scholarly journals Non-Hermitian and topological photonics: optics at an exceptional point

Nanophotonics ◽  
2020 ◽  
Vol 10 (1) ◽  
pp. 403-423 ◽  
Author(s):  
Midya Parto ◽  
Yuzhou G. N. Liu ◽  
Babak Bahari ◽  
Mercedeh Khajavikhan ◽  
Demetrios N. Christodoulides
Keyword(s):  
Phase Transitions ◽  
Special Class ◽  
Field Theories ◽  
Exceptional Point ◽  
Quantum Field Theories ◽  
Quantum Field ◽  
Wave Dynamics ◽  
The Past ◽  
Time Symmetry ◽  
Wide Range

AbstractIn the past few years, concepts from non-Hermitian (NH) physics, originally developed within the context of quantum field theories, have been successfully deployed over a wide range of physical settings where wave dynamics are known to play a key role. In optics, a special class of NH Hamiltonians – which respects parity-time symmetry – has been intensely pursued along several fronts. What makes this family of systems so intriguing is the prospect of phase transitions and NH singularities that can in turn lead to a plethora of counterintuitive phenomena. Quite recently, these ideas have permeated several other fields of science and technology in a quest to achieve new behaviors and functionalities in nonconservative environments that would have otherwise been impossible in standard Hermitian arrangements. Here, we provide an overview of recent advancements in these emerging fields, with emphasis on photonic NH platforms, exceptional point dynamics, and the very promising interplay between non-Hermiticity and topological physics.

scholarly journals Liquid-gas phase transitions and CK symmetry in quantum field theories

2017 ◽  
Vol 95 (7) ◽  
Author(s):  
Hiromichi Nishimura ◽  
Michael C. Ogilvie ◽  
Kamal Pangeni
Keyword(s):  
Phase Transitions ◽  
Gas Phase ◽  
Field Theories ◽  
Quantum Field Theories ◽  
Quantum Field

Zero Temperature Phase Transitions in Gauge Theories

1997 ◽  
Vol 12 (06) ◽  
pp. 1195-1203
Author(s):  
L. C. R. Wijewardhana
Keyword(s):  
Phase Transitions ◽  
Gauge Theories ◽  
Critical Value ◽  
Gauge Field Theories ◽  
Field Theories ◽  
Temperature Phase ◽  
Quantum Field Theories ◽  
Quantum Field ◽  
Zero Temperature ◽  
Massless Fermion

Quantum field theories can exist in different phases depending on the number of massless fermion flavors they have. The vacuum structure of such a theory can be changed by varying the flavor number across a critical value. In this lecture we discuss such structure changing phase transitions in three and four dimensional gauge field theories.

scholarly journals The landscape and the multiverse: What’s the problem?

Synthese ◽  
2021 ◽  
Author(s):  
James Read ◽  
Baptiste Le Bihan
Keyword(s):  
String Theory ◽  
Quantum Gravity ◽  
Current Source ◽  
Field Theories ◽  
Quantum Field Theories ◽  
Quantum Field ◽  
The Past ◽  
Empirical Criterion ◽  
Scientific Status ◽  
Vast Range

AbstractAs a candidate theory of quantum gravity, the popularity of string theory has waxed and waned over the past four decades. One current source of scepticism is that the theory can be used to derive, depending upon the input geometrical assumptions that one makes, a vast range of different quantum field theories, giving rise to the so-called landscape problem. One apparent way to address the landscape problem is to posit the existence of a multiverse; this, however, has in turn drawn heightened attention to questions regarding the empirical testability and predictivity of string theory. We argue first that the landscape problem relies on dubious assumptions and does not motivate a multiverse hypothesis. Nevertheless, we then show that the multiverse hypothesis is scientifically legitimate and could be coupled to string theory for other empirical reasons. Looking at various cosmological approaches, we offer an empirical criterion to assess the scientific status of multiverse hypotheses.

scholarly journals SIMMETRIA PARITÀ-TEMPO IN OTTICA: VERSO UNA NUOVA INGEGNERIA DELLA LUCE

2020 ◽  
Author(s):  
Stefano Longhi
Keyword(s):  
Optical Materials ◽  
Photonic Devices ◽  
Field Theories ◽  
Sensor Technology ◽  
Quantum Field Theories ◽  
Quantum Field ◽  
Time Symmetry ◽  
Laser Technologies ◽  
Design And Manufacturing ◽  
Theoretical Developments

The introduction of the concept of parity-time symmetry in optics, inspired by recent theoretical developments in quantum mechanics and quantum-field theories, is revolutionizing our ability to design and manufacturing synthetic optical materials and photonic devices for molding the flow of light at the micro- and nano-scale, with novel functionalities impossible with ordinary materials and with important applications in the fields of laser technologies, integrated photonics and sensor technology. In this note I will illustrate the basic theoretical grounds of optical materials with paritytime symmetry and I will present the main recent applications to photonic technologies.

scholarly journals ON TOPOLOGICAL DEFECT FORMATION IN THE PROCESS OF SYMMETRY BREAKING PHASE TRANSITIONS

2002 ◽  
Vol 16 (04) ◽  
pp. 93-106 ◽  
Author(s):  
ELEONORA ALFINITO ◽  
ORESTE ROMEI ◽  
GIUSEPPE VITIELLO
Keyword(s):  
Phase Transitions ◽  
Temperature Effects ◽  
Defect Formation ◽  
Topological Defect ◽  
Equilibrium Phase ◽  
Zero Order ◽  
Field Theories ◽  
Quantum Field Theories ◽  
Quantum Field ◽  
Volume Effects

By resorting to some results in quantum field theories with spontaneous breakdown of symmetry, we show that an explanation based on microscopic dynamics can be given for the fact that topological defect formation is observed during the process of non-equilibrium phase transitions characterized by a non-zero order parameter. We show that the Nambu–Goldstone particle acquires an effective non-zero mass due to boundary (finite volume) effects and this is related to the size of the defect. We also relate such volume effects with temperature effects.

scholarly journals Observation of anti-parity-time-symmetry, phase transitions and exceptional points in an optical fibre

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Arik Bergman ◽  
Robert Duggan ◽  
Kavita Sharma ◽  
Moshe Tur ◽  
Avi Zadok ◽  
...  
Keyword(s):  
Phase Transitions ◽  
Brillouin Scattering ◽  
Optical Gain ◽  
Single Mode ◽  
Exceptional Point ◽  
Small Scale ◽  
Time Symmetry ◽  
Topological Features ◽  
Gain And Loss ◽  
Exotic Physics

AbstractThe exotic physics emerging in non-Hermitian systems with balanced distributions of gain and loss has recently drawn a great deal of attention. These systems exhibit phase transitions and exceptional point singularities in their spectra, at which eigen-values and eigen-modes coalesce and the overall dimensionality is reduced. So far, these principles have been implemented at the expense of precise fabrication and tuning requirements, involving tailored nano-structured devices with controlled optical gain and loss. In this work, anti-parity-time symmetric phase transitions and exceptional point singularities are demonstrated in a single strand of single-mode telecommunication fibre, using a setup consisting of off-the-shelf components. Two propagating signals are amplified and coupled through stimulated Brillouin scattering, enabling exquisite control over the interaction-governing non-Hermitian parameters. Singular response to small-scale variations and topological features arising around the exceptional point are experimentally demonstrated with large precision, enabling robustly enhanced response to changes in Brillouin frequency shift.

scholarly journals Formfactors of Relativistic Composite Particle Interactions in Unified Nonlinear Spinorfield Models

1985 ◽  
Vol 40 (7) ◽  
pp. 752-773
Author(s):  
H. Stumpf
Keyword(s):  
Composite Particle ◽  
Particle Interaction ◽  
High Energy ◽  
Field Theories ◽  
Quantum Field Theories ◽  
Statistical Interpretation ◽  
Quantum Field ◽  
Mapping Procedure ◽  
Effective Dynamics ◽  
Rough Approximation

Unified nonlinear spinorfield models are self-regularizing quantum field theories in which all observable (elementary and non-elementary) particles are assumed to be bound states of fermionic preon fields. Due to their large masses the preons themselves are confined and below the threshold of preon production the effective dynamics of the model is only concerned with bound state reactions. In preceding papers a functional energy representation, the statistical interpretation and the dynamical equations were derived and the effective dynamics for preon-antipreon boson states and three preon-fermion states (with corresponding anti-fermions) was studied in the low energy limit. The transformation of the functional energy representation of the spinorfield into composite particle functional operators produced a hierarchy of effective interactions at the composite particle level, the leading terms of which are identical with the functional energy representation of a phenomenological boson-fermion coupling theory. In this paper these calculations are extended into the high energy range. This leads to formfactors for the composite particle interaction terms which are calculated in a rough approximation and which in principle are observable. In addition, the mathematical and physical interpretation of nonlocal quantum field theories and the meaning of the mapping procedure, its relativistic invariance etc. are discussed.

scholarly journals Categorification of algebraic quantum field theories

2021 ◽  
Vol 111 (2) ◽  
Author(s):  
Marco Benini ◽  
Marco Perin ◽  
Alexander Schenkel ◽  
Lukas Woike
Keyword(s):  
Universal Algebra ◽  
Finite Groups ◽  
Physical Interpretation ◽  
Field Theories ◽  
Quantum Field Theories ◽  
Quantum Field ◽  
Algebraic Quantum

AbstractThis paper develops a concept of 2-categorical algebraic quantum field theories (2AQFTs) that assign locally presentable linear categories to spacetimes. It is proven that ordinary AQFTs embed as a coreflective full 2-subcategory into the 2-category of 2AQFTs. Examples of 2AQFTs that do not come from ordinary AQFTs via this embedding are constructed by a local gauging construction for finite groups, which admits a physical interpretation in terms of orbifold theories. A categorification of Fredenhagen’s universal algebra is developed and also computed for simple examples of 2AQFTs.

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