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arXiv:1110.0660 · New Journal of Physics

A quantum relay chip based on telecommunication integrated optics technology

Anthony Martin, Olivier Alibart, Marc de Micheli, Daniel B. Ostrowsky, Sébastien Tanzilli

Published Feb 1, 2012• 71 citations
arXivHTMLPDF

Abstract

We investigate an integrated optical circuit on lithium niobate designed to implement a teleportation-based quantum relay scheme for one-way quantum communication at a telecom wavelength. Such an advanced quantum circuit merges for the first time both optical–optical and electro-optical nonlinear functions necessary for implementing the desired on-chip single-qubit teleportation. On the one hand, spontaneous parametric down-conversion is used to produce entangled photon pairs. On the other, we take advantage of two photon routers, consisting of electro-optically controllable couplers, to separate the paired photons and to carry out a Bell state measurement, respectively. After having validated all the individual functions in the classical regime, we performed a Hong–Ou–Mandel experiment to mimic a one-way quantum communication link. Such a quantum effect, seen as a prerequisite towards achieving teleportation, has been obtained at one of the routers when the chip was coupled to an external single-photon source. The two-photon interference pattern shows a net visibility of 80%, which validates the proof of principle of a 'quantum relay circuit' for qubits carried by telecom photons. In the case of optimized losses, such a chip could increase the maximal achievable distance of one-way quantum key distribution links by a factor of 1.8. Our approach and results emphasize the potential of integrated optics on lithium niobate as a key technology for future reconfigurable quantum information manipulation.

DOI
10.1088/1367-2630/14/2/025002

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We investigate an integrated optical circuit on lithium niobate designed to implement a teleportation-based quantum relay scheme for one-way quantum communication at a telecom wavelength. Such an advanced quantum circuit merges for the first time both optical–optical and electro-optical nonlinear functions necessary for implementing the desired on-chip single-qubit teleportation. On the one hand, spontaneous parametric down-conversion is used to produce entangled photon pairs. On the other, we take advantage of two photon routers, consisting of electro-optically controllable couplers, to separate the paired photons and to carry out a Bell state measurement, respectively. After having validated all the individual functions in the classical regime, we performed a Hong–Ou–Mandel experiment to mimic a one-way quantum communication link. Such a quantum effect, seen as a prerequisite towards achieving teleportation, has been obtained at one of the routers when the chip was coupled to an external single-photon source. The two-photon interference pattern shows a net visibility of 80%, which validates the proof of principle of a 'quantum relay circuit' for qubits carried by telecom photons. In the case of optimized losses, such a chip could increase the maximal achievable distance of one-way quantum key distribution links by a factor of 1.8. Our approach and results emphasize the potential of integrated optics on lithium niobate as a key technology for future reconfigurable quantum information manipulation.
Periodically poled lithium niobate waveguides (PPLN/W) are nowadays considered to be one of the most useful toolboxes for quantum communication experiments. Thanks to the high optical confinement over longer lengths than in bulk configurations (a few cm in our case), such structures provide highly efficient non-linear interactions, both in down- and up-conversion regimes. Within the framework of long-distance quantum communication at telecom wavelength, PPLN/Ws have therefore been proved to be a key ingredient for building ultra-bright sources of energy-time, time-bin, as well as polarization entangled pairs of photons, up-conversion based detectors for telecom photon detection and photonic quantum interfaces for coherent wavelength conversion, as well as quantum relays in the entanglement swapping configuration. During the presentation, we will discuss some recent experimental advances regarding two quantum relay scenarios employed to extend the maximum achievable distance of quantum communication. Based on picosecond regime operation, the first relies on the entanglement swapping configuration, and the other on single qubit teleportation using a telecom oriented chip dedicated to one-way quantum communication. In the first realization, we demonstrate that the utilization of PPLN/Ws and standard components available from the telecommunications industry, associated with the picosecond operation regime enables reaching near-perfect two-photon interference (or coalescence) while maintaining high effective photon pair rates. Using pairs of photons emitted around 1550 nm and appropriate filtering stages, we obtain the highest coalescence net visibility, i.e., of 99%, ever reported. As coalescence is seen a major step towards entanglement swapping, we believe that our picosecond guided-wave scheme provides an efficient trade-off between CW and femtosecond regimes, and emphasize why it should lead to realistic quantum relay and repeater schemes, namely by offering an reduced-constraint solution to the synchronization issue when two completely independent lasers are employed. We shall focus on our experimental demonstration and detail a comparative study of performance with similar reported experiments. As a second realization, we will give further directions towards the integration of several functions on a single optical chip, such as a photon pair generator and electro-optically controllable couplers. The idea is to realize a telecom-like quantum relay chip on lithium niobate through which teleportation of single qubits can be done so as to provide the necessary relay function in a compact, stable, efficient, and user-friendly fashion. We will discuss preliminary results obtained with this device for fully fiber-based one-way quantum communication systems. We will conclude by emphasizing the large potential of what we call "guided-wave quantum communication" developed in our laboratory.
This manuscript presents the numerical study, manufacture processes, and experimental characterization of an integrated optical circuit intended to be at the heart of a quantum relay particularly designed for qubits encoded on photos as telecom wavelengths. In spite of progress in photonics and telecommunications technologies, losses in optical fibres and especially darkcounts in the detectors limit the maximum achievable distance for quantum communication to about a hundred kms. The quantum relay, based on quantum teleportation, makes it possible to increase the communication signal-to-noise ratio and thus to push this maximum distance forward. In this context, we show that integrated optics offers compact and stable components suitable for insertion of a “relay-ship” in fibre-based quantum communication systems. We adapted a quantum relay model to our particular case showing the relevance of such a structure with realistic parameters. Subsequently we determined the properties of all the necessary optical functions using BPM simulation. Actually, a photon-pair source and two electro-optically controlled, 50 / 50 beam splitters have to be merged on a single chip. In addition, tapered-waveguide sections have been designed at each input / output of the chip in order to improve coupling between fibres and integrated structures. All the required optical functions on the chip were tested and validated by performing characterizations in both classical and single-photon regimes. As a conclusion, we showed that this “quantum relay-chip” could increase the maximal achievable distance of a quantum communication link by a factor of 1,7.
A consequent tendency toward high-performance quantum information processing is to develop the fully integrated photonic chip. Here, we report the on-chip generation and manipulation of entangled photons based on reconfigurable lithium-niobate waveguide circuits. By introducing a periodically poled structure into the waveguide circuits, two individual photon-pair sources with a controllable electro-optic phase shift are produced within a Hong-Ou-Mandel interferometer, resulting in a deterministically separated identical photon pair. The state is characterized by 92.9±0.9% visibility Hong-Ou-Mandel interference. The photon flux reaches ∼1.4×10(7) pairs nm-1 mW-1. The whole chip is designed to contain nine similar units to produce identical photon pairs spanning the telecom C and L band by the flexible engineering of nonlinearity. Our work presents a scenario for on-chip engineering of different photon sources and paves the way to fully integrated quantum technologies.
Integrated quantum optics becomes a consequent tendency towards practical quantum information processing. Here, we report the on-chip generation and manipulation of photonic entanglement based on reconfigurable lithium niobate waveguide circuits. By introducing periodically poled structure into the waveguide interferometer, two individual photon-pair sources with controllable phase-shift are produced and cascaded by a quantum interference, resulting in a deterministically separated identical photon pair. The state is characterized by 92.9% visibility Hong-Ou-Mandel interference. Continuous morphing from two-photon separated state to bunched state is further demonstrated by on-chip control of electro-optic phase-shift. The photon flux reaches ~1.4*10^7 pairs nm-1 mW-1. Our work presents a scenario for on-chip engineering of different photon sources and paves a way to the fully integrated quantum technologies.
Progress in integrated photonics enables the combination of several elementary functions on single substrates for the realization of advanced functionalized chips. We report a monolithic integrated quantum photonic realization on lithium niobate, where nonlinear optics and electro-optics properties have been harnessed simultaneously for generating heralded configurable, two-photon states. Taking advantage of a picosecond pump laser and telecom components, we demonstrate the production of various path-coded heralded two-photon states, showing 94% raw visibility for Hong-Ou-Mandel interference. The versatility and performance of such a highly integrated photonic entanglement source enable exploring more complex quantum information processing protocols finding application in communication, metrology and processing tasks.
© 2016 WILEY-VCH Verlag GmbH & Co. KGaA. The on-chip integration of quantum light sources has enabled the realization of complex quantum photonic circuits. However, for the practical implementation of such circuits in quantum information applications, it is crucial to develop sources delivering entangled quantum photon states with on-demand tunability. Here we propose and experimentally demonstrate the concept of a widely tunable quantum light source based on spontaneous parametric down-conversion in a simple nonlinear directional coupler. We show that spatial photon-pair correlations and entanglement can be reconfigured on-demand by tuning the phase difference between the pump beams and the phase mismatch inside the structure. We experimentally demonstrate the generation of split states, robust N00N states, various intermediate regimes and biphoton steering on a single chip. Furthermore we theoretically investigate other regimes allowing all-optically tunable generation of all Bell states and flexible control of path-energy entanglement. Such wide-range capabilities of a structure comprised of just two coupled nonlinear waveguides are attributed to the intricate interplay between linear coupling and nonlinear phase matching. This scheme provides an important advance towards the realization of reconfigurable quantum circuitry. An integrated all-optically tunable source of two-photon quantum states based on spontaneous parametric down-conversion is experimentally demonstrated in a directional coupler consisting of two lithium niobate waveguides. The degree of entanglement and shape of two-photon spatial correlations is widely tunable by varying the phase mismatch and relative phases of the two pump beams. The operating principle is suitable for practical implementation of reconfigurable photon sources in on-chip quantum circuits.