Imperial College London

Dr Alex S. Clark

Faculty of Natural SciencesDepartment of Physics

Research Associate(Royal Society University Research Fellow)
 
 
 
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Contact

 

+44 (0)20 7594 2986alex.clark Website

 
 
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Location

 

Blackett 211Blackett LaboratorySouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

46 results found

Grandi S, Nielsen MP, Cambiasso J, Boissier S, Major K, Reardon C, Krauss TF, Oulton R, Hinds E, Clark Aet al., Hybrid plasmonic waveguide coupling of photons from a single molecule, APL Photonics, ISSN: 2378-0967

We demonstrate the emission of photons from a single molecule into a hybrid gap plasmon waveguide (HGPW). Crystals of anthracene, doped with dibenzoterrylene (DBT), are grown on top of the waveguides. We investigate a single DBT molecule coupled to the plasmonic region of one of the guides, and determine its in-plane orientation, excited state lifetime and saturation intensity. The molecule emits light into the guide, which is remotely out-coupled by a grating. The second-order autocorrelation and cross-correlation functions show that the emitter is a single molecule and that the light emerging from the grating comes from that molecule. The couplinge fficiency is found to be βWG = 11.6(1:5)%. This type of structure is promising for building new functionality into quantum-photonic circuits, where localised regions of strong emitter-guide coupling can be interconnected by low-loss dielectric guides.

Journal article

Grandi S, Nielsen MP, Cambiasso J, Boissier S, Major KD, Reardon C, Krauss TF, Oulton RF, Hinds EA, Clark ASet al., 2019, Hybrid plasmonic waveguide coupling of photons from a single molecule

We demonstrate the emission of photons from a single molecule into a hybridgap plasmon waveguide (HGPW). Crystals of anthracene, doped withdibenzoterrylene (DBT), are grown on top of the waveguides. We investigate asingle DBT molecule coupled to the plasmonic region of one of the guides, anddetermine its in-plane orientation, excited state lifetime and saturationintensity. The molecule emits light into the guide, which is remotelyout-coupled by a grating. The second-order auto-correlation andcross-correlation functions show that the emitter is a single molecule and thatthe light emerging from the grating comes from that molecule. The couplingefficiency is found to be $\beta_{WG}=11.6(1.5)\%$. This type of structure ispromising for building new functionality into quantum-photonic circuits, wherelocalised regions of strong emitter-guide coupling can be interconnected bylow-loss dielectric guides.

Working paper

Polisseni C, Kho KW, Grandi S, Major K, Lien YH, Hwang J, Clark AS, Hinds EAet al., 2019, Novel method of sub-wavelength thin film growth for single photon emission from dye molecules

Conference paper

Boissier S, Schofield R, Major K, Grandi S, Boissier S, Hinds E, Clark Aet al., 2018, Efficient excitation of dye molecules for single photon generation, Journal of Physics Communications, Vol: 2, ISSN: 2399-6528

A reliable photon source is required for many aspects of quantum technology. Organic molecules are attractive for this application because they can have high quantum yield and can be photostable, even at room temperature. To generate a photon with high probability, a laser must excite the molecule efficiently. We develop a simple model for that efficiency and discuss how to optimise it. We demonstrate the validity of our model through experiments on a single dibenzoterrylene (DBT) molecule in an anthracene crystal. We show that the excitation probability cannot exceed 75% at room temperature, but can increase to over 99% if the sample is cooled to liquid nitrogen temperature. The possibility of high photon generation efficiency with only modest cooling is a significant step towards a reliable photon source that is simple and practical.

Journal article

Grandi S, Major KD, Polisseni C, Boissier S, Clark AS, Hinds EAet al., 2016, Quantum dynamics of a driven two-level molecule with variable dephasing, Physical Review A, Vol: 94, ISSN: 1094-1622

The longitudinal (1) and transverse (2) decay rates of a two-level quantum system have a profound influenceon its evolution. Atomic systems with 2 = 121 have been studied extensively, but with the rise of solid-statequantum devices it is also important to consider the effect of stronger transverse relaxation due to interactionswith the solid environment. Here we study the quantum dynamics of a single organic dye molecule driven by alaser. We measure the variation of 2 with temperature and determine the activation energy for thermal dephasingof the optical dipole. Then we measure the second-order correlation function g(2)(τ ) of the light emitted by themolecule for various ratios 2/1 and saturation parameters S. We show that the general solution to the opticalBloch equations accurately describes the observed quantum dynamics over a wide range of these parameters,and we discuss the limitations of the various approximate expressions for g(2)(τ ) that appear in the literature.DOI:

Journal article

Polisseni C, Major KD, Boissier S, Grandi S, Clark AS, Hinds EAet al., 2016, Coupling dye molecules to a silicon nitride waveguide, Australian Conference on Optical Fibre Technology (ACOFT)

© OSA 2016. A dibenzoterrylene (DBT) molecule can emit single-photons into a waveguide. We have grown and characterised thin, DBT-doped anthracene crystals on photonic structures, including a silicon nitride ridge waveguide from which we detect single-photons.

Conference paper

Polisseni C, Major K, Boissier S, Grandi S, Clark A, Hinds EAet al., A stable, single-photon emitter in a thin organic crystal for application to quantum-photonic devices, Optics Express, ISSN: 1094-4087

Journal article

Collins MJ, Clark AS, Xiong C, Maegi E, Steel MJ, Eggleton BJet al., 2015, Random number generation from spontaneous Raman scattering, Applied Physics Letters, Vol: 107, ISSN: 1077-3118

We investigate the generation of random numbers via the quantum process of spontaneous Ramanscattering. Spontaneous Raman photons are produced by illuminating a highly nonlinearchalcogenide glass (As2S3) fiber with a CW laser at a power well below the stimulated Ramanthreshold. Single Raman photons are collected and separated into two discrete wavelengthdetuning bins of equal scattering probability. The sequence of photon detection clicks is convertedinto a random bit stream. Postprocessing is applied to remove detector bias, resulting in a final bitrate of 650 kb/s. The collected random bit-sequences pass the NIST statistical test suite for onehundred 1 Mb samples, with the significance level set to a ¼ 0:01. The fiber is stable, robust andthe high nonlinearity (compared to silica) allows for a short fiber length and low pump powerfavourable for real world application.

Journal article

He J, Bell BA, Casas-Bedoya A, Zhang Y, Clark AS, Xiong C, Eggleton BJet al., 2015, Ultracompact quantum splitter of degenerate photon pairs, Optica, Vol: 2, Pages: 779-782, ISSN: 2334-2536

Integrated sources of indistinguishable photons have attracted a lot of attention because of their applications in quantum communication and optical quantum computing. Here, we demonstrate an ultracompact quantum splitter for degenerate photon pairs based on a monolithic silicon chip. It incorporates a Sagnac loop and a microring resonator with a total footprint of 0.011  mm2, generating and deterministically splitting indistinguishable photon pairs using two-photon interference. The ring resonator provides an enhanced photon generation rate, and the Sagnac loop ensures the photons travel through equal path lengths and interfere with the correct phase to enable the reversed Hong–Ou–Mandel (HOM) effect to take place. In the experiment, we observed a HOM dip visibility of 94.5±3.3%, indicating the generated photons are in a suitable state for further integration with other components for quantum applications, such as controlled-NOT gates.

Journal article

major K, lien Y, polisseni C, grandi S, kho K, clark A, hwang J, Hinds EAet al., 2015, Growth of optical-quality anthracene crystals, doped with dibenzoterrylenefor controlled single photon production, Review of Scientific Instruments, Vol: 86, ISSN: 1089-7623

Dibenzoterrylene (DBT) molecules within a crystalline anthracene matrix show promise as quantum emitters for controlled, single photon production. We present the design and construction of a chamber in which we reproducibly grow doped anthracene crystals of optical quality that are several mm across and a few micrometres thick. We demonstrate control of the DBT concentration over the range 6 { 300 parts per trillion and show that these DBT molecules are stable single-photon emitters. We interpret our data with a simple model that provides some information on the vapour pressure of DBT.

Journal article

Jizan I, Helt LG, Xiong C, Collins MJ, Choi D-Y, Chae CJ, Liscidini M, Steel MJ, Eggleton BJ, Clark ASet al., 2015, Bi-photon spectral correlation measurements from a silicon nanowire in the quantum and classical regimes, SCIENTIFIC REPORTS, Vol: 5, ISSN: 2045-2322

The growing requirement for photon pairs with specific spectral correlations in quantum optics experiments has created a demand for fast, high resolution and accurate source characterisation. A promising tool for such characterisation uses classical stimulated processes, in which an additional seed laser stimulates photon generation yielding much higher count rates, as recently demonstrated for a χ(2) integrated source in A. Eckstein et al. Laser Photon. Rev. 8, L76 (2014). In this work we extend these results to χ(3) integrated sources, directly measuring for the first time the relation between spectral correlation measurements via stimulated and spontaneous four wave mixing in an integrated optical waveguide, a silicon nanowire. We directly confirm the speed-up due to higher count rates and demonstrate that this allows additional resolution to be gained when compared to traditional coincidence measurements without any increase in measurement time. As the pump pulse duration can influence the degree of spectral correlation, all of our measurements are taken for two different pump pulse widths. This allows us to confirm that the classical stimulated process correctly captures the degree of spectral correlation regardless of pump pulse duration, and cements its place as an essential characterisation method for the development of future quantum integrated devices.

Journal article

Zhang X, Jizan I, He J, Clark AS, Choi D-Y, Chae CJ, Eggleton BJ, Xiong Cet al., 2015, Enhancing the heralded single-photon rate from a silicon nanowire by time and wavelength division multiplexing pump pulses, OPTICS LETTERS, Vol: 40, Pages: 2489-2492, ISSN: 0146-9592

Journal article

Xiong C, Collins MJ, Steel MJ, Krauss TF, Eggleton BJ, Clark ASet al., 2015, Photonic Crystal Waveguide Sources of Photons for Quantum Communication Applications, IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, Vol: 21, ISSN: 1077-260X

Journal article

Lefrancois S, Clark AS, Eggleton BJ, 2015, Optimizing optical Bragg scattering for single-photon frequency conversion, PHYSICAL REVIEW A, Vol: 91, ISSN: 2469-9926

Journal article

Jizan I, Clark AS, Helt LG, Collins MJ, Maegi E, Xiong C, Steel MJ, Eggleton BJet al., 2014, High-resolution measurement of spectral quantum correlations in the telecommunication band, OPTICS COMMUNICATIONS, Vol: 327, Pages: 45-48, ISSN: 0030-4018

Journal article

Clark AS, Xiong C, Tanzilli S, Steel MJet al., 2014, Special Issue on Nonlinear Quantum Photonics, OPTICS COMMUNICATIONS, Vol: 327, Pages: 1-2, ISSN: 0030-4018

Journal article

Polisseni C, Kho KW, Grandi S, Major K, Lien YH, Hwang J, Clark AS, Hinds EAet al., 2014, Novel method of sub-wavelength thin film growth for single photon emission from dye molecules

Conference paper

Polisseni C, Kho KW, Grandi S, Major K, Lien YH, Hwang J, Clark AS, Hinds EAet al., 2014, Novel method of sub-wavelength thin film growth for single photon emission from dye molecules

Conference paper

Solntsev AS, Setzpfandt F, Clark AS, Wu CW, Collins MJ, Xiong C, Schreiber A, Katzschmann F, Eilenberger F, Schiek R, Sohler W, Mitchell A, Silberhorn C, Eggleton BJ, Pertsch T, Sukhorukov AA, Neshev DN, Kivshar YSet al., 2014, Generation of Nonclassical Biphoton States through Cascaded Quantum Walks on a Nonlinear Chip, PHYSICAL REVIEW X, Vol: 4, ISSN: 2160-3308

Journal article

He J, Clark AS, Collins MJ, Li J, Krauss TF, Eggleton BJ, Xiong Cet al., 2014, Degenerate photon-pair generation in an ultracompact silicon photonic crystal waveguide, OPTICS LETTERS, Vol: 39, Pages: 3575-3578, ISSN: 0146-9592

Journal article

Meany T, Ngah LA, Collins MJ, Clark AS, Williams RJ, Eggleton BJ, Steel MJ, Withford MJ, Alibart O, Tanzilli Set al., 2014, Hybrid photonic circuit for multiplexed heralded single photons, LASER & PHOTONICS REVIEWS, Vol: 8, Pages: L42-L46, ISSN: 1863-8880

Journal article

Monat C, Grillet C, Collins M, Clark A, Schroeder J, Xiong C, Li J, O'Faolain L, Krauss TF, Eggleton BJ, Moss DJet al., 2014, Integrated optical auto-correlator based on third-harmonic generation in a silicon photonic crystal waveguide, NATURE COMMUNICATIONS, Vol: 5, ISSN: 2041-1723

Journal article

Vo TD, He J, Magi E, Collins MJ, Clark AS, Ferguson BG, Xiong C, Eggleton BJet al., 2014, Chalcogenide fiber-based distributed temperature sensor with sub-centimeter spatial resolution and enhanced accuracy, OPTICS EXPRESS, Vol: 22, Pages: 1560-1568, ISSN: 1094-4087

Journal article

Xiong C, Vo TD, Collins MJ, Li J, Krauss TF, Steel MJ, Clark AS, Eggleton BJet al., 2013, Bidirectional multiplexing of heralded single photons from a silicon chip, OPTICS LETTERS, Vol: 38, Pages: 5176-5179, ISSN: 0146-9592

Journal article

Engin E, Bonneau D, Natarajan CM, Clark AS, Tanner MG, Hadfield RH, Dorenbos SN, Zwiller V, Ohira K, Suzuki N, Yoshida H, Iizuka N, Ezaki M, O'Brien JL, Thompson MGet al., 2013, Photon pair generation in a silicon micro-ring resonator with reverse bias enhancement, OPTICS EXPRESS, Vol: 21, Pages: 27826-27834, ISSN: 1094-4087

Journal article

Carpenter J, Xiong C, Collins MJ, Li J, Krauss TF, Eggleton BJ, Clark AS, Schroeder Jet al., 2013, Mode multiplexed single-photon and classical channels in a few-mode fiber, OPTICS EXPRESS, Vol: 21, Pages: 28794-28800, ISSN: 1094-4087

Journal article

Husko CA, Clark AS, Collins MJ, De Rossi A, Combrie S, Lehoucq G, Rey IH, Krauss TF, Xiong C, Eggleton BJet al., 2013, Multi-photon absorption limits to heralded single photon sources, SCIENTIFIC REPORTS, Vol: 3, ISSN: 2045-2322

Journal article

Collins MJ, Xiong C, Rey IH, Vo TD, He J, Shahnia S, Reardon C, Krauss TF, Steel MJ, Clark AS, Eggleton BJet al., 2013, Integrated spatial multiplexing of heralded single-photon sources, NATURE COMMUNICATIONS, Vol: 4, ISSN: 2041-1723

Journal article

Bell B, Kannan S, McMillan A, Clark AS, Wadsworth WJ, Rarity JGet al., 2013, Multicolor Quantum Metrology with Entangled Photons, PHYSICAL REVIEW LETTERS, Vol: 111, ISSN: 0031-9007

Journal article

McMillan AR, Labonte L, Clark AS, Bell B, Alibart O, Martin A, Wadsworth WJ, Tanzilli S, Rarity JGet al., 2013, Two-photon interference between disparate sources for quantum networking, SCIENTIFIC REPORTS, Vol: 3, ISSN: 2045-2322

Journal article

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