Fredrik K. Fatemi

National Institute of Standards and Technology, GAI, Maryland, United States

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Publications (75)118.74 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Optical nanofibers (ONFs) provide a rich platform for exploring atomic and optical phenomena even when they support only a single spatial mode. Nanofibers supporting higher-order modes (HOMs) provide additional degrees of freedom to enable complex evanescent field profiles for interaction with the surrounding medium, but local control of these profiles requires nondestructive evaluation of the propagating fields. Here, we use Rayleigh scattering for rapid measurement of the propagation of light in few-mode ONFs. Imaging the Rayleigh scattered light provides direct visualization of the spatial evolution of propagating fields throughout the entire fiber, including the transition from core-cladding guidance to cladding-air guidance. We resolve the interference between HOMs to determine local beat lengths and modal content along the fiber, and show that the modal superposition in the waist can be systematically controlled by adjusting the input superposition. With this diagnostic we can measure variations in the radius of the fiber waist to below 3 nm in situ using purely optical means. This nondestructive technique also provides useful insight into light propagation in ONFs.
    Optica 05/2015; 2(5):416. DOI:10.1364/OPTICA.2.000416
  • Fredrik K. Fatemi · Guy Beadie
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    ABSTRACT: We use high-resolution imaging of Rayleigh scattered light through the side of few-mode optical fibers to measure the local spatial structure of propagating vector fields. We demonstrate the technique by imaging both pure modes and superpositions of modes in the LP01 and LP11 families. Direct imaging not only gives high-resolution beat length measurements, but also records the local propagation dynamics including those due to perturbations. The imaging setup uses polarization discrimination to monitor both the transverse and the longitudinal polarization components simultaneously.
    Optics Express 02/2015; 23(3):3831. DOI:10.1364/OE.23.003831 · 3.49 Impact Factor
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    Fredrik K Fatemi · Guy Beadie
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    ABSTRACT: We have used common path interferometry for rapid determination of the electric field and complex modal content of vector beams, which have spatially-varying polarization. We combine a reference beam with a signal beam prior to a polarization beam splitter for stable interferograms that preserve intermodal phase shifts even in noisy environments. Interferometric decomposition into optical modes (IDIOM) provides a direct, sensitive measure of the complete electric field, enabling rapid modal decomposition and is ideally suited to single-frequency laser sources. We apply the technique to beams exiting optical fibers that support up to 10 modes. We also use the technique to characterize the fibers by determining a scattering matrix that transforms an input superposition of modes into an output superposition. Furthermore, because interferograms are linear in the field, this technique is very sensitive and can accurately reconstruct beams with signal-to-noise < 1.
    Optics Express 12/2013; 21(26):32291-305. DOI:10.1364/OE.21.032291 · 3.49 Impact Factor
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    ABSTRACT: Hybrid quantum systems can be formed that combine the strengths of multiple platforms while avoiding the weaknesses. Here we report on progress toward a hybrid quantum system of neutral atom spins coupled to superconducting qubits. We trap laser-cooled rubidium atoms in the evanescent field of an ultrathin optical fiber, which will be suspended a few microns above a superconducting circuit that resonates at the hyperfine frequency of the Rb atoms, allowing magnetic coupling between the atoms and superconductor. As this will be done in a dilution refrigerator environment, the technical demands on the optical fiber is severe. We have developed and optimized a tapered fiber fabrication system, achieving optical transmission in excess of 99.95% , and fibers that can sustain 400 mW of optical power in a UHV environment. We have also optimized tapered fibers that can support higher order optical modes with high transmission (> 97%), which may be useful for different optical potential geometries. We have developed an in-situ tunable high-Q superconducting microwave resonator that can be tuned to within the resonator linewidth of the 6.8 GHz frequency of the Rb hyperfine transition.
    Proceedings of SPIE - The International Society for Optical Engineering 09/2013; DOI:10.1117/12.2024362 · 0.20 Impact Factor
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    ABSTRACT: Optical nanofibers confine light to subwavelength scales, and are of interest for the design, integration, and interconnection of nanophotonic devices. Here we demonstrate high transmission (> 97%) of the first family of excited modes through a 350 nm radius fiber, by appropriate choice of the fiber and precise control of the taper geometry. We can design the nanofibers so that these modes propagate with most of their energy outside the waist region. We also present an optical setup for selectively launching these modes with less than 1% fundamental mode contamination. Our experimental results are in good agreement with simulations of the propagation. Multimode optical nanofibers expand the photonic toolbox, and may aid in the realization of a fully integrated nanoscale device for communication science, laser science or other sensing applications.
    Optics Express 08/2013; 21(15). DOI:10.1364/OE.21.018325 · 3.49 Impact Factor
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    ABSTRACT: Biocompatible, near-infrared luminescent gold nanoclusters (AuNCs) are synthesized directly in water using poly(ethylene glycol)-dithiolane ligands terminating in either a carboxyl, amine, azide, or methoxy group. The ≈1.5 nm diameter AuNCs fluoresce at ≈820 nm with quantum yields that range from 4–8%, depending on the terminal functional group present, and display average luminescence lifetimes approaching 1.5 μs. The two-photon absorption (TPA) cross-section and two-photon excited fluorescence (TPEF) properties are also measured. Long-term testing shows the poly(ethylene glycol) stabilized AuNCs maintain colloidal stability in a variety of media ranging from saline to tissue culture growth medium along with tolerating storage of up to 2 years. DNA and dye-conjugation reactions confirm that the carboxyl, amine, and azide groups can be utilized on the AuNCs for carbodiimide, succinimidyl ester, and CuI-assisted cycloaddition chemistry, respectively. High signal-to-noise one- and two-photon cellular imaging is demonstrated. The AuNCs exhibit outstanding photophysical stability during continuous-extended imaging. Concomitant cellular viability testing shows that the AuNCs also elicit minimal cytotoxicity. Further biological applications for these luminescent nanoclustered materials are discussed.
    Particle and Particle Systems Characterization 05/2013; 30(5-5):453-466. DOI:10.1002/ppsc.201200140 · 0.54 Impact Factor
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    ABSTRACT: To create a hybrid quantum system, we plan to trap neutral atoms in the evanescent optical field from an optical nanofiber and move them to within a few microns above a SQUID in a dilution refrigerator that operates at 10 mK. A key component in this experiment is a long section (10 cm) of optical fiber with a uniform diameter of about 500 nm, sufficiently small that the light propagates on the surface of the fiber as an evanescent wave. We have produced suitably long nanofibers with carefully tapered sections that allow matching of the optical field in the tapered and untapered sections. We have achieved more than 99.95% transmission of the fundamental mode and good evanescent fields; as well as more than 85% transmission when using higher order modes. A single-beam, magneto-optical trap that uses optical gratings captures and cools atoms to load on the nanofiber to work at cryogenic temperatures. We will present our technique, key results, and progress towards trapping atoms on the fibers.
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    ABSTRACT: We have demonstrated efficient propagation of the first excited TE01, TM01, and HE21 modes in a nanofiber with a radius of 400 nm. As we decrease the taper angle from 4 mrad to 1 mrad, the propagation becomes more adiabatic and the transmission improves from 20% to 85%. We have also demonstrated that the choice of drawn fiber can have a significant impact on the propagation characteristics.
    Proceedings of SPIE - The International Society for Optical Engineering 03/2013; 8637. DOI:10.1117/12.2004429 · 0.20 Impact Factor
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    Joseph A Pechkis · Fredrik K Fatemi
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    ABSTRACT: We demonstrate guiding of cold 85Rb atoms through a 100-micron-diameter hollow core dielectric waveguide using cylindrical hollow modes. We have transported atoms using blue-detuned light in the 1st order, azimuthally-polarized TE01 hollow mode, and the 2nd order hollow modes (HE31, EH11, and HE12), and compared these results with guidance in the red-detuned, fundamental HE11 mode. The blue-detuned hollow modes confine atoms to low intensity along the capillary axis, far from the walls. We determine scattering rates in the guides by directly measuring the effect of recoil on the atoms. We observe higher atom numbers guided using red-detuned light in the HE11 mode, but a 10-fold reduction in scattering rate using the 2nd order modes, which have an r4 radial intensity profile to lowest order. We show that the red-detuned guides can be used to load atoms into the blue-detuned modes when both high atom number and low perturbation are desired.
    Optics Express 06/2012; 20(12):13409-18. DOI:10.1364/OE.20.013409 · 3.49 Impact Factor
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    ABSTRACT: Atoms confined to evanescent-field traps or lattices near tapered optical fibers are strongly coupled to photons propagating through the fiber. This strong coupling is ideal for quantum technologies and sensors. Previously, light propagation and strong atom-photon interactions have been demonstrated in fibers with submicron diameters, small enough to admit only the HE11 mode. Higher order cylindrical vector modes, which have azimuthally-varying polarization profiles, open another set of trapping geometries in fibers with diameters slightly above the HE11 cutoff value. In this work, we discuss propagation experiments in tapered fibers that allow the first excited family of modes. We have observed stable transmission of the TE01, TM01, and HE21 modes in 1.2-micron-diameter fiber, currently with 25% throughput. Transmitted power and beam profiles monitored during the drawing process show interesting power exchange between core and cladding modes, and by adjusting the drawing parameters we have experimentally probed the propagation behavior. Work supported by ONR, ARO, the Fulbright Foundation and the NSF through the PFC at JQI.
  • Joseph A. Pechkis · Fredrik K. Fatemi
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    ABSTRACT: We have guided cold rubidium atoms in blue-detuned hollow optical modes of a hollow fiber. These higher order modes allow large optical depth, low scattering rates, and efficient use of guide laser power. Atoms are transported through a 3-cm-long hollow fiber with a 100 micron diameter using the first three optical modes of the fiber. We compare guiding properties in the red-detuned, fundamental HE11 mode with the blue-detuned TE01 (first order) and HE12 (second order) modes. Using guide laser powers below 50 mW and detunings below 1.5 nm, we have directly measured recoil scattering rates in the three different guides and found that atoms in the HE12 mode typically have a 10x lower recoil scattering rate compared to the red-detuned HE11 mode for equal guide peak intensity. Furthermore, we have observed optical depths of ˜20 for the blue-detuned guides with recoil scattering rates below 10 Hz. We will discuss our ongoing experiments using the atoms in these guides. This work supported by the Office of Naval Research and the Defense Advanced Research Projects Agency.
  • Mark Bashkansky · Fredrik K. Fatemi · Igor Vurgaftman
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    ABSTRACT: Quantum memory is regarded as one of the essential components in the fields of quantum computing and quantum communication. Warm atomic vapor cells for quantum memory, as originally described in DLCZ (for Duan, Lukin, Cirac, and Zoller) protocol, are appealing due to the perceived reduction in experimental complexity and commercial availability. However, published studies on quantum memory using warm vapor cells were performed under widely dissimilar experimental conditions and reported ambiguous results. In order for the memory to exhibit non-classical behavior to a high degree of certainty, the cross-correlation value between the Stokes and anti-Stokes photons needs to be greater than two. In this work we demonstrate quantum memory with cross-correlation value between the Stokes and anti-Stokes photons greater than two lasting for 4 μs using warm Rb vapor with buffer gas for nearly co-propagating write and read beams.
    Proceedings of SPIE - The International Society for Optical Engineering 05/2012; DOI:10.1117/12.918306 · 0.20 Impact Factor
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    Mark Bashkansky · Fredrik K Fatemi · Igor Vurgaftman
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    ABSTRACT: The realization of quantum memory using warm atomic vapor cells is appealing because of their commercial availability and the perceived reduction in experimental complexity. In spite of the ambiguous results reported in the literature, we demonstrate that quantum memory can be implemented in a single cell with buffer gas using the geometry where the write and read beams are nearly co-propagating. The emitted Stokes and anti-Stokes photons display cross-correlation values greater than 2, characteristic of quantum states, for delay times up to 4 microseconds.
    Optics Letters 01/2012; 37(2):142-4. DOI:10.1364/OL.37.000142 · 3.18 Impact Factor
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    Fredrik K. Fatemi
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    ABSTRACT: We demonstrate the use of cylindrical vector beams - beams with spatially varying polarization - for detecting and preparing the spin of a warm rubidium vapor in a spatially dependent manner. We show that a modified probe vector beam can serve as an atomic spin analyzer for an optically pumped medium, which spatially modulates absorption of the beam. We also demonstrate space-variant atomic spin by optical pumping with the vector beams. The beams are thus beneficial for making singleshot polarization-dependent measurements, as well as for providing a means of preparing samples with position-dependent spin.
    Optics Express 12/2011; 19(25):25143-50. DOI:10.1364/OE.19.025143 · 3.49 Impact Factor
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    G S Pati · F K Fatemi · M S Shahriar
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    ABSTRACT: We report observation of query pulse length dependent Ramsey interference (QPLD-RI), using pulsed Raman excitation in rubidium vapor. This is observed when a long, attenuated query pulse is used during pulsed Raman excitation. We explain the physical mechanism behind the QPLD-RI using a Bloch vector model. We also use numerical solutions to time-dependent density matrix equations to simulate this interference effect, showing qualitative agreement with experimental results. Presence of such interference could create a potential source of error in a vapor cell Raman clock constructed using frequency-domain Ramsey interference (FDRI).
    Optics Express 11/2011; 19(23):22388-401. DOI:10.1364/OE.19.022388 · 3.49 Impact Factor
  • Matthew L. Terraciano · Spencer E. Olson · Fredrik K. Fatemi
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    ABSTRACT: We have observed time-varying spin relaxation of trapped cold atoms due to photon scattering in blue-detuned, crossed, hollow Laguerre-Gaussian beams. These beams are formed by imparting an azimuthal phase of ℓφ to a Gaussian beam, where ℓ is an integer, and have an intensity distribution that scales with r2ℓ to the lowest order. For all degrees of anharmonicity, we observe a time-varying spin-relaxation rate due to energy-dependent photon scattering. For ℓ=8, we directly measure temperature-dependent scattering rates and show that by removing the most energetic atoms from the trap, a more purely spin-polarized sample remains. The results agree well with Monte Carlo simulations, and we present a simple functional form for the spin-relaxation curves.
    Physical Review A 08/2011; 84(2). DOI:10.1103/PhysRevA.84.025402 · 2.99 Impact Factor
  • Fredrik Fatemi · Guy Beadie
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    ABSTRACT: Cylindrical vector beams (CVBs), which have an azimuthally varying polarization profile, are ideal for investigating polarization-dependent effects in a single measurement. In this work, we demonstrate EIT with a uniform pump field that is probed by the CVB in a warm vapor of Rb85. The CVB can be formed containing either all linear polarizations or all degrees of ellipticity. The presence of EIT is recorded by a CCD camera so that the effects of different polarizations can be distinguished simultaneously. The polarization dependence of EIT results in strong spatial modulation of the transmitted probe intensity. We discuss our technique for generating the CVBs, interpret the images based on the relevant coupling strengths, and discuss future CVB experiments and applications.
  • Gour S. Pati · Fredrik K. Fatemi · Mark Bashkansky · Selim M. Shahriar
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    ABSTRACT: Pulsed coherent population trapping in atomic vapor provides a convenient method for generating frequency narrowed atomic resonance using Ramsey interference. Here, we present our experimental results showing high-contrast and sub-kilohertz Ramsey interference fringes produced by coherently prepared 85Rb atoms using Raman excitation formed in D1 line transitions. A test system for atomic clock has been constructed to measure light shift for both continuous and pulsed Raman excitation cases. Our measurements show that light shift measured using pulsed Raman excitation, is reduced compared to the continuous excitation case. Our ability to measure light shift is currently limited by the resolution of the frequency counter, and performance of the locking electronics used.
    Proceedings of SPIE - The International Society for Optical Engineering 02/2011; DOI:10.1117/12.880779 · 0.20 Impact Factor
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    Spencer E. Olson · Andrew J. Christlieb · Fredrik K. Fatemi
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    ABSTRACT: Parallel code presents a non-trivial problem of load balancing computational workload throughout a system of hardware and software resources. The task of load balancing is further complicated when the number of allowable processors changes through time. This paper presents a two-component load-balancing mechanism using optimal initial workload distribution and dynamic load maintenance. The initial guess is provided by inversion of the workload distribution function. Workload distribution inversion enables efficient domain decomposition for arbitrary workloads and easily compensates for changes in system resources. Dynamic load balancing is provided by process feedback control as used, for example, in control mechanisms of physical processes. Proportional, integral, and differential (PID) feedback readily allows controls to compensate for runtime-changes of the workload distribution function. This paper demonstrates a one-dimensional realization of the ideas presented here. We apply this load-balancing technique to our gridless direct simulation Monte Carlo algorithm. We demonstrate that the method does indeed maintain uniform workload distribution across available resources as the workload and usable system resources undergo change through time.
    Computer Physics Communications 12/2010; 181(12):2063-2071. DOI:10.1016/j.cpc.2010.06.045 · 2.41 Impact Factor
  • Fredrik K. Fatemi · G. Beadie
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    ABSTRACT: We have used cylindrical vector beams to probe an optically pumped warm rubidium vapor. Optical pumping produces a spatial modulation of the vector beam according to the spin state of the atoms.