arXiv subjects

Han-gyeol Lee

Publications and source records attributed to Han-gyeol Lee.

9 recordsLinked to original sources

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↗

arXiv2017

Robust two-level system control by a detuned and chirped laser pulse

We propose and demonstrate a robust control scheme by ultrafast nonadiabatic chirped laser pulse, designed for targeting coherent superpositions of two-level systems. Robustness against power fluctuation is proved by our numerical study and a proof-of-principle experiment performed with femtosecond laser interaction on cold atoms. They exhibit for the final driven dynamics a cusp on the Bloch sphere, corresponding to a zero curvature of fidelity. This solution is particularly simple and thus applicable to a wide range of potential applications.

quant-ph↗

arXiv2017

Single-laser-pulse implementation of arbitrary ZYZ rotations of an atomic qubit

Arbitrary rotation of a qubit can be performed with a three-pulse sequence; for example, ZYZ rotations. However, this requires precise control of the relative phase and timing between the pulses, making it technically challenging in optical implementation in a short time scale. Here we show any ZYZ rotations can be implemented with a single laser-pulse, that is {\it a chirped pulse with a temporal hole}. The hole of this shaped pulse induces a non-adiabatic interaction in the middle of the adiabatic evolution of the chirped pulse, converting the central part of an otherwise simple Z-rotation to a Y rotation, constructing ZYZ rotations. The result of our experiment performed with shaped femtosecond laser pulses and cold rubidium atoms shows strong agreement with the theory.

physics.atom-ph↗

arXiv2016

Selective excitation in a three-state system using a hybrid adiabatic-nonadiabatic interaction

The chirped-pulse interaction in the adiabatic coupling regime induces cyclic permutations of the energy states of a three-level system in the $V$-type configuration, which process is known as the three-level chirped rapid adiabatic passage. Here we show that a spectral hole in a chirped pulse can turn on and off one of the two adiabatic crossing points of this process, reducing the system to an effective two-level system. The given hybrid adiabatic-nonadiabatic transition results in selective excitation of the three-level system, controlled by the laser intensity and spectral position of the hole as well as the sign of the chirp parameter. Experiments are performed with shaped femtosecond laser pulses and the three lowest energy-levels (5S$_{1/2}$, 5P$_{1/2}$, and 5P$_{3/2}$) of atomic rubidium ($^{85}$Rb), of which the result shows good agreement with the theoretically analyzed dynamics. The result indicates that our method, being combined with the ordinary chirped-RAP, implements an adiabatic transitions between the two excited states. Furthermore the laser intensity-dependent control may have applications including selective excitations of atoms or ions arranged in space when being used in conjunction with laser beam profile programming.

physics.atom-ph↗

arXiv2016

In situ single-atom array synthesis by dynamic holographic optical tweezers

Cooling and trapping of atoms by light has enabled one to build and manipulate quantum systems at the single atom level. Such a bottom-up approach becomes one of the fascinating challenges toward scalable and highly controllable quantum systems, e.g., a large-scale quantum information machine. Their implementation requires crucial pre-requisites: scalablity, site distinguishability, and reliable single-atom loading into sites. The widely adopted methods satisfies the two former conditions relatively well, but the last condition, filling single atoms onto individual sites, relies mostly on the probabilistic loading, implying that loading a pre-defined set of atoms in given positions will be hampered exponentially. Two approaches are readily thinkable to overcome this issue: increasing the single-atom loading efficiency and relocating abundant atoms into unfilled positions. Realizing the relocation is directly related to how many atoms can be transportable in a designer way. Here, we demonstrate a dynamic holographic single-atom tweezers with unprecedented degrees of freedom of 2N. In a proof-of-principle experiment conducted with cold rubidium atoms, simultaneous rearrangements of N=9 single atoms are successfully performed. This method may be further applicable to deterministic N single-atom loading, coherent transport, and controlled collisions.

physics.atom-ph↗

arXiv2016

Quantum dynamics of a two-state system induced by a chirped zero-area pulse

It is well known that area pulses make Rabi oscillation and chirped pulses in the adiabatic interaction regime induce complete population inversion of a two-state system. Here we show that chirped zero-area pulses could engineer an interplay between the adiabatic evolution and Rabi-like oscillations. In a proof-of-principle experiment utilizing spectral chirping of femtosecond laser pulses with a resonant spectral hole, we demonstrate that the chirped zero-area pulses could induce, for example, complete population inversion and return of the cold rubidium atom two-state system. Experimental result agrees well with the theoretically considered overall dynamics, which could be approximately modeled to a Ramsey-like three-pulse interaction, where the $x$- and $z$- rotations are respectively driven by the hole and the main pulse.

physics.atom-ph↗

arXiv2015

Rabi oscillations of Morris-Shore transformed $N$-state systems by elliptically polarized ultrafast laser pulses

We present an experimental investigation of ultrafast-laser driven Rabi oscillations of atomic rubidium. Since the broadband spectrum of an ultrafast laser pulse simultaneously couples all the electronic hyperfine transitions between the excited and ground states, the complex excitation linkages involved with the D1 or D2 transition are energy degenerate. Here, by applying the Morris-Shore transformation, it is shown that this multi-state system is reduced to a set of independent two-state systems and dark states. In experiments performed by ultrafast laser interactions of atomic rubidium in the strong interaction regime, we demonstrate that the ultrafast dynamics of the considered multi-state system is governed by a sum of at most two decoupled Rabi oscillations when this system interacts with ultrafast laser pulses of any polarization state. We further show the implication of this result to possible controls of photo-electron polarizations.

physics.atom-ph↗

arXiv2014

Ultrafast Rabi oscillation of a Gaussian atom ensemble

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 magneto-optical 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 $R_x(π/2)R_y(π)R_x(π/2)$ to develop a robust method to achieve a higher fidelity population inversion of the atom ensemble.

physics.atom-ph↗

arXiv2011

Optical repumping of triplet $P$-states enhances magneto-optical trapping of ytterbium atoms

Radiative decay from the excited $^1P_1$ state to metastable $^3P_2$ and $^3P_0$ states is expected to limit attainable trapped atomic population in a magneto-optic trap of ytterbium (Yb) atoms. In experiments we have carried out with optical repumping of $^3P_{0,2}$ states to $^3P_1$, we observe enhancement of trapped atoms yield in the excited $^1P_1$ state. The individual decay rate to each metastable state is measured and the results show an excellent agreement with the theoretical values.

physics.atom-ph↗