SIGLEAvailable from British Library Document Supply Centre- DSC:DN056650 / BLDSC - British Librar... more SIGLEAvailable from British Library Document Supply Centre- DSC:DN056650 / BLDSC - British Library Document Supply CentreGBUnited Kingdo
An incomplete quantum measurement can induce non-trivial dynamics between degenerate subspaces. A... more An incomplete quantum measurement can induce non-trivial dynamics between degenerate subspaces. A closed sequence of such projections produces a non-abelian holonomy (generalized geometric phase). We show how to induce unitary evolution from such finite sequences and construct a near deterministic repeat-until-success protocol. We also prove necessary and sufficient criteria on subspace dimension required for unitary subspace discrete dynamics.
Terrestrial free-space (FS) quantum key distribution (QKD) is ideally suited for deployment in de... more Terrestrial free-space (FS) quantum key distribution (QKD) is ideally suited for deployment in dense urban environments. The transition from laboratory to commercial deployment, however, raises a number of important engineering and deployment issues. Here, we investigate these issues for efficient BB84 using a weak coherent pulse-decoy state protocol. We calculate expected key lengths for different environmental conditions and when the scope for optimisation of protocol parameters is restricted due to practical considerations. In particular, we find that for a fixed receiver basis choice probability, it can be advantageous to allow the transmitter to have a different basis choice probability depending on varying channel loss and background light levels. Finally, we examine the effects of pulse intensity uncertainty finding that they can dramatically reduce the key length. These results can be used to determine the loss budget for the FS optics of a QKD systems and assist in their design.
SIGLEAvailable from British Library Document Supply Centre- DSC:DN056650 / BLDSC - British Librar... more SIGLEAvailable from British Library Document Supply Centre- DSC:DN056650 / BLDSC - British Library Document Supply CentreGBUnited Kingdo
An incomplete quantum measurement can induce non-trivial dynamics between degenerate subspaces. A... more An incomplete quantum measurement can induce non-trivial dynamics between degenerate subspaces. A closed sequence of such projections produces a non-abelian holonomy (generalized geometric phase). We show how to induce unitary evolution from such finite sequences and construct a near deterministic repeat-until-success protocol. We also prove necessary and sufficient criteria on subspace dimension required for unitary subspace discrete dynamics.
Terrestrial free-space (FS) quantum key distribution (QKD) is ideally suited for deployment in de... more Terrestrial free-space (FS) quantum key distribution (QKD) is ideally suited for deployment in dense urban environments. The transition from laboratory to commercial deployment, however, raises a number of important engineering and deployment issues. Here, we investigate these issues for efficient BB84 using a weak coherent pulse-decoy state protocol. We calculate expected key lengths for different environmental conditions and when the scope for optimisation of protocol parameters is restricted due to practical considerations. In particular, we find that for a fixed receiver basis choice probability, it can be advantageous to allow the transmitter to have a different basis choice probability depending on varying channel loss and background light levels. Finally, we examine the effects of pulse intensity uncertainty finding that they can dramatically reduce the key length. These results can be used to determine the loss budget for the FS optics of a QKD systems and assist in their design.
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Papers by Daniel Oi