Abstract
Ultracold collisions of Bose–Einstein condensates can be used to generate a large number of counter-propagating pairs of entangled atoms, which collectively form a thin spherical shell in momentum space, called a scattering halo. Here we generate a scattering halo initially composed of pairs in a symmetric entangled state in spin, and observe a coherent oscillation with an anti-symmetric state during their separation, due to the presence of an inhomogeneous magnetic field. We demonstrate a novel method of magnetic gradiometry based on the evolution of pairwise correlation, which is insensitive to common-mode fluctuations of the magnetic field. Furthermore, the highly multimode nature and narrow radial width of scattering halos enable a 3D reconstruction of the interrogated field. Based on this, we apply Ramsey interferometry to realise a 3D spatial reconstruction of the magnetic field without the need for a scanning probe.
Highlights
Ultracold collisions of Bose-Einstein condensates can be used to generate a large number of counterpropagating pairs of entangled atoms, which collectively form a thin spherical shell in momentum space, called a scattering halo
Ultracold atom microscopes rely on reconstruction of the magnetic field via imaging density modulations in elongated trapped ensembles [16, 18], or in-trap atom interferometry [14] for AC magnetometry, whilst scanning the trapped cloud over the interrogation area
We report on proof-of-principle demonstration of entanglement-based magnetic gradiometry using strongly entangled pairs of atoms created from a collision between two Bose-Einstein condensates (BECs) [20]
Summary
Different pulse sequences are implemented for the two schemes reported here, namely entanglement-based magnetic gradiometry (Fig. 1(b)) and magnetometry (Fig. 1(c)). A Stern-Gerlach (SG) sequence separates the different mJ -sublevels and the 3D position of each atom is detected in the far-field (416 ms free-fall) with a quantum efficiency of η ≈ 0.1, where each mJ -scattering halo is a thin spherical shell (see Fig. 1(d)). The interrogation sequence for magnetometry begins 3 ms after the |↑ -halo is created – at which point the halo diameter has expanded to be D ≈ 360 μm – when we apply a π/2 rotation pulse which prepares each atom in an equal superposition of |↑ and |↓ (see Fig. 1(c)). (a) Normalised polarisation P (markers) and fitted Ramsey signal (lines) for selected regions on the halo indicated in (b). (b) Spatial distribution of the measured magnetic field B on the scattering halo, and a histogram of B. All error bars and shaded regions indicate a 1σ standard error in the mean
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