QUIE2T Quantum Information Entanglement-Enabled Technologies

Fundamental quantum mechanics and decoherence

Quantum information was born, in part, via research on the famous Einstein-Podolski-Rosen paradox and the issue of quantum non-locality. In turn, quantum information led the discussion to move beyond purely qualitative aspects of non-locality to defining and investigating quantitative aspects. In particular, it is now understood that non-locality is one of the central aspects of quantum mechanics. More generally, quantum information profits substantially from studying the fundamental aspects of quantum mechanics and, at the same time, yields new points of view, raising hopes of gaining a deeper understanding of the very basis of quantum mechanics.

The study of decoherence is intertwined with the field of quantum information science in at least three ways. Key challenges of the next years in the study of decoherence with methods, tools and intuition from quantum information science will include the following:

• To understand the fundamental role of classical correlations and entanglement in the decoherence process itself, and to flesh out the robustness of entangled states under typical decoherence processes;
• To engineer further ways to prevent decoherence in applications of quantum information processing, by exploiting decoherence-free subspaces, entanglement distillation, and dynamical decoupling procedures as bang-bang control;
• To support and contribute to experiments on decoherence to further understand the quantum to classical transition, and to determine what decoherence models are appropriate in what contexts.

Key references
[1] P. Zanardi and M. Rasetti, "Noiseless quantum codes", Phys. Rev. Lett. 79, 3306 (1999)
[2] L. Viola, "On quantum control via encoded dynamical decoupling", quant-ph/0111167
[3] W. Dür and H. J. Briegel, "Stability of macroscopic entanglement under decoherence", Phys. Rev. Lett. 92, 180403 (2004)
[4] A. R. R. Carvalho, F. Mintert, and A. Buchleitner, "Decoherence and multipartite entanglement", Phys. Rev. Lett. 93, 230501 (2004)
[5] R. F. Werner and M. M. Wolf, "Bell inequalities and entanglement", Quant. Inf. Comp. 1, 1 (2001)
[6] J. Barrett, N. Linden, S. Massar, S. Pironio, S. Popescu, and D. Roberts, "Non-local correlations as an information theoretic resource", Phys. Rev. A 71, 022101 (2005)
[7] D. Perez-Garcia, M.M. Wolf, C. Palazuelos, I. Villanueva, and M. Junge, "Unbounded violation of tripartite Bell inequalities", Comm. Math. Phys. 279, 455 (2008)
[8] M. Navascués, S. Pironio, and A. Acín, "A convergent hierarchy of semidefinite programs characterizing the set of quantum correlations", New J. Phys. 10, 073013 (2008)

Quantum effects in opto-mechanical and nano-mechanical systems

Recently, partly driven by experimental progress, theoretical ideas have been proposed to cool mechanical physical systems such as massive micro-mirrors to close to their quantum ground state, giving rise to observable quantum effects. In particular, opto-mechanical systems, where mechanical degrees of freedom are coupled to coherent optical systems, allow for such a cooling by suitably exploiting radiation pressure effects. Indeed, the preparation of such systems in superposition or entangled states appears within reach. Such systems may give rise to ultra-sensitive force sensors as well as to primitives for quantum information devices. They can also be combined with other physical architectures to give rise to promising hybrid architectures.

Key references
[1] C. Fabre, M. Pinard, S. Bourzeix, A. Heidmann, E. Giacobino, and S. Reynaud, "Quantum-noise reduction using a cavity with a movable mirror", Phys. Rev. A 49, 1337 (1994)
[2] S. Mancini, V. I. Manko, and P. Tombesi, "Ponderomotive control of quantum macroscopic coherence", Phys. Rev. A 55, 3042 (1997)
[3] I. Martin, A. Shnirman, L. Tian, and P. Zoller, "Ground-state cooling of mechanical resonators", Phys. Rev. B 69, 125339 (2004)
[4] J. Eisert, M. B. Plenio, S. Bose, and J. Hartley, "Towards quantum entanglement in nanoelectromechanical devices", Phys. Rev. Lett. 93, 190402 (2004)
[5] D. Vitali, S. Gigan, A. Ferreira, H. R. Böhm, P. Tombesi, A. Guerreiro, V. Vedral, A. Zeilinger, and M. Aspelmeyer, "Optomechanical entanglement between a movable mirror and a cavity field", Phys. Rev. Lett. 98, 030405 (2007)
[6] F. Marquardt and S. M. Girvin, "Optomechanics", Physics 2, 40 (2009)
[7] M. Wallquist, K. Hammerer, P. Zoller, C. Genes, M. Ludwig, F. Marquardt, P. Treutlein, J. Ye, and H. J. Kimble, arXiv:0912.4424 [quant-ph]

Quantum coherence in biological systems

The question to which quantum coherence and entanglement plays a role in biological systems is receiving increasing attention also from a perspective of quantum information theory. There is experimental evidence that in the functioning of the energy transport in photosynthetic light-harvesting complexes, such as the Fenna-Matthews-Olson photosynthetic complex, long-lived coherence effects may play an important role. Quantum information ideas can contribute to an understanding of the role of noise, stochastic resonance effects, coherence, entanglement and quantum-walk-like dynamics in such systems. Hence, principles and techniques, both numerical and analytical, that have been developed over the last decade in quantum information science may find a new area of application here. This potentially fruitful new arena is now beginning to be explored bringing together quantum information scientists with bio-physicists from theory and experiment thus opening up a new arena of interdisciplinary research.

Key references
[1] G. S. Engel, T. R. Calhoun, E. L. Read, T.-K. Ahn, T. Mancal, Y-C. Cheng, R. E. Blankenship, and G. R. Fleming, Nature 446, 782 (2007)
[2] A. Olaya-Castro, C. F. Lee, F. Fassioli-Olsen, and N. F. Johnson, "Efficiency of energy transfer in a light-harvesting system under quantum coherence", Phys. Rev. B 78, 085115 (2008)
[3] M. Mohseni, P. Rebentrost, S. Lloyd and A. Aspuru-Guzik, "Environment-assisted quantum walks in photosynthetic energy transfer", J. Chem. Phys. 129, 174106 (2008)
[4] M.B. Plenio and S.F. Huelga, "Dephasing assisted transport: Quantum networks and biomolecules", New J. Phys. 10, 113019 (2008)
[5] H. J. Briegel and S. Popescu, "Entanglement and intra-molecular cooling in biological systems? - A quantum thermodynamic perspective", arXiv:0806.4552 [quant-ph]
[5] F. Caruso, A. W. Chin, A. Datta, S. F. Huelga, and M. B. Plenio, "Highly efficient energy excitation transfer in light-harvesting complexes: The fundamental role of noise-assisted transport", J. Chem. Phys. 131, 105106 (2009)