Topics, Q

* Idea: Non-topological solitons which exist classically for any fixed value of an unbroken global charge Q.
@ References: Kusenko PLB(97) [small charge]; Graham PLB(01)ht [quantum effects, stability]; Deshaies-Jacques & MacKenzie PRD(06)ht [in Maxwell-Chern-Simons theory]; Tsumagari PhD(09)-a0910 [formation and stationary properties].

Q-Glass > see solid matter.

Q-Manifold > see manifolds [supermanifolds].

* Idea: The simplest generalization of the Schwarzschild solution that contains a quadrupole parameter.
@ References: Toktarbay & Quevedo G&C(14)-a1510 [generalized to the stationary case].

Q-Screen > see thermodynamical laws [generalized second law].

@ References: Prikas NPB(04) [in 2+1 dimensions], PLB(05) [in scalar-tensor theories].

QBism > s.a. indefinite causal structures; probabilities in quantum theory [Bayesian approach].
* Idea: In general, the view that science is a tool that each of us can use to organize our own personal experience, and is thus about the subject (the user of science) and not just about the object (the world external to that user); Called QBism by Fuchs and Schack.
@ Books: von Baeyer 16, rev McQueen a1707.
@ General references: Fuchs a1003; Mermin PT(12)jul; Fuchs et al AJP(14)aug-a1311, comment Nauenberg AJP(15)mar-a1502, reply Fuchs et al a1502 [introduction, and locality]; Mermin a1312 [and classical mechanics]; Mermin nat(14)mar [intro]; Fuchs a1405 [history, long collection of letters and documents]; Mermin a1406 [clarification]; Mermin a1409-conf [what John Bell might have thought of it]; Stacey PTRS(16)-a1412 [John von Neumann was not a quantum Bayesian]; Fuchs & Schack PS(15)-a1412; Fuchs a1601-in; Fuchs M&M-a1705 [reasons for QBism]; Bub a1711; DeBrota & Stacey a1810 [FAQs]; Stacey a1812 [and the Ithaca Interpretation]; Mohrhoff a1905 ["B" is for Bohr]; Mohrhoff a1907-conf; Stacey a1911 [looking back]; Pienaar FP(20)-a2004 [some answers]; Mohrhoff a2005 [ontology]; Barzegar FP(20)-a2006; Fuchs & Stacey a2012.
@ Appraisals, criticisms: Marchildon FP(15)-a1403; Mohrhoff a1409 [critical appraisal]; Khrennikov ch(18)-a1412, a1604 [reflections by an external observer]; Kupczynski a1505; Gründler a1606 [and non-locality]; Mohrhoff a1608; Zwirn a1912; Fayngold a2003 [basic tenets unsubstantiated].

QCD > s.a. QCD phenomenology.

QED > s.a. modified versions, in curved spacetime [including (quantum) gravity effects], and QED phenomenology.

Quadratic Curvature Terms > see higher-order gravity.

Quadratic Equation > see elementary algebra.

Quadratic Form / Function > s.a. Bilinear Form.
$ Def: A quadratic form on a vector space V is a function f : V → \(\mathbb R\) that can be written as f(v) = i li(v) li'(v), where li and li' are linear for all i.
* Relationships: Any quadratic form defines a positive-definite bilinear form.
* Sesquilinear form: A quadratic form on a complex vector space, which is linear in one argument and anti-linear in the other; Used to define (complex) Hilbert spaces.
@ References: O'Meara 63; Coll & Morales JMP(93) [signature].

Quadrilateralland > see Relational Theories.

Quadrupole Formula for Gravitational-Radiation Energy Loss > s.a. gravitational radiation / brane phenomenology; multipoles.
* Assumptions: Velocities are small, and T00 dominates the stress-energy tensor; The approximation ignores the internal structure of the star and orbiting particle, and is valid in the large-distance limit.
* Formula:

−dE/dt = ∑i, j = 13 (G/45c5) (d3Qij / dt3)2,   Qij = d3x μ(x) (3 xi xj − δij r2) .

@ References: in Misner et al 73; Ehlers et al ApJ(76) [controversy]; Walker & Will PRL(80); in Wald 84; Winicour GRG(87); Helfer PRD(93); Ashtekar et al PRD(15)-a1510 [with a positive cosmological constant].

Quality Factor Q > see oscillator.

* Idea: A non-division algebra; Similarly to quaternions, quantions preserve the core features of associativity and complex conjugation, while giving up the notion of division; They have been used as a framework for electroweak theory on curved spacetime.
@ References: Moldoveanu a0901 [and unification of quantum mechanics and relativity].

> General frameworks: see quantum mechanics; quantum field theory; Third Quantization.
> Operator-based approaches: see canonical quantization; quantum formalism; geometric quantization; representations; stochastic quantization.
> Histories-based approaches: see histories quantum theory; path integral quantization.
> Modified approaches: see deformed quantum theory; modified quantum theory; relativistic quantum theory.

@ References: Baez & Pollard Ent(15)-a1311.

Quantum Action Principle > see renormalization [algebraic]; Schwinger's Variational Principle.

Quantum Algebra > s.a. quantum group.
@ References: Pillin CMP(96) [deformed Heisenberg algebra]; Jaganathan mp/00-intro, mp/01-proc; Celeghini & del Olmo EPL(03)ht/01 [and quantum theory]; Banica & Collins JGP(08) [Pauli representation of quantum permutation algebra].

Quantum Billiard > see spectral geometry.

Quantum Carpet
* Idea: A generic spacetime pattern formed in the probability distributions P(x, t) of 1D quantum particles, first discovered in 1995; It is related to the Talbot Effect and to quantum state revivals.
@ References: Hall et al JPA(99)qp [and travelling waves]; Friesch et al NJP(00); Berry et al pw(01)jun.

Quantum Channel
@ References: Gour & Wilde a1808 [entropy].

Quantum Cosmology > s.a. FLRW quantum cosmology.

Quantum Darwinism > see decoherence.

Quantum Deformation > see deformation quantization; differential geometry; hamiltonian dynamics; quantum particle models.

Quantum Discord

Quantum Dot > see quantum technology.

Quantum Eraser > see under Erasure.

Quantum Field Theory > s.a. approaches; effective theories; effects; states; types of theories.

Quantum Field Theory in Curved Spacetime > s.a. various backgrounds and effects.

Quantum Graphity > see discrete geometry models / computation [universe as computer].

Quantum Gravity > s.a. 2D; 3D; approaches; canonical; matter phenomenology; semiclassical quantum gravity; ...

Quantum Group

Quantum Interest > see quantum field theory effects.

Quantum Jump / Transition > see quantum states.

Quantum Logic > see logic.

Quantum Maps
@ References: Milz et al a1708.

Quantum Mechanics > s.a. effects; experiments; formulations; histories; interpretations; semiclassical; states; systems; ...

Quantumness (Degree of Non-Classicality) > see classical limit of quantum theory; correlations.

Quantum Non-Demolition Experiments > see experiments in quantum mechanics; Non-Demolition Principle.

Quantum Optics > see optics.

Quantum Potential > see pilot-wave interpretation.

Quantum Protectorate > see composite quantum systems.

Quantum Revival > see quantum states.

Quantum Spacetime > s.a. proposals.

Quantum States [including revivals].

Quantum Walk > see random walk.

Quark > see hadrons; QCD phenomenology [including quark-gluon plasma].

Quark Nugget > see QCD effects / dark matter types; early-universe baryogenesis.

Quark Star > see astronomical objects.

* Idea: Bound states of a heavy quark Q = c, b and the corresponding antiquark.
@ References: Eichten et al RMP(08) [rev].
> Online resources: see Wikipedia page.

Quartic Equation > see elementary algebra.


Quasicondensation > see quantum phase transitions.


* Idea: A space locally modelled on \(\mathbb R\)k modulo the action of a discrete, possibly infinite, group.

Quasilocal Formulation of Field Theory > see quasilocal formulation of general relativity; quasilocal mass / reference frames.

Quasinormal Modes > see black-hole perturbations.

Quasiorder > s.a. Preorder.
$ Def: A transitive relation.
* Relationships: A finite quasiordered set is the same as a finite topological space (> see poset).
* Example: The refinement relation between covers of a topological space is a reflexive quasiorder (a preorder or direction), but it is not antisymmetric.
@ General references: in Isbell 64, p3.
@ Related topics: Ding DM(09) [canonical antichains].

Quasiparticle > s.a. particle types; Fracton; Hole; Magnon; Orbiton; Phonon; Polaron; Roton.
* Idea: A composite object produced when one "immerses" a particle in a quantum many-body system, for instance an electron in a solid; The particle "swims" shrouded by a cloud of excitations of its new environment, which modifies its physical properties (mass, charge, etc.); The most famous example is a "hole".
* Polariton: A mixed photonic and electronic excitation; > s.a. black-hole analogs; bose-einstein condensation; photon phenomenology.
@ General references: Powell CP(20)-a2008 [pedagogical rev].
@ Bogoliubov quasiparticles: Zhang et al PRL(06)cm/05, Horváth et al cm/05 [in a superfluid].
@ Polaritons: Karzig et al PRX(15) [topological polaritons]; Ohadi et al PRX(15) [polariton condensates and their uses]; > s.a. bose-einstein condensates.
@ Other types: Schirotzek et al PRL(09) + Chevy Phy(09) [fermionic analog of a solid-state polaron]; Soluyanov Phy(17) [type-II Dirac fermions].
> Online resources: see Wikipedia page.

Quasiperiodic Function > not to be confused with an Almost Periodic Function.
* Idea: A function of the form

f(x) = ∑j=1n cj exp{i kjx} ,

for some integer n and real numbers cj, kj; They form an algebra and can be endowed with the sup norm, and is naturally isomorphic to the algebra of continuous functions on the Bohr compactification of \(\mathbb R\).
* In dynamical systems: Many dynamical systems are a complex mix of chaotic and quasiperiodic behaviors, and chaotic trajectories near quasiperiodic points can have long near-quasiperiodic transients.
@ References: Das et al EPL(16)-a1512 [computational technique for analyzing quasiperiodicity and distinguishing it from chaos].
> Online resources: see Wikipedia page.

Quasiperiodic Tiling > see crystals [quasicrystals]; tilings.

Quasiprobabilities > see probability in quantum theory.

Quasiset Theory > s.a. locality.
* Idea: The mathematical theory of collections of indistinguishable objects.
@ General references: Sant'Anna qp/04 [and undecidable finite sets].
@ And identical particles: Sant'Anna qp/98, & Santos FP(00)qp/99; Sant'Anna FPL(05)qp/04; Domenech & Holik FP(07)-a0705; Domenech et al FP(08)-a0803; Sant'Anna QSMF(19)-a1910 [individuality and the double-slit experiment].
> Online resources: see Wikipedia page.

Quasispherical Metric > see types of metrics.

Quasi-Topological Gravity > see black holes in modified theories; gravitational thermodynamics.

Quasitopological Group > see Topological Group.


Qubit, Qudit > see discrete quantum systems.

Quillen Determinant
@ References: Furutani JGP(04) [line bundle].


Quintic Equation > see elementary algebra.

Quintom Dark Energy
* Idea: A hybrid of quintessence and phantom dark energy which involves the participation of two real scalar fields playing the roles of those two types of dark energy.
@ Cosmology: Lazkoz & León PLB(06); Cai et al PRP(10).

Quipper > see quantum computing.

Quirky Matter > see types of dark matter.

Quiver Gauge Theory > s.a. particle physics.
@ References: Szabo & Valdivia JHEP(14)-a1404 [covariant].

Quiver Varieties
@ References: Ginzburg m.QA/00.

Quons > see particle statistics.

Quotient Function
$ Def: The function Q(x):= (1−x)/(1+x).
@ References: Lindell & Sihvola AJP(98)mar [applications].

Qutrit > see quantum systems; entanglement; black-hole entropy.

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