A peek at quantum optics between the pages

In a March 2012 book review in Physics Today, University of Notre Dame atomic physicist H. Gordon Berry noted that atomic physicists have won the Nobel Prize in Physics every fourth year since Claude Cohen-Tannoudji, Steven Chu, and William Phillips won it in 1997. Berry’s comment suggested that 2013 might be ‘another atomic year.’ If the 2012 prize, awarded for ‘ground-breaking experimental methods that enable measuring and manipulation of individual quantum systems’ is an early indication, the atomic winning streak may be picking up steam.

The latest Nobel laureates in physics are Serge Haroche of the Collège de France in Paris and David Wineland of NIST in Boulder, Colorado. Both developed methods to examine, control, and count particles: Haroche’s system measures trapped photons by passing atoms through an optical cavity, and Wineland’s measures trapped ions by probing them with photons. With such systems, decoherence can be investigated by measuring the evolution of entangled quantum states described in Erwin Schrödinger’s cat thought experiments; Wineland’s group has extended the research to building quantum logic gates, the first step in quantum computing, and to making more precise atomic clocks. A list of Physics Today articles by both scientists appears in the online summary of the 2012 Prize .

Dressing atoms

A handful of books reviewed in Physics Today may also be useful for understanding the theory behind this year’s Nobel research. Advances in Atomic Physics: An Overview (World Scientific, 2011), the subject of Berry’s review, is written by David Guéry-Odelin and Haroche’s PhD adviser, Cohen-Tannoudji, whom the reviewer describes as ‘second to none in his understanding of the modern theory and application of atom–photon interactions.’ According to the review, the book’s strength is its sections on ‘physics of quantum correlations in entangled states and the many variants of Bose–Einstein condensation.’ At 700-plus pages, the book may be a useful reference for researchers and for graduate students, particularly those conducting atom-laser graduate research.

The reviewer’s objections are that the book does not provide a ‘detailed discussion on exciting new links to quantum computing through entangled states.’ Nor does it, as its title suggests, fully cover all the advances in atomic physics; instead, it focuses on the authors’ expertise in atom–photon interactions. Berry suggests that the book should have been packaged as an update to Cohen-Tannoudji, Jacques Dupont-Roc, and Gilbery Grynberg’s two-decades-old text, Atom-Photon Interactions: Basic Processes and Applications (Wiley, 1992). That book, reviewed in Physics Today by the University of Arizona’s Pierre Meystre, is itself an update to the authors’ earlier, foundational text on quantum electrodynamics, the theoretical framework for the methods developed by Haroche and Wineland. No doubt Haroche is a beneficiary of what the reviewer describes as the more sophisticated education in quantum mechanics offered in France’s elite schools, especially the French ‘dressed-atom formalism approach … that offers unique insight into many aspects of light–matter interactions.’

Take a hint

For an atomic text that covers more ground, Berry recommends Atomic Physics: An Exploration Through Problems and Solutions (2nd edition, Oxford University Press, 2008) by Dmitry Budker, Derek Kimball, and David DeMille. Yale University’s Steve Lamoreaux, who reviewed the first edition in March 2005 , says Atomic Physics ‘provides all the background required to understand the theory and specific operation of most experiments in modern physics.’ The book’s authors employ the pedagogical approach of ‘presenting the subject as a series of short tutorial questions followed by hints and solutions.’ According to the reviewer, students who master a tutorial receive a sound understanding of the relevant issues and preparation to read the relevant professional papers. Chapters related to the work by Haroche and Wineland include chapter 2, ‘Atoms in external fields;' chapter 3, ‘Interaction of atoms with light;' and chapter 8, ‘Experimental methods.’

If you want the background straight from the horse’s mouth, Haroche’s Exploring the Quantum: Atoms, Cavities, and Photons (Oxford University Press, 2006), written with Jean-Michel Raimond, is a text that Meystre thinks Schrödinger himself would have loved. In his 2007 review , Meystre describes Exploring the Quantum as an ‘elegant and beautifully produced book’ that takes readers ‘through topics ranging from superradiance and micromasers, to quantum gates, to multiparticle entanglement, to the life and death of Schrödinger cats.’ In particular, chapter 2 presents a ‘whirlwind pedagogical review’ of quantum interference, quantum entanglement, and quantum teleportation.

Quantum dream or nightmare?

In addressing a much-anticipated potential application, Exploring the Quantum also ‘teaches readers how to recast familiar two-state-system physics in terms of qubits manipulated by quantum gates and to represent that physics by quantum-circuit equivalents.’ Not surprisingly, the book is less detailed in its discussion of trapped ions, which is the focus of Wineland’s work, and their potential application to quantum computing. But Meystre says the authors’ presentation nonetheless ‘builds a clear bridge between quantum physics and quantum information science.’

However, in a 1996 Physics Today article titled ‘Quantum computing: Dream or nightmare? ,’ Haroche and Raimond caution that strategies for controlling the effects of decoherence are more likely to teach us about ‘the processes that would ultimately make the undertaking [of building a quantum computer] fail.’ Instead, they say, the real promise of such strategies is ‘a deeper insight into the most counterintuitive theory yet discovered by physicists.’