PROFILE Profile of David Wineland and Serge Haroche, 2012 Nobel Laureates in Physics William D. Phillips1 Laser Cooling and Trapping Group, National Institute of Standards and Technology, Gaithersburg, MD 20899

As a postdoctoral student at the Massachu- Wineland and Haroche realized a long- setts Institute of Technology in 1978, I trolled standing dream of quantum physics: studying the literature, seeking inspiration for my the behavior of single quantum objects. The career as an experimental physicist. One founders of quantum mechanics believed article that caught my attention described that studying a single quantum system, like the first laser-cooling experiment. David a single atom or a single photon, was beyond Wineland et al. at the National Bureau of the realm of experimental possibility. Many Standards (NBS, now the National Institute believed that it did not even make sense to of Standards and Technology) in Boulder, talk about a single atom; only the behavior CO, had trapped a cloud of hot (about 700 K) of an ensemble could be meaningful. In fact, ions and cooled them to near absolute zero Schrödinger asserted: “...we never experi- < (T 40 K) by shining light on them (1). (See ment with just one electron or atom ... In National Institute of Standards and Tech- also ref. 2, which reports an independent and thought experiments, we sometimes assume nology physicist David Wineland adjusts an nearly simultaneous demonstration of laser that we do; this invariably entails ridiculous ultraviolet laser beam used to manipulate cooling of ions.) Later that year, I was hired ...” consequences (5). The groups of ions in a high-vacuum apparatus contain- by NBS in Gaithersburg, MD and, inspired Haroche and Wineland turned this idea ’ ing an “ion trap.” Copyright Geoffrey by Wineland s landmark experiment, began on its head; not only did they use individ- Wheeler. to work on laser-cooling of neutral atoms. ual atoms and photons to elucidate some Earlier, in 1975 with Hans Dehmelt, Wine- of the strangest aspects of quantum me- land had first proposed laser cooling (3), si- chanics, they have even used them to make microwaves) in a cavity, where the photons multaneously with Ted Hansch and Art practical devices. bounce back and forth between two mirrors Schawlow (4). I often talk about laser-cooling, A key advance of Wineland’s group was to a billion times before escaping. Cooling the showing a slide of the idea’s origins and go from trapping a cloud of many “hot” ions mirrors to less than a kelvin nearly elimi- remarking that among Wineland, Dehmelt, (a few degrees above absolute zero) to hold- nates the thermal photons in the cavity so Hansch, and Schwalow, three had received ing individual ions in the trap “ground state.” Haroche’s group could study one or a few Nobel prizes in physics. On October 9, Quantum mechanics shows that the energy photons that they deliberately put into the 2012, the Royal Swedish Academy of Scien- of center-of-mass motion of any confined cavity. By passing single atoms through the ces completed the foursome by awarding particle takes on only specific (quantized) cavity and analyzing the state of the atoms the 2012 Nobel Prize in Physics to David values. Ordinary particles at ordinary tem- as they emerged, Haroche’sgroupdeter- Wineland. The award is shared with Serge peratures are distributed among millions mined exactly how many photons the cav- Haroche of the Collège de France, Paris “for and millions of such energy levels. How- ity held. In a dramatic demonstration of a ground-breaking experimental methods that ever, at the temperatures in Wineland’s classic thought-experiment, Haroche and enable measuring and manipulation of in- experiment, microdegrees above absolute colleagues put an indeterminate number dividual quantum systems.” zero, the single ion is—with near 100% of photons into the cavity, then began to probability—in one particular energy level, measure the number, watching the cavity the lowest, ground state. Starting with such progressively “collapse” to a specific(but a pure and well-defined quantum state, unpredictable) number of photons. Then, Wineland and his colleagues experimentally as photons slowly leaked out of the cavity, demonstrated some of the classic thought- they could see the “death” of each individual experiments of modern physics. Among photon. Haroche et al. also created “cat” these experiments were the observation of states where the cavity, before measure- quantum jumps as a single atom changed ment, was in a superposition containing its state after absorbing or emitting a photon “ ” and the creation of Schrödinger cat states: Author contributions: W.D.P. wrote the paper.

having an ion in two macroscopically sepa- A more detailed description with more extensive references is at: Serge Haroche (Right) and assistant Igor Dotsenko rated places at the same time. http://www.nobelprize.org/nobel_prizes/physics/laureates/2012/ (Left) at work in the laboratory. Copyright Harochedidmuchthesamething,but advanced-physicsprize2012_02.pdf. CNRS Photothèque/Christophe Lebedinsky. trapping photons, particles of light (or 1E-mail: [email protected].

7110–7111 | PNAS | April 30, 2013 | vol. 110 | no. 18 www.pnas.org/cgi/doi/10.1073/pnas.1221825110 Downloaded by guest on September 28, 2021 PROFILE two different classical fields, but collapsed quantum information the “qubits” store in- ments, including ones from the laborato- into just one when measured. formationinquantumobjectslikesingle ries of Haroche and Wineland, have made Wineland’sworkhasledtothebest- atoms or photons—objects that can, like the difficulties seems less daunting. We everperformanceofanatomicclock.A Schrödinger’s cat, be in two states at the still don’t know if quantum computers single aluminum ion “ticking” at the fre- same time. Ironically, in 1996 Haroche and that are capable of doing calculations that quency of light, about 1015 times per sec- colleague Jean-Michel Raimond wrote a pro- no ordinary computer could hope to ac- ond, produced a clock, the systematic vocative article (6) entitled “Quantum com- complish will ever be made, but the work uncertainty of which was better than a part puting: Dream or nightmare,” pointing of Wineland and Haroche and of their col- in 1017. Optical clocks will probably one out the seemingly insurmountable diffi- leagues all over the world has brought this day replace the cesium atomic clocks— culties to making a quantum computer. and other goals, once merely the stuff of nowwithaccuraciesofafewpartsin New theoretical and experimental develop- dreams, closer to reality. 1016—that currently define time. The work of Haroche and Wineland has given a big push to quantum information 1 Wineland DJ, Drullinger RE, Walls FL (1978) Radiation- 4 Hänsch TW, Schawlow AL (1975) Cooling of gases by “ ” pressure cooling of bound resonant absorbers. Phys Rev Lett laser radiation. Opt Commun 13:68–69. science. In digital technology, bits of infor- 40:1639–1642. 5 Schrödinger E (1952) Are there quantum jumps? Part II. Br J Philos mation are embodied as electronic switches 2 Neuhauser W, Hohenstatt M, Toschek PE, Dehmelt H (1978) 3:233–242. turned on or off, spots on a CD or DVD Optical-sideband cooling of visible atom cloud confined in parabolic 6 Haroche S, Raimond J-M (1996) Quantum computing: Dream or well. Phys Rev Lett 41:233–236. nightmare? Phys Today 49:51–52. burned or not burned, or patches on a hard 3 Wineland DJ, Dehmelt H (1975) Proposed 1014Δν < ν laser fluores- + disk magnetized one way or another. In cence spectroscopy on Tl mono-ion oscillator. Bull Am Phys Soc 20:637.

Phillips PNAS | April 30, 2013 | vol. 110 | no. 18 | 7111 Downloaded by guest on September 28, 2021