Applied Physics
Applications based on quantum optics depend on the ability to produce and detect single photons and to reliably send them around circuits where the information they carry can be manipulated. Most approaches to date have been modular, with photon production, detection, and manipulation being separate elements. The poor coupling between these separate elements incurs high losses that render reliable applications impractical. Gerrits et al. have developed an integrated approach that combines a superconducting transition edge sensor capable of resolving individual photons with a silica optical waveguide. The integrated on-chip approach results in low losses for the photons and therefore presents a feasible route toward scalable photonic quantum processing devices that are sufficiently complex to be useful in applications such as quantum computing, metrology, and simulation.
Phys. Rev. A 84 , 60301R (2011)
Applied Physics
Applications based on quantum optics depend on the ability to produce and detect single photons and to reliably send them around circuits where the information they carry can be manipulated. Most approaches to date have been modular, with photon production, detection, and manipulation being separate elements. The poor coupling between these separate elements incurs high losses that render reliable applications impractical. Gerrits et al. have developed an integrated approach that combines a superconducting transition edge sensor capable of resolving individual photons with a silica optical waveguide. The integrated on-chip approach results in low losses for the photons and therefore presents a feasible route toward scalable photonic quantum processing devices that are sufficiently complex to be useful in applications such as quantum computing, metrology, and simulation.
Phys. Rev. A 84 , 60301R (2011)
Quantum information science aims to harness uniquely quantum mechanical properties to enhance measurement and information technologies, and to explore fundamental aspects of quantum physics. Of the various approaches to quantum computing [1], photons are particularly appealing for their low-noise properties and ease of manipulation at the single qubit level [2]. Encoding quantum information in photons is also an appealing approach to quantum communication, metrology (eg. [3]), measurement (eg. [4]) and other quantum technologies [5]. However, the implementation of optical quantum circuits with bulk optics has reached practical limits. We have developed an integrated waveguide approach to photonic quantum circuits for high performance, miniaturisation and scalability [6]. Here we report high-fidelity silica-on-silicon integrated optical realisations of key quantum photonic circuits, including two-photon quantum interference and a controlled-NOT logic gate [7]. We have demonstrated controlled manipulation of up to four photons on-chip, including high-fidelity single qubit operations, using a lithographically patterned resistive phase shifter [8]. We have used this architecture to implement a small-scale compiled version of Shorʼs quantum factoring algorithm [9] and demonstrated heralded generation of tuneable four photon entangled states from a six photon input [10]. We have combined waveguide photonic circuits with superconducting single photon detectors [11]. We describe complex quantum interference behaviour in multi-mode interference devices with up to eight inputs and outputs [12], and quantum walks of correlated particles in arrays of coupled waveguides [13]. Finally, we give an overview of our recent work on fundamental aspects of quantum measurement [14,15] and single photon sources [16,17].
Quantum information science aims to harness uniquely quantum mechanical properties to enhance measurement and information technologies, and to explore fundamental aspects of quantum physics. Of the various approaches to quantum computing [1], photons are particularly appealing for their low-noise properties and ease of manipulation at the single qubit level [2,3]. Encoding quantum information in photons is also an appealing approach to quantum communication, metrology (eg. [4]), measurement (eg. [5]) and other quantum technologies [6]. However, the implementation of optical quantum circuits with bulk optics has reached practical limits. We have developed an integrated waveguide approach to photonic quantum circuits for high performance, miniaturization and scalability [7]. Here we report high-fidelity silica-on-silicon integrated optical realizations of key quantum photonic circuits, including two-photon quantum interference and a controlled-NOT logic gate [8]. We have demonstrated controlled manipulation of up to four photons on-chip, including highfidelity single qubit operations, using a lithographically patterned resistive phase shifter [9]. We have used this architecture to implement a small-scale compiled version of Shor's quantum factoring algorithm [10], demonstrated heralded generation of tunable four photon entangled states from a six photon input [11], a reconfigurable two-qubit circuit [12], and combined waveguide photonic circuits with superconducting single photon detectors [13]. We describe complex quantum interference behavior in multi-mode interference devices with up to eight inputs and outputs [14], and quantum walks of correlated particles in arrays of coupled waveguides [15]. Finally, we give an overview of our recent work on fundamental aspects of quantum measurement [16,17] and diamond [18,19] and nonlinear [20,21] photon sources.
Optical chips for quantum photonics are cutting-edge technology, merging photonics and quantum mechanics to manipulate light at the quantum level. These chips are crucial for advancing quantum computing, secure communication, and precision sensing by integrating photonic components such as waveguides, beam splitters, and detectors to manipulate single photons, the fundamental carriers of quantum information. Key advancements in optical chips include low-loss waveguides, efficient single-photon sources, and high-fidelity quantum gates, all essential for scalable quantum circuits. Integrating these circuits on a chip offers significant advantages in miniaturization, stability, and reproducibility over traditional bulk optics setups. Recent breakthroughs in materials science and nanofabrication have propelled the field forward, enabling the production of chips with higher precision and lower defect rates. Silicon photonics, in particular, has become a prominent platform due to its compatibility with existing semiconductor manufacturing processes, facilitating the integration of quantum photonic circuits with classical electronic systems. Here, we share our vision of the future of optical chips for quantum photonics, which hold promise for various applications. In quantum computing, they enable the development of compact and scalable quantum processors. In communication, they provide the foundation for ultra-secure quantum networks through quantum key distribution. In sensing, they allow for high-precision measurements that surpass classical limits. As research progresses, optical chips are expected to play a critical role in realizing the full potential of quantum technologies.
In the past decades quantum optics has been at the forefront of quantum innovative technologies. For practical applications, scalable platforms for implementation of quantum optical circuits are vital. This thesis presents two new platforms for scalable implementation of quantum optical circuits, namely, modular approach and monolithic integration. Here, we take the first steps towards the integration of three main elements of every quantum optics circuits: Single-photon emitters, single-photon detectors, and quantum logics. Until now, most quantum optical circuits used separate platforms for single-photon generation and detection. The main challenge in the integration of these technologies, which have different requirements, has slowed down the research in the field. Here, we integrate sources and detectors by first fabricating the devices on their own platform and then transferring and combining them together. Plasma enhanced chemical vapor deposition of silicon nitride followed by etching optical waveguides connect these elements. Removing the Poissonian optical excitation field from the quantum circuit is necessary for integration. Classical optical excitation can be avoided if the sources are electrically pumped. However, fabrication of high-quality electrically pumped sources, suitable for integration, has been limited. The experiments described in chapter 4 are our first step towards addressing the mentioned problem. Defect-free nanowires are grown on <100> direction and their optoelectronic performance are characterized. Nanowire quantum dots, thanks to their waveguiding, purity, coherence and their potentials for deterministic integration with other optical circuits, are promising single-photon sources for on-chip quantum optics. However, precise control of the emission energy of the quantum dots by growth has not become possible yet. Chapter 5 describes a method for on-chip tuning of emission energy of nanowire quantum dots using strain fields. We show the emission energy of independent nanowire quantum dots can be brought into degeneracy without affecting their single-photon emission properties. The quantum optical components have to be routed and connected together to form functional circuits. On a chip, this is usually carried out using optical waveguides. Moreover, manipulation of single photons has to be done in a scalable fashion. Again optical waveguides and ring resonators are very good candidates for this task. Therefore, understanding the behavior of these circuits such as their losses, polarization dependence, and temperature behavior is important. The experiment described in chapter 6 studies the behavior of plasma enhanced silicon nitride waveguides in cryogenic temperatures. We concluded in this chapter that due to weak thermo-optic sensitivity of silicon nitride at cryogenic temperatures, the available thermal budget on the system should be carefully considered. An important step in achieving a scalable platform for quantum optical circuits is deterministic and efficient integration of single-photon sources. In chapter 7, we demonstrate successful integration of III-V nanowire quantum dots with silicon nitride waveguides. The nanowires are deterministically selected and transferred from the original growth chip to the new substrate where they are integrated with low-loss silicon nitride waveguides. Our measurements show that the integrated sources preserve their high quality emission properties. In chapter 8, we describe an alternative approach: amodular method for scalable quantum optics. The proposed technique is based on coupling the single-photon from sources into optical fibers where the photons can be processed and then fed into the single-photon detectors. This approach has high flexibility and is easier to implement but as described in the chapter, at the moment, losses in the interfaces between optical fibers and single-photon sources are a major limiting factor. We conclude the thesis with some possible future directions and exciting new results on integration of single-photon detectors with sources and waveguides. Finally, primary results on on-chip single-photon filtering and removal of the optical excitation field are demonstrated.
We develop quantum devices for the generation, manipulation and detection of light at the single photon level. Quantum dot devices allow for the generation of single and entangled photons at various frequencies including telecom wavelengths. We also develop single photon detectors with high efficiency based on NbTIN superconducting nanostructures, low noise and high time resolution to enable a range of applications including quantum communication, quantum sensing and integrated photonics. To allow for complex systems, integrated quantum optics circuits where we combine quantum sources and superconducting detectors are under development.
Direct UV-written silica-on-silicon provides an attractive platform for quantum optics, offering the key benefits of low propagation losses and excellent optical fibre compatibility. This work has aimed to develop the necessary techniques and components for completely integrated quantum optics experiments to be carried out using this platform, on a larger scale than previously possible. Arrays of matched on-chip photon sources based on birefringence-matched spontaneous four-wave mixing (FWM) are demonstrated, both at 800 nm and in the telecommunications C-band, along with progress towards further integration of these sources. Thermo-optic phase shifters, for use in room temperature quantum circuits, have been optimised via modelling, and a range of alternative modulator technologies have been explored. Further work has been concerned with the development of a modular system for quantum optics, comprising a set of duplicate reconfigurable modules and the necessary drive electronics and software, with the intent of simplifying the task of identifying and quantifying manufacturing imperfections in large integrated experiments. Efforts have also been made to improve the detection efficiency of on-chip transition edge sensor (TES) single photon detectors, including the use of longer absorbers and high reflectors for multiple absorption passes; this has resulted in the demonstration of a photon-number-resolving detector with a Bragg grating enhanced quantum efficiency of 87%. Approaches for further increasing the detection efficiency are considered and a device for on-chip Hong-Ou-Mandel and photon subtraction experiments using these detectors is reported.