QTC - Quantum Tunnelling Composite: High-impact Strategies - What You Need to Know: Definitions, Adoptions, Impact, Benefits, Maturity, Vendors

Kevin Roebuck

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Quantum tunnelling composites (or QTCs) are composite materials of metals and non-conducting elastomeric binder, used as pressure sensors. They utilise quantum tunnelling: without pressure, the conductive elements are too far apart to conduct electricity; when pressure is applied, they move closer and electrons can tunnel through the insulator. The effect is far more pronounced than would be expected from classical (non-quantum) effects alone, as classical electrical resistance is linear (proportional to distance), while quantum tunnelling is exponential with decreasing distance, allowing the resistance to change by a factor of up to 1012 between pressured and unpressured states.

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In easy to read chapters, with extensive references and links to get you to know all there is to know about QTC right away. A quick look inside: Quantum tunnelling composite, Photodetection, Brus equation, Charge qubit, Colossal magnetoresistance, Conductance quantum, Coulomb blockade, Coulomb staircase, Electrically detected magnetic resonance, Enhancement or quenching of QD, Q-wire and QW radiations, Flux qubit, Giant magnetoresistance, Intersubband polariton, Magnetocapacitance, Molecular beam, Multiple exciton generation, Nanocrystal solar cell, Phase qubit, Quantum bus, Quantum dot, Quantum dot display, Quantum dot solar cell, Quantum efficiency, Quantum electrodynamics, Quantum flux parametron, Quantum Hall effect, Quantum heterostructure, Quantum mirage, Quantum point contact, Quantum spin Hall effect, Quantum well, Quantum wire, Quantum-confined Stark effect, Quiteron, Rapid single flux quantum, Spin valve, Superconducting quantum computing, Superconducting tunnel junction, Trion (physics), Anomalous magnetic dipole moment, Bhabha scattering, Bremsstrahlung, Compton scattering, Delbruck scattering, Di-positronium, Electron, Gauge fixing, Gupta-Bleuler formalism, Møller scattering, Photon, Positron, Positronium, Positronium hydride, Precision tests of QED, Quantum beats, Self-energy, Vacuum polarization, Vertex function, Ward-Takahashi identity...and Much, Much More!

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• Computers
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• Publié par: Emereo Publishing
• Date de parution: 24 octobre 2012
• Nombre de lectures: 0
• EAN13: 9781743380055
• Langue: English
• Poids de l'ouvrage: 10 Mo

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Contents

Articles Quantum tunnelling composite

Photodetection

Brus equation

Charge qubit Colossal magnetoresistance Conductance quantum Coulomb blockade Coulomb staircase Electrically detected magnetic resonance Enhancement or quenching of QD, Q-wire and QW radiations Flux qubit Giant magnetoresistance Intersubband polariton Magnetocapacitance Molecular beam Multiple exciton generation Nanocrystal solar cell Phase qubit Quantum bus Quantum dot Quantum dot display Quantum dot solar cell Quantum efficiency Quantum electrodynamics Quantum flux parametron Quantum Hall effect Quantum heterostructure Quantum mirage Quantum point contact Quantum spin Hall effect Quantum well Quantum wire Quantum-confined Stark effect Quiteron

1 2 3 4 5 6 7 9 10 11 12 14 17 18 18 18 19 21 24 25 34 39 44 46 57 58 61 61 62 64 65 67 68 70

Rapid single flux quantum Spin valve Superconducting quantum computing Superconducting tunnel junction Trion (physics) Anomalous magnetic dipole moment Bhabha scattering Bremsstrahlung

Compton scattering Delbruck scattering Di-positronium Electron Gauge fixing Gupta–Bleuler formalism Møller scattering Photon Positron Positronium Positronium hydride Precision tests of QED Quantum beats Self-energy Vacuum polarization Vertex function Ward–Takahashi identity

References Article Sources and Contributors Image Sources, Licenses and Contributors

Article Licenses License

70 72 73 74 77 78 80 85 90 95 97 98 121 127 129

131 149 152 155 155 159 161 163 164 165

168 172

174

Quantum tunnelling composite

Quantum tunnelling composite

Quantum tunnelling composites(orQTCs) are composite materials of metals and non-conducting elastomeric binder, used as pressure sensors. They utilise quantum tunnelling: without pressure, the conductive elements are too far apart to conduct electricity; when pressure is applied, they move closer and electrons can tunnel through the insulator. The effect is far more pronounced than would be expected from classical (non-quantum) effects alone, as classical electrical resistance is linear (proportional to distance), while quantum tunnelling is exponential with 12 decreasing distance, allowing the resistance to change by a factor of up to 10 between pressured and unpressured [1] states.

Applications QTC has been implemented within clothing to make“smart”, touchable membrane control panels to control electronic devices within the clothing, e.g. mp3 players or mobile phones. This allows equipment to be operated without removing clothing layers or opening fastenings and makes standard equipment usable in extreme weather or environmental conditions such as Arctic/Antarctic exploration or spacesuits. However, eventually, due to the low cost of QTC, this technology will become available to the general user. [2] In February 2008 the newly formed company QIO Systems Inc gained in a deal with Peratech the worldwide exclusive license to the intellectual property and design rights for the electronics and textile touchpads based on QTC [3] technology and for the manufacture and sale of ElekTex (QTC-based) textile touchpads for use in both consumer [4] and commercial applications. Lummi has announced a prototype flashlight which uses QTC in a dimmer-type switch.

Discovery [5] QTCs were discovered in 1996, and PeraTech Ltd was established to investigate them further.

References [1] D. Bloor, A. Graham, E. J. Williams, P. J. Laughlin, and D. Lussey (2006). "Metal–polymer composite with nanostructured filler particles and amplified physical properties".Applied Physics Letters88: 102103. Bibcode2006ApPhL..88j2103B. doi:10.1063/1.2183359. [2] http://www.qiosystems.com [3] http://www.eleksen.com/?page=news/index.asp&newsID=84 [4] http://www.talk2myshirt.com/blog/archives/421 [5] http://www.peratech.com/qtcmaterial.php

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Photodetection

Photodetection

This article is intended for those who are interested in the theoretical description of quantum process of photodetection. Readers who are interested in the applications of photodetection processes may want to read photodetector. [1] In his historic paper, entitled " The Quantum Theory of Optical Coherence," Roy J. Glauber set a solid foundation for the quantum electronics/quantum optics enterprise. The experimental development of the optical maser and later laser at that time had made the classical concept of optical coherence inadequate. Glauber started from the quantum theory of light detection by considering the process of photoionization in which a photodetector is triggered by an ionizing absorption of a photon. In the quantum theory of radiation, the electric field operator in the Coulomb gauge may be written as the sum of positive and negative frequency parts

where

One may expand

in terms of the normal modes as follows:

where are the unit vectors of polarization; this expansion has the same form as the classical expansion except that now the field amplitudes are operators. Glauber showed that, for an ideal photodetector situated at a point in a radiation field, the probability of observing a photoionization event in this detector between time and is proportional to , where

and specifies the state of the field. Since the radiation field is a quantum-mechanical one, we do not know the exact properties of the incident light, and the prabability should be averaged, as in the classical theory, to be proportional to

where the angular brackets mean an average over the light field. The significance of the quantum theory of coherence is in the ordering of thecreationanddestructionoperators and :

Since is not equal to for a light field, the order makes the quantum statistical measurements (such as photon counting) quite different from the classical ones, i.e., the nonclassical properties of light, such as photon antibunching. Moreover, Glauber's theory of photodetection is of far-reaching fundamental significance to interpretation of [2] quantum mechanics. The Glauber detection theory differs from the Born probabilistic interpretation, in that it expresses the meaning of physical law in terms of measured facts (relationships), counting events in the detection processes, without assuming the particle model of matter. These concepts quite naturally lead to a relational approach to quantum physics.

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Photodetection

References [1] R. J. Glauber, Phys. Rev. 130, 2529 (1963). [2] M. Born, Z. Phys. 37, 863 (1926). For an English translation, see Quantum Theory and Measurement ed. J. A. Wheeler and W. H. Zurek, Princeton Univ. Press, New Jersey, 1983, pp. 52-55.

Brus equation

TheBrus Equationcan be used to describe the emission energy of quantum dot semiconductor nanocrystals (such as CdSe nanocrystals) in terms of the band gap energy (E ), Planck's constant (h), the radius of the quantum dot (r), gap the mass of the excited electron (m *), and the mass of the electron hole (m *). e h The radius of the quantum dot affects the wavelength of the emitted light due to quantum confinement, and this equation describes the effect of changing the radius of the quantum dot on the wavelength of light emitted. (Remember, ΔE = hc/λ where c = the speed of light in m/s). This is useful, as it allows for the experimental calculation of the radius of a quantum dot. 2 2 [1] The overall equation is: ΔE(r) = E + [h^ /8r^ (1/m * + 1/m *)] gap e h E , m *, and m * are unique for each nanocrystal composition. For example, with CdSe nanocrystals: gap e h -19 E (CdSe) = 1.74 eV (=2.8*10^ Joules) gap -31 m * (CdSe) = 0.13*m = 0.13*mass of an electron = 1.18*10^ kg e e -31 and, m * (CdSe) = 0.45*m = 0.45*mass of an electron = 4.09*10^ kg h e

References [1] Kippeny, T; Swafford, L.A.; Rosenthal, S.A.; (2002).Journal of Chemical Education79: 1094b1100.

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Charge qubit

Charge qubit

In quantum computing, acharge qubitis a superconducting qubit whose basis states are charge states (i.e. states which represent the presence or absence of excess Cooper pairs in the island). A charge qubit is formed by a tiny superconducting island (also known as a Cooper-pair box) coupled by a Josephson junction to a superconducting reservoir (see figure). The state of the qubit is determined by the number of Cooper pairs which have tunneled across the junction. In contrast with the charge state of an atomic or molecular ion, the charge states of such an "island" involve a macroscopic number of conduction electrons of the island. The quantum superposition of charge states can be achieved by tuning the gate voltage U that controls the chemical potential of the island. The charge qubit is typically read-out by electrostatically coupling the island to an extremely sensitive electrometer such as the radio-frequency single-electron transistor.

Typical T1 times for a charge qubit are on the order of 1-2 μs.

Circuit diagram of a Cooper pair box circuit. The island (dotted line) is formed by the superconducting electrode between the gate capacitor and the junction capacitance.

References [1] • V. Bouchiat, D. Vion, P. Joyez, D. Esteve and M. H. Devoret, "Quantum coherence with a single Cooper pair" , Physica ScriptaT76, 165-170 (1998) • Y. Nakamura, Yu. A. Pashkin and J. S. Tsai, "Coherent control of macroscopic quantum states in a [2] single-Cooper-pair box" ,Nature398, 786-788 (1999) • K. W. Lehnert, B. A. Turek, K. Bladh, L. F. Spietz, D. Gunnarsson, P. Delsing and R. J. Schoelkopf, [3] "Measurement of the excited-state lifetime of a microelectronic circuit" ,Physical Review Letters90, 027002 (2003)

References [1] http://iramis.cea.fr/spec/Pres/Quantro/Qsite/publi/articles/fichiers/preprints/98-PScripta-Bouchiat-SSbox.pdf [2] http://www.nature.com/nature/journal/v398/n6730/full/398786a0.html [3] http://www.eng.yale.edu/rslab/papers/konradT1PRL.pdf

4

Colossal magnetoresistance

Colossal magnetoresistance

Colossal magnetoresistance(CMR) is a property of some materials, mostly manganese-based perovskite oxides, that enables them to dramatically change their electrical resistance in the presence of a magnetic field. The magnetoresistance of conventional materials enables changes in resistance of up to 5%, but materials featuring CMR may demonstrate resistance changes by orders of magnitude. [1] Initially discovered in mixed-valence perovskite manganites in the 1950s by G. H. Jonker and J. H. van Santen., a first theoretical description in terms of the double-exchange mechanism was given early on. In this model, the spin orientation of adjacent Mn-moments is associated with kinetic exchange of e -electrons. Consequently, alignment of g the Mn-spins by an external magnetic field causes higher conductivity. Relevant experimental work was done by [2] [3] [4] [5] Volger, Wollan and Koehler, and later on by Jirak et al. and Pollert et al. However the double exchange model did not adequately explain the high insulating-like resistivity above the [6] [7] [8] transition temperature. In the 1990s, work by R. von Helmholt et al. and Jin et al. initiated a large number of further studies. Although there is still no complete understanding of the phenomenon, there is a variety of theroetical and experimental work providing a deeper understanding of the relevant effects.

One prominent model is the so-calledhalf-metallic ferromagnetic model, which is based on spin-polarized (SP) band structure calculations using the local spin-density approximation (LSDA) of the density functional theory (DFT) where separate calculations are carried out for spin-up and spin-down electrons. The half-metallic state is concurrent with the existence of a metallic majority spin band and a nonmetallic minority spin band in the ferromagnetic phase.

This model is not the same as the Stoner Model of itinerant ferromagnetism. In the Stoner model, a high density of states at the Fermi level makes the nonmagnetic state unstable. With SP calculations on covalent ferromagnets, the exchange-correlation integral in the LSDA-DFT takes the place of the Stoner parameter. The density of states at the [9] Fermi level does not play a special role. A significant advantage of the half-metallic model is that it does not rely on the presence of mixed-valency as does the double exchange mechanism and it can therefore explain the observation of CMR in stoichiometric phases like the pyrochlore Tl Mn O . Microstructural effects have also been 2 2 7 investigated for polycrystalline samples and it has been found that the magnetoresistance is often dominated by the tunneling of spin polarized electrons between grains, giving rise to an intrinsic grain-size dependence to the [10] [11] magnetoresistance. Hitherto, however, a fully quantitative understanding of the CMR effect has been elusive and it is still the subject of current research activities. Early prospects of great opportunities for the development of new technologies have not yet come to fruition.

References [1] G. H. Jonker and J. H. Van Santen,Physica16(1950), p. 377 [2] J. Volger.Physica20(1954), p. 49 [3] E.O. Wollan and W.C. Koehler.Phys. Rev.100(1955), p. 545 [4] Z.B. Z. Jirak et al.,JMMM53(1985), p. 153 [5] E. Pollert et al.,J. Phys. Chem. Solids43(1982), p. 1137 [6] J. N. Lalena and D. A. Cleary "Principles of Inorganic Materials Design," 2nd ed., John Wiley & Sons, New York, p. 361 (2010). [7] R. von Helmolt, J. Wecker, B. Holzapfel, L. Schultz K. and Samwer,Ba MnOGiant negative magnetoresistance in perovskitelike La 2/3 1/3 x ferromagnetic films, Phys. Rev. Lett.71(1993), p. 2331 (http://link.aps.org/doi/10.1103/PhysRevLett.71.2331), doi:10.1103/PhysRevLett.71.2331 [8] S. Jin et al.,Science264(1994), p. 413 [9] R. Zeller Computational Nanoscience: Do It Yourself, J. Grotendorst, S. Blũgel, D. Marx (Eds.), John von Neumann Institute for Computing, Jũlich, NIC Series, Vol. 31, ISBN 3-00-017350-1, pp. 419-445, 2006. [10] J. N. Lalena and D. A. Cleary "Principles of Inorganic Materials Design," 2nd ed., John Wiley & Sons, New York, p. 361-362 (2010). [11] For a review see: E. Dagotto. Nanoscale Phase Separation and Colossal Magnetoresistance. Springer 2003.

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Colossal magnetoresistance

•

Colossal magnetoresistance, A. P. Ramirez, J. Phys.: Condens. Matter9, 8171-8199 (1997) doi:10.1088/0953-8984/9/39/005

External links • New Clues to Mechanism for Colossal Magnetoresistance (http://www.physorg.com/news106576042.html) • Theory group at Oak Ridge National Laboratory (http://www.ornl.gov/sci/cmsd/theory/cmr/index.html) • Physicsweb article February 1999 (http://physicsweb.org/articles/world/12/2/12)

Conductance quantum

2 Theconductance quantum(G) is the quantized unit of conductance. It is defined asG= 2e/h = 0 0 c5c1 1c1 [1] 7.7480917346(25) × 10 Ωd eΩ . It appears when measuring the conductance of a quantum point 12900 contact. The name conductance quantum is somewhat misleading, since it implies that there can only be conductances that are integer multiples ofG. This is not the case, instead conductance quantum means the conductance of one 0 conductance channel, if the probability of an electron entering this channel being transmitted is unity. If this probability is not unity, there must be a correction for the particular conductance channel.

References [1] Barry N. Taylor, Peter J. Mohr (2010). "CODATA Value: Conductance Quantum" (http:/ /physics.nist.gov/cgi-bin/cuu/ Value?conqu2e2sh).The NIST Reference on Constants, Units, and Uncertainty(http://physics.nist.gov/cuu/index.html). National Institute of Standards and Technology. . Retrieved 2011-06-23.

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Coulomb blockade

Coulomb blockade

In physics, aCoulomb blockade(abbreviated CB), named after Charles-Augustin de Coulomb's electrical force, is the increased resistance at small bias voltages of an electronic device comprising at least one low-capacitance tunnel junction. Because of the CB, the resistances of devices are not constant at low bias voltages, but increase to infinity for zero bias (i.e. no current flows).

Coulomb Blockade in a Tunnel Junction Schematic representation of an electron A tunnel junction is, in its simplest form, a thin insulating barrier tunnelling through a barrier between two conducting electrodes. If the electrodes are superconducting, Cooper pairs (with a charge of two elementary charges) carry the current. In the case that the electrodes arenormalconducting, i.e. neither superconducting nor semiconducting, electrons (with a charge of one elementary charge) carry the current. The following reasoning is for the case of tunnel junctions with an insulating barrier between two normal conducting electrodes (NIN junctions).

According to the laws of classical electrodynamics, no current can flow through an insulating barrier. According to the laws of quantum mechanics, however, there is a nonvanishing (larger than zero) probability for an electron on one side of the barrier to reach the other side (see quantum tunnelling). When a bias voltage is applied, this means that there will be a current, neglecting additional effects, the tunnelling current will be proportional to the bias voltage. In electrical terms, the tunnel junction behaves as a resistor with a constant resistance, also known as an ohmic resistor. The resistance depends exponentially on the barrier thickness. Typical barrier thicknesses are on the order of one to several nanometers. An arrangement of two conductors with an insulating layer in between not only has a resistance, but also a finite capacitance. The insulator is also called dielectric in this context, the tunnel junction behaves as a capacitor. Due to the discreteness of electrical charge, current through a tunnel junction is a series of events in which exactly one electron passes (tunnels) through the tunnel barrier (we neglect cotunneling, in which two electrons tunnel simultaneously). The tunnel junction capacitor is charged with one elementary charge by the tunnelling electron, c19 causing a voltage buildup , where is the elementary charge of 1.6×10 coulomb and the capacitance of the junction. If the capacitance is very small, the voltage buildup can be large enough to prevent another electron from tunnelling. The electrical current is then suppressed at low bias voltages and the resistance of the device is no longer constant. The increase of the differential resistance around zero bias is called theCoulomb blockade.

Observing the Coulomb Blockade In order for theCoulomb blockadeto be observable, the temperature has to be low enough so that the characteristic charging energy (the energy that is required to charge the junction with one elementary charge) is larger than the c15 thermal energy of the charge carriers. For capacitances above 1 femtofarad (10 farad), this implies that the temperature has to be below about 1 kelvin. This temperature range is routinely reached for example by dilution refrigerators. To make a tunnel junction in plate condenser geometry with a capacitance of 1 femtofarad, using an oxide layer of electric permittivity 10 and thickness one nanometer, one has to create electrodes with dimensions of approximately 100 by 100 nanometers. This range of dimensions is routinely reached for example by electron beam lithography and appropriate pattern transfer technologies, like the Niemeyer-Dolan technique, also known as shadow evaporation

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