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| [[File:NIST Josephson voltage standard.jpg|thumb|alt=Image of a Josephson voltage standard chip containing approximately three hundred thousand microfabricated Josephson junctions.|Image of a Josephson voltage standard chip containing approximately 300,000 microfabricated Josephson junctions. Image credit: [[NIST]].]]
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| The '''superconducting tunnel junction''' (STJ) — also known as a '''superconductor–insulator–superconductor tunnel junction''' (SIS) — is an [[electronics|electronic]] device consisting of two [[superconductors]] separated by a very thin layer of [[Insulator (electrical)|insulating]] material. Current passes through the junction via the process of [[quantum tunneling]]. The STJ is a type of [[Josephson junction]], though not all the properties of the STJ are described by the Josephson effect.
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| These devices have a wide range of applications, including high-sensitivity [[Cryogenic particle detectors|detectors]] of [[electromagnetic radiation]], [[SQUID|magnetometers]], [[RSFQ|high speed digital circuit]] elements, and [[superconducting quantum computing|quantum computing]] circuits.
| | Today, there are several other types of web development and blogging software available to design and host your website blogs online and that too in minutes, if not hours. It is used by around 25% of all new websites, and there are more than 27 thousand plugins currently available. One really cool features about this amazing and free wp plugin is that the code it generates is completely portable. Hosted by Your Domain on Another Web Host - In this model, you first purchase multiple-domain webhosting, and then you can build free Wordpress websites on your own domains, taking advantage of the full power of Wordpress. This particular wordpress plugin is essential for not only having the capability where you improve your position, but to enhance your organic searches for your website. <br><br>You just download ready made templates to a separate directory and then choose a favorite one in the admin panel. If you have any sort of inquiries relating to where and how you can utilize [http://snipitfor.me/wordpress_dropbox_backup_3262185 wordpress backup plugin], you can contact us at our webpage. If a newbie missed a certain part of the video then they could always rewind. A Wordpress plugin is a software that you can install into your Wordpress site. Now, I want to anxiety that not every single query will be answered. That's a total of 180$ for each Wordpress theme if you sell 3 links and keep the designer link for your own website, or 240$ if you sell all links. <br><br>You can down load it here at this link: and utilize your FTP software program to upload it to your Word - Press Plugin folder. Word - Press has ensured the users of this open source blogging platform do not have to troubleshoot on their own, or seek outside help. Setting Up Your Business Online Using Free Wordpress Websites. Enough automated blog posts plus a system keeps you and your clients happy. There are plenty of tables that are attached to this particular database. <br><br>The next thing I did after installing Wordpress was to find myself a free good-looking Wordpress-theme offering the functionality I was after. Find more information about Design To Wordpress here. To do this, you should link your posts to other relevant posts that you've created. So, we have to add our social media sharing buttons in website. The popularity of Word - Press has increased the demand for Word - Press themes and these themes sells like hot cake on the internet. <br><br>You will know which of your Word - Press blog posts are attracting more unique visitors which in turn will help you develop better products and services for your customers. In fact portfolio Word - Press themes is a smooth and attractive but considerably flawed Word - Press theme in creating simpler to the photographers or designers to develop a specific internet site showcasing their most current perform since it appear modern-day and has fantastic typography and large photographs which would develop an attractive wanting portfolio internet site. It can be concluded that white label SEO comprise of a third party who resells a contract involving IT expert or consultant, SEO professional and end user. with posts or testimonials updated as they are uploaded to a particular section of the website. Your topic is going to be the basis of your site's name. |
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| ==Quantum tunneling==
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| [[File:STJ Device Sketch.jpg|thumb|alt=Illustration of a thin-film superconducting tunnel junction.|Illustration of a thin-film superconducting tunnel junction (STJ). The superconducting material is light blue, the insulating tunnel barrier is black, and the substrate is green.]]
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| [[File:STJ Energy Diagram.jpg|thumb|alt=Energy diagram of a superconducting tunnel junction.|Energy diagram of a superconducting tunnel junction. The vertical axis is energy, and the horizontal axis shows the [[density of states]]. [[Cooper pairs]] exist at the [[Fermi energy]], indicated by the dashed lines. A bias voltage V is applied across the junction, shifting the Fermi energies of the two superconductors relative to each other by an energy eV, where e is the [[electron]] charge. [[Quasiparticle]] states exist for energies greater than Δ from the Fermi energy, where Δ is the superconducting energy gap. Green and blue indicate empty and filled quasiparticle states, respectively, at zero temperature.]]
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| [[File:STJ IV Curve.jpg|thumb|alt=Sketch of the current-voltage curve of a superconducting tunnel junction.|Sketch of the current-voltage (I-V) curve of a superconducting tunnel junction. The [[Cooper pair]] tunneling current is seen at V = 0, while the [[quasiparticle]] tunneling current is seen for V > 2Δ/e and V < -2Δ/e.]]
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| All [[Electrical current|currents]] flowing through the STJ pass through the insulating layer via the process of [[quantum tunneling]]. There are two components to the tunneling current. The first is from the tunneling of [[Cooper pairs]]. This supercurrent is described by the ac and dc [[Josephson effect|Josephson relations]], first predicted by [[Brian David Josephson]] in 1962.<ref>B. D. Josephson, "Possible new effects in superconductive tunnelling," ''Physics Letters'' '''1''', 251 (1962), {{doi|10.1016/0031-9163(62)91369-0}}</ref> For this prediction, Josephson received the [[Nobel prize in physics]] in 1973. The second is the [[quasiparticle]] current, which, in the limit of zero temperature, arises when the energy from the bias voltage <math>eV</math> exceeds twice the value of superconducting energy gap Δ. At finite temperature, a small quasiparticle tunneling current — called the subgap current — is present even for voltages less than twice the energy gap due to the thermal promotion of quasiparticles above the gap.
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| If the STJ is irradiated with [[photons]] of frequency <math>f</math>, the dc current-voltage curve will exhibit both Shapiro steps and steps due to photon-assisted tunneling. Shapiro steps arise from the response of the supercurrent and occur at voltages equal to <math>nhf/(2e)</math>, where <math>h</math> is [[Planck's constant]], <math>e</math> is the [[electron]] charge, and <math>n</math> is an [[integer]].<ref>S. Shapiro, "Josephson currents in superconducting tunneling: The effect of microwaves and other observations" ''Physical Review Letters'' '''11''', 80 (1963), {{doi|10.1103/PhysRevLett.11.80}}</ref> Photon-assisted tunneling arises from the response of the quasiparticles and gives rise to steps displaced in voltage by <math>nhf/e</math> relative to the gap voltage.<ref>M. Tinkham, ''Introduction to Superconductivity'', 2nd edition, Dover Publications, 1996</ref>
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| == Device fabrication ==
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| The device is typically [[Semiconductor device fabrication|fabricated]] by first depositing a thin film of a superconducting metal such as [[aluminum]] on an insulating substrate such as [[silicon]]. The deposition is performed inside a [[vacuum chamber]]. [[Oxygen]] gas is then introduced into the chamber, resulting in the formation of an insulating layer of [[aluminum oxide]] (<math>Al_{2}O_{3}</math>) with a typical thickness of several [[nanometers]]. After the vacuum is restored, an overlapping layer of superconducting metal is deposited, completing the STJ. To create a well-defined overlap region, a procedure known as the [[Niemeyer-Dolan technique]] is commonly used. This technique uses a suspended bridge of [[resist]] with a double-angle deposition to define the junction.
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| [[Aluminum]] is widely used for making superconducting tunnel junctions because of its unique ability to form a very thin (2-3 nm) insulating [[Aluminum oxide|oxide]] layer with no defects that [[short-circuit]] the insulating layer. The [[superconducting]] critical temperature of aluminum is approximately 1.2 [[kelvin]] (K). For many applications, it is convenient to have a device that is superconducting at a higher temperature, in particular at a temperature above the [[boiling point]] of [[liquid helium]], which is 4.2 K at atmospheric pressure. One approach to achieving this is to use [[niobium]], which has a superconducting critical temperature in bulk form of 9.3 K. Niobium, however, does not form an oxide that is suitable for making tunnel junctions. To form an insulating oxide, the first layer of niobium can be coated with a very thin layer (approximately 5 nm) of aluminum, which is then oxidized to form a high quality aluminum oxide tunnel barrier before the final layer of niobium is deposited. The thin aluminum layer is [[Proximity effect (superconductivity)|proximitized]] by the thicker niobium, and the resulting device has a superconducting critical temperature above 4.2 K.<ref>A. A. Joseph, J. Sese, J. Flokstra, & H. G. Kerkhoff, "Structural testing of the HYPRES niobium process," ''IEEE Transactions on Applied Superconductivity'', '''15''', 106 (2005), {{doi|10.1109/TASC.2005.849705}}</ref> Early work used [[lead]]-lead oxide-lead tunnel junctions.<ref>G. J. Dolan, T. G. Phillips, and D. P. Woody, "Low‐noise 115‐GHz mixing in superconducting oxide‐barrier tunnel junctions," ''Applied Physics Letters'' '''34''', 347 (1979), {{doi|10.1063/1.90783}}</ref> [[Lead]] has a superconducting critical temperature of 7.2 K in bulk form, but lead oxide tends to develop defects (sometimes called pinhole defects) that short-circuit the tunnel barrier when the device is thermally cycled between [[cryogenic]] temperatures and room temperature, and as result lead is no longer widely used to make STJs.
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| ==Applications==
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| ===Radio astronomy===
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| STJs are the most sensitive [[heterodyne]] receivers in the 100 GHz to 1000 GHz frequency range, and hence are used for [[radio astronomy]] at these frequencies.<ref>J. Zmuidzinas and P. L. Richards, "Superconducting detectors and mixers for millimeter and submillimeter astrophysics," ''Proceedings of the IEEE'' '''92''', 1597 (2004), {{doi|10.1109/JPROC.2004.833670}}</ref> In this application, the STJ is [[DC bias|dc biased]] at a voltage just below the gap voltage (|V| = 2Δ/e). A high frequency signal from an astronomical object of interest is focused onto the STJ, along with a [[local oscillator]] source. Photons absorbed by the STJ allow quasiparticles to tunnel via the process of photon-assisted tunneling. This photon-assisted tunneling changes the current-voltage curve, creating a nonlinearity that produces an output at the difference frequency of the astronomical signal and the local oscillator. This output is a frequency down-converted version of the astronomical signal.<ref>M. J. Wengler, "Submillimeter-wave detection with superconducting tunnel diodes," ''Proceedings of the IEEE'' '''80''', 1810 (1992), {{doi|10.1109/5.175257}}</ref> These receivers are so sensitive that an accurate description of the device performance must take into account the effects of [[quantum noise]].<ref>J. R. Tucker, "Quantum limited detection in tunnel junction mixers," ''IEEE Journal of Quantum Electronics'' '''15''', 1234 (1979), {{doi|10.1109/JQE.1979.1069931}}</ref>
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| ===Single-photon detection===
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| In addition to [[heterodyne]] detection, STJs can also be used as direct detectors. In this application, the STJ is biased with a dc voltage less than the gap voltage. A [[photon]] absorbed in the superconductor breaks [[Cooper pairs]] and creates [[quasiparticles]]. The quasiparticles tunnel across the junction in the direction of the applied voltage, and the resulting tunneling current is proportional to the photon energy. STJ devices have been employed as single-photon detectors for photon frequencies ranging from [[X-rays]] to the [[infrared]].<ref>[http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=33525 STJ detectors from the European Space Agency], accessed 8-17-11</ref>
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| ===SQUIDs===
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| The [[superconducting quantum interference device]] or [[SQUID]] is based on a superconducting loop containing Josephson junctions. SQUIDs are the world's most sensitive [[magnetometer]]s, capable of measuring a single [[magnetic flux quantum]].
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| ===Quantum computing===
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| [[Superconducting quantum computing]] utilizes STJ-based circuits, including [[charge qubit]]s, [[flux qubit]]s and [[phase qubit]]s.
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| ===RSFQ===
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| The STJ is the primary active element in [[rapid single flux quantum]] or [[RSFQ]] fast logic circuits.<ref>K. K. Likharev and V. K. Semenov, "RSFQ logic/memory family: a new Josephson-junction technology for sub-terahertz-clock-frequency digital systems," ''IEEE Transactions on Applied Superconductivity'' '''1''', 3 (1991) {{doi|10.1109/77.80745}}</ref>
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| ===Josephson voltage standard===
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| Shapiro steps arise from Cooper pairs synchronizing with an external source of electromagnetic radiation and can be used to convert a frequency to a dc voltage. Because frequency can be measured with very high precision, this effect is used as the basis of the Josephson voltage standard, which defines the international standard volt.<ref>C. A. Hamilton, R. L. Kautz, R. L. Steiner, and F. L. Lloyd, "A practical Josephson voltage standard at 1 V," ''IEEE Electron Device Letters'' '''6''', 623 (1985), {{doi|10.1109/EDL.1985.26253}}</ref><ref>[http://www.nist.gov/pml/div686/devices/voltage.cfm Quantum voltage metrology at NIST], accessed 11-5-11</ref>
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| ==References==
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| {{Reflist}}
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| ==See also==
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| * [[Superconductivity]]
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| * [[Josephson effect]]
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| * [[Macroscopic quantum phenomena]]
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| * [[Quantum tunneling]]
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| * [[Superconducting quantum interference device]] (SQUID)
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| * [[Superconducting quantum computing]]
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| * [[Rapid single flux quantum]] (RSFQ)
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| * [[Cryogenic particle detectors]]
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| [[Category:Superconductivity]]
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| [[Category:Josephson effect]]
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| [[Category:Quantum electronics]]
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| [[Category:Superconducting detectors]]
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| [[Category:Sensors]]
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| [[Category:Radio astronomy]]
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| [[Category:Mesoscopic physics]]
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Today, there are several other types of web development and blogging software available to design and host your website blogs online and that too in minutes, if not hours. It is used by around 25% of all new websites, and there are more than 27 thousand plugins currently available. One really cool features about this amazing and free wp plugin is that the code it generates is completely portable. Hosted by Your Domain on Another Web Host - In this model, you first purchase multiple-domain webhosting, and then you can build free Wordpress websites on your own domains, taking advantage of the full power of Wordpress. This particular wordpress plugin is essential for not only having the capability where you improve your position, but to enhance your organic searches for your website.
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