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Transmission of entangled photons studied by quantum tomography: do we need plasmonic resonances?

Mathilde Remy, Bojana M. Bokić, Wakana Kubo, Yves Caudano, Branko Kolarić

Published Jun 26, 2019• 0 citations
OpenAlex

Abstract

We performed quantum tomography to reveal the robustness of quantum correlations of photons entangled in polarisation after their interaction with plasmonic and nonplasmonic environments at normal incidence.The experimental findings clearly show that the visibility of quantum correlations survives the interaction, and that the presence of plasmonic resonances has not any significant influence on the survival of polarisation correlations for transmitted photon pairs.The results indicate that quantum states can be encoded into the multiple motions of a many-body electronic system without demolishing their quantum nature.The plasmonic structures and their resonances only enhance the overall transmission.Thus, they could benefit the pair detection rate, that is the number of coincidences per unit of time, but they do not affect the visibility of quantum correlations.We also performed quantum tomography of the entangled pairs after interaction with the continuous planar gold film as a function of the incidence angle.The latter illustrates the loss of polarization correlations that arises from the partially polarizing properties of the isotropic sample out of normal incidence.Our work shows that plasmonic structures are not needed to exploit quantum entanglement if the rate of coincidence counting is sufficient.

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arXiv:1310.7956•Optics Letters•Jan 13, 2014•24 citations
We performed quantum tomography to reveal the robustness of quantum correlations of photons entangled in polarisation after their interaction with plasmonic and nonplasmonic environments at normal incidence.The experimental findings clearly show that the visibility of quantum correlations survives the interaction, and that the presence of plasmonic resonances has not any significant influence on the survival of polarisation correlations for transmitted photon pairs.The results indicate that quantum states can be encoded into the multiple motions of a many-body electronic system without demolishing their quantum nature.The plasmonic structures and their resonances only enhance the overall transmission.Thus, they could benefit the pair detection rate, that is the number of coincidences per unit of time, but they do not affect the visibility of quantum correlations.We also performed quantum tomography of the entangled pairs after interaction with the continuous planar gold film as a function of the incidence angle.The latter illustrates the loss of polarization correlations that arises from the partially polarizing properties of the isotropic sample out of normal incidence.Our work shows that plasmonic structures are not needed to exploit quantum entanglement if the rate of coincidence counting is sufficient.
Abstract We performed quantum tomography to reveal the robustness of quantum correlations of photons entangled in polarisation after their interaction with plasmonic and nonplasmonic environments at normal incidence. The experimental findings clearly show that the visibility of quantum correlations survives the interaction, and that the presence of plasmonic resonances has not any significant influence on the survival of polarisation correlations for transmitted photon pairs. The results indicate that quantum states can be encoded into the multiple motions of a many-body electronic system without demolishing their quantum nature. The plasmonic structures and their resonances only enhance the overall transmission. Thus, they could benefit the pair detection rate, that is the number of coincidences per unit of time, but they do not affect the visibility of quantum correlations. We also performed quantum tomography of the entangled pairs after interaction with the continuous planar gold film as a function of the incidence angle. The latter illustrates the loss of polarization correlations that arises from the partially polarizing properties of the isotropic sample out of normal incidence. Our work shows that plasmonic structures are not needed to exploit quantum entanglement if the rate of coincidence counting is sufficient.
Two-photon states emitted from spontaneous parametric downconversion (SPDC) can exhibit quantum correlations in various degrees of freedom. On the other hand, plasmonic nanostructures show enhanced transmission thanks to the conversion of light into surface plasmon polaritons. It has been shown previously that polarization, time-energy and orbital angular momentum entanglement are preserved in such structures. The fact that surface plasmons are collective charge density waves, consisting of billions of electrons makes this observation remarkable. Here we show that spatial entanglement is also preserved by characterizing it after the photons interacted with gold nanopillar arrays. The detection is realized with novel single photon avalanche diode (SPAD) arrays with high spatial and temporal resolution. By measuring the spatial correlations of the photon in the near- and far-fields, we can characterize the state with respect to spatial entanglement with and without the nano-structure.
This thesis investigates properties of quantum states of light while travelling as surface plasmon polaritons in plasmonic waveguides and structures. The bosonic nature of SPPs has been shown in previous work by performing a Hong-Ou-Mandel interference experiment with a plasmonic scattering-based beam splitter. Here, we show the same interference with a higher statistical power thanks to an improved set-up. A visibility of 59 ± 1 % is obtained in the two-photon interference, clearly breaking the classical limit of 50 %. The importance of the phase-relations between the different modes in the beam splitter is experimentally probed. The output state of the interference is then further analyzed by a quantum state tomography set-up. This makes it possible to quantify the entanglement generated in the interference. As the interference happens in the plasmonic beam splitter, this shows, to our knowledge for the first time, entanglement generated in a plasmonic structure. Together with the recent results in terms of entanglement and coherence preservation of SPPs, this clearly shows the potential of quantum plasmonic devices. To move into the realm of applications, we also investigate theoretically the enhancements in sensitivity quantum states of light can deliver for plasmonic sensing. It is shown that despite the losses, quantum metrology techniques can be useful in an interferometer with plasmonic waveguides. Considering the strengths and successes of plasmonic sensing techniques in a wide range of fields, we envision that entangled and squeezed states of light will become a new route to push the limits in sensitivity.
Previous experiments have shown that surface plasmon polaritons (SPPs) preserve their entangled state and do not cause measurable decoherence. However, essentially all of them were done using SPPs whose dispersion was in the linear “photon-like” regime. We report in this presentation on experiments showing how transition to “true-plasmon” non-linear dispersion regime, which occurs near SPP resonance frequency, will affect quantum coherent properties of light. To generate a polarization-entangled state we utilize type-I parametric down-conversion, occurring in a pair of non-linear crystals (BiBO), glued together and rotated by 90 degrees with respect to each other. For state projection measurements, we use a pair of polarizers and single-photon avalanche diode coincidence count detectors. We interpose a plasmonic hole array in the path of down-converted light before the polarizer. Without the hole array, we measure visibility V=99-100% and Bell’s number S=2.81±0.03. To study geometrical effects we fabricated plasmonic hole arrays (gold on optically polished glass) with elliptical holes (axes are 190nm and 240nm) using focused ion beam. When we put this sample in our system we measured the reduction of visibility V=86±5% using entangled light. However, measurement using classical light gave exactly the same visibility; hence, this reduction is caused only by the difference in transmission coefficients of different polarizations. As samples with non-linear dispersion we fabricated two-layer (a-Si - Au) and three-layer (a-Si – Au – a-Si) structures on optically polished glass with different pitches and circular holes. The results of measurements with these samples will be discussed along with the theoretical investigations.
Previous experiments have shown that surface plasmon polaritons (SPPs) preserve their entangled state and do not cause measurable decoherence. However, essentially all of them were done using SPPs whose dispersion was in the linear “photon-like” regime. We report in this presentation on experiments showing how transition to “true-plasmon” non-linear dispersion regime, which occurs near SPP resonance frequency, will affect quantum coherent properties of light. To generate a polarization-entangled state we utilize type-I parametric down-conversion, occurring in a pair of non-linear crystals (BiBO), glued together and rotated by 90 degrees with respect to each other. For state projection measurements, we use a pair of polarizers and single-photon avalanche diode coincidence count detectors. We interpose a plasmonic hole array in the path of down-converted light before the polarizer. Without the hole array, we measure visibility V=99-100% and Bell’s number S=2.81±0.03. To study geometrical effects we fabricated plasmonic hole arrays (gold on optically polished glass) with elliptical holes (axes are 190nm and 240nm) using focused ion beam. When we put this sample in our system we measured the reduction of visibility V=86±5% using entangled light. However, measurement using classical light gave exactly the same visibility; hence, this reduction is caused only by the difference in transmission coefficients of different polarizations. As samples with non-linear dispersion we fabricated two-layer (a-Si - Au) and three-layer (a-Si – Au – a-Si) structures on optically polished glass with different pitches and circular holes. The results of measurements with these samples will be discussed along with the theoretical investigations.
We report perfect two-photon quantum interference with near-unity visibility in a resonant tunneling plasmonic structure in folded Kretschmann geometry. This is despite absorption-induced loss of unitarity in plasmonic systems. The effect is traced to perfect destructive interference between the squares of amplitude reflection and transmission coefficients. We further highlight yet another remarkable potential of coincidence measurements as a probe with better resolution as compared to standard spectroscopic techniques. The finer features show up in both angle resolved and frequency resolved studies.