报告题目：Commitment protocols based on quantum complementarity
报告人： Dr. Nikola Paunkovic
Abstract ： An important class of cryptographic protocols is based on the exchange of agents' commitments (to a bit value, acceptance/rejection of a contract, etc.). I will present commitment protocols whose security is based on quantum complementarity — the impossibility of simultaneously measuring two noncommuting observables. In quantum mechanics, one has to decide to measure only one out of two possible mutually unbiased observables of a physical system, and obtain information about only one of the two features of a system. Thus, the choice of measurement can be interpreted as a commitment, and the measurement outcome used as a proof of this particular choice (i.e., commitment). This is somewhat the opposite approach to that used in classical solutions: instead of (securely) imprinting the information of a commitment choice into a state of a physical system (writing down an encrypted message on a piece of paper, for example), the choice is done by acquiring information about only one out of two possible features of a physical system. The main focus of the talk will be on a fair and optimistic quantum contract signing protocol. I will also present a simultaneous dense coding and a practical two-state quantum bit commitment schemes. Finally, if time permits, I will briefly introduce a few other security protocols developed during past few years at the Institute for telecommunications in Lisbon: a public-key cryptosystem based on coherent states of light, and a related one based on quantum walks, as well as two bit-string all-or-nothing oblivious transfer schemes (one based on quantum state computational indistinguishability, and the other based on single-qubit rotations). Brief info. for Dr. Nikola Paunkovic Researcher at Instituto de Telecommunicações, Lisbon. Education: 1998 B.Sc. in Theoretical Physics, Faculty of Physics, University of Belgrade, Serbia. Thesis: “Nonlocality and Quantum Teleportation”, done under the supervision of prof. Fedor Herbut. 2004 D.Phil. in Theoretical Physics, Centre for Quantum Computation, Clarendon Laboratory, Oxford University, UK Thesis: The Role of Indistinguishability of Identical Particles in Quantum Information Processing, done under joint supervision of prof. Artur Ekert and prof. Vlatko Vedral. Research interests: Macroscopic distinguishability, phase transitions and the emergence of classicality from quantum physics; Entanglement and indistinguishability; Entanglement in many-body systems; Quantum walks; The concept of indistinguishability in quantum mechanics; Secure quantum communication protocols; Quantum information and gravity - the effects of curvature and torsion on the angular momentum in Bell and interference experiments; Gravity-matter entanglement in Loop Quantum Gravity.