The silicon-vacancy center (Si-V) is an optically active defect in diamond (referred to as a color center) that is receiving an increasing amount of interest in the diamond research community. This interest is driven primarily by the coherent optical properties of the Si-V, especially compared to the well-known and extensively-studied nitrogen-vacancy center (N-V).
The Si-V center is formed by replacing two neighboring carbon atoms in the diamond lattice with one silicon atom, which places itself between the two vacant lattice sites. This configuration has a D3d point group symmetry.
The Si-V center is a single-hole (spin-1/2) system with ground and excited electronic states located within the diamond bandgap. The ground and excited electronic states have two orbital states split by spin–orbit coupling. Each of these spin–orbit states is doubly degenerate by spin, and this splitting can be affected by lattice strain. Phonons in the diamond lattice drive transitions between these orbital states, causing rapid equilibration of the orbital population at temperatures above ca. 1 K. [2]
All four transitions between the two ground and two excited orbital states are dipole allowed with a sharp zero-phonon line (ZPL) at 738 nm (1.68 eV) [3] and minimal phononic sideband in a roughly 20 nm window around 766 nm. [4] The Si-V center emits much more of its emission into its ZPL, approximately 70% (Debye–Waller factor of 0.7), than most other optical centers in diamond, such as the nitrogen-vacancy center (Debye–Waller factor ~ 0.04). [5] The Si-V center also has higher excited states that relax quickly to the lowest excited states, allowing off-resonant excitation.
The Si-V center has an inversion symmetry, and no static electric dipole moment (to the first order); it is therefore insensitive to the Stark shift that could result from inhomogeneous electric fields within the diamond lattice. This property, together with the weak electron-phonon coupling, results in a narrow ZPL in the Si-V center, which is mostly limited by its intrinsic lifetime. [6] Bright photoluminescence, narrow optical lines, and ease of finding optically indistinguishable Si-V centers favor them for applications in solid-state quantum optics.
Although the optical transitions of the Si-V center preserve the electron spin, the rapid phonon-induced mixing between the Si-V orbital states causes spin decoherence. Yet it is possible to use the 29Si nuclear spin of the Si-V as a qubit for quantum information applications. [7] [8] [9]
An exciton is a bound state of an electron and an electron hole which are attracted to each other by the electrostatic Coulomb force. It is an electrically neutral quasiparticle that exists in insulators, semiconductors and some liquids. The exciton is regarded as an elementary excitation of condensed matter that can transport energy without transporting net electric charge.
Photoluminescence is light emission from any form of matter after the absorption of photons. It is one of many forms of luminescence and is initiated by photoexcitation, hence the prefix photo-. Following excitation, various relaxation processes typically occur in which other photons are re-radiated. Time periods between absorption and emission may vary: ranging from short femtosecond-regime for emission involving free-carrier plasma in inorganic semiconductors up to milliseconds for phosphoresence processes in molecular systems; and under special circumstances delay of emission may even span to minutes or hours.
Cathodoluminescence is an optical and electromagnetic phenomenon in which electrons impacting on a luminescent material such as a phosphor, cause the emission of photons which may have wavelengths in the visible spectrum. A familiar example is the generation of light by an electron beam scanning the phosphor-coated inner surface of the screen of a television that uses a cathode ray tube. Cathodoluminescence is the inverse of the photoelectric effect, in which electron emission is induced by irradiation with photons.
In solid-state physics, a band gap, also called a bandgap or energy gap, is an energy range in a solid where no electronic states exist. In graphs of the electronic band structure of solids, the band gap refers to the energy difference between the top of the valence band and the bottom of the conduction band in insulators and semiconductors. It is the energy required to promote an electron from the valence band to the conduction band. The resulting conduction-band electron are free to move within the crystal lattice and serve as charge carriers to conduct electric current. It is closely related to the HOMO/LUMO gap in chemistry. If the valence band is completely full and the conduction band is completely empty, then electrons cannot move within the solid because there are no available states. If the electrons are not free to move within the crystal lattice, then there is no generated current due to no net charge carrier mobility. However, if some electrons transfer from the valence band to the conduction band, then current can flow. Therefore, the band gap is a major factor determining the electrical conductivity of a solid. Substances having large band gaps are generally insulators, those with small band gaps are semiconductor, and conductors either have very small band gaps or none, because the valence and conduction bands overlap to form a continuous band.
This is a timeline of quantum computing.
Silicon carbide (SiC), also known as carborundum, is a hard chemical compound containing silicon and carbon. A semiconductor, it occurs in nature as the extremely rare mineral moissanite, but has been mass-produced as a powder and crystal since 1893 for use as an abrasive. Grains of silicon carbide can be bonded together by sintering to form very hard ceramics that are widely used in applications requiring high endurance, such as car brakes, car clutches and ceramic plates in bulletproof vests. Large single crystals of silicon carbide can be grown by the Lely method and they can be cut into gems known as synthetic moissanite.
In condensed matter physics, a supersolid is a spatially ordered material with superfluid properties. In the case of helium-4, it has been conjectured since the 1960s that it might be possible to create a supersolid. Starting from 2017, a definitive proof for the existence of this state was provided by several experiments using atomic Bose–Einstein condensates. The general conditions required for supersolidity to emerge in a certain substance are a topic of ongoing research.
A polaron is a quasiparticle used in condensed matter physics to understand the interactions between electrons and atoms in a solid material. The polaron concept was proposed by Lev Landau in 1933 and Solomon Pekar in 1946 to describe an electron moving in a dielectric crystal where the atoms displace from their equilibrium positions to effectively screen the charge of an electron, known as a phonon cloud. This lowers the electron mobility and increases the electron's effective mass.
In solid-state physics, the electron mobility characterises how quickly an electron can move through a metal or semiconductor when pulled by an electric field. There is an analogous quantity for holes, called hole mobility. The term carrier mobility refers in general to both electron and hole mobility.
A Rydberg atom is an excited atom with one or more electrons that have a very high principal quantum number, n. The higher the value of n, the farther the electron is from the nucleus, on average. Rydberg atoms have a number of peculiar properties including an exaggerated response to electric and magnetic fields, long decay periods and electron wavefunctions that approximate, under some conditions, classical orbits of electrons about the nuclei. The core electrons shield the outer electron from the electric field of the nucleus such that, from a distance, the electric potential looks identical to that experienced by the electron in a hydrogen atom.
Imperfections in the crystal lattice of diamond are common. Such defects may be the result of lattice irregularities or extrinsic substitutional or interstitial impurities, introduced during or after the diamond growth. The defects affect the material properties of diamond and determine to which type a diamond is assigned; the most dramatic effects are on the diamond color and electrical conductivity, as explained by the electronic band structure.
The nitrogen-vacancy center is one of numerous point defects in diamond. Its most explored and useful property is its photoluminescence, which allows observers to read out its spin-state. The NV center's electron spin, localized at atomic scales, can be manipulated at room temperature by external factors such as magnetic, or electric fields, microwave radiation, or optical light, resulting in sharp resonances in the intensity of the photoluminescence. These resonances can be explained in terms of electron spin related phenomena such as quantum entanglement, spin–orbit interaction and Rabi oscillations, and analysed using advanced quantum optics theory. An individual NV center can be used as a basic unit for a quantum computer, a qubit, and used for quantum cryptography. Further potential applications in novel fields of electronics and sensing include spintronics, masers, and quantum sensors. If the charge is not specified the term "NV center" refers to the negatively charged NV− center.
As the devices continue to shrink further into the sub-100 nm range following the trend predicted by Moore’s law, the topic of thermal properties and transport in such nanoscale devices becomes increasingly important. Display of great potential by nanostructures for thermoelectric applications also motivates the studies of thermal transport in such devices. These fields, however, generate two contradictory demands: high thermal conductivity to deal with heating issues in sub-100 nm devices and low thermal conductivity for thermoelectric applications. These issues can be addressed with phonon engineering, once nanoscale thermal behaviors have been studied and understood.
Photonic molecules are a theoretical natural form of matter which can also be made artificially in which photons bind together to form "molecules". They were first predicted in 2007. Photonic molecules are formed when individual (massless) photons "interact with each other so strongly that they act as though they have mass". In an alternative definition, photons confined to two or more coupled optical cavities also reproduce the physics of interacting atomic energy levels, and have been termed as photonic molecules.
Valleytronics is an experimental area in semiconductors that exploits local extrema ("valleys") in the electronic band structure. Certain semiconductors have multiple "valleys" in the electronic band structure of the first Brillouin zone, and are known as multivalley semiconductors. Valleytronics is the technology of control over the valley degree of freedom, a local maximum/minimum on the valence/conduction band, of such multivalley semiconductors.
The germanium-vacancy center (Ge-V) is an optically active defect in diamond, which can be created by doping germanium into diamond during its growth or by implanting germanium ions into diamond after its growth. Its properties are similar to those of the silicon-vacancy center in diamond (SiV). Ge-V can behave as a single-photon source and shows potential for quantum and nanoscience applications due to its narrow zero-phonon line (ZPL) and minimal phononic-sideband.
Graphene is a semimetal whose conduction and valence bands meet at the Dirac points, which are six locations in momentum space, the vertices of its hexagonal Brillouin zone, divided into two non-equivalent sets of three points. The two sets are labeled K and K'. The sets give graphene a valley degeneracy of gv = 2. By contrast, for traditional semiconductors the primary point of interest is generally Γ, where momentum is zero. Four electronic properties separate it from other condensed matter systems.
In physics, optically detected magnetic resonance (ODMR) is a double resonance technique by which the electron spin state of a crystal defect may be optically pumped for spin initialisation and readout.
In quantum computing, quantum memory is the quantum-mechanical version of ordinary computer memory. Whereas ordinary memory stores information as binary states, quantum memory stores a quantum state for later retrieval. These states hold useful computational information known as qubits. Unlike the classical memory of everyday computers, the states stored in quantum memory can be in a quantum superposition, giving much more practical flexibility in quantum algorithms than classical information storage.
Silicon carbide color centers are point defects in the crystal lattice of silicon carbide, which are known as color centers. These color centers have multiple uses, some of which are in photonics, semiconductors, and quantum applications like metrology and quantum communication. Defects in materials have a plethora of applications, but the reason defects, or color centers in silicon carbide are significant is due to many important properties of these color centers. Silicon carbide as a material has second-order nonlinearity, as well as optical transparency and low two-photon absorption. This makes silicon carbide viable to be an alternate platform for many things, including but not limited to nanofabrication, integrated quantum photonics, and quantum systems in large-scale wafers.
