Establishing a reliable method to form scalable neutral-atom platforms is an essential cornerstone for quantum computation, quantum simulation and quantum many-body physics. Here we demonstrate a real-time transport of single atoms using holographic microtraps controlled by a liquid-crystal spatial light modulator. For this, an analytical design approach to flicker-free microtrap movement is devised and cold rubidium atoms are simultaneously rearranged with 2N motional degrees of freedom, representing unprecedented space controllability. We also accomplish an in situ feedback control for single-atom rearrangements with the high success rate of 99% for up to 10 μm translation. We hope this proof-of-principle demonstration of high-fidelity atom-array preparations will be useful for deterministic loading of N single atoms, especially on arbitrary lattice locations, and also for real-time qubit shuttling in high-dimensional quantum computing architectures.
We propose and demonstrate three-dimensional rearrangements of single atoms. In experiments performed with single 87Rb atoms in optical microtraps actively controlled by a spatial light modulator, we demonstrate various dynamic rearrangements of up to N = 9 atoms including rotation, 2D vacancy filling, guiding, compactification, and 3D shuffling. With the capability of a phase-only Fourier mask to generate arbitrary shapes of the holographic microtraps, it was possible to place single atoms at arbitrary geometries of a few μm size and even continuously reconfigure them by conveying each atom. For this purpose, we loaded a series of computer-generated phase masks in the full frame rate of 60 Hz of the spatial light modulator, so the animation of phase mask transformed the holographic microtraps in real time, driving each atom along the assigned trajectory. Possible applications of this method of transformation of single atoms include preparation of scalable quantum platforms for quantum computation, quantum simulation, and quantum many-body physics.
Deterministic loading of single atoms onto arbitrary two-dimensional lattice points has recently been demonstrated, where by dynamically controlling the optical-dipole potential, atoms from a probabilistically loaded lattice were relocated to target lattice points to form a zero-entropy atomic lattice. In this atom rearrangement, how to pair atoms with the target sites is a combinatorial optimization problem: brute-force methods search all possible combinations so the process is slow, while heuristic methods are time-efficient but optimal solutions are not guaranteed. Here, we use the Hungarian matching algorithm as a fast and rigorous alternative to this problem of defect-free atomic lattice formation. Our approach utilizes an optimization cost function that restricts collision-free guiding paths so that atom loss due to collision is minimized during rearrangement. Experiments were performed with cold rubidium atoms that were trapped and guided with holographically controlled optical-dipole traps. The result of atom relocation from a partially filled 7-by-7 lattice to a 3-by-3 target lattice strongly agrees with the theoretical analysis: using the Hungarian algorithm minimizes the collisional and trespassing paths and results in improved performance, with over 50% higher success probability than the heuristic shortest-move method.
We investigate coherent control of the two-photon transition pathways of a four-level atomic system in a diamond configuration. When an ultrashort laser pulse interacts with this system in the ground state 5S 1/2 of rubidium, the two-photon transition probability amplitude of 5D 3/2 is obtained by a summation of all possible resonant and nonresonant two-photon transition probability amplitudes via 5P 1/2 and 5P 3/2. Second-order perturbation theory predicts that the maximal constructive interference of the transition probability amplitudes occurs when the phases of eight different spectrum blocks satisfy four different phase relations. Experiments carried out with spectrally phase-coded laser pulses show good agreement with the theoretical prediction.
We investigate Rabi oscillation of an atom ensemble in Gaussian spatial distribution. By using the ultrafast laser interaction with the cold atomic rubidium vapor spatially confined in a magnetooptical trap, the oscillatory behavior of the atom excitation is probed as a function of the laser pulse power. Theoretical model calculation predicts that the oscillation peaks of the ensemble-atom Rabi flopping fall on the simple Rabi oscillation curve of a single atom and the experimental result shows good agreement with the prediction. We also test the the three-pulse composite interaction Rx(π/2)Ry(π)Rx(π/2) to develop a robust method to achieve a higher fidelity population inversion of the atom ensemble.PACS numbers: 32.80. Qk, 32.80.Wr, 42.65.Re Rabi oscillation is a fundamental concept in physics with a significant pedigree first discovered in the context of nuclear magnetic resonance (NMR) [1][2][3] and later extended to atomic physics and quantum optics [4,5]. In the presence of an oscillatory driving field E(t) = A(t) cos(ωt), a two-state quantum system undergoes a cyclic change of Bloch vector ρ manifested by the precessionabout an effective torque Ω = (−µA(t)/2 , 0, δ), where µ is the transition dipole moment between the two energy states, A(t) is the field envelope, and δ is the frequency detuning under the slowly-varying envelope approximation [4]. This generic feature of Rabi oscillation is universally found in a vast variety of material systems ranging from simple atoms and molecules [6][7][8][9][10] When a two-state atom interacts with a resonant (δ = 0) laser pulse, the dynamics of the excited state probability, which we may refer to as single-atom Rabi oscillation (SARO), is represented bywhere Θ o is the pulse area defined by Θ o = µA(t)dt/ . Since the pulse area is subject to both the pulse duration and the electric-field envelope, Rabi oscillations of an ultra-short time scale can be implemented by ultrafast optical interaction at a strong-enough laser intensity regime. However, the spatial extent of the laser beam over the laser-atom interaction region inevitably causes spatial average effect that often leads to vanishing of the oscillatory behavior. To overcome this problem, homogenizing the spatial profile of laser beams [22,23] and * Electronic address: jwahn@kaist.ac.kr adapting chirped laser interaction [24] have been considered. This paper aims quantitative analysis of spatially averaged Rabi oscillation. For this, we use the atom ensemble localized in a magneto-optical trap (MOT) [25] interacted with ultrafast laser pulses. As a theoretical model to investigate the spatially inhomogeneous interaction, we consider a Gaussian laser beam propagating along z direction. The pulse area in Eq. (2) is then represented in the polar coordinate system aswhere r = x 2 + y 2 , w(z) is the beam waist at z, w o = w(0) is the minimal beam waist, Θ o is the maximal pulse area, and Θ z = w o Θ o /w(z). When we assume the atom density profile in the MOT is also a Gaussian, i.e., ρ(r, z) = ρ o e −(r 2 +z 2 ...
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