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Showing posts with label Cdms. Show all posts
Showing posts with label Cdms. Show all posts

Monday, July 09, 2012

Majorana Particles in Computation


An artist's conception of the Majorana - a previously elusive subatomic particle whose existence has never been confirmed - until now. Dutch nano-scientists at the technological universities of Delft and Eindhoven, say they have found evidence of the particle. To find it, they devised miniscule circuitry around a microscopic wire in contact with a semiconductor and a superconductor. Lead researcher Leo Kouwenhoven. SOUNDBITE (English), NANOSCIENTIST OF DELFT UNIVERSITY, LEO KOUWENHOVEN, SAYING: "The samples that we use for measuring the Majorana fermions are really very small, you can see the holder of the sample, the sample is actually inside here and if you zoom in, you can actually see little wires and if you zoom in more, you see a very small nano-meter scale sample, where we detected one pair of Majoranas." When a magnetic field was applied along the the 'nanowire', electrons gathered together in synchrony as a Majorana particle. These subatomic particles could be used to encode information, turning them into data to be used inside a tiny, quantum computer. SOUNDBITE (English), NANOSCIENTIST OF DELFT UNIVERSITY, LEO KOUWENHOVEN, SAYING: "The goal is actually to develop those nano-scale devices into little circuits and actually make something like a quantum computer out of it, so they have special properties that could be very useful for computation, a particural kind of computation which we call quantum computation, which would replace actually our current computers by computers that are much more efficient than what we have now." The Majorana fermion's existence was first predicted 75 years ago by Italian Ettore Majorana. Probing the Majorana's particles could allow scientists to understand better the mysterious realm of quantum mechanics. Other groups working in solid state physics are thought to be close to making similar announcements....heralding a new era in super-powerful computer technology. Were he alive today Majorana may well be amazed at the sophisticated computer technology available to ordinary people in every day life. But compared to the revolution his particle may be about to spark, it will seem old fashioned in the not too distant future. Jim Drury, Reuters







Majorana fermion

Composition Elementary
Statistics Fermionic
Status Hypothetical
Antiparticle Itself
Theorised Ettore Majorana, 1937

A Majorana fermion is a fermion that is its own anti-particle. The term is sometimes used in opposition to Dirac fermion, which describes particles that differ from their antiparticles. It is common that bosons (such as the photon) are their own anti-particle. It is also quite common that fermions can be their own anti-particle, such as the fermionic quasiparticles in spin-singlet superconductors (where the quasiparticles/Majorana-fermions carry spin-1/2) and in superconductors with spin-orbital coupling, such as Ir, (where the quasiparticles/Majorana-fermions do not carry well defined spins).

Contents

 

Theory


The concept goes back to Ettore Majorana's 1937 suggestion[1] that neutral spin-1/2 particles can be described by a real wave equation (the Majorana equation), and would therefore be identical to their antiparticle (since the wave function of particle and antiparticle are related by complex conjugation).

The difference between Majorana fermions and Dirac fermions can be expressed mathematically in terms of the creation and annihilation operators of second quantization. The creation operator γj creates a fermion in quantum state j, while the annihilation operator γj annihilates it (or, equivalently, creates the corresponding antiparticle). For a Dirac fermion the operators γj and γj are distinct, while for a Majorana fermion they are identical.

 

Elementary particle


No elementary particle is known to be a Majorana fermion. However, the nature of the neutrino is not yet definitely settled; it might be a Majorana fermion or it might be a Dirac fermion. If it is a Majorana fermion, then neutrinoless double beta decay is possible; experiments are underway to search for this type of decay.
The hypothetical neutralino of supersymmetric models is a Majorana fermion.

 

Quasiparticle


In superconducting materials, Majorana fermions can emerge as (non-fundamental) quasiparticles.[2] (People also name protected zero-energy mode as Majorana fermion. The discussions in the rest of this article are actually about such protected zero-energy mode, which is quite different from the propagating particle introduced by Majorana.) The superconductor imposes electron hole symmetry on the quasiparticle excitations, relating the creation operator γ(E) at energy E to the annihilation operator γ(−E) at energy −E. At the Fermi level E=0, one has γ=γ so the excitation is a Majorana fermion. Since the Fermi level is in the middle of the superconducting gap, these are midgap states. A quantum vortex in certain superconductors or superfluids can trap midgap states, so this is one source of Majorana fermions.[3][4][5] Shockley states at the end points of superconducting wires or line defects are an alternative, purely electrical, source.[6] An altogether different source uses the fractional quantum Hall effect as a substitute for the superconductor.[7]

It was predicted that Majorana fermions in superconductors could be used as a building block for a (non-universal) topological quantum computer, in view of their non-Abelian anyonic statistics.[8]

 

Experiments in superconductivity


In 2008 Fu and Kane provided a groundbreaking development by theoretically predicting that Majorana fermions can appear at the interface between topological insulators and superconductors.[9][10] Many proposals of a similar spirit soon followed. An intense search to provide experimental evidence of Majorana fermions in superconductors[11][12] first produced some positive results in 2012.[13][14] A team from the Kavli Institute of Nanoscience at Delft University of Technology in the Netherlands reported an experiment involving indium antimonide nanowires connected to a circuit with a gold contact at one end and a slice of superconductor at the other. When exposed to a moderately strong magnetic field the apparatus showed a peak electrical conductance at zero voltage that is consistent with the formation of a pair of Majorana quasiparticles, one at either end of the region of the nanowire in contact with the superconductor.[15]

This experiment from Delft marks a possible verification of independent theoretical proposals from two groups[16][17] predicting the solid state manifestation of Majorana fermions in semiconducting wires.

It is important to note that the solid state manifestations of Majorana fermions are emergent low-energy localized modes of the system (quasiparticles) which are not fundamental new elementary particles as originally envisioned by Majorana (or as the neutrino would be if it turns out to be a Majorana fermion), but are effective linear combinations of half-electrons and half-holes which are topological anyonic objects obeying non-Abelian statistics.[8] The terminology "Majorana fermion" is thus not a good nomenclature for these solid state Majorana modes.

 

References

  1. ^ E. Majorana (1937). "Teoria simmetrica dell’elettrone e del positrone" (in Italian). Nuovo Cimento 14: 171. English translation.
  2. ^ F. Wilczek (2009). "Majorana returns". Nature Physics 5 (9): 614. Bibcode 2009NatPh...5..614W. DOI:10.1038/nphys1380.
  3. ^ N.B. Kopnin; Salomaa (1991). "Mutual friction in superfluid 3He: Effects of bound states in the vortex core". Physical Review B 44 (17): 9667. Bibcode 1991PhRvB..44.9667K. DOI:10.1103/PhysRevB.44.9667.
  4. ^ G.E. Volovik (1999). "Fermion zero modes on vortices in chiral superconductors". JETP Letters 70 (9): 609. Bibcode 1999JETPL..70..609V. DOI:10.1134/1.568223.
  5. ^ N. Read; Green (2000). "Paired states of fermions in two dimensions with breaking of parity and time-reversal symmetries and the fractional quantum Hall effect". Physical Review B 61 (15): 10267. Bibcode 2000PhRvB..6110267R. DOI:10.1103/PhysRevB.61.10267.
  6. ^ A. Yu. Kitaev (2001). "Unpaired Majorana fermions in quantum wires". Physics-Uspekhi (supplement) 44 (131): 131. Bibcode 2001PhyU...44..131K. DOI:10.1070/1063-7869/44/10S/S29.
  7. ^ G. Moore; Read (1991). "Nonabelions in the fractional quantum Hall effect". Nuclear Physics B 360 (2–3): 362. Bibcode 1991NuPhB.360..362M. DOI:10.1016/0550-3213(91)90407-O.
  8. ^ a b C. Nayak, S. Simon, A. Stern, M. Freedman, and S. Das Sarma (2008). "Non-Abelian anyons and topological quantum computation". Reviews of Modern Physics 80: 1083.
  9. ^ L. Fu; C. L. Kane (2008). "Superconducting Proximity Effect and Majorana Fermions at the Surface of a Topological Insulator". Physical Review Letters 10 (9): 096407. DOI:10.1103/PhysRevLett.100.096407.
  10. ^ L. Fu; C. L. Kane (2009). "Josephson current and noise at a superconductor/quantum-spin-Hall-insulator/superconductor junction". Physical Review B 79 (16): 161408. DOI:10.1103/PhysRevB.79.161408.
  11. ^ J. Alicea. New directions in the pursuit of Majorana fermions in solid state systems. arXiv:1202.1293.
  12. ^ C. W. J. Beenakker. Search for Majorana fermions in superconductors. arXiv:1112.1950.
  13. ^ E. S. Reich (28 February 2012). "Quest for quirky quantum particles may have struck gold". Nature News. DOI:10.1038/nature.2012.10124.
  14. ^ Jonathan Amos (13 April 2012). "Majorana particle glimpsed in lab". BBC News. Retrieved 15 April 2012.
  15. ^ V. Mourik; K. Zuo; S.M. Frolov; S.R. Plissard; E.P.A.M. Bakkers; L.P. Kouwenhoven (12 April 2012). "Signatures of Majorana fermions in hybrid superconductor-semiconductor nanowire devices". Science. arXiv:1204.2792. DOI:10.1126/science.1222360.
  16. ^ R. Lutchyn; J. Sau; S. Das Sarma (2010). "Majorana Fermions and a Topological Phase Transition in Semiconductor-Superconductor Heterostructures". Physical Review Letters 105 (7): 077001. Bibcode 2010PhRvL.105g7001L. DOI:10.1103/PhysRevLett.105.077001.
  17. ^ Y. Oreg; G. Refael; F. von Oppen (2010). "Helical Liquids and Majorana Bound States in Quantum Wires". Physical Review Letters 105 (17): 177002. DOI:10.1103/PhysRevLett.105.177002.


The Majorana experiment will search for neutrinoless double-beta decay of 76Ge. The discovery of this process would imply that the neutrino is a Majorana fermion (its own anti-particle) and allow a measurement of the effective Majorana neutrino mass. The first stage of the experiment, the Majorana Demonstrator, will consist of 60kg of germanium crystal detectors in three cryostats. Half of these will be made from natural germanium and half from germanium enriched in 76Ge. The goals of the Demonstrator are to test a claim for measurement of neutrinoless double beta-decay by Klapdor-Kleingrothaus et al. (2006), to demonstrate a low enough background to justify the construction of a larger tonne-scale experiment, and to demonstrate the scalability of the technology to the tonne scale. The experiment will be located at the 4850 ft level of the Sanford Laboratory in Lead, South Dakota. See: The Majorana neutrinoless double beta-decay experiment





See Also: Sounding Off on the Dark Matter Issue

Friday, September 23, 2011

Measurement of the neutrino velocity with the OPERA detector

New results from OPERA on neutrino propertieslive from Main Amphitheatre.

“This result comes as a complete surprise,” said OPERA spokesperson, Antonio Ereditato of the University of Bern. “After many months of studies and cross checks we have not found any instrumental effect that could explain the result of the measurement. While OPERA researchers will continue their studies, we are also looking forward to independent measurements to fully assess the nature of this observation.” 


 “When an experiment finds an apparently unbelievable result and can find no artefact of the measurement to account for it, it’s normal procedure to invite broader scrutiny, and this is exactly what the OPERA collaboration is doing, it’s good scientific practice,” said CERN Research Director Sergio Bertolucci. “If this measurement is confirmed, it might change our view of physics, but we need to be sure that there are no other, more mundane, explanations. That will require independent measurements.”See:OPERA experiment reports anomaly in flight time of neutrinos from CERN to Gran Sasso




Have we considered their mediums of expression to know that we have witnessed Cerenkov radiation as a process in the faster than light, to know the circumstances of such expressions to have been understood as backdrop measures of processes we are familiar with. Explain the history of particulate expressions from vast distances across our universe?

The OPERA Detector


This is something very different though and it will be very interesting the dialogue and thoughts shared so as to look at the evidence in a way that helps us to consider what is sound in it's understanding, as speed of light.

See Also:

Thursday, August 12, 2010

Dark Matter

(Click on Image)


Friedman Equation What is pdensity.

What are the three models of geometry? k=-1, K=0, k+1

Negative curvature

Omega=the actual density to the critical density
If we triangulate Omega, the universe in which we are in, Omegam(mass)+ Omega(a vacuum), what position geometrically, would our universe hold from the coordinates given?  

See Also:
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I am not sure if it is proper to take such expressions of dark energy and dark matter as they are perceived in the universe and apply them to a "dynamical movement of a kind,"  as an expression of that Universe?

Part of that "Toposense" you might say?




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IN their figure 2. Hyperbolic space, and their comparative relation to the M.C.Escher's Circle Limit woodcut, Klebanov and Maldacena write, " but we have replaced Escher's interlocking fish with cows to remind readers of the physics joke about the spherical cow as an idealization of a real one. In anti-de Sitter/conformal theory correspondence, theorists have really found a hyperbolic cow."

Click on image for larger version. See:Solving quantum field theories via curved spacetimes by Igor R. Klebanov and Juan M. Maldacena

See:

Thursday, July 29, 2010

Lighting up the dark universe


Image ...
The CHASE detector. The end of the magnet (orange) can be seen on the right.

Exploring our dark universe is often the domain of extreme physics. Traces of dark matter particles are searched for by huge neutrino telescopes located underwater or under Antarctic ice, by scientists at powerful particle colliders, and deep underground.  Clues to mysterious dark energy will be investigated using big telescopes on Earth and experiments that will be launched into space.
But an experiment doesn’t have to be exotic to explore the unexplained. At the International Conference on High Energy Physics, which ended today in Paris, scientists unveiled the first results from the GammeV-CHASE experiment, which used 30 hours’ worth of data from a 10-meter-long experiment to place the world’s best limits on the existence of dark energy particles.
CHASE, which stands for Chameleon Afterglow Search, was constructed at Fermilab to search for hypothetical particles called chameleons. Physicists theorize that these particles may be responsible for the dark energy that is causing the accelerating expansion of our universe.

“One of the reasons I felt strongly about doing this experiment is that it was a good example of a laboratory experiment to test dark energy models,” says CHASE scientist Jason Steffen, who presented the results at ICHEP. “Astronomical surveys are important as well, but they’re not going to tell us everything.” CHASE was a successor to Fermilab’s GammeV experiment, which searched for chameleon particles and another hypothetical particle called the axion.

See: Lighting up the dark universe by Katie Yurkewicz Posted in ICHEP 2010

See Also:Backreaction: Detection of Dark Energy on Earth? - Improbable

Monday, December 21, 2009

Sounding off on Economic Constraints in Experimentation

I mean most understand that the economic spending "is the choice" as to whether an area of research will be continued to be funded or not, according to the direction that research council choose. Limited resources according to the times? This is not a reflection of the absurdity of going in a certain direction, but one of where the money is to allocated from a scientific endeavor and standpoint.


Finally, tantalisingly, the Cryogenic Dark Matter Search (CDMS) released the results of its latest (and final) effort to search for the Dark Matter that seems to make up most of the matter in the Universe, but doesn’t seem to be the same stuff as the normal atoms that we’re made of. Under some theories, the dark matter would interact weakly with normal matter, and in such a way that it could possibly be distinguished from all the possible sources of background. These experiments are therefore done deep underground — to shield from cosmic rays which stream through us all the time — and with the cleanest and purest possible materials — to avoid contamination with both both naturally-occurring radioactivity and the man-made kind which has plagued us since the late 1940s.See:Doctors, Deep Fields and Dark Matter (Bold added for emphasis by me)


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ZEPLIN-III-Project

Observational studies of the rotation of galaxies and groups of galaxies strongly suggest the existence of a dominating amount of matter invisible at any electromagnetic wavelengths. One of the favoured forms of this "missing mass", both theoretically and observationally, is the WIMP (Weakly Interacting Massive Particle). These cold WIMPs are expected to be scattered by the nuclei of typical detector material at a rate of less than one per kg per day, yielding energy depositions in the 1-50 keV energy range.

ZEPLIN-III is a two-phase (liquid/gas) xenon detector looking for galactic WIMP dark matter at the Boulby Underground Laboratory, North Yorkshire, UK, at a depth of 1100 m. At this depth the cosmic-ray background is reduced by a factor of a million. The WIMP target consists of 12 kg of cold liquid xenon topped by a thin layer of xenon gas. These are viewed by an array of 31 photomultiplier tubes immersed in the liquid.

The detector operates at higher electric fields than other, similar systems, namely its predecessor ZEPLIN-II, and provides high-precision reconstruction of the interaction point in three dimensions. Together with the low-background construction (mainly high-purity copper), these features will give ZEPLIN-III higher sensitivity in direct WIMP searches.



The ZEPLIN-III Collaboration includes the University of Edinburgh, Rutherford Appleton Laboratory, Imperial College London, LIP-Coimbra (Portugal) and ITEP-Moscow (Russia).






ZEPLIN-III PICTURE GALLERY

Photomultiplier array covered by electrode grid 

Sunday, December 13, 2009

SuperCDMS An Improvement on Detection

So far no WIMP interaction has been observed, so the sensitivity needs to be improved further. This will be achieved by increasing the total detector mass (and with this the probability that a WIMP interacts in the detector) and at the same time reducing the background and improving the discrimination power. This effort started in 2009 under the name SuperCDMS.

The first set of new detectors has been installed in the experimental setup at Soudan and is operating since summer 2009. First tests show that the background levels are in the expected range. Over the course of the next year all CDMS detectors will be replaced by the new larger detectors. The active mass will increase by more than a factor of three to about 15 kg.
See:CDMS and SuperCDMS Experiments
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It is known since the 1930's that a significant part of the mass of the universe is invisible. This invisible material has been named Dark Matter. Weakly Interacting Massive Particles (WIMPs) are considered as one of the most convincing explanation for this phenomenon.See:SuperCDMS Queen's Home
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SNOLAB is an underground science laboratory specializing in neutrino and dark matter physics. Situated two km below the surface in the Vale Inco Creighton Mine located near Sudbury Ontario Canada, SNOLAB is an expansion of the existing facilities constructed for the Sudbury Neutrino Observatory (SNO) solar neutrino experiment. SNOLAB follows on the important achievements in neutrino physics achieved by SNO and other underground physics measurements. The primary scientific emphasis at SNOLAB will be on astroparticle physics with the principal topics being:
Low Energy Solar Neutrinos;
Neutrinoless Double Beta Decay;
Cosmic Dark Matter Searches;
Supernova Neutrino Searches.

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The Sudbury Neutrino Laboratory, located two kilometres below the surface, is the site of groundbreaking international research.

 The 17-metre-wide SNO detector in Vale Inco’s Creighton Mine.
Ernest Orlando, Lawrence Berkeley National Laboratory

Update:
Latest Results in the Search for Dark Matter
Thursday, December 17, 2009

 

 

Dark Matter Detected, or Not? Live Blogging the Seminar

by JoAnne

Saturday, December 12, 2009

Sounding Off on the Dark Matter Issue

Fermilab

If dark matter can pull gravitationally, it has mass

So here is an article of 2006 with some interesting information. Now these experimental procedures are always interesting to me because of the type of detectors that were dreamt up in which to measure some aspect of the reality supposed, and realized, by noise in the background.


For scientists to "hear" a dark matter particle, it must hit an atom in one of the crystals at the heart of the CDMS detectors. The crystals are kept cold—close to absolute zero—to reduce atomic movement, keeping the crystals quiet. The detectors "listen" for vibrations inside the crystal, like ears listening for vibrations in the air.

The detectors contain two kinds of crystals, germanium and silicon. A germanium atom is larger than a silicon one: Its nucleus has 73 protons and neutrons compared to silicon's 28. This size difference helps CDMS sort out yet another source of background—neutrons. High-energy cosmic rays and radioactive decays in the matter surrounding the detectors can produce neutrons. Hitting atoms in the crystals, these neutrons cause a "sound" in the detectors similar to the one made by the predicted dark matter particles.
See: Listening for whispers of dark matter




Model of the Cryogenic Dark Matter Search which translates actual data into sound and light. We have not yet had a dark matter interaction, but we have lots of particles hitting the detectors and that is what you are watching. A downloadable version is at my webpage http://www.hep.umn.edu/~prisca More info on our experiment can be found at http://cdms.berkeley.edu and http://www.soudan.umn.edu

So lets mover forward here to Dec 10, while waiting to hear on Dec 17 for more news.

The CDMS collaboration has completed the analysis of the final CDMS-II runs, which more than doubled the total data from all previous runs combined. The collaboration is working hard to complete the first scientific publication about these new results and plans to submit the manuscript to arXiv.org before the two primary CDMS talks scheduled for Thursday, Dec. 17, at Fermilab and at SLAC. See:The search for dark matter:has CDMS found something?

Update:
Latest Results in the Search for Dark Matter
Thursday, December 17, 2009

Dark Matter Detected, or Not? Live Blogging the Seminar

by JoAnne