The first one can represent, for example, the number 3 (in binary) and the second one the number 7. In general three physical bits can be prepared in 2 3 = 8 different configurations that can represent, for example, the integers from 0 to 7. However, a register composed of three classical bits can store only one number at a given moment of time. Enter… (More)
We propose a proof of the security of EPR-based quantum key distribution against enemies with unlimited computational power. The proof holds for a protocol using interactive error-reconciliation scheme. We assume in this paper that the legitimate parties receive a given number of single photon signals and that their measurement devices are perfect.
We present an extension of the first proof for the unconditional security of the BB84 quantum key distribution protocol which was given by Mayers. We remove the constraint that a perfect BB84 quantum source is required and the proof given here covers a range of practical quantum sources. Nothing is assumed about the detector except that the efficiency with… (More)
We describe in detail a general strategy for implementing a conditional geometric phase between two spins. Combined with single-spin operations , this simple operation is a universal gate for quantum computation, in that any unitary transformation can be implemented with arbitrary precision using only single-spin operations and conditional phase shifts.… (More)
We have measured the three-body decay of a Bose-Einstein condensate of ru-bidium (87 Rb) atoms prepared in the doubly polarized ground state F = m F = 2. Our data are taken for a peak atomic density in the condensate varying between 2 × 10 14 cm −3 at initial time and 7 × 10 13 cm −3 , 16 seconds later. Taking into account the influence of the uncondensed… (More)
Modifications to a previous proof of the security of EPR-based quantum key distribution are proposed. This modified version applies to a protocol using three conjugate measurement bases rather than two. A higher tolerable error rate is obtained for the three-basis protocol.