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1. A Single-Aperture, Single-Pixel Reader for Optical Frequency Identification

   https://doi.org/10.1109/ISCAS51556.2021.9401470  

   Fan, Xiaozhe; Hidalgo, James; Leon-Salas, Walter D. (May 2021, 2021 IEEE International Symposium on Circuits and Systems (ISCAS))

   null (Ed.)

   This paper presents a single-aperture, single-pixel reader for communication with Optical Frequency Identification (OFID) tags. OFID tags use solar cells to transmit and receive information wirelessly as well as to harvest radiant energy. Due to its single-aperture architecture, the reader's optical system provides a shared optical path for reception and transmission. Also, physical alignment between the reader and an OFID tag is visually guided using the reader's emitted light, securing a robust data link as long as the OFID tag is illuminated. In this paper, a description of the reader's optical and electronic sub-systems are presented. The transmitter and receiver circuits are described in detail. The transmitter, built with a linear LED driver, achieves a power efficiency of nearly 87%. The receiver, featuring a third-order bandpass filter, reduces both low-frequency and high-frequency ambient noise. A prototype of the reader was fabricated and housed in a custom 3D-printed enclosure. Test results show that the reader is able to receive modulated luminescent signals from an OFID tag at a distance of 1 m and at a data rate of 3 kbps. 

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2. An optical chip for a single atom single photon source

   Zhang, Jin; Oh, Eunji; Yu, Zhaoning; Mehlenbacher, Brandon; Kats, Mikhail; Goldsmith, Randall; Saffman, Mark (June 2021, DAMOP 2021, Bulletin of the American Physical Society)

   We report on progress towards a single atom, single photon source using a fiber connected optical chip. Quantum experiments with cold atoms are burdened by the complexity of the experimental apparatus. Using fiber connectorized optics and a grating MOT suitable for cooling Rb atoms we fabricate a pre-aligned device usable as a single photon source for quantum communication experiments. The device integrates a grating MOT with a single beam dipole trap produced by a fiber and GRIN lens combination. MOT atoms are loaded into the dipole trap and then used as a source of single photons which are collected by the same optical fiber. We will report on details of the fabrication of the optical chip, experimental characterization, and progress towards generating high purity single photons. 

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3. A single-point Reshetnyak’s theorem

   https://doi.org/10.1090/tran/9415  

   Kangasniemi, Ilmari; Onninen, Jani (May 2025, Transactions of the American Mathematical Society)

   We prove a single-value version of Reshetnyak’s theorem. Namely, if a non-constant map $f\in W_{\mathrm{l}\mathrm{o}\mathrm{c}}^{1,n}(\mathrm{\Omega },{\mathbb{R}}^n)$ from a domain $\mathrm{\Omega }\subset {\mathbb{R}}^n$ satisfies the estimate $\left|Df\right(x){|}^n\le K{J}_f(x)+\mathrm{\Sigma }(x\left)\right|f\left(x\right)-y_0{|}^n$ at almost every $x\in \mathrm{\Omega }$ for some $K\ge 1$, $y_0\in {\mathbb{R}}^n$ and $\mathrm{\Sigma }\in L_{\mathrm{l}\mathrm{o}\mathrm{c}}^{1+\epsilon }\left(\mathrm{\Omega }\right)$, then $f^{-1}\left\{y_0\right\}$ is discrete, the local index $i(x,f)$ is positive in $f^{-1}\left\{y_0\right\}$, and every neighborhood of a point of $f^{-1}\left\{y_0\right\}$ is mapped to a neighborhood of $y_0$. Assuming this estimate for a fixed $K$ at every $y_0\in {\mathbb{R}}^n$ is equivalent to assuming that the map $f$ is $K$-quasiregular, even if the choice of $\mathrm{\Sigma }$ is different for each $y_0$. Since the estimate also yields a single-value Liouville theorem, it hence appears to be a good pointwise definition of $K$-quasiregularity. As a corollary of our single-value Reshetnyak’s theorem, we obtain a higher-dimensional version of the argument principle that played a key part in the solution to the Calderón problem. 

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4. A fully-integrated single-photon source based on single Rb atoms

   HICKMAN, Garrett; VOLLBRECHT, Cecilia; MEHLENBACHER, Brandon; Yu, ZHAONING; XIAO, Yuzhe; Goldsmith, RANDALL; KATS, Mikhail; SAFFMAN, Mark (May 2019, 50th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics APS Meeting)

   We describe recent work towards a fully-integrated single-photon source based on the use of single atoms captured from a grating magneto-optical trap (GMOT). Single Rb atoms from a ber-coupled GMOT will be loaded into an optical dipole trap formed by light from an integrated polarization-maintaining (PM) ber. Trapped single atoms will be excited to the 2P1/2 state using resonant light. The resulting single-photon fluorescence will be collected through the same PM ber as is used for trapping, and routed to further experiments. We describe progress towards an intermediate imple- mentation incorporating integrated optical bers and free space light sources. The completed, fully-integrated single-photon source will have numerous applications in quantum communications and quantum information processing, and particularly in improvement of the performance of quantum key distribution systems. 

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5. Nanopores map the acid-base properties of a single site in a single DNA molecule

   https://doi.org/10.1093/nar/gkae518  

   Smith, Drew C.; Thomas, Christopher A.; Craig, Jonathan M.; Brinkerhoff, Henry; Abell, Sarah J.; Franzi, Michaela C.; Carrasco, Jessica D.; Hoshika, Shuichi; Benner, Steven A.; Gundlach, Jens H.; et al (June 2024, Nucleic Acids Research)

   Abstract Nanopores are increasingly powerful tools for single molecule sensing, in particular, for sequencing DNA, RNA and peptides. This success has spurred efforts to sequence non-canonical nucleic acid bases and amino acids. While canonical DNA and RNA bases have pKas far from neutral, certain non-canonical bases, natural RNA modifications, and amino acids are known to have pKas near neutral pHs at which nanopore sequencing is typically performed. Previous reports have suggested that the nanopore signal may be sensitive to the protonation state of an individual moiety. We sequenced ion currents with the MspA nanopore using a single stranded DNA containing a single non-canonical DNA base (Z) at various pH conditions. The Z-base has a near-neutral pKa ∼ 7.8. We find that the measured ion current is remarkably sensitive to the protonation state of the Z-base. We demonstrate how nanopores can be used to localize and determine the pKa of individual moieties along a polymer. More broadly, these experiments provide a path to mapping different protonation sites along polymers and give insight in how to optimize sequencing of polymers that contain moieties with near-neutral pKas. 

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