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A universal quantum information processor for scalable quantum communication and networks.

Yang X, Xue B, Zhang J, Zhu S - Sci Rep (2014)

Bottom Line: Here, we present a theoretical proposal to efficiently and conveniently achieve a universal quantum information processor (QIP) via atomic coherence in an atomic ensemble.By employing EIT-based nondegenerate four-wave mixing processes, the generation, exchange, distribution, and manipulation of light-light, atom-light, and atom-atom multipartite entanglement can be efficiently and flexibly achieved in a deterministic way with only coherent light fields.This method greatly facilitates the operations in quantum information processing, and holds promising applications in realistic scalable quantum communication and quantum networks.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, Shanghai University, Shanghai 200444, China.

ABSTRACT
Entanglement provides an essential resource for quantum computation, quantum communication, and quantum networks. How to conveniently and efficiently realize the generation, distribution, storage, retrieval, and control of multipartite entanglement is the basic requirement for realistic quantum information processing. Here, we present a theoretical proposal to efficiently and conveniently achieve a universal quantum information processor (QIP) via atomic coherence in an atomic ensemble. The atomic coherence, produced through electromagnetically induced transparency (EIT) in the Λ-type configuration, acts as the QIP and has full functions of quantum beam splitter, quantum frequency converter, quantum entangler, and quantum repeater. By employing EIT-based nondegenerate four-wave mixing processes, the generation, exchange, distribution, and manipulation of light-light, atom-light, and atom-atom multipartite entanglement can be efficiently and flexibly achieved in a deterministic way with only coherent light fields. This method greatly facilitates the operations in quantum information processing, and holds promising applications in realistic scalable quantum communication and quantum networks.

No MeSH data available.


Related in: MedlinePlus

The dependence of correlations Va1-b1 (a),  (b), and  (c) at zero Fourier frequency on the coherence decay rate γ0, and the other parameters are the same as those in Fig. 2.
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f4: The dependence of correlations Va1-b1 (a), (b), and (c) at zero Fourier frequency on the coherence decay rate γ0, and the other parameters are the same as those in Fig. 2.

Mentions: The robustness of entanglement is a key issue for practical quantum applications. In the present Λ-type atomic system, it critically depends on the coherence decay rate of the lower doublet. This is clearly demonstrated in Fig. 4 by examining the influence of the coherence decay rate γ0 on the correlations Va1-b1, , and at zero Fourier frequency. Va1-b1, Va1-, and with the initial values of about 2, 1, and 1, respectively, would increase with the increase of the coherence decay rate γ0, which means the degree of entanglement would be weakened. When the coherence decay rate γ0 grows large enough, Va1-b1 nearly becomes equal to 4, whereas and approximately approach 2. In the realistic hot atomic ensemble, the source of decoherence associated to the ground states is mainly due to the finite interaction time between atoms and light. According to the experimental conditions in Refs. [17, 28, 33] with the beam radius r being of about 300 um and cell temperature of about 400 K, it can be inferred that the dephasing time of the atomic spin coherence is on the order of microsecond; correspondingly, the coherence decay rate of the lower doublet is about several MHz. As seen from Fig. 4, this low relaxation rate has a negligible impact on the entanglement. In order to conveniently and successfully measure the entanglement, the experimental setup with a square-box pattern for the laser beams having spatial separation and nearly complete cancellation of Doppler broadening done in Ref. [28], and the dual-homodyne detection method in Ref. [17] together with the photodetector (S3883 Si pin photodiodes) having quantum efficiency of about 96% used in Ref. [33], can be employed. Moreover, it is well known that, in the Λ-type atomic system, the correlation time of the entangled fields and the storage time of the quantum memory are determined by the coherence decay time of the atomic lower doublet, which, in practice, can be long (~ms or even ~s2425263435). Therefore, this EIT-based multi-Λ-type atomic system can be a potential candidate for a quantum repeater, through which quantum state distribution over long distance can be achieved via successive entanglement exchange and distribution. In addition, as depicted in Fig. 5, bipartite entanglements between the scattering fields, Stokes and anti-Stokes fields, as well as the atomic coherence excitation are independent of the intensity /α/2 of the scattering fields. So we can use bright enough beams to carry quantum information as long as the detunings Δ1 and Δ2 of the scattering fields are sufficiently large and the atomic coherence is strong enough.


A universal quantum information processor for scalable quantum communication and networks.

Yang X, Xue B, Zhang J, Zhu S - Sci Rep (2014)

The dependence of correlations Va1-b1 (a),  (b), and  (c) at zero Fourier frequency on the coherence decay rate γ0, and the other parameters are the same as those in Fig. 2.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4197420&req=5

f4: The dependence of correlations Va1-b1 (a), (b), and (c) at zero Fourier frequency on the coherence decay rate γ0, and the other parameters are the same as those in Fig. 2.
Mentions: The robustness of entanglement is a key issue for practical quantum applications. In the present Λ-type atomic system, it critically depends on the coherence decay rate of the lower doublet. This is clearly demonstrated in Fig. 4 by examining the influence of the coherence decay rate γ0 on the correlations Va1-b1, , and at zero Fourier frequency. Va1-b1, Va1-, and with the initial values of about 2, 1, and 1, respectively, would increase with the increase of the coherence decay rate γ0, which means the degree of entanglement would be weakened. When the coherence decay rate γ0 grows large enough, Va1-b1 nearly becomes equal to 4, whereas and approximately approach 2. In the realistic hot atomic ensemble, the source of decoherence associated to the ground states is mainly due to the finite interaction time between atoms and light. According to the experimental conditions in Refs. [17, 28, 33] with the beam radius r being of about 300 um and cell temperature of about 400 K, it can be inferred that the dephasing time of the atomic spin coherence is on the order of microsecond; correspondingly, the coherence decay rate of the lower doublet is about several MHz. As seen from Fig. 4, this low relaxation rate has a negligible impact on the entanglement. In order to conveniently and successfully measure the entanglement, the experimental setup with a square-box pattern for the laser beams having spatial separation and nearly complete cancellation of Doppler broadening done in Ref. [28], and the dual-homodyne detection method in Ref. [17] together with the photodetector (S3883 Si pin photodiodes) having quantum efficiency of about 96% used in Ref. [33], can be employed. Moreover, it is well known that, in the Λ-type atomic system, the correlation time of the entangled fields and the storage time of the quantum memory are determined by the coherence decay time of the atomic lower doublet, which, in practice, can be long (~ms or even ~s2425263435). Therefore, this EIT-based multi-Λ-type atomic system can be a potential candidate for a quantum repeater, through which quantum state distribution over long distance can be achieved via successive entanglement exchange and distribution. In addition, as depicted in Fig. 5, bipartite entanglements between the scattering fields, Stokes and anti-Stokes fields, as well as the atomic coherence excitation are independent of the intensity /α/2 of the scattering fields. So we can use bright enough beams to carry quantum information as long as the detunings Δ1 and Δ2 of the scattering fields are sufficiently large and the atomic coherence is strong enough.

Bottom Line: Here, we present a theoretical proposal to efficiently and conveniently achieve a universal quantum information processor (QIP) via atomic coherence in an atomic ensemble.By employing EIT-based nondegenerate four-wave mixing processes, the generation, exchange, distribution, and manipulation of light-light, atom-light, and atom-atom multipartite entanglement can be efficiently and flexibly achieved in a deterministic way with only coherent light fields.This method greatly facilitates the operations in quantum information processing, and holds promising applications in realistic scalable quantum communication and quantum networks.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, Shanghai University, Shanghai 200444, China.

ABSTRACT
Entanglement provides an essential resource for quantum computation, quantum communication, and quantum networks. How to conveniently and efficiently realize the generation, distribution, storage, retrieval, and control of multipartite entanglement is the basic requirement for realistic quantum information processing. Here, we present a theoretical proposal to efficiently and conveniently achieve a universal quantum information processor (QIP) via atomic coherence in an atomic ensemble. The atomic coherence, produced through electromagnetically induced transparency (EIT) in the Λ-type configuration, acts as the QIP and has full functions of quantum beam splitter, quantum frequency converter, quantum entangler, and quantum repeater. By employing EIT-based nondegenerate four-wave mixing processes, the generation, exchange, distribution, and manipulation of light-light, atom-light, and atom-atom multipartite entanglement can be efficiently and flexibly achieved in a deterministic way with only coherent light fields. This method greatly facilitates the operations in quantum information processing, and holds promising applications in realistic scalable quantum communication and quantum networks.

No MeSH data available.


Related in: MedlinePlus