We investigate single-occupancy dipole trap arrays loaded with a gas of either fermions or bosons presenting some isolated defects consisting in empty sites, i.e., holes. The tunneling interaction between neighboring sites is used to prepare multi-site dark states for the holes allowing for the coherent manipulation of their external degrees of freedom. By means of an ab initio integration of the Schr\odinger equation, we investigate the adiabatic transport of holes between the two extreme traps of a triple-well potential as well as the preparation of a defect-free trap domain. Furthermore, a quantum-trajectory approach based on the de Broglie--Bohm formulation of quantum mechanics is used to get detailed physical insight into the transport process. We extend the previous results to a single hole in a dipole trap array of arbitrary length by means of the Hubbard model, where hole creation and annihilation operators are introduced. Finally, we discuss the use of the hole for the construction of a coherent single hole diode and a coherent single hole transistor.
We investigate single-occupancy dipole trap arrays loaded with a gas of either fermions or bosons presenting some isolated defects consisting in empty sites, i.e., holes. The tunneling interaction between neighboring sites is used to prepare multi-site dark states for the holes allowing for the coherent manipulation of their external degrees of freedom. By means of an ab initio integration of the Schr\odinger equation, we investigate the adiabatic transport of holes between the two extreme traps of a triple-well potential as well as the preparation of a defect-free trap domain. Furthermore, a quantum-trajectory approach based on the de Broglie--Bohm formulation of quantum mechanics is used to get detailed physical insight into the transport process. We extend the previous results to a single hole in a dipole trap array of arbitrary length by means of the Hubbard model, where hole creation and annihilation operators are introduced. Finally, we discuss the use of the hole for the construction of a coherent single hole diode and a coherent single hole transistor.
We investigate arrays of three traps with two fermionic or bosonic atoms. The tunneling interaction between neighboring sites is used to prepare multisite dark states for the empty site (i.e., the hole) which allows for the coherent manipulation of its external degrees of freedom. By means of an ab initio integration of the Schr\"odinger equation, we investigate the adiabatic transport of a hole between the two extreme traps of a triple-well potential. Furthermore, a quantum-trajectory approach based on the de Broglie--Bohm formulation of quantum mechanics is used to get physical insight into the transport process. Finally, we discuss the use of the hole for the construction of a coherent single hole diode and a coherent single hole transistor.
This chapter discusses an efficient and robust technique to coherently transport a single neutral atom, a single hole, or even a Bose–Albert Einstein condensate between the two extreme traps of a triple-well optical potential. It describes the main features of the optical microtrap array system used to isolate and manipulate individual neutral atoms. The chapter also discusses the main ideas behind the coherent control of matter wave tunneling based on adiabatic passage. It explains both a coherent single-hole diode and a coherent single-hole transistor in a triple-well potential. The chapter presents a single-hole diode by using the collisional interaction between two bosons as a control parameter to allow the whole transport from left to right, and inhibit the transport from right to left. Atomtronics is one of the foremost bottom-top approaches to quantum information science, where neutral atoms in optical, magnetic, and electric potentials form the building blocks of coherent diode and transistor-like devices.
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.
Ultracold atoms in optical lattices are a powerful platform for the study of quantum many-body physics. The combination of a high degree of isolation from the environment and external control over all relevant parameters makes these systems ideal candidates for the quantum simulation of fundamental lattice models. However, since the atoms are trapped in standing waves of interfering laser beams, the available trap geometries are constrained to regular lattices and single-site control is limited. In this thesis, an alternative experimental platform is investigated. Here, the combination of a microlens array and a spatial light modulator is used to provide a two-dimensional optical microtrap array for ultracold atoms. This setup allows for versatile trap geometries and comprehensive single-site control. The experimental feasibility of the described platform is investigated in the following way. First, the light field generating the microtrap array is simulated using a detailed model of the optical setup. The computed intensity distribution is proportional to the optical dipole potential for the atoms. Second, the simulation results are used to obtain the Hubbard parameters for multiple alkalies from numerical calculations as well as approximative analytical methods. It is shown that the strongly correlated regimes of the Bose-Hubbard model can be reached at sufficiently large tunneling rates. In addition, the impact of fluctuations in the trap parameters is investigated. Third, two approaches are considered for the preparation of low-entropy many-body states. On the one hand, a loading scheme is investigated which starts from a Bose-Einstein condensate and is used in optical lattice experiments. Here, the depth of the microtrap array is increased adiabatically. On the other hand, an array of isolated traps, which is initialized with one atom per site in the respective motional ground state, is considered as starting point. The itinerant regime of the Hubbard model is accessed by an adiabatic decrease of the trap depth. An analysis of ramp-induced excitations and external heating processes shows the feasibility of both approaches. Demonstrating the potential of the investigated platform, two applications are described. On the one hand, the tunneling dynamics of ultracold atoms between weakly coupled ring lattices is analyzed. Controlled by the interaction strength, multiple phenomena can be observed: Josephson oscillations exhibiting collapse and revival, inter-action-induced self-trapping, and tunneling resonances. On the other hand, the implementation of a scheme for universal quantum computing based on time-continuous quantum walks of interacting particles is proposed. Here, the information is encoded into the position of atomic wave packets moving through a planar graph which is built from optical microtraps and implements a quantum circuit. Details of an experimental implementation are discussed for both applications using the results derived in the preceding parts of this thesis.
Albert Benseny,a Joan Baguda`,a Xavier Oriols,b Gerhard Birkl,c Atomtronics is one of the foremost bottom-top approaches to quan- tum information science, where neutral atoms in optical, magnetic, and electric potentials form the building blocks of coherent diode and transistor-like devices. In this context, we discuss in this chapter an efficient and robust technique to coherently transport a single neutral atom, a single hole, or even a Bose-Einstein condensate (BEC) between the two extreme traps of a triple-well optical potential. Solving the corresponding quantum dynamics in terms of Bohmian trajectories, we investigate this adiabatic transport process and present a very counterintuitive effect: by slowing down the total time duration of the transport process, it is possible to achieve sudden particle accelerations yielding ultrahigh atomic velocities.a 3.1 Introduction 191 3.1.1 Atomtronics 191 3.1.2 Three-level atom optics 192 3.1.3 Adiabatic transport with trajectories 195 3.2 Physical System: Neutral Atoms in Optical Microtraps 198 3.2.1 One-dimensional Hamiltonian 200 3.3 Adiabatic Transport of a Single Atom 201 3.3.1 The matter wave STIRAP paradox with Bohmian trajectories 201 3.3.2 Velocities and accelerations of Bohmian trajectories 202 3.4 Adiabatic Transport of a Single Hole 206 3.4.1 Hole transfer as an array-cleaning technique 206 3.4.2 Adiabatic transport of a hole in an array of three traps 208 3.4.2.1 Three-level approximation description 208 3.4.2.2 Numerical simulations 210 3.4.3 Hole transport fidelity 212 3.4.4 Bohmian trajectories for the hole transport 213 3.4.5 Atomtronics with holes 215 3.4.5.1 Single hole diode 215 3.4.5.2 Single-hole transistor 217 3.5 Adiabatic Transport of a Bose-Einstein Condensate 219 3.5.1 Madelung hydrodynamic formulation 222 3.5.2 Numerical simulations 223 3.6 Conclusions 227 Electronics is the branch of science and technology that deals with the controlled flow of electrons. Most of today’s electronic devices use semiconductor diodes and transistors to manipulate electronic current. Notably, the miniaturization of these devices is getting closer and closer to the single atom scale, reaching the limit of Moore’s law [1].a Nowadays, the electronics top-bottom approach is crossing the frontier between the classical and the quantum realm, where quantum effects such as quantum tunneling and quantum correlations, that is, entanglement, are unavoidable. In particular, the transition from the classical to the quantum world constitutes one of the physical scenarios where the Bohmian formulation can give more insight into the underlying physics. See chapter 1 for a detailed discussion of these aspects and chapter 6 for a particular application of Bohmian trajectories to quantum electronic devices.
We trap atoms in versatile two-dimensional (2D) arrays of optical potentials, prepare flexible 2D spin configurations, perform site-selective coherent manipulation, and demonstrate the implementation of simultaneous measurements of different system properties, such as dephasing and decoherence. This approach for the flexible manipulation of atomic quantum systems is based on the combination of 2D arrays of microlenses and 2D arrays of liquid crystal light modulators. This offers extended types of control for the investigation of quantum degenerate gases, quantum information processing, and quantum simulations.