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Physical Review A

Cavity coherent-state cloning via Raman scattering

Moorad Alexanian

Published Mar 21, 2003• 10 citations
Publisher

Abstract

The Raman interaction of atoms singly traversing a two-mode cavity constitutes a quantum-cloning machine for coherent states. The quality of the two identical output coherent states is independent of the initial, albeit different, coherent state, initially present inside the cavity. The cloning of nonorthogonal states indicates that the entanglement of the output states for an arbitrary initial state is the essence of the no-cloning theorem.

DOI
10.1103/physreva.67.033809

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The Raman interaction of atoms singly traversing a two-mode cavity constitutes a quantum-cloning machine for coherent states. The quality of the two identical output coherent states is independent of the initial, albeit different, coherent state, initially present inside the cavity. The cloning of nonorthogonal states indicates that the entanglement of the output states for an arbitrary initial state is the essence of the no-cloning theorem.
We present a scheme to realize a general quantum cloning machine via cavity-assisted interaction. First, this scheme can prepare entangled states of three remote trapped atoms including the W state and the GHZ state. Based on this approach, the quantum information carried by a photon pulse or a trapped atom can be copied to other two trapped atoms. According to the known information of the initial state, the equipment can provide the optimal symmetric (asymmetric) universal and phase-covariant quantum cloning. Further, via the cavity input-output process, the quantum cloning can be realized with high fidelity, even if the atom is not localized in the Lamb-Dicke regime.
An efficient scheme is proposed to implement a quantum cloning machine in separate cavities based on a hybrid interaction between electron-spin systems placed in the cavities and an optical coherent pulse. The coefficient of the output state for the present cloning machine is just the direct product of two trigonometric functions, which ensures that different types of quantum cloning machine can be achieved readily in the same framework by appropriately adjusting the rotated angles. The present scheme can implement optimal one-to-two symmetric (asymmetric) universal quantum cloning, optimal symmetric (asymmetric) phase-covariant cloning, optimal symmetric (asymmetric) real-state cloning, optimal one-to-three symmetric economical real-state cloning, and optimal symmetric cloning of qubits given by an arbitrary axisymmetric distribution. In addition, photon loss of the qubus beams during the transmission and decoherence effects caused by such a photon loss are investigated.
We analyze the possibility of copying (that is, cloning) arbitrary states of a quantum-mechanical spin-1/2 system. We show that there exists a ``universal quantum-copying machine'' (i.e., transformation) which approximately copies quantum-mechanical states such that the quality of its output does not depend on the input. We also examine a machine which combines a unitary transformation and a selective measurement to produce good copies of states in the neighborhood of a particular state. We discuss the problem of measurement of the output states. \textcopyright{} 1996 The American Physical Society.
Beyond the no-cloning theorem, the universal symmetric quantum cloning machine was first addressed by Bu\ifmmode \check{z}\else \v{z}\fi{}ek and Hillery. Here, we realized the $\stackrel{\ensuremath{\rightarrow}}{1}$2 qubit Bu\ifmmode \check{z}\else \v{z}\fi{}ek-Hillery cloning machine with linear optical devices. This method relies on the representation of several qubits by a single photon. We showed that the fidelities between the two output qubits and the original qubit are both 56\frac{5}{6}65​ (which proved to be the optimal fidelity of $\stackrel{\ensuremath{\rightarrow}}{1}$2 qubit universal cloner) for arbitrary input pure states.
We present a scheme to realize a special quantum cloning machine via input-output cavities. The cloning machine can copy information from one atom to another distant atom. Choosing different parameters, the method can perform optimal symmetric (asymmetric) universal quantum cloning and optimal symmetric (asymmetric) phase-covariant cloning. Compared to previous schemes, our scheme is more insensitive to actual environmental noise and can get higher fidelity in a current cavity quantum electrodynamics system with an entangled state acting as a quantum channel than a single-photon pulse.