Fidelity enhancement by logical qubit encoding

We demonstrate coherent control of two logical qubits encoded in a decoherence free subspace (DFS) of four dipolar-coupled protons in an NMR quantum information processor. A pseudopure fiducial state is created in the DFS, and a unitary logical qubit entangling operator evolves the system to a logic...

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Veröffentlicht in:Physical review letters 2007-11, Vol.99 (22), p.220501-220501, Article 220501
Hauptverfasser: Henry, Michael K, Ramanathan, Chandrasekhar, Hodges, Jonathan S, Ryan, Colm A, Ditty, Michael J, Laflamme, Raymond, Cory, David G
Format: Artikel
Sprache:eng
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Zusammenfassung:We demonstrate coherent control of two logical qubits encoded in a decoherence free subspace (DFS) of four dipolar-coupled protons in an NMR quantum information processor. A pseudopure fiducial state is created in the DFS, and a unitary logical qubit entangling operator evolves the system to a logical Bell state. The four-spin molecule is partially aligned by a liquid crystal solvent, which introduces strong dipolar couplings among the spins. Although the system Hamiltonian is never fully specified, we demonstrate high fidelity control over the logical degrees of freedom. In fact, the DFS encoding leads to higher fidelity control than is available in the full four-spin Hilbert space.
ISSN:0031-9007
1079-7114
DOI:10.1103/PhysRevLett.99.220501