Quantum Entanglement

1. Quantum Entanglement Modern Physics 5/10/11 Spring 2011 Ben Miller, Alexander DeCarli, Kevin Shaw

2. What is it?

3. How do particles become Entangled?

4. Parametric Down Conversion • A laser (usually ultraviolet for its high frequency) sends a photon through a nonlinear crystal such as Beta Barium Borate • The photon bumps an electron to an excited state • When the electron comes back down and releases its photon, there is a chance it will split • If it splits, the two photons are equally half of the energy • These two photons are entangled • The overlapping of the cones represents the entanglement • The two photons are also polarized opposite of one another

5. Einstein called this "Spooky action at a distance."

6. What is the “spookiness?” • Bell-state Quantum Eraser • The split photons are opposite in polarization • The double-slit selectively filter between polarizations (e.g. right slit allows clockwise) • A filter in front of Detector A for polarizations as well • If the A filter restricts the polarized light, then the polarization entering the double-slit is known and no interference • If the A filter allows all light, then polarization entering the double-slit is not known and interference shows up in both detectors. • How do photons at B know that polarization is no longer restricted at A?

7. History • Quantum Entanglement comes from the ERP paradox paper. • The paper was written by Albert Einstein, Nathan Rosen and Boris Podosky in 1935. • ERP is a topic in physics concerned with measuring and describing microscopic systems. • The three men felt that quantum mechanical theory was incomplete. • By incomplete, they were talking about entanglement but did not have a name for it.

8. More History • Erwin Schrodinger read this paper and wrote to Einstein talking about the idea and called it “entanglement.” • Schrodinger later wrote a paper that defined the idea of entanglement. • Both Einstein and Schrodinger were dissatisfied with the idea. • In 1964 entanglement was tested and disproved by John Bell because it violated certain systems but since then other experiments have proved it to be true. • Each experiment had its flaws though.

9. Applications • Quantum Communication • Quantum Teleportation • Quantum Cryptography • A quantum system in an entangled state can be used as a quantum information channel to perform tasks that are faster than classical systems.

10. Macroscopic observation • Typically, entanglement experiments involve entangling pairs of photons and observing the changes in one effecting the changes in the other • Italian physicists thought of an idea where the effects of entanglement could be easily detected • A pair of photons could be entangled and then separated. One of the photons could then be amplified into a shower of thousands of other photons, all entangled to the lone other photon • Nicolas Gisin from the University of Geneva in Switzerland decided to test this with humans. • The beam of macro photons could be shown in one of two positions on a wall depending on the polarization of the lone microscopic photon, which defined the group. • The human tests were successful and matched with the results of a photon detector • A flaw was discovered in which detection of the photon would still occur after the entanglement connection was supposedly broken, suggesting a flaw in amplification and the inherent flaws in any detector • This flaw also hints that this particular experiment may not have been a micro-macro entanglement condition, but work is being done to enhance amplification with lasers • Clearly, humans can not be used

11. Communication • "Superdense coding" • We typically use bits in computer processing, or in this case, classical bits • In Quantum Mechanics, information can be stored using qubits, which describe a quantum state • Information can be obtained via measurement of the qubit • In theory, qubits can contain other dimensions of information, but the predictability of determining information is only completely effective on a 1:1 scale of information from classical to quantum • This means that effectively, a qubit can only reliable store as much as a classical bit • Useless? Not with entanglement. Qubitscan be entangled in pairs and therefore two classical bits per qubit can be reached. • This is a doubling of efficiency known as "superdense coding"

12. Teleportation • - Has to do with transmitting a qubit from one location to another without the qubit being moved through free space  - This can be used in the idea of a quantum computer, which would take advantage of changes in quantum states in order to rapidly send and process data  - With the qubit's use of other dimension, more advanced algorithms can be used, in theory, to solve specific problems significantly faster and more effective than any classical computer  - However, it is important to note that a classical computer can simulate a quantum one, therefore a quantum computer would not be able to solve a problem that a classical computer could not.  - Typically, qubits are used to define and alter particle spin

13. Your Welcome • Ben Miller • Alexander DeCarli • Kevin Shaw

14. Sources • http://www.davidjarvis.ca/entanglement/quantum-entanglement.shtml • http://www.technologyreview.com/blog/arxiv/24797/ • http://en.wikipedia.org/wiki/Quantum_entanglement • http://plato.stanford.edu/entries/qt-entangle/ • http://www.blogcdn.com/www.engadget.com/media/2007/02/d-wave-quantum-2.jpg • http://discovermagazine.com/2007/may/quantum-leap/d-wave_processor2_lg.jpg • http://www.cpfreviews.com/Photon-Proton/DCP_5238_Proton_Beam_McKinl.jpg • http://lightzombies.com/store/images/Photon%20II%20Beam%20%20NVG.jpg • http://focus.aps.org/files/focus/v24/st11/freq_doubler.jpg

15. Article on quantum entanglement at high temperatures.http://www.technologyreview.com/blog/arxiv/24797/