Single photon detection and manipulation in photonic integrated circuits

• Main Author: Yanikgonul, Salih
• Other Authors: Cesare Soci
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2021
• Subjects: Engineering::Electrical and electronic engineering::Optics, optoelectronics, photonics; Science::Physics::Atomic physics::Solid state physics
• Online Access: https://hdl.handle.net/10356/151499
• Institution: Nanyang Technological University

One way to achieve a scalable quantum computing and communication platform is to construct a network of quantum systems. Building a quantum network with photonic integrated circuits (PICs) is a promising avenue as they provide a platform on which quantum information can be generated and manipulated via integrated photonic structures. One such example would be a hybrid PIC with quantum light sources, modulators, interferometers, and single-photon detectors for complete on-chip single-photon processing. To date, reports of waveguide-coupled single-photon detectors have been limited to operation at infrared telecommunication wavelengths. However, many relevant quantum systems operate in the visible spectrum, which makes efficient, low-noise integrated single-photon detectors for visible wavelengths highly desirable. In addition to on-chip detection, coherent modulation of photon states is of paramount importance for integrated quantum information processing. In this regard, the novel concept of coherent perfect absorption (CPA) provides new ways of controlling quantum states of light in hybrid quantum systems. Compared to conventional Mach-Zehnder intensity modulators which only redistribute photons between two outputs, interferometric modulators based on CPA can deterministically prevent the propagation of residual photons in complex networks and eliminate undesired interference or crosstalk at other network arms. Such a hybrid platform holds the promise of performing linear optical quantum computing (LOQC) protocols in a scalable architecture with on-chip readout of quantum information. This thesis focuses on manipulation and detection of photons in its two parts. In the first part, a new class of silicon waveguide-integrated avalanche photodiodes (APDs) on silicon-on-insulator photonic platform for visible wavelengths are designed, fabricated, and characterized. The devices with p-n + and p-i-n + junction structures and various geometries are investigated, and 2D Monte Carlo simulations are performed in order to optimize device performance. Operated in linear mode at 685 nm, we achieved a gain-bandwidth product exceeding 200 GHz along with a sub- µA dark current, which are on par or even superior to state-of-the-art similar devices. Operated in Geiger mode, it turns out that our devices are affected by high dark count rate for which we provide in-depth analysis and propose solutions. The second part of the thesis focuses on single photon manipulation experiments per-formed by phase-stabilized interferometers with CPA capability. With the end goal of an integrated CPA interferometer, we tested our ideas of coherent control of single photons via CPA on a coherent optical fiber network and proved their applicability. Besides serving as an easily accessible testbed, such optical fiber networks are also indispensable for long haul distribution and exchange of quantum information. Regardless of being integrated or fiberized, a fundamental challenge to any interferometer operation is phase noise; its elimination without degrading the efficiency of quantum channels is of the upmost importance to protect quantum coherence. To deal with the phase noise, fiberized quantum optics experiments often employ resource demanding stabilization techniques, which cause additional losses and possible interference on the quantum channel. Here, first, we develop an active phase stabilization scheme by single-photon counting, and then apply it to a quantum network operating at the single-photon level. Our method can overcome the phase noise with no need for auxiliary laser and additional optical components required in conventional approaches, and it achieved a competitive phase stability while preserving the efficiency of quantum channels. Next, we show that a phase-stabilized interferometric modulator based on CPA can be used to control the absorption probability of single photons via phase modulation. We demonstrate that CPA at the single-photon level can be used for all-optical dissipative single-photon switching, which provides increased functionalities over nonlinear approaches for all-optical signal processing. Moreover, by utilizing different optical response of our CPA interferometer to symmetric and anti-symmetric wavefunctions of photons, we showed an application of our coherent network in filtering quantum states of photons where quantum information is encoded in superposition of two spatial modes. Our work may find applications in quantum information protocols such as in dual-rail encoding. Harnessing the functionality of different physical systems for storage, processing, and readout of quantum information, hybrid photonics approach described in this thesis provides a viable path towards scalable quantum information processing. In this thesis, we reported the first integrated avalanche photodetection at visible wavelengths, and by tailoring optical properties of designer materials, we achieved two successful demonstrations of quantum light manipulation in coherent optical networks stabilized by our phase stabilization method. Overcoming hybrid integration and device engineering challenges would pave the way for performing on-chip LOQC with integrated readout capability.