As a conventional approach, optical dipole trap (ODT) arrays with linear polarization have been widely used to assemble neutral-atom qubits for building a quantum computer. However, due to the inherent scalar differential light shifts (DLS) of qubit states induced by trapping fields, the microwave-driven gates acting on single qubits suffer from errors on the order of 10^{-3}. Here, we construct a DLS compensated ODT array based upon a recently developed magic-intensity trapping technique. In such a magic-intensity optical dipole trap (MI-ODT) array, the detrimental effects of DLS are efficiently mitigated so that the performance of global microwave-driven Clifford gates is significantly improved. Experimentally, we achieve an average error of (4.7±1.1)×10^{-5} per global gate, which is characterized by randomized benchmarking in a 4×4 MI-ODT array. Moreover, we experimentally study the correlation between the coherence time and gate errors in a single MI-ODT with an optimum error per gate of (3.0±0.7)×10^{-5}. Our demonstration shows that MI-ODT array is a versatile platform for building scalable quantum computers with neutral atoms.
As a conventional approach, optical dipole trap (ODT) arrays with linear polarization have been widely used to assemble neutral-atom qubits for building a quantum computer. However, due to the inherent scalar differential light shifts (DLS) of qubit states induced by trapping fields, the microwave-driven gates acting on single qubits suffer from errors on the order of 10^{-3}. Here, we construct a DLS compensated ODT array based upon a recently developed magic-intensity trapping technique. In such a magic-intensity optical dipole trap (MI-ODT) array, the detrimental effects of DLS are efficiently mitigated so that the performance of global microwave-driven Clifford gates is significantly improved. Experimentally, we achieve an average error of (4.7±1.1)×10^{-5} per global gate, which is characterized by randomized benchmarking in a 4×4 MI-ODT array. Moreover, we experimentally study the correlation between the coherence time and gate errors in a single MI-ODT with an optimum error per gate of (3.0±0.7)×10^{-5}. Our demonstration shows that MI-ODT array is a versatile platform for building scalable quantum computers with neutral atoms.
We demonstrate that the coherence of a single mobile atomic qubit can be well preserved during a transfer process among different optical dipole traps (ODTs). This is a prerequisite step in realizing a large-scale neutral atom quantum information processing platform. A qubit encoded in the hyperfine manifold of an ^{87}Rb atom is dynamically extracted from the static quantum register by an auxiliary moving ODT and reinserted into the static ODT. Previous experiments were limited by decoherences induced by the differential light shifts of qubit states. Here, we apply a magic-intensity trapping technique which mitigates the detrimental effects of light shifts and substantially enhances the coherence time to 225±21 ms. The experimentally demonstrated magic trapping technique relies on the previously neglected hyperpolarizability contribution to the light shifts, which makes the light shift dependence on the trapping laser intensity parabolic. Because of the parabolic dependence, at a certain "magic" intensity, the first order sensitivity to trapping light-intensity variations over ODT volume is eliminated. We experimentally demonstrate the utility of this approach and measure hyperpolarizability for the first time. Our results pave the way for constructing scalable quantum-computing architectures with single atoms trapped in an array of magic ODTs.
We construct a polarization-mediated magic-intensity (MI) optical dipole trap (ODT) array, in which the detrimental effects of light shifts on the mixed-species qubits are efficiently mitigated so that the coherence times of the mixed-species qubits are both substantially enhanced and balanced for the first time. This mixed-species magic trapping technique relies on the tunability of the coefficient of the third-order cross term and ground state hyperpolarizability, which are inherently dependent on the degree of circular polarization of the trapping laser. Experimentally, polarization of the ODT array for ^{85}Rb qubits is finely adjusted to a definite value so that its working magnetic field required for magic trapping amounts to the one required for magically trapping ^{87}Rb qubits in another ODT array with fully circular polarization. Ultimately, in such a polarization-mediated MI-ODT array, the coherence times of ^{87}Rb and ^{85}Rb qubits are, respectively, enhanced up to 891±47 ms and 943±35 ms. Moreover, we reveal that the noise of the elliptic polarization causes dephasing effect on the ^{85}Rb qubits but it could be efficiently mitigated by choosing the dynamical range of active polarization device. We also show that light shifts seen by qubits in an elliptically polarized MI-ODT can be more efficiently compensated due to the decrease in the ground state hyperpolarizability. It is anticipated that the novel mixed-species MI-ODT array is a versatile platform for building scalable quantum computers with neutral atoms.
We characterize single-qubit Clifford gate operations with randomized benchmarking in a 2D array of neutral-atom qubits and demonstrate global and site selected gates with high fidelity. An average fidelity of F2=0.9983(14) is measured for global microwave-driven gates applied to a 49-qubit array. Single-site gates are implemented with a focused laser beam to Stark shift the microwaves into resonance at a selected site. At Stark selected single sites we observe F2=0.9923(7) and an average spin-flip crosstalk error at other sites of 0.002(9).
Neutral atoms are a promising platform for scalable quantum computing, however, prior demonstration of high fidelity gates or low-loss readout methods have employed restricted numbers of qubits. Using randomized benchmarking of microwave-driven single-qubit gates, we demonstrate average gate errors of 7(2)×10^{-5} on a 225 site atom array using conventional, destructive readout. We further demonstrate a factor of 1.7 suppression of the primary measurement errors via low-loss, nondestructive, and state-selective readout on 49 sites while achieving gate errors of 2(9)×10^{-4}.
As an important candidate for quantum simulation and quantum computation, a microscopic array of single atoms confined in optical dipole traps is advantageous in controlled interaction, long coherence time, and scalability of providing thousands of qubits in a small footprint of less than 1 mm2. Recently, several breakthroughs have greatly advanced the applications of neutral atom system in quantum simulation and quantum computation, such as atom-by-atom assembling of defect-free arbitrary atomic arrays, single qubit addressing and manipulating in two-dimensional and three-dimensional arrays, extending coherence time of atomic qubits, controlled-NOT (C-NOT) gate based on Rydberg interactions, high fidelity readout, etc.In this paper, the experimental progress of quantum computation based on trapped single neutral atoms is reviewed, along with two contributions done by single atom group in Wuhan Institute of Physics and Mathematics of Chinese Academy of Sciences. First, a magic-intensity trapping technique is developed and used to mitigate the detrimental decoherence effects which are induced by light shift and substantially enhance the coherence time to 225 ms which is 100 times as large as our previous coherence time thus amplifying the ratio between coherence time and single qubit operation time to 105. Second, the difference in resonant frequency between the two atoms of different isotopes is used to avoid crosstalking between individually addressing and manipulating nearby atoms. Based on this heteronuclear single atom system, the heteronuclear C-NOT quantum gate and entanglement of an Rb-85 atom and an Rb-87 atom are demonstrated via Rydberg blockade for the first time. These results will trigger the quests for new protocols and schemes to use the double species for quantum computation with neutral atoms. In the end, the challenge and outlook for further developing the neutral atom system in quantum simulation and quantum computation are also reviewed.
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.