The ability to control multidimensional quantum systems is central to the development of advanced quantum technologies. We demonstrate a multidimensional integrated quantum photonic platform able to generate, control, and analyze high-dimensional entanglement. A programmable bipartite entangled system is realized with dimensions up to 15 × 15 on a large-scale silicon photonics quantum circuit. The device integrates more than 550 photonic components on a single chip, including 16 identical photon-pair sources. We verify the high precision, generality, and controllability of our multidimensional technology, and further exploit these abilities to demonstrate previously unexplored quantum applications, such as quantum randomness expansion and self-testing on multidimensional states. Our work provides an experimental platform for the development of multidimensional quantum technologies.
Graphene-based photodetectors, taking the advantages of high carrier mobility and broadband absorption in graphene, have recently experienced rapid development. However, their performance with respect to responsivity and bandwidth is still limited by weak light-graphene interaction and large resistance-capacitance product. Here, we demonstrate a waveguide coupled integrated graphene plasmonic photodetector on a silicon-on-insulator platform. Benefiting from plasmonic enhanced graphene-light interaction and subwavelength confinement of the optical energy, we achieve a small-footprint grapheneplasmonic photodetector working at the telecommunication window, with large bandwidth beyond 110 GHz and high intrinsic responsivity of 360 mA/W. Attributed to the unique electronic bandstructure of graphene and its ultra-broadband absorption, operational wavelength range extending beyond mid-infrared, and possibly further, can be anticipated. Our results show that the combination of graphene with plasmonic devices has great potential to realize ultra-compact and high-speed optoelectronic devices for graphene-based optical interconnects. arXiv:1808.04815v3 [physics.app-ph]
Quantum key distribution provides an efficient means to exchange information in an unconditionally secure way. Historically, quantum key distribution protocols have been based on binary signal formats, such as two polarization states, and the transmitted information efficiency of the quantum key is intrinsically limited to 1 bit/photon. Here we propose and experimentally demonstrate, for the first time, a high-dimensional quantum key distribution protocol based on space division multiplexing in multicore fiber using silicon photonic integrated lightwave circuits. We successfully realized three mutually unbiased bases in a four-dimensional Hilbert space, and achieved low and stable quantum bit error rate well below both the coherent attack and individual attack limits. Compared to previous demonstrations, the use of a multicore fiber in our protocol provides a much more efficient way to create high-dimensional quantum states, and enables breaking the information efficiency limit of traditional quantum key distribution protocols. In addition, the silicon photonic circuits used in our work integrate variable optical attenuators, highly efficient multicore fiber couplers, and Mach-Zehnder interferometers, enabling manipulating high-dimensional quantum states in a compact and stable manner. Our demonstration paves the way to utilize state-of-the-art multicore fibers for noise tolerance high-dimensional quantum key distribution, and boost silicon photonics for high information efficiency quantum communications.npj Quantum Information (2017) 3:25 ; doi:10.1038/s41534-017-0026-2 INTRODUCTION Quantum key distribution (QKD) is an attractive quantum technology that provides a means to securely share secret keys between two clients (Alice and Bob).1-4 Traditional QKD is based on binary signal formats, such as the BB84 protocol where the quantum information is encoded in the polarization domain.5 Four polarization states create a set of two mutually unbiased basis (MUBs) in a two-dimensional Hilbert space which are used for establishing quantum keys between two parties. In these binary QKD systems the information efficiency is limited to 1 bit/photon. Recently, tremendous efforts have been put into developing novel protocols to increase the information efficiency.6-10 Highdimensional QKD (HD-QKD) based on qudit encoding (unit of information in a N dimension space) is an efficient technique to achieve high information efficiency for QKD systems.
We design and experimentally verify a topology optimized low-loss and broadband two-mode (de-)multiplexer, which is (de-)multiplexing the fundamental and the first-order transverse-electric modes in a silicon photonic wire. The device has a footprint of 2.6 µm x 4.22 µm and exhibits a loss <1.2 dB in a 100 nm bandwidth measured around 1570 nm. The measured cross talk is <-12 dB and the extinction ratio is >14 dB in the C-band. Furthermore, we demonstrate that the design method can be expanded to include more modes, in this case including also the second order transverse-electric mode, while maintaining functionality.
Graphene opens up for novel optoelectronic applications thanks to its high carrier mobility, ultralarge absorption bandwidth, and extremely fast material response. In particular, the opportunity to control optoelectronic properties through tuning of Fermi level enables electro-optical modulation, optical-optical switching, and other optoelectronics applications. However, achieving a high modulation depth remains a challenge because of the modest graphene-light interaction in the graphene-silicon devices, typically, utilizing only a monolayer or few layers of graphene. Here, we comprehensively study the interaction between graphene and a microring resonator, and its influence on the optical modulation depth. We demonstrate graphene-silicon microring devices showing a high modulation depth of 12.5 dB with a relatively low bias voltage of 8.8 V. On-off electro-optical switching with an extinction ratio of 3.8 dB is successfully demonstrated by applying a square-waveform with a 4 V peak-to-peak voltage.Key words: graphene photonics, silicon microring resonator, electro-optical modulation, high modulation depth In addition to holding novel electronic properties, graphene is now also emerging as a material of interest in the area of optoelectronics. Graphene has many unique properties, such as zero-band gap and tunable Fermi level [1, 2], ultra-broad absorption bandwidth [3,4], high carrier mobility around 200000 cm 2 V -1 s -1 at room temperature [5,6], and a super high Kerr coefficient for high nonlinearity applications [7,8]. Those interesting properties give rise to many potential applications [9,10], such as wafer-scale integrated circuits [11], solar cells [12,13], high-speed graphene-silicon electro-optical modulators [14][15][16], optical-optical switches [17,18], saturation absorbers [19][20][21], photodetectors [22][23][24], and nonlinear media for four-wave mixing (FWM) [25,26].The deployment of graphene on top of a silicon waveguide is an efficient mean to make graphene-silicon hybrid devices. In order to electrostatically tune the Fermi level of graphene, there is a need to sandwich a thin layer of material with a high dielectric constant (e.g. Al 2 O 3 [27,28] or Si 3 N 4 [29]) between the silicon layer and the added layer of graphene. When this graphene-silicon capacitor is biased, carriers can be either accumulated on the graphene sheet, or swept out from the graphene sheet, resulting in a convenient tuning of the Fermi level and, thus, optical absorption [14]. This technology has enabled highspeed electro-optical modulators [14][15][16]. However, the strong light confinement in the high-index silicon gives a modest optical field overlap with the graphene layer. Hence, the graphene-light interaction is consequently too low to obtain a significant modulation depth. In order to enhance the modulation depth,
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