Absence of spin superradiance in resonatorless magnets

Yukalova

2010

Phys. Rev. B

The possibility of realizing the superradiant regime of electromagnetic emission by the assembly of quantum dots is considered. The overall dynamical process is analyzed in detail. It is shown that there can occur several qualitatively different stages of evolution. The process starts with dipolar waves triggering the spontaneous radiation of individual dots. This corresponds to the fluctuation stage, when the dots are not yet noticeably correlated with each other. The second is the quantum stage, when the dot interactions through the common radiation field become more important, but the coherence is not yet developed. The third is the coherent stage, when the dots radiate coherently, emitting a superradiant pulse. After the superradiant pulse, the system of dots relaxes to an incoherent state in the relaxation stage. If there is no external permanent pumping, or the effective dot interactions are weak, the system tends to a stationary state during the last stationary stage, when coherence dies out to a low, practically negligible, level. In the case of permanent pumping, there exists the sixth stage of pulsing superradiance, when the system of dots emits separate coherent pulses.

Section: Stochastic Mean-field Approximationmentioning

confidence: 99%

Dynamics of quantum dot superradiance

Yukalova

2010

Phys. Rev. B

“…It is important to stress that in order to organize coherent spin motion, that is necessary for realizing fast spin reversal, the presence of the resonant electric circuit is compulsory. If this circuit is absent, then dipolar interactions destroy spin coherence and do not allow for their coherent motion [130,131].…”

Section: Spin Dynamicsmentioning

confidence: 99%

Dipolar and spinor bosonic systems

2018

Laser Phys.

Self Cite

The main properties and methods of describing dipolar and spinor atomic systems, composed of bosonic atoms or molecules, are reviewed. The general approach for the correct treatment of Bose-condensed atomic systems with nonlocal interaction potentials is explained. The approach is applied to Bose-condensed systems with dipolar interaction potentials. The properties of systems with spinor interaction potentials are described. Trapped atoms and atoms in optical lattices are considered. Effective spin Hamiltonians for atoms in optical lattices are derived. The possibility of spintronics with cold atom is emphasized. The present review differs from the previous review articles by concentrating on a thorough presentation of basic theoretical points, helping the reader to better follow mathematical details and to make clearer physical conclusions.Cold atomic and molecular bosonic systems have recently been the objects of intensive research, both experimental and theoretical. First, the attention has been concentrated on dilute systems, composed of particles characterized by local interaction potentials, independent of spins, whose properties are well described by the s-wave scattering length. There are several books [1-4] and review articles [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] covering different aspects of such bosonic systems with spin-independent local interaction potentials.In the present review, bosonic atoms or molecules are treated interacting through nonlocal interaction potentials, such as dipolar potential, and interacting through spinor forces that are local but depending on the effective spins related to hyperfine states. Although there exist reviews devoted to dipolar [20][21][22][23][24][25] and spinor [26,27] systems (see also [3,28]) the present paper differs from them in the following aspects. First, our aim here is not a brief enumeration of particular cases, numerical calculations, and different experiments, but the attention here is concentrated on the principal theoretical points allowing for the correct treatment of dipolar and spinor systems. Second, more attention is payed to the derivation of effective spin Hamiltonians for atoms and molecules in optical lattices. Third, the possibility of spintronics with cold atoms and molecules, interacting through dipolar and spinor forces, is discussed.The exposition of the material is organized so that the main mathematical points be clear to the reader. More technical details can be found in the tutorials [29,30]. Throughout the paper, the system of units is employed where the Boltzmann and Planck constants are set to one, k B = 1 and = 1.As is evident, the equation for the vacuum coherent field (2.40) differs form the equation (2.34) for the condensate function that is a coherent field, but, generally, not the vacuum coherent field. Equation (2.40) is a particular case of (2.34), where there are no uncondensed particles, so that ρ 1 , σ 1 , as well as ξ, are zero.One often confuses equation (2.40) for the vacuum coherent field with me...

“…The other mechanism that sometimes is assumed to be present in collectivizing the rotational motion of spins in a solid-state system is the Dicke effect caused by the photon exchange between moving spins, similarly to the developing coherence and superradiance in an ensemble of radiating atoms [21] or ions [22]. Moving spins really represent dipole emitters of photons [23,24], with the natural width…”

Section: Magnetic Nanomolecules and Nanoclustersmentioning

confidence: 99%

“…being of order 10 18 and making the correlations due to photon exchange absolutely irrelevant for spin systems [24,25]. The motion of spins in magnets is triggered by spin waves and mutual correlations can be induced only by the resonator feedback field [3,4,24,25]. The amplifying role of the resonator is called the Purcell effect [26].…”

Section: Magnetic Nanomolecules and Nanoclustersmentioning

confidence: 99%

Spintronics with Magnetic Nanomolecules and Graphene Flakes

Henner

Belozerova

et al. 2015

J Supercond Nov Magn

We show how the magnetization of nano-objects can be efficiently regulated. Several types of nanosystems are considered: magnetics nanomolecules, magnetic nanoclusters, polarized nanomolecules, and magnetic graphene. These nano-objects and the structures composed of them enjoy many common properties, with the main difference being in the type of particle interactions. The possibility of governing spin dynamics is important for spintronics.