By using the Green-function approach to the quantization of the electromagnetic field, the procrustean distillation for quantum entanglement by the anisotropic magnetodielectric metamaterial has been proposed. We study the distillation of the non-maximally entangled pure states by a single layer of the anisotropic magnetodielectric metamaterial. The Clauser–Horne–Shimony–Holt parameter S for the entangled pure state has been calculated theoretically. It is shown that near the resonant peak of transmission for the y-polarized photon, the parameter S for the output states get the maximal value. Near the resonant peak of the transmission for the x-polarized photon, the entanglement of the output state is lower than the input state. For the frequency far from the resonant peak, the entanglement of the output state is dependent on the input state. Finally we find that the maximally entangled output is always appearing near the resonant frequency of the transmission for the y-polarized photon, no matter how low the entanglement of the input state is. This means that our method to realize the quantum distillation is effective.
By using the Green-function approach to the quantization of the electromagnetic field, the procrustean distillation for quantum entanglement by the anisotropic magnetodielectric metamaterial has been proposed. We study the distillation of the non-maximally entangled pure states by a single layer of the anisotropic magnetodielectric metamaterial. The Clauser–Horne–Shimony–Holt parameter S for the entangled pure state has been calculated theoretically. It is shown that near the resonant peak of transmission for the y-polarized photon, the parameter S for the output states get the maximal value. Near the resonant peak of the transmission for the x-polarized photon, the entanglement of the output state is lower than the input state. For the frequency far from the resonant peak, the entanglement of the output state is dependent on the input state. Finally we find that the maximally entangled output is always appearing near the resonant frequency of the transmission for the y-polarized photon, no matter how low the entanglement of the input state is. This means that our method to realize the quantum distillation is effective.
By using the Green-function approach to the problem of quantization of the electromagnetic field, the propagation of quantized radiation through dispersive and absorptive anisotropic multilayer structures is studied. Input–output relations are derived. Based on these relations, an efficient method to perform procrustean distillation and concentration for quantum entanglement has been proposed. The Clauser–Horne–Shimony–Holt parameter for an entangled pure state, the quantum relative entropy and linear entropy for a mixed state have been calculated theoretically. It is shown that the efficiency of such a method is not only much higher for the distillation of non-maximally entangled pure states than those using partial polarizers, but it is also good for the concentration for the mixed states. Both the purity and the degree of entanglement of the mixed states can be improved simultaneously several times by using such a method. Another advantage of the scheme is that it can be widely adjusted by a proper choice of the structural parameters and the external field.
We propose a scheme for the distillation of partially entangled two-photon Bell and three-photon W states using metamaterials. The distillation of partially entangled Bell states is achieved by using two metamaterials with polarization dependence, one of which is rotated by π/2 around the direction of propagation of the photons. On the other hand, the distillation of three-photon W states is achieved by using one polarization dependent metamaterial and two polarization independent metamaterials. Upon transmission of the photons of the partially entangled states through the metamaterials the entanglement of the states increases and they become distilled. This work opens up new directions in quantum optical state engineering by showing how metamaterials can be used to carry out a quantum information processing task.
The practical development of quantum plasmonic circuits incorporating non-classical interference [1] and sources of entangled states calls for a versatile quantum theoretical framework which can fully describe the generation and detection of entangled photons and plasmons. However, majority of the presently used theoretical approaches are typically limited to the toy models assuming loss-less and nondispersive elements or including just a few resonant modes. Here, we present a rigorous Green function approach describing entangled photon-plasmon state generation through spontaneous wave mixing in realistic metal-dielectric nanostructures. Our approach is based on the local Huttner-Barnett quantization scheme [2], which enables problem formulation in terms of a Hermitian Hamiltonian where the losses and dispersion are fully encoded in the electromagnetic Green functions. Hence, the problem can be addressed by the standard quantum mechanical perturbation theory, overcoming mathematical difficulties associated with other quantization schemes. We derive explicit expressions with clear physical meaning for the spatially dependent two-photon detection probability, single-photon detection probability and single-photon density matrix. In the limiting case of low-loss nondispersive waveguides our approach reproduces the previous results [3,4]. Importantly, our technique is far more general and can quantitatively describe generation and detection of spatially-entangled photons in arbitrary metal-dielectric structures taking into account actual losses and dispersion. This is essential to perform the design and optimization of plasmonic structures for generation and control of quantum entangled states. [1] J.S. Fakonas, H. Lee, Y.A. Kelaita and H.A. Atwater, Nature Photonics 8, 317(2014) [2] W. Vogel and D.-G. Welsch, Quantum Optics, Wiley (2006). [3] D.A. Antonosyan, A.S. Solntsev and A.A. Sukhorukov, Phys. Rev. A 90 043845 (2014) [4] L.-G. Helt, J.E. Sipe and M.J. Steel, arXiv: 1407.4219
Metasurfaces have proven themselves an exotic ability to harness light at nano-scale, being important not only for classical but also for quantum optics. Dynamic manipulation of the quantum states is at the heart of quantum information processing; however, such function has been rarely realized with metasurfaces so far. Here, we report an all-optical dynamic modulation of the photonic quantum states using the nonlinear metasurface. The metasurface consists of a metallic nanostructure combined with a photoisomerizable azo layer. By tuning the plasmonic resonance through optically switching the azo molecules between their binary isomeric states, we have realized dynamic control of transmission efficiencies of orthogonally polarized photons and also the phase delay between them, thereby an entangled state was efficiently controlled. As an illustration, a quantum state distillation has been demonstrated to recover a Bell state from a non-maximally entangled one to that with fidelities higher than 98%. Our work would enrich the functions of the metasurface in the quantum world, from static to dynamic modulation, making the quantum metasurface going practical.
Photonic quantum technologies have been extensively studied in quantum information science, owing to the high-speed transmission and outstanding low-noise properties of photons. However, applications based on photonic entanglement are restricted due to the diffraction limit. In this work, we demonstrate for the first time the maintaining of quantum polarization entanglement in a nanoscale hybrid plasmonic waveguide composed of a fiber taper and a silver nanowire. The transmitted state throughout the waveguide has a fidelity of 0.932 with the maximally polarization entangled state Φ(+). Furthermore, the Clauser, Horne, Shimony, and Holt (CHSH) inequality test performed, resulting in value of 2.495 ± 0.147 > 2, demonstrates the violation of the hidden variable model. Because the plasmonic waveguide confines the effective mode area to subwavelength scale, it can bridge nanophotonics and quantum optics and may be used as near-field quantum probe in a quantum near-field micro/nanoscope, which can realize high spatial resolution, ultrasensitive, fiber-integrated, and plasmon-enhanced detection.
Linearly polarized projections are the tacit means for performing Clauser-Horne-Shimony-Holt (CHSH) Bell-inequality tests using polarization-entangled photon pairs. The inequality is valid for all states on the Poincaré-Bloch sphere, but few laboratory studies have investigated violations with the full sphere. In this article, we explore the experimental verifications of the predicted violations of the CHSH inequality with Bell and non-Bell states with same and different linear and elliptically polarized basis states for each photon. We find that Bell states violate CHSH when using the same basis for both photons, regardless of their ellipticity, whereas they show no violations for photon projections in different bases. We found non-Bell maximally-entangled states for which the converse is true.