Number-resolved preparation of mesoscopic atomic ensembles

Abstract

The analysis of entangled atomic ensembles and their application for interferometry beyond the standard quantum limit requires an accurate determination of the number of atoms. We present an accurate fluorescence detection technique for atoms that is fully integrated into an experimental apparatus for the production of many-particle entangled quantum states. Number-resolved fluorescence measurements with single-atom accuracy for 1 up to 30 atoms are presented. According to our noise analysis, we extrapolate that the single-atom accuracy extends to a limiting atom number of 390(20) atoms. We utilize the accurate atom number detection for a number stabilization of the laser-cooled atomic ensemble. For a target ensemble size of 7 atoms prepared on demand, we achieve a 92(2)% preparation fidelity and reach number fluctuations 18(1) dB below the shot noise level using real-time feedback on the magneto-optical trap.

Rapid generation and number-resolved detection of spinor Rubidium Bose-Einstein condensates

“…The counting noise depends on the total number of atoms and is well described by Gaussian functions with a width σ N = 0.169+0.0017N . Assuming a linear scaling, this al-lows for single-particle detection of more than 400 atoms, in correspondence to our earlier quantification [28]. The data can now be binned at half-integer binning limits, with a number assignment fidelity ranging from 99.7% at 1 atom to 99.0% at 15 atoms.…”

“…Due to spatial constraints, the new horizontal beams enter the science glass cell under an angle of 35 • . This changed angle results in a higher background scattering in our detection objective and therefore in higher background noise σ bg,new = 0.15 compared to 0.03 in the previous set-up [28]. Fig.…”

“…The BEC generation relies on a macroscopic quadrupole trap combined with a crossed-beam optical dipole trap (cODT). The fluorescence detection is a fiber-based second generation from an earlier implementation [28]. This article describes the experimental set-up and the obtained results, also as a reference for the quantum detector tomography reported in the accompanying publication [1].…”

“…We detect the number of selected atoms in the F = 1 manifold with an improved mMOT set-up that is based on the system described in Ref. [28]. The initial version of the detection set-up included beams distributed via free-space optics so that they could be superimposed Schematic of the experimental sequence.…”

Nonlinear interferometry beyond classical limit facilitated by cyclic dynamics

“…Nonlinear interferometry based on time reversal protocol [11][12][13] was proposed to circumvent low-noise detection unanimously required in entanglement-enhanced metrology based on linear interferometry, where the improvement to measurement signal-to-noise ratio (SNR) comes from reduced quantum noise by correlations between entangled particles [19][20][21][22][23][24][25][26]. To benefit from such squeezed noise, however, other noises especially the readout (or detection) noise must be made smaller, which is technically challenging for ensembles of large particle numbers [27][28][29]. Nonlinear interferometry improves SNR by magnifying signal instead, hence it is inherently robust against detection noise [11][12][13].…”