arXiv subjects

Jaewook Ahn

Publications and source records attributed to Jaewook Ahn.

At least 37 records · Page 2Linked to original sources

arXiv2023

Quantum Programming of the Satisfiability Problem with Rydberg Atom Graphs

Finding a quantum computing method to solve nondeterministic polynomial time (NP)-complete problems is currently of paramount importance in quantum information science. Here an experiment is presented to demonstrate the use of Rydberg atoms to solve (i.e., to program and obtain the solution of) the satisfiability (3-SAT) problem, which is the prototypical NP-complete problem allowing general programming of all NP problems. Boolean expressions of the 3-SAT problem are programmed with the blockade interactions of Rydberg atom graphs and their many-body ground states are experimentally obtained, to determine the satisfiabilities of the given 3-SAT problem instances quantum mechanically.

quant-ph↗

arXiv2022

Optical tweezers throw and catch single atoms

Single atoms movable from one place to another would enable a flying quantum memory that can be used for quantum communication and quantum computing at the same time. Guided atoms, e.g., by optical tweezers, provide a partial solution, but the benefit of flying qubits could be lost if they still interact with the guiding means. Here we propose and experimentally demonstrate freely-flying atoms that are not guided but are instead thrown and caught by optical tweezers. In experiments, cold atoms at 40 micro Kelvin temperature are thrown up to a free-flying speed of 0.65 m/s over a travel distance of 12.6 micrometer at a transportation efficiency of 94(3)%, even in the presence of other optical tweezers or atoms en route. This performance is not fundamentally limited but by current settings of optical tweezers with limited potential depth and width. We provide a set of proof-of-principle flying atom demonstrations, which include atom transport through optical tweezers, atom arrangements by flying atoms, and atom scattering off optical tweezers. Our study suggests possible applications of flying atoms, not only in fundamental studies such as single-atom low-energy collisions, but also non-photon quantum communication and flying-qubit-based quantum computing.

quant-ph↗

arXiv2022

Quantum tomography of Rydberg atom graphs by configurable ancillas

Tomographic reconstruction of the many-body quantum state of a scalable qubit system is of paramount importance in quantum computing technologies. However, conventional approaches which use tomographically orthogonal base measurements require precise and individual qubit controls which are often experimentally daunting. Here, we propose, as a quantum-mechanically robust alternative, to use configurable ancillas of which the continuously-tunable interactions can generate independent base measurements tomographically sufficient for the quantum state reconstruction of the system of interest. Experimental tests are performed for Rydberg atom arrays in $N$-body $W$ states, of which the results demonstrate reliable high-fidelity full quantum state reconstruction of the proposed method.

quant-ph↗

arXiv2022

Quantum simulation of Ising spins on Platonic graphs

We present quantum simulation experiments of Ising-like spins on Platonic graphs, which are performed with two-dimensional arrays of Rydberg atoms and quantum-wire couplings. The quantum wires are used to couple otherwise uncoupled long-distance atoms, enabling topology-preserving transformtions of the three-dimensional graphs to the two-dimensional plane. We implement three Platonic graphs, tetrahedron, cube, and octahedron of Platonic solids, and successfully probe their ground many-body spin configurations before and after the quasi-adiabatic control of the system Hamiltonians from the paramagnetic phase to anti-ferromagnetic-like phases. Our small-scale quantum simulations of using less than 22 atoms are limited by experimental imperfections, which can be easily improved by the state-of-the-art Rydberg-atom technologies for more than 1000-atom scales. Our quantum-wire approach is expected to pave a new route towards large-scale quantum simulations.

quant-ph↗

arXiv2022

Rydberg wire gates for universal quantum computation

Rydberg atom arrays offer flexible geometries of strongly-interacting neutral atoms, which are useful for many quantum applications such as quantum simulation and quantum computation. Here we consider a gate-based quantum computing scheme for a Rydberg-atom array. We utilize auxiliary atoms which are used as a quantum wire to mediate controllable interactions among data-qubit atoms. We construct universal quantum gates for the data atoms, by using single-atom addressing operations. Standard one-, two-, and multi-qubit solutions are explicitly obtained as respective sequences of pulsed operations acting on individual data and wire atoms. A detailed resource estimate is provided for an experimental implementation of this scheme in a Rydberg quantum simulator.

quant-ph↗

arXiv2021

Rydberg Quantum Wires for Maximum Independent Set Problems with Nonplanar and High-Degree Graphs

One prominent application of near-term quantum computing devices is to solve combinatorial optimization such as non-deterministic polynomial-time hard (NP-hard) problems. Here we present experiments with Rydberg atoms to solve one of the NP-hard problems, the maximum independent set (MIS) of graphs. We introduce the Rydberg quantum wire scheme with auxiliary atoms to engineer long-ranged networks of qubit atoms. Three-dimensional (3D) Rydberg-atom arrays are constructed, overcoming the intrinsic limitations of two-dimensional arrays. We demonstrate Kuratowski subgraphs and a six-degree graph, which are the essentials of non-planar and high-degree graphs. Their MIS solutions are obtained by realizing a programmable quantum simulator with the quantum-wired 3D arrays. Our construction provides a way to engineer many-body entanglement, taking a step toward quantum advantages in combinatorial optimization.

quant-ph↗

arXiv2021

Machine learning identification of symmetrized base states of Rydberg atoms

Studying the complex quantum dynamics of interacting many-body systems is one of the most challenging areas in modern physics. Here, we use machine learning (ML) models to identify the symmetrized base states of interacting Rydberg atoms of various atom numbers (up to six) and geometric configurations. To obtain the data set for training the ML classifiers, we generate Rydberg excitation probability profiles that simulate experimental data by utilizing Lindblad equations that incorporate laser intensities and phase noise. Then, we classify the data sets using support vector machines (SVMs) and random forest classifiers (RFCs). With these ML models, we achieve high accuracy of up to 100% for data sets containing only a few hundred samples, especially for the closed atom configurations such as the pentagonal (five atoms) and hexagonal (six atoms) systems. The results demonstrate that computationally cost-effective ML models can be used in the identification of Rydberg atom configurations.

quant-ph↗

arXiv2021

Quantum annealing of Cayley-tree Ising spins at small scales

Significant efforts are being directed towards developing a quantum annealer capable of solving combinatorial optimization problems. The challenges are Hamiltonian programming and large-scale implementations. Here we report quantum annealing demonstration of Ising Hamiltonians programmed with up to $N=22$ spins mapped on various Cayley tree graphs. Experiments are performed with a Rydberg-atom quantum simulator, in which rubidium single atoms are arranged in three dimensional space in such a way that their Rydberg atoms and blockaded strong couplings respectively represent the nodes and edges of each graph. Three different Cayley-tree graphs of $Z=3$ neighbors and of up to $S=4$ shells are constructed, and their ground-state phases and Néel's order formations are probed. In good agreement with model calculations, the anti-ferromagnetic phase in regular Cayley trees and frustrated competing ground-states in a dual-center Cayley tree are directly observed. This demonstrates the possibilities of high-dimensional qubit connection programming in quantum simulators.

quant-ph↗

arXiv2021

Nonlocal adhesion models for two cancer cell phenotypes in a multidimensional bounded domain

Cell-cell adhesion is an inherently nonlocal phenomenon. Numerous partial differential equation models with nonlocal term have been recently presented to describe this phenomenon, yet the mathematical properties of nonlocal adhesion model are not well understood. Here we consider a model with two kinds of nonlocal cell-cell adhesion, satisfying no-flux conditions in a multidimensional bounded domain. We show global-in-time well-posedness of the solution to this model and obtain the uniform boundedness of solution.

math.AP↗

arXiv2021

Global well-posedness of logarithmic Keller-Segel type systems

We consider a class of logarithmic Keller-Segel type systems modeling the spatio-temporal behavior of either chemotactic cells or criminal activities in spatial dimensions two and higher. Under certain assumptions on parameter values and given functions, the existence of classical solutions is established globally in time, provided that initial data are sufficiently regular. In particular, we enlarge the range of chemotatic sensitivity $χ$, compared to known results, in case that spatial dimensions are between two and eight. In addition, we provide new type of small initial data to obtain global classical solution, which is also applicable to the urban crime model. We discuss long-time asymptotic behaviors of solutions as well.

math.AP↗

arXiv2020

Quantum-Ising Hamiltonian programming in trio, quartet, and sextet qubit systems

Rydberg-atom quantum simulators are of keen interest because of their possibilities towards high-dimensional qubit architectures. Here we report three-dimensional conformation spectra of quantum-Ising Hamiltonian systems with programmed qubit connections. With a Rydberg-atom quantum simulator, various connected graphs, in which vertices and edges represent atoms and blockaded couplings, respectively, are constructed in two or three-dimensional space and their eigenenergies are probed during their topological transformations. Star, complete, cyclic, and diamond graphs, and their geometric intermediates, are tested for four atoms and antiprism structures for six atoms. Spectroscopic resolution (dE/E) less than 10% is achieved and the observed energy level shifts and merges through structural transformations are in good agreement with the model few-body quantum-Ising Hamiltonian.

quant-ph↗

arXiv2019

Rydberg atom entanglements in the weak coupling regime

We present an entanglement scheme for Rydberg atoms using the van der Waals interaction phase induced by Ramsey-type pulsed interactions. This scheme realizes not only controlled phase operations between atoms at a distance larger than Rydberg blockade distance, but also various counter-intuitive entanglement examples, including two-atom entanglement in the presence of a closer third atom and $W$-state generation for partially-blockaded three atoms. Experimental realization is conducted with single rubidium atoms loaded in an array of optical tweezer dipole traps, to demonstrate the proposed entanglement generations and measurements.

physics.atom-ph↗

arXiv2019

Ultrafast time-scale Berry-phase gates of atomic clock states

Extremely fast qubit controls can greatly reduce the calculation time in quantum computation, and potentially resolve the finite-time decoherence issues in many physical systems. Here, we propose and experimentally demonstrate pico-second time-scale controls of atomic clock state qubits, using Berry-phase gates implemented with a pair of chirped laser pulses. While conventional methods of microwave or Raman transitions do not allow atomic qubit controls within a time faster than the hyperfine free evolution period, our approach of ultrafast Berry-phase gates accomplishes fast clock-state operations. We also achieves operational robustness against laser parametric noises, since geometric phases are determined by adiabatic evolution pathway only, without being affected by any dynamic details. The experimental implementation is conducted with two linearly polarized, chirped ultrafast optical pulses, interacting with five single rubidium atoms in an array of optical tweezer dipole traps, to demonstrate the proposed ultrafast clock-state gates and their operational robustness.

quant-ph↗

arXiv2019

Coherent and dissipative dynamics of entangled few-body systems of Rydberg atoms

Experimentally observed quantum few-body dynamics of neutral atoms excited to a Rydberg state are numerically analyzed with Lindblad master equation formalism. For this, up to five rubidium atoms are trapped with optical tweezers, arranged in various two-dimensional configurations, and excited to Rydberg 67S state in the nearest-neighbor blockade regime. Their coherent evolutions are measured with time-varying ground-state projections. The experimental results are analyzed with a model Lindblad equation with the homogeneous and inhomogeneous dampings determined by systematic and statistical error analysis. The coherent evolutions of the entangled systems are successfully reproduced by the resulting model analysis for the experimental results with optimal parameters in consistent with external calibrations.

physics.atom-ph↗

arXiv2018

Subpicosecond $X$ rotations of atomic clock states

We demonstrate subpicosecond-time-scale population transfer between the pair of hyperfine ground states of atomic rubidium using a single laser-pulse. Our scheme utilizes the geometric and dynamic phases induced during Rabi oscillation through the fine-structure excited state in order to construct an $X$ rotation gate for the hyperfine-state qubit system. Experiment performed with a femtosecond laser and cold rubidium atoms, in a magneto-optical trap, shows over 98\% maximal population transfer between the clock states.

physics.atom-ph↗

arXiv2018

Leakage suppression by ultrafast pulse shaping

We consider the leakage suppression problem of a three-level system in which the first two levels are the qubit system and the third, weakly-coupled to the second, is the leakage state. We show that phase- and amplitude-controlled two (three) pulses are sufficient for arbitrary qubit controls from the ground (an arbitrary) initial state, with leakage suppressed up to the first order of perturbation without additional pulse-area cost. A proof-of-principle experiment was performed with shaped femtosecond optical pulses and atomic rubidium showing a good agreement with the theory.

physics.atom-ph↗

arXiv2017

Detailed Balance of Thermalization dynamics in Rydberg atom quantum simulators

Dynamics of large complex systems, such as relaxation towards equilibrium in classical statistical mechanics, often obeys a master equation. The equation significantly simplifies the complexities but describes essential information of occupation probabilities. A related fundamental question is the thermalization, a coherent evolution of an isolated many-body quantum state into a state that seems to be in thermal equilibrium. It is valuable to find an effective equation describing this complex dynamics. Here, we experimentally investigate the question by observing sudden quench dynamics of quantum Ising-like models implemented in our quantum simulator, defect-free single-atom tweezers in conjunction with Rydberg atom interaction. We find that saturation of local observables, a thermalization signature, obeys a master equation experimentally constructed by time-resolved monitoring the occupation probabilities of prequench states and imposing the principle of the detailed balance. Our experiment agrees with theories, and demonstrates the detailed balance in a thermalization dynamics that does not require coupling to baths or postulated randomness.

quant-ph↗

arXiv2017

Doppler-free coherent-control spectroscopy with a colliding pair of shaped pulses

We demonstrate the use of the ultrafast spatial coherent-control method to resolve the fine-structure two-photon transitions of atomic rubidium. Counter-propagating ultrafast optical pulses with spectral phase and amplitude programmed with our optimized solutions successfully induced the two-photon transitions through $5S_{1/2}$-$5P_{1/2}$-$5D$ and $5S_{1/2}$-$5P_{3/2}$-$5D$ pathways, both simultaneously and at distinct spatial locations. Three different pulse-shaping solutions are introduced that combine amplitude shaping, which avoids direct intermediate resonances, and phase programming, which enables the remaining spectral components to be coherently interfered through the targeted transition pathways. Experiments were performed with a room-temperature vapor cell, and the results agree well with theoretical analysis.

physics.atom-ph↗