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Abstract
This paper proposes a scheme to enhance the fidelity of symmetric and asymmetric quantum cloning using a hybrid system based on nitrogen-vacancy (N-V) centers. By setting different initial states, the present scheme can implement optimal symmetric (asymmetric) universal (phase-covariant) quantum cloning, so that the copies with the assistance of a Current-biased Josephson junction (CBJJ) qubit and four transmission-line resonators (TLRs) can be obtained. The scheme consists of two stages: cjhothe first stage is the implementation of the conventional controlled-phase gate, and the second is the realization of different quantum cloning machines (QCM) by choosing a suitable evolution time. The results show that the probability of success for QCM of a copy of the equatorial state can reach 1. Furthermore, the | W 4 ± ⟩ entangled state can be generated in the process of the phase-covariant quantum anti-cloning. Finally, the decoherence effects caused by the N-V center qubits and CBJJ qubit are discussed.
Highlights
It is well-known that an unknown quantum state cannot be copied precisely [1]
Ct = 1.8 pF, the full-wave frequency of the transmission-line resonators (TLRs) is ωc /2π = 2.8583 GHz, and the N-V center transition j j j frequency ω10 /2π = 2.87 GHz, the detuning ω10 − ωc = 0.073 GHz 1 GHz, and with rotating-wave approximation (RWA), the interaction Hamiltonian of the jth N-V center interacts with the jth TLR, described by: j j iδj t
100 MHz, φj /2π ∼ 1000 MHz [40], and the off-resonant condition φj ηt−c, the Current-biased Josephson junction (CBJJ)–TLR off-resonant j j case is satisfied; whereas if the jth TLR with inductance Ft = 60.7 nH, capacitance Ct = 2 pF, j the full-wave frequency ωc /2π = 2.87 GHz [41], it is equal to zero-field splitting Dgs /2π = 2.87
Summary
It is well-known that an unknown quantum state cannot be copied precisely [1]. The original paper of this theorem [1] shows that the quantum no-cloning theorem is a consequence of the quantum state superposition principle. Phase-covariant QCM plays an important role in applications in quantum cryptography, and it has a higher quality of reproduction of all equator states than common QCM. This could be realized by coupling the system to be cloned to the auxiliary system. Hamiltonian functions of the system; Section 4 introduces our scheme in detail, which could be used to realize a multi-purpose quantum simulator and be used for equator state quantum cloning, with a high quality of reproduction; Section 5 discusses how to realize quantum anti-cloning, and to generate the |W4± i entangled state.
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