Abstract Devices based on group II–VI semiconductors, and in particular ZnSe, show several advantages for single‐photon sources in comparison to group III–V and group IV devices. Additionally, the spin system of the neutral 19F donor has strong potential as a quantum memory. Here, we summarize these advantages and some initial demonstrations of the promise of 19F:ZnSe for quantum information, including the observation of the interference of photons from independent single 19F:ZnSe emitters and the fabrication of 19F‐doped microdisk cavities showing low‐threshold lasing.
Abstract Devices based on group II–VI semiconductors, and in particular ZnSe, show several advantages for single‐photon sources in comparison to group III–V and group IV devices. Additionally, the spin system of the neutral 19F donor has strong potential as a quantum memory. Here, we summarize these advantages and some initial demonstrations of the promise of 19F:ZnSe for quantum information, including the observation of the interference of photons from independent single 19F:ZnSe emitters and the fabrication of 19F‐doped microdisk cavities showing low‐threshold lasing.
Abstract An optical quantum memory is a device that can store photonic quantum information and release it after a controlled time. It is an essential component for overcoming channel losses in large‐scale quantum networks. Optical quantum memories have been demonstrated with various physical systems including atomic gases, single atoms in optical cavities, and rare‐earth‐ion doped solids. Now, quantum memories are marching toward miniaturization and integration for large‐scale practical applications. Solid state systems stand as a natural choice due to the physical stability and ease of micro or nano fabrication using well‐established techniques. In the past decade, considerable efforts have been devoted to developing photonic integrated quantum memories, that is, quantum memories based on micro/nano‐photonic structures manufactured in solids. Remarkable performances have been achieved with integrated quantum memories, with the advantages of lower laser/electric power requirements, small volumes, large storage densities, and easy implementations. In this article, the basic concepts of optical quantum memories, the state‐of‐the‐art technologies for fabricating integrated quantum memories in rare‐earth ions doped crystals, and recent advances are introduced, and the roadmap for developing practically useful devices for applications in quantum networks is discussed.
We demonstrate quantum interference between photons generated by the radiative decay processes of excitons that are bound to isolated fluorine donor impurities in ZnSe/ZnMgSe quantum-well nanostructures. The ability to generate single photons from these devices is confirmed by auto-correlation experiments, and indistinguishability of single photons from two independent devices is confirmed via a Hong-Ou-Mandel dip. These results indicate that donor impurities in appropriately engineered semiconductor structures can portray atom-like homogeneity and coherence properties, potentially enabling scalable technologies for future large-scale optical quantum computers and quantum communication networks.
Semiconductor provides a physics-rich environment to host various quantum light sources applicable for quantum information processing. These light sources are capable of deterministic generation of non-classical photon streams that demonstrate antibunching photon statistics, strong indistinguishability, and high-fidelity entanglement. Some of them have even successfully transitioned from proof-of-concept to engineering efforts with steadily improving performance [ 1 ] . Here, we briefly summarize recent efforts and progress in the race towards ideal quantum light sources based on semiconductor materials. The focus of this report will be on group III–V semiconductor quantum dots, defects in wide band-gap materials, emitters in two-dimensional van der Waals layered hosts, and carbon nanotubes, as these systems are well-positioned to benefit from recent breakthroughs in nanofabrication and materials growth techniques.
Abstract Rare‐earth dopants are arguably one of the most studied optical centers in solids, with applications spanning from laser optoelectronics, biosensing, lighting to displays. Nevertheless, harnessing rare‐earth dopants’ extraordinary coherence properties for quantum information technologies is a relatively new endeavor, and has been rapidly advancing in recent years. Leveraging the state‐of‐the‐art photonic technologies, on‐chip rare‐earth quantum devices functioning as quantum memories, single photon sources and transducers have emerged, often with potential performances unrivaled by other solid‐state quantum technologies. These existing quantum devices, however, nearly exclusively rely on macroscopic bulk materials as substrates, which may limit future scalability and functionalities of such quantum systems. Thus, the development of new platforms beyond single crystal bulk materials has become an interesting approach. In this review article, we summarize the latest progress towards nanoscale, low‐dimensional rare‐earth doped materials for enabling next generation rare‐earth quantum devices. Different platforms with a variety of synthesis methods are surveyed. Their key metrics measured to date are presented and compared. Special attention is placed on the connection between the topology of each platform to its target device applications. Lastly, an outlook for near term prospects of these platforms are given, with a hope to spur broader interests in rare‐earth doped materials as a promising candidate for quantum information technologies.
The recent developments of optoelectronics do promote the progress in many other fields. For quantum information processing, we made efforts in manufacturing quantum devices by using optoelectronic techniques. We designed quantum dot embedded nanocavities to serve as efficient quantum emitters; using spectral multiplexing technique, we fabricated a heralded single-photon source, emitting highly pure and speedy single photons; and defects in GaN were observed serving as room temperature quantum random number generators. An entangled photon emitter with visibility of 97% was developed using cascaded second-order nonlinear optical process in PPLN waveguides; and Si3N4 microrings were effectively applied to establish photon entanglers. Readout circuits were optimized to fabricate specific single-photon avalanche detectors, and telecomm-band single-photon avalanche detectors have been improved to 128 × 32 arrays for quantum imaging. A multiplexed quantum memory was explored to simultaneously store 1650 single photons. Opto-electro-mechanical devices were studied or fabricated in order to measure minor quantities in quantum level. These works may shed light on quantum information technology for the future.
Several solid-state quantum information processor proposals are based on silicon [16-18, 20, 52], including the original architecture conceived by Kane in 1998 [22], in which the quantum information was stored in the spin states of 31P donors. The interest raised by silicon in the field of quantum information is twofold. On the one hand, it represents the main semiconductor used for large- scale fabrication. On the other hand, it owns interesting physical properties suitable for preserving andmanipulating quantum states, such as long coherence times and relatively low disturbance of nuclear spins, which are further enhanced by employing purified 28Si. The employment of individual donors in silicon covers all the aspects of quantum information encoding and processing, like quantumbit (qubit) storage, implementation of quantum logic gates, coherent transfer of quantum states, and readout schemes. This chapter is devoted to the physics of few dopants in nanometric silicon devices and their applications to quantum information processing purposes. In the first part, an overview of the physics of themost common donors and acceptors in silicon is presented. Next, the quantum information key concepts and their implementation in donor-based architectures are discussed. Finally, decoherence effects and the concept of measurement of quantum states are presented for the case of electron states bound to donors in silicon. Between the sixties and the early eighties of the twentieth century, all the theoretical and experimental aspects related to the doping of bulk silicon have been investigated and explained. A silicon crystal consists of a diamond lattice constituted by two interleaved cubic lattices (face-centered cubic, FCC), the second of which has the origin in the center of the tetrahedron given by the origin (0,0,0) and the centers of the faces 100. Each Si atom has four valence electrons, which create a covalent bond with the shared electrons of four other Si atoms. The substitution of silicon atoms with atoms of a group V element (indicated as donors, typically P, As, and Sb in silicon) generates an n-doped silicon crystal (n-Si). Each donor introduces an eccess electron in the crystal, and it provides new energy levels in the band gap, close to the conduction band edge. Similarly, substituting silicon atoms with atoms of a group III element (an acceptor, typically B in silicon) generates a p-doped silicon crystal (p-Si). Each acceptor introduces an electron hole in the crystal, and it provides new energy levels in the band gap, close to the valence band. The diffusion of impurities in semiconductors alters the conduction properties from an insulating to a metallic regime. Depending on the different doping concentration, the wavefunction of the electron (hole) states introduced by each donor (acceptor) may overlap negligibly or substantially with those of neighboring sites. Such a transition from low doping to high doping as a function of the average distance between neighboring sites is described in terms of an Anderson-Mott transition and produces additional impurity bands (Hubbard bands) below the conduction band edge at sufficiently high concentration [1, 34]. The transport is governed by mechanisms based on localized states at low density, while it is based on delocalized states at high density. Four conventional regimes of impurity concentration are defined [50]. The dilute concentration of impurities holds for n < 1 · 1016 cm−3. There, the problem of the donor is that of a hydrogen atom with a scaled Rydberg and radius. Between the densities n of 1 ·1016 cm−3 and 2 · 1017 cm−3 (rNN = 11.9 nm), respectively, the regime is called semidilute, and it is characterized by formation of pairs. Above 2 · 1017 cm−3 and below the metallic behavior, which occurs at 3.7 · 1018 cm−3, the regime is called intermediate, and the formation of random clusters leads to effects generally accounted by the Hubbard band formation. Above n > 3.7 · 1018 cm−3, silicon is treated as a metal. In this section the physics of the first three regimes of donor concentration and the Anderson-Mott transition are described. The Anderson-Mott transition has been observed down to microscopic scale by employing arrays of few deterministically implanted As ions (see chapter 5) in Si transistors [39]. Analogous arguments and treatment can be given to acceptor concentration regimes.