We propose a simplified parity meter for photonic qubits with cross-Kerr nonlinearities, homodyne measurement, and some optical elements. Our scheme has lower error probability than the protocol proposed in Nemoto and Munro [Phys. Rev. Lett. 93, 250502 (2004)]. Based on the present parity meter, we achieve cluster-state preparation, a complete Bell-state analyzer, and quantum teleportation. All of these schemes are nearly deterministic in the regime with little noise and include less optical elements, which makes our schemes more meaningful for large-scale quantum computing.
We demonstrate quantum information can be transferred between two distant participants without any physical particles traveling between them. The key procedure of the counterfactual scheme is to entangle two nonlocal qubits with each other without interaction, so the scheme can also be used to generate nonlocal entanglement counterfactually. We here illustrate the scheme by using flying photon qubits and Rydberg atom qubits assisted by a mesoscopic atomic ensemble. Unlike the typical teleportation, the present scheme can transport an unknown qubit in a nondeterministic manner without prior entanglement sharing or classical communication between the two distant participants.
We demonstrate efficient schemes of deterministic entanglement generation and quantum state transfer (QST) with the nitrogen-vacancy (NV) centers in diamond confined in separated microtoroidal resonators via single-photon input-output process. Assisted by the polarization of input photon pulse and the electron spin state of NV center, high fidelity NV center entangled states and photonic entangled states can be generated, respectively. The analyses of experimental feasibility show that our schemes work well with low quality resonators and weak coupling between qubits, which may be beneficial for exploring large-scale quantum information processing with diamond-based solid-state devices.
To date, all schemes for entanglement distribution needed to send entangled particles or a separable mediating particle among distant participants. Here, we propose a counterfactual protocol for entanglement distribution against the traditional forms, that is, two distant particles can be entangled with no physical particles travel between the two remote participants. We also present an alternative scheme for realizing the counterfactual photonic entangled state distribution using Michelson-type interferometer and self-assembled GaAs/InAs quantum dot embedded in a optical microcavity. The numerical analysis about the effect of experimental imperfections on the performance of the scheme shows that the entanglement distribution may be implementable with high fidelity.
We propose an entanglement concentration protocol to concentrate an arbitrary partially-entangled four-photon cluster state. As a pioneering three-step entanglement concentration scheme, our protocol only needs a single-photon resource to assist the concentration in each step, which makes this protocol more economical. With the help of the linear optical elements and weak cross-Kerr nonlinearity, one can obtain a maximally-entangled cluster state via local operations and classical communication. Moreover, the protocol can be iterated to obtain a higher success probability and is feasible under current experimental conditions.
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