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Topic: Coherent state

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  Coherent state - Wikipedia, the free encyclopedia
In quantum mechanics a coherent state is a specific kind of quantum state of the quantum harmonic oscillator whose dynamics most closely resemble the oscillating behaviour of a classical harmonic oscillator system.
The coherent state's location in the complex plane (phase space) is centered at the position and momentum of a classical oscillator of the same phase θ and amplitude (or the same complex electric field value for a electromagnetic wave).
In quantum field theory and string theory, a generalization of coherent states to the case of infinitely many degrees of freedom is used to define a vacuum state with a different vacuum expectation value from the original vacuum.
en.wikipedia.org /wiki/Coherent_state   (1685 words)

 Coherent state -- Facts, Info, and Encyclopedia article   (Site not responding. Last check: 2007-10-08)
Consequently, in the case of a bosonic field, a coherent state is a specific superposition of levels (and hence particle numbers) which most closely mimics a stable classical wave.
These two states are examples of the opposite extremes in the concept of ((physics) the property of matter and electromagnetic radiation that is characterized by the fact that some properties can be explained best by wave theory and others by particle theory) wave-particle duality.
Not only does a coherent state go to a classical sinusoidal wave in the limit of large α but the detection statistics of it are equal to that of a classical stable wave for all values of α.
www.absoluteastronomy.com /encyclopedia/c/co/coherent_state.htm   (1422 words)

 Quantum state - Open Encyclopedia   (Site not responding. Last check: 2007-10-08)
The coherent state α> (α a complex number) which describes a state with minumum uncertainty in phase and amplitude.
A mixed state needs a statistical description in addition to the quantum description, this is provided by the density matrix which extends quantum mechanics to quantum statistical mechanics.
The coherent state is a coherent superposition of Fock states with the distribution sketched on the schema.
open-encyclopedia.com /Quantum_state   (427 words)

 Encyclopedia: Squeezed coherent state
For an amplitude-squeezed state, the most narrow distribution of the wave packet is reached at the field maximum, resulting in a amplitude that is defined more precisely than the one of a coherent state.
For a phase-squeezed state the most narrow distribution is reached at field zero, resulting in an average phase value that is better defined than the one of a coherent state.
Various squeezed coherent states, generalized to the case of many degrees of freedom, are used in various calculations in quantum field theory, for example Unruh effect and Hawking radiation (generally: particle production in curved backgrounds).
www.nationmaster.com /encyclopedia/Squeezed-coherent-state   (2122 words)

 Quantum mechanics - Wikipedia, the free encyclopedia
In the mathematically rigorous formulation of quantum mechanics, developed by Paul Dirac and John von Neumann, the possible states of a quantum mechanical system are represented by unit vectors (called "state vectors") residing in a complex separable Hilbert space (variously called the "state space" or the "associated Hilbert space" of the system).
The time evolution of a quantum state is described by the Schrödinger equation, in which the Hamiltonian, the operator corresponding to the total energy of the system, generates time evolution.
During a measurement, the probability that a system collapses from a given initial state to a particular eigenstate is given by the square of the absolute value of the probability amplitudes between the initial and final states.
en.wikipedia.org /wiki/Quantum_mechanics   (4110 words)

 Visualizing the Decoherence Effect
A particularly interesting state is the coherent state shown in figure 5.
Figure 6 shows a superposition of states; this is a superposition of two coherent states, and when the gaussian peaks are near to each other, they show a clear interference pattern.
Now, prepare the system such that the first particle is in the superposition of coherent states as in figure 6, the second particle is in its ground state, and the particles interact.
www.geocities.com /scjphysicist/decoh.html   (1258 words)

 The Brain Research Institute: States of Consciousness   (Site not responding. Last check: 2007-10-08)
According to the Vedas, this state of restful alertness or transcendental consciousness is considered to be the fundamental mode or ground state of human conscious experience.
During the process of transcending, sustained periods of marked coherence in brain activity and spontaneous respiratory suspension are closely correlated with subjective reports of awareness without thought.
In this model, the state of restful alertness is produced by a coordinated response of orienting and habituating processes.
www.brainresearchinstitute.org /research/states_consc.html   (531 words)

 NIST Ion Storage Group   (Site not responding. Last check: 2007-10-08)
By means of resolved-sideband stimulated-Raman Cooling, the ion can be cooled further to the ground state of motion (n=0) with high probability (98% in one dimension, 95% in three dimensions).
A coherent state corresponds to a well-localized wavepacket (identical in shape to the Gaussian
Coherent states are the closest quantum-mechanical analogue to a classical particle oscillating in a harmonic potential.
tf.nist.gov /ion/qucomp/nonclass.htm   (406 words)

 Method for coherent steady-state imaging of constant-velocity flowing fluids - US Patent 6587708   (Site not responding. Last check: 2007-10-08)
The coherent steady-state signal is a result of isochromats along an infinite number of spin coherence pathways refocusing together at the same instant as each new rf pulse in the sequence (so-called "rf echo").
This "echoing" coherence pathway has a multitude of transverse magnetization components, each having gone through different numbers of free precession periods, either all in the transverse plane or some in the transverse plane and some along the longitudinal direction.
The rest of the coherence pathways are non-echoing pathways, and will have to go through a certain number of free precession periods in the transverse plane before they are converted to the echoing pathway.
www.patentstorm.us /patents/6587708.html   (7189 words)

 Chapter 4: Challenges to Implementing Systemic Reform
Because teachers are more familiar with the tests than with the state's written objectives, and because test results are reported to the public and used for school improvement planning, the state assessment program has had the impact of encouraging teachers to change the content of their instruction in these new directions.
Second, the State Board of Education is adopting a set of professional development standards to be used in reviewing and approving local district applications for state professional development funds, and for coordinating professional development funding and activities across the state department of education.
In each state, a state agency sets the requirements for teacher certification, but as one requirement specifies that the candidate must successfully complete a program in a higher education institution (or other specially designated program, such as that run by the Los Angeles Unified School District).
www.ed.gov /pubs/SER/SysReform/chap4b2.html   (4199 words)

 Solid state pulsed coherent laser radar for short range velocimetry applications - Patent 5317376
A coherent laser radar as an aircraft air data sensor uses the aerosols in the atmosphere to scatter some of the transmitted energy from the laser source back to a receiver where the Doppler shift is used to measure the aircraft velocity component along the transmitter line of sight.
Recently, a pulsed coherent laser radar was developed that used a single laser source to generate both the transmitter and local oscillator beams.
Coherent detection (optical heterodyning) requires a local oscillator beam that is both temporally and spectrally stable over the entire detection period.
www.freepatentsonline.com /5317376.html   (5360 words)

 Josephson junction - Wikipedia, the free encyclopedia
The effects of the junction's internal electrical resistance will be large compared to its small capacitance.
An overdamped junction will quickly reach a unique equilibrium state for any given set of conditions.
Underdamped junctions do not have unique equilibrium states, but are hysteretic.
www.wikipedia.org /wiki/Josephson_junction   (301 words)

 Coherent states of Quantum Harmonic Oscillator   (Site not responding. Last check: 2007-10-08)
Schrödinger's coherent states were discovered by Schrödinger in 1927.
Today, these states of harmonic oscillator, so called coherent states, are known as Glauber states, and they are known as single harmonic oscillator prototypes of the coherent states of oscillating electromagnetic field, which are the model of ideal continuous wave laser field, or an electromagnetic field of unmodulated radio wave.
The probability distribution of the coherent state behaves as the n=0 state whose shape moves as a classical oscillator with the frequency omega.
www-troja.fjfi.cvut.cz /~ladi/HO   (316 words)

 The Squeezed Coherent State
A squeezed coherent state is more general than the coherent state, but its properties are similar.
A coherent state is a special case of a squeezed state.
The principle difference between the coherent and squeezed coherent state is that the variances of momentum and position are not constant.
webphysics.davidson.edu /Projects/AnAntonelli/node47.html   (343 words)

 ipedia.com: Quantum state Article   (Site not responding. Last check: 2007-10-08)
In quantum mechanics this is described using a mathematical representation such as a state vector or a density operator.
, which is known as the wavefunction, is a special representation of the quantum state, namely, its projection in the real space.
The coherent state α> (α a complex number) which describes a state of definite phase.
www.ipedia.com /quantum_state.html   (477 words)

 Quantum-Optical Catalysis   (Site not responding. Last check: 2007-10-08)
Although the quantum theory of light describes many exotic states like the single photon and the vacuum, there are also states that are essentially the same as those described in Maxwell's wave theory of light.
These are called coherent states, denoted by the symbol &alpha> (greek letter alpha), and first used in the context of quantum optics by Roy Glauber in the 1960s.
The detection of a photon by the SPD triggers the homodyne detector, because a single photon in the one channel means that the coherent superposition is produced in the other channel.
grad.physics.sunysb.edu /~meardley/quoptics   (950 words)

 Solid state pulsed coherent Doppler radar - Patent 4160248
The circuits 11, 12 and 13 constitute the local oscillator circuits and are used as a coherent oscillator to be mixed with the Doppler return signals traveling the path from antenna 20, microwave switch 19, duplexer 18, rf receiver amplifier 21, rf switch 22 and mixer 13.
During the "ON" state, the process described above is performed, and the output from the rf amplifier is an amplified, frequency-translated version of the input to the SSB.
During the "OFF" state, the SSB and rf amplifier are set into a high isolation state, and the rf phase shifting in the SSB is stopped.
www.freepatentsonline.com /4160248.html   (2647 words)

 physics - Quantum optics
A frequently encountered state of the light field is the coherent state as introduced by R. Glauber in 1963.
Via certain nonlinear interactions, a coherent state can be transformed into a squeezed coherent state, which can exhibit super- or sub-Poissonean photon statistics.
Atoms are considered as quantum mechanical oscillators with a discrete energy spectrum with the transitions between the energy eigenstates being driven by the absorption or emission of light according to Einstein's theory with the oscillator strength depending on the quantum numbers of the states.
www.physicsdaily.com /physics/Quantum_optics   (761 words)

For single thermal atoms, the coherence length is determined by the thermal de Broglie wavelength and is thus limited to the micron range, even for temperatures as small as 1 microkelvin.
A mixture of atomic and molecular states is created and probed by sudden changes in the magnetic field, which lead to oscillations in the number of atoms that remain in the condensate.
Students may state that a wave is a solution to the wave equation; professionals may make some ambiguous statement about propagation velocity; mathematicians tend to give a formal characterization based on the hyperbolic character of certain differential equations.
scienceweek.com /2003/sw030404.htm   (10906 words)

 Pseudobands in non-SU(3) odd-mass nuclei and coherent state structures of quadrupole phonons.
Pseudobands in non-SU(3) odd-mass nuclei and coherent state structures of quadrupole phonons.
Paar (Univ. Zagreb) - Pseudobands in non-SU(3) odd-mass nuclei and coherent state structures of quadrupole phonons.
Ground state symmetric rotor bands are described as coherent-state structures of deformation in a quadrupole-phonon model.
www.hazu.hr /~paar/Abstracts/135.htm   (183 words)

 What is a coherent state?   (Site not responding. Last check: 2007-10-08)
A coherent state is an eigenstate of the destruction operator in a
In occupation formalism, a coherent state is an eigenstate of the
A coherent state is a state in which a large number of identical particles
www.groupsrv.com /science/about7741.html   (525 words)

 Electric-Field Uncertainties   (Site not responding. Last check: 2007-10-08)
Uncertainty regions for various types of quantum states are shown in the left column, together with the time dependences of x(t) (or p(t)) (blue-grey curves) and their uncertainties (light blue shaded area), in the right column.
(a) The uncertainty region for the vacuum state is a circle centered at the origin.
As with the squeezed-vacuum state (b), the electric field shows a periodic reduction and enhancement of its uncertainty.
www-personal.engin.umich.edu /~nori/squeezed/animations.htm   (178 words)

 KLUEDO - Semiclassical Approximations in Phase Space with Coherent States
We present a complete derivation of the semiclassical limit of the coherent state propagator in one dimension, starting from path integrals in phase space.
We show that the arbitrariness in the path integral representation, which follows from the overcompleteness of the coherent states, results in many different semiclassical limits.
Finally we show how the semiclassical coherent state propagators lead to WKB-type quantization rules and to approximations for the Husimi distributions of stationary states.
kluedo.ub.uni-kl.de /volltexte/2001/1339/index.html   (203 words)

 A Coherent State
The interaction of an atom with a coherent field state is the closest quantum mechanical analog to the situation modeled in BlochApp.
Figure: The oscillation of the probability of the lower state of an atom initially in the upper state interacting with a coherent state,
This result is a general one for all coherent states.
webphysics.davidson.edu /Projects/AnAntonelli/node74.html   (496 words)

 'Divided State': coherent look at controversy   (Site not responding. Last check: 2007-10-08)
Orem, Utah, the self-titled "Family City USA" in the reddest of the red states, was the center of political debate last year during the waning weeks of the presidential election.
"This Divided State," the new documentary by filmmaker Steven Greenstreet, is an unnarrated film that offers an inside look into Orem's Utah Valley State College and its decision to invite controversial filmmaker Michael Moore to speak on campus.
A contextually brilliant film, "This Divided State" has 12 more stops on its nationwide college tour and is slated for DVD release late this summer.
www.thelantern.com /news/2005/04/08/Arts/divided.State.Coherent.Look.At.Controversy-918304.shtml   (516 words)

 Class minutes---week 6
they remain coherent states even in the presence of an arbitrary time-dependent homogeneous force.
In particular, if you start with the ground state and drive it with such a force, you get a coherent state.
and oscillators, and coherent state evolution for an oscillator (including the driven case).
www.glue.umd.edu /~tajac/622c/622minutes6.html   (607 words)

 Detailed Characterization of Coherent Dark States: Excited State
Although the coherent dark state is basically a ground state affair the excited state does play a role in several aspects, the position (see Light Shift), the amplitude (preparation rate), and the width (destruction rate).
The most obvious influence of the excited states is a change in line shape when the detuning of the lasers from the optical resonance is changed (see figure).
A detailed investigation of these changes allows one to see that the contrast of the dark resonance is maximum when the strong carrier is tuned to the strongest transition into the excited state.
www.iap.uni-bonn.de /dunkel/det_Excited.html   (264 words)

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