Browsing by Author "Dong, Lin"
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Item Cavity-assisted dynamical spin-orbit coupling in cold atoms(American Physical Society, 2014) Dong, Lin; Zhou, Lu; Wu, Biao; Ramachandhran, B.; Pu, Han; Rice Quantum InstituteWe consider ultracold atoms subjected to a cavity-assisted two-photon Raman transition. The Raman coupling gives rise to effective spin-orbit interaction which couples the atom's center-of-mass motion to its pseudospin degrees of freedom. Meanwhile, the cavity photon field is dynamically affected by the atom. This feedback between the atom and photons leads to a dramatic modification of the atomic dispersion relation, and further leads to dynamical instability of the system. We propose to detect the change in the cavity photon number as a direct way to demonstrate dynamical instability.Item Effects of spin-orbit coupling on Jaynes-Cummings and Tavis-Cummings models(American Physical Society, 2016) Zhu, Chuanzhou; Dong, Lin; Pu, Han; Rice Center for Quantum MaterialsWe consider ultracold atoms inside a ring optical cavity that supports a single plane-wave mode. The cavity field, together with an external coherent laser field, drives a two-photon Raman transition between two internal pseudospin states of the atom. This gives rise to an effective coupling between atom's pseudospin and external center-of-mass (COM) motion. For the case of a single atom inside the cavity, We show how the spin-orbit coupling modifies the static and dynamic properties of the Jaynes-Cummings (JC) model. In the case of many atoms in thermodynamic limit, we show that the spin-orbit coupling modifies the Dicke superradiance phase transition boundary and the non-superradiant normal phase may become reentrant in some regimes.Item Gapless topological Fulde-Ferrell superfluidity induced by an in-plane Zeeman field(American Physical Society, 2014) Hu, Hui; Dong, Lin; Cao, Ye; Pu, Han; Liu, Xia-JiTopological superfluids are recently discovered quantum matter that hosts topologically protected gapless edge states known as Majorana fermions—exotic quantum particles that act as their own antiparticles and obey non-Abelian statistics. Their realizations are believed to lie at the heart of future technologies such as fault-tolerant quantum computation. To date, the most efficient scheme to create topological superfluids and Majorana fermions is based on the Sau-Lutchyn-Tewari-Das Sarma model with a Rashba-type spin-orbit coupling on the x-y plane and a large out-of-plane (perpendicular) Zeeman field along the z direction. Here we propose an alternative setup, where the topological superfluid phase is driven by applying an in-plane Zeeman field. This scheme offers a number of different features, notably Cooper pairings at finite center-of-mass momentum (i.e., Fulde-Ferrell pairing) and gapless excitations in the bulk. As a result, gapless topological quantum matter with an inhomogeneous pairing order parameter appears. It features unidirectional Majorana surface states at boundaries, which propagate in the same direction and connect two Weyl nodes in the bulk. We demonstrate the emergence of such exotic topological matter and the associated Majorana fermions in spin-orbit coupled atomic Fermi gases, and we determine its parameter space. The implementation of our scheme in semiconductor/superconductor heterostructures is briefly discussed.Item Germanium/silicon of the Ediacaran-Cambrian Laobao cherts: Implications for the bedded chert formation and paleoenvironment interpretations(American Geophysical Union, 2015) Dong, Lin; Shen, Bing; Lee, Cin-Ty A.; Shu, Xu-jie; Peng, Yang; Sun, Yuanlin; Tang, Zhuanhong; Rong, Hong; Lang, Xianguo; Ma, Haoran; Yang, Fan; Guo, WenSedimentary strata of the terminal Ediacaran (635–542 Ma) to early Cambrian (542–488 Ma) Laobao-Liuchapo bedded cherts in the South China Block include the Ediacaran Oxidation Event and the Cambrian explosion. Understanding the origin and depositional environment of the bedded cherts may provide insight into how the Earth's surface environment changed between the Proterozoic and Phanerozoic. We measured major and trace element compositions and Ge/Si ratios of the Laobao cherts from northern Guangxi province. The Laobao cherts were deposited in the deep basinal environment of the South China Block. We show that the composition of the Laobao cherts is determined by a mixture of four components: quartz, clay, carbonate, and pyrite/iron-oxide. The quartz component is the dominant component of the Laobao cherts. The maximum estimated Ge/Si of the quartz component is between 0.4 and 0.5 μmol/mol, which is close to the Ge/Si of modern seawater and biogenic silica but 1 order of magnitude lower than that of hydrothermal fluids. These Ge/Si systematics suggest that normal seawater rather than mid-ocean ridge hydrothermal fluids is the primary Si source for the Laobao cherts. The Ge/Si of the clay component varies between 1 and 10 μmol/mol, which is comparable to the Ge/Si of typical marine clays, but 10–100 times lower than that of chert nodules from early Ediacaran beds (the Doushantuo Formation) predating the terminal Ediacaran Laobao cherts studied here. Our observations indicate that the clay component Ge/Si ratio decreased from the early Ediacaran to the late Ediacaran. We speculate that high Ge/Si ratios in clays reflect the preferential chelation of Ge by dissolved organic compounds adsorbed onto clays. If so, this suggests that the decrease in Ge/Si ratio of the clay component in the Ediacaran signifies a decrease in the total dissolved organic carbon content of seawater toward the Ediacaran-Cambrian transition, consistent with oxidation of the oceans during the late Ediacaran. Finally, the seawater origin of the Laobao cherts also suggests that replacement of carbonate may not be the primary cause for bedded chert formation. Instead, direct precipitation from seawater or early diagenetic silicification of calcareous sediments, perhaps due to the emergence of Si-accumulation bacteria, may have been responsible for the bedded Laobao-Liuchapo chert formation in South China Block.Item Synthetic Spin-Orbit and Light Field Coupling in Ultra-cold Quantum Gases(2017-04-19) Dong, Lin; Pu, HanUltra-cold quantum gases subjected to light-induced synthetic gauge potentials have become an emergent field of theoretical and experimental studies. Because of the novel application of two-photon Raman transitions, ultra-cold neutral atoms behave like charged particles in magnetic field. The Raman coupling naturally gives rise to an effective spin-orbit interaction which couples the atom’s center-of-mass motion to its selected pseudo-spin degrees of freedom. Combined with unprecedented controllability of interactions, geometry, disorder strength, spectroscopy, and high resolution measurement of momentum distribution, etc., we are truly in an exciting era of ful- filling and going beyond Richard Feynman’s vision of realizing quantum simulators to better understand the quantum mechanical nature of the universe, manifested immensely in the ultra-cold regimes. In this dissertation, we present a collection of theoretical progresses made by the doctoral candidate and his colleagues and collaborators. From the past few years of work, we mainly address three aspects of the synthetic spin-orbit and light field induced coupling in ultracold quantum gases: a) The ground-state physics of single- particle system, two-body bound states, and many-body systems, all of which are subjected to spin-orbit coupling originated from synthetic gauge potentials; b) The symmetry breaking, topological phase transition and quench dynamics, which are conveniently offered by the realized experimental setup; c) The proposal and impli- cations of light field induced dynamical spin-orbit coupling for atoms inside optical cavity. Our work represents an important advancement of theoretical understanding to the active research frontier of ultra-cold atom physics with spin-orbit coupling.