Massless particle photon has been serving as the information carrier in a large number of classical communication systems in the form of electromagnetic waves. With the advancements in quantum optics, due to the progress in the design and development of high-quality optical cavities and improvements in the connement of atoms, ions, and molecules using sophisticated optical traps and optical lattices, individual photons can now be generated, manipulated, and guided. These capabilities of controlling individual photons herald the emergence of quantum communication systems used in quantum optics [1-4]. Quantum communication is the art of communicating quantum states between spatially separated locations. A photon is generally used as the carrier for transferring quantum information (encoded into quantum states) from the transmit node to the receive node of the quantum communication system.
Massless particle photon has been serving as the information carrier in a large number of classical communication systems in the form of electromagnetic waves. With the advancements in quantum optics, due to the progress in the design and development of high-quality optical cavities and improvements in the connement of atoms, ions, and molecules using sophisticated optical traps and optical lattices, individual photons can now be generated, manipulated, and guided. These capabilities of controlling individual photons herald the emergence of quantum communication systems used in quantum optics [1-4]. Quantum communication is the art of communicating quantum states between spatially separated locations. A photon is generally used as the carrier for transferring quantum information (encoded into quantum states) from the transmit node to the receive node of the quantum communication system.
Photons are very promising resources for the whole field of quantum information processing. Bulk optics are currently not suitable for the realization of complex quantum optical schemes due to several drawbacks. The ongoing miniaturization of photonic structures due to the availability of sophisticated nanofabrication has provided huge opportunities for physical research of novel phenomena in nanophotonic systems and quantum technological applications. These include quantum information processing such as quantum computing, quantum communication, quantum metrology, and quantum sensing. Quantum communication is already quite advanced with several quantum key distribution (QKD) systems commercially available offering absolute security. Photonic quantum technologies are enabling breakthroughs in experimental tests of quantum physics and are close to practical applications of quantum technologies in imaging, secure communications, ultrasensitive metrology and quantum computing. There are several advantages to encoding a quantum bit onto a photon: the preparation and manipulation of single photons is easy, and the photonic qubit is a natural candidate for quantum imaging and communications. Furthermore, the qubit can be encoded in various degrees of freedom such as on the position, phase, time-bin, energy, angular momentum, polarization of the photon—or a combination of these. This flexibility leads to enormous opportunities for scientific exploration and in practical applications. This special issue on “Photonic Quantum Technologies” presents selected papers on photonic quantum systems from leading groups in the world. The articles represent a flavor of the cutting-edge research that is going on in this area. The studied material systems range from molecules to semiconductor quantum emitters. A major challenge is the design of telecom photon emitters with high efficiency, good yield, spectral purity, stability and the possibility of mass manufacture. We believe that this Special Issue will provide an overview of recent exciting developments in the field of photonic quantum technologies, serving to keep researchers up-to-date with the latest progress and spurring on new concepts in this field.
Nanophotonics describes optical science and technology at the nanoscale that offers challenging opportunities for studying fundamental processes of interaction between the radiation eld and the matter on a scale much smaller than the wavelength of radiation. The use of such conned interaction to spatially localized processes offers exciting opportunities to chemists. Nanophotonics is considered to be of immense technological signicance. The evolution and development of the nanophotonics technology with the increased need for an internetworking broadband communication had lead to the development of more sophisticated optical networks. Those networks are now interconnected CONTENTS Summary ........................................................................................................................................ 21 2.1 Introduction ..........................................................................................................................22 2.2 Nanometer Connement and Fabrication of Matter ......................................................22 2.3 Application of Computational Intelligence in Photonics Technology .........................23
Quantum communication and quantum computation are novel methods of information transfer and information processing, all fundamentally based on the principles of quantum physics. The performances outdo their classical counterparts in many aspects [1,2]. In almost all quantum communication and quantum computation schemes, quantum entanglement [3] plays a decisive role. In essence, an entangled system can carry all information (e.g., on their polarization properties) only in their correlations, while no individual subsystem carries any information. This leads to correlations that are much stronger than classically allowed [89, 100], which is a powerful resource for information processing. It is therefore important to be able to generate, manipulate, and distribute entanglement as accurately and as efficiently as possible.
Quantum networks hold the potential to enable quantum-secured communication, distributed quantum computing, and non-local quantum sensing. To realize these applications, a versatile quantum network infrastructure must support entanglement between network nodes capable of storing, processing, and distributing quantum information, alongside high-fidelity photonic qubits that efficiently interface with these nodes. The silicon-vacancy (SiV) center in diamond, coupled to nanophotonic cavities, has recently emerged as a promising platform to meet these requirements. This system provides access to an electron spin as an optically active communication qubit and a 29Si nuclear spin as a memory qubit, capable of storing quantum information for extended periods. We first demonstrate that the SiV center's electron spin can efficiently generate single photons with complex spatiotemporal waveforms, facilitated by a novel asymmetric nanophotonic cavity design. We then establish a two-node quantum network between two SiV centers housed in separate laboratories and connected via optical fiber. To do so, we use photonic qubits to mediate entanglement between two spatially separated electron spins, as well as between two spatially separated nuclear spins. Finally, using bidirectional quantum frequency conversion, we convert the photonic qubits to telecommunication frequencies, enabling entanglement generation between the two nuclear spins via a 35 km fiber deployed in the Boston metropolitan area. These advancements mark progress toward large-scale, deployable quantum networks using SiV centers coupled to nanophotonic cavities.
Underlying matter and light are their building blocks of tiny atoms and photons. The ability to control and utilize matter-light interactions down to the elementary single atom and photon level at the nano-scale opens up exciting studies at the frontiers of science with applications in medicine, energy, and information technology. Of these, an intriguing front is the development of quantum networks where N >> 1 single-atom nodes are coherently linked by single photons, forming a collective quantum entity potentially capable of performing quantum computations and simulations. Here, a promising approach is to use optical cavities within the setting of cavity quantum electrodynamics (QED). However, since its first realization in 1992 by Kimble et al., current proof-of-principle experiments have involved just one or two conventional cavities. To move beyond to N >> 1 nodes, in this thesis we investigate a platform born from the marriage of cavity QED and nanophotonics, where single atoms at ~100 nm near the surfaces of lithographically fabricated dielectric photonic devices can strongly interact with single photons, on a chip. Particularly, we experimentally investigate three main types of devices: microtoroidal optical cavities, optical nanofibers, and nanophotonic crystal based structures. With a microtoroidal cavity, we realized a robust and efficient photon router where single photons are extracted from an incident coherent state of light and redirected to a separate output with high efficiency. We achieved strong single atom-photon coupling with atoms located ~100 nm near the surface of a microtoroid, which revealed important aspects in the atom dynamics and QED of these systems including atom-surface interaction effects. We present a method to achieve state-insensitive atom trapping near optical nanofibers, critical in nanophotonic systems where electromagnetic fields are tightly confined. We developed a system that fabricates high quality nanofibers with high controllability, with which we experimentally demonstrate a state-insensitive atom trap. We present initial investigations on nanophotonic crystal based structures as a platform for strong atom-photon interactions. The experimental advances and theoretical investigations carried out in this thesis provide a framework for and open the door to strong single atom-photon interactions using nanophotonics for chip-integrated quantum networks.
Quantum communication leverages the physical properties of entanglement and superposition to create networks capable of connecting quantum computers, sensors, and secure nodes. Photons are a particularly viable information vehicle as they are unaffected by a broad range of environmental variables. They are also very versatile, supporting the teleportation of quantum information upon interacting with information-carrying qubits, whether these qubits are generated by a quantum computer or a random qubit source. Existing and emerging technologies will be discussed, as well as perspectives on the open challenges of the field.