nomenon in quantum mechanics in
which a particle or system does not
have a deÜnite state but exists as an
intermediate form of two ‘entangled’
states. One of these states is realized
when a ‘measurement’ is made.
quantum jump A change in a system (e.g. an atom or molecule) from
one quantum state to another.
quantum mechanics A system of
mechanics that was developed from
*quantum theory and is used to explain the properties of atoms and
molecules. Using the energy *quantum as a starting point it incorporates Heisenberg’s *uncertainty
principle and the *de Broglie wavelength to establish the wave–particle
duality on which *Schrödinger’s
equation is based. This form of quantum mechanics is called wave mechanics. An alternative but equivalent
formalism, *matrix mechanics, is
based on mathematical operators.
quantum number See atom; spin.
quantum simulation The mathematical modelling of systems of large
numbers of atoms or molecules by
computer studies of relatively small
clusters. It is possible to obtain information about solids and liquids in
this way and to study surface properties and reactions.
quantum state The state of a
quantized system as described by its
quantum numbers. For instance, the
state of a hydrogen *atom is described by the four quantum numbers n, l, m, m s . In the ground state
they have values 1, 0, 0, and ½ respectively.
quantum statistics A statistical
description of a system of particles
that obeys the rules of *quantum
mechanics rather than classical mechanics. In quantum statistics, energy states are considered to be
quantized. If the particles are treated
as indistinguishable, Bose–Einstein
statistics apply if any number of particles can occupy a given quantum
state. Such particles are called
bosons. All known bosons have an
angular momentum nh, where n is
zero or an integer and h is the Planck
constant. For identical bosons the
*wave function is always symmetric.
If only one particle may occupy each
quantum state, Fermi–Dirac statistics
apply and the particles are called
fermions. All known fermions have a
total angular momentum (n + ½)h/2π
and any wave function that involves
identical fermions is always antisymmetric.
quantum theory The theory devised by Max *Planck in 1900 to account for the emission of the
black-body radiation from hot bodies.
According to this theory energy is
emitted in quanta (see quantum),
each of which has an energy equal to
hν, where h is the *Planck constant
and ν is the frequency of the radiation. This theory led to the modern
theory of the interaction between
matter and radiation known as
*quantum mechanics, which generalizes and replaces classical mechanics and Maxwell’s electromagnetic
theory. In nonrelativistic quantum
theory particles are assumed to be
neither created nor destroyed, to
move slowly relative to the speed of
light, and to have a mass that does
not change with velocity. These assumptions apply to atomic and molecular phenomena and to some
aspects of nuclear physics. Relativistic quantum theory applies to particles that have zero rest mass or
travel at or near the speed of light.
quantum theory of radiation
The theory that describes the emission and absorption of electromagnetic radiation. Since it is a quantum
quantum jump
448
q
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which a particle or system does not
have a deÜnite state but exists as an
intermediate form of two ‘entangled’
states. One of these states is realized
when a ‘measurement’ is made.
quantum jump A change in a system (e.g. an atom or molecule) from
one quantum state to another.
quantum mechanics A system of
mechanics that was developed from
*quantum theory and is used to explain the properties of atoms and
molecules. Using the energy *quantum as a starting point it incorporates Heisenberg’s *uncertainty
principle and the *de Broglie wavelength to establish the wave–particle
duality on which *Schrödinger’s
equation is based. This form of quantum mechanics is called wave mechanics. An alternative but equivalent
formalism, *matrix mechanics, is
based on mathematical operators.
quantum number See atom; spin.
quantum simulation The mathematical modelling of systems of large
numbers of atoms or molecules by
computer studies of relatively small
clusters. It is possible to obtain information about solids and liquids in
this way and to study surface properties and reactions.
quantum state The state of a
quantized system as described by its
quantum numbers. For instance, the
state of a hydrogen *atom is described by the four quantum numbers n, l, m, m s . In the ground state
they have values 1, 0, 0, and ½ respectively.
quantum statistics A statistical
description of a system of particles
that obeys the rules of *quantum
mechanics rather than classical mechanics. In quantum statistics, energy states are considered to be
quantized. If the particles are treated
as indistinguishable, Bose–Einstein
statistics apply if any number of particles can occupy a given quantum
state. Such particles are called
bosons. All known bosons have an
angular momentum nh, where n is
zero or an integer and h is the Planck
constant. For identical bosons the
*wave function is always symmetric.
If only one particle may occupy each
quantum state, Fermi–Dirac statistics
apply and the particles are called
fermions. All known fermions have a
total angular momentum (n + ½)h/2π
and any wave function that involves
identical fermions is always antisymmetric.
quantum theory The theory devised by Max *Planck in 1900 to account for the emission of the
black-body radiation from hot bodies.
According to this theory energy is
emitted in quanta (see quantum),
each of which has an energy equal to
hν, where h is the *Planck constant
and ν is the frequency of the radiation. This theory led to the modern
theory of the interaction between
matter and radiation known as
*quantum mechanics, which generalizes and replaces classical mechanics and Maxwell’s electromagnetic
theory. In nonrelativistic quantum
theory particles are assumed to be
neither created nor destroyed, to
move slowly relative to the speed of
light, and to have a mass that does
not change with velocity. These assumptions apply to atomic and molecular phenomena and to some
aspects of nuclear physics. Relativistic quantum theory applies to particles that have zero rest mass or
travel at or near the speed of light.
quantum theory of radiation
The theory that describes the emission and absorption of electromagnetic radiation. Since it is a quantum
quantum jump
448
q
www.AzShimi.ir www.AzShimi.com