Notepad/enter/Machine Tips (Quantum)/Resources/Concepts Review/Physics/Particle Terms.md

• Anyon - a type of quasiparticle that occurs only in two-dimentional systems

  • Can be Abelian (discovered 2020) or Non-Abelian (generated with trapped ions) explained here.
  • Inferred from quantum topology - novel properties of shapes made by quantum systems

• Band structure - the range of energy levels that electrons may have within a solid-state object, as well as energies they may not have.

• Bosons - !

• Fermions - elementary subatomic particle

  • follows Fermi-Dirac statistics [with half-odd integer spin ](!)

• Fermi gas - a collection of non-interacting fermions (particles with half-integer spin) in a constant energy well.

  • behaves like an ideal gas at low particle number density& high temperature
  • concentrates a small number of particles per energy
  • prohibited from condensing into a Bose-Einstein condensate
  • may form a Cooper pair & condensate if weakly-interacting
  • pressure of Fermi-gas is non-zero even at zero-temperature unlike ideal gas
  • this pressure is what stabilizes a neutron star (is a fermi gas of neutrons )
  • pressure helps against inward pull of gravity for white dwarf star ( is a fermi gas of electrons ) which would otherwise collapse the star into a black hole
    • when a star is massive enough to overcome pressure, it can collapse into singularity.
    • Fermi temperature of a gas depends on mass of fermions and density of energy states

• Free electron model - solid-state model for metals. Describes behavior of charge carriers in a metallic solid.

  • where metals are composed of a quantum electron gas where ions play almost no role
  • predictive when applied to alkali & noble metals
  • 4 main assumptions
  1. free electron approximation : ion & valence electrons ignored other than to keep charge neutrality for the metal
  2. independent electron approximation : interactions between electrons ignored because electrostatic fields in metals are weak due to screening effect, respective quadratic relation exists between energy and momentum.
  3. relaxation-time approximation: unknown scattering mechanism occurs s.t. electron probability of collision = inversely proportional to the relation time \tau which represent the average time between collisions. Electronic configuration is not causing these collisions.
  4. pauli exclusion principle : each quantum state of the system can be occupied by a single electron. Restriction of electron states taken into account by Fermi-Dirac statistic which are derived by Sommerfield expansion of occupancy for energies around the Fermi level.

• FQHE - Fractional Quantum Hall effect shows precisely quantized plateaus at fractional values

  • measuring extremely directly is beyond reproach.

• Hadron - when a subatomic particle is neither a Boson or Fermion

• Jeans instability - causes collapse of interstellar gas clouds and subsequent star formation

  • when gas pressure is not strong enough to prevent gravitational collapse of a region fille with matter.
  • can give rise to fragmentation in certain conditions
  • this is why stars usually form in clusters (stellar nursery)

• Langmuir waves - plasma oscillations, instability occuring in electron density in conducting materials such as plasmas or metals in the UV region.

  • frequency depends only weakly on wavelength of oscillation
  • the instability in the dialectric function of a free electron gas
  • parallel in form to Jeans instability waves
  • may give rise to negative mass

• Phonons - quantized quasiparticle sound waves, similar to photons as quantized light waves

  • is an excited state in the quantization of the modes of vibrations for elastic structures of interacting particles
  • long-wavelength phonons give rise to sound. !

• Plasmons - a quasiparticle of plasma oscillations, just as photons are quasiparticles of optical oscillations

  • plasmon + photon = plasmon polariton (at optical frequencies)

• Polariton - The result of a combination of a photon with a polar excitation of a material. These are Bosonic quasiparticles resulting from a coupling of electromagnetic waves with an electric/magnetic dipole-carrying excitation.

  • 2018, scientists reported 3-photon form of light, involving polaritons, useful for development of quantum computers.
  • Many kinds of polaritons exist:
    • phonon polaritons
    • exciton polaritons aka excitons
    • intersubband polaritons
    • surface plasmon polaritons
    • Bragg polaritons ("Braggoritons")
    • Plexcitons
    • Magon polaritons
    • Pi-tons
    • Cavity polaritons

• Quasiparticles - or collective excitations are when a microscopically complicated system such as a solid behaves as if it contained different weakly interacting particles in vacuum.

  • ex. electron passing through semiconductor behaves differently (as if it has an effective mass traveling unperturbed in a vacuum) and so is refered to as an electron quasiparticle.
  • quasiparticles only exists inside of many-particle systems (primarily solids)

• Tachyon - a hypothetical faster-than-light particle

  • The implications of such a particle are vast.

The term quasar - Quasi stellar radio telescope - The term "quasar" was first used in an article by astrophysicist Hong-Yee Chiu in May 1964, in Physics Today, to describe certain astronomically puzzling objects:[14]

So far, the clumsily long name "quasi-stellar radio sources" is used to describe these objects. Because the nature of these objects is entirely unknown, it is hard to prepare a short, appropriate nomenclature for them so that their essential properties are obvious from their name. For convenience, the abbreviated form "quasar" will be used throughout this paper.

Now we know them as black holes.

E-VLBI - VLBI has traditionally operated by recording the signal at each telescope on magnetic tapes or disks, and shipping those to the correlation center for replay. In 2004 it became possible to connect VLBI radio telescopes in close to real-time, while still employing the local time references of the VLBI technique, in a technique known as e-VLBI. In Europe, six radio telescopes of the European VLBI Network (EVN) were connected with Gigabit per second links via their National Research Networks and the Pan-European research network GEANT2, and the first astronomical experiments using this new technique were successfully conducted.[15]

The image to the right shows the first science produced by the European VLBI Network using e-VLBI. The data from each of the telescopes were routed through the GÉANT2 network and on through SURFnet to be the processed in real time at the European Data Processing centre at JIVE.[15]