin states are encoded by circular Rydberg states coupled through dipole-dipole interaction. These states benefit from longer lifetimes compared to the low angular momentum states used for current quantum simulations. In addition, they can be laser-trapped through the ponderomotive effect, and their lifetime can be further enhanced by spontaneous emission inhibition. We present in this thesis the first step towards the implementation of the proposed quantum simulator. We first prepare an array of rubidium 87 atoms trapped individually in optical tweezers. These atoms are subsequently excited to the circular Rydberg state n = 52 and transferred to hollow bottle-beam traps. We thus demonstrate the ponderomotive trapping of these states over durations of several milliseconds. We take advantage of the optical detection of the states thus prepared with various experiments. We characterize the trapping potential by measuring its transverse frequency. We finally conclude with the coherent manipulation of these trapped circular states through Rabi oscillations and Ramsey interferometry to determine their coherence.
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.
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.
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.
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±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.
In recent years, advances in optical tweezers arrays have enabled the trapping and control of individual atoms. This makes it possible to simulate condensed matter systems by arranging atoms in an array that mimics the crystalline structure of real materials. This approach, known as quantum simulation, was first envisioned by R. Feynman and is now being implemented by several research groups worldwide. In order to induce interactions between atoms, they are prepared in highly excited atomic states, known as Rydberg states. In particular, circular Rydberg states, which possess maximal angular momentum, exhibit lifetimes of several milliseconds, much longer than those of other Rydberg states. This property makes them particularly interesting for the development of new quantum technologies. In this work, we present the first building blocks of a quantum simulator based on circular Rydberg states of strontium atoms. This includes the development of a new cryogenic apparatus in which individual strontium atoms are trapped in optical tweezers. Using an alkaline-earth element allows us to exploit its two valence electrons for different tasks. One electron is excited to the circular state with principal quantum number n = 52, while the ionic core behaves as a Sr+ ion, which can be directly trapped by the tweezers. Moreover, we observe coherent oscillations between singlet and triplet spin states, due to the spin-orbit coupling of the electron in the circular state. These oscillations allow us to measure, with high precision, QED corrections to the Landé g5S1/2 factor of the ground state of Sr+.