Quantum information technology

The basic ideas in quantum information processing (QIP) dates from several decades back, however the research development based on these ideas started only a little more than a decade ago. The initial ideas of quantum information processing emerged from the fundamental difference between quantum physics and classical physics. It was, and still is, hard to analyse quantum systems in general, and in particular when a quantum system gets bigger, it soon becomes intractable even with high performance computers. To analyse a quantum system, Feynman suggested that we should use a computer based on quantum physics. This is the initial idea of quantum information processing. By contrast to quantum computers, all non-quantum-physicsbased computers, that is, all the existing ones including high performance computers, are now called “classical computers” indicating computers based on classical physics. The research on quantum information processing did not take off until 1990s. Until then, the technology to manipulate quantum was yet not ready, and more importantly, the theory for QIP was not developed enough to show the way to efficiently use quantum nature to carry out computation. Quantum key distribution (QKD) was one of the first QIP protocols successfully implemented and developed in 1990s. QKD is a protocol to exchange secure key material between authenticated users at a distance. Thanks to a property that overlapping quantum states cannot be cloned without trace of interaction, the protocol can detect an eavesdropper by measuring the quantum states and post-processing the signals via classical communication between the users. As one-time pad using QKD was proven to be secure against an eavesdropper who has unbounded ability, unlike conventional cryptogra-