Hitoshi Inamori

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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. Thus(More)
Quantum Key Distribution (QKD) employs quantum features such as the uncertainty principle and quantum correlations to provide for unconditionally secure communications [1]. In classical cryptography no mechanism is known for unconditionally secure key distribution. The importance of QKD protocols within cryptography is paramount as they allow for the(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.
Environment induced decoherence, and other quantum processes, have been proposed in the literature to explain the apparent spontaneous selection—out of the many mathematically eligible bases—of a privileged measurement basis that corresponds to what we actually observe. This paper describes such processes, and demonstrates that—contrary to common belief—no(More)
Gauge structure, playing a predominant role in quantum eld theories, turns out to arise quite naturally in the description of ordinary quantum mechanical systems: the energy eigenspaces of a quantum mechanical system which depends upon slowly varying external parameters reveal, systematically , to be endowed with a gauge potential, called Berry's(More)
We present a proof of unconditional security of a practical quantum key distribution protocol. It is an extension of a previous result obtained by Mayers [1, 2], which proves unconditional security provided that a perfect single photon source is used. In present days, perfect single photon sources are not available and, therefore, practical implementations(More)
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