arXiv subjects

Boon Long Ng

Publications and source records attributed to Boon Long Ng.

4 recordsLinked to original sources

arXiv2026

Narrowband four-photon states from spontaneous four-wave mixing

We observe time-correlated four photons within a correlation window of 20ns from spontaneous four-wave mixing via a double-Lambda scheme in a cold cloud of Rb-87 atoms. In contrast to high-power pulsed pumping of chi^(2) nonlinear processes in crystals, our scheme generates correlated four-photon states by direct continuous-wave pumping at nominal powers. We verify the presence of genuinely correlated four-photon states over accidentals by higher-order intensity cross-correlation measurements and accidental subtraction. We infer a time-correlated four-photon generation rate of 2.5(4)x10^6 counts per second close to saturation. The photons produced are near-resonant with atomic transitions, and have a bandwidth in the order of MHz, making them readily compatible with quantum networking applications involving atoms.

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arXiv2023

Fano Resonance in Excitation Spectroscopy and Cooling of an Optically Trapped Single Atom

Electromagnetically induced transparency (EIT) can be used to cool an atom in a harmonic potential close to the ground state by addressing several vibrational modes simultaneously. Previous experimental efforts focus on trapped ions and neutral atoms in a standing wave trap. In this work, we demonstrate EIT cooling of an optically trapped single neutral atom, where the trap frequencies are an order of magnitude smaller than in an ion trap and a standing wave trap. We resolve the Fano resonance feature in fluorescence excitation spectra and the corresponding cooling profile in temperature measurements. A final temperature of around 6 $μ$K is achieved with EIT cooling, a factor of two lower than the previous value obtained using olarization gradient cooling.

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arXiv2022

Observation of the Mollow Triplet from an optically confined single atom

Resonance fluorescence from atomic systems consists of a single spectral peak that evolves into a Mollow triplet for a strong excitation field. Photons from different peaks of the triplet show distinct photon correlation that make the fluorescence a useful light source for quantum information purpose. We characterize the fluorescence of a single optically trapped $^{87}$Rb atom that is excited resonantly at different power levels. Second-order correlation measurements reveal the single photon nature of the fluorescence concurrently with Rabi oscillations of a strongly excited atom. The asymmetry in correlations between photons from two sidebands of the fluorescence spectrum when the atom is exposed to an off-resonant field further indicates that there is a preferred time-ordering of the emitted photons from different sidebands.

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arXiv2020

Coherence of a dynamically decoupled single neutral atom

Long qubit coherence and efficient atom-photon coupling are essential for advanced applications in quantum communication. One technique to maintain coherence is dynamical decoupling, where a periodic sequence of refocusing pulses is employed to reduce the interaction of the system with the environment. We experimentally study the implementation of dynamical decoupling on an optically-trapped, spin-polarized $^{87}$Rb atom. We use the two magnetic-sensitive $5S_{1/2}$ Zeeman levels, $\lvert{F=2,\ m_{F}=-2}\rangle$ and $\lvert{F=1,\ m_{F}=-1}\rangle$ as qubit states, motivated by the possibility to couple $\lvert{F=2,\ m_{F}=-2}\rangle$ to $5P_{3/2}$ the excited state $\lvert{F'=3,\ m'_{F}=-3}\rangle$ via a closed optical transition. With more refocusing pulses in the dynamical decoupling technique, we manage to extend the coherence time from 38(3)$μ$s to more than two milliseconds. We also observe a strong correlation between the motional states of the atom and the qubit coherence after the refocusing, which can be used as a measurement basis to resolve trapping parameters.

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