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Quantum eraser experiment

February 11, 2024

In quantum mechanics, a quantum eraser experiment is an interferometer experiment that demonstrates several fundamental aspects of quantum mechanics, including quantum entanglement and complementarity.[1][2]: 328  The quantum eraser experiment is a variation of Thomas Young's classic double-slit experiment. It establishes that when action is taken to determine which of 2 slits a photon has passed through, the photon cannot interfere with itself. When a stream of photons is marked in this way, then the interference fringes characteristic of the Young experiment will not be seen. The experiment also creates situations in which a photon that has been "marked" to reveal through which slit it has passed can later be "unmarked." A photon that has been "unmarked" will interfere with itself once again, restoring the fringes characteristic of Young's experiment.[3]

History edit

The quantum eraser experiment was proposed in 1982 in Marlan Scully and Kai Drühl in the paper Quantum eraser: A proposed photon correlation experiment concerning observation and "delayed choice" in quantum mechanics, as a realizable way to test the hitherto untested predictions of quantum mechanics. As inspirations, the paper mentions Eugene Wigner's focus on the measurement problem, conversations with Willis Lamb, and John Archibald Wheeler's thought experiments. The paper also points out that the experiment could be run in delayed choice mode, as conceptualized by Wheeler's thought experiments, what is now known as a delayed-choice quantum eraser.[4]

The experiment edit

Concept edit

This experiment involves an apparatus with two main sections. After two entangled photons are created, each is directed into its own section of the apparatus. Anything done to learn the path of the entangled partner of the photon being examined in the double-slit part of the apparatus will influence the second photon, and vice versa. The advantage of manipulating the entangled partners of the photons in the double-slit part of the experimental apparatus is that experimenters can destroy or restore the interference pattern in the latter without changing anything in that part of the apparatus. Experimenters do so by manipulating the entangled photon, and they can do so before or after its partner has passed through the slits and other elements of experimental apparatus between the photon emitter and the detection screen. Under conditions where the double-slit part of the experiment has been set up to prevent the appearance of interference phenomena (because there is definitive "which path" information present), the quantum eraser can be used to effectively erase that information. In doing so, the experimenter restores interference without altering the double-slit part of the experimental apparatus.[3]

A variation of this experiment, delayed-choice quantum eraser, allows the decision whether to measure or destroy the "which path" information to be delayed until after the entangled particle partner (the one going through the slits) has either interfered with itself or not.[5] In delayed-choice experiments quantum effects can mimic an influence of future actions on past events.[6] However, the temporal order of measurement actions is not relevant.[7]

Procedure edit

 
Figure 1. Crossed polarizations prevent interference fringes

First, a photon is shot through a specialized nonlinear optical device: a beta barium borate (BBO) crystal.[3] This crystal converts the single photon into two entangled photons of lower frequency, a process known as spontaneous parametric down-conversion (SPDC). These entangled photons follow separate paths. One photon goes directly to a polarization-resolving detector, while the second photon passes through the double-slit mask to a second polarization-resolving detector. Both detectors are connected to a coincidence circuit, ensuring that only entangled photon pairs are counted. A stepper motor moves the second detector to scan across the target area, producing an intensity map. This configuration yields the familiar interference pattern.

 
Figure 2. Introduction of polarizer in upper path restores interference fringes below

Next, a circular polarizer is placed in front of each slit in the double-slit mask, producing clockwise circular polarization in light passing through one slit, and counter-clockwise circular polarization in the other slit (see Figure 1). (Which slit corresponds to which polarization depends on the polarization reported by the first detector.) This polarization is measured at the second detector, thus "marking" the photons and destroying the interference pattern (see Fresnel–Arago laws).

Finally, a linear polarizer is introduced in the path of the first photon of the entangled pair, giving this photon a diagonal polarization (see Figure 2). Entanglement ensures a complementary diagonal polarization in its partner, which passes through the double-slit mask. This alters the effect of the circular polarizers: each will produce a mix of clockwise and counter-clockwise polarized light. Thus the second detector can no longer determine which path was taken, and the interference fringes are restored.

A double slit with rotating polarizers can also be accounted for by considering the light to be a classical wave.[8] However this experiment uses entangled photons, which are not compatible with classical mechanics.

Other applications edit

Quantum erasure technology can be used to increase the resolution of advanced microscopes.[9]

Common misconception edit

A common misunderstanding about this experiment is that it may be used to instantaneously communicate information between two detectors.[10] Simple causation, however, precludes foisting "given" information on the observed outcomes. It is important to understand the role of the coincidence detector in this experimental setup. The linear polarizer in the top path is effectively filtering out half the entangled photons, and via the coincidence detector, is filtering out the corresponding photons in the bottom path. The coincidence detector can only function by comparing data from both sensors, making it impossible to use this setup for instant communication.

In other words, only a small percentage of the light passing through the BBO crystal is split into entangled pairs. The vast majority of photons passing through the crystal are not split, and must be removed from the final data set as unwanted noise. Since there is no way for the detectors to measure whether or not a photon had been part of an entangled pair, that decision is made by looking at the timing, and filtering out any photons that are not picked up at the same time as their 'twin' at the other detector. Thus, when a pair of entangled photons is created, but one of the two is blocked by a polarizer and lost, the remaining photon will be filtered out of the data set as if it was one of the many non-entangled photons. When viewed this way, it is not surprising that making changes to the upper path can have an impact to measurements taken on the lower path, as the two measurements are being compared and used to filter the data.

Note that in the final state of this experimental setup, measurements on the lower path always show a smeared out pattern on the raw data. Seeing an interference pattern is only possible by filtering the data with the coincidence detector and only looking at photons that were 1/2 of an entangled pair.

References edit

  1. ^ Englert, Berthold-Georg (1999). (PDF). Zeitschrift für Naturforschung. 54 (1): 11–32. Bibcode:1999ZNatA..54...11E. doi:10.1515/zna-1999-0104. S2CID 3514379. Archived from the original (PDF) on 2017-08-09. Retrieved 2019-04-10.
  2. ^ Baggott, J. E. (2013). The quantum story: a history in 40 moments (Impression: 3 ed.). Oxford: Oxford Univ. Press. ISBN 978-0-19-965597-7.
  3. ^ a b c Walborn, S. P.; Terra Cunha, M. O.; Pádua, S.; Monken, C. H. (2002-02-20). "Double-slit quantum eraser". Physical Review A. 65 (3). arXiv:quant-ph/0106078. doi:10.1103/PhysRevA.65.033818. ISSN 1050-2947.
  4. ^ Scully, Marian O.; Drühl, Kai (1982). "Quantum eraser: A proposed photon correlation experiment concerning observation and "delayed choice" in quantum mechanics". Physical Review A. 25 (4). doi:10.1103/PhysRevA.25.2208.
  5. ^ Yoon-Ho, Kim; Yu, R.; Kulik, S.P.; Shih, Y.H.; Scully, Marlan (2000). "A Delayed Choice Quantum Eraser". Physical Review Letters. 84 (1): 1–5. arXiv:quant-ph/9903047. Bibcode:2000PhRvL..84....1K. doi:10.1103/PhysRevLett.84.1. PMID 11015820. S2CID 5099293.
  6. ^ Fankhauser, Johannes (2019). "Taming the Delayed Choice Quantum Eraser". Quanta. 8: 44–56. arXiv:1707.07884. doi:10.12743/quanta.v8i1.88. S2CID 53574007.
  7. ^ Ma, Xiao-song; Kofler, Johannes; Zeilinger, Anton (2016). "Delayed-choice gedanken experiments and their realizations". Rev. Mod. Phys. 88 (1): 015005. arXiv:1407.2930. Bibcode:2016RvMP...88a5005M. doi:10.1103/RevModPhys.88.015005. S2CID 34901303.
  8. ^ Chiao, R Y; Kwia, P G; Steinberg, A M (June 1995). "Quantum non-locality in two-photon experiments at Berkeley". Quantum and Semiclassical Optics: Journal of the European Optical Society Part B. 7 (3): 259–278. arXiv:quant-ph/9501016. Bibcode:1995QuSOp...7..259C. doi:10.1088/1355-5111/7/3/006. S2CID 118987962.
  9. ^ Aharonov, Yakir; Zubairy, M. Suhail (2005). "Time and the Quantum: Erasing the Past and Impacting the Future". Science. 307 (5711): 875–879. Bibcode:2005Sci...307..875A. CiteSeerX 10.1.1.110.2955. doi:10.1126/science.1107787. PMID 15705840. S2CID 16606155.
  10. ^ Kastner, R. E. (2019-07-01). "The 'Delayed Choice Quantum Eraser' Neither Erases Nor Delays". Foundations of Physics. 49 (7): 717–727. arXiv:1905.03137. doi:10.1007/s10701-019-00278-8. ISSN 0015-9018.Kastner (2019): 'Delayed Choice Quantum Eraser Neither Erases Nor Delays', Foundations of Physics

External links edit

February 11, 2024
quantum, eraser, experiment, quantum, mechanics, quantum, eraser, experiment, interferometer, experiment, that, demonstrates, several, fundamental, aspects, quantum, mechanics, including, quantum, entanglement, complementarity, quantum, eraser, experiment, var. In quantum mechanics a quantum eraser experiment is an interferometer experiment that demonstrates several fundamental aspects of quantum mechanics including quantum entanglement and complementarity 1 2 328 The quantum eraser experiment is a variation of Thomas Young s classic double slit experiment It establishes that when action is taken to determine which of 2 slits a photon has passed through the photon cannot interfere with itself When a stream of photons is marked in this way then the interference fringes characteristic of the Young experiment will not be seen The experiment also creates situations in which a photon that has been marked to reveal through which slit it has passed can later be unmarked A photon that has been unmarked will interfere with itself once again restoring the fringes characteristic of Young s experiment 3 Contents 1 History 2 The experiment 2 1 Concept 2 2 Procedure 3 Other applications 4 Common misconception 5 References 6 External linksHistory editThe quantum eraser experiment was proposed in 1982 in Marlan Scully and Kai Druhl in the paper Quantum eraser A proposed photon correlation experiment concerning observation and delayed choice in quantum mechanics as a realizable way to test the hitherto untested predictions of quantum mechanics As inspirations the paper mentions Eugene Wigner s focus on the measurement problem conversations with Willis Lamb and John Archibald Wheeler s thought experiments The paper also points out that the experiment could be run in delayed choice mode as conceptualized by Wheeler s thought experiments what is now known as a delayed choice quantum eraser 4 The experiment editConcept edit This experiment involves an apparatus with two main sections After two entangled photons are created each is directed into its own section of the apparatus Anything done to learn the path of the entangled partner of the photon being examined in the double slit part of the apparatus will influence the second photon and vice versa The advantage of manipulating the entangled partners of the photons in the double slit part of the experimental apparatus is that experimenters can destroy or restore the interference pattern in the latter without changing anything in that part of the apparatus Experimenters do so by manipulating the entangled photon and they can do so before or after its partner has passed through the slits and other elements of experimental apparatus between the photon emitter and the detection screen Under conditions where the double slit part of the experiment has been set up to prevent the appearance of interference phenomena because there is definitive which path information present the quantum eraser can be used to effectively erase that information In doing so the experimenter restores interference without altering the double slit part of the experimental apparatus 3 A variation of this experiment delayed choice quantum eraser allows the decision whether to measure or destroy the which path information to be delayed until after the entangled particle partner the one going through the slits has either interfered with itself or not 5 In delayed choice experiments quantum effects can mimic an influence of future actions on past events 6 However the temporal order of measurement actions is not relevant 7 Procedure edit nbsp Figure 1 Crossed polarizations prevent interference fringesFirst a photon is shot through a specialized nonlinear optical device a beta barium borate BBO crystal 3 This crystal converts the single photon into two entangled photons of lower frequency a process known as spontaneous parametric down conversion SPDC These entangled photons follow separate paths One photon goes directly to a polarization resolving detector while the second photon passes through the double slit mask to a second polarization resolving detector Both detectors are connected to a coincidence circuit ensuring that only entangled photon pairs are counted A stepper motor moves the second detector to scan across the target area producing an intensity map This configuration yields the familiar interference pattern nbsp Figure 2 Introduction of polarizer in upper path restores interference fringes belowNext a circular polarizer is placed in front of each slit in the double slit mask producing clockwise circular polarization in light passing through one slit and counter clockwise circular polarization in the other slit see Figure 1 Which slit corresponds to which polarization depends on the polarization reported by the first detector This polarization is measured at the second detector thus marking the photons and destroying the interference pattern see Fresnel Arago laws Finally a linear polarizer is introduced in the path of the first photon of the entangled pair giving this photon a diagonal polarization see Figure 2 Entanglement ensures a complementary diagonal polarization in its partner which passes through the double slit mask This alters the effect of the circular polarizers each will produce a mix of clockwise and counter clockwise polarized light Thus the second detector can no longer determine which path was taken and the interference fringes are restored A double slit with rotating polarizers can also be accounted for by considering the light to be a classical wave 8 However this experiment uses entangled photons which are not compatible with classical mechanics Other applications editQuantum erasure technology can be used to increase the resolution of advanced microscopes 9 Common misconception editA common misunderstanding about this experiment is that it may be used to instantaneously communicate information between two detectors 10 Simple causation however precludes foisting given information on the observed outcomes It is important to understand the role of the coincidence detector in this experimental setup The linear polarizer in the top path is effectively filtering out half the entangled photons and via the coincidence detector is filtering out the corresponding photons in the bottom path The coincidence detector can only function by comparing data from both sensors making it impossible to use this setup for instant communication In other words only a small percentage of the light passing through the BBO crystal is split into entangled pairs The vast majority of photons passing through the crystal are not split and must be removed from the final data set as unwanted noise Since there is no way for the detectors to measure whether or not a photon had been part of an entangled pair that decision is made by looking at the timing and filtering out any photons that are not picked up at the same time as their twin at the other detector Thus when a pair of entangled photons is created but one of the two is blocked by a polarizer and lost the remaining photon will be filtered out of the data set as if it was one of the many non entangled photons When viewed this way it is not surprising that making changes to the upper path can have an impact to measurements taken on the lower path as the two measurements are being compared and used to filter the data Note that in the final state of this experimental setup measurements on the lower path always show a smeared out pattern on the raw data Seeing an interference pattern is only possible by filtering the data with the coincidence detector and only looking at photons that were 1 2 of an entangled pair References edit Englert Berthold Georg 1999 Remarks on Some Basic Issues in Quantum Mechanics PDF Zeitschrift fur Naturforschung 54 1 11 32 Bibcode 1999ZNatA 54 11E doi 10 1515 zna 1999 0104 S2CID 3514379 Archived from the original PDF on 2017 08 09 Retrieved 2019 04 10 Baggott J E 2013 The quantum story a history in 40 moments Impression 3 ed Oxford Oxford Univ Press ISBN 978 0 19 965597 7 a b c Walborn S P Terra Cunha M O Padua S Monken C H 2002 02 20 Double slit quantum eraser Physical Review A 65 3 arXiv quant ph 0106078 doi 10 1103 PhysRevA 65 033818 ISSN 1050 2947 Scully Marian O Druhl Kai 1982 Quantum eraser A proposed photon correlation experiment concerning observation and delayed choice in quantum mechanics Physical Review A 25 4 doi 10 1103 PhysRevA 25 2208 Yoon Ho Kim Yu R Kulik S P Shih Y H Scully Marlan 2000 A Delayed Choice Quantum Eraser Physical Review Letters 84 1 1 5 arXiv quant ph 9903047 Bibcode 2000PhRvL 84 1K doi 10 1103 PhysRevLett 84 1 PMID 11015820 S2CID 5099293 Fankhauser Johannes 2019 Taming the Delayed Choice Quantum Eraser Quanta 8 44 56 arXiv 1707 07884 doi 10 12743 quanta v8i1 88 S2CID 53574007 Ma Xiao song Kofler Johannes Zeilinger Anton 2016 Delayed choice gedanken experiments and their realizations Rev Mod Phys 88 1 015005 arXiv 1407 2930 Bibcode 2016RvMP 88a5005M doi 10 1103 RevModPhys 88 015005 S2CID 34901303 Chiao R Y Kwia P G Steinberg A M June 1995 Quantum non locality in two photon experiments at Berkeley Quantum and Semiclassical Optics Journal of the European Optical Society Part B 7 3 259 278 arXiv quant ph 9501016 Bibcode 1995QuSOp 7 259C doi 10 1088 1355 5111 7 3 006 S2CID 118987962 Aharonov Yakir Zubairy M Suhail 2005 Time and the Quantum Erasing the Past and Impacting the Future Science 307 5711 875 879 Bibcode 2005Sci 307 875A CiteSeerX 10 1 1 110 2955 doi 10 1126 science 1107787 PMID 15705840 S2CID 16606155 Kastner R E 2019 07 01 The Delayed Choice Quantum Eraser Neither Erases Nor Delays Foundations of Physics 49 7 717 727 arXiv 1905 03137 doi 10 1007 s10701 019 00278 8 ISSN 0015 9018 Kastner 2019 Delayed Choice Quantum Eraser Neither Erases Nor Delays Foundations of PhysicsExternal links editA more technical analysis of the quantum eraser experiment A Scientific American article A Do It Yourself Quantum Eraser note SciAm online subscribers only Retrieved from https en wikipedia org w index php title Quantum eraser experiment amp oldid 1200051931, wikipedia, wiki, book, books, library,

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