Optomechanics, the study of the mechanical effects of light on massive objects, has a long and distinguished history. It took off nearly 50 years ago, when Arthur Ashkin demonstrated that small dielectric balls can be accelerated and trapped using the radiation-pressure forces associated with focused laser beams. That led to the development of optical tweezers, a tool with wide-ranging applications in biological science.
A parallel development, investigations into the strong enhancement of mechanical effects created by resonant light scattering, led to the laser cooling of ions and neutral atoms. That was followed by the realization of atomic Bose–Einstein condensates in 1995 and the subsequent explosion in the study of quantum degenerate atomic systems. Critical breakthroughs can also be traced back to work on optical gravitational-wave antennas that started in the 1970s and 1980s. It is in that context that researchers understood the role of fundamental quantum optical effects in mechanical position measurements and the resulting standard quantum limit and advanced the idea of back-action evading measurements.
Quantum optomechanics, the field that evolved from those developments, promises to provide motion and force detection near the fundamental limits imposed by quantum mechanics. The field provides the basis for the quantum state control of truly macroscopic objects and for experiments that may lead to a more profound understanding of quantum mechanics.
Light can interact with matter either resonantly or nonresonantly, and both interactions present challenges. Resonance can result in a large enhancement of an interaction, but it is limited to a narrow range of wavelengths. Nonresonant interactions, on the other hand, present the considerable advantage of being largely wavelength independent, but they produce a smaller effect. Cavity optomechanics combines the best of both worlds through the use of carefully engineered resonant structures.
The two books under review offer complementary views of those developments. Quantum Optomechanics is coauthored by experimentalist Warwick Bowen and theorist Gerard Milburn, major contributors to the field. It is a graduate-level text that focuses largely on the quantum theory of optomechanical systems and has little to say about experiments, except in very general terms. Cavity Optomechanics: Nano- and Micromechanical Resonators Interacting with Light is a collection of 12 invited articles by leading experts from both sides of the Atlantic. It is edited by Markus Aspelmeyer, Tobias Kippenberg, and Florian Marquardt, researchers who have achieved some of the field’s most significant recent discoveries. It covers both classical and quantum aspects of optomechanics, with a good balance between theory and experiment.
Quantum Optomechanics assumes a high level of theoretical sophistication and is a challenging text, even for theoretically oriented students. That is most evident in the authors’ inclusion of advanced concepts not typically covered in a graduate curriculum. An introductory discussion of the basic physics of optomechanical systems, perhaps in classical terms, would have helped reduce the steepness of the learning curve for newcomers. Furthermore, the exercises mostly fill gaps in derivations, and they will primarily be of interest to theory-inclined students. The book will therefore be most useful to readers who are already well versed in the basic physics of optomechanics and want to dig deeply into the quantum theory of detection, noise, quantum coherent control, and related topics.
Those theory-minded readers will find much to admire in the book. Quantum Optomechanics skillfully reviews a wealth of important results on those topics. For example, the book’s clear and authoritative discussions cover the various troublesome noises, including measurement and back action, typical of quantum measurements. It also nicely treats the consequent standard quantum limit of mechanical position measurements. Advanced topics such as single-photon optomechanics receive their due, and the authors include a useful introduction to hybrid quantum systems—although perhaps a too brief one in view of the growing importance of the topic. The last chapter, on gravitational decoherence, gives a hint at one of the directions that might be opened up by the availability of quantum optomechanical sensors.
Cavity Optomechanics is more user-friendly. Although not a textbook, many of its chapters would be useful in a graduate course or could serve as a valuable introduction for newcomers. The book opens with some brief remarks by the editors, followed by a concise introduction to the theory of cavity optomechanics, with a simple classical description and a clear discussion of basic quantum aspects. The next chapters give an overview of significant advances in the field through 2014. They cover various topics from both theoretical and experimental points of view, including cavity systems with suspended mirrors, optomechanical crystal devices, LC circuits, ultracold ensembles of thousands of atoms, visible light, microwaves, and more. A final chapter on hybrid systems nicely complements the corresponding chapter in Quantum Optomechanics.
The chapters on hybrid systems are not the only point at which readers will find value in consulting both Quantum Optomechanics and Cavity Optomechanics. Together, the two books make for an authoritative introduction to optomechanics that will serve the needs of graduate students and more experienced researchers interested in moving into the fast-growing field. Cavity Optomechanics provides an introduction to many of the most interesting experimental systems, and Quantum Optomechanics brings readers up to speed on the state of the art of the theory. Students and researchers concentrating on experimental physics may find that Cavity Optomechanics is often sufficient. Theorists would be well advised to dig deep into Quantum Optomechanics as well.
Pierre Meystre is a Regents Professor Emeritus of Physics and Optical Sciences at the University of Arizona and editor-in-chief of the American Physical Society’s journals. His research interests include theoretical quantum optics, atomic physics, ultracold science, and quantum optomechanics.
