Related Experiment Video
Updated: Aug 29, 2025
07:56
A Photonic System for Generating Unconditional Polarization-Entangled Photons Based on Multiple Quantum Interference
Published on: September 5, 2019
8.6K
Annihilation of exceptional points from different Dirac valleys in a 2D photonic system
M Król1, I Septembre2, P Oliwa1
1Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Warsaw, Poland.
Nature Communications
|September 12, 2022
Summary
Researchers demonstrated a novel non-Hermitian topological transition in a liquid crystal microcavity. Increasing non-Hermiticity caused exceptional points from different Dirac points to annihilate, clearing band singularities.
Area of Science:
- Topological physics
- Non-Hermitian systems
- Condensed matter physics
Background:
- Topological physics utilizes eigenstate singularities like Dirac points and exceptional points (EPs).
- Non-Hermitian topological transitions typically involve EP creation/annihilation linked to Dirac points.
- Previous studies focused on single Dirac point transitions with increasing non-Hermiticity.
Purpose of the Study:
- To experimentally demonstrate a new type of non-Hermitian topological transition.
- To investigate the annihilation of exceptional points originating from different Dirac points (valleys).
- To explore the role of non-Hermiticity in valley-dependent topological phenomena.
Main Methods:
- Utilized a liquid crystal microcavity with voltage-controlled birefringence.
- Implemented TE-TM photonic spin-orbit-coupling.
- Introduced non-Hermiticity via polarization-dependent losses.
Main Results:
- Demonstrated the annihilation of exceptional points from different Dirac points by increasing non-Hermiticity.
- Showcased control over EP positions through the degree of non-Hermiticity.
- Achieved a system free of band singularities after intervalley EP annihilation.
Conclusions:
- Established a new mechanism for non-Hermitian topological transitions involving intervalley EP annihilation.
- Opened the field of non-Hermitian valley-physics.
- Highlighted the interplay between Hermitian topology and non-Hermitian phase transitions.
Related Concept Videos
03:06The Pauli Exclusion Principle
46.0K
The arrangement of electrons in the orbitals of an atom is called its electron configuration. We describe an electron configuration with a symbol that contains three pieces of information:
46.0K
01:25Deactivation Processes: Jablonski Diagram
835
Luminescence, the emission of light by a substance that has absorbed energy, is a process that involves the interaction of molecules with light. The energy-level diagram, or Jablonski diagram, is a graphical representation of these interactions, illustrating the various states and transitions a molecule can undergo. In a typical Jablonski diagram, the lowest horizontal line represents the ground-state energy of the molecule, which is usually a singlet state. This state represents the energies...
835
01:16Second Uniqueness Theorem
1.1K
Consider a region consisting of several individual conductors with a definite charge density in the region between these conductors. The second uniqueness theorem states that if the total charge on each conductor and the charge density in the in-between region are known, then the electric field can be uniquely determined.
In contrast, consider that the electric field is non-unique and apply Gauss's law in divergence form in the region between the conductors and the integral form to the...
In contrast, consider that the electric field is non-unique and apply Gauss's law in divergence form in the region between the conductors and the integral form to the...
1.1K
01:25Divergence and Curl of Electric Field
6.0K
The divergence of a vector is a measure of how much the vector spreads out (diverges) from a point. For example, an electric field vector diverges from the positive charge and converges at the negative charge. The divergence of an electric field is derived using Gauss's law and is equal to the charge density divided by the permittivity of space. Mathematically, it is expressed as
6.0K
01:29Potential Due to a Polarized Object
460
A neutral atom consists of a positively charged nucleus surrounded by a negatively charged electron cloud. When placed in an external electric field, the external electric force pulls the electrons and nucleus apart, opposite to the intrinsic attraction between the nucleus and the electrons. The opposing forces balance each other with a slight shift between the center of masses of the nucleus and the electron cloud, resulting in a polarized atom. On the other hand, a few molecules, like water,...
460
01:18First Law: Particles in Two-dimensional Equilibrium
5.2K
Recall that a particle in equilibrium is one for which the external forces are balanced. Static equilibrium involves objects at rest, and dynamic equilibrium involves objects in motion without acceleration; but it is important to remember that these conditions are relative. For instance, an object may be at rest when viewed from one frame of reference, but that same object would appear to be in motion when viewed by someone moving at a constant velocity.
Newton's first law tells us about...
Newton's first law tells us about...
5.2K