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Topic: Quantum states

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In the News (Sun 23 Jun 19)

  Quantum state - Wikipedia, the free encyclopedia
A partially known quantum state, such as an ensemble with some quantum numbers fixed, can be described by a density operator.
The simplest understanding of basis states is obtained by examining the quantum harmonic oscillator.
A mixed quantum state is a statistical distribution of pure states.
en.wikipedia.org /wiki/Quantum_state   (580 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).
For instance, the well-known model of the quantum harmonic oscillator uses an explicitly non-relativistic expression for the kinetic energy of the oscillator, and is thus a quantum version of the classical harmonic oscillator.
Quantum electrodynamics is a quantum theory of electrons, positrons, and the electromagnetic field, and served as a role model for subsequent quantum field theories.
en.wikipedia.org /wiki/Quantum_mechanics   (5466 words)

 Quantum Consciousness . Stuart Hameroff
The boundary between the quantum and classical worlds is unclear, and the transition between the two is commonly described as quantum state reduction, collapse of the wave function, or decoherence.
The theory of decoherence reconciles the Copenhagen interpretation with quantum superpositions in the absence of measurement or conscious observation.
As the states of tubulin are controlled by quantum mechanical internal forces (van der Waals London forces), they may exist in quantum superposition of multiple states ("quantum bits, or "qubits"), and microtubules may be seen as quantum computers involved in cellular organization.
www.quantumconsciousness.org /overview.html   (2321 words)

 oe magazine - Light Entanglements   (Site not responding. Last check: 2007-10-21)
This protocol of state sharing via entanglement, and recovery of the original state by disentangling, was inspired by a discrete QIS protocol for sharing quantum secrets and adapted to the continuous-variable case.
Reconstructing the state after ignoring mode 3′′ only requires the inclusion of a beamsplitter and creation of an effective Mach-Zehnder interferometer, but ignoring mode 1′′ means that we have to use photodetection, feed-forward, and a local oscillator, all with their intrinsic noise contributions.
Quantum dots emitting at 480 and 500 nm, for example, differ by only about 50 cadmium and selenium atoms, so reproducible synthetic methods require control down to the level of tens of atoms as the crystals are grown.
oemagazine.com /fromTheMagazine/aug04/quantum.html   (2767 words)

 [No title]
The NIST quantum error correction method is a way of using a set of three atomic qubits to detect and correct data-handling errors in one of the qubits.
An ion’s quantum state includes properties such as the orientation of its “magnetic moment” (which can be thought of as a little compass needle inside the ion, with north and south poles).
When a qubit is measured by probing it with a laser, the state collapses to 0 or 1, with a rate of occurrence that depends on the angle of the ion’s tilt (or the probability of its being 1 or 0).
www.nist.gov /public_affairs/releases/quantum_repairkit.htm   (1800 words)

 Relational Quantum Mechanics
The difficulty in the interpretation of quantum mechanics derives from the fact that the theory was first constructed for describing microscopic systems (atoms, electrons, photons) and the way these interact with macroscopic apparatuses built to measure their properties.
Quantum events only happen in interactions between systems, and the fact that a quantum event has happened is only true with respect to the systems involved in the interaction.
Relational interpretations of quantum mechanics propose a solution to the interpretational difficulties of quantum theory based on the idea of weakening the notions of the state of a system, event, and the idea that a system, at a certain time, may just have a certain property.
plato.stanford.edu /entries/qm-relational   (5152 words)

 NIST demonstrates 'Teleportation' of atomic states for quantum computing
The quantum state of an atom is a description of such things as its energy, motion, magnetic field and other physical properties.
Quantum computing with atomic qubits requires manipulation of information contained in the quantum states of the atoms.
The properties that were teleported included the "spin state" of the ion (up, down or a superposition of the two), and the "phase" (which has to do with the relative positions of the peaks and troughs of an ion's wave properties).
www.eurekalert.org /pub_releases/2004-06/nios-nd061404.php   (804 words)

 Alternate View Column AV-62
An essential rule of the quantum world is that the state vector can never be completely known because no measurement can determine it completely (except in the special case that it has been prepared in some particular state or some member of a known "basis" group of states in advance).
This bizarre property of quantum systems was discovered in the formalism of quantum mechanics by Albert Einstein and his coworkers Podolsky and Rosen and is known as EPR non-locality.
There is a way around this quantum roadblock which exploits the peculiarities of EPR nonlocality to transmit the complete description of the state of a quantum system over nature's privileged communication channel without performing measurements that extract a complete description of the state vector as information.
www.npl.washington.edu /AV/altvw62.html   (1769 words)

 Parallel Power
A quantum computer's central processor, its Pentium chip, could conceivably be nothing more than a beaker of some suitable liquid, whose molecules would include a variety of atomic spin states specially chosen to perform a set task.
Flip a coin in the quantum realm and the outcome won't be heads or tails.
The quantum states of phosphorus atoms are particularly long-lived, so the hope is that they will provide qubits that are resistant to decoherence.
www.fortunecity.com /emachines/e11/86/qcomp1.html   (2218 words)

 Quantum Entanglement and Information
The puzzle is that the quantum state of the particle pair is inconsistent with the assignment of labels to the particles separately that could be associated with appropriately correlated values for the outcomes of position and momentum measurements.
Linearity of the state space means that for any two qubit states — call them 0 and 1 — that are orthogonal in the space of qubit states, there are qubit states that are represented by linear superpositions or sums of 0 and 1, with certain coefficients.
The impossibility of copying an unknown quantum state, or a state that is known to belong to a set of nonorthogonal states with a certain probability, and the existence of a trade-off relation between information gain and state disturbance, is the basis of the application of quantum information to cryptography.
plato.stanford.edu /entries/qt-entangle   (5628 words)

 Physics News Update
Quantum gravitational states have been observed for the first time.
Quantum properties--such as the quantization of energies, wavelike dynamics including interference, and an irreducible uncertainty in the simultaneous measurement of position and momentum--usually emerge only at the atomic level or under special circumstances (e.g.
Physicists at the Institute Laue-Langevin reactor in Grenoble, France employ a beam of ultracold neutrons.
www.aip.org /enews/physnews/2002/split/573-1.html   (428 words)

 NIST Ion Storage Group   (Site not responding. Last check: 2007-10-21)
When extended to many quantum bits, the parallelism of quantum superpositions allows exponential increase in speed relative to classical computers in certain algorithms, most notably an algorithm for factoring large numbers (P. Shor, ATandT) which is of interest in the field of cryptography.
In such a computer, the quantum bits are "wired" together by virtue of their collective motion in the trap, and externally applied laser light entangles quantum bits and allows the construction of quantum logic gates.
Quantum logic operations with trapped ions are limited by the coupling between the ion motion and the environment, resulting in quantum decoherence.
tf.nist.gov /ion/qucomp/intro.htm   (476 words)

 BBC NEWS | Science/Nature | Teleportation goes long distance
This enables the properties, or "quantum states", of light particles to be transferred between the sender (Alice) and the receiver (Bob).
Quantum teleportation relies on an aspect of physics known as "entanglement", whereby the properties of two particles can be tied together even when they are far apart.
As a result of this measurement, Bob transforms the quantum state of the other photon in the entangled pair into that of the input photon.
news.bbc.co.uk /2/hi/science/nature/3576594.stm   (545 words)

 Alternate View Column AV-45
The two quantum states of the particle, "photon reflected" and "photon transmitted", are superimposed, with definite observable consequences.
The mathematics of state superposition is special because quantum mechanics describes each state function as a complex variable that has a real part and an "imaginary" part (that behaves like the square root of -1).
This is not normally done in quantum mechanics, but it should be OK. It seems to be consistent with both the formalism of the theory and its usual interpretation, provided the states are isolated from measurement and outside interaction while evolving.
www.npl.washington.edu /AV/altvw45.html   (1946 words)

 ipedia.com: Identical particles Article   (Site not responding. Last check: 2007-10-21)
There are two main categories of identical particles: bosons, which can share quantum states, and fermions, which are forbidden from sharing quantum states (this property of fermions is known as the Pauli exclusion principle.) Examples of bosons are photons, gluons, phonons, and helium-4 atoms.
The eigenvalues of P are +1 and -1, and the corresponding eigenvectors are the symmetric and antisymmetric states:
The probability of obtaining two particles in the 0> state is 0.25; the probability of obtaining two particles in the 1> state is 0.25; and the probability of obtaining one particle in the 0> state and the other in the 1> state is 0.5.
www.ipedia.com /identical_particles.html   (2472 words)

 quantumredshift   (Site not responding. Last check: 2007-10-21)
This is achieved by imposing a quantum condition on the second of the two equations governing the behaviour of the Bohr atom (the orbital energy equation).
Therefore Corollary 2 states: Within a quantum interval, atomic quantities that are affected by smooth changes in the properties of the physical vacuum will vary in such a way that energy is conserved.
He stated that “… if the universe had constant linear dimensions in both dynamical and atomic units, the increase in redshift with distance (or equivalently, with lookback time) would imply an increase in c at past epochs, or that c was decreasing as time moves forward” [55].
www.setterfield.org /quantumredshift.htm   (9041 words)

 QDD : A Quantum Computer Emulation Library
QDD is unique in that the its emulation of quantum computing is based upon a Binary Decision Diagram (BDD) representation of the quantum state.
Quantum Fog is similar to QCL and Open QuBit in that it provides an exact simulation of quantum behavior, but it differs in that it uses Bayesian Nets to represent the quantum state.
Bayesian Nets are used in Quantum Fog because of their expressivness and because they are considered a natural vehicle for working with the conditional probabilities typically encountered in entangled quantum states.
thegreves.com /david/QDD/qdd.html   (894 words)

 LANL | Quantum Tutorial | Orthogonal Quantum States
The examples of photons with vertical ("V") or horizontal ("H") polarization introduce the concept of orthogonal quantum states.
It is a remarkable property of photons that any other single-photon polarization state can be formed from a suitable linear combination of "V" and "H" states, possibly with complex coefficients.
We say that single-photon polarization is a two-state (or two-level) quantum system, and that "V" and "H" form a basis for the space of polarizations (an example of a Hilbert space).
www.lanl.gov /science/centers/quantum/ortho.shtml   (126 words)

 The Quantum World   (Site not responding. Last check: 2007-10-21)
The logic elements of a quantum computer could be, for example, the "half-up, half-down" Schroedinger cat-state rather than the definite up and down states a classical computer would use.
Two such states might then interact in such a way as to produce an even more complex final state which contains -- again, all at once -- representations of all the numbers in the 1024 ¥ 1024 multiplication table.
As soon as any measurement is made on the quantum "multiplication table" state, for example, the computer will respond with just a single answer out of the 1024 ¥ 1024 possible answers that could have emerged.
www.idmon.freeserve.co.uk /quant9.htm   (1154 words)

Teleportation promises to be quite useful as an information processing primitive, facilitating long range quantum communication (perhaps unltimately leading to a "quantum internet"), and making it much easier to build a working quantum computer.
In the past, the idea of teleportation was not taken very seriously by scientists, because it was thought to violate the uncertainty principle of quantum mechanics, which forbids any measuring or scanning process from extracting all the information in an atom or other object.
But now it is known that, through the phenomenon of quantum teleportation, they can deliver exactly that part of the information in an object which is too delicate to be scanned out and delivered by conventional methods.
www.research.ibm.com /quantuminfo/teleportation   (1034 words)

 Wired News: Spin Doctors Create Quantum Chip
University of Michigan scientists have created the first quantum microchip, which could be a giant stride in the race to produce a new generation of brawny, super-fast computers.
So, on a semiconductor chip roughly the size of a postage stamp, the Michigan scientists designed and built a device known as an ion trap, which allowed them to isolate individual charged atoms and manipulate their quantum states.
Known as quantum superposition, the ability of the qubit to occupy two quantum states at once means that it can execute computations at an exponentially faster rate.
www.wired.com /news/technology/0,70001-0.html?tw=rss.index   (708 words)

 Quantum Gravitational States Observed For First Time
Quantum properties usually show up only at the atomic level.
Observing such properties in phenomena governed by the electromagnetic or the weak and strong nuclear forces is common.
The researchers report seeing a minimum (quantum) energy of 1.4 picoelectron volts (1.4 x 10^-12 eV), which corresponds to a vertical velocity of 1.7 cm/sec.
unisci.com /stories/20021/0121021.htm   (483 words)

 Quantum States
Generally, the quantum state of a physical system is specified by a non-zero vector in a Hilbert space over the complex numbers (call it
In quantum mechanics, the angular momentum is quantized: its magnitude (measured along the axis of rotation) must be
But I just noted that the set of states is ``isomorphic'' to the Riemann sphere.
math.ucr.edu /home/baez/lie/node10.html   (289 words)

 Quantum Mechanics: 1-Dimensional Particle States Applet   (Site not responding. Last check: 2007-10-21)
This java applet is a quantum mechanics simulation that shows the behavior of a single particle in bound states in one dimension.
To view a state, move the mouse over its energy level on the potential graph.
You may also select a single state by picking one of the phasors at the bottom and double-clicking on it.
www.falstad.com /qm1d   (229 words)

 Lukin Group at Harvard University: Home
The emphasis is on studies of quantum systems consisting of interacting photons, atoms, molecules and electrons coupled to realistic environments.
We are developing new techniques for controlling the quantum dynamics of such systems, and studying fundamental physical phenomena associated with them.
In the course of this work we are also exploring the emerging interfaces between quantum optics and atomic physics on the one hand, and condensed matter and mesoscopic physics on the other.
lukin.physics.harvard.edu   (889 words)

 STM Image Gallery - The Corral Reef
The discovery of the STM's ability to image variations in the density distribution of surface state electrons created in the artists a compulsion to have complete control of not only the atomic landscape, but the electronic landscape also.
The ripples in the ring of atoms are the density distribution of a particular set of quantum states of the corral.
Intrigued with the possibility of observing "Quantum Chaos", the artists constructed a stadium shaped structure in the hopes of observing so-called "scarring" of the density distribution of the surface state electron density.
www.almaden.ibm.com /vis/stm/corral.html   (288 words)

Research on quantum information technology has advanced a great deal since the previous meeting.
Mesoscopic physics, such as spins in nano-scale semiconductor structures, micro-fabricated superconducting junctions and extraordinary metal contacts have now been not only theoretically but also experimentally established as important solid-state elements of quantum information devices.
The book also contains some papers on information theory from the viewpoint of quantum algorithms, indicating that further collaboration between physics and computer science promises to produce fruitful results in quantum information technology.
www.worldscibooks.com /physics/5924.html   (161 words)

 Samuel L. Braunstein's articles
Quantum interferometric optical lithography: exploiting entanglement to beat the diffraction limit.
Statistical distance and the geometry of quantum states.
Macroscopic quantum superpositions by means of single-atom dispersion.
www-users.cs.york.ac.uk /~schmuel/cv.html   (1593 words)

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