Quantum Effects of Chiral Materials and Chiral Vacuum. （我们研究手性材料和手性真空中量子效应）

Physics: We can summarize the physics as follows: In chiral superconductors, Gaussian curvature plays the same role as magnetic field in normal superconductors.

Meaning: Chiral superconductors are thought as the best platform for topological computation. However, a very important question still remains unsolved: Do intrinsic chiral superconductors exist? And if they exist, how do we identify them without ambiguity? Here we proposed using geometric Josephson effect to identify chiral superconductivity.

(2) We propose a new geometric way to move charge-neutral chiral vortices.

PHYSICAL REVIEW LETTERS 129, 016801 (2022). Link: https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.129.016801

Physics: We can summarize the physics as follows: Geometry tells super current how to flow; super current tells geometry how to curve. (This reminds us the physics of general relativity, where geometry tells matter how to move, and matter tells geometry how to curve 🙂

Meaning: Chiral vortices could hold Majorana bound states which are essential for topological quantum computation. To do topological quantum computation, one needs to be able to control the position of the vortices. Moving vortices in superconductors is hard because the large associated magnetic flux energy. However, moving vortices in superfluids is also hard. Although there is no associated magnetic flux energy, there is no additional knot to move the vortices because the vortices in superfluid are charge neutral. Here, we propose using geometric curvature to control the position of chiral superfluid vortices.

News and Report: https://tdli.sjtu.edu.cn/EN/customize/733

(3) Prediction of the transverse shift of chiral quasiparticles

PHYSICAL REVIEW LETTERS 115, 156602 (2015). Link: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.115.156602

Physics: In photonics, when a photon reflected at an interface, there are both the longitudinal shift and transverse shift. While the longitudinal shift exists for any quantum particle, the transverse shift was only discussed in the photonics context.

Meaning: For the first time, we predicted the transverse shift for chiral quasiparticles in condensed matter systems. Our prediction was subsequently generalized to other condensed matter systems, such as superconductors.

II. Quantum Effects in Chiral Vacuum

(1) We discover using chiral materials can generate repulsive Casimir force in the vacuum

PHYSICAL REVIEW B 99, 125403 (2019) (Editors’ Suggestion and Featured in Physics). Link: https://journals.aps.org/prb/pdf/10.1103/PhysRevB.99.125403

Physics: In modern physics, we know that the (EM) vacuum is defined as the zero photon state. However, quantum mechanics tells us that photons can be created and annihilated in a short time scale. These transiently appeared virtual photons could mediate a long range force between charge neutral object, for instance two pieces of metallic plate. This vacuum quantum fluctuations induced force is know as the Casimir force. Casimir force is an attractive force, and can be very large in the nano scale. How to stabilize a system against the attractive Casimir force in the nanoscale is a long pursued question. Here, we predicted that using chiral materials as a mediator to generate repulsive Casimir force, so that nano mechanic will not stick together due to the attractive Casimir force.

News and Reports: https://physics.aps.org/articles/v12/s26

https://phys.org/news/2019-03-tuning-quantum-vacuum-repulsive.html

(2) Together with Frank Wilczek, we came up with the new concept called Quantum Atmosphere

PHYSICAL REVIEW B 99, 201104 (R) (2019) https://journals.aps.org/prb/abstract/10.1103/PhysRevB.99.201104

Physics: Symmetry and symmetry breaking are the central principle in modern physics. However, some symmetry or symmetry breaking pattern are hidden in materials and not easily detected by known methods. These symmetry are called hidden symmetry. For example, a chiral Chern insulator (or Haldane insulator) breaks time reversal symmetry, but it will not generate a finite magnetic field. Then how do we detect the time-reversal symmetry breaking of a Chern insulator? We propose that quantum fluctuations will transmit symmetry breaking information of a material to its nearby vacuum. The vacuum in proximate to a symmetry-breaking material is called its quantum atmosphere.

Meaning: We show that putting a spin close to a chiral Chern insulator will induce an anomalous Zeeman splitting even though there is no magnetic field. We further show that all variations of symmetry breaking pattern of a material can be reflected in its quantum atmosphere.

News and Reports: Our work is reported by one of the most famous public service journal quanta magazine: https://www.quantamagazine.org/quantum-atmospheres-may-reveal-secrets-of-matter-20180925/

(3) Predict Using Chiral Cavity to Select Chiral Molecules

PHYSICAL REVIEW LETTERS 131, 223601 (2023). Link: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.131.223601

Physics: The notion of chirality dates back to 1848, when Louis Pasteur observed two crystals that, similar to our hands, were mirror images of each other but could not completely superposed on each other. Chirality is a basic concept of nature; many organic molecules in life only appear in one type of chirality, not the other. A pair of molecules that are mirror images of each other are called enantiomers. Due to the similarity in physical properties of enantiomers, how to effectively identify and select molecules with specific chirality has become an important key scientific issue. Our group proposed that in a gyrotropic microcavity, vacuum quantum fluctuations can lead to chirality-dependent energy spectrum shifts. Since the microcavity causes enantiomers of opposite chirality to have different ground state energies, the reaction barriers they need to cross when participating in chemical reactions are also different . Therefore, this effect can be used to effectively produce molecules with specific chirality through chemical reactions.

News and Reports: https://tdli.sjtu.edu.cn/EN/customize/1111