Generation of Two-Atom Cluster State via Cavity QED

We propose a physical scheme for generating a two-atom cluster state through the simultaneous interaction of two two-level atoms with a single-mode cavity field prepared initially in an odd-coherent state under a large-detuned limit. The influence of the dissipation constant, the intensity of the field and the imperfect manipulation on the preparation scheme are investigated. It is shown that when the intensity of the cavity is large enough, the influence of the cavity decay is ettlciently suppressed. The possible error in the implementation of the cluster state is negligible when the time difference between two atoms crossing the cavity axis is small. It is suggested that the scheme can be realized by current technologies.     

Preparation of multi-atom cluster state and teleportation of arbitrary two-atom state via thermal cavity

We propose one cavity QED (CQED) scheme for generating an arbitrary 2-level-atom cluster state. Besides, by using a 4-atom cluster state as quantum channel, we propose another CQED scheme for teleporting any unknown two-atom state. In both schemes, the dynamics processes are essentially quite similar. The Rabi frequency of the classical driving field is much bigger than the detuning between the atoms and the cavity. Hence both schemes are insensitive to the cavity decay. The necessary time for implementation is much shorter than the Rydberg-atom lifespan, therefore atom decays do not need to be considered. Moreover, in the teleportation scheme the discrimination of the 16 mutually orthogonal 4-atom cluster states is transformed into the discrimination of single-atom product states, consequently the discrimination difficulty is degraded and the scheme is more easily implemented.     

Schemes for Generating Cluster States via Cavity Systems

We propose a scheme for generating an N-atom cluster state via cavity quantum electrodynamics （ CQED）. In our scheme, there is no transfer of quantum information between the atoms and the cavity, i.e., the cavity is always in the vacuum state, so the cavity decay can be suppressed. Also, the generated cluster state is the entanglement of the ground states, so the atomic spontaneous emission can be avoided. Therefore, the cluster state generated in our scheme has a longer lifetime. Furthermore, the requirement on the quality factor of the cavity greatly loosened for the cavity is only virtually excited.     

Preparation of the four-qubit cluster states in cavity QED and the trapped-ion system

This paper proposes a simple scheme to generate a four-atom entangled cluster state in cavity quantum electrodynamics. With the assistantce of a strong classical field the cavity is only virtually excited and no quantum information will be transferred from the atoms to the cavity during the preparation for a four-atom entangled cluster state, and thus the scheme is insensitive to the cavity field states and cavity decay. Assuming that deviation of laser intensity is 0.01 and that of simultaneity for the interaction is 0.01, it shows that the fidelity of the resulting four-atom entangled cluster state is about 0.9886. The scheme can also be used to generate a four-ion entangled cluster state in a hot trapped-ion system. Assuming that deviation of laser intensity is 0.01, it shows that the fidelity of the resulting four-ion entangled cluster state is about 0.9990. Experimental feasibility for achieving this scheme is also discussed.     

One-dimensional cluster state generated in one step via one cavity

A scheme to generate multi-atom one-dimensional cluster state via one microwave cavity with an additional driven classical field is proposed. According to the scheme, one-dimensional cluster state with 2k-atom can be prepared in one step via one cavity, one-dimensional cluster state with (2k-1)-atom can be generated by measuring the2kth-atom of an 2k-atom cluster state in a certain basis. This scheme avoids cavity-field induced decay and may achieve one-dimensional cluster states with ideal success probability.     

Efficient scheme of quantum SWAP gate and multi-atom cluster state via cavity QED

In this paper, we propose a physical scheme to realize quantum SWAP gate by using a large-detuned single-mode cavity field and two identical Rydberg atoms. It is shown that the scheme can also be used to create multi-atom cluster state. During the interaction between atom and cavity, the cavity is only virtually excited and thus the scheme is insensitive to the cavity field states and cavity decay. With the help of our scheme it is very simple to prepare the N-atom cluster state with perfect fidelity and probability. The practical feasibility of this method is also discussed.     

Efficient scheme of quantum SWAP gate and multi-atom cluster state via cavity QED

In this paper, we propose a physical scheme to realize quantum SWAP gate by using a large-detuned single-mode cavity field and two identical Rydberg atoms. It is shown that the scheme can also be used to create multi-atom cluster state. During the interaction between atom and cavity, the cavity is only virtually excited and thus the scheme is insensitive to the cavity field states and cavity decay. With the help of our scheme it is very simple to prepare the $N$-atom cluster state with perfect fidelity and probability. The practical feasibility of this method is also discussed.     

Generation of four-atom cluster states in thermal cavity and implementing remote controlled not gate

We propose an experimentally feasible scheme for preparing a four-atom cluster state in a thermal cavity. In the scheme, the cavity field is only virtually excited and the photon-number-dependent part in the effective Hamiltonian is cancelled so that the system is insensitive to the cavity decay and the thermal field. At the same time, the scheme can be generalized to prepare n-atom cluster states with the success probability 100\%. In addition, using the four-atom cluster state, we also propose a simpler scheme for implementing a remote--controlled not gate (CNOT) without the Bell states measurement.     

The quantum vacuum as the origin of the speed of light

We present an economical scheme of five-party quantum state sharing (FQSTS) of an arbitrary m-atom with five-atom cluster state in cavity QED. It is found that the five-partite cluster state can be used for FQSTS of an arbitrary m-atom state. The implementation of this scheme does not involve Bell-basis or GHZ-basis measurements, which makes it more convenient in a practical application than some previous schemes. The scheme is also insensitive to the cavity decay and the thermal field.     

Scheme for Generating Cluster States with Charge Qubits in a Cavity

Based on superconducting charge qubits （SCCQs） coupled to a single-mode microwave cavity, we propose a scheme for generating charge cluster states. For all SCCQs, the controlled gate voltages are all in their degeneracy points, the quantum information is encoded in two logic states of charge basis. The generation of the multi-qubit cluster state can be achieved step by step on a pair of nearest-neighbor qubits. Considering effective long-rang coupling, we provide an efficient way to one-step generating of a highly entangled cluster state, in which the qubit-qubit coupling is mediated by the cavity mode. Our quantum operations are insensitive to the initial state of the cavity mode by removing the influence of the cavity mode via the periodical evolution of the system. Thus, our operation may be against the decoherence from the cavity.     

Teleportation of arbitrary unknown two-atom statewith cluster state via thermal cavity

This paper proposes a scheme for implementing the teleportation of an arbitrary unknown two-atom state by using a cluster state of four identical 2-level atoms as quantum channel in a thermal cavity. The two distinct advantages of the present scheme are： （i） The discrimination of 16 orthonormal cluster states in the standard teleportation protocol is transformed into the discrimination of single-atom states. Consequently, the discrimination difficulty of states is degraded. （ii） The scheme is insensitive to the cavity field state and the cavity decay for the thermal cavity is only virtually excited when atoms interact with it. Thus, the scheme is more feasible.     

Scheme for Implementing Controlled Dense Coding with Six-Atom Cluster State in Cavity QED

We propose an experimentally feasible protocol for implementing controlled dense coding with a six-atom cluster state in cavity QED. In the scheme, we investigate that the atoms interact simultaneously with the highly detuned single-mode cavity and the strong classical driving field, and thus our scheme is not sensitive to both the cavity decay and the thermal field. In addition, the four-atom entangled states can be exactly distinguished by performing the single-atom measurements in cavity QED, therefore our scheme might be implemented in a simple way.     

Generation of a Five-Atom Cluster State in Cavity QED

We present a scheme for the generation of a five-atom cluster state in cavity QED. During the preparation no quantum information is transferred from the atoms to the cavity, and thus the scheme is insensitive to the cavity field states and cavity decay.     

Scheme for n phase gates operation and one-step preparation of highly entangled cluster state

In the system with superconducting quantum interference devices (SQUIDs) in a cavity, we propose a scheme for simultaneous implementing n phase gates and one step preparing the highly entangled cluster states based on the two-channel Raman interaction. In our scheme, the system is independent to the photon number of the cavity field, the cavity field can be initially in an arbitrary state, which is convenient for the experimental operation. The n phase gates operation and the cluster state generation are realized by using only the two lower flux states of the SQUID and the excited state would not be excited so that the influence of the decoherence due to spontaneous emission of the SQUID’s levels is possible to minimize. More importantly, the operation time of the phase gates is independent of the number n of the qubits. Finally, the experimental feasibility is also discussed in detail.     

Generation of strongly squeezed states for a cavity field with a single atom

We propose a scheme to realize strong squeezing for a cavity field with a single three-level atom. In the scheme the atom is sent through the cavity initially filled with a coherent field. The atom dispersively interacts with the cavity field, which is displaced by a microwave resource during the interaction. Then, a selective measurement on the atom collapses the field to a superposition of an even coherent state with a vacuum state, which exhibits strong squeezing. The scheme can also be generalized to the two-mode case.     

Effective Scheme for Generating Cluster States in Cavity QED

We propose a scheme to prepare many two-mode cavities into one-dimensional cluster states in the context of cavity QED. The left-circularly polarized state and right-circularly polarized state of the cavity are encoded as the logic zero and one of the qubits. In the scheme, the atomic spontaneous emission is suppressed, and the fidelity is unaffected by the cavity decay on the assumption that the detection efficiencies of all the photondetectors are 1.     

Implement a measurement of GHZ entanglement for a multipartite system via cavity QED

We propose a scheme for implementing a measurement of GHZ entanglement for a multipartite system via cavity QED. In the scheme the atoms interact simultaneously with a highly detuned cavity mode with the assistant of a classical field. The scheme is insensitive to the cavity decay and the thermal field. A set of GHZ states can be exactly distinguished via detecting atomic state in a simple way.     

A Scheme for Generating Entangled Squeezed States Based on Cavity QED

We propose a scheme for generating entangled squeezed vacuum states of electromagnetical fields. The scheme is based on cavity QED. In this scheme, an atom interacts, successively, with a classical field, two quantum cavity fields, and another classical field. By detecting the final states of the atom, the two quantum cavity fields will be projected to an entangled state.     

Quantum State Sharing of an Arbitrary Two-Atom State by Using a?Six-Atom Cluster State in Cavity QED

We demonstrate that a six-atom cluster state can be used to realize the deterministic quantum state sharing of an arbitrary two-atom state in cavity QED. The scheme does not involve Bell-state measurement and is insensitive to both the cavity decay and the thermal field. In our scheme, any one of the two agents is sufficient to reconstruct the original state under the condition that he/she obtains the help of the other one, but only one of them cannot.     

Scheme for Concentration of Unknown Greeberger-Horne-Zeilinger Entangled States via Cavity Decay

We present a scheme for entanglement concentration of an unknown atomic non-maximally entangled GHZ state via cavity decay. In the scheme, the atom trapped in a cavity is manipulated by laser field, so the maximally entangled GHZ state can be obtained by performing certain operation, which can be realized by illuminating the atom in a cavity. Our method is robust against spontaneous atomic decay.