Universality of quantum diffractive collisions and the quantum pressure standard

Abstract

This work demonstrates that quantum diffractive collisions are governed by a universal law characterized by a single parameter that can be determined experimentally. Specifically, we report a quantitative form of the universal, cumulative energy distribution transferred to initially stationary sensor particles by quantum diffractive collisions. The characteristic energy scale corresponds to the localization length associated with the collision-induced quantum measurement, and the shape of the universal function is determined only by the analytic form of the interaction potential at long range. Using cold 87 Rb sensor atoms confined in a magnetic trap, we observe experimentally p QDU6 , the universal function specific to van der Waals collisions, and use it to realize a self-defining particle pressure sensor that can be used for any ambient gas. This provides the first primary and quantum definition of the Pascal, applicable to any species and therefore represents a fundamental advance for vacuum and pressure metrology. The quantum pressure standard realized here is compared with a state-of-the-art orifice flow standard transferred by an ionization gauge calibrated for N 2 . The pressure measurements agree at the 0.5% level. m d 4 2 t  º p s ̶ [4]. Here m t is the mass of the sensor particle and s ̶ is the thermally-averaged total collision cross section, including contributions from both elastic and inelastic scattering. We further demonstrate that s ̶ is independent of the short-range interaction between the colliding particles with van der Waals long-range interactions.It is well known that collisions resulting in small momentum transfer are dominated by quantum diffractive scattering [4,5]. Such collisions occur with small scattering angles 0 q  and are predominantly determined by OPEN ACCESS RECEIVED

Cross-calibration of atomic pressure sensors and deviation from quantum diffractive collision universality for light particles

“…Laser cooled atoms confined in a magnetic or magneto-optical trap can be used as sensors of absolute pressure and particle flux measurements in vacuum [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. For example, the background gas density or pressure can be determined by observing loss of trapped atoms induced by collisions with ambient atoms or molecules.…”

“…We have recently demonstrated a different approach to determine the collision cross section by measuring the dependence of loss of trapped atoms on the trap depth [11]. Such measurements rely on the universal function (p QDU6 ) for the energy distribution imparted to the sensor atom by quantum diffractive collisions mediated by van der Waals interactions.…”

Comparison of two multiplexed portable cold-atom vacuum standards

“…Cold-atom vacuum standards promise to deliver accurate measurements of vacuum in the ultra-high vacuum (UHV, < 10 −6 Pa) and extreme-high vacuum (XHV, < 10 −9 Pa) regimes. [1][2][3][4][5] In these regimes, hot-cathode ionization gauges, such as Bayard-Alpert gauges and their derivatives, are the typical means of pressure measurement. [6][7][8] Yet they suffer from several known systematics, including unwanted X-rayinduced currents, electron stimulated desorption of ions and neutrals, and thermal outgassing.…”

“…Thus far, all cold-atom vacuum standards have been laboratory-scale devices and are not suitable replacements for an ionization gauges. 1,4,5 Here, we directly compare two portable cold-atom vacuum standards (pCAVS) based on ultracold lithium, the main components of which have been used to demonstrate a compact apparatus for laser cooling and trapping of strontium. 9 The gauge head (not including the laser system) fits within a roughly 15 cm × 35 cm × 50 cm cuboid; the vacuum components of our standard comprise a total volume of approximately 1.3 L. The cost of the cold-atom vacuum standard is primarily driven by the laser system used to cool, trap, and count the atoms.…”

Study of loss dynamics of strontium in a magneto-optical trap

“…* Electronic mail: umakant.rapol@iiserpune.ac.in While previous studies on BGC-induced shifts have mainly focused on H 2 because it is typically the dominant species present in the vacuum chamber, it is anticipated that as the clock uncertainties continue to improve, it may become necessary to account for the contribution of other background gas species such as N 2 . Dispersion coefficients have been estimated for collisions of N 2 with alkali, noble, and various molecular gases and collisional cross sections have been reported for Rb−N 2 [21,22], Ne*−N 2 [23,24], Na−N 2 [25] and Ar−N 2 [26], but so far Sr−N 2 collisional properties have not been investigated.…”