arXiv subjects

Eunmi Chae

Publications and source records attributed to Eunmi Chae.

At least 19 recordsLinked to original sources

arXiv2026

High-fidelity entanglement of polar molecules by dynamic geometric control

In quantum information systems made of optical tweezer arrays of ultracold molecules, thermal motion of molecules degrades the coherence of their interactions, which limits entanglement fidelity and the concomitant scientific applicability of these systems. We show that by controlling the geometry of the dipolar interaction, even when a molecule occupies many motional states in the tweezer, coherence can be preserved. We characterize several geometries that suppress sensitivity to thermal fluctuations. We further use programmable, coherence-preserving motion of the molecules during entanglement to refocus dephasing from relative positional jitter of the tweezers, which is relevant even on the 10 nm scale. These methods yield substantially improved dipolar coherence and enable generation of two-molecule entanglement with a Bell state fidelity of $\mathcal{F}= 0.976^{+0.008}_{-0.011}$ in directly laser-cooled molecules.

physics.atom-ph↗

arXiv2026

Spectroscopy of the $\mathbf{X^2\Sigma^+(v=2) \rightarrow A^2\Pi_{1/2}(v=1)}$ Transition in MgF: Hyperfine Structures and Spectroscopic Constants

We report spectroscopic results of the $X^2\Sigma^+(v=2) \rightarrow A^2\Pi_{1/2}(v=1)$ transition in magnesium monofluoride (MgF). Using Doppler-free Laser-Induced Fluorescence (LIF) spectroscopy on the $X^2\Sigma^+(v=2) \rightarrow A^2\Pi_{1/2}(v=1)$ transition, we resolved 47 hyperfine components distributed over 11 transition lines in X and A states. An effective Hamiltonian -- comprising contributions from vibrational, rotational, $\Lambda$-doubling, and hyperfine interactions -- was presented to model the energy structure of the $A^2\Pi_{1/2}(v=1)$ state. The spectroscopic parameters, including the rotational constant, the $\Lambda$-doubling parameter, and the hyperfine interaction constants, were extracted using a least-square fitting and Markov Chain Monte Carlo (MCMC) procedure. Our study reveals that the spectroscopic constants show subtle changes compared to the $A^2\Pi_{1/2}(v=0)$ state. These results provide critical spectroscopic benchmarks for optimizing optical cycling schemes in MgF, thereby advancing optical cycling efficiency in the magneto-optical trapping of MgF.

physics.atom-ph↗

arXiv2025

Optimization of experimental parameters for laser-slowing and magneto-optical trapping of MgF molecules

Diatomic molecules are promising systems for quantum science applications due to their complex energy structures and strong dipole-dipole interactions. Achieving ultracold temperatures is essential for these applications, but the complexity of molecular energy levels requires precise optimization of experimental parameters for laser slowing and magneto-optical trapping (MOT). Here, we simulate and optimize the complete process of slowing and trapping MgF molecules, from a buffer-gas beam source to MOT capture, using Bayesian optimization. By combining laser slowing and MOT simulations, we identify parameters that maximize the capture velocity and the ratio of trapped molecules. Our results demonstrate a maximum MOT capture velocity of 82.5 m/s, and 28.6% of the molecules that reach the MOT region are trapped under optimal conditions. These findings provide insights into experimental setups for MgF and similar molecules, offering a framework for advancing molecular laser cooling and quantum experiments.

physics.atom-ph↗

arXiv2025

Optical cycling of MgF molecules within the hyperfine states in X(N=1) state

We investigated the optical cycling effect of the $\mathrm{X}^2\Sigma(v=0,\ N=1^-) - \mathrm{A}^2\Pi_{1/2}(v'=0,\ J'=1/2^+)$ band of MgF molecules, specifically the $\mathrm{P_1/Q_{12}(1)}$ transition, which serves as the main transition in the quasi-closed cycling scheme for the laser cooling. A higher number of scattered photons was observed when all three frequency components of the $\mathrm{P_1/Q_{12}(1)}$ transition were simultaneously applied using acousto-optic modulators (AOMs). Optimal conditions were identified by scanning the detuning of frequency components, the laser beam power ratio, and the total laser beam power, and the results were confirmed through rate equation simulations. Under these optimized conditions, and with an applied magnetic field, the scattering rate was enhanced by approximately a factor of six. These results refine the implementation of optical cycling in MgF and lay the groundwork for laser slowing and magneto-optical trapping (MOT) experiments.

physics.atm-clus↗

arXiv2024

A conveyor-belt magneto-optical trap of CaF

We report the experimental realization of a conveyor-belt magneto-optical trap for calcium monofluoride (CaF) molecules. The obtained highly-compressed cloud has a mean radius of 64(5) $\mu$m and a peak number density of $3.6(5) \times 10^{10}$ cm$^{-3}$, a 600-fold increase over the conventional red-detuned MOTs of CaF, and the densest molecular MOT observed to date. Subsequent loading of these molecules into an optical dipole trap yields up to $2.6 \times 10^4$ trapped molecules at a temperature of 14(2) $\mu$K with a peak phase-space density of $\sim 2.4 \times 10^{-6}$. This opens new possibilities for a range of applications utilizing high-density, optically trapped ultracold molecules.

physics.atom-ph↗

arXiv2024

Machine learning-enhanced optical tweezers for defect-free rearrangement

Optical tweezers constitute pivotal tools in Atomic, Molecular, and Optical(AMO) physics, facilitating precise trapping and manipulation of individual atoms and molecules. This process affords the capability to generate desired geometries in both one-dimensional and two-dimensional spaces, while also enabling real-time reconfiguration of atoms. Due to stochastic defects in these tweezers, which cause catastrophic performance degradation especially in quantum computations, it is essential to rearrange the tweezers quickly and accurately. Our study introduces a machine learning approach that uses the Proximal Policy Optimization model to optimize this rearrangement process. This method focuses on efficiently solving the shortest path problem, ensuring the formation of defect-free tweezer arrays. By implementing machine learning, we can calculate optimal motion paths under various conditions, resulting in promising results in model learning. This advancement presents new opportunities in tweezer array rearrangement, potentially boosting the efficiency and precision of quantum computing research.

physics.atom-ph↗

arXiv2023

Comprehensive peak-width analysis in matter-wave diffraction under grazing incidence conditions

Thermal energy atom scattering at a surface with grazing incidence conditions is an innovative method for investigating dispersive atom-surface interactions with potential application in quantum sensing interferometry. The complete establishment of this technique would require a detailed peak analysis, which has yet to be achieved. We examined peak-width fluctuations in atomic and molecular beams diffracted by a grating under grazing incidence conditions. Careful measurements and analyses of the diffraction patterns of He atoms and D$_2$ molecules from three square-wave gratings with different periods and radii of curvature enabled the identification of factors influencing the variations in the width as a function of the grazing incidence angle. The effects of macroscopic surface curvature, grating magnification, and beam emergence are substantial under these conditions but negligible for incidence angles close to the normal. Our results shed light on the phenomena occurring in grazing incidence thermal energy atom scattering.

physics.atom-ph↗

arXiv2023

Raman sideband cooling of molecules in an optical tweezer array to the 3-D motional ground state

Ultracold polar molecules are promising for quantum information processing and searches for physics beyond the Standard Model. Laser cooling to ultracold temperatures is an established technique for trapped diatomic and triatomic molecules. Further cooling of the molecules to near the motional ground state is crucial for reducing various dephasings in quantum and precision applications. In this work, we demonstrate Raman sideband cooling of CaF molecules in optical tweezers to near their motional ground state, with average motional occupation quantum numbers of $\bar{n}_{x}=0.16(12)$, $\bar{n}_{y}=0.17(17)$ (radial directions), $\bar{n}_{z}=0.22(16)$ (axial direction) and a 3-D motional ground state probability of $54\pm18\%$. This paves the way to increase molecular coherence times in optical tweezers for robust quantum computation and simulation applications.

physics.atom-ph↗

arXiv2022

Laser cooling of molecules

A recent progress on laser cooling of molecules is summarized. Since the development during 1980s for atomic species, laser cooling has been the very beginning step to cool and trap atoms for frontier research on quantum simulations, quantum sensing and precision measurements. Despite the complex internal structures of molecules, laser cooling of molecules have been realized with the deepened understanding of molecular structures and interaction between light and molecules. The development of laser technology over the last decades have also been a great aid for laser cooling of molecules because many lasers are necessary to successfully cool the molecules. A detailed principle and development of laser cooling of molecules as well as the current status of the field are reviewed to give an introductory of the growing field of ultracold molecular physics.

physics.atom-ph↗

arXiv2022

Dipolar spin-exchange and entanglement between molecules in an optical tweezer array

Due to their intrinsic electric dipole moments and rich internal structure, ultracold polar molecules are promising candidate qubits for quantum computing and for a wide range of quantum simulations. Their long-lived molecular rotational states form robust qubits while the long-range dipolar interaction between molecules provides quantum entanglement. Using a molecular optical tweezer array, single molecules can be moved and separately addressed for qubit operations using optical and microwave fields, creating a scalable quantum platform. Here, we demonstrate long-range dipolar spin-exchange interactions in pairs of CaF molecules trapped in an optical tweezer array. We control the anisotropic interaction and realize the spin-$\frac{1}{2}$ quantum XY model by encoding an effective spin-$\frac{1}{2}$ system into the rotational states of the molecules. We demonstrate a two-qubit (two-molecule) gate to generate entanglement deterministically, an essential resource for all quantum information applications. Employing interleaved tweezer arrays, we demonstrate high fidelity single site molecular addressability.

physics.atom-ph↗

arXiv2022

Fast optical transport of ultracold molecules over long distances

Optically trapped laser-cooled polar molecules hold promise for new science and technology in quantum information and quantum simulation. Large numerical aperture optical access and long trap lifetimes are needed for many studies, but these requirements are challenging to achieve in a magneto-optical trap (MOT) vacuum chamber that is connected to a cryogenic buffer gas beam source, as is the case for all molecule laser cooling experiments so far. Long distance transport of molecules greatly eases fulfilling these requirements as molecules are placed into a region separate from the MOT chamber. We realize a fast transport method for ultracold molecules based on an electronically focus-tunable lens combined with an optical lattice. The high transport speed is achieved by the 1D red-detuned optical lattice, which is generated by interference of a focus-tunable laser beam and a focus-fixed laser beam. Efficiency of 48(8)% is realized in the transport of ultracold calcium monofluoride (CaF) molecules over 46 cm distance in 50 ms, with a moderate heating from 32(2) μK to 53(4) μK. Positional stability of the molecular cloud allows for stable loading of an optical tweezer array with single molecules.

physics.atom-ph↗

arXiv2022

Dual optical frequency combs with ultra-low relative phase jitters from 550 nm to 1020 nm for precision spectroscopy

Here, ultra-low relative phase jitters over a wide optical spectrum were achieved for dual Ti:Sapphire optical frequency combs. The two optical frequency combs were independently phase-locked to a Sr optical lattice clock laser delivered through a commercial optical fiber network. We confirmed that the relative phase jitters between the two combs integrated from 8.3 mHz to 200 kHz were below 1 rad, corresponding to a relative linewidth of below 8.3 mHz, over the entire wavelength of the optical frequency combs ranging from 550 nm to 1020 nm. Our work paves the way for ultrahigh-precision dual-comb spectroscopy covering a wide optical spectral range with a simple setup, and provides an absolute optical frequency reference with great stability over a wide range of wavelengths.

physics.optics↗

arXiv2021

Rotational Coherence Times of Polar Molecules in Optical Tweezers

Qubit coherence times are critical to the performance of any robust quantum computing platform. For quantum information processing using arrays of polar molecules, a key performance parameter is the molecular rotational coherence time. We report a 93(7) ms coherence time for rotational state qubits of laser cooled CaF molecules in optical tweezer traps, over an order of magnitude longer than previous systems. Inhomogeneous broadening due to the differential polarizability between the qubit states is suppressed by tuning the tweezer polarization and applied magnetic field to a "magic" angle. The coherence time is limited by the residual differential polarizability, implying improvement with further cooling. A single spin-echo pulse is able to extend the coherence time to nearly half a second. The measured coherence times demonstrate the potential of polar molecules as high fidelity qubits.

physics.atom-ph↗

arXiv2021

Observation of Microwave Shielding of Ultracold Molecules

Harnessing the potential wide-ranging quantum science applications of molecules will require control of their interactions. Here, we use microwave radiation to directly engineer and tune the interaction potentials between ultracold calcium monofluoride (CaF) molecules. By merging two optical tweezers, each containing a single molecule, we probe collisions in three dimensions. The correct combination of microwave frequency and power creates an effective repulsive shield, which suppresses the inelastic loss rate by a factor of six, in agreement with theoretical calculations. The demonstrated microwave shielding shows a general route to the creation of long-lived, dense samples of ultracold molecules and evaporative cooling.

physics.atom-ph↗

arXiv2021

A compact green Ti:Sapphire astro-comb with 43-GHz repetition frequency

A compact green astro-comb with 43-GHz repetition rate is developed based on a Ti:Sapphire optical frequency comb (OFC) and a mode-selecting cavity. The OFC's large repetition rate of 1.6 GHz eases the requirements for the mode-selecting cavity. Unnecessary frequency-modes of the OFC are suppressed down to $5 \times 10^{-4}$ at 535 nm - 550 nm using a single mode-selecting cavity with 70-MHz linewidth. The radial velocity precision $σ\sim 1.4$ m/s is achieved at the High Dispersion Echelle Spectrosraph for the Okayama 188-cm telescope of the National Astronomical Observatory of Japan using our astro-comb. With further improvements of the mode-selecting cavity and removal of fiber modal noises, our system will provide a simple, compact, and precise astro-comb setup in visible wavelength region.

astro-ph.IM↗

arXiv2020

Entanglement via rotational blockade of MgF molecules in a magic potential

Diatomic polar molecules are one of the most promising platforms of quantum computing due to their rich internal states and large electric dipole moments. Here, we propose entangling rotational states of adjacent polar molecules via a strong electric dipole-dipole interaction. The splitting of 1.27 kHz between two entangled states is predicted for MgF molecules in an optical tweezer array. The resolution of the entangled states can be achieved in a magic potential for the molecules where the rotational states have the same trap frequencies. The magic potential can be formed by tuning the angle between the molecules' quantization axis and the linear polarization of trapping light, so-called magic angle. We calculate the magic angle for MgF molecules in a reasonable experimental condition and obtain that the trap frequencies of the two involved states can be matched within a few 10s of Hz. Establishing entanglement between molecules, our results provide a first step towards quantum computing using diatomic polar molecules.

physics.atom-ph↗

arXiv2019

Direct Phase Locking of a Ti:Sapphire Optical Frequency Comb to a Remote Optical Frequency Standard

We report on an ultralow noise optical frequency transfer from a remotely located Sr optical lattice clock laser to a Ti:Sapphire optical frequency comb through telecom-wavelength optical fiber networks. The inherent narrow linewidth of the Ti:Sapphire optical frequency comb eliminates the need for a local reference high-finesse cavity. The relative fractional frequency instability of the optical frequency comb with respect to the remote optical reference was $6.7(1) \times 10^{-18}$ at 1 s and $1.05(3) \times 10^{-19}$ at 1,000 s including a 2.9 km-long fiber network. This ensured the optical frequency comb had the same precision as the optical standard. Our result paves the way for ultrahigh-precision spectroscopy and conversion of the highly precise optical frequency to radio frequencies in a simpler setup.

physics.ins-det↗

arXiv2017

Radio Frequency Magneto-Optical Trapping of CaF with High Density

We demonstrate significantly improved magneto-optical trapping of molecules using a very slow cryogenic beam source and RF modulated and DC magnetic fields. The RF MOT confines $1.1(3) \times 10^5$ CaF molecules at a density of $4(1) \times 10^6$ cm$^{-3}$, which is an order of magnitude greater than previous molecular MOTs. Near Doppler-limited temperatures of $340(20)$ $μ$K are attained. The achieved density enables future work to directly load optical tweezers and create optical arrays for quantum simulation.

physics.atom-ph↗