Topic
Spin-½
About: Spin-½ is a research topic. Over the lifetime, 40423 publications have been published within this topic receiving 796639 citations.
Papers published on a yearly basis
Papers
More filters
15 Dec 2007
TL;DR: In this paper, a review of quantumphase transition from one state to another is provided by adjusting a tuning parameter other than temperature, and their consequences for finite temperature experiments are discussed.
Abstract: Thermal fluctuations induced by increasing temperature can change the state of matter, for example, when water boils to steam. It also is possible to change the state of matter at absolute zero temperature by quantum fluctuations demanded by Heisenberg's uncertainty principle. In this case, the quantumphase transition from one state to another is provided by adjusting a tuning parameter other than temperature. A few characteristic examples of quantumphase transitions are reviewed, and their consequences for finite temperature experiments are discussed.
Keywords:
quantum phase transitions;
broken symmetry;
Landau theory;
Berry phases;
confinement;
quantum criticality;
deconfined criticality;
spin gap;
monopole;
valence bond solid
1,270 citations
TL;DR: In this paper, it was shown that the divergence arising in the quantum theory of gravitation can be removed by the familiar methods used in quantum electrodynamics, and it was proved that for infrared gravitons this divergence cancels in the sum of all such diagrams.
Abstract: It is shown that the infrared divergences arising in the quantum theory of gravitation can be removed by the familiar methods used in quantum electrodynamics. An additional divergence appears when infrared photons or gravitons are emitted from noninfrared external lines of zero mass, but it is proved that for infrared gravitons this divergence cancels in the sum of all such diagrams. (The cancellation does not occur in massless electrodynamics.) The formula derived for graviton bremsstrahlung is then used to estimate the gravitational radiation emitted during thermal collisions in the sun, and we find this to be a stronger source of gravitational radiation (though still very weak) than classical sources such as planetary motion. We also verify the conjecture of Dalitz that divergences in the Coulomb-scattering Born series may be summed to an innocuous phase factor, and we show how this result may be extended to processes involving arbitrary numbers of relativistic or nonrelativistic particles with arbitrary spin.
1,253 citations
TL;DR: In this article, a measurement of the spin asymmetry and determination of the structure function g1 in deep inelastic muon-proton scattering was carried out for the first time.
1,240 citations
TL;DR: This work proposes that magnetic monopoles emerge in a class of exotic magnets known collectively as spin ice: the dipole moment of the underlying electronic degrees of freedom fractionalises into monopoles, which would account for a mysterious phase transition observed experimentally in spin ice in a magnetic field.
Abstract: We are familiar with elementary particles that carry either negative or positive electric charge, such as electrons and protons, but there is no evidence of elementary particles with a net magnetic charge. Magnets tend to come with inseparable north and south poles, and there are no known magnetic monopoles despite concerted efforts to find them. But an intriguing theoretical study now proposes that magnetic monopoles may exist, not as elementary particles, but as emergent particles in exotic condensed matter magnetic systems such as 'spin ice'. The theory, based on an analogy to fractional electric charges seen, for example, in quantum Hall systems in two dimensions, can explain a mysterious phase transition that has been observed experimentally in spin ice. The cover, by Alessandro Canossa, depicts a magnetic monopole (red sphere) emerging from break-up of the dipole moment (arrows) of the underlying electronic degrees of freedom in spin ice. A theoretical study proposes that magnetic monopoles may appear not as elementary but as emergent particles in complex, strongly-correlated magnetic systems such as spin ice, in analogy to fractional electric charges in quantum Hall systems. This theory explains a mysterious phase transition in spin ice that has been observed experimentally. Electrically charged particles, such as the electron, are ubiquitous. In contrast, no elementary particles with a net magnetic charge have ever been observed, despite intensive and prolonged searches (see ref. 1 for example). We pursue an alternative strategy, namely that of realizing them not as elementary but rather as emergent particles—that is, as manifestations of the correlations present in a strongly interacting many-body system. The most prominent examples of emergent quasiparticles are the ones with fractional electric charge e/3 in quantum Hall physics2. Here we propose that magnetic monopoles emerge in a class of exotic magnets known collectively as spin ice3,4,5: the dipole moment of the underlying electronic degrees of freedom fractionalises into monopoles. This would account for a mysterious phase transition observed experimentally in spin ice in a magnetic field6,7, which is a liquid–gas transition of the magnetic monopoles. These monopoles can also be detected by other means, for example, in an experiment modelled after the Stanford magnetic monopole search8.
1,225 citations
TL;DR: It is found that in a reasonable time, a qubit can be directly transmitted with better than classical fidelity across the full length of chains of up to 80 spins, and the channel allows distillable entanglement to be shared over arbitrary distances.
Abstract: We propose a scheme for using an unmodulated and unmeasured spin chain as a channel for short distance quantum communications. The state to be transmitted is placed on one spin of the chain and received later on a distant spin with some fidelity. We first obtain simple expressions for the fidelity of quantum state transfer and the amount of entanglement sharable between any two sites of an arbitrary Heisenberg ferromagnet using our scheme. We then apply this to the realizable case of an open ended chain with nearest neighbor interactions. The fidelity of quantum state transfer is obtained as an inverse discrete cosine transform and as a Bessel function series. We find that in a reasonable time, a qubit can be directly transmitted with better than classical fidelity across the full length of chains of up to 80 spins. Moreover, our channel allows distillable entanglement to be shared over arbitrary distances.
1,220 citations