Instruct: Given a question, retrieve documents that can help answer the question.
Query: What is a qubit?
In quantum computing, a charge qubit is a qubit whose basis states are charge states (e.g. states which represent the presence or absence of excess Cooper pairs in the island). In superconducting quantum computing, a charge qubit is formed by a tiny superconducting island (also known as a Cooper-pair box) coupled by a Josephson junction to a superconducting reservoir (see figure). The state of the qubit is determined by the number of Cooper pairs which have tunneled across the junction. In contrast with the charge state of an atomic or molecular ion, the charge states of such an "island" involve a macroscopic number of conduction electrons of the island. The quantum superposition of charge states can be achieved by tuning the gate voltage U that controls the chemical potential of the island. The charge qubit is typically read-out by electrostatically coupling the island to an extremely sensitive electrometer such as the radio-frequency single-electron transistor.
As the field has progressed new quantum algorithms have been developed which provide short and long term routes towards the demonstration of the superiority of quantum computers over their classical counterparts. Cluster state computation is now generally accepted as the approach that will be used to develop a fully fledged quantum computer. Whilst development of quantum computer will require the synthesis of many different aspects of integrated optics, boson sampling seeks to demonstrate the power of quantum computation via technologies readily available and is therefore a very promising near term algorithm to doing so. In fact shortly after its proposal there were several small scale experimental demonstrations of the boson sampling algorithm
A continuous-time quantum walk (CTQW) is a quantum walk on a given (simple) graph that is dictated by a time-varying unitary matrix that relies on the Hamiltonian of the quantum system and the adjacency matrix. The concept of a CTQW is believed to have been first considered for quantum computation by Edward Farhi and Sam Gutmann; since many classical algorithms are based on (classical) random walks, the concept of CTQWs were originally considered to see if there could be quantum analogues of these algorithms with e.g. better time-complexity than their classical counterparts. In recent times, problems such as deciding what graphs admit properties such as perfect state transfer with respect to their CTQWs have been of particular interest.
Early on, the company designed smaller ST-506-compatible versions of its hard drives, the "Q500" series, using the same servo system. In 1985, it introduced the Plus Hardcard, which was essentially a smaller version of the Q500, designed to fit in an ISA slot. In 1986, Quantum entered the then-new SCSI market with the Q280 80MB drive, which was one of the first mass-market drives to use embedded servo. Later on, Quantum combined the Q280's embedded controller design with the servo hardware from the Q500 series, and developed the "ProDrive" range, which was also its first drive family to support the ATA interface.
The quark bomb explodes at the moment of construction at the factory. The rest of its existence is a slow process of quark fission, which turns the avalanche-like destruction of atoms into a slow, rhythmical, gradual destruction of 10 grams of copper dust - the best known explosive trigger. If the bomb is shot at, which destroys its mechanisms, then the unstoppable process of atomic fission begins at full strength. The only way to get rid of a quark bomb is to jettison it in deep space at least 3-4 light years from the nearest stellar body or nebula. Occasionally, quark fission can be transferred from one planet to another through tiny meteorites, dust particles, molecules of ionized gas, etc.
The use of split-complex numbers dates back to 1848 when James Cockle revealed his tessarines. William Kingdon Clifford used split-complex numbers to represent sums of spins. Clifford introduced the use of split-complex numbers as coefficients in a quaternion algebra now called split-biquaternions. He called its elements "motors", a term in parallel with the "rotor" action of an ordinary complex number taken from the circle group. Extending the analogy, functions of a motor variable contrast to functions of an ordinary complex variable.
The quark model, together with quantum mechanics predicts that there should be orbital excitations of particles. The lowest lying of these states are ones where the two light quarks (the up and down) combine into a spin-0 state, one unit of orbital angular momentum is added, and this combines with the intrinsic spin of the charm quark to make a , pair of particles. The higher of these (the (2625)) was discovered in 1993 by ARGUS. At first it was not clear what state had been discovered, but the subsequent discovery of the lower state (2593) by CLEO clarified the situation. The decay modes, the masses, the measured widths, and the decays via two charged pions rather than one charged and one neutral pion, all confirm the identification of the states.
The world’s first transistor computer was built at the University of Manchester in November 1953. The computer was built by Richard Grimsdale, then a research student in the Department of Electrical Engineering and later a Professor of Electronic Engineering at Sussex University. The machine used point-contact transistors, made in small quantities by STC and Mullard. These consisted of a single crystal of germanium with two fine wires, resembling the crystal and cat’s whisker of the 1920s. These transistors had the useful property that a single transistor could possess two stable states. ... The development of the machine was severely hampered by the unreliability of the transistors, which consumed 150 watts.
The quattrino is an ancient Italian currency denomination largely used in Central Italy, especially in Tuscany and Rome. Its name derives from the Latin "quater denari", because its value was equal to four "denari". Consequently, its value was one third of a soldo. It disappeared after the unification of Italy in 1861, when the Italian lira was introduced as an equivalent of the french franc.
Logic sentences that can be expressed in classical propositional calculus have an equivalent expression in Boolean algebra. Thus, Boolean logic is sometimes used to denote propositional calculus performed in this way. Boolean algebra is not sufficient to capture logic formulas using quantifiers, like those from first order logic. Although the development of mathematical logic did not follow Boole's program, the connection between his algebra and logic was later put on firm ground in the setting of algebraic logic, which also studies the algebraic systems of many other logics. The problem of determining whether the variables of a given Boolean (propositional) formula can be assigned in such a way as to make the formula evaluate to true is called the Boolean satisfiability problem (SAT), and is of importance to theoretical computer science, being the first problem shown to be NP-complete. The closely related model of computation known as a Boolean circuit relates time complexity (of an algorithm) to circuit complexity.
Whereas in elementary algebra expressions denote mainly numbers, in Boolean algebra they denote the truth values "false" and "true". These values are represented with the bits (or binary digits), namely 0 and 1. They do not behave like the integers 0 and 1, for which 1 + 1 = 2, but may be identified with the elements of the two-element field GF(2), that is, integer arithmetic modulo 2, for which 1 + 1 = 0. Addition and multiplication then play the Boolean roles of XOR (exclusive-or) and AND (conjunction) respectively, with disjunction "x"∨"y" (inclusive-or) definable as "x" + "y" - "xy".
The third thread in the development of quantum field theory was the need to handle the statistics of many-particle systems consistently and with ease. In 1927, Pascual Jordan tried to extend the canonical quantization of fields to the many-body wave functions of identical particles using a formalism which is known as statistical transformation theory; this procedure is now sometimes called second quantization. In 1928, Jordan and Eugene Wigner found that the quantum field describing electrons, or other fermions, had to be expanded using anti-commuting creation and annihilation operators due to the Pauli exclusion principle (see Jordan–Wigner transformation). This thread of development was incorporated into many-body theory and strongly influenced condensed matter physics and nuclear physics.
Boolean logic is a system of syllogistic logic invented by 19th-century British mathematician George Boole, which attempts to incorporate the "empty set", that is, a class of non-existent entities, such as round squares, without resorting to uncertain truth values.
By 2000, Steve Jobs expressed interest in developing a portable music player. But Rubinstein demurred, saying the necessary components were not yet available. While on a routine supplier visit to Toshiba Corp. in February, 2001, however, Rubinstein first saw the tiny, 1.8-inch hard disk drive that became a critical component of the iPod. While Toshiba engineers had developed the drive, they were not sure how it could be used. At a Tokyo hotel later that evening, Rubinstein met with Jobs, who was in Japan on separate business. "I know how to do it now. All I need is a $10 million check," he told Jobs.
The Rabi frequency is the radian frequency of the Rabi cycle undergone for a given atomic transition in a given light field. This is thus the frequency of fluctuations in the populations of the two atomic levels involved in that atomic transition in that situation. It is proportional to the strength of the coupling between the light and the atomic transition and to the amplitude ("not" intensity) of the light's electric field. Rabi flopping between the levels of a 2-level system illuminated with light exactly resonant with the transition will occur at the Rabi frequency; when the incident light is detuned from resonance then this occurs at the generalized Rabi frequency. The Rabi frequency is a semiclassical concept as it is based on a quantum atomic transition and a classical light field.
In Rubik's cubers' parlance, a memorised sequence of moves that has a desired effect on the cube is called an algorithm. This terminology is derived from the mathematical use of "algorithm", meaning a list of well-defined instructions for performing a task from a given initial state, through well-defined successive states, to a desired end-state. Each method of solving the Rubik's Cube employs its own set of algorithms, together with descriptions of what effect the algorithm has, and when it can be used to bring the cube closer to being solved.
In 1968, deep inelastic scattering experiments at the Stanford Linear Accelerator Center (SLAC) showed that the proton contained much smaller, point-like objects and was therefore not an elementary particle. Physicists were reluctant to firmly identify these objects with quarks at the time, instead calling them "partons"—a term coined by Richard Feynman. The objects that were observed at SLAC would later be identified as up and down quarks as the other flavors were discovered. Nevertheless, "parton" remains in use as a collective term for the constituents of hadrons (quarks, antiquarks, and gluons).
The idea of quantum field theory began in the late 1920s with British physicist [[Paul Dirac]], when he attempted to [[quantization (physics)|quantise]] the [[electromagnetic field]] – a procedure for constructing a quantum theory starting from a classical theory.
Hard disk drives store data in the magnetic polarization of small patches of the surface coating on a disk. The maximum areal density is defined by the size of the magnetic particles in the surface, as well as the size of the "head" used to read and write the data. The areal density of disk storage devices has increased dramatically since IBM introduced the IBM 350 disk storage, the first hard disk drive in 1956 at an areal density of 2,000 bit/in. The growth rate has matched Moore's Law with the density reaching 1 Tbit/in in 2014. In 2015, Seagate introduced a hard drive at a density of 1.34 Tbit/in, about 600 million times that of the first disk drive. It is expected that current recording technology can be "feasibly" expected to scale to at least 5 Tbit/in in the near future. New technologies like Heat-assisted magnetic recording (HAMR) and Microwave Assisted Magnetic Recording (MAMR) are under development and are expected to continue magnetic areal density progress.
Fairchild's strategy for competing in the transistor market was to be fast and flexible. Rather than tying their research and development to lengthy 1-3 year military contracts, they financed development through Fairchild Camera. This enabled them to focus on promising ideas and develop them quickly. IBM was interested in obtaining transistors for a navigation computer for the B-70 bomber. Fairchild contracted to provide transistors to meet the specifications for IBM's core-memory driver. They developed complementary NPN and PNP transistors which could be used as a matched pair in a variety of circuit applications. Gordon Moore and David Allison worked on the NPN transistor, while Jean Hoerni developed the PNP transistor using boron diffusion. Scaling up to production of components in quantity presented major technological challenges, and Moore's NPN transistor was ready for production before Hoerni's PNP transistor. By August 1958, within 8 months of the company's creation, Fairchild was delivering Mesa transistors to IBM. Once it became available, the mesa transistor was desired for a wide variety of military applications. The speed with which it had been developed gave Fairchild a virtual monopoly on the fast-growing market for the next year. The most significant contract came from Autonetics, which was developing the navigation and control computer for the Minuteman ICBM.
In physics, a theoretical lower-bound unit of time called the Planck time has been proposed, that being the time required for light to travel a distance of 1 Planck length. The Planck time is theorized to be the smallest time measurement that will ever be possible, roughly 10 seconds. Within the framework of the laws of physics as they are understood today, for times less than one Planck time apart, one can neither measure nor detect any change. It is therefore physically impossible, with current technology, to determine if any action exists that causes a reaction in "an instant", rather than a reaction occurring after an interval of time too short to observe or measure.
4k is a computer virus which infects COM files and EXE files. The virus was one of the first to employ stealth tactics. Infected systems will hang, after September 22 every year, which is also the date of birth Bilbo Baggins, a character from "The Lord of the Rings". The code was intended to display the message "Frodo Lives", but hangs in all known variants.
Most models of quantum computation require the use of qubits for computation. Some models use qubits and in this case the first statement is logically extended. Quantum mechanically a qubit is defined as 2 level system with some energy gap. This can sometimes be difficult to implement physically and so we can focus on a particular transition of atomic levels, etc. Whatever the system we choose, we require that the system remain (almost) always in the subspace of these two levels and in doing so we can say it is a well characterised qubit. An example of a system that is not well characterised would be 2 one-electron quantum dots (potential wells where we only allow for single electron occupations). The electron being in one well or the other is properly characterised as a single qubit, however if we consider a state such as formula_1 then this would correspond to a two qubit state. Such a state is not physically allowed (we only permit single electron occupation) and so we cannot say that we have 2 well characterised qubits.
In quantum information Qubits are the equivalent to bits in classical systems. A qubit is a property that when measured only can be found to be in one of two states, that is used to transmit information. The polarization of a photon or the nuclear spin are examples of two state systems that can be used as qubits.
In quantum computing, and more specifically in superconducting quantum computing, flux qubits (also known as persistent current qubits) are micrometer sized loops of superconducting metal interrupted by a number of Josephson junctions, functioning as quantum bits. The junction parameters are engineered during fabrication so that a persistent current will flow continuously when an external magnetic flux is applied. As only an integer number of flux quanta are allowed to penetrate the superconducting ring, clockwise or counter-clockwise currents are developed in the loop to compensate (screen or enhance) a non-integer external flux bias. When the applied flux through the loop area is close to a half integer number of flux quanta, the two lowest energy eigenstates of the loop will be a quantum superposition of the clockwise and counter-clockwise currents. The two lowest energy eigenstates differ only by the relative quantum phase between the composing current-direction states. Higher energy eigenstates correspond to much larger persistent currents, that induce an additional flux quantum to the qubit loop, thus are well separated energetically from the lowest two eigenstates. This separation, known as the "qubit non linearity" criteria, allows operations with the two lowest eigenstates only, effectively creating a two level system. Usually, the two lowest eigenstates will serve as the computational basis for the logical qubit.
In a paper entitled: "Solid-state quantum memory using the P nuclear spin", published in the October 23, 2008 issue of the journal "Nature", a team of scientists from the U.K. and U.S. reported the first relatively long (1.75 seconds) and coherent transfer of a superposition state in an electron spin "processing" qubit to a nuclear spin "memory" qubit. This event can be considered the first relatively consistent quantum data storage, a vital step towards the development of quantum computing. Recently, a modification of similar systems (using charged rather than neutral donors) has dramatically extended this time, to 3 hours at very low temperatures and 39 minutes at room temperature. Room temperature preparation of a qubit based on electron spins instead of nuclear spin was also demonstrated by a team of scientists from Switzerland and Australia.