The interference of matter waves is a direct consequence of wave-particle duality and lies at the heart of quantum mechanics. Today, with the validity of quantum theory being widely ascertained, we are beyond proof-of-principle demonstrations and are transforming this phenomenon into a measurement tool for practical applications via the development of quantum technologies. Atom interferometry is a special type of quantum technology, which is particularly suitable for the detection of gravity. Its potential for absolute, low-drift measurements with options for noise suppression could bring wide-ranging benefits for applications that are important across economies. This journey from the laboratory into the real world of applications requires the understanding and mitigation of the effects of external influences on the system.
The interference of matter waves is a direct consequence of wave-particle duality and lies at the heart of quantum mechanics. Today, with the validity of quantum theory being widely ascertained, we are beyond proof-of-principle demonstrations and are transforming this phenomenon into a measurement tool for practical applications via the development of quantum technologies. Atom interferometry is a special type of quantum technology, which is particularly suitable for the detection of gravity. Its potential for absolute, low-drift measurements with options for noise suppression could bring wide-ranging benefits for applications that are important across economies. This journey from the laboratory into the real world of applications requires the understanding and mitigation of the effects of external influences on the system.
Atom de Broglie wave interferometry has emerged as a tool capable of addressing a diverse set of questions in gravitational and condensed matter physics, and as an enabling technology for advanced sensors in geodesy and navigation. This talk will review basic principles, then discuss recent applications and future directions. Scientific applications to be discussed include measurement of G (Newton’s constant), tests of the Equivalence Principle and post-Newtonian gravity, and study of the Kosterlitz-Thouless phase transition in layered superfluids. Technology applications include development of precision gryoscopes and gravity gradiometers. The talk will conclude with speculative remarks looking to the future: Can atom interference methods be sued to detect gravity waves? Can non-classical (entangled/squeezed state) atom sources lead to meaningful sensor performance improvements?
Abstract The possibility of interferometry with atoms follows directly from wave particle duality. The wave-like propagation of particles, such as atoms, means that they undergo interference and diffraction in an analogous way to light. This chapter explains how such matter waves have been used in interferometers that measure rotation and gravitational acceler ation to a precision comparable with the best optical instruments. As in many important developments in physics, atom interferometry relies on simple principles-the first part of this chapter uses only elementary optics and the de Broglie relation.
The wave properties of matter in quantum mechanics first postulated by de Broglie in 1923 as well as Einstein’s theory of general relativity have radically changed our perception of the world at the beginning of the twentieth century. While each theory is extremely successful and well tested within its range of validity, a unification of both theories has so far resisted any attempt. However, the advances in precision of modern matter-wave interferometers have paved the way to designing experiments at the interface of gravity and quantum mechanics. Indeed, quantum mechanical devices are on the brink of becoming sensitive enough to challenge predictions of general relativity such as the weak equivalence principle or set bounds on alternative gravitational theories. Reaching sensitivities required for these experiments necessitates a careful assessment of deleterious effects some of which might be atom-atom interactions or the influence of the gravitational potential of the laboratory setup itself. Estimation of the size of such effects calls for refined theoretical tools for the description of light-pulse atom interferometry which is the subject of the present thesis.
Atom interferometry is a quantum sensor technology that uses ultra-cold atoms placed in entangled quantum states to detect minute changes in local fields arising from gravitational waves and ultra-light dark matter. Their extreme sensitivity to accelerations has been demonstrated for measurements of Newton’s gravitation constant, tests of the Equivalence Principle, and measurement of local gravity gradients. The search for ultra-light dark matter and measurements of gravitational waves requires interferometer baselines greater than approximately 100 m. In understanding the fundamental systematics and backgrounds of these detectors, we have discovered that atmospheric and seismic effects, even though physically decoupled from the atoms which are in vacuum and free-fall, are still detectable by the quantum phase of the atoms. From a different perspective these “noise” sources are also interesting signals that we may be able to understand better with these sensor platforms leading to cross-disciplinary studies in Earth sciences.
Gravity gradiometers based on atom-wave interferometry hold the promise for increased sensitivity, and suitability for space applications. This capability will significantly advance our knowledge of solid Earth and the oceans, as well as other solar system planets and their moons. The quantum interferometer gravity gradiometer is based on atom-wave interferometry, and is intrinsically more sensitive than laser interferometers, because of the finite mass of the atom and the shorter de Broglie wavelengths associated with atom waves. Recent advances in laser cooling and trapping have made quantum interferometer applications practical. In this paper the principle of the operation of the quantum gravity gradiometer will first be described, together with the progress in its development to date. Estimates for the performance, and projections for the sensitivity will also be presented, together with potential applications to gravity science. Over the past few years advanced in laser cooling has brought about a significant progress towards realization of ultra-high sensitivity gravity gradiometers based on atom wave (matter wave) interferometry. These instruments represent a powerful potential for sensitive measurements of the components of the gravity gradient tensor from space to provide access to three-dimensional maps of geophysical structures deep below the surface. The exquisite sensitivity associated with atom-wave interferometry holds a great promise for new gravity mapping and monitoring capabilities - higher measurement sensitivity, finer spatial resolution, and, most importantly, temporal monitoring. This implies measurement opportunities for the Earth Observing System to develop comprehensive models for the understanding of the planetary inner structure and dynamics, changes in ice sheets and ocean currents, changes in underground water storage, and weather, earthquake, and volcano prediction capabilities. In this paper, we will review briefly the principles of the quantum gravity gradiometer and its advantages in the space environment. We will then describe our laboratory experiment and report some of the component development work towards a space-borne system. Gravity gradiometers based on atom interferometers are currently under development at the Jet propulsion Laboratory under NASA sponsorship.
Gravity plays a central role in our understanding of the Earth and the Universe. It is the dominant force at astronomic scales, shaping star systems and galaxies. It is also a pivotal field in the geosciences, allowing access to the physical shape of the Earth, defining height systems, and tracking mass transport, for example water in climate change research, inside volcanoes, or along seismic faults. Finally, it could become a crucial resource for engineering, opening the way to a renewal of underground exploration techniques, both for natural resources and civil engineering legacy. In fundamental physics, gravity nevertheless remains a riddle. From its origins to the first direct detection of gravitational waves in 2015, the theory of general relativity has accumulated successes. Our understanding of the microscopic world, through quantum mechanics and the standard model of particle physics is a similar success story, culminating with the detection of the BEH boson in 2012. Nevertheless, unification theories remain inaccessible and testing both the hypotheses and predictions of our theories remains the safest way towards the discovery of new physics. Here, key research areas relate to tests of the universality of free fall, at the heart of general relativity theory, or the creation of macroscopic superposition states of massive particles, a genuine marker of the quantum world. Novel applications in the geosciences also require improved gravity sensors. For multiple applications in engineering and geodesy, the ideal device is easily transportable and has low energy consumption. Nevertheless, higher-order references are necessary to enable an accurate definition of a gravity standard across the world. Such gravity references could also be combined with state-of-the-art laser gyroscopes into quantum Earth observatories. In this manuscript, we introduce a new generation of matter wave sensors based on very long baseline atom interferometry (VLBAI). Exploring the properties of massive quantum objects at the scales of meters and seconds, they will provide new insights into fundamental physics questions and serve as testbeds for novel atomic inertial sensors on ground and in space. We provide the motivation and working principles for absolute gravity sensing with VLBAI, and discuss in particular the specific trade-offs arising from the use of an extended baseline in atom interferometry. We also present the core design of the Hannover VLBAI facility. Finally, we demonstrate that through a unique and carefully characterized 10 m-long magnetically shielded baseline, this devices offers the required environment for next-generation atomic gravity reference sensors and tests of fundamental physics.