سمينار دانشجويي

1. سمينار دانشجويي “Delay choice Experiment" ارائه دهنده: رضا امین زاده نیک آذر ماه 91

3. What We Hear in This Lecture • Wave-Particle Duality • Double-slit experiment • Delayed Choice Experiment • Quantum Eraser

4. Wave-Particle Duality Antiquity (Egypt, Greece): particles towards or from the eye (Epicure, Aristotle, Euclid) XVIIth cent.: Waves (as “riddles on water”) Huyghens Newton (Opticks, 1702): particles (of various colours)

5. XIXth cent. The triumph of waves Young, Fresnel (1822): interference, diffraction, polarisation: light is a transverse wave Maxwell (1870): light is an electromagnetic wave

6. Early XXth: Photons(particles come back) • Einstein (1905). Light made of quanta, elementary grains of energy and momentum (named “photons” in 1926 only). 􀂾Quantitative predictions for the photoelectric effect E = hν p = hν / c How to reconcile the particle description with typical wave phenomenon of diffraction, interference, polarisation? Particle or wave? 􀂾Ideas not accepted until Millikan’s experiments on photoelectric effect (1915). 􀂾Nobel award to Einstein (1922) for the photoelectric effect 􀂾Compton’s experiments (1923): momentum of photon in the X ray domain

7. Wave particle duality Light is both waves (capable to interfere) and an ensemble of particles with defined energy and momentum… Similarly particles such as electrons behave like a wave (diffraction, interference) Einstein 1909 Louis de Broglie 1923

8. Double-slit experiment .

9. Delayed Choice Experiment • Proposed by John Archibald Wheeler in 1978 • The method of detection in this experiment can be changed after the photon passes the double slit, so it is possible to delay the choice of whether to detect the path of the particle, or detect its interference with itself Father of black hole

10. The arrangement is set in such a way that this part is constructive The arrangement is set in such a way that this part is destructive In this case each photon is detected with one of these detectors. This experiment is done with a single photon So photon behaves like a particle It seems that causality is reversed!!? Maalool taghaddom bar ellat darad!!????????? Semi -transparent mirror Now photon behaves like a wave Time interval between of two successive emission is long enough

11.  An implementation of the experiment in 2007 showed that the act of observation ultimately decides whether the photon will behave as a particle or wave. Cho, Adrian. After a Short Delay, Quantum Mechanics Becomes Even Weirder. ScienceNOW Daily News. 16 February 2007

12. Quantum Eraser Experiment • The Which-way information that once established can be erased. •  The idea was first proposed by Marlan O. Scully and K. Druhl.(1982) M. O. Scully and K. Druhl, Phys. Rev. A, 25,2208 (1982)

13. Marlan O. Scully • 1963: Graduates from Yale University with M.S. in Physics • 1966: Graduates from Yale University with Ph.D. in Physics • 1969: Professor of Physics and Optical Sciences, University of Arizona, through 1980 • 1980: Distinguished Professor of Physics, University of New Mexico, through 1992 • 1992: Professor of Physics, Texas A&M University, through 1996 • 2004: Professor of Chemical Engineering, Texas A&M University, through present • 2005: Professor of Mechanical and Aerospace Engineering and Materials Science, Princeton University, through present

14. BBO(Beta-Barium Borate) Crystal These photons are correlated in that they are created simultaneously, and they both have the same polarization (Here vertical to the plane of the experiment).

15. BBO(Beta-Barium Borate) Crystal

16. Assume that the photons have the same frequency and they are indistinguishable, so: Intensities at the two detectors are identical, and are proportional to

17. Analogous to knowing which of the two slits a photon passes through. (good start!!?) The which-way effect can be seen when the upper mirror is removed. In that case there is no reflectedsphoton associated with the reflectediphoton, whichallows us todistinguishbetween the twoiphotons.

18. BBO(Beta-Barium Borate) Crystal Plate that rotates the polarization from V to H No interference Because, we have a which-way situation Distinguishing the reflected i photon then distinguishes the reflected s photon, since these are all produced in pairs.

19. By expressing the photon state in terms of states rotated through ±45 degree, We have:

20. Plate that rotates the polarization from V to H By putting a 45 degree filter in front of the upper detector, BBO(Beta-Barium Borate) Crystal We have, So the which-way information is erased & We have fringes!!?

22. Thanks for listening