"Effects of decoherence and imperfections for quantum information processing"
EC IST-FET Project IST-2001-38869  of European Union



1. Toulouse (UPS) Key persons: B.Georgeot, D.L.Shepelyansky (network coordinator)
2. Darmstadt (TUD) G. Alber (node leader)
3. Univ. dell Insubria, Como (INFM) Key persons: G.Benenti, G.Casati (node leader)
4. Royal Holloway, Univ. of London (RHUL) R.Schack (node leader)

The aim of this project is the investigation of decoherence and error correction in quantum processors solving physical problems for which new and useful results may be achievable using 40-60 qubits. New algorithms will be developed for these problems, which will include complex quantum dynamics, nonlinear classical evolution, electron transport in disordered materials and metal-insulator transitions. A numerical code package will be developed to simulate these new algorithms and to model decoherence and imperfection effects for realistic quantum computers with up to 30 qubits. Using this code package, decoherence time scales and critical thresholds for multi-qubit residual imperfections will be determined. Quantum error-correcting codes will be tested with this package to reduce these decoherence effects in the specific algorithms developed within this project.

- decoherence time scales for noisy gates and dissipative coupling to environment
- universal laws for many-body chaos and fidelity drop induced by static imperfections
- efficient quantum algorithms for computationally hard physical problems
- numerical code package simulating new algorithms with up to 30 qubits
- numerical tests of quantum error correction codes
- stability bounds for the operability of realistic quantum processors

\epsfig{file=waveletA.eps,width=6cm} \epsfig{file=waveletB.eps,width=6cm}  

Matrix elements of a dynamical system based on the quantum wavelet transform in the computational basis on a quantum computer with 12 qubits. Left: perfect computer; right:computer with moderate static imperfections $\epsilon=0.0005$ .