Question: Which American physicist and winner of the Nobel Prize in Physics in 1955 worked with Robert Retherford to perform the experiment that revealed Lamb shift?
Context: Chien-Shiung Wu (; May 31, 1912 – February 16, 1997) was a Chinese-American experimental physicist who made significant contributions in the field of nuclear physics.  Wu worked on the Manhattan Project, where she helped develop the process for separating uranium metal into uranium-235 and uranium-238 isotopes by gaseous diffusion.  She is best known for conducting the Wu experiment, which contradicted the hypothetical law of conservation of parity.  This discovery resulted in her colleagues Tsung-Dao Lee and Chen-Ning Yang winning the 1957 Nobel Prize in physics, and also earned Wu the inaugural Wolf Prize in Physics a mere two decades later in 1978.  Her expertise in experimental physics evoked comparisons to Marie Curie.  Her nicknames include "the First Lady of Physics", "the Chinese Madame Curie", and the "Queen of Nuclear Research". Clinton Joseph Davisson (October 22, 1881 – February 1, 1958), was an American physicist who won the 1937 Nobel Prize in Physics for his discovery of electron diffraction in the famous Davisson-Germer experiment.  Davisson shared the Nobel Prize with George Paget Thomson, who independently discovered electron diffraction at about the same time as Davisson. Since 1901, the Nobel Prize in Literature (Swedish: "Nobelpriset i litteratur" ) has been awarded annually to an author from any country who has, in the words of the will of Alfred Nobel, produced "in the field of literature the most outstanding work in an ideal direction" (original Swedish: "den som inom litteraturen har producerat det mest framstående verket i en idealisk riktning").  Though individual works are sometimes cited as being particularly noteworthy, here "work" refers to an author's work as a whole.  The Swedish Academy decides who, if anyone, will receive the prize in any given year.  The academy announces the name of the chosen laureate in early October.  It is one of the five Nobel Prizes established by the will of Alfred Nobel in 1895; the others are the Nobel Prize in Chemistry, Nobel Prize in Physics, Nobel Peace Prize, and Nobel Prize in Physiology or Medicine. Prof Albert Abraham Michelson (surname pronunciation anglicized as "Michael-son") FFRS HFRSE LLD (December 19, 1852 – May 9, 1931) was an American physicist known for his work on measuring the speed of light and especially for the Michelson–Morley experiment.  In 1907 he received the Nobel Prize in Physics, becoming the first American to win the Nobel Prize in a science. Willis Eugene Lamb Jr. ( ; July 12, 1913 – May 15, 2008) was an American physicist who won the Nobel Prize in Physics in 1955 "for his discoveries concerning the fine structure of the hydrogen spectrum."  The Nobel Committee that year awarded half the prize to Lamb and the other half to Polykarp Kusch, who won "for his precision determination of the magnetic moment of the electron."  Lamb was able to determine precisely a surprising shift in electron energies in a hydrogen atom (see Lamb shift).  Lamb was a professor at the University of Arizona College of Optical Sciences. Polykarp Kusch (January 26, 1911 – March 20, 1993) was a German-American physicist.  In 1955, the Nobel Committee gave a divided Nobel Prize for Physics, with one half to going to Kusch for his accurate determination that the magnetic moment of the electron was greater than its theoretical value, thus leading to reconsideration of—and innovations in—quantum electrodynamics.  (The other 1955 physics laureate was Willis Eugene Lamb, who won for his work on the spectrum of hydrogen.) Robert Curtis Retherford (1912 – 1981) was an American physicist.  He was a graduate student of Willis Lamb at Columbia Radiation Laboratory.  Retherford and Lamb performed the famous experiment revealing Lamb shift in the fine structure of hydrogen, a decisive experimental step toward a new understanding of quantum electrodynamics. In physics, the Lamb shift, named after Willis Lamb, is a difference in energy between two energy levels "S" and "P" (in term symbol notation) of the hydrogen atom which was not predicted by the Dirac equation, according to which these states should have the same energy. This is a list of Danish Nobel laureates.  Since the Nobel Prize was established per the will of Swedish inventor Alfred Nobel in 1895, 12 of the prize winners have been from Denmark.  The first Danish Nobel laureate was Niels Ryberg Finsen, who won a Nobel Prize for medicine in 1903 for his work in using light therapy to treat diseases.  The most recent Danish Nobel Prize winner was Jens Skou who won the prize in chemistry for his discovery over the enzyme, Na+/K+-ATPase in 1997.  To date, of the 13 Nobel Prizes won by Danish people, 5 have been for medicine, 3 have been for physics, 3 have been for literature, 1 has been for chemistry and one has been for peace. The Nobel Prize in Physics (Swedish: "Nobelpriset i fysik" ) is a yearly award given by the Royal Swedish Academy of Sciences for those who conferred the most outstanding contributions for mankind in the field of physics.  It is one of the five Nobel Prizes established by the will of Alfred Nobel in 1895 and awarded since 1901; the others being the Nobel Prize in Chemistry, Nobel Prize in Literature, Nobel Peace Prize, and Nobel Prize in Physiology or Medicine.
Answer: Willis Lamb