We demonstrate the transfer of a single atom in a ring optical lattice with the aid of an auxiliary moving tweezer and investigate the influences on fidelity of the qubit encoded in the atom. When the tweezer has deeper trap depth and moves across the lattice, it is observed that an atom in one site follows the movement. The transfer efficiency of one atom to the destination site reaches up to 95%. This scheme is suitable for scalable quantum registers because of no influence on the other sites. We obtain atomic qubit fidelity during the transfer process by using quantum state tomography. Extracted fidelity indicates that the eigenstate is well preserved, while the superposition state is influenced. In combination with spin-echo measurement, dephasing mechanisms in this process are analyzed and discussed in detail. Loss of qubit fidelity is found to result from heating effects induced by this process and pointing instabilities of the trap laser. Our results pave the way for quantum computation with single atoms trapped in a scalable optical lattice.
We demonstrate the transfer of a single atom in a ring optical lattice with the aid of an auxiliary moving tweezer and investigate the influences on fidelity of the qubit encoded in the atom. When the tweezer has deeper trap depth and moves across the lattice, it is observed that an atom in one site follows the movement. The transfer efficiency of one atom to the destination site reaches up to 95%. This scheme is suitable for scalable quantum registers because of no influence on the other sites. We obtain atomic qubit fidelity during the transfer process by using quantum state tomography. Extracted fidelity indicates that the eigenstate is well preserved, while the superposition state is influenced. In combination with spin-echo measurement, dephasing mechanisms in this process are analyzed and discussed in detail. Loss of qubit fidelity is found to result from heating effects induced by this process and pointing instabilities of the trap laser. Our results pave the way for quantum computation with single atoms trapped in a scalable optical lattice.
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.
Programmable neutral-atom arrays offer a promising route toward scalable quantum computing, where coherent qubit transfer enables non-local connectivity and reduces resource overhead. However, transfer speed and motional heating remain key bottlenecks for fast and deep quantum circuits. Here, we employ a fiber array neutral-atom quantum computing architecture with site-resolved control of trap depths to realize smooth amplitude exchange between static and moving traps, thereby enabling fast and coherent qubit transfer with ultralow motional heating. With a 10 μs in situ transfer between static and moving traps, we obtain a per-cycle heating rate of 0.156(9) μK, sustain over 500 cycles with negligible atom loss, and achieve a quantum state fidelity of 0.99992(5) per cycle. For inter-site transfer between two separated static traps, the operation takes 120 μs with 0.783(17) μK heating per transfer, and remains negligible atom loss for up to 100 repeated cycles with a fidelity of 0.9998(1) per transfer. Furthermore, through experimental studies of parallel transfer, we establish a model that elucidates the relationship between array inhomogeneity and the transfer heating rate. This fast, low-heating coherent transfer capability provides a practical route for improving both speed and fidelity in atom-shuttling based quantum computing.
Abstract Programmable neutral-atom arrays offer a promising route toward scalable quantum computing, where coherent qubit transfer enables non-local connectivity and reduces resource overhead. However, transfer speed and motional heating remain key bottlenecks for fast and deep quantum circuits. Here, we employ a fiber array neutral-atom quantum computing architecture with site-resolved control of trap depths to realize smooth amplitude exchange between static and moving traps, thereby enabling fast and coherent qubit transfer with ultralow motional heating. With a 10-μs in situ transfer between static and moving traps, we obtain a per-cycle heating rate of 0.156(9) μK, sustain over 500 cycles with negligible atom loss, and achieve a quantum state fidelity of 0.99992 (5) per cycle. For inter-site transfer between two separated static traps, the operation takes 120 μs with 0.783(17) μK heating per transfer, and exhibits negligible atom loss for up to 100 repeated cycles with a fidelity of 0.9998 (1) per transfer. Furthermore, through experimental studies of parallel transfer, we establish a model that elucidates the relationship between array inhomogeneity and the transfer heating rate. This fast, low-heating coherent transfer capability provides a practical route for improving both speed and fidelity in atom-shuttling based quantum computing.
Coupling identical quantum emitters to a photonic integrated circuit (PIC) is a key step for scaling up emitter-photon interfaces for quantum science and information processing. Neutral atoms are attractive candidates due to their indistinguishability and controllability. However, experimental realizations of efficient atom trapping on a PIC while achieving strong single atom-photon coupling has so-far remained elusive. Here, we demonstrate near-deterministic single-atom loading on a microring resonator circuit, reaching single-atom cooperativity parameter C > 1 for strong coupling in cavity quantum electrodynamics. We utilize a precision optical conveyor belt, formed by a moving optical lattice in an optical tweezer, to steadily deliver trapped atoms onto a PIC. By continuously monitoring the transmission of probe photons through the circuit, which is sensitive to the proximity of single atoms near a microring resonator, we detect mean occupancy of 1.5 from 70 occupied lattice sites in a conveyor-belt transport of 4 nm position reproducibility. Based upon real-time feedback, we deterministically transfer the delivered atoms into a stationary trap on the microring, achieving 82% (18%) probability of single-(two-)atom transfer. Our technique can be extended to deterministic, highly efficient atom array assembly, providing a scalable route for neutral atom integration with PICs of complex functionalities.
We present a complete architecture for scalable quantum computation with ultracold atoms in optical lattices using optical tweezers focused to the size of a lattice spacing. We discuss three different two-qubit gates based on local collisional interactions. The gates between arbitrary qubits require the transport of atoms to neighboring sites. We numerically optimize the nonadiabatic transport of the atoms through the lattice and the intensity ramps of the optical tweezer in order to maximize the gate fidelities. We find overall gate times of a few $100\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}$s, while keeping the error probability due to vibrational excitations and spontaneous scattering below ${10}^{\ensuremath{-}3}$. The requirements on the positioning error and intensity noise of the optical tweezer and the magnetic field stability are analyzed and we show that atoms in optical lattices could meet the requirements for fault-tolerant scalable quantum computing.
A qubit made up of an ensemble of atoms is attractive due to its resistance to atom losses. In this work, we consider an experimentally feasible protocol to coherently load a spin-dependent optical lattice from a spatially overlapping Bose-Einstein condensate. Identifying each lattice site as a qubit, with an empty or filled site as the qubit basis, we discuss how high-fidelity single-qubit operations, two-qubit gates between arbitrary pairs of qubits, and nondestructive measurements could be performed. In this setup, the effect of atom losses has been mitigated, the atoms never need to be removed from the ground state manifold, and separate storage and computational bases for the qubits are not required, all of which can be significant sources of decoherence in many other types of atomic qubits.