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CREOL, The College of Optics & Photonics

Seminar: "Completing Bohr’s Complementarity" by Xiao-Feng Qian

Monday, October 30, 2017 1:00 PM to 2:00 PM
CREOL Room 103

Dr. Xiaofeng Qian
The Institute of Optics, and Department of Physics & Astronomy
University of Rochester


The understanding of the nature of light has been one of the most fundamental and ancient issues of
science history. Wave and particle are two dominating interpretations of light. The debate of light being
either a particle or a wave has gone back and forth over the centuries from Newton’s corpuscular theory and Huygens’ wave description in the 17th century, through the prevalence of wave interpretation in the 19th century due to Fresnel, Young, and Maxwell, all the way to Einstein’s photoelectric effect of photon description and de Broglie’s matter wave theory in early 20th century. The widely accepted qualitative resolution has been Bohr’s complementarity principle which states that light is actually BOTH wave and particle but they are two mutually exclusive properties [1]. Initiative search of a comprehensive quantitative analysis of this wave-particle duality picture wasn’t carefully pursued until around the 1980s by Wootters-Zurek, Glauber, and Mandel [2]. The consequence has been the famous complementary constraint relation for single photons, i.e., D2 + V 2  1, repeatedly rediscovered around the 1990s by Greenberger-Yasin, Jaeger-Horne-Shimony, and Englert [3], with visibility V representing wave property and distinguishability D labeling particle behavior. Unfortunately, even almost 40 years after its discovery, no careful attention has been paid to the fact that the inequality D2 + V 2  1 embodies neither completeness nor exclusivity, two essential factors of Bohr’s complementarity. Something must be missing.
We solve the issue by performing a quantitative analysis of light’s wave and particle (ray) properties in the classical regime. We recover the relation V 2 + D2  1 for a generic classical light field. By taking into account a previously neglected third key property of the field, i.e., classical entanglement (measured by concurrence C [4]), a generic complete three-way complementary relation V 2+D2+C2 = 1 is observed for the first time to satisfy both completeness and exclusivity. Experimental results of an optical beam interfering through a Mach-Zehnder interferometer has confirmed the theoretical predictions [5]. The three-way relation reveals fundamental coherence constraints of light fields, and it also suggests a modified view of the traditional complementary wave-particle duality for light. The results are also valid for single quantum particles indicating its universality. This work is the result of collaboration with J.H. Eberly and A.N. Vamivakas at Rochester. We would like to thank discussions with G.S. Agarwal, B. Englert, P. Milonni, M. Raymer, W. Schleich, W. Zurek. Support from NSF grants PHY-1203931, PHY-1505189, and INSPIRE PHY-1539859, as well as ARO W911NF-14-1-063, ONR N00014-14-1-0260, and a Univ. Rochester Research Award is acknowledged.


Dr. Xiaofeng Qian received his Ph.D. degree in 2014 from the Department of Physics and Astronomy, University of Rochester, supervised by Dr. Joseph H Eberly. He then became a Visiting Scientist and subsequently an Instructor/Fellow at the same department. Since July 2015 he joined the Institute of Optics at the University of Rochester as a Research Associate. His research focuses on experimental and theoretical issues of quantum and coherence optics. His works in the emerging field of optical coherence/entanglement has received various attention in the physics and optics communities with coverages from professional organizations and science-news websites.

For additional information:

Ayman Abouraddy

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