Schäffner, Dominik (2022)
Interacting Neutral Atoms in a Scalable Platform of Optical Tweezers for Quantum Computation and Sensing.
Technische Universität Darmstadt
doi: 10.26083/tuprints-00020344
Dissertation, Erstveröffentlichung, Verlagsversion

Kurzbeschreibung (Abstract)

Arrays of optical tweezers provide a versatile environment to store neutral-atom quantum systems with precise control over their internal and external degrees of freedom. These configurations offer a wide range of applications in a variety of research fields including quantum computation and simulation, quantum many-body physics, and quantum sensing. The micro-optical platform presented in this work provides a large-scale tweezer array comprising hundreds of focused-beam dipole potentials with diffraction-limited waists of 1.45(10) µm. Exploiting light-assisted collisions allows for preparation of 191(17) individual laser-cooled rubidium atoms into a typical number of 361 sites of a quadratic-grid array with trap depths corresponding to temperatures in the millikelvin regime. In the context of this thesis, a technique was implemented to transform an arbitrary distribution of atoms within the array into a predefined pattern via sequential transport between sites. Surpassing the stochastic loading process, this allows to commence experiments from a well-defined initial configuration, compensate for atom loss during an experimental cycle, and decrease the necessary number of time-consuming laser cooling phases. Based on this approach, defect-free configurations consisting of up to 111 atoms could be demonstrated. This paved the way to conduct experiments which have been impossible to carry out before within a reasonable amount of time. Significant progress has been made towards the realization of two-qubit operations in this experimental platform. Site-selective coherent coupling from the 5S½ ground to a 82S½ Rydberg state via a two-photon process was implemented yielding Rabi frequencies of up to 2π · 0.78(5) MHz. Following this, Rydberg-blockade between atoms at neighboring array sites separated by 7.0(2) µm was achieved using a sequential addressing scheme. Additional advances were made regarding the coherent coupling between the hyperfine ground states which led to sub-microsecond π-pulse durations in the large-scale array. On that basis, the tweezer platform was turned into a two-dimensional site-resolved sensor array for magnetic fields. Using a total of 270 individual-atom sensors covering an area of 119 µm × 98 µm allows for parallelized detection of external magnetic fields with a sensitivity of 100 nT and a spatial resolution of 7 µm. Utilizing a single-atom probe in a movable optical tweezer, significantly enhanced the spatial resolution while the sensitivity stayed in agreement with the result obtained via parallelized detection. Furthermore, novel concepts to extend the available tweezer configurations of the present quantum platform have been evaluated. This includes the implementation of spatial light modulation with digital micromirror devices (DMD) as well as 3D-printed microlens arrays. Applying DMD-based addressing of microlenses, dynamic reconfiguration of tweezer geometries could be demonstrated with individual-site control. In addition, 3D printing was found to offer even further flexibility in the configuration of the microlens array itself. This led to the development of a hybrid tweezer setup combining the stability involved with microlens-based platforms, the short-term modification of the fundamental lens arrangement based on rapid prototyping of user-definable microlens arrays, and the DMD-based reconfigurability with real-time control for the creation of versatile tweezer geometries.

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