arXiv subjects

Tong Dang

Publications and source records attributed to Tong Dang.

4 recordsLinked to original sources

arXiv2026

Kelvin-Helmholtz vortices in the Martian +E hemisphere downstream of crustal magnetic anomalies

At unmagnetized planetary bodies, the Kelvin-Helmholtz (KH) instability at the solar-wind boundary is a key driver of atmospheric escape, fundamentally shaping long-term climate evolution. This shear-driven plasma mixing is theoretically predicted to be asymmetric, strongly favoring the hemisphere where the solar-wind electric field points toward the planet (-E hemisphere). Here we report the observation of a coherent train of fully developed KH vortices in the traditionally unfavorable +E hemisphere of Mars, using in-situ MAVEN measurements. Contemporaneous upstream constraints from Tianwen-1 confirm a steady interplanetary magnetic field, indicating sustained shear-driven growth rather than a transient boundary response. We find that these vortices developed within an expanded, weak-field boundary layer downstream of strong southern crustal magnetic anomalies. Our analysis suggests that regional boundary structuring can override the large-scale hemispheric preference to facilitate localized KH growth. These findings demonstrate that shear-driven escape pathways can operate in traditionally unfavorable regions, altering our understanding of atmospheric volatile loss at weakly magnetized planets.

astro-ph.EP↗

arXiv2024

Remote Detection Optical Magnetometry

Sensitive magnetometers have been applied in a wide range of research fields, including geophysical exploration, bio-magnetic field detection, ultralow-field nuclear magnetic resonance, etc. Commonly, magnetometers are directly placed at the position where the magnetic field is to be measured. However, in some situations, for example in near space or harsh environments, near nuclear reactors or particle accelerators, it is hard to place a magnetometer directly there. If the magnetic field can be detected remotely, i.e., via stand-off detection, this problem can be solved. As optical magnetometers are based on optical readout, they are naturally promising for stand-off detection. We review various approaches to optical stand-off magnetometry proposed and developed over the years, culminating in recent results on measuring magnetic fields in the mesosphere using laser guide stars, magnetometry with mirrorless-lasing readout, and proposals for satellite-assisted interrogation of atmospheric sodium.

physics.atom-ph↗

arXiv2023

Electrical Tuning of Neutral and Charged Excitons with 1-nm Gate

Electrical control of individual spins and photons in solids is key for quantum technologies, but scaling down to small, static systems remains challenging. Here, we demonstrate nanoscale electrical tuning of neutral and charged excitons in monolayer WSe2 using 1-nm carbon nanotube gates. Electrostatic simulations reveal a confinement radius below 15 nm, reaching the exciton Bohr radius limit for few-layer dielectric spacing. In situ photoluminescence spectroscopy shows gate-controlled conversion between neutral excitons, negatively charged trions, and biexcitons at 4 K. Important for quantum information processing applications, our measurements indicate gating of a local 2D electron gas in the WSe2 layer, coupled to photons via trion transitions with binding energies exceeding 20 meV. The ability to deterministically tune and address quantum emitters using nanoscale gates provides a pathway towards large-scale quantum optoelectronic circuits and spin-photon interfaces for quantum networking.

cond-mat.mes-hall↗

arXiv2021

Satellite-assisted laser magnetometry with mesospheric sodium

Magnetic field sensing provides crucial insights into various geophysical phenomena such as atmospheric currents, crustal magnetism, and oceanic circulation. In this paper, a method for remote detection of magnetic fields using mesospheric sodium with an assisting satellite is proposed. Sodium atoms in the mesosphere are optically pumped with a ground-based laser beam. A satellite-borne detector is used to measure magneto-optical rotation of the polarization of a probe laser beam by the sodium atoms. This sensitive magnetometry method benefits from direct detection of laser photons and complements existing space- and aircraft-borne techniques by probing magnetic fields at upper-atmospheric altitudes inaccessible to those.

physics.atom-ph↗