Theoretische Quantenphysik

Decoherence and error correction

Current developments in quantum information processing impressively demonstrate the practical potential of quantum physics. In quantum computation, for example, characteristic quantum phenomena, such as interference and entanglement, are exploited for solving computational tasks more efficiently than it is possible by any known classical means. However, interference and entanglement are fragile phenomena, which can be destroyed easily by uncontrolled interactions with an environment. In order to protect quantum information against the resulting decoherence, powerful methods of error correction have been developed over the last few years.

The main aim of quantum error correction is to reverse the perturbing influence of an uncontrollable environment. Whether such an inversion is possible or not and how it can be achieved most efficiently, depends on the physical interaction between the quantum system considered and its environment. In quantum optical systems spontaneous decay processes are frequently occurring sources of errors. Recently, a new class of error-correcting quantum codes was developed, which is capable of correcting errors arising from such spontaneous decay processes. These jump codes exploit in an optimal way information about errors which is obtained from continuous observation of the environment. Thus, with the help of suitabe quantum gates which guarantee that such a code space is not left at any time during a quantum computation, it is possible to stabilize quantum information processing units against spontaneous decay processes. Furthermore, our group also developed a new stochastic decoupling method (PAREC -- Pauli-random-error-correction). In contrast to already known deterministic decoupling methods it is capable of suppressing decoherence over long times more efficiently.

D. Geberth, O. Kern, G. Alber, and I. Jex, Eur. Phys. J. D 46, 381 (2008)
O. Kern and G. Alber, Phys. Rev. A 73, 062302 (2006)
O. Kern and G. Alber, Phys. Rev. Lett. 95, 250501 (2005)
O. Kern and G. Alber, Eur. Phys. J. D 36, 241 (2005)
O. Kern, G. Alber, and D. L. Shepelyansky, Eur. Phys. J. D 32, 153 (2005)
G. Alber, Th. Beth, Ch. Charnes, A. Delgado, M. Grassl, and M. Mussinger, Phys. Rev. A 68, 012316 (2003)
G. Alber, A. Delgado, and M. Mussinger, Prog. Phys. 49, 901 (2001)
G. Alber, Th. Beth, Ch. Charnes, A. Delgado, M. Grassl, and M. Mussinger, Phys.Rev. Lett. 86, 4402 (2001)

Contact

Prof. Dr. Gernot Alber

Institut für Angewandte Physik

Hochschulstraße 4a
64289 Darmstadt, Germany

+49-6151/16-20400 (fax: 20402)

gernot.alber@physik.tu-...