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Quantum Entanglement


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Quantum Entanglement

  1. 1.   Alexis Diaz  Alexis Diaz  SPCS 2015 ­ Frontiers of Physics   Research Paper  30 July 2015  ______________________________________________________________________________    Quantum Entanglement Isn’t so Spooky!    In the 1930s, Albert Einstein was upset with quantum mechanics, he proposed a thought                            experiment, where according to the theory an event at one point in the universe could                              instantaneously affect another event arbitrarily far away. He called this spooky action at a                            distance because he believed it to be absurd. It seemed to imply faster than the speed of light                                    communication. Now this superluminal communication result did not correspond with any of the                          works circulating at the time and was not supported by the concepts that defined Quantum                              Mechanics. Something his theory of relativity ruled out. This spooky action at a distance stood                              alone.   The Einstein­Podolsky­Rosen Paradox  The EPR Paradox is a thought experiment intended to demonstrate an inherent paradox in the                              early formulations of ​quantum theory​. It is among the best­known examples of ​quantum                          entanglement​. The paradox involves ​two particles which are entangled with each other according                          to quantum mechanics. Under the Copenhagen interpretation of quantum mechanics, each                      particle is individually in an uncertain state until it is measured, at which point the state of that                                    particle becomes certain.  But nowadays we can perform this experiment and see this apparent spookiness. In order to                              understand it, we must first understand spin. All fundamental particles have a property called                            spin. It is an analogy used to convey its angular momentum, or the propensity and orientation in                                  space, rather than action. The spin of a particle can be measured in accordance with its direction.                                  This measurement can have only one of two outputs. Either the particle spin is aligned with the                                 
  2. 2.   Alexis Diaz  direction of measurement, which is known as spin up. Or it is opposite the measurement, which                                is known as spin down. After the measurement, the particle retains its spin.   The experiment Einstein proposed can be carried out using two particles . However; these need                              to be prepared in a certain way. For example, generated spontaneously from energy.    The Results   Conservation laws state that the total angular momentum of the universe must remain constant, it                              is easy to follow that if one particle is measured with spin up, the other measured in the same                                      direction must have spin down. Emphasis put upon the fact this works only when the two                                particles are measured in the same direction that their spins must be opposite.   Einstein was a proponent for the idea that each particle was created with a clearly defined spin.                                  However; this would not work. Imagine their spins were vertical and opposite. If they are both                                measured each particle has fifty­fifty chance for spin up. There would thus exist a fifty percent                                probability that both measurements would yield the same result and this would violate the law of                                conservation of angular momentum. According to quantum mechanics, these particles do not                        have a well defined spin. They are entangled, which means their spin is opposite that of each                                 
  3. 3.   Alexis Diaz  other. At the point of which the particle and its spin is measured, the other entangled particle’s                                  measurements immediately become known and clearly defined. This was checked thoroughly                      and repeatedly by experiments. The angle of the detectors or the distance between them does not                                affect the experiment. This is especially peculiar given the nature of locality. The principle of                              locality is violated when it states that an object is only directly influenced by its immediate                                surroundings.Therefore, the principle of locality implies that an event at one point cannot cause a                              simultaneous result at another point. If these fundamental principles hold true for the rest of the                                quantum mechanic world it would seem fair to assume that no two particles can relay an                                immediate effect on one another across vast distances.     Quantum Entanglement: A Description   This phenomenon occurs in what can be described                as quantum entanglement. Two particles light years              away with undefined spins, where the            measurement of one particle instantaneously          influences the other to have the opposite spin. An                  anomaly that suggests that information has been              relayed faster than the speed of light. Though some theorists interpreted the results this way,                              Einstein did not. Einstein was a big proponent of predictability and determinism and proposed                            that the information of what the spin’s direction would take was always there, but the hidden                                information was not previously known until it was measured. There is an analogy ​suggested by                              Dr. Brian Greene, of Columbia University to describe this alternate explanation. “Pretend ​that                          you and a friend buy a pair of gloves. You place one glove inside one box and the other glove                                        inside another box. You take one box and travel to one side of the universe. Your friend takes the                                      other box and travels to the other side. You open your box, and find the left glove. You know                                      immediately that your friend is going to open the box and find the right glove. You don’t need to                                      call your friend on the telephone. Nor do you need to see inside the second box to confirm this                                      fact. The gloves are, in a sense, entangled. One glove can tell you all you need to know about the                                        other.” (Maliszewski, 2014)  
  4. 4.   Alexis Diaz  A similar analogy is that of what Bohr suggests. Given two spinning wheels with a fifty percent                                  of landing on two different colors. The wheels would land on opposing colors in each instant.                                The event is described to represent the “spooky” aspect of quantum entanglement.   Take Away Points  Although Bohr is correct in asserting that their is no predictability factor in quantum                            entanglement, his representation of how quantum entanglement works is misleading. ​There is no                          information transmitted or signal is sent. When the box was opened, you knew the information of                                the other. The opening of the box alters the description of the “quantum state,” the math                                describing the entangled system containing the two particles. The math is the collapse of the                              wave function by the act of measurement. The wave function for the system of particles is a                                  nonseparable wave function, so interfering with particle y through measurement modifies the                        wave function for particle x as well. Two entangled particles share the one wave function. It is                                  nonseparable because the two particles share at least one fundamental property, for example                          mass, spin, energy, momentum, etc. There is no “spooky” action at a distance, rather it is                                entanglement.  Real­Life Applications:  Namely Teleportation  Quantum entanglement has applications in the emerging technologies of today. Among these                        quantum teleportation seems most enticing for its allure and convenience. The concept of                          quantum teleportation uses entangled particles to transmit information. Quantum teleportation                    can be achieved through the use of three photons:    Photon A​: The photon to be teleported  Photon B​: The transporting photon  Photon C​: The photon that is entangled with photon ​B  “If researchers tried to look too closely at photon ​A ​without entanglement, they'd bump it, and                                thereby change it. By entangling photons ​B ​and ​C​, researchers can extract some information                            about photon ​A​, and the remaining information would pass on to ​B ​by way of entanglement, and                                  then on to photon ​C​. When researchers apply the information from photon ​A ​to photon ​C​, they                                  create an exact replica of photon ​A​. However, photon ​A ​no longer exists as it did before the                                    information was sent to photon ​C​.” (Bonsor, 2015) 
  5. 5.   Alexis Diaz  In practice, physicists at the University of Geneva have succeeded in teleporting the quantum                            state of a photon to a crystal over 25 kilometers of optical fiber.   This is only skimming the surface of the potential for quantum entanglement. The technology is                              already underway and results are promising considering they follow predictions. I urge the                          populus to put effort towards exploring this idea as it may well be our next best means of                                    conventional transportation.                                            
  6. 6.   Alexis Diaz  Bibliography    Afp. "Physicists Make Big Leap In Quantum Teleportation." Business Insider. ​Business Insider,  Inc, 21 Sept. 2014. Web. 31 July 2015.  <­make­huge­leap­in­quantum­teleportation­2014­9>.    Bonsor, Kevin, and Robert Lamb. "How Teleportation Will Work."​HowStuffWorks., n.d. Web. 31 July 2015.  <­vs­myth/everyday­myths/teleportation1.htm>.    Clegg, Brian. "Chapter 7: Mirror, Mirror." ​The God Effect: Quantum Entanglement, Science's  Strangest Phenomenon.​ New York: St. Martin's, 2006. 208­11. Print.    Dickerson, Kelly. "Longer Distance Quantum Teleportation Achieved."​Longer Distance  Quantum Teleportation Achieved​. Live Science, 8 Dec. 2014. Web. 31 July 2015.  <­09­quantum­teleportation.html>.    "SEVERAL FAILED ATTEMPTS TO EXPLAIN QUANTUM ENTANGLEMENT." Interview  by Paul Maliszewski. ​TIMOTHYMcSWEENEY’S ​31 July 2014: 13­15. Web. 31 July 2015.  <­failed­attempts­to­explain­quantum­entanglement >.    Vergano, Dan. ""Spooky" Quantum Entanglement Reveals Invisible Objects."​ National  Geographic News.​ National Geographic, 27 Aug. 2014. Web. 31 July 2015.  <­quantu m­imaging­cats­undetected­photon­science%2F>.       
  7. 7.   Alexis Diaz