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Applied Physics Letters

Qubit–qubit entanglement mediated by epsilon-near-zero waveguide reservoirs

Ibrahim Issah, Hümeyra Çağlayan

Published Nov 29, 2021• 16 citations
Publisher

Abstract

This work investigates qubit entanglement in rolled-up and plasmonic rectangular epsilon-near-zero (ENZ) waveguide reservoirs. We explore the robust entanglement of qubits coupled to these reservoirs using the concurrence metric formalism and the emergence of driven steady-state entanglement under continuous pumping. The results indicate that the proposed rolled-up ENZ waveguide shows a high long-range entanglement of qubits embedded within as compared to the rectangular ENZ waveguide channel.

DOI
10.1063/5.0073134

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This work investigates qubit entanglement in rolled-up and plasmonic rectangular epsilon-near-zero (ENZ) waveguide reservoirs. We explore the robust entanglement of qubits coupled to these reservoirs using the concurrence metric formalism and the emergence of driven steady-state entanglement under continuous pumping. The results indicate that the proposed rolled-up ENZ waveguide shows a high long-range entanglement of qubits embedded within as compared to the rectangular ENZ waveguide channel.
Multi-qubit entanglement is of paramount importance to perform truly secure quantum optical communication operations. In this work, we present efficient long-range entanglement mediated by plasmonic waveguides operating at their cut-off frequency, where they exhibit an effective epsilon-near-zero (ENZ) response. Only the excited ENZ mode at plasmonic waveguides has a strong and homogeneous electric field distribution compared to different modes excited at groove and rod waveguides, resulting in an efficient two- and multi-qubit entanglement that can persist over extended time periods and long distances. Efficient multipartite entanglement from three equidistantly arranged two-level quantum emitters (qubits) inside the ENZ waveguide is also demonstrated by using three different multi-qubit entanglement criterions, i.e., pairwise concurrence, negativity, and genuine multipartite entanglement. The findings of this work stress the importance of ENZ plasmonic waveguides as an ideal nanophotonic platform to support efficient quantum optical effects.
The resonance energy transfer and entanglement between two-level quantum emitters are typically limited to sub-wavelength distances due to the inherently short-range nature of the dipole-dipole interactions. Moreover, the entanglement of quantum systems is hard to preserve for a long time period due to decoherence and dephasing mainly caused by radiative and nonradiative losses. In this work, we outperform the aforementioned limitations by presenting efficient long-range inter-emitter entanglement and large enhancement of resonance energy transfer between two optical qubits mediated by epsilon-near-zero (ENZ) and other plasmonic waveguide types, such as V-shaped grooves and cylindrical nanorods. More importantly, we explicitly demonstrate that the ENZ waveguide resonant energy transfer and entanglement performance drastically outperforms the other waveguide systems. Only the excited ENZ mode has an infinite phase velocity combined with a strong and homogeneous electric field distribution, which leads to a giant energy transfer and efficient entanglement independent of the emitters' separation distances and nanoscale positions in the ENZ nanowaveguide, an advantageous feature that can potentially accommodate multi-qubit entanglement. Moreover, the transient entanglement can be further improved and become almost independent of the detrimental decoherence effect when an optically active (gain) medium is embedded inside the ENZ waveguide. We also present that efficient steady-state entanglement can be achieved by using a coherent external pumping scheme. Finally, we report a practical way to detect the steady-state entanglement by computing the second-order correlation function. The presented findings stress the importance of plasmonic ENZ waveguides in the design of the envisioned on-chip quantum communication and information processing plasmonic nanodevices.
Multiqubit entanglement is extremely important to perform truly secure quantum optical communication and computing operations. However, the efficient generation of long-range entanglement over extended time periods between multiple qubits randomly distributed in a photonic system remains an outstanding challenge. This constraint is mainly due to the detrimental effects of decoherence and dephasing. To alleviate this issue, we present engineered epsilon-near-zero (ENZ) nanostructures that can maximize the coherence of light–matter interactions at room temperature. We investigate a practical ENZ plasmonic waveguide system, which simultaneously achieves multiqubit entanglement in elongated distances, extended time periods, and, even more importantly, independent of the emitters' positions. More specifically, we present efficient transient entanglement between three and four optical qubits mediated by ENZ with results that can be easily generalized to an arbitrary number of emitters. The entanglement between multiple qubits is characterized by computing the negativity metric applied to the proposed nanophotonic ENZ configuration. The ENZ response is found to be substantially advantageous to boost the coherence between multiple emitters compared to alternative plasmonic waveguide schemes. Finally, the super-radiance collective emission response at the ENZ resonance is utilized to design a high fidelity two-qubit quantum phase gate that can be used in various emerging quantum computing applications.
Abstract Entanglement is paramount in quantum information processing. Many quantum systems suffer from spatial decoherence in distances over a wavelength and cannot be sustained over short time periods due to dissipation. However, long range solutions are required for the development of quantum information processing on chip. Photonic reservoirs mediating the interactions between qubits and their environment are suggested. Recent research takes advantage of extended wavelength inside near-zero refractive index media to solve the long-range problem along with less sensitivity on the position of quantum emitters. However, those recent proposals use plasmonic epsilon near-zero waveguides that are intrinsically lossy. Here, we propose a fully dielectric platform, compatible with the Nitrogen Vacancy (NV) diamond centers on-chip technology, to drastically improve the range of entanglement over 17 free-space wavelengths, or approximatively 12.5 µm, using mu near-zero metamaterials. We evaluate transient and steady state concurrence demonstrating an order of magnitude enhancement compared to previous works. This is, to the best of our knowledge, the first time that such a long distance is reported using this strategy. Moreover, value of the zero time delay second order correlation function g12(2)(0){g}_{12}^{(2)}(0)g12(2)​(0) g 12 ( 2 ) ( 0 ) are provided, showing antibunching signature correlated with a high degree of concurrence.
Abstract Preservation of an entangled state in a quantum system is one of the major goals in quantum technological applications. However, entanglement can be quickly lost into dissipation when the effective interaction among the qubits becomes smaller compared to the noise‐injection from the environment. Thus, a medium that can sustain the entanglement of distantly spaced qubits is essential for practical implementations. This work introduces the fabrication of a rolled‐up zero‐index waveguide which can serve as a unique reservoir for the long‐range qubit–qubit entanglement. We also present the numerical evaluation of the concurrence (entanglement measure) via Ansys Lumerical FDTD simulations using the parameters determined experimentally. The calculations demonstrate the feasibility and supremacy of the experimental method. We develop and fabricate this novel structure using cost‐effective self‐rolling techniques. The results of this study redefine the range of light‐matter interactions and show the potential of the rolled‐up zero‐index waveguides for various classical and quantum applications such as quantum communication, quantum information processing, and superradiance.