Quantum theory has been extremely successful in explaining many aspects of the world around us. Despite this achievement, fundamental aspects of the quantum theory are as mysterious as they were to the founders of the theory. Especially remarkable is the feature that a particle somehow obtains information about different "paths" it could have taken. This observation leads to the question of what would happen if such quantum effects could be observed in macroscopic objects. If the laws of quantum mechanics remain valid for large objects, one seems to be forced to accept that cats can be alive and dead at the same time (following Schroedinger's famous thought experiment). However, others question whether such a drastic conclusion is justified based on the current support for the theory. The fact is that all experiments to date that directly tested the quantum superposition of individual objects are restricted to photons, atoms, molecules and ensemble of electrons. Furthermore the quantum theory is faced with problems when trying to unify it with the theory of relativity. It is not possible either on theoretical or experimental grounds, therefore, to rule out the possibility that quantum mechanics does not apply to large objects.
Optical technology has progressed to the level that it is conceivable to put a small mirror into a superposition of two quantum states. The experiment will be done with a particularly tiny mirror, smaller in diameter than a human hair but still about ten billion times more massive than any object previously brought into a quantum superposition. This award provides support for the mirror and cantilever fabrication as well as for designing a liquid-helium cooled apparatus and performing supporting theoretical work. Furthermore it provides travel support for establishing a close collaboration with international experts on sub-millikelvin systems.
Testing quantum mechanics in this unexplored regime is first of all of fundamental importance. The optical control of micro-mechanical systems, in particular the application of optical cooling techniques, is however also expected to be of broad interest in metrology and could also be used for several different experiments such as generating squeezed light and resonance enhanced Casimir forces. This research program involves significant educational component, and the research is excellent for teaching fundamental properties of quantum mechanics and micro-mechanical systems and for training young researchers in state-of-the-art technologies in a multi-disciplinary and international environment.
Quantum states of optomechanical systems Quantum theory has been extremely successful in explaining many aspects of the world around us. Despite this achievement the fundamental aspects of the quantum theory are as mysterious as they were to the founders of the theory. Especially the remarkable feature that a "particle" somehow obtains information about different "paths" it could have taken leads to the question of what would happen if such quantum superpositions could be amplified to the macroscopic level. Technology has progressed to the level that a quantum superposition experiment is conceivable for a tiny mirror, smaller in diameter than the diameter of a human hair but still many orders of magnitude more massive than object previously brought into a quantum superposition. This award has supported the design, fabrication and testing of such mirror/cantilever systems working at operation temperatures down to 100mK. Novel fabrication techniques have been developed and new insights have been obtained about limitations of optical reconators with one tiny mirror. Figure 1 shows one of the "trampoline" resonators developed during the project. Furthermore the award provided travel support for establishing a close collaboration with international experts on sub-milli Kelvin high-mechanical stability systems. Figure 2 shows the optical cryogenic insert that contains at it centre the mirror/cantilever systems. With this system optical cooling of the mirror has been investigated. Testing quantum mechanics in this unexplored regime is first of all of fundamental importance. The optical control of micro-mechanical systems, in particular the application of optical cooling techniques, is however also expected to be of broad interest in metrology and could also be used for several different experiments such as generating squeezed light and resonance enhanced Casimir forces.
