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arXiv:1408.2070

Integrated Quantum Controlled-NOT Gate Based on Dielectric-Loaded Surface Plasmon Polariton Waveguide

Siyi Wang, Qingqing Cheng, Yan-Xiao Gong, Ping Xu, L. Li, T. Li, Shining N. Zhu

Published Aug 9, 2014• 1 citation
arXivHTMLPDF

Abstract

It has been proved that surface plasmon polariton (SPP) can well conserve and transmit the quantum nature of entangled photons. Therefore, further utilization and manipulation of such quantum nature of SPP in a plasmonic chip will be the next task for scientists in this field. In quantum logic circuits, the controlled-NOT (CNOT) gate is the key building block. Here, we implement the first plasmonic quantum CNOT gate with several-micrometer footprint by utilizing a single polarization-dependent beam-splitter (PDBS) fabricated on the dielectric-loaded SPP waveguide (DLSPPW). The quantum logic function of the CNOT gate is characterized by the truth table with an average fidelity of. Its entangling ability to transform a separable state into an entangled state is demonstrated with the visibilities of and for non-orthogonal bases. The DLSPPW based CNOT gate is considered to have good integratability and scalability, which will pave a new way for quantum information science.

DOI
10.48550/arxiv.1408.2070

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It has been proved that surface plasmon polariton (SPP) can well conserve and transmit the quantum nature of entangled photons. Therefore, further utilization and manipulation of such quantum nature of SPP in a plasmonic chip will be the next task for scientists in this field. In quantum logic circuits, the controlled-NOT (CNOT) gate is the key building block. Here, we implement the first plasmonic quantum CNOT gate with several-micrometer footprint by utilizing a single polarization-dependent beam-splitter (PDBS) fabricated on the dielectric-loaded SPP waveguide (DLSPPW). The quantum logic function of the CNOT gate is characterized by the truth table with an average fidelity of. Its entangling ability to transform a separable state into an entangled state is demonstrated with the visibilities of and for non-orthogonal bases. The DLSPPW based CNOT gate is considered to have good integratability and scalability, which will pave a new way for quantum information science.
The ability to manipulate quantum states of light by integrated devices may open new perspectives both for fundamental tests of quantum mechanics and for novel technological applications. However, the technology for handling polarization-encoded qubits, the most commonly adopted approach, is still missing in quantum optical circuits. Here we demonstrate the first integrated photonic controlled-NOT (CNOT) gate for polarization-encoded qubits. This result has been enabled by the integration, based on femtosecond laser waveguide writing, of partially polarizing beam splitters on a glass chip. We characterize the logical truth table of the quantum gate demonstrating its high fidelity to the expected one. In addition, we show the ability of this gate to transform separable states into entangled ones and vice versa. Finally, the full accessibility of our device is exploited to carry out a complete characterization of the CNOT gate through a quantum process tomography. As quantum information processing continues to develop apace, the need for integrated photonic devices becomes ever greater for both fundamental measurements and technological applications. To this end, Crespiet al.demonstrate a high-fidelity photonic controlled-NOT gate on a glass chip.
To build universal quantum computers, an essential step is to realize the so-called controlled-NOT (CNOT) gate. Quantum photonic integrated circuits are well recognized as an attractive technology offering great promise for achieving large-scale quantum information processing, due to the potential for high fidelity, high efficiency, and compact footprints. Here, we demonstrate a supercompact integrated quantum CNOT gate on silicon by using the concept of symmetry breaking of a six-channel waveguide superlattice. The present path-encoded quantum CNOT gate is implemented with a footprint of $4.8\ifmmode\times\else\texttimes\fi{}4.45\text{ }\text{ }\ensuremath{\mu}{\mathrm{m}}^{2}$ ($\ensuremath{\sim}3\ensuremath{\lambda}\ifmmode\times\else\texttimes\fi{}3\ensuremath{\lambda}$) as well as a high-process fidelity of $\ensuremath{\sim}0.925$ and a low excess loss of <0.2  dB<0.2\text{ }\text{ }\mathrm{dB}<0.2  dB. The footprint is shrunk significantly by $\ensuremath{\sim}10\text{ }000$ times compared to those previous results based on dielectric waveguides. This offers the possibility of realizing practical large-scale quantum information processes and paving the way to the applications across fundamental science and quantum technologies.
Compact controlled-NOT (CNOT) gates are essential for achieving large-scale quantum information processing. Recently, metasurfaces have been emerging as a promising miniaturized platform for quantum optics thanks to their advanced light field manipulation capability and subwavelength thickness. Here we report, for the first time, to our knowledge, the experimental demonstration of a quantum CNOT gate realized with a single-layer Pancharatnam–Berry phase-based dielectric metasurface. The metasurface completes the functions of three beam splitters, reducing the thickness of the logic gate to the subwavelength scale. The truth table fidelity reaches as high as 94.7% and state fidelities of the generated maximally entangled Bell states exceed 80%. This provides an ultrathin device for quantum information processing and holds promise for advancing quantum technology.
Light-matter interactions underlie many quantum technologies, yet whether quasiparticles formed from such interactions preserve the full quantum state of light remains unresolved. Surface plasmon polaritons (SPPs), a class of polaritons formed by interacting photons with free-electron oscillations at metal-dielectric interfaces, are prime candidates to explore this question. Here we demonstrate quantum interference between single photons and SPPs using an Au-SiNx_{\mathrm{x}}x​ integrated photonic-plasmonic device. Our results reveal that SPPs retain the indistinguishability of their excitation photons, establishing SPP as a viable quantum information carrier and opening a potential route toward photonic-plasmonic quantum circuitry.
Surface plasmon polaritons (SPPs) are collective excitations of free electrons propagating along a metal-dielectric interface. Although some basic quantum properties of SPPs, such as the preservation of entanglement, the wave-particle duality of a single plasmon, the quantum interference of two plasmons, and the verification of entanglement generation, have been shown, more advanced quantum information protocols have yet to be demonstrated with SPPs. Here, we experimentally realize quantum state teleportation between single photons and SPPs. To achieve this, we use polarization-entangled photon pairs, coherent photon-plasmon-photon conversion on a metallic subwavelength hole array, complete Bell-state measurements and an active feed-forward technique. The results of both quantum state and quantum process tomography confirm the quantum nature of the SPP mediated teleportation. An average state fidelity of [Formula: see text] and a process fidelity of [Formula: see text], which are well above the classical limit, are achieved. Our work shows that SPPs may be useful for realizing complex quantum protocols in a photonic-plasmonic hybrid quantum network.
Plasmonics offers sub-diffraction confinement of light, which affords enhanced coupling to emitter systems (e.g.quantum dots).This feature makes possible a range of on-chip quantum photonic components -most notably single-photon sources and switches.This potential use of plasmonics, along with the nonlinearity provided by emitter systems, opens up quantum plasmonics as a viable route to realising quantum information processing.In this setting, the excitation of single surface plasmon polaritons (SPPs) on waveguides via single photons and the confirmation of single-photon states upon output is an important goal.In the work reported here, plasmonic waveguides were experimentally probed with single photons.A measurement of the secondorder quantum coherence function yielded a value of g (2) (0) = 0.160 ± 0.002.A value less than 0.5 is indicative of single-excitation states.Furthermore, to confirm successful SPP excitation, the transverse-magnetic mode restriction and exponential decay of SPPs were verified.Having firmly established the ability to probe plasmonic waveguides in the classical and quantum regimes, quantum random number generation was implemented using a plasmonic beam splitter.The random bit sequences produced passed the NIST Statisitical Test Suite once post-processed to correct for a slightly asymmetric beamsplitter.