Showing papers by "Choy Heng Lai published in 2005"

Experimental Quantum Cloning with Prior Partial Information

Abstract: When prior partial information about a state to be cloned is available, it can be cloned with a fidelity higher than that of universal quantum cloning. We experimentally verify this intriguing relationship between the cloning fidelity and the prior information by reporting the first experimental optimal quantum state-dependent cloner, using nuclear magnetic resonance techniques. Our experiments may further cast important implications into many quantum information processing protocols.

Phase synchronization between two essentially different chaotic systems.

Abstract: In this paper, we numerically investigate phase synchronization between two coupled essentially different chaotic oscillators in drive-response configuration. It is shown that phase synchronization can be observed between two coupled systems despite the difference and the large frequency detuning between them. Moreover, the relation between phase synchronization and generalized synchronization is compared with that in coupled parametrically different systems. In the systems studied, it is found that phase synchronization occurs after generalized synchronization in coupled essentially different chaotic systems.

Bistable chaos without symmetry in generalized synchronization.

Abstract: Frequently, multistable chaos is found in dynamical systems with symmetry. We demonstrate a rare example of bistable chaos in generalized synchronization (GS) in coupled chaotic systems without symmetry. Bistable chaos in GS refers to two chaotic attractors in the response system which both synchronize with the driving dynamics in the sense of GS. By choosing appropriate coupling, the coupled system could be symmetric or asymmetric. Interestingly, it is found that the response system exhibits bistability in both cases. Three different types of bistable chaos have been identified. The crisis bifurcations which lead to the bistability are explored, and the relation between the bistable attractors is analyzed. The basin of attraction of the bistable attractors is extensively studied in both parameter space and initial condition space. The fractal basin boundary and the riddled basin are observed and they are characterized in terms of the uncertainty exponent.

Phase synchronization of a pair of spiral waves.

Abstract: The interaction of a pair of spiral waves with different independent rotation frequencies is studied In a very large frequency mismatch searching region, we observe three different pattern formation phenomena: (a) phase-synchronization-induced invasion under a relatively small frequency mismatch, ie, the spiral wave with slower frequency (longer period) is swept away by a traveling wave, which is induced and phase synchronized by the faster spiral wave; (b) the coexistence of two spiral waves at sufficiently large parameter mismatch; and (c) an intermediate state, a non-phase-synchronous invasion, that is, similarly the slower spiral wave is swept by an approximate planar wave, whose frequency, however, is intermediate between those of the faster and slower waves A point-source model is studied to analyze all these phenomena in a unified way

Chaotic resonance: two-state model with chaos-induced escape over potential barrier.

Abstract: We consider the resonant effects of chaotic fluctuations on a strongly damped particle in a bistable potential driven by weak sinusoidal perturbation. We derive analytical expressions of chaos-induced transition rate between the neighboring potential wells based on the inhomogeneous Smoluchowski equation. Our first-order analysis reveals that the transition rate has the form of the Kramers escape rate except for a perturbed prefactor. This modification to the prefactor is found to arise from the statistical asymmetry of the chaotic noise. By means of the two-state model and the chaos-induced transition rate, we arrive at an analytical expression of the signal-to-noise ratio (SNR). Our first-order SNR shows that chaotic resonance can correspond directly to stochastic resonance.

Public-key encryption based on generalized synchronization of coupled map lattices

Abstract: Currently used public-key cryptosystems are based on difficulties in solving certain numeric theoretic problems, in which the way to predict the private key from the knowledge of the public key is computationally infeasible. Here we propose a method of constructing public-key cryptosystems by generalized synchronization of coupled map lattices, in which the difficulty in predicting the synchronous function is used as the trap-door function to deduce the private key from the public key. In specific, we implement this idea on the method of “Merkle’s puzzles,” and find that, incorporated with the chaotic dynamics, this traditional method is equipped with some new features and can be practical in certain situations.

Construction of a secure cryptosystem based on spatiotemporal chaos and its application in public channel cryptography

Abstract: By combining the one-way coupled chaotic map lattice system with a bit-reverse operation, we construct a new cryptosystem which is extremely sensitive to the system parameters even for low-dimensional systems. The security of this new algorithm is investigated and mechanism of the sensitivity is analyzed. We further apply this cryptosystem to the public channel cryptography, based on "Merkle's puzzles", by employing it both as pseudo-random-number (PN) generators and symmetric encryptor. With the properties of spatiotemporal chaos, the new scheme is rich with new features and shows some advantages in comparison with the conventional ones.

Spatially periodic and temporally chaotic pattern in coupled nonidentical chaotic systems

Abstract: A particular spatio-temporal pattern, the spatially periodic and temporally chaotic pattern (SPTCP), can be observed in coupled one-way ring and linear array systems. This is a state chaotic in time while periodic in space in a strict sense. In this work, a driven system, of coupled nonidentical chaotic elements, which supports this structure is studied. We find that the appearance of the pattern is closely connected with the cascade of generalized synchronization in the ring. In particular, the establishment of the spatial periodicity of the SPTCP is determined by the condition that all of the coupled sites in the ring stay in the generalized synchronous state.