NODOS · Non-adiabatic quantum dynamics in novel optical superlattices

Non-adiabatic quantum dynamics in novel optical superlattices

Whereas the 20th century was characterized by the investigation of quantum mechanical effects, the 21st century will witness the utilization of these effects in a number of high impact quantum technologies such as quantum computation, quantum communication, and in general the controlled assembly of complex but useful quantum systems. The combined field of quantum information science and ultra-cold atom physics will be a crucial part of this quantum engineering. Progress in this field will enhance our understanding of strongly correlated materials and deliver valuable resources for quantum information processing. Short description of results: The NODOS project has focussed on the development of a novel experimental setup capable of going beyond the state-of-the-art in single atom manipulation in optical lattices. The work has been split into three main categories: • Completing the set-up of the new experiment with single atom manipulation capabilities. The setup of such a complicated novel experiment requires a huge research and development effort. One major shift in the long term strategy of the project was the incorporation of a new and very promising technique, light manipulation using Digital-Mirror-Devices (DMD). The design and implementation process will be described in more detail below. • Theoretical work to explore novel methods of single atom control. In parallel to the experimental development, new quantum computer algorithms exploring the full potential of the novel lattice configurations were explored. Most notably this resulted in a detailed characterization of this new quantum computing architecture demonstrating very promising performance. • Quantum non demolition (QND) measurements Towards the end of the project period, the new experiment reached a sufficiently advanced stage to combine high-precision imaging with the quantum non demolition measurements developed in parallel. This allowed for the first ever characterization of the effects of repeated probing of a quantum phase transition. The setup of new high resolution experiment The new experiment is planned to extend the state-of-art in a number of ways. First, it will be the first combination of QND measurements and high resolution imaging. Secondly it will feature a novel single atom manipulation mechanism using super lattices. For a high resolution experiment the crucial element is the imaging system and the science chamber around it, because it places the limitation on the achievable resolution. A four chamber experiment was built: a 2D MOT chamber supplying an atomic beam for a 3D MOT, which is then loaded into a magnetic trap. This is then mechanically transported to an intermediate “cube” chamber, where the first BEC and first experiments have been performed while work on the design and construction of the crucial final science chamber was finalised. After extensive correspondence with various companies, the high resolution imaging system is ordered and in production and the important last view-port before the objective has been produced and tested to satisfaction. A special high reflection coating has been developed and applied to the lattice view-ports to allow for an ultra-stable design of the several lattice frequencies. This will be crucial when implementing the superlattices in the future. Theory: a superlattice based quantum computing architecture To date, the only experimental demonstration of single atom manipulation in optical lattices used a highly focused light beam propagated through a high numerical aperture imaging system. Although successful this technique has a number of drawbacks for large scale implementation in quantum technologies. First, it is an extremely expensive method which will not be widespread in the near future. Secondly, the laser beam has intrinsic pointing instabilities which will ultimately limit the fidelity of the quantum gate operations. Instead we suggest the use of a superposition of two close lying optical lattices. In reference [MB1] we developed the theoretical modelling of both one and two qubit gates and identified the most promising parameters, which are currently pursued in the new experiment. The attached figure shows a proposal to implement one- and two-qubit gates in an optical superlattice. Quantum non demolition measurements QND measurements have been explored extensively for room temperature vapour cells and in a growing number of experiments with cold and ultra-cold atoms, however, not systematically in optical lattices, which is the long term goal of our research endeavour. In these experiments a first demonstration of the non-destructive probing of a quantum phase transition, here to a BEC, was characterized. Such a development was made possible by the high resolution imaging system implemented in the project. This is an important step towards the final goal of similar investigations with strongly correlated phases in optical lattices, because it established the methodology and demonstrates the important fundamental trade-off between measurement precision and destructivity of the probing. The findings will be detailed in our forthcoming publication [MB2] Group website: www.phys.au.dk/qmmg [MB1] N. B Jørgensen, M. G. Bason, J. F. Sherson, One- and two-qubit quantum gates using superimposed optical-lattice potentials, Phys. Rev. A 89, 032306 (2014) [MB2] M. G. Bason, R. Heck, R. Müller, M. Napolitano, O. Eliasson, A. Thorsen, W. Zhang, J. Arlt, J. F. Sherson, Non-destructive observation of quantum phase transitions, to be submitted to Phys. Rev. Lett.

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