arXiv subjects

Hanlae Jo

Publications and source records attributed to Hanlae Jo.

8 recordsLinked to original sources

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

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

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↗

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↗