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Optically synthetic spin-helical particles: an enabling platform for colliding, reacting and engineering novel quantum matters

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Professor Yong Chen, Purdue University
When
19 September 2019 from 3:45 PM to 4:45 PM
Where
117 Osmond
Contact Name
Zhiqiang Mao
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Spin is one of the most fundamental quantum properties of particles. Particles whose spin states are uniquely determined by (or “locked to”) their momentum states – so called “spin-helical” or “spin-less” particles (because the usual spin degeneracy is removed) --- have attracted broad and lasting interests in physics. For example, neutrinos were thought to be such spin-helical particles in the simplest model (with antineutrinos carrying the opposite helicity). In recent years, there have been explosive interests in condensed matter physics in spin-helical electrons (e.g., in “topological insulators”) with potential applications ranging from spintronics to topological quantum computing. In this talk, I will describe how atoms (in our case ultracold 87Rb bosons in a Bose-Einstein condensate, BEC) can be “dressed” into “spin-helical” particles using lasers and microwaves that coherently couple different spin and momentum states, resulting in “synthetic” gauge fields (including spin-orbit coupling, SOC) and “synthetic” dimensions. By performing a “quantum quench” in the optical coupling field, we realize a “quantum fluid collider” between two (dressed) spinor BECs to induce a spin current, and study how such spin transport is affected by SOC, revealing rich phenomena arising from the interplay between quantum interference and many-body interactions [1]. We also demonstrate a new approach of quantum control of chemical reactions (photo-association of molecules from atoms) --- a “quantum chemistry interferometry” --- by preparing reactants in (spin) quantum superposition states and interfering multiple reaction pathways [2]. By cyclic coupling of spin states as “synthetic dimensions”, we realize a symmetry protected (bosonic) topological state [3], where the BEC acquires an emergent crystalline order on a “synthetic” Hall subject to a radial synthetic magnetic flux. The system has a nonsymmorphic symmetry leading to protected crossings in the topological bandstructure, where the BEC exhibits Bloch oscillations mimicking transport on a Mobius strip. Our system can offer a rich playground for AMO physics, quantum chemistry, condensed matter physics, and even particle physics and cosmology.

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