Andrew B. Young, Arthur Thijssen, Daryl M. Beggs, Petros Androvitsaneas, L. Kuipers, John G. Rarity, Stephen Hughes, Ruth Oulton "Polarization engineering in photonic crystal waveguides for spin-photon entanglers" Phys. Rev. Lett. 115, 153901 (2015)
Abstract: By performing a full analysis of the projected local density of states (LDOS) in a photonic crystal waveguide, we show that phase plays a crucial role in the symmetry of the light-matter interaction. By considering a quantum dot (QD) spin coupled to a photonic crystal waveguide (PCW) mode, we demonstrate that the light-matter interaction can be asymmetric, leading to unidirectional emission and a deterministic entangled photon source. Further we show that understanding the phase associated with both the LDOS and the QD spin is essential for a range of devices that that can be realised with a QD in a PCW. We also show how quantum entanglement can completely reverse photon propagation direction, and highlight a fundamental breakdown of the semiclassical dipole approximation for describing light-matter interactions in these spin dependent systems.
Lifeng Chen, Mike P.C. Taverne, Xu Zheng, Jia-De Lin, Ruth Oulton, Martin Lopez-Garcia, Ying-Lung D. Ho, John G. Rarity "Evidence of near-infrared partial photonic bandgap in polymeric rod-connected diamond structures" Optics Express, Vol. 23, Issue 20, pp. 26565-26575 (2015)
Abstract: We present the simulation, fabrication, and optical characterization of low-index polymeric rod-connected diamond (RCD) structures. Such complex three-dimensional photonic crystal structures are created via direct laser writing by two-photon polymerization. To our knowledge, this is the first measurement at near-infrared wavelengths, showing partial photonic bandgaps for this structure. We characterize structures in transmission and reflection using angular resolved Fourier image spectroscopy to visualize the band structure. Comparison of the numerical simulations of such structures with the experimentally measured data show good agreement for both P- and S-polarizations.
Ryzhov, I. I. and Poltavtsev, S. V. and Kavokin, K. V. and Glazov, M. M. and Kozlov, G. G. and Vladimirova, M. and Scalbert, D. and Cronenberger, S. and Kavokin, A. V. and Lemaître, A. and Bloch, J. and Zapasskii, V. S., "Measurements of nuclear spin dynamics by spin-noise spectroscopy" Applied Physics Letters, 106, 242405 (2015)
Abstract: We exploit the potential of the spin noise spectroscopy (SNS) for studies of nuclear spindynamics in n-GaAs. The SNS experiments were performed on bulk n-type GaAs layers embedded into a high-finesse microcavity at negative detuning. In our experiments, nuclear spinpolarisation initially prepared by optical pumping is monitored in real time via a shift of the peak position in the electron spin noise spectrum. We demonstrate that this shift is a direct measure of the Overhauser field acting on the electron spin. The dynamics of nuclear spin is shown to be strongly dependent on the electron concentration.
A. V. Poshakinskiy, S. A. Tarasenko "Spatiotemporal spin fluctuations caused by spin-orbit-coupled Brownian motion" Phys. Rev. B 92, 045308
Abstract: We develop a theory of thermal fluctuations of spin density emerging in a two-dimensional electron gas. The spin fluctuations probed at spatially separated spots of the sample are correlated due to Brownian motion of electrons and spin-obit coupling. We calculate the spatiotemporal correlation functions of the spin density for both ballistic and diffusive transport of electrons and analyze them for different types of spin-orbit interaction including the isotropic Rashba model and persistent spin helix regime. The measurement of spatial spin fluctuations provides direct access to the parameters of spin-orbit coupling and spin transport in conditions close to the thermal equilibrium.
S.A. Tarasenko, M.V. Durnev, M.O. Nestoklon, E.L. Ivchenko, Jun-Wei Luo, Alex Zunger "Split Dirac cones in HgTe/CdTe quantum wells due to symmetry-enforced level anticrossing at interfaces" Phys. Rev. B 91, 081302(R)
Abstract: We describe the fine structure of Dirac states in HgTe/CdHgTe quantum wells of critical and close-to-critical thickness and demonstrate the formation of an anticrossing gap between the tips of the Dirac cones driven by interface inversion asymmetry. By combining symmetry analysis, atomistic calculations, and k-p theory with interface terms, we obtain a quantitative description of the energy spectrum and extract the interface mixing coefficient. The zero-magnetic-field splitting of Dirac cones can be experimentally revealed in studying magnetotransport phenomena, cyclotron resonance, Raman scattering, or THz radiation absorption.
D. S. Smirnov, M. M. Glazov, E. L. Ivchenko, L. Lanco "Theory of optical spin control in quantum dot microcavities" Phys. Rev. B 92, 115305 (2015)
Abstract: We present a microscopic theory of optical initialization, control and detection for a single electron spin in a quantum dot embedded into a zero-dimensional microcavity. The strong coupling regime of the trion and the cavity mode is addressed. We demonstrate that efficient spin orientation by a single circularly polarized pulse is possible in relatively weak transverse magnetic fields. The possibilities for spin control by additional circularly polarized pulse are analyzed. Under optimal conditions the Kerr and Faraday rotation angles induced by the spin polarized electron may reach tens of degrees.
M. M. Glazov and V. S. Zapasskii, "Linear optics, Raman scattering, and spin noise spectroscopy," Opt. Express 23, 11713-11723 (2015)
Abstract: Spin noise spectroscopy (SNS) is a new method for studying magnetic resonance and spin dynamics based on measuring the Faraday rotation noise. In strong contrast with methods of nonlinear optics, the spectroscopy of spin noise is considered to be essentially nonperturbative. Presently, however, it became clear that the SNS, as an optical technique, demonstrates properties lying far beyond the bounds of conventional linear optics. Specifically, the SNS shows dependence of the signal on the light power density, makes it possible to penetrate inside an inhomogeneously broadened absorption band and to determine its homogeneous width, allows one to realize an effective pump-probe spectroscopy without any optical nonlinearity, etc. This may seem especially puzzling when taken into account that SNS can be considered just as a version of Raman spectroscopy, which is known to be deprived of such abilities. In this paper, we clarify this apparent inconsistency.
Abstract: We report on a magneto-photoluminescence (PL) study of Mn modulation-doped InAs/InGaAs/InAlAs quantum wells. Two PL lines corresponding to the radiative recombination of photoelectrons with free and bound-on-Mn holes have been observed. In the presence of a magnetic field applied in the Faraday geometry both lines split into two circularly polarized components. While temperature and magnetic field dependences of the splitting are well described by the Brillouin function, providing an evidence for exchange interaction with spin polarized manganese ions, the value of the splitting exceeds the expected value of the giant Zeeman splitting by two orders of magnitude for a given Mn density. Possible reasons of this striking observation are discussed.
Sergey V. Lobanov, Thomas Weiss, Nikolay A. Gippius, Sergei G. Tikhodeev, Vladimir D. Kulakovskii, Kuniaki Konishi, Makoto Kuwata-Gonokami "Polarization control of quantum dot emission by chiral photonic crystal slabs" Vol. 40, Issue 7, pp. 1528-1531 (2015)
Abstract: We investigate theoretically the polarization properties of the quantum dot's optical emission from chiral photonic crystal structures made of achiral materials in the absence of external magnetic field at room temperature. The mirror symmetry of the local electromagnetic field is broken in this system due to the decreased symmetry of the chiral modulated layer. As a result, the radiation of randomly polarized quantum dots normal to the structure becomes partially circularly polarized. The sign and degree of circular polarization are determined by the geometry of the chiral modulated structure and depend on the radiation frequency. A degree of circular polarization up to 99% can be achieved for randomly distributed quantum dots, and can be close to 100% for some single quantum dots.
Lopez-Garcia, M. and Ho, Y.-L. D. and Taverne, M. P. C. and Chen, L.-F. and Murshidy, M. M. and Edwards, A. P. and Serry, M. Y. and Adawi, A. M. and Rarity, J. G. and Oulton, R., "Efficient out-coupling and beaming of Tamm optical states via surface plasmon polariton excitation" Applied Physics Letters, 104, 231116 (2014)
Abstract: We present evidence of optical Tamm states to surface plasmon polariton (SPP) coupling. We experimentally demonstrate that for a Bragg stack with a thin metal layer on the surface, hybrid Tamm-SPP modes may be excited when a grating on the air-metal interface is introduced. Out-coupling via the grating to free space propagation is shown to enhance the transmission as well as the directionality and polarization selection for the transmitted beam. We suggest that this system will be useful on those devices, where a metallic electrical contact as well as beaming and polarization control is needed.
S.V. Poltavtsev, I.I. Ryzhov, M.M. Glazov, G.G. Kozlov, V.S. Zapasskii, A.V. Kavokin, P.G. Lagoudakis, D.S. Smirnov, E.L. Ivchenko "Spin noise spectroscopy of a single-quantum-well microcavity" Phys. Rev. B 89, 081304(R)
Abstract: We report on the first experimental observation of spin noise in a single semiconductor quantum well embedded into a microcavity. The great cavity-enhanced sensitivity to fluctuations of optical anisotropy has allowed us to measure the Kerr rotation and ellipticity noise spectra in the strong coupling regime. The spin noise spectra clearly show two resonant features: a conventional magneto-resonant component shifting towards higher frequencies with magnetic field and an unusual "nonmagnetic" component centered at zero frequency and getting suppressed with increasing magnetic field. We attribute the first of them to the Larmor precession of free electron spins, while the second one being presumably due to hyperfine electron-nuclei spin interactions.
L. Langer, S.V. Poltavtsev, I.A. Yugova, M. Salewski, D.R. Yakovlev, G. Karczewski, T. Wojtowicz, I.A. Akimov, M. Bayer "Photon echoes retrieved from semiconductor spins: access for long-term optical memories" Nature Photonics 8, 851–857 (2014)
Abstract: The possibility to store optical information is important for classical and quantum communication. Atoms or ions as well as color centers in crystals offer suitable two-level systems for absorbing incoming photons. To obtain a reliable transfer of coherence, strong enough light-matter interaction is required, which may enforce use of ensembles of absorbers, but has the disadvantage of unavoidable inhomogeneities leading to fast dephasing. This obstacle can be overcome by echo techniques that allow recovery of the information as long as the coherence is preserved. Albeit semiconductor quantum structures appear appealing for information storage due to the large oscillator strength of optical transitions, inhomogeneity typically is even more pronounced for them and most importantly the optical coherence is limited to nanoseconds or shorter. Here we show that by transferring the information to electron spins the storage times for the optical coherence can be extended by orders of magnitude up to the spin relaxation time. From the spin reservoir it can be retrieved on purpose by inducing a stimulated photon echo. We demonstrate this for an n-doped CdTe/(Cd,Mg)Te quantum well for which the storage time thereby could be increased by more than three orders of magnitude from the picosecond-range up to tens of nanoseconds.
M. S. Kuznetsova, K. Flisinski, I. Ya. Gerlovin, M. Yu. Petrov, I. V. Ignatiev, S. Yu. Verbin, D. R. Yakovlev, D. Reuter, A. D. Wieck, M. Bayer "Nuclear magnetic resonances in (In,Ga)As/GaAs quantum dots studied by resonant optical pumping" Phys. Rev. B 89, 125304
Abstract: The photoluminescence polarizations of (In,Ga)As/GaAs quantum dots annealed at different temperatures are studied as a function of external magnetic field (Hanle curves). In these dependencies, remarkable resonant features appear due to all-optical nuclear magnetic resonances (NMR) for optical excitation with modulated circular polarization. Application of an additional radio-frequency field synchronously with the polarization modulation strongly modifies the NMR features. The resonances can be related to transitions between different nuclear spin states split by the strain-induced gradient of the crystal field and by the externally applied magnetic field. A theoretical model is developed to simulate quadrupole and Zeeman splittings of the nuclear spins in a strained quantum dot. Comparison with the experiment allows us to uniquely identify the observed resonances. The large broadening of the NMR resonances is attributed to variations of the quadrupole splitting within the quantum dot volume, which is well described by the model.
V. I. Kukushkin, I. M. Mukhametzhanov, I. V. Kukushkin, V. D. Kulakovskii, I. V. Sedova, S. V. Sorokin, A. A. Toropov, S. V. Ivanov, and A. S. Sobolev "Control of semiconductor quantum dot emission intensity and polarization by metal nanoantennas" Phys. Rev. B 90, 235313.
Abstract: We have studied the amplified emission properties of nanoislands with CdSe quantum dots in ZnSe/CdSe/ZnSe heterostructures surrounded by metallic antennas. It has been found that variations of the optical antenna length give rise to periodic amplification of the integral emission intensity. The period of the discovered oscillations corresponds to the wavelength of the surface plasmon-polariton mode propagating in the metallic antenna. The nature of observed periodicity was confirmed by results of numerical simulations for linear antennas. It has been established that the velocity of surface polaritons depends not only on the parameters of the dielectric constants of the metal and of the semiconductor substrate but also on the width of the metallic antenna. The influence of antenna antisymmetry (its helicity) on selective amplification of the degree of circular polarization of photoexcitation has been investigated. We found that plasmon-polariton standing waves induced in S-type (curved) antennas by circularly polarized light, which was used for quantum dot photoexcitation, result in enhanced polarization selectivity of the quantum dot emission. The selectivity of the polarization of photoexcitation is a periodic function of the helical antenna length.
A. V. Poshakinskiy, A. N. Poddubny "Time-dependent photon correlations for incoherently pumped quantum dot strongly
coupled to the cavity mode"
Journal of Experimental and Theoretical Physics, February 2014, Volume 118, Issue 2, pp 205-216
Abstract: The time dependence of correlations between the photons emitted from a microcavity with an embedded quantum dot under incoherent pumping is studied theoretically. Analytic expressions for the second-order correlation function g (2)(t) are presented in strong and weak coupling regimes. The qualitative difference between the incoherent and coherent pumping schemes in the strong coupling case is revealed: under incoherent pumping, the correlation function demonstrates pronounced Rabi oscillations, but in the resonant pumping case, these oscillations are suppressed. At high incoherent pumping, the correlations decay monoexponentially. The decay time nonmonotonically depends on the pumping value and has a maximum corresponding to the self-quenching transition.
B. le Feber, N. Rotenberg, D. M. Beggs & L. Kuipers “Simultaneous measurement of nanoscale electric and magnetic optical fields”
Abstract: Control of light–matter interactions at the nanoscale has advanced fields such as quantum optics, photovoltaics and telecommunications. These advances are driven by an improved understanding of the nanoscale behaviour of light, enabled by direct observations of the local electric fields near photonic nanostructures. With the advent of metamaterials that respond to the magnetic component of light, schemes have been developed to measure the nanoscale magnetic field. However, these structures interact not only with the magnetic field, but also with the electric field of light. Here, we demonstrate the essential simultaneous detection of both electric and magnetic fields with subwavelength resolution. By explaining our measurements through reciprocal considerations, we create a route towards designing probes sensitive to specific desired combinations of electric and magnetic field components. Simultaneous access to nanoscale electric and magnetic fields will pave the way for new designs of optical nanostructures and metamaterials.
A. A. Maksimov, I. I. Tartakovskii, E. V. Filatov, S. V. Lobanov, N. A. Gippius, S. G. Tikhodeev, C. Schneider, M. Kamp, S. Maier, S. Höfling, and V. D. Kulakovskii "Circularly polarized light emission from chiral spatially-structured planar semiconductor microcavities" Phys. Rev. B 89, 045316
Abstract: We demonstrate a method for control of the polarization of emission of quantum dots (QDs) embedded in an active layer of a planar microcavity. This method involves a modification of the electromagnetic mode structure in a planar microcavity which is achieved by fabrication of a chiral gammadion layer structure with partial etching of the upper Bragg mirror. A polarization degree as high as 81% has been demonstrated experimentally without the use of a static magnetic field or birefringent wave plates; this is in full agreement with the theoretical simulations for the fabricated structure. Theoretical optimization has shown that a polarization degree of up to 99% can be achieved in optimized structures with randomly positioned quantum dots, and to an even higher degree when the QDs have controlled positions.
M. S. Kuznetsova, K. Flisinski, I. Ya. Gerlovin, I. V. Ignatiev, K. V. Kavokin, S. Yu. Verbin, D. R. Yakovlev, D. Reuter, A. D. Wieck, M. Bayer "Hanle effect in (In,Ga)As quantum dots: Role of nuclear spin fluctuations" Phys. Rev. B 87, 235320
Abstract: The role of nuclear spin fluctuations in the dynamic polarization of nuclear spins by electrons is investigated in (In,Ga)As quantum dots. The photoluminescence polarization under circularly polarized optical pumping in transverse magnetic fields (Hanle effect) is studied. A weak additional magnetic field parallel to the optical axis is used to control the efficiency of nuclear spin cooling and the sign of nuclear spin temperature. The shape of the Hanle curve is drastically modified with changing this control field, as observed earlier in bulk semiconductors and quantum wells. However, the standard nuclear spin cooling theory, operating with the mean nuclear magnetic field (Overhauser field), fails to describe the experimental Hanle curves in a certain range of control fields. This controversy is resolved by taking into account the nuclear spin fluctuations owed to the finite number of nuclei in the quantum dot. We propose a model describing cooling of the nuclear spin system by electron spins experiencing fast vector precession in the random Overhauser fields of nuclear spin fluctuations. The model allows us to accurately describe the measured Hanle curves and to determine the parameters of the electron-nuclear spin system of the studied quantum dots.
R. Giri, S. Cronenberger, M. M. Glazov, K. V. Kavokin, A. Lemaître, J. Bloch, M. Vladimirova, and D. Scalbert "Nondestructive Measurement of Nuclear Magnetization by Off-Resonant Faraday Rotation" Phys. Rev. Lett. 111, 087603
Abstract: We report on the nondestructive measurement of nuclear magnetization in n-GaAs via cavity enhanced Faraday rotation. In contrast with the existing optical methods, this detection scheme does not require the presence of detrimental out-of-equilibrium electrons. Specific mechanisms of the Faraday rotation are identified for (i) nuclear spins situated within the localized electron orbits, these spins are characterized by fast dynamics, (ii) all other nuclear spins in the sample characterized by much slower dynamics. Our results suggest that even in degenerate semiconductors nuclear spin relaxation is limited by the presence of localized electron states and spin diffusion, rather than by Korringa mechanism.
K.V. Kavokin, A.V. Koudinov "Dynamical polarization of nuclear spins by acceptor-bound holes in a zinc blende semiconductor" Phys. Rev. B 88, 235202
Abstract: The ground state of an acceptor-bound hole in a zinc-blende semiconductor is formed by four eigenstates of the total angular momentum, which is a vector sum of spin and orbital moment of the hole. As a result, the hyperfine interaction of the hole with lattice nuclei becomes anisotropic and coordinate-dependent. We develop a theory of dynamic polarization of nuclear spins by the acceptor-bound hole, giving full account for its complex spin structure. The rate of hole-nuclear flip-flop transitions is shown to depend on the angle between the total angular momentum of the hole and the position vector of the nucleus with respect to the acceptor center. The resulted spatially inhomogeneous spin polarization of nuclei gives rise to non-equidistant spin splitting of the hole, which can be detected by methods of optical or microwave spectroscopy.
L. E. Golub, E. L. Ivchenko "Spin-dependent phenomena in semiconductors in strong electric fields" New Journal of Physics,Volume 15, December 2013
Abstract: We develop a theory of spin-dependent phenomena in the streaming regime characterized by ballistic acceleration of electrons in the moderate electric field until they achieve the optical phonon energy and abruptly emit the phonons. It is shown that the Dyakonov-Perel spin relaxation is drastically modified in this regime, the current-induced spin orientation remarkably increases, reaches a high value ~2% in the electric field ~1kV/cm and falls with the further increase in the field. The spin polarization enhancement is caused by squeezing of the electron momentum distribution in the direction of drift. We also predict field-induced oscillatory dynamics of spin polarization of the photocarriers excited into the conduction band by a short circularly-polarized optical pulse.
J Beetz, T Braun, C Schneider, S Höfling and M Kamp "Anisotropic strain-tuning of quantum dots inside a photonic crystal cavity" Semiconductor Science and Technology, Volume 28, Number 12.
Abstract: We report on anisotropic strain induced fine-tuning of semiconductor quantum dots (QDs) embedded into a photonic crystal nanocavity. Due to a complete removal of the sample substrate we achieve large spectral tuning ranges of up to 5.83 meV for the QD emission lines, which is sufficient to readily establish spectral resonance with the high Q cavity mode. When the QD emission lines are swept through the mode, we observe an enhancement of the QD emission in this weakly coupled QD–resonator system.
Luxmoore, I. J. and Wasley, N. A. and Ramsay, A. J. and Thijssen, A. C. T. and Oulton, R. and Hugues, M. and Fox, A. M. and Skolnick, M. S., "Optical control of the emission direction of a quantum dot" Applied Physics Letters, 103, 241102 (2013),
Abstract: Using the helicity of a non-resonant excitation laser, control over the emission direction of an InAs/GaAs quantum dot is demonstrated. The quantum dot is located off-center in a crossed-waveguide structure, such that photons of opposite circular polarization are emitted into opposite waveguide directions. By preferentially exciting spin-polarized excitons, the direction of emission can therefore be controlled. The directional control is quantified by using the ratio of the intensity of the light coupled into the two waveguides, which reaches a maximum of ±35%.
Abstract: We use polarization-resolved near-field measurements, in conjunction with electromagnetic theory, to separate and quantify the electric and magnetic optical response of subwavelength holes in thick gold films. Using 1550 nm light, we determine the amplitudes of the electric and magnetic polarizabilities of holes with diameters ranging from 600 to 1000 nm. Additionally, we study the scattered field distributions that arise from the interactions of the holes with surface plasmon polaritons, and show that forward-backward scattering ratios as high as 2.5:1 are possible. Our study provides experimental access and theoretical understanding of the full electromagnetic polarizability that describes the optical response of metallic holes at telecom wavelengths, which is a prototypical structure in currently explored optical signal processing and sensing devices.
N. Rotenberg, D. M. Beggs, J. E. Sipe2and L. Kuipers “Resonant coupling from a new angle: coherent control through geometry” OPTICS EXPRESS 21, 16504 (2013)
Abstract: We demonstrate that interference of absorption pathways can be used to control resonant coupling of light to guided modes in a manner analogous to quantum coherent control or electronically induced transparency. We illustrate the control of resonant coupling that interference affords using a plasmonic test system where tuning the phase of a grating is sufficient to vary the transfer of energy into the surface plasmon polariton by a factor of over 10^6. We show that such a structure could function as a one-way coupler, and present a simple explanation for the underlying
V.V. Belykh, N. N. Sibeldin, V. D. Kulakovskii, M. M. Glazov, M. A. Semina, C. Schneider, S. Hoefling, M. Kamp, and A. Forchel “Coherence Expansion and Polariton Condensate Formation in a Semiconductor Microcavity” Phys. Rev. Lett. 110, 137402 (2013)
Abstract: The dynamics of the expansion of the first order spatial coherence g1 for a polariton system in a high-Q GaAs microcavity was investigated on the basis of Young’s double slit experiment under 3 ps pulse excitation at the conditions of polariton Bose-Einstein condensation. It was found that in the process of condensate formation the coherence expands with a constant velocity of about 10^8 cm/s. The measured coherence is smaller than that in a thermal equilibrium system during the growth of condensate density and well exceeds it at the end of condensate decay. The onset of spatial coherence is governed by polariton relaxation while condensate amplitude and phase fluctuations are not suppressed.
M. V. Durnev, M. M. Glazov, and E. L. Ivchenko, M. Jo, T. Mano, T. Kuroda, and K. Sakoda, S. Kunz, G. Sallen, L. Bouet, X. Marie, D. Lagarde, T. Amand, and B. Urbaszek “Magnetic field induced valence band mixing in  grown semiconductor quantum dots” Phys. Rev. B 87 085315 (2013)
Abstract: We present a microscopic theory of the magnetic field induced mixing of heavy-hole states °æ3/2 in GaAs droplet dots grown on (111)A Ga-rich surfaces. The proposed theoretical model takes into account the striking dot shape with trigonal symmetry revealed in atomic force microscopy. Our calculations of the hole states are carried out within the Luttinger Hamiltonian formalism, supplemented with allowance for the triangularity of the confining potential. They are in quantitative agreement with the experimentally observed polarization selection rules, emission line intensities and energy splittings in both longitudinal and transverse magnetic fields for neutral and charged excitons in all measured single dots.
A N Poddubny, M M Glazov and N S Averkiev “Collective effects in emission of localized excitons strongly coupled to a microcavity photon”
New Journal of Physics 15, 025016 (2013)
Abstract: A theory of nonlinear emission of localized excitons coupled to the optical mode of the microcavity is presented. Numerical results are compared with analytical ones. The effects of exciton–exciton interaction within the quantum dots and with the reservoir formed by non-resonant pumping are considered. It is demonstrated that the nonlinearity due to the interaction strongly affects the shape of the emission spectra. The collective superradiant mode of the excitons is shown to be stable against the nonlinear effects.
A. N. Poddubny, Pavel A. Belov, and Yuri S. Kivshar, “Purcell effect in wire metamaterials”, Phys. Rev. B 87, 035136 (2013)
Abstract: We study theoretically the enhancement of spontaneous emission in wire metamaterials. We analyze the dependence of the Purcell factor on the wire dielectric constant for both electric and magnetic dipole sources and find an optimal value of the dielectric constant for maximizing the Purcell factor for the electric dipole. We obtain analytical expressions for the Purcell factor and also provide estimates for the Purcell factor in realistic structures operating in both microwave and optical spectral ranges.
I. J. Luxmoore, N. A. Wasley, A. J. Ramsay, A. C. T. Thijssen, R. Oulton, M. Hugues, S. Kasture, A.V. Gopal, A. M. Fox, M. S. Skolnick “Interfacing Spins in an InGaAs Quantum Dot to a Semiconductor Waveguide Circuit Using Emitted Photons”, Phys. Rev. Lett 110, 037402 (2013)
Abstract: An in-plane spin-photon interface is essential for the integration of quantum dot spins with optical circuits. The optical dipole of a quantum dot lies in the plane and the spin is optically accessed via circularly polarized selection rules. Hence, a single waveguide, which can transport only one in-plane linear polarization component, cannot communicate the spin state between two points on a chip. To overcome this issue, we introduce a spin-photon interface based on two orthogonal waveguides, where the polarization emitted by a quantum dot is mapped to a path-encoded photon. We demonstrate operation by deducing the spin using the interference of in-plane photons. A second device directly maps right and left circular polarizations to antiparallel waveguides, surprising for a nonchiral structure but consistent with an off-center dot.
E.A. Chekhovich, M.M. Glazov, A.B. Krysa, M. Hopkinson, P. Senellart, A. Lemaitre, M.S. Skonick, A.I. Tartakovskii, "Element-sensitive measurement of the hole–nuclear spin interaction in quantum dots" Nature Physics 9,74 (2013)
Abstract: It has been proposed that valence-band holes can form robust spin qubitsowing to their weaker hyperfine coupling compared with electrons. However, it was demonstrated recently that the hole hyperfine interaction is not negligible, although a consistent picture of the mechanism controlling its magnitude is still lacking. Here we address this problem by measuring the hole hyperfine constant independently for each chemical element in InGaAs/GaAs, InP/GaInP and GaAs/AlGaAs quantum dots. Contrary to existing models we find that the hole hyperfine constant has opposite signs for cations and anions and ranges from −15% to +15% relative to that for electrons. We attribute such changes to the competing positive contributions of p-symmetry atomic orbitals and the negative contributions of d-orbitals. These findings yield information on the orbital composition of the valence band and enable a fundamentally new approach for verification of computed Bloch wavefunctions in semiconductor nanostructures. Furthermore, we show that the contribution of cationic d-orbitals leads to a new mechanism of hole spin decoherence.
A.C.T. Thijssen, M.D. Cryan, J.G. Rarity, R. Oulton, “Transfer of arbitrary quantum emitter states to near-field photon superpositions in nanocavities” Optics Express 20, 22412 (2012).
Abstract: We present a method to analyze the suitability of particular photonic cavity designs for information exchange between arbitrary superposition states of a quantum emitter and the near-field photonic cavity mode. As an illustrative example, we consider whether quantum dot emitters embedded in “L3” and “H1” photonic crystal cavities are able to transfer a spin superposition state to a confined photonic superposition state for use in quantum information transfer. Using an established dyadic Green’s function (DGF) analysis, we describe methods to calculate coupling to arbitrary quantum emitter positions and orientations using the modified local density of states (LDOS) calculated using numerical finite-difference time-domain (FDTD) simulations. We find that while superposition states are not supported in L3 cavities, the double degeneracy of the H1 cavities supports superposition states of the two orthogonal modes that may be described as states on a Poincaré-like sphere. Methods are developed to comprehensively analyze the confined superposition state generated from an arbitrary emitter position and emitter dipole orientation.
Abstract: We study the reflection of polarized optical pulses from resonant photonic structures formed by periodic, Fibonacci, and gradient sequences of quantum wells. The form and polarization of the reflected pulse are shown to be determined by the structure design and optical length. In structures with periodic quantum well arrangement, the response to ultrashort pulse is an optical signal with a sharp rise followed by an exponential decay or Bessel beats depending on the structure length. The duration of reflected pulses nonmonotonically depends on the number of quantum wells reaching the minimum for a certain structure length which corresponds to the transition from superradiant to photonic-crystalline regime. We also study the conversion of pulse polarization in the longitudinal external magnetic field which splits the exciton resonance. Comparing periodic, Fibonacci, and gradient structures we show that the latter are more efficient for the conversion from linear to circular polarization.
M. Glazov and E. Ivchenko, "Spin noise in quantum dot ensembles", Physical Review B86, 115308 (2012).
Abstract: We study theoretically spin fluctuations of resident electrons or holes in singly charged quantum dots. The effects of external magnetic field and effective fields caused by the interaction of electron and nuclei spins are analyzed. The fluctuations of spin Faraday, Kerr, and ellipticity signals revealing the spin noise of resident charge carriers are calculated for the continuous wave probing at the singlet trion resonance.
Abstract: A theoretical description of electron spin orientation and detection by short optical pulses is proposed for ensembles of singly charged semiconductor nanocrystals. The complex structure of the valence band in spherical nanocrystals is taken into account. We demonstrate that the direction of electron spin injected by the pump pulse depends on both the pump pulse helicity and the pump pulse power. It is shown that a train of optical pulses can lead to the complete orientation of the resident electron spin. The microscopic theory of the spin Faraday, Kerr and ellipticity effects is developed and the spectral sensitivity of these signals is discussed. We show that under periodic pumping pronounced mode-locking of electron spins takes place and manifests itself as significant spin signals at negative delays between pump and probe pulses.