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In physics, polaritons are quasiparticles resulting from strong coupling of electromagnetic waves with an electric or magnetic dipole-carrying excitation. They are an expression of the common quantum phenomenon known as level repulsion, also known as the avoided crossing principle. Polaritons describe the crossing of the dispersion of light with any interacting resonance. To this extent polaritons can also be thought of as the new normal modes of a given material or structure arising from the strong coupling of the bare modes, which are the photon and the dipolar oscillation. The polariton is a bosonic quasiparticle, and should not be confused with the polaron, which is an electron plus an attached phonon cloud.
Quantum dots (QDs) or semiconductor nanocrystals are semiconductor particles a few nanometres in size with optical and electronic properties that differ from those of larger particles via quantum mechanical effects. They are a central topic in nanotechnology and materials science. When a quantum dot is illuminated by UV light, an electron in the quantum dot can be excited to a state of higher energy. In the case of a semiconducting quantum dot, this process corresponds to the transition of an electron from the valence band to the conductance band. The excited electron can drop back into the valence band releasing its energy as light. This light emission (photoluminescence) is illustrated in the figure on the right. The color of that light depends on the energy difference between the conductance band and the valence band, or the transition between discrete energy states when the band structure is no longer well-defined in QDs.
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.
Atomic coherence is the induced coherence between levels of a multi-level atomic system.
Oleg Sushkov is a professor at the University of New South Wales and a leader in the field of high temperature super-conductors. Educated in Russia in quantum mechanics and nuclear physics, he now teaches in Australia.
The spin qubit quantum computer is a quantum computer based on controlling the spin of charge carriers in semiconductor devices. The first spin qubit quantum computer was first proposed by Daniel Loss and David P. DiVincenzo in 1997, also known as the Loss–DiVincenzo quantum computer. The proposal was to use the intrinsic spin-½ degree of freedom of individual electrons confined in quantum dots as qubits. This should not be confused with other proposals that use the nuclear spin as qubit, like the Kane quantum computer or the nuclear magnetic resonance quantum computer.
Mesoscopic physics is a subdiscipline of condensed matter physics that deals with materials of an intermediate size. These materials range in size between the nanoscale for a quantity of atoms and of materials measuring micrometres. The lower limit can also be defined as being the size of individual atoms. At the microscopic scale are bulk materials. Both mesoscopic and macroscopic objects contain many atoms. Whereas average properties derived from constituent materials describe macroscopic objects, as they usually obey the laws of classical mechanics, a mesoscopic object, by contrast, is affected by thermal fluctuations around the average, and its electronic behavior may require modeling at the level of quantum mechanics.
Atomtronics is an emerging type of computing consisting of matter-wave circuits which coherently guide propagating ultra-cold atoms. The systems typically include components analogous to those found in electronic or optical systems, such as beam splitters and transistors. Applications range from studies of fundamental physics to the development of practical devices.
Ghost imaging is a technique that produces an image of an object by combining information from two light detectors: a conventional, multi-pixel detector that does not view the object, and a single-pixel (bucket) detector that does view the object. Two techniques have been demonstrated. A quantum method uses a source of pairs of entangled photons, each pair shared between the two detectors, while a classical method uses a pair of correlated coherent beams without exploiting entanglement. Both approaches may be understood within the framework of a single theory.
A topological insulator is a material whose interior behaves as an electrical insulator while its surface behaves as an electrical conductor, meaning that electrons can only move along the surface of the material.
Nicholas Harrison FRSC FinstP is an English theoretical physicist known for his work on developing theory and computational methods for discovering and optimising advanced materials. He is the Professor of Computational Materials Science in the Department of Chemistry at Imperial College London where he is co-director of the Institute of Molecular Science and Engineering.
Yambo is a computer software package for studying many-body theory aspects of solids and molecule systems. It calculates the excited state properties of physical systems from first principles, e.g., from quantum mechanics law without the use of empirical data. It is an open-source software released under the GNU General Public License (GPL). However the main development repository is private and only a subset of the features available in the private repository are cloned into the public repository and thus distributed.
The toric code is a topological quantum error correcting code, and an example of a stabilizer code, defined on a two-dimensional spin lattice. It is the simplest and most well studied of the quantum double models. It is also the simplest example of topological order—Z2 topological order (first studied in the context of Z2 spin liquid in 1991). The toric code can also be considered to be a Z2 lattice gauge theory in a particular limit. It was introduced by Alexei Kitaev.
Single-photon sources are light sources that emit light as single particles or photons. These sources are distinct from coherent light sources (lasers) and thermal light sources such as incandescent light bulbs. The Heisenberg uncertainty principle dictates that a state with an exact number of photons of a single frequency cannot be created. However, Fock states can be studied for a system where the electric field amplitude is distributed over a narrow bandwidth. In this context, a single-photon source gives rise to an effectively one-photon number state. Photons from an ideal single-photon source exhibit quantum mechanical characteristics. These characteristics include photon antibunching, so that the time between two successive photons is never less than some minimum value. This behaviour is normally demonstrated by using a beam splitter to direct about half of the incident photons toward one avalanche photodiode, and half toward a second. Pulses from one detector are used to provide a ‘counter start’ signal, to a fast electronic timer, and the other, delayed by a known number of nanoseconds, is used to provide a ‘counter stop’ signal. By repeatedly measuring the times between ‘start’ and ‘stop’ signals, one can form a histogram of time delay between two photons and the coincidence count- if bunching is not occurring, and photons are indeed well spaced, a clear notch around zero delay is visible.
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.
Bose–Einstein condensation of polaritons is a growing field in semiconductor optics research, which exhibits spontaneous coherence similar to a laser, but through a different mechanism. A continuous transition from polariton condensation to lasing can be made similar to that of the crossover from a Bose–Einstein condensate to a BCS state in the context of Fermi gases. Polariton condensation is sometimes called “lasing without inversion”.
In quantum computing, a qubit is a unit of information analogous to a bit in classical computing, but it is affected by quantum mechanical properties such as superposition and entanglement which allow qubits to be in some ways more powerful than classical bits for some tasks. Qubits are used in quantum circuits and quantum algorithms composed of quantum logic gates to solve computational problems, where they are used for input/output and intermediate computations.
Jonathan James Finley is a Professor of Physics at the Technical University of Munich in Garching, Germany, where he holds the Chair of Semiconductor Nanostructures and Quantum Systems. His focus is on quantum phenomena in semiconductor nanostructures, photonic materials, dielectric and metallic films, among others, for applications in quantum technology. At such, he made major contributions to the characterization and understanding of the optical, electronic and spintronic properties of quantum dots and wires both from group-IV and II-VI materials and oxides.
Christine A. Muschik is an assistant professor in the Department of Physics and Astronomy at the University of Waterloo as well as a part of the Institute for Quantum Computing. She completed her PhD in 2011 at the Max-Planck-Institute for Quantum Optics. She completed postdoctoral fellowships at the Institute for Quantum Optics and Quantum Information in Innsbruck and the Institute of Photonic Sciences in Castelldefels. As of 2020, she has over 2000 citations on over 50 publications. She has also been featured in several articles in Nature magazine, MIT Technology Review, and Physics World.
Jeremy Levy is an American physicist who is a Distinguished Professor of Physics at the University of Pittsburgh.
References
- ↑ London-nano.com Archived 13 February 2010 at the Wayback Machine profile at London Centre for Nanotechnology.
- ↑ "See current UCL profile". Archived from the original on 11 May 2010. Retrieved 9 January 2010.
- ↑ See list of publications at UCL: http://www.cmmp.ucl.ac.uk/~ajf/publications.html Archived 4 January 2010 at the Wayback Machine
- ↑ "OA Notes" (PDF). The Abingdonian.
- ↑ "Alison Smart (Soprano) – Short Biography". Bach-cantatas.com. 27 June 2007. Retrieved 9 January 2010.
