Preparation of n-qubit Greenberger-Horne-Zeilinger entangled states in cavity QED: An approach with tolerance to nonidentical qubit-cavity coupling constants

We propose a way for generating $n$-qubit Greenberger-Horne-Zeilinger (GHZ) entangled states with a three-level qubit system and (n-1) four-level qubit systems in a cavity. This proposal does not require identical qubit-cavity coupling constants, and thus is tolerant to qubit-system parameter nonuniformity and nonexact placement of qubits in a cavity. The proposal does not require adjustment of the qubit-system level spacings during the entire operation. Moreover, it is shown that entanglement can be deterministically generated using this method and the operation time is independent of the number of qubits. The present proposal is quite general, which can be applied to physical systems such as various types of superconducting devices coupled to a resonator or atoms trapped in a cavity.Comment: 3 figures, accepted by Phys. Rev.

Proposal for realizing a multiqubit tunable phase gate of one qubit simultaneously controlling n target qubits using cavity QED

We propose a way to realize a multiqubit tunable phase gate of one qubit simultaneously controlling n target qubits with atoms in cavity QED. In this proposal, classical pulses interact with atoms outside a cavity only, thus the experimental challenge of applying a pulse to an intra-cavity single atom without affecting other atoms in the same cavity is avoided. Because of employing a first-order large detuning, the gate can be performed fast when compared with the use of a second-order large detuning. Furthermore, the gate operation time is independent of the number of qubits. This proposal is quite general, which can be applied to various superconducting qubits coupled to a resonator, NV centers coupled to a microsphere cavity or quantum dots in cavity QED.Comment: 4 pages, 5 figures, accepted by Phys. Rev.

Extracting an arbitrary relative phase from a multiqubit two-component entangled state

We show that an arbitrary relative phase can be extracted from a multiqubit two-component (MTC) entangled state by local Hadamard transformations and measurements along a single basis only. In addition, how to distinguish a MTC entangled state with an arbitrary entanglement degree and relative phase from a class of multiqubit mixed states is discussed.Comment: 4 pages, REVTEX, accepted by Physical Review

Robust and scalable optical one-way quantum computation

We propose an efficient approach for deterministically generating scalable cluster states with photons. This approach involves unitary transformations performed on atoms coupled to optical cavities. Its operation cost scales linearly with the number of qubits in the cluster state, and photon qubits are encoded such that single-qubit operations can be easily implemented by using linear optics. Robust optical one-way quantum computation can be performed since cluster states can be stored in atoms and then transferred to photons that can be easily operated and measured. Therefore, this proposal could help performing robust large-scale optical one-way quantum computation.Comment: 6 pages, 4 figure