Results 1 - 10 of 5415
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[en] We describe an experimental realization of the Deutsch-Jozsa quantum algorithm to evaluate the properties of a two-bit Boolean function in the framework of one-way quantum computation. For this purpose, a two-photon six-qubit cluster state was engineered. Its peculiar topological structure is the basis of the original measurement pattern allowing the algorithm realization. The good agreement of the experimental results with the theoretical predictions, obtained at ∼1 kHz success rate, demonstrates the correct implementation of the algorithm.
[en] We propose a scheme for perfect transfer of an unknown qubit state via the discrete-time quantum walk on a line or a circle. For this purpose, we introduce an additional coin operator which is applied at the end of the walk. This operator does not depend on the state to be transferred. We show that perfect state transfer over an arbitrary distance can be achieved only if the walk is driven by an identity or a flip coin operator. Other biased coin operators and the Hadamard coin allow perfect state transfer over finite distances only. Furthermore, we show that quantum walks ending with a perfect state transfer are periodic. (paper)
[en] This paper proposes an efficient semi-quantum private comparison protocol (SQPC) using single photons, which allows two classical participants to securely compare the equality of their secret with the help of an almost-dishonest third party. Because of the use of single photons, the SQPC is more practical and the qubit efficiency of the proposed protocol is higher than the existing semi-quantum private comparison protocols. Moreover, the proposed protocol can resist several well-known attacks including outsider and insider’s attacks.
[en] We present a quantum approach to a signaling game; a special kind of extensive game of incomplete information. Our model is based on quantum schemes for games in strategic form where players perform unitary operators on their own qubits of some fixed initial state and the payoff function is given by a measurement on the resulting final state. We show that the quantum game induced by our scheme coincides with a signaling game as a special case and outputs nonclassical results in general. As an example, we consider a quantum extension of the signaling game in which the chance move is a three-parameter unitary operator whereas the players' actions are equivalent to classical ones. In this case, we study the game in terms of Nash equilibria and refine the pure Nash equilibria adapting to the quantum game the notion of a weak perfect Bayesian equilibrium. (paper)
[en] The coexistence relation of quantum effects is a fundamental structure, describing those pairs of experimental events that can be implemented in a single setup. Only in the simplest case of qubit effects is an analytic characterization of coexistent pairs known. We generalize the qubit coexistence characterization to all pairs of effects in arbitrary dimensions that belong to the von Neumann algebra generated by two projections. We demonstrate the presented mathematical machinery by several examples, and show that it covers physically relevant classes of effect pairs. (paper)
[en] A protocol for quantum private comparison of equality (QPCE) is proposed based on five-particle cluster state with the help of a semi-honest third party (TP). In our protocol, TP is allowed to misbehave on its own but can not conspire with either of two parties. Compared with most two-user QPCE protocols, our protocol not only can compare two groups of private information (each group has two users) in one execution, but also compare just two private information. Compared with the multi-user QPCE protocol proposed, our protocol is safer with more reasonable assumptions of TP. The qubit efficiency is computed and analyzed. Our protocol can also be generalized to the case of 2N participants with one TP. The 2N-participant protocol can compare two groups (each group has N private information) in one execution or just N private information. (paper)
[en] We demonstrate a simple way to realize control of population transfer and creation of two orthogonal maximally superposition states in a Λ-type four-level system with closely spaced doublet target states via a pair of pump and chirped Stokes pulses. It is illustrated that the population in the initial state can be selectively, completely and robustly transferred to either of the doublet target states via chirped adiabatic passage with the suitable chirp rate and frequency detuning of the Stokes pulse. Besides, creation of two orthogonal maximally superposition states between the initial state and intermediate state with equal amplitude but inverse relative phases is also shown, which may have potential applications in the preparations of quantum bits. (letter)
[en] We investigate an efficient quantum error correction of a fully correlated noise. Suppose the noise is characterized by a quantum channel whose error operators take fully correlated forms given by σxxn, σyxn and σzxn, where n>2 is the number of qubits encoding the codeword. It is proved that (i) n qubits codeword encodes (n-1) data qubits when n is odd and (ii) n qubits codeword implements an error-free encoding, which encode (n-2) data qubits when n is even. Quantum circuits implementing these schemes are constructed. -- Highlights: → An efficient quantum error correction of a fully correlated noise is studied. → n-qubit codeword encodes (n-1) data qubits when n is odd. → n-qubits codeword implements an error-free encoding of (n-2) data qubits when n is even. → Quantum circuits implementing these schemes are constructed.
[en] Two schemes are proposed to realize the controlled remote preparation of an arbitrary four-qubit cluster-type state via a partially entangled channel. We construct ingenious measurement bases at the sender’s and the controller’s locations, which play a decisive role in the proposed schemes. The success probabilities can reach 50% and 100%, respectively. Compared with the previous proposals, the success probabilities are independent of the coefficients of the entangled channel. (paper)