Stroboscopic back-action evasion in a dense alkali-metal vapor

We explore experimentally quantum non-demolition (QND) measurements of atomic spin in a hot potassium vapor in the presence of spin-exchange relaxation. We demonstrate a new technique for back-action evasion by stroboscopic modulation of the probe light. With this technique we study spin noise as a function of polarization for atoms with spin greater than 1/2 and obtain good agreement with a simple theoretical model. We point that in a system with fast spin-exchange, where the spin relaxation rate is changing with time, it is possible to improve the long-term sensitivity of atomic magnetometry by using QND measurements

High Bandwidth Atomic Magnetometery with Continuous Quantum Non-demolition Measurements

We describe an experimental study of spin-projection noise in a high sensitivity alkali-metal magnetometer. We demonstrate a four-fold improvement in the measurement bandwidth of the magnetometer using continuous quantum non-demolition (QND) measurements. Operating in the scalar mode with a measurement volume of 2 cm^3 we achieve magnetic field sensitivity of 22 fT/Hz^(1/2) and a bandwidth of 1.9 kHz with a spin polarization of only 1%. Our experimental arrangement is naturally back-action evading and can be used to realize sub-fT sensitivity with a highly polarized spin-squeezed atomic vapor.Comment: 4 page

Ležaj sa stisnutim slojem ferofluida, uz anisotropnu permeabilnost, parametar klizne brzine materijala i tromost vrtnje

We present a theoretical study of the effect of anisotropic permeability and slip velocity on the action of the squeeze film formed when a secant-shaped circular upper plate with a porous facing approaches an impermeable and flat circular lower plate, considering also rotation of the plates. Expressions for the dimensionless pressure, load capacity and the response time are given by a differential equation. Computed values of dimensionless load capacity and response time are displayed in tabular form. It has been found that they decrease with increasing values of radial permeability, slip parameter and rotational inertia. However, they increase with increasing values of axial permeability and material constant of the Jenkins model. They have also been found to increase when the speed of the lower plate is higher than that of the upper plate.Opisujemo teoriju djelovanja anizotropne permeabilnosti i brzine klizanja na učinak stisnutog sloja koji nastaje kada se gornja ploča sekantnog oblika s poroznom površinom nasloni na nepropusnu i ravnu kružnu donju ploču. Bezdimenzijski tlak, nosivost i vrijeme odziva izražavamo diferencijalnom jednadžbom. Izračunate vrijednosti za nosivost i vrijeme odziva prikazujemo u tablicama. Nalazi se da one opadaju pri porastu radijalne permeabilnosti, parametra klizanja i momenta tromosti. Međutim, one se povećavaju pri porastu aksijalne permeabilnosti i konstante materijala prema Jenkinsovom modelu. Također nalazimo da rastu kada je brzina gornje veća od brzine donje ploče

Učinak brzine posmika u poroznom ležaju s klizačem u obliku sekante i s ferofluidnim mazivom

We analysed a bearing with a secant shaped slider and with the stator having a porous facing backed by a solid wall, using a magnetic fluid lubricant flowing as per Jenkins model. Computed values of the bearing characteristics are displayed in tabular form. The load capacity, friction on the slider and the coefficient of friction decreased with increasing values of the slip parameter. The load capacity decreased and friction as well as the coefficient of friction increased with increasing values of the material parameter. However, the position of the centre of pressure did not significantly alter owing to the changes in slip parameter. But it slowly shifted towards the inlet when the material parameter increased.Analiziramo ležaj s klizačem u obliku sekante u kojemu je stator porozan s čvrstom podlogom, a rabi magnetsko tekuće mazivo koje teče prema Jenkinsovom modelu. Izračunate vrijednosti značajki ležaja prikazuju se u tablicama. Nosivost, trenje klizača i koeficijent trenja smanjuju se pri povećanju parametra posmicanja, a nosivost i trenje smanjuju se pri povećanju parametra materijala. Položaj središta tlaka ne mijenja se bitno zbog promjena parametra posmicanja, ali se pomalo pomiče prema ulazu pri povećanju parametra materijala

Ležaj sa stisnutim slojem ferofluida, uz anisotropnu permeabilnost, parametar klizne brzine materijala i tromost vrtnje

We present a theoretical study of the effect of anisotropic permeability and slip velocity on the action of the squeeze film formed when a secant-shaped circular upper plate with a porous facing approaches an impermeable and flat circular lower plate, considering also rotation of the plates. Expressions for the dimensionless pressure, load capacity and the response time are given by a differential equation. Computed values of dimensionless load capacity and response time are displayed in tabular form. It has been found that they decrease with increasing values of radial permeability, slip parameter and rotational inertia. However, they increase with increasing values of axial permeability and material constant of the Jenkins model. They have also been found to increase when the speed of the lower plate is higher than that of the upper plate.Opisujemo teoriju djelovanja anizotropne permeabilnosti i brzine klizanja na učinak stisnutog sloja koji nastaje kada se gornja ploča sekantnog oblika s poroznom površinom nasloni na nepropusnu i ravnu kružnu donju ploču. Bezdimenzijski tlak, nosivost i vrijeme odziva izražavamo diferencijalnom jednadžbom. Izračunate vrijednosti za nosivost i vrijeme odziva prikazujemo u tablicama. Nalazi se da one opadaju pri porastu radijalne permeabilnosti, parametra klizanja i momenta tromosti. Međutim, one se povećavaju pri porastu aksijalne permeabilnosti i konstante materijala prema Jenkinsovom modelu. Također nalazimo da rastu kada je brzina gornje veća od brzine donje ploče

Učinak brzine posmika u poroznom ležaju s klizačem u obliku sekante i s ferofluidnim mazivom

We analysed a bearing with a secant shaped slider and with the stator having a porous facing backed by a solid wall, using a magnetic fluid lubricant flowing as per Jenkins model. Computed values of the bearing characteristics are displayed in tabular form. The load capacity, friction on the slider and the coefficient of friction decreased with increasing values of the slip parameter. The load capacity decreased and friction as well as the coefficient of friction increased with increasing values of the material parameter. However, the position of the centre of pressure did not significantly alter owing to the changes in slip parameter. But it slowly shifted towards the inlet when the material parameter increased.Analiziramo ležaj s klizačem u obliku sekante u kojemu je stator porozan s čvrstom podlogom, a rabi magnetsko tekuće mazivo koje teče prema Jenkinsovom modelu. Izračunate vrijednosti značajki ležaja prikazuju se u tablicama. Nosivost, trenje klizača i koeficijent trenja smanjuju se pri povećanju parametra posmicanja, a nosivost i trenje smanjuju se pri povećanju parametra materijala. Položaj središta tlaka ne mijenja se bitno zbog promjena parametra posmicanja, ali se pomalo pomiče prema ulazu pri povećanju parametra materijala