Alexander Ling

University of Maryland, College Park, Maryland, United States

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Publications (31)57.79 Total impact

  • Alexander Ling, Jingyun Fan, Alan Migdall
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    ABSTRACT: We report on our efforts in integrating a source and detection system of photon pairs that have a high end-to-end system efficiency. This requires combining appropriate detectors and photon pair sources. Preliminary measurements show that an observed heralding efficiency of 65% for single photons is readily achieved.
    Proceedings of SPIE - The International Society for Optical Engineering 08/2010; · 0.20 Impact Factor
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    ABSTRACT: We map the transverse profile of light beams using photon-number-resolving detectors, and observe compression of beam profiles for higher detected photon-number, enabling contrast enhancement between two Airy disk beams at the Rayleigh limit.
    Lasers and Electro-Optics (CLEO) and Quantum Electronics and Laser Science Conference (QELS), 2010 Conference on; 06/2010
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    ABSTRACT: We show that with simple spectral filtering, the Schmidt number for the transmitted photon-pairs (with 90% transmittance) which are produced via type-II parametric down-conversion in a KTP waveguide equals to unity to within 0.2 %.
    05/2010;
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    ABSTRACT: We report on an experimental implementation of an interface between quantum dots (QD) and parametric downconversion (PDC). We present a PDC source compatible with QD emission and our efforts to demonstrate such compatibility.
    05/2010;
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    ABSTRACT: We use strain to tune into resonance two different, remote quantum dots and show that the emitted photons will produce Hong-Ou-Mandel interference. Pulsed excitation will allow deterministic timing of these indistinguishable photons.
    05/2010;
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    ABSTRACT: We experimentally map the transverse profile of diffractionlimited beams using photon-number-resolving detectors.We observe strong compression of diffracted beam profiles for high detected photon number. This effect leads to higher contrast than a conventional irradiance profile between two Airy disk-beams separated by the Rayleigh criterion.
    Optics Express 03/2010; 18(6):6033-9. · 3.53 Impact Factor
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    ABSTRACT: We analyze the generation of single spatial mode, spectrally uncorrelated photon pairs via type II spontaneous parametric down-conversion in a Potassium Titanyl Phosphate (KTP) waveguide using real experimental parameters. We show that this source can be used as an efficient, heralded, pure-state single-photon source.
    Optics Express 02/2010; 18(4):3708-18. · 3.53 Impact Factor
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    ABSTRACT: We use strain to tune into resonance two different, remote quantum dots and show that the emitted photons will produce Hong-Ou-Mandel interference.
    Lasers and Electro-Optics (CLEO) and Quantum Electronics and Laser Science Conference (QELS), 2010 Conference on; 01/2010
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    Alexander Ling, Jun Chen, Jingyun Fan, Alan Migdall
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    ABSTRACT: We report the development of a fiber-based single spatial-mode source of photon-pairs where the efficiency of extracting photon-pairs is increased through the use of fiber-end expansion and Bragg filters. This improvement in efficiency enabled a spectrally bright and pure photon-pair source having a small second-order correlation function (0.03) and a raw spectral brightness of 44,700 pairs s(-1)nm(-1)mW(-1). The source can be configured to generate entangled photon-pairs, characterized via optimal and minimal quantum state tomography, to have a fidelity of 97% and tangle of 92%, without subtracting any background.
    Optics Express 11/2009; 17(23):21302-12. · 3.53 Impact Factor
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    Alexander Ling, Jun Chen, Jingyun Fan, Alan Migdall
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    ABSTRACT: We report the development of a fiber-based single-spatial-mode source of photon-pairs where the efficiency of extracting photon pairs is 14× higher than a previous implementation [16]. This critical improvement in efficiency enabled a spectrally bright and pure photon-pair source having a small second-order correlation function (0.03) and a raw spectral brightness of 44,700 pairs/(s nm mW). The source can be configured to generate entangled photon-pairs, characterized via optimal and minimal quantum state tomography, to have a fidelity of 97% and tangle of 92%, without correcting for accidentals.
    Proceedings of SPIE - The International Society for Optical Engineering 08/2009; · 0.20 Impact Factor
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    ABSTRACT: We present a systematic study of a correlated photon-pair source based on a periodically-poled KTiOPO4 (PPKTP) waveguide. The waveguide was fabricated on a KTiOPO4 crystal supporting type-II parametric down-conversion. In addition, periodic poling was applied along the waveguide to quasi-phase-match the type-0 down-conversion process. The design pump wavelength is 532 nm, and the wavelengths of the down-converted, correlated photons are around 900 nm and 1300 nm. We examine the two-photon correlation spectra and singlephoton spectra at a variety of temperature and power settings for both type-0 and type II down-conversion processes. Our study shows that the waveguide source has a number of advantages compared to its bulk-crystal counterpart, including higher spectral brightness, narrower emission bandwidth and single spatial-mode output. With greatly simplified engineering, this compact, highly efficient, low photon-loss, and cost-effective waveguide source of correlated photon pairs is promising for future chip-scale quantum information processing applications.
    Proceedings of SPIE - The International Society for Optical Engineering 08/2009; · 0.20 Impact Factor
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    Alexander Ling, Jun Chen, Jingyun Fan, Alan Migdall
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    ABSTRACT: We report the development of a fiber-based single spatial mode source of photon-pairs where the efficiency of extracting photon-pairs is improved over a previous source [18] through the use of fiber-end expansion and Bragg filters. This improvement in efficiency enabled a spectrally bright and pure photon-pair source having a small second-order correlation function (0.03) and a raw spectral brightness of 44,700 pairs/(s nm mW). The source can be configured to generate entangled photon-pairs,characterized via optimal and minimal quantum state tomography, to have a fidelity of 97% and tangle of 92%, without subtracting any background. Comment: Manuscript was edited to provide additional information on the end-tapered photonic crystal fibers and high efficiency volume Bragg gratings. The analysis of the extraction efficiency was also expanded, and experimental uncertainties included where relevant. This paper has been accepted for publication in Optics Express
    06/2009;
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    ABSTRACT: We demonstrate a bright, bandwidth-engineerable, compact, quasi-phase-matched single-waveguide source generating photon pairs near 900 nm and 1300 nm. Coincidence spectra are measured for a periodically-poled KTiOPO4waveguide for both type-0 and type-I spontaneous parametric down-conversion.
    05/2009;
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    ABSTRACT: We demonstrate a bright, bandwidth-tunable, quasi-phase-matched single-waveguide source generating photon pairs near 900 nm and 1300 nm. Two-photon coincidence spectra are measured at a range of operating temperatures of a periodically-poled KTiOPO(4) (PPKTP) waveguide, which supports both type-0 and type-II spontaneous parametric down-conversion. We map out relative contributions of two-photon to one-photon fluorescence for a range of operating parameters. Such a versatile device is highly promising for future chip-scale quantum information processing.
    Optics Express 05/2009; 17(8):6727-40. · 3.53 Impact Factor
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    ABSTRACT: We present an overview of how fiber-based sources of entangled photons have evolved to meet the requirements of quantum-information applications and we present one of those applications, one that addresses an ancient philosophical question.
    03/2009;
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    ABSTRACT: Compared with their bulk-crystal counterparts, SPDC in second-order (chi^(2)) nonlinear optical waveguides has been used to generate correlated photons that are naturally emitted into a single spatial mode in a collinear geometry, easing the effort in efficient photon collection and leading the potential to make chip-scale devices for quantum-information-processing applications. Here towards building chip-scale devices for quantum-information-processing applications, we performed the first spectral characterization of correlated two-photon, and single-photon emission for both type-0 and type-I spontaneous parametric down-conversion (SPDC) in a periodically-poled KTiOPO4 (PPKTP) waveguide.
    03/2009;
  • Alexander Ling, Jun Chen, Jingyun Fan, Alan Migdall
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    ABSTRACT: We report a source of 2-photons that can be extracted with near unit efficiency. The reduced mode area of solid-core microstructure fibers lets a light pulse induce significant nonlinear optical interaction inside a short fiber, making it easy to generate 2-photon entanglement. However, the photon extraction efficiency is low due to the small core size (d˜1 mum) that requires high numerical aperture (NA) lenses to couple light in and out of the fiber. Tapering the core at the fiber end to 10 mum allows the use of anti-reflection-coated lenses of smaller NA, to achieve a single-photon extraction efficiency of etaf = 96%. Using a pair of volume holographic gratings for selecting any wavelength of interest increased our spectral transmittance for that wavelength to etag = (98%)^2, enabling a near unit efficiency in extracting a single photon from the fiber source: etafetag = 92.2%. The final 2-photon detection efficiency of 10% includes the efficiencies of single-photon detection modules (˜ 70% each) and single-mode fiber collection (˜ 50% per channel). At an average pump power of P = 50 muW and a laser repetition rate of R = 76 MHz, we detect 50 photon pairs s-1 with g^(2)(0) = 0.0055 and a coincidence-to-accidental ratio of 900:1. Higher pair rates at the same g^(2) level can be achieved by increasing R. With better photon detection, this source may enable loophole-free Bell tests.
    10/2008;
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    ABSTRACT: Quantum theory predicts and experiments confirm that nature can produce correlations between distant events that are non-local in the sense of violating a Bell inequality1. Nevertheless, Bell's strong sentence 'Correlations cry out for explanations' (ref. 2) remains relevant. The maturing of quantum information science and the discovery of the power of non-local correlations, for example for cryptographic key distribution beyond the standard quantum key distribution schemes3, 4, 5, strengthen Bell's wish and make it even more timely. In 2003, Leggett proposed an alternative model for non-local correlations6 that he proved to be incompatible with quantum predictions. We present here a new approach to this model, along with new inequalities for testing it. These inequalities can be derived in a very simple way, assuming only the non-negativity of probability distributions; they are also stronger than previously published and experimentally tested Leggett-type inequalities6, 7, 8, 9. The simplest of the new inequalities is experimentally violated. Then we go beyond Leggett's model, and show that we cannot ascribe even partially defined individual properties to the components of a maximally entangled pair.
    Nature Physics 07/2008; 4(9):681-685. · 20.60 Impact Factor
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    ABSTRACT: Tomography of the two qubit density matrix shared by Alice and Bob is an essential ingredient for guaranteeing an acceptable margin of confidentiality during the establishment of a secure fresh key through the Quantum Key Distribution (QKD) scheme. We show how the Singapore protocol for key distribution is optimal from this point of view, due to the fact that it is based on so called SIC POVM qubit tomography which allows the most accurate full tomographic reconstruction of an unknown density matrix on the basis of a restricted set of experimental data. We illustrate with the help of experimental data the deep connections that exist between SIC POVM tomography and discrete Wigner representations. We also emphasise the special role played by Bell states in this approach and propose a new protocol for Quantum Key Distribution during which a third party is able to concede or to deny A POSTERIORI to the authorized users the ability to build a fresh cryptographic key.
    Physical Review A 07/2008; · 2.99 Impact Factor
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    ABSTRACT: We report on a complete free-space field implementation of a modified Ekert91 protocol for quantum key distribution using entangled photon pairs. For each photon pair we perform a random choice between key generation and a Bell inequality. The amount of violation is used to determine the possible knowledge of an eavesdropper to ensure security of the distributed final key.
    Physical Review A 06/2008; · 2.99 Impact Factor