Optical tweezer arrays of neutral atoms have emerged as a promising platform for studying quantum physics. These individual atoms can be carefully prepared in single quantum states, and easily manipulated with microwaves and lasers. MHz scale interactions are accessible at several micron scale distances by exciting these atoms to Rydberg states. These arrays can also be created in arbitrary 2D geometries with the use of a spatial light modulator. Adding the capability of a second species opens new possibilities in non-destructive measurement and quantum simulation of bipartite systems with widely tunable parameters. In this thesis, we describe our efforts to build a flexible platform for studying quantum phenomena utilizing two species of atoms, sodium and cesium. In particular, we discuss the laser technology and setups required to create dual species optical tweezer arrays. These arrays are made defect-free with real-time rearrangement of atoms using a separate set of tweezers created with acousto-optical deflectors. We then describe how to excite these atoms coherently to the Rydberg state with coherence times in Cs as long as 20 microseconds. With these techniques established, we are able to probe an Ising critical point in 1D and 2D systems with up to 81 atoms. In particular, we measure and confirm the value of the universal critical exponent, $\eta$, via adiabatic preparation of the ground state at the critical point. Then, we measure the interactions between sodium and cesium atoms setting the stage for future experiments. Lastly, a theoretical proposal is presented where Rydberg atoms can be used to enhance the interaction rates of ultracold polar molecules, as well as measure their states non-destructively.
Optical tweezer arrays of neutral atoms have emerged as a promising platform for studying quantum physics. These individual atoms can be carefully prepared in single quantum states, and easily manipulated with microwaves and lasers. MHz scale interactions are accessible at several micron scale distances by exciting these atoms to Rydberg states. These arrays can also be created in arbitrary 2D geometries with the use of a spatial light modulator. Adding the capability of a second species opens new possibilities in non-destructive measurement and quantum simulation of bipartite systems with widely tunable parameters. In this thesis, we describe our efforts to build a flexible platform for studying quantum phenomena utilizing two species of atoms, sodium and cesium. In particular, we discuss the laser technology and setups required to create dual species optical tweezer arrays. These arrays are made defect-free with real-time rearrangement of atoms using a separate set of tweezers created with acousto-optical deflectors. We then describe how to excite these atoms coherently to the Rydberg state with coherence times in Cs as long as 20 microseconds. With these techniques established, we are able to probe an Ising critical point in 1D and 2D systems with up to 81 atoms. In particular, we measure and confirm the value of the universal critical exponent, η, via adiabatic preparation of the ground state at the critical point. Then, we measure the interactions between sodium and cesium atoms setting the stage for future experiments. Lastly, a theoretical proposal is presented where Rydberg atoms can be used to enhance the interaction rates of ultracold polar molecules, as well as measure their states non-destructively.
Optical tweezer arrays of neutral atoms have emerged as a versatile platform for analog quantum simulation and digital quantum computation, combining scalability, reconfigurable geometry, and flexible microscopic control. In the first part of this work, we develop a 133Cs Rydberg simulator and demonstrate coherent Rydberg excitation in a rearrangeable array of more than 100 atoms. We then use this platform to probe critical many-body physics, extracting the scaling dimensions of the Ising universality class from an adiabatically prepared critical state. Dual-species arrays extend these capabilities by introducing spectroscopic selectivity and independently tunable interspecies interactions. Motivated by these opportunities, we develop a dual-species Rydberg array of 23Na and 133Cs atoms. The large separation between the optical transitions of the two species allows qubits encoded in one species to be cooled, trapped, imaged, and excited while the other species remains largely undisturbed. At the same time, strong van der Waals interactions provide a programmable coupling between the two arrays. We use this platform to demonstrate a proof-of-principle multi-qubit stabilizer readout based on an interaction-compensated protocol. In this setting, spectroscopic separation becomes an architectural advantage: it enables in-situ ancilla control and readout without requiring atom transport between separate interaction and measurement zones. Consequently, a multi-qubit entangling operation that would otherwise be decomposed into a sequence of two-qubit gates can be implemented as a native, effectively constant-depth primitive. These results point toward faster and more scalable syndrome extraction in neutral-atom quantum error correction, and establish dual-species Rydberg arrays as a promising architecture connecting programmable quantum simulation with fault-tolerant quantum computation.
Over the past decade, quantum information science has progressed from few-qubit demonstrations to experiments with hundreds of qubits. Neutral atom processors based on individual atoms trapped in arrays of optical tweezers have emerged as a leading candidate due to their inherent scalability and flexible connectivity. Advanced protocols like measurement-based state preparation and quantum error correction, however, require efficient crosstalk-free mid-circuit operations for the readout, reset, and replenishment of a subset of qubits. In typical single-species atom arrays, where all atoms are identical and on-resonance, such operations necessitate complex overheads from single-site addressing, coherent transport, or shielding techniques, to mitigate the qubit decoherence induced from photons scattered by neighboring atoms. To address this challenge of engineering scalable quantum architectures compatible with efficient control techniques, we introduce and implement the first dual-species atom array platform, and explore new dynamics inaccessible in single-species arrays. In this approach, two atomic species are addressed independently due to the spectral separation between their control wavelengths. We engineer two-dimensional arrays from individual rubidium (Rb) and cesium (Cs) atoms in up to 512 optical tweezers, and show that the two species can be independently trapped, cooled, and imaged with state-of-the-art performance metrics. Harnessing this intrinsic crosstalk-free control, we establish the key primitives of mid-circuit readout, real-time processing and feed-forward, and coherent mid-circuit reloading. By integrating these capabilities, we realize in-sequence, real-time correction of correlated phase errors via a spectator qubit protocol. Next, we excite atoms to Rydberg states in the Förster regime, accessing hitherto unobserved enhanced interspecies Rydberg interactions, and program them to implement the first interspecies CNOT gate. We combine this multispecies entanglement with mid-circuit readout to achieve quantum non-demolition measurement of a Rb-qubit using an auxiliary Cs-qubit, circumventing physical qubit transport. Finally, leveraging the two qubit modalities, we present the first experimental demonstration of quantum cellular automata in atom arrays using only global addressing, and prepare a 17-qubit Cs cluster state with Rb-mediated interactions. The dual-species platform and techniques established in this thesis pave the way toward measurement-based algorithms and real-time feedback control in large-scale quantum systems.
Neutral atoms trapped and manipulated by laser light provide experimentally well accessible quantum systems allowing for a high degree of control over external and internal degrees of freedom. Arrays of dipole traps in which the atoms are confined individually in a configurable geometry constitute a versatile platform for quantum simulation and information applications. By exciting these atoms into Rydberg states, interactions of variable strength and range can be introduced into the system, allowing for the implementation of entangling gate operations or spin Hamiltonians. A crucial requirement for these schemes to function in a reliable way is the ability to create defect-free arrays of single atoms. This is generally a challenge in these types of systems, as common atom loading schemes are limited to roughly 50% probability of filling each site. In this work, a technique for the rearrangement of atoms within a scalable architecture based on micro-optical lens arrays was developed and implemented, resulting in the creation of uniformly filled regions containing more than 100 atoms, which represent the largest defect-free structures realized so far in systems of this kind. This was accomplished by filling the empty traps in a pre-defined pattern with an atom one by one using an optical tweezer. Thus, structures with up to 5 x 5 atoms could be rendered defect-free in more than 99% of attempts. Although the success rate drops below unity for larger clusters, a value of 3.1% for a 100-atom structure is still viable for experiments working with post-selection methods. The filling fraction of even the largest examined structures was observed to be higher than 88%, surpassing common loading schemes by a significant margin. The measurements presented in this thesis build on a region of the array containing 361 sites, being limited by available laser power. In contrast, the addressable range of the optical tweezer includes more than 1500 sites and microlens arrays with up to a million lenses are commercially available. By implementing coherent Rydberg excitation of this assembled atom array, significant progress toward a universal quantum computer or flexible quantum simulator has been made. Using a two-photon excitation scheme, coherent dynamics between the ground and Rydberg state could be observed simultaneously in a 5 x 5 region of the array, with two-photon Rabi frequencies on the order of Omega = 2Pi x 500kHz measured for a Rydberg laser beam waist of w_0,B = 18.7(10) µm. The choice of an appropriate Rydberg state and interatomic spacing led to the presence of strong nearest-neighbor interactions and allowed for the demonstration of the Rydberg blockade effect by observing a collective enhancement of the Rabi frequency consistent with the expected scaling ~ sqrt(N) as well as the suppression of multiple excitations. This mechanism represents the fundamental constituent of a two-qubit gate operation. The architecture introduced in this work offers a scalability unique among quantum simulation platforms and the presented results underpin its potential to propel the atom-optical approach for quantum information processing beyond the threshold of quantum supremacy. Different approaches for scaling up the system have been explored, indicating that defect-free structures of more than 1000 atoms are within range with feasible experimental improvements. Through a detailed analysis of the factors limiting the coherence of the observed dynamics, strategies for future experimental improvements have been developed. Among these, increasing the coupling strength to the Rydberg state into the megahertz regime by increasing laser power and implementing single-site addressing represents the most straight-forward and promising approach.
A frontier challenge in quantum science and technology is the construction of scalable quantum systems which can operate in regimes beyond classical simulatability. Such systems can be used as tools for simulating and exploring complex phenomena in quantum physics; they can also be used to benchmark and test quantum algorithms. Several experimental platforms, based on a variety of quantum mechanical building blocks, are currently being pursued with these goals in mind, with state-of-the-art systems capable of controlling up to around fifty particles. In this thesis, we present the development of a new platform based on individually controlled neutral atoms. In this approach, hundreds of individual atoms are trapped in an array of optical tweezers, and they are sorted in real-time into programmable geometries in one and two dimensions. After initialization of an array, atom interactions are switched on by coherent excitation to highly excited Rydberg states, resulting in a rich spin Hamiltonian. We experimentally advance several key aspects of this platform, developing new tools for controlling strongly interacting atom arrays and probing novel quantum phases and non-equilibrium dynamics. We additionally utilize Rydberg interactions to entangle atoms, demonstrating high fidelity universal quantum logic gates as well as the preparation of fully entangled Schrödinger cat states. This work highlights the prospects for scalable quantum simulation and quantum information processing beyond the limit of classical computation using neutral atom arrays.
This thesis describes experimental and theoretical work towards a novel dual species platform for Rydberg quantum information processing employing ultracold samples of potassium (K) and rubidium (Rb) atoms. The dual-species setup combined with the possibility of deploying arrays of ultracold atomic ensembles trapped in optical tweezers will pave the way for a new generation of Rydberg single-photon optical transistors with high input photon rate. Firstly, by using degenerate fermionic 40K samples as the storage medium one can take advantage of the Pauli exclusion principle which offers protection against loss and dephasing mechanisms of Rydberg polaritons, while the bosonic 87Rb species can be used as a benchmark. Secondly, simultaneously trapping nearby ensembles of the two species opens up the possibility of creating strong interactions between photons of different ”colours”, as well as the independent control of parameters of the atomic storage medium. A theoretical study conducted in the first part of this thesis reveals multiple experimentally accessible pair combinations of K and Rb atoms in their respective Rydberg states which have high interaction strength. These K-Rb pair states offer long-range interaction suitable for such a spatially isolated transistor setup. The subsequent part presents experimental work towards a dual species Rydberg optical transistor. This includes the establishment of a laser system to access Rydberg states in both species, and a feedback system to reduce atom number fluctuations. Lastly, non-destructive measurements of Rydberg states, using electromagnetically induced transparency and the newly established setup, are presented for ultracold samples of 40K and 87Rb.
The ability to locally control and measure subsets of ancilla qubits in an efficient and crosstalk-free manner is a key ingredient in quantum error correction (QEC). Dual-species neutral atom arrays offer an ideal implementation of these capabilities, enabling independent state preparation, manipulation, and detection on each species. In this work, we realize such a dual-species Rydberg array of Na and Cs atoms trapped in co-localized 2D optical tweezer arrays, using Na as an ancilla to measure stabilizers of surrounding Cs data qubits. We identify the finite interspecies Rydberg-Rydberg interaction strength as a practical obstacle to high-fidelity multi-body entanglement and show that, by tuning the Rabi frequency and the detuning of the Rydberg driving field, the resulting geometric phase error can be compensated. This yields a protocol for simultaneous, non-destructive, in situ stabilizer readout of multiple data qubits via global pulses alone. Using this protocol, we demonstrate non-destructive measurement of Pauli-Z stabilizers on four-qubit Cs plaquettes via a single global Rydberg pulse sequence. Our results demonstrate dual-species tweezer arrays as a promising route towards scalable QEC and open the door to new quantum control protocols leveraging both interspecies and intraspecies interactions.