Ockeloen, C.F.

Spreeuw, R.J.C.

Tauschinsky, A.F.

van Druten, N.J.

Whitlock, S.

English

International Migration, Integration and Social Cohesion online publications

UvA-DARE is a service provided by the library of the University of Amsterdam (https://dare.uva.nl)UvA-DARE (Digital Academic Repository)Improved detection of small atom numbers through image processingTauschinsky, A.F.; Ockeloen, C.F.; van Druten, N.J.; Whitlock, S.; Spreeuw, R.J.C.Publication date2013Document VersionFinal published versionPublished inApplication note DU934N-BR-DDLink to publicationCitation for published version (APA):Tauschinsky, A. F., Ockeloen, C. F., van Druten, N. J., Whitlock, S., & Spreeuw, R. J. C.(2013). Improved detection of small atom numbers through image processing. Applicationnote DU934N-BR-DD. http://www.lot-oriel.com/files/downloads/andor/en/AP_Improved_detection_of_small_atom_numbers.pdfGeneral rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s)and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an opencontent license (like Creative Commons).Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, pleaselet the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the materialinaccessible and/or remove it from the website. Please Ask the Library: https://uba.uva.nl/en/contact, or a letterto: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. Youwill be contacted as soon as possible.Download date:09 Mar 2023Improved detection of small atom numbers  through image processing A. F. Tauschinsky, C. F. Ockeloen, N. J. van Druten, S. Whitlock, R. J. C. Spreeuw  Van der Waals-Zeeman Institute for Experimental Physics, University of Amsterdam, The Netherlands (February 2013)Application NoteLOT-QuantumDesign GmbH. Im Tiefen See 58. D-64293 Darmstadt.  +49 6151 8806 0.  info@lot-qd.de. www.lot-qd.com/ccd IntroductionTrapped ultracold atoms and quantum degenerate gases are novel systems for the study of many-body quantum physics and are key to new technologies such as trapped atom interferometer and atomic clocks. Essential to such applications is the ability to precisely measure the populations of a pair of atomic ensembles in, for example, a double-well potential for Josephson physics or atom interferometry or the spin states of an atomic clock.Experimental SetupWe have recently demonstrated [1] improved detection of trapped ensembles of ultracold atoms through ad-vanced post-processing and optimal analysis of laser-illuminated absorption images. This crucially depends on the properties of the camera used for absorption imaging. This allows us to better measure the intrinsic atom number fluctuations in a magnetic lattice potential [3], but has important implications for most experiments on ultracold atoms relying on absorption imaging for data acquisition.CCDAOPSabFIG. 1. (a) Schematic depiction of the mirror imaging setup, showing the atom chip (A), probe beam (P), lens system (O, S) and CCD camera. The angle of the probe beam has been exaggerated to illustrate the reflection setup. (b) Close-up around the atom chip surface. Part of the probe light is reflected before and part after passing through the atoms, depicted by solid and dashed lines, respectively. The two separate shadows cast by the atoms are then imaged onto separate regions of the CCD camera.Absorption imaging is the standard method for detect-ing trapped neutral atoms. Here atoms are briefly exposed to a nearly homogeneous probe laser, typi-cally tuned to resonance with an atomic transition and the resulting absorption signal A is imaged onto a CCD camera. Subsequently the atoms are ejected from the trap and a reference image R is recorded to normal-ize intensity variations of the probe. A dark image may also be recorded without the probe to subtract any stray light or CCD dark counts. From this data it is possible to extract information on the two-dimensional density distribution of the atoms.n(atoms/pixel)02468101250 µmFIG. 2. Typical absorption image of the atomic distribution (90 x 71 pixels) for a hold time of 1.6 s. Four independent atomic ensembles are visible (horizontally distributed) with two mirror images (vertically separated). The two center-most clouds each contain ~400 atoms. Dashed boxes indicate the background pixels for the fringe removal algorithm and the signal regions are indicated by solid lines.Our experiments employ a back-illuminated deep-de-pletion CCD camera (Andor iKon-M DU934N-BR-DD) with a quantum efficiency of Qe ≈ 0.9 at = 780 nm, a measured gain of g = 0.87 ±0.05 counts/photon and a readout noise level of σrd ≈ 14 electrons (A/D rate 2.5 MHz, pre-amplifier gain 4.6 electrons/count). The resolution of our optical system is 9.6 µm (Rayleigh criterion) with a pixel area of Δ = (3.3 ±0.1 µm)2 in the object plane. The probe is slightly inclined with respect to the gold-coated chip surface to create two mirror images of the atoms (fig. 2). The imaging setup is depicted in figure 1 and an example of the resulting images can be seen in figure 2.Improved detection of small atom numbers  through image processing A. F. Tauschinsky, C. F. Ockeloen, N. J. van Druten, S. Whitlock, R. J. C. Spreeuw  Van der Waals-Zeeman Institute for Experimental Physics, University of Amsterdam, The Netherlands (February 2013)Application NoteLOT-QuantumDesign GmbH. Im Tiefen See 58. D-64293 Darmstadt.  +49 6151 8806 0.  info@lot-qd.de. www.lot-qd.com/ccd ResultsFigure 3 shows the imaging noise with and without fringe removal [2], var(A/Q) and var(A/R) respective-ly, calculated for a signal-free region (separate from the fringe-removal background region) for various probe intensities.  100 300 1000 3000 1000010−410−310−210−1R var(A/R),var(A/Q)  Raw imagesFringe removalPredicted noiseUltimate limit102103104123R var(A/R)var(A/Q)FIG. 3. Imaging noise for various probe intensities with and without fringe removal, var(A/Q) (circles) and var(A/R) (squares) respectively. The predicted photon shot-noise plus camera readout noise is shown as a solid line. The dashed line shows the ultimate photon shot-noise limit.Without fringe removal the measured noise is in good agreement with the expected photon shot noise and readout noise given our CCD parameters. Application of the fringe removal algorithm with a basis of 250 reference images reduces the measured variances by a factor of 1.9 ± 0.3 over the full range of intensities. Re-markably, even in the absence of fringes, the algorithm reduces the photon shot-noise contribution originating from R. This is possible since the optimal reference image is the (weighted) average over many reference images, allowing an additional decrease of uncor-related noise by up to a factor of 2. For our chosen imaging parameters the remaining noise from pixel to pixel is σn = 1.3 ±0.3 atoms, close to the ultimate limit of 1.1 atoms due to photon shot noise in A. There is also a small residual correlated noise component which fluctuates on a length scale comparable to our cloud size with an rms amplitude of 0.06 ±0.01 atoms.References[1] C. Ockeloen, A. Tauschinsky, R. Spreeuw, and S. Whitlock. Detection of small atom numbers through image processing. Physical Review A, 82(6):061606, December 2010. [2] Caspar F. Ockeloen. Probing fluctuations in a lat-tice of mesoscopic atomic ensembles. Msc. thesis, University of Amsterdam, 2010. URL http://www.science.uva.nl/research/aplp/eprints/Caspar_Ockeloen_MSc2010.pdf.[3] S. Whitlock, C. F. Ockeloen, and R. J. C. Spre-euw. Sub-Poissonian Atom-Number Fluctuations by Three-Body Loss in Mesoscopic Ensembles. Physical Review Let-ters, 104(12):120402, March 2010. ContactDr. N.J. van DrutenVan der Waals-Zeeman Institute for Experimental Physics Universiteit van AmsterdamScience Park 904Room C4.2551098 XH AmsterdamThe NetherlandsE-mail: N.J.vanDruten@uva.nlPhone: +31 (20) 525 7118Web: http://www.science.uva.nl/~druten

Improved detection of small atom numbers through image processing

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Improved detection of small atom numbers through image processing

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