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Photonics for Quantum (PfQ)

Generating and manipulating high dimensional path entanglement on a silicon photonic chip

Gregory A. Howland

Published Jul 19, 2023• 0 citations
Publisher

Abstract

Silicon photonic foundries offer one path for scaling quantum photonic integrated circuits to useful sizes composed of many circuit elements. I will describe our group’s work using the AIM Photonics Foundry to create sources of high-dimensional entanglement across many waveguide paths by exciting arrays of microring-resonator photon pair sources in parallel. Aspects of our work include efficient schemes to certify and quantify entanglement, multi-mode components for manipulating high-dimensional states of light, and advanced packaging techniques.

DOI
10.1117/12.2674879

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Silicon photonic foundries offer one path for scaling quantum photonic integrated circuits to useful sizes composed of many circuit elements. I will describe our group’s work using the AIM Photonics Foundry to create sources of high-dimensional entanglement across many waveguide paths by exciting arrays of microring-resonator photon pair sources in parallel. Aspects of our work include efficient schemes to certify and quantify entanglement, multi-mode components for manipulating high-dimensional states of light, and advanced packaging techniques.
We present a silicon photonic integrated circuit (PIC) designed to generate high-dimensional (HD) entanglement across four discrete waveguide path modes. Our PIC is foundry fabricated and fully packaged with electrical wirebonds and an epoxy bonded fiber array. We performed a partial characterization of our system’s density matrix by demonstrating spectral indistinguishability of photon pairs, measuring the joint coincidence distribution of photon pairs across all pairs of output modes, and measuring the coherences of different mode pairs using two-photon interference. Using a quantitative entanglement witness, we have determined that our system generates at least 1.45 ± 0.15 ebits of HD photonic entanglement.
Silicon quantum photonics promises to take quantum optics to the large scale, where single photons carry the quantum information which can accelerate difficult computational problems, provide perfectly secure communication, or allow high-accuracy measurements. The silicon photonics platform offers miniature, high-yield, and high-performance photonics which are integrable with CMOS electronics and telecommunications-band optics. To date, only non-scalable photon-pair sources, based on spontaneous four-wave mixing (SFWM) in straight silicon waveguides have been shown to interfere [1]. Until now, single-photon experiments in silicon [2] have exclusively used an off-chip apparatus, such as a silica arrayed waveguide grating, to control and manipulate photon frequency. We present a silicon-on-insulator quantum photonic device (Fig. 1a) able to generate and analyse two maximally entangled qubits. We use this device to demonstrate high-visibility quantum interferencebetween resonant SFWM sources (analogous to [1]), phase-stable frequency-selection, and quantum state tomography. We varied the phase  to obtain the fringes shown in Fig. 1b, with a visibility of 96.8%. This high visibility indicates that the two microring sources are substantially identical. We setup the entangled state via the on-chip 17-dB extinction filters, and used quantum state tomography to analyse it (Fig. 1c). We measured a fidelity of 0.8. This is the first time an entangled state of photonic qubits has been both generated and analysed on-chip, and this generation has been done in a way which is scalable to larger photon number. These results represent a new step towards fully silicon-integrated quantum photonics.
Abstract Entanglement is a counterintuitive feature of quantum physics that is at the heart of quantum technology. High-dimensional quantum states offer unique advantages in various quantum information tasks. Integrated photonic chips have recently emerged as a leading platform for the generation, manipulation and detection of entangled photons. Here, we report a silicon photonic chip that uses interferometric resonance-enhanced photon-pair sources, spectral demultiplexers and high-dimensional reconfigurable circuitries to generate, manipulate and analyse path-entangled three-dimensional qutrit states. By minimizing on-chip electrical and thermal cross-talk, we obtain high-quality quantum interference with visibilities above 96.5% and a maximally entangled-qutrit state with a fidelity of 95.5%. We further explore the fundamental properties of entangled qutrits to test quantum nonlocality and contextuality, and to implement quantum simulations of graphs and high-precision optical phase measurements. Our work paves the path for the development of multiphoton high-dimensional quantum technologies.
Abstract High-dimensional quantum entanglement is an important resource for emerging quantum technologies such as quantum communication and quantum computation. The scalability of metres-long experimental setups limits high-dimensional entanglement in bulk optics. Advancements in quantum technology hinge on reproducible, and reconfigurable quantum devices—including photon sources, which are challenging to achieve in a scalable manner using bulk optics. Advances in nanotechnology and CMOS-compatible integration techniques have enabled the generation of entangled photons on millimeter-scale chips, significantly enhancing scalability, stability, replicability, and miniaturization for real-world quantum applications. In recent years we have seen several chip-scale demonstrations with different discrete degrees of freedom including path, frequency-bin, time-bin, and transverse modes, on many material platforms. A complete quantum photonic integrated circuit requires the generation, manipulation, and detection of quantum states, involving various active and passive quantum photonic components which further increase the degree of complexity. Here, we focus on the high-dimensional versions of qubits—qudits—and review the nonlinear optical processes that facilitate on-chip high-dimensional entangled photon sources, and the currently used material platforms. We discuss a range of current implementations of on-chip high-dimensional entangled photon sources and demonstrated applications. We comment on the current challenges due to the limitations of individual material platforms and present future opportunities in hybrid and heterogeneous integration strategies for the next generation of integrated quantum photonic chips.