Ordinarily, light particles – photons – don\u2019t interact. If two photons collide in a vacuum, they simply pass through each other.<\/p>\n
An efficient way to make photons interact could open new prospects for both classical optics and quantum computing, an experimental technology that promises large speedups on some types of calculations.<\/p>\n
In recent years, physicists have\u00a0enabled<\/a>\u00a0photon-photon interactions using atoms of rare elements cooled to very low temperatures.<\/p>\n But in the latest issue of\u00a0Physical Review Letters<\/em>, MIT researchers describe a new technique for enabling photon-photon interactions at room temperature, using a silicon crystal with distinctive patterns etched into it.<\/p>\n In physics jargon, the crystal introduces \u201cnonlinearities<\/a>\u201d into the transmission of an optical signal.<\/p>\n \u201cAll of these approaches that had atoms or atom-like particles require low temperatures and work over a narrow frequency band,\u201d says Dirk Englund, an associate professor of electrical engineering and computer science at MIT and senior author on the new paper.<\/p>\n \u201cIt\u2019s been a holy grail to come up with methods to realize single-photon-level nonlinearities at room temperature under ambient conditions.\u201d<\/p>\n Joining Englund on the paper are Hyeongrak Choi, a graduate student in electrical engineering and computer science, and Mikkel Heuck, who was a postdoc in Englund\u2019s lab when the work was done and is now at the Technical University of Denmark.<\/p>\n Quantum computers harness a strange physical property called \u201csuperposition,\u201d in which a quantum particle can be said to inhabit two contradictory states at the same time.<\/p>\n The spin, or magnetic orientation, of an electron, for instance, could be both up and down at the same time; the polarization of a photon could be both vertical and horizontal.<\/p>\n If a string of quantum bits \u2014 or qubits, the quantum analog of the bits in a classical computer \u2014 is in superposition, it can, in some sense, canvass multiple solutions to the same problem simultaneously, which is why quantum computers promise speedups.<\/p>\n Most experimental qubits use ions trapped in oscillating magnetic fields, superconducting\u00a0circuits<\/a>, or \u2014 like Englund\u2019s own research \u2014\u00a0defects<\/a>\u00a0in the crystal structure of diamonds. With all these technologies, however, superpositions are difficult to maintain.<\/p>\n Because photons aren\u2019t very susceptible to interactions with the environment, they\u2019re great at maintaining superposition; but for the same reason, they\u2019re difficult to control. And quantum computing depends on the ability to send control signals to the qubits.<\/p>\n That\u2019s where the MIT researchers\u2019 new work comes in. If a single photon enters their device, it will pass through unimpeded. But if two photons \u2014 in the right quantum states \u2014 try to enter the device, they\u2019ll be reflected back.<\/p>\n The quantum state of one of the photons can thus be thought of as controlling the quantum state of the other. And quantum information theory has established that simple quantum \u201cgates\u201d of this type are all that is necessary to build a universal quantum computer.<\/p>\n The researchers\u2019 device consists of a long, narrow, rectangular silicon crystal with regularly spaced holes etched into it. The holes are widest at the ends of the rectangle, and they narrow toward its center.<\/p>\n Connecting the two middle holes is an even narrower channel, and at its center, on opposite sides, are two sharp concentric tips. The pattern of holes temporarily traps light in the device, and the concentric tips concentrate the electric field of the trapped light.<\/p>\n The researchers prototyped the device and showed that it both confined light and concentrated the light\u2019s electric field to the degree predicted by their theoretical models.<\/p>\n But turning the device into a quantum gate would require another component, a dielectric sandwiched between the tips. (A dielectric is a material that is ordinarily electrically insulating but will become polarized \u2014 all its positive and negative charges will align in the same direction \u2014 when exposed to an electric field.)<\/p>\n When a light wave passes close to a dielectric, its electric field will slightly displace the electrons of the dielectric\u2019s atoms. \u00a0When the electrons spring back, they wobble, like a child\u2019s swing when it\u2019s pushed too hard. This is the nonlinearity that the researchers\u2019 system exploits.<\/p>\n The size and spacing of the holes in the device are tailored to a specific light frequency \u2014 the device\u2019s \u201cresonance frequency.\u201d But the nonlinear wobbling of the dielectric\u2019s electrons should shift that frequency.<\/p>\n Ordinarily, that shift is mild enough to be negligible. But because the sharp tips in the researchers\u2019 device concentrate the electric fields of entering photons, they also exaggerate the shift.<\/p>\n A single photon could still get through the device. But if two photons attempted to enter it, the shift would be so dramatic that they\u2019d be repulsed.<\/p>\n The device can be configured so that the dramatic shift in resonance frequency occurs only if the photons attempting to enter it have particular quantum properties \u2014 specific combinations of polarization or phase, for instance.<\/p>\n The quantum state of one photon could thus determine the way in which the other photon is handled, the basic requirement for a quantum gate.<\/p>\n Englund emphasizes that the new research will not yield a working quantum computer in the immediate future. Too often, light entering the prototype is still either scattered or absorbed, and the quantum states of the photons can become slightly distorted.<\/p>\n But other applications may be more feasible in the near term. For instance, a version of the device could provide a reliable source of single photons, which would greatly abet a range of research in quantum information science and communications.<\/p>\n \u201cThis work is quite remarkable and unique because it shows strong light-matter interaction, localization of light, and relatively long-time storage of photons at such a tiny scale in a semiconductor,\u201d says Mohammad Soltani, a nanophotonics researcher in Raytheon BBN Technologies\u2019 Quantum Information Processing Group.<\/p>\n \u201cIt can enable things that were questionable before, like nonlinear single-photon gates for quantum information. It works at room temperature, it\u2019s solid-state, and it\u2019s compatible with semiconductor manufacturing. This work is among the most promising to date for practical devices, such as quantum information devices.\u201d<\/p>\n MIT News<\/a><\/p>\n A prototype device enables photon-photon interactions at room temperature.<\/p>\n","protected":false},"author":340957,"featured_media":155132,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[31750],"tags":[35,9245],"class_list":["post-215806","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-science","tag-headline","tag-quantum-computing"],"_links":{"self":[{"href":"https:\/\/mybroadband.co.za\/news\/wp-json\/wp\/v2\/posts\/215806"}],"collection":[{"href":"https:\/\/mybroadband.co.za\/news\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/mybroadband.co.za\/news\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/mybroadband.co.za\/news\/wp-json\/wp\/v2\/users\/340957"}],"replies":[{"embeddable":true,"href":"https:\/\/mybroadband.co.za\/news\/wp-json\/wp\/v2\/comments?post=215806"}],"version-history":[{"count":1,"href":"https:\/\/mybroadband.co.za\/news\/wp-json\/wp\/v2\/posts\/215806\/revisions"}],"predecessor-version":[{"id":215808,"href":"https:\/\/mybroadband.co.za\/news\/wp-json\/wp\/v2\/posts\/215806\/revisions\/215808"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/mybroadband.co.za\/news\/wp-json\/wp\/v2\/media\/155132"}],"wp:attachment":[{"href":"https:\/\/mybroadband.co.za\/news\/wp-json\/wp\/v2\/media?parent=215806"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/mybroadband.co.za\/news\/wp-json\/wp\/v2\/categories?post=215806"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/mybroadband.co.za\/news\/wp-json\/wp\/v2\/tags?post=215806"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}Photonic independence<\/h3>\n
Unsympathetic resonance<\/h3>\n
Practical potential<\/h3>\n
Now read:\u00a0First robot cop to join Dubai police<\/a><\/h3>\n","protected":false},"excerpt":{"rendered":"