M. S. Skolnick

The University of Sheffield, Sheffield, England, United Kingdom

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Publications (659)1886.8 Total impact

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    ABSTRACT: Resonantly-driven quantum emitters offer a very promising route to obtain highly coherent sources of single photons required for applications in quantum information processing (QIP). Realising this for on-chip scalable devices would be important for scientific advances and practical applications in the field of integrated quantum optics. Here we report on-chip quantum dot (QD) resonance fluorescence (RF) efficiently coupled into a single-mode waveguide, a key component of a photonic integrated circuit, with negligible resonant laser background and show that the QD coherence is enhanced by more than a factor of four compared to off-resonant excitation. Single-photon behaviour is confirmed under resonant excitation and fast fluctuating charge dynamics are revealed in autocorrelation g((2)) measurements. The potential for triggered operation is verified in pulsed RF. These results pave the way to a novel class of integrated quantum-optical devices for on-chip quantum information processing with embedded resonantly-driven quantum emitters.
    Nano Letters 11/2014; · 12.94 Impact Factor
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    ABSTRACT: We demonstrate an approach to realize the population inversion of a single InGaAs/GaAs quantum dot, which is driven by a laser pulse tuned within the neutral exciton phonon sideband. The inversion is achieved by rapid thermalization of the optically dressed states via phonon-assisted relaxation. A maximum exciton population of 0.67 $\pm$ 0.06 is measured for a laser tuned 0.83 meV to higher energy and the phonon sideband is mapped using a two-color pump-probe technique. Our experiments reveal that, in accordance with theory, the phonon-bath provides additional functionality for an optically driven quantum dot qubit.
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    ABSTRACT: New functionalities in nonlinear optics will require systems with giant optical nonlinearity as well as compatibility with photonic circuit fabrication techniques. Here we introduce a new platform based on strong light-matter coupling between waveguide photons and quantum-well excitons. On a sub-millimeter length scale we generate sub-picosecond bright temporal solitons at a pulse energy of only 0.5 pico-Joules. From this we deduce an unprecedented nonlinear refractive index 3 orders of magnitude larger than in any other ultrafast system. We study both temporal and spatio-temporal nonlinear effects and for the first time observe dark-bright spatio-temporal solitons. Theoretical modelling of soliton formation in the strongly coupled system confirms the experimental observations. These results show the promise of our system as a high speed, low power, integrated platform for physics and devices based on strong interactions between photons.
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    ABSTRACT: Quasi-two-dimensional (2D) films of layered metal-chalcogenides have attractive optoelectronic properties. However, photonic applications of thin films may be limited owing to weak light absorption and surface effects leading to reduced quantum yield. Integration of 2D films in optical microcavities will permit these limitations to be overcome owing to modified light coupling with the films. Here we present tunable microcavities with embedded monolayer MoS2 or few monolayer GaSe films. We observe significant modification of spectral and temporal properties of photoluminescence (PL): PL is emitted in spectrally narrow and wavelength-tunable cavity modes with quality factors up to 7400; PL life-time shortening by a factor of 10 is achieved, a consequence of Purcell enhancement of the spontaneous emission rate. This work has potential to pave the way to microcavity-enhanced light-emitting devices based on layered 2D materials and their heterostructures, and also opens possibilities for cavity QED in a new material system of van der Waals crystals.
    Nano Letters 08/2014; · 12.94 Impact Factor
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    ABSTRACT: Semiconductor microcavities operating in the polaritonic regime are highly non-linear, high speed systems due to the unique half-light, half-matter nature of polaritons. Here, we report for the first time the observation of propagating multi-soliton polariton patterns consisting of multi-peak structures either along (x) or perpendicular to (y) the direction of propagation. Soliton arrays of up to 5 solitons are observed, with the number of solitons controlled by the size or power of the triggering laser pulse. The break-up along the x direction occurs due to interplay of bistability, negative effective mass and polariton-polariton scattering, while in the y direction the break-up results from nonlinear phase-dependent interactions of propagating fronts. We show the experimental results are in good agreement with numerical modelling. Our observations are a step towards ultrafast all-optical signal processing using sequences of solitons as bits of information.
    arXiv:1407.7713. 07/2014;
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    ABSTRACT: We demonstrate the monolithic integration of an on-demand quantum emitter in the form of a single self-assembled InGaAs quantum dot with an air clad, free standing directional coupler acting as a beam-splitter for anti-bunched light.
    CLEO: QELS_Fundamental Science; 06/2014
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    ABSTRACT: We present a method to implement 3-dimensional polariton confinement with in-situ spectral tuning of the cavity mode. Our tunable microcavity is a hybrid system consisting of a bottom semiconductor distributed Bragg reflector (DBR) with a cavity containing quantum wells (QWs) grown on top and a dielectric concave DBR separated by a micrometer sized gap. Nanopositioners allow independent positioning of the two mirrors and the cavity mode energy can be tuned by controlling the distance between them. When close to resonance we observe a characteristic anticrossing between the cavity modes and the QW exciton demonstrating strong coupling. For the smallest radii of curvature concave mirrors of 5.6 $\mu$m and 7.5 $\mu$m real-space polariton imaging reveals submicron polariton confinement due to the hemispherical cavity geometry.
    Applied Physics Letters 05/2014; · 3.52 Impact Factor
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    ABSTRACT: Advances in nanotechnology provide techniques for the realisation of integrated quantum-optical circuits for on-chip quantum information processing(QIP). The indistinguishable single photons, required for such devices can be generated by parametric down-conversion, or from quantum emitters such as colour centres and quantum dots(QDs). Among these, semiconductor QDs offer distinctive capabilities including on-demand operation, coherent control, frequency tuning and compatibility with semiconductor nanotechnology. Moreover, the coherence of QD photons can be significantly enhanced in resonance fluorescence(RF) approaching at its best the coherence of the excitation laser. However, the implementation of QD RF in scalable on-chip geometries remains challenging due to the need to suppress stray laser photons. Here we report on-chip QD RF coupled into a single-mode waveguide with negligible resonant laser background and show that the coherence is enhanced compared to off-resonant excitation. The results pave the way to a novel class of integrated quantum-optical devices for on-chip QIP with embedded resonantly-driven quantum emitters.
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    ABSTRACT: A fundamental component of an integrated quantum optical circuit is an on-chip beam-splitter operating at the single-photon level. Here we demonstrate the monolithic integration of an on-demand quantum emitter in the form of a single self-assembled InGaAs quantum dot (QD) with a compact (>10 um), air clad, free standing directional coupler acting as a beam-splitter for anti-bunched light. The device was tested by using single photons emitted by a QD embedded in one of the input arms of the device. We verified the single-photon nature of the QD signal by performing Hanbury Brown- Twiss (HBT) measurements and demonstrated single-photon beam splitting by cross-correlating the signal from the separate output ports of the directional coupler.
    Applied Physics Letters 04/2014; 104(23). · 3.52 Impact Factor
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    ABSTRACT: Decoherence in quantum logic gates (qubits) due to interaction with the surrounding environment is a major obstacle to the practical realization of quantum information technologies. For solid state electron-spin qubits the interaction with nuclear spins is the main problem. One particular, neradicable source of electron decoherence arises from decoherence of the nuclear spin bath, driven by nuclear-nuclear dipolar interactions. Due to its many-body nature nuclear decoherence is difficult to predict, especially for an important class of strained nanostructures where nuclear quadrupolar effects have a significant but largely unknown impact. Here we report direct measurement of nuclear spin bath coherence in individual strained InGaAs/GaAs quantum dots: nuclear spin-echo coherence times in the range T2~1.2 - 4.5 ms are found. Based on these T2 values we demonstrate that quadrupolar interactions make nuclear fluctuations in strained quantum dots much slower compared to lattice matched GaAs/AlGaAs structures. Such fluctuation suppression is particularly strong for arsenic nuclei due to the effect of atomic disorder of gallium and indium alloying. Our findings demonstrate that quadrupolar effects can help to solve the long-standing challenge of designing a scalable hardware for quantum computation: III-V semiconductor spin-qubits can be engineered to have a noise-free nuclear spin bath (previously achievable only in nuclear spin-0 semiconductors, where qubit network interconnection and scaling is challenging).
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    ABSTRACT: We present a waveguide-coupled photonic crystal H1 cavity structure in which the orthogonal dipole modes couple to spatially separated photonic crystal waveguides. Coupling of each cavity mode to its respective waveguide with equal efficiency is achieved by adjusting the position and orientation of the waveguides. The behavior of the optimized device is experimentally verified for where the cavity mode splitting is larger and smaller than the cavity mode linewidth. In both cases, coupled Q-factors up to 1600 and contrast ratios up to 10 are achieved. This design may allow for spin state readout of a self-assembled quantum dot positioned at the cavity center or function as an ultra-fast optical switch operating at the single photon level.
    Optics Express 02/2014; 22(3):2376-85. · 3.53 Impact Factor
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    ABSTRACT: We report on the two-dimensional gap-soliton nature of exciton-polariton macroscopic coherent phases (PMCP) in a square lattice with a tunable amplitude. The resonantly excited PMCP forms close to the negative mass M point of the lattice band structure with energy within the lattice band gap and its wave function localized within a few lattice periods. The PMCPs are well described as gap solitons resulting from the interplay between repulsive polariton-polariton interactions and effective attractive forces due to the negative mass. The solitonic nature accounts for the reduction of the PMCP coherence length and optical excitation threshold with increasing lattice amplitude.
    Physical Review Letters 10/2013; 111(14):146401. · 7.73 Impact Factor
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    ABSTRACT: Compound-cavity laser diodes are mode locked at a harmonic of the fundamental round-trip frequency to achieve repetition rates of up to 2.1 THz. The devices are fabricated from GaAs/AlGaAs material at a wavelength of 860 nm and incorporate two gain sections with an etched slot reflector between them, and a saturable absorber section. Autocorrelation studies are used to investigate device behavior for different reflector types and reflectivity. These lasers may find applications in terahertz imaging, medicine, ultrafast optical links, and atmospheric sensing. {copyright} 2001 American Institute of Physics.
    Applied Physics Letters 08/2013; 78:3571-3573. · 3.52 Impact Factor
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    ABSTRACT: We report on the spin properties of bright polariton solitons supported by an external pump to compensate losses. We observe robust circularly polarised solitons when a circularly polarised pump is applied, a result attributed to phase synchronisation between nondegenerate TE and TM polarised polariton modes at high momenta. For the case of a linearly polarised pump either s+ or s- circularly polarised bright solitons can be switched on in a controlled way by a s+ or s- writing beam respectively. This feature arises directly from the widely differing interaction strengths between co- and cross-circularly polarised polaritons. In the case of orthogonally linearly polarised pump and writing beams, the soliton emission on average is found to be unpolarised, suggesting strong spatial evolution of the soliton polarisation, a conclusion supported by polarisation correlation measurements. The observed results are in agreement with theory, which predicts stable circularly polarised solitons and unstable linearly polarised solitons resulting in spatial evolution of their polarisation.
    Physical Review Letters 06/2013; · 7.73 Impact Factor
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    ABSTRACT: We study experimentally the dependence of dynamic nuclear spin polarization on the power of non-resonant optical excitation in two types of individual neutral semiconductor quantum dots: InGaAs/GaAs and GaAs/AlGaAs. We show that the mechanism of nuclear spin pumping via second order recombination of optically forbidden (''dark'') exciton states recently reported in InP/GaInP quantum dots [Phys. Rev. B 83, 125318 (2011)] is relevant for material systems considered in this work. In the InGaAs/GaAs dots this nuclear spin polarization mechanism is particularly pronounced, resulting in Overhauser shifts up to ~80 micro-eV achieved at optical excitation power ~1000 times smaller than the power required to saturate ground state excitons. The Overhauser shifts observed at low-power optical pumping in the interface GaAs/AlGaAs dots are generally found to be smaller (up to ~40 micro-eV). Furthermore in GaAs/AlGaAs we observe dot-to-dot variation and even sign reversal of the Overhauser shift which is attributed to dark-bright exciton mixing originating from electron-hole exchange interaction in dots with reduced symmetry. Nuclear spin polarization degrees reported in this work under ultra-low power optical pumping are comparable to those achieved by techniques such as resonant optical pumping or above-gap pumping with high power circularly polarized light. Dynamic nuclear polarization via second-order recombination of ''dark'' excitons may become a useful tool in single quantum dot applications, where manipulation of the nuclear spin environment or electron spin is required.
    Physical review. B, Condensed matter 06/2013; 88(4). · 3.66 Impact Factor
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    ABSTRACT: Quantum dot (QD) systems containing electron spins may hold a role in a future photonic quantum circuit as a means of storing a quantum state in a spin superposition. In general, the spin superposition state maps directly to a photon emitted out of the plane (kz) with the photon in a polarization superposition. In waveguides, however, this is more difficult: one requires a waveguide mode that is able to transmit both TEx and TEy modes in coherent superposition. We have already demonstrated a cross-waveguide design, as shown in Fig 1(a), that converts spin superposition states to a path encoding when the QD is located close to the waveguide centre.
    International Quantum Electronics Conference; 05/2013

Publication Stats

10k Citations
1,886.80 Total Impact Points


  • 1992–2014
    • The University of Sheffield
      • • Department of Physics and Astronomy
      • • Department of Electronic and Electrical Engineering
      Sheffield, England, United Kingdom
  • 2010–2013
    • Paul Drude Institute for Solid State Electronics
      Berlín, Berlin, Germany
  • 1998–2013
    • University of Exeter
      • Department of Physics and Astronomy
      Exeter, England, United Kingdom
  • 2008
    • Polish Academy of Sciences
      • Instytut Fizyki
      Warsaw, Masovian Voivodeship, Poland
    • Federal University of Minas Gerais
      • Departamento de Física
      Belo Horizonte, Estado de Minas Gerais, Brazil
  • 2007
    • University of North Carolina at Charlotte
      • Department of Physics & Optical Science
      Charlotte, NC, United States
  • 2006–2007
    • University of Bristol
      • Department of Electrical and Electronic Engineering
      Bristol, ENG, United Kingdom
  • 2000–2006
    • University of Cambridge
      • Department of Physics: Cavendish Laboratory
      Cambridge, ENG, United Kingdom
    • Imperial College London
      Londinium, England, United Kingdom
  • 2001–2005
    • University of Surrey
      • • Advanced Technology Institute (ATI)
      • • Department of Physics
      Guildford, ENG, United Kingdom
    • Paul Sabatier University - Toulouse III
      Tolosa de Llenguadoc, Midi-Pyrénées, France
    • University of Rome Tor Vergata
      • Dipartimento di Ingegneria Civile e Ingegneria Informatica (DICII)
      Roma, Latium, Italy
  • 2000–2002
    • University of Southampton
      • Faculty of Physical and Applied Sciences
      Southampton, ENG, United Kingdom
  • 1998–2001
    • University of Oxford
      • Department of Physics
      Oxford, England, United Kingdom
  • 1998–2000
    • University of Hull
      Kingston upon Hull, England, United Kingdom
  • 1982–2000
    • University of Nottingham
      • Department of Electrical and Electronic Engineering
      Nottigham, England, United Kingdom