Within the TU/e Kat-1 team, we aim to realize an implementation of a full-stack hybrid quantum computer. At its core, our quantum processor is based on neutral rubidium-85 atoms confined in optical tweezers, with qubit states encoded in the hyperfine splitting of the ground state. Within this poster, we present our plans and initial results of an upgraded experimental setup aimed at achieving higher gate fidelities. Key improvements include the design of a new four-coil configuration for driving global microwave transitions with arbitrary polarization and increased homogeneity. In addition, we introduce an alignment-free, dual-wavelength local addressing system based on shared acousto-optical deflectors. This system suppresses beam-pointing instabilities between the addressing and trapping beams. Together, these developments are expected to enhance the robustness and fidelity of both our global and local qubit operations.
Within the TU/e Kat-1 team, we aim to realize an implementation of a full-stack hybrid quantum computer. At its core, our quantum processor is based on neutral rubidium-85 atoms confined in optical tweezers, with qubit states encoded in the hyperfine splitting of the ground state. Within this poster, we present our plans and initial results of an upgraded experimental setup aimed at achieving higher gate fidelities. Key improvements include the design of a new four-coil configuration for driving global microwave transitions with arbitrary polarization and increased homogeneity. In addition, we introduce an alignment-free, dual-wavelength local addressing system based on shared acousto-optical deflectors. This system suppresses beam-pointing instabilities between the addressing and trapping beams. Together, these developments are expected to enhance the robustness and fidelity of both our global and local qubit operations.
Within the TU/e Kat-1 collaboration, we aim to construct a full-stack hybrid quantum computer. At its core, our quantum processor consists of individually trapped Rubidium-85 atoms in optical tweezers, with qubit states encoded in the hyperfine splitting of the atomic ground state. In this poster, we briefly introduce neutral-atom quantum computing and present the redesign and initial characterization of our experimental plat form, developed to support mid-circuit measurements as a crucial first step towards quantum error correction (QEC). Key improvements include the design of a four-loop antenna configuration for driving global microwave transitions with arbitrary polarizations and increased homogeneity. In addition, we introduce an alignment-free dual-wavelength local addressing system. This system suppresses relative beam-pointing instabilities between the trapping and addressing beams, enabling us to locally apply stable differential Stark shifts. Together with the global microwaves, this enables local state shelving into the ground-state Zeeman levels, which in turn allows site-selective mid circuit measurements- an important step towards the realization of QEC on our platform.
Qubits encoded in the electronic states of single atoms trapped in arrays of optical tweezers are a promising platform for a universal quantum computer. These qubits can be prepared in a well-defined quantum state, coherently manipulated using a nearresonant driving field, and their state detected with high fidelity. The most promising aspect of this platform is the large scalability, with arrays of up to 6100 qubits demonstrated[62].We present our progress in developing such a system with an array of single 85Rbatoms. We provide an overview of the experimental setup constructed for this purpose. Typically 50 atoms are loaded from a MOT into a 10×10 array of optical tweezers with sub-micrometer waists, with only a single atom present in a tweezer. The occupation of the tweezers is determined using a fluorescence image. We provide a characterisation of the trapping potentials experienced by the atoms. This characterisation is performed by measuring properties of the atoms in the tweezers, allowing for an in situ characterisation. In particular, the trap depth and trap frequencies were characterised. The temperature of the atoms after the initial fluorescence image was determined using the release and recapture technique [101] and the trapping lifetime of the atom was measured. With the ability to prepare, manipulate, and read out the electronic state of the atoms, an array of hyperfine qubits has been created. The qubits are encoded in the hyperfine clock states as |0⟩ := 52S1/2 |F = 2,mF = 0⟩ and |1⟩ := 52S1/2 |F = 3,mF = 0⟩. These long-lived first-order Zeeman shift insensitive states exhibit good coherence times, which we have characterized as T1=205 ± 3 ms , T2* = 2.01 ± 0.02 ms, andT2 echo = 67.1 ± 0.1 ms. State preparation is achieved by repetitions of optical and microwave pulses, to which the |0⟩ state is dark, allowing for population to accumulate in this state. The coherent evolution of the qubits have been performed using 3.035 GHz microwave radiation. The antenna used to produce this radiation is a home-built fullwave loop antenna. The antenna has allowed for addressing the qubits with Rabi frequencies up to Ω/2π ≈ 160 kHz. We have implemented the single-qubit Clifford gates using the global microwave drive. We determine using randomized benchmarking an166 Summary average gate fidelity of 0.99949(3), limited by Rabi frequency inhomogeneity over the array. To combat this fidelity limitation, we repeated the randomized benchmarking using the pulse length error robust SCROFULOUS pulses [135], which resulted in an increased gate fidelity of 0.999653(5). As a further extension of the capabilities of the system, we demonstrated a preliminary implementation of addressing a single atom int he array by applying a local Rz rotation to the selected qubit using a Stark shifting laser. The high level of control of the microwave radiation has allowed for an experimental verification of control noise-fidelity relations proposed by [115]. We have found good agreement between the experimentally measured fidelities and the proposed analytical relations developed using the stochastic Schrödinger equation. As a preliminary step towards implementing a two-qubit gate, we have performed coherent excitation of the |1⟩ state to the |r ⟩ :=602S1/2 |mJ = −1/2> Rydberg state using an off-resonant two-photon excitation. The low contrast of the Rabi oscillations on the |1⟩↔|r ⟩ transition was investigated using a simple Lindblad master equation based model. The largest contributors to the reduced contrast is SPAM error, intermediate state scattering and laser phase noise. Since Rydberg atoms interact via the van der Waals interaction, the spacing between atoms must be deterministically controlled. For this purpose, we have used an additional optical tweezer which can be dynamically moved using an acousto-optic deflector to rearrange the stochastically filled array into a desired configuration. By placing 2 atoms a distance ≈ 5 μm apart, we have demonstrated the p2 enhancement of the Rabi oscillation on the |1⟩↔|r ⟩ transition, a required first step towards implementing an entangling gate between the hyperfine qubits. To extend the temperature-limited T2* coherence time, we have implemented Λ-enhanced gray molasses cooling. We have opted to perform this cooling on the D2line as it is experimentally convenient to use this transition. Because using this transition for this purpose has not been reported in this isotope of Rb, we studied the efficacy of this cooling scheme under these circumstances. The reduced excited state hyperfine splitting of 85Rb compared to 87Rb has allowed for the study of the efficacy of this technique in the presence of additional transitions that may inhibit the cooling performance. Despite the challenges of the smaller hyperfine splitting, we have cooled the atoms to4.0±0.2 μK. This additional cooling is partially negated by the heating from the qubit state preparation procedure, but the additional cooling has allowed for the average T2*to be extended from ⟨T2*⟩ = 3.4 ± 0.1 ms to ⟨T2*⟩ = 5.3 ± 0.2 ms.
Abstract The results of experiments on the implementation of single-qubit quantum gates with a single 87Rb atom in an optical dipole trap with a wavelength of 850 nm are presented. The trap is formed by a long focal-length objective lens located outside the vacuum chamber of a magneto-optical trap. An atom is detected using a resonance fluorescence signal with an sCMOS video camera. The experiments involved the trapping and confinement of a single atom at times up to 50 s, optical pumping by polarized laser radiation, microwave transitions between two hyperfine sublevels of the ground state, and the measurement of the quantum state of the atom by pushing it from the trap. Rabi oscillations are observed during the “clock” microwave transition 5S1/2(F = 2, MF = 0) → 5S1/2(F = 1, MF = 0) between two operating qubit levels at a frequency of up to 4.2 kHz, a contrast of up to 95%, and a coherence time of up to 3 ms. These oscillations correspond to the implementation of two basic single-qubit quantum operations (Hadamard gate, NOT gate) from various initial qubit states with an average fidelity of 95.2 ± 3%.
Optical tweezer arrays of neutral atoms have been demonstrated in recent years to be a useful platform for quantum simulation, computation, and metrology. Realizing the full potential of these applications requires increasing qubit numbers while simultaneously maintaining high-fidelity control, which has proved a major challenge across quantum platforms. To date, quantum science experiments have typically been operated with at most hundreds of qubits. In this thesis, we review the relevant physics of the optical tweezer array architecture and present the technical advances involved in scaling the platform to 6,100 atomic qubits. In tandem with scalability, we demonstrate robust vacuum design, state-of-the-art coherence times, and high single-qubit gate fidelities. To capitalize on the intrinsic connectivity of the architecture at large scale, we investigate long-distance coherent atom transport and briefly describe progress towards two-qubit gate implementation. Finally, we discuss the prospects for scaling the optical tweezer array platform further by an order of magnitude.
Neutral atom arrays have rapidly emerged as a leading platform for quantum computing, boasting scalable, configurable arrays of single atoms trapped in optical tweezers, fast, high-fidelity entangling gates through Rydberg interactions, and programmable, parallelized control of qubit operations. Coupling an atom array to an optical cavity opens a new frontier. Leveraging enhanced light-atom interactions in cavity quantum electrodynamics, cavity- coupled atom arrays acquire capabilities that can further expand the neutral atom toolbox, including cavity-enhanced atom readouts, atom-photon entanglement, and photon-mediated interactions between distant atoms. This thesis presents a quantum hardware platform that integrates an array of neutral atoms with a high-finesse optical cavity. After describing the design and development of the experimental apparatus, I demonstrate high-fidelity atom state readout through the cavity, achieving improved speed and atom survival compared to conventional free-space imaging methods. I then introduce a new technique for selectively controlling atom-cavity coupling on arbitrary subsets of the array, using local AC Stark shifts on the excited states of the atoms. Building on these tools, I demonstrate fast, non-destructive cavity-based readout of atom arrays, a crucial bottleneck of atom array platforms. I also showcase real-time measurement and feedback capabilities with a demonstration of classical error correction, using a register of atomic bits. Finally, I describe progress toward implementing single- and two-qubit gates within the cavity-coupled system. By combining coherent control, tunable interactions, and high-fidelity, non-destructive readout integrated and real-time feedback, the cavity-coupled Rydberg atom array offers a promising path toward fault-tolerant quantum computing.
In quantum computers, the superposition of quantum states is used to perform calculations that are theoretically impossible or infeasible with classical computers, such as solving the traveling salesman problem for many nodes or conducting unstructured searches for large databases. Due to its scalable and flexible nature, neutral atoms trapped in optical tweezers are a promising technology for performing quantum computation. Here, qubit configurations are not static, allowing arbitrary geometries to be realized, and schemes where qubits are exchanged are readily available. The quantum level structure of neutral atoms is used to encode a qubit between two states, forming the basis for quantum computing. As the atoms are cooled to their electronic and motional ground states, transitions between qubit zero and qubit one can be driven with high fidelity. A multi-qubit gate is then realized when two or more atoms interact, e.g., by moving them close together, or by increasing their dipole radius when they are excited to a Rydberg state. Up to now, different qubits have been realized in neutral atoms, most notably ⁸⁷Rb, where the electronic ground state splits into two sublevels, which are used as encoding of a qubit. We describe progress on realizing a quantum computer based on ⁸⁸Sr. As a boson, its electronic ground state exhibits no hyperfine splitting, such that SPAM errors can be eliminated. The qubit is encoded in the ground state together with the highly studied, long-lived clock state, allowing for high-fidelity control of the transition. In this thesis, we present how the apparatus creates an ultra-high vacuum, as long-lived atoms are necessary for high-performance quantum algorithms. We show the main ideas behind the laser systems used for cooling, trapping, and driving the single-qubit transition. Our work demonstrates that coherently moving atoms is a feasible operation in quantum computing, allowing for the exchange of qubits, the shuttling of qubits to separate registers, or enabling additional phase gates. The results presented here establish ⁸⁸Sr as a viable candidate for quantum computing and lay the foundation for future fault-tolerant quantum systems.