Scientific Project and Intellectual Merit: The grant will support theoretical investigations into the ultimate limits to the precision of optical and atomic interferometry. The research will exploit recent advances in the foundations of quantum mechanics and also in quantum information theory, to develop designs and models of quantum interferometers which have the potential to be orders of magnitude more sensitive than current devices. Interferometry is at the heart of much the science of precision measurement, and the work will lead to a new understanding of the limits imposed by quantum mechanics on the sensitivity of such devices.
Broader Impact: Precision interferometry is the engine behind many types of sensing and measuring devices, such as atomic clocks used in GPS, optical interferometers used in sensitive magnetic field measurements, such as in medical magnetic imaging. Understanding the limits to the sensitivity of such devices could lead to breakthroughs particularly in such sensor technology and open new scientific and commercial vistas that exploit such sensitivity. The work is also at the interface of quantum information processing, which can lead to exponentially faster quantum computers. Two graduate students will be trained in this field of quantum atomic and optical interferometry, an interdisciplinary activity with synergy to a number of the most exciting and fast moving areas of quantum sciences and technologies.
Interferometry is a technique where waves are superimposed upon each other giving rise to an interference pattern from which information carried by the waves may be extracted. Optical interferometry experiments, using visible light waves, were responsible for some of the most important scientific discoveries of the early1900s, including confirmation of Einstein’s theory of relativity by using interferometry to carefully measure the speed of light. More recently in the late 1900s and on into the 2000s atomic interferometry has become a robust technology where atomic de Broglie waves are interfered and used to make precision measurements of rotations and accelerations for use in everything from inertial guidance systems to oil prospecting. Our work has particularly focused on the fundamental limits to the signal-to-noise ratio in optical and atomic interferometers, and exploiting techniques lifted from quantum information theory to improve the signal to noise in practical devices. The connection to quantum computing can be seen in that optical and atomic quantum computers are in their essence large, complex, and finely tuned optical and atomic interferometers. In this way a quantum computer is a large interferometer that is able to solve mathematical problems that are intractable on a classical computer and a quantum interferometer is a device that is capable of making measurements with a precision and signal-to-noise ratio that is potentially much better than on a classical interferometer. In both cases the quantum devices exploit some of the stranger aspects of quantum mechanics, such as quantum entanglement and Schrödinger cat states for improved performance. A primary particular focus of this project then has been to adapt well-developed methods from quantum computing theory to the less well-developed techniques of quantum interferometry. It has been known for some years that exotic entangled, or Schrödinger cat, or other non-classical states can in principle improve the signal-to-noise ratio in optical and atomic interferometers, such non-classical states are very susceptible to noise from the environment that degrades performance of the interferometers. Our key idea is that such exotic states are also used in quantum information processors, where noise also degrades performance, but that in this field quantum error mitigation protocols are well developed to allow the quantum computer to run in a fault tolerant manner. We have spent the three years of this project investigating how quantum error mitigation protocols used in robust quantum information processing may be used to instead perform robust quantum interferometry with applications to metrology, remote and local sensing, improved imaging, and inertial navigation devices. We have had a great deal of success in this project and the results show that indeed it is possible to construct quantum interferometers that are robust against noise for such applications. This is the primary technical merit of the project. In terms of broader impact, optical interferometers are widely used in industry and science for measuring small displacements, characterizing optical systems (including fiber optical networks), laser ranging or Doppler laser radar, remote sensing, and in oceanography. Hence our improvements to optical interferometers by quantum methods have a large array of practical applications. Our work in optical interferometry has also immediate applications to improved imaging methods such as microscopy and lithography, where the latter is the technology for mass-producing computer chips. In the arena of atomic interferometers, the field is newer and less well developed, but such interferometers — due to the large mass of atoms compared with photons — are exquisitely sensitive to accelerations, rotations, and gravitational fields. This makes atomic interferometry a primary candidate for building the components that are used in inertial navigation systems that are critical for underwater, underground, or space applications where GPS is not available. Our particular work in atomic interferometry has cumulated in a design of an atomic gyroscope that has a particularly enhance performance when it comes to stability of the signal. This project, over the three-year period of performance, has involved two graduate students and a number of undergraduate students, including two visiting summer students and a local high school student who worked with us on her award-winning science fair project. We take great pride in having a diverse group of young people including particularly undergraduates who have been from under represented minorities. The project resulted in over 14 refereed journal publications (3 with undergraduate co-authors), and 21 presentations at conferences (7 presented by undergraduate students and 5 of which were invited). During the period of performance the principle investigator also spent 6 months on sabbatical in China and the US and had time to write a popular book on the history of quantum computing and quantum technologies, Schrödinger’s Killer App, which appeared in print in May of 2013: www.taylorandfrancis.com/books/details/9781439896730/.
