Abstract: Yasuhiko Arakawa Quantum dot cavity quantum electrodynamics for advanced light sources Yasuhiko Arakawa, Satoshi Iwamoto, and Yasutomo Ota Institute for Nano Quantum Information Electronics, Institute for Photonics Electr0nics Convergence, Institute of Industrial Science The University of Tokyo 4-6-1 Komaba, Tokyo 153-85051, Japan arakawa@iis.u-yokyo,ac.jp Cavity quantum electrodynamics (QED) has addressed the interaction between atomic states and photons in cavities under the weak or the strong coupling regime. In particular, solid-state cavity-QED provides a platform for seeking the frontier of physics of quantum optics as well as its applications. One of the most fascinating systems for the solid-state cavity-QED is semiconductor quantum dots (QDs) embedded in photonic crystal (PhC) nanocavities[1,2].

In this presentation, we discuss our advances in the QD cavity-QED with PhC nanocavities. First, we discuss the current state of the art of realization of the strong coupling regime, including achievement of the highest figure of merits (the ratio of the QD-cavity coupling strength g to the cavity decay rate k, i.e., g/k ) in a single QD embedded in two-dimensional (2D) PhC nanocavities. Lasing oscillation in a single or few QD(s) in the PhC nanocavities is also demonstrated and theoretically examined[3,4]. Finally, our recent progress in new types of light sources is discussed, such as a nanowire QD (NWQD) single photon source operated at room temperature[5], a spontaneous two-photon sources[6], and NWQD lasers with and without plasmonic effects[7.8].

References

[1] Y. Arakawa and H. Sakaki, Appl. Phys. Lett. 40, 939 (1982) [2] Y. Arakawa, S. Iwamoto, M. Nomura, A. Tandaechanurat, and Y. Ota, IEEE J. of Select. Top. in Quant. Electron., 18, 1818 (2012) [3] M. Nomura, N. Kumagai, S. Iwamoto, Y. Ota, and Y. Arakawa, Nature Phys. 6, 279, (2010). [4] K. Kamide, S. Iwamoto, and Y. Arakawa, Phys. Rev. Lett. 113, 143604 (2014) [5] M. Holmes, K Choi, S. Kako, M. Arita, and Y. Arakawa, NanoLett. 14, 982 (2014) [6] Y. Ota, S. Iwamoto, N. Kumagai, and Y. Arakawa, Phys. Rev. Lett. 107, 233602 (2011) [7] J. Ho, J. Tatebayashi , S. Sergent , C. Fong , S. Iwamoto , and Y. Arakawa, ACS Photonics 2 165 (2014) [8] J. Tatebayashi, S. Kako, Y. Ota, S. Iwamoto, and Y. Arakawa, Nature Photon. 9, 501 (2015)

Abstract: Takao Someya Ultraflexible organic devices for wearable and implantable electronics Takao Someya 1 : Department of Electrical and Electronic Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan 2 : Exploratory Research for Advanced Technology (ERATO), Japan Science and Technology Agency (JST), 2-11-16, Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan * someya@ee.t.u-tokyo.ac.jp Flexible and stretchable electronic devices are expected to open up a new class of applications ranging from flexible displays, wearable sensors, flexible RFID, to flexible large-area sensors and actuators. As one of the promising applications of flexible and stretchable electronics, biomedical sensors have attracted much attention recently. Sensors and electronic circuits for healthcare and medical applications have been fabricated using silicon and other rigid electronic materials. In order to minimize the discomfort of wearing rigid sensors, it is highly desirable to use soft electronic materials particularly for devices that come directly into contact with the skin and/or biological tissues. In this regard, electronics manufactured on thin polymeric films are very attractive: in general, a thinner substrate provides better mechanical flexibility. However, directly manufacturing sensors or electronic circuits on ultrathin polymeric films with thicknesses of several micrometers or less is a difficult task when conventional semiconductor processes are used. In this paper, we report on the recent progresses of ultrathin, ultra-lightweight, ultraflexible, organic devices, such as organic thin-film transistor (TFT) integrated circuits, organic photovoltaic (OPV) cells, and organic light-emitting diodes (OLEDs) on polymeric films with a thickness of only 1 μm. The ultrathin organic devices are used to fabricate human-machine interfaces such as touch sensors and wearable electronic systems such as an electromyogram (EMG) measurement sheet with a two-dimensional array of organic amplifiers.

Abstract: Heiner Linke

Reversible electron-hole separation in a hot carrier solar cell

S Limpert1, S Bremner1, and H Linke2

1 School of Photovoltaic and Renewable Energy Engineering, University of New South Wales, 2052

Sydney, Australia

2 NanoLund and Solid State Physics, Lund University, Box 118, 221 00 Lund, Sweden

E-mail: heiner.linke@ftf.lth.se

Hot-carrier solar cells are envisioned to utilize energy filtering to extract power from photogenerated electron-hole pairs before they thermalize with the lattice, and thus potentially offer higher power conversion efficiency compared to conventional, single absorber solar cells. The efficiency of hot-carrier solar cells can be expected to strongly depend on the details of the energy filtering process, a relationship which to date has not been satisfactorily explored. Here, we establish the conditions under which electron-hole separation in hot-carrier solar cells can occur reversibly, that is, at maximum energy conversion efficiency. We find that, under specific conditions, the energy conversion efficiency of a hot-carrier solar cell can exceed the Carnot limit set by the intra-device temperature gradient alone, due to the additional contribution of the quasi-Fermi level splitting in the absorber. To achieve this, we consider a highly selective energy filter such as a quantum dot embedded into a one-dimensional conductor. We also establish that the open-circuit voltage of a hot-carrier solar cell is not limited by the band gap of the absorber, due to the additional thermoelectric contribution to the voltage. Additionally, we find that a hot-carrier solar cell can be operated in reverse as a thermally driven solid-state light emitter. In addition this theoretical analysis, I will also report on first experimental results in a nanowire-based energy filter device.

S Limpert, S Bremner, and H Linke, to appear in New J. Phys (2015)

Abstract: Seigo Tarucha Valley current generation in double gated bilayer graphene Seigo Tarucha Department of Applied Physics, The University of Tokyo Center for Emergent Matter Science, Riken tarucha@ap.t.u-tokyo.ac.jp

Valley degree of freedom is defined for an electronic system having degenerate band structure in a certain crystal configuration and can be used to generate non-dissipative current with accompanying no net charge flow by means of breaking the spatial inversion symmetry. Graphene and transition metal dichalcogenide are two typical valley materials having K and K’ valleys due to the existence of two sub-lattices. The valley current has only been studied in monolayer graphene on h-BN where the spatial inversion symmetry is structurally broken by the superlattice potential. We use a double gated bilayer graphene device to electrically break the spatial inversion symmetry and control the Berry curvature. We use valley hall effect to generate a transverse pure valley current and inverse valley hall effect to detect the current. In this device the Fermi energy and the bandgap are independently varied and this allows to study existence of valley hall effect in the insulating regime where the local resistivity increases with lowering temperature. The insulating regime near the charge neutrality point is particularly interesting because the electric field to valley current conversion is less dissipative in contrast to the case for conventional spin or valley hall systems.

Abstract: Andreas Wacker Simulating Quantum Cascade Lasers under Operating Conditions Andreas Wacker, Lund University The quantum cascade laser (QCL) [1] has become an important device for IR radiation allowing a large variety of spectroscopic applications[2]. QCLs are based on optical transitions between electronic subbands in semiconductor heterostructures. Here the choice of the layer structure allows to specify the separation of the upper and lower laser level, and lasers covering two decades of the optical spectrum have been realized. The inversion between these levels is obtained by the specific current flow in biased structures. Thus the operation is based on an intriguing interplay between tunneling and scattering transitions which requires a quantum treatment. Over the last decade our group has developed a simulation package based on nonequilibrium Green’s functions which allows for a quantitative modeling[3]. The Green’s functions provide full information for the system based on a fully consistent microscopic quantum kinetic approach. Thus all relevant quantities such as the current density and the gain spectrum can be evaluated based on nominal sample parameters. Under lasing operation, the optical field strongly affects the carrier kinetics. This provides an increased current and a reduction in gain in good agreement with experimental data[4,5]. Comparing with computationally less demanding schemes, it is found that second-order currents are of relevance for realistic device simulations[4]. [1] J. Faist et al., Science 264, 553 (1994). [2] R.F. Curl et al., Chem. Phys. Lett. 487, 1 (2010). [3] A. Wacker, M. Lindskog, and D.O. Winge, IEEE Journal of Selected Topics in Quantum Electronics 19, 1200611 (2013). [4] M. Lindskog et al., Appl. Phys. Lett. 105, 103106 (2014). [5] D.O. Winge, M. Lindskog, and A. Wacker, Optics Express 22, 18389 (2014).

Abstract: Haruki Sanada Transport of electron spin coherence in persistent spin helix condition Haruki Sanada1, Yoji Kunihashi1, Hideki Gotoh1, Koji Onomitsu1, Makoto Kohda2, Junsaku Nitta2 and Tetsuomi Sogawa1 1NTT Basic ResearchLaboratories, NTT Corporation,Atsugi, Japan 2Department of Materials Science, Tohoku University, Sendai, Japan Transporting electron spins in spin-orbit coupled systems is the key to developing future spintronics devices.Conduction electrons moving in semiconductors experience the spin-orbit interaction (SOI) as an effective magnetic field, which enables us to rotate the electron spins in the absence of an external magnetic field. At the same time, the fluctuations in the spin-orbit effective magnetic field originating from the random scattering of electrons also cause undesirable spin decoherence, which limits the length scale of spin transport.Here, we reportthe long-distance drift transport of electron spins in semiconductors[1],where the SOIswereset ata spatialsymmetrygeneratinga persistent spin helix (PSH)[2]. The sample consisted of a 25-nm-thick GaAs/AlGaAs(001) quantum wellembedded in a HEMT structure. Thewafer wasprocessed into a cross-shaped channel with a top gate electrode(Fig. 1). This structure allowedus to applyin-plane voltagesVxand Vyto drift electrons, and a verticalgate voltage Vgto tunethe strengths of Rashba SOIs. The spatial spin distribution of drifting spins was measured using Kerr rotation microscopy at T= 8 K. A circularly polarized pump light from a cw Ti:sapphire laser generates electron spins at a certain position and a linearly polarized light probes the Kerr rotation K, which is proportional to the spin density at the focusedposition.Figure 2a shows a Vgdependence of Kscanned along the [1-10] directionforVx= 50 mVand Vy= 0 mV. Even in the absence of an external magnetic field, we observed spin precession resulting fromSOIs. By varying the vertical gate voltageVg, the spatial frequency of the drifting spinprecessionwascontinuouslymodulated via the electric-field-dependentRashbaSOI. This behavior was well reproduced by asimulation based on a spin-drift-diffusion model as shown in Fig. 2b.Acomparison of theexperiment and the simulationrevealed that aPSH state, whereDresselhaus and Rashba SOIsare balanced,is achievedaround Vg= -4.4V and the spin decay length is maximized near the PSH condition. [1] Y. Kunihashi, et al., submitted. -4.5 -4.4 -4.3 Vg (V) 100 50 0 x ( m) Experiment Simulation -300 30 y ( m) -30 0 30 x ( m) -1 0 1 K (a. u.) -300 30 y ( m) -30 0 30 x ( m) -1 0 1 K (a. u.) a b Fig. 2(a)xand Vgdependence of the spindensity measured for electronsdrifting in xdirection.(b) Simulatedspin density plottedas a function of xand the Rashba SOI parameter . Dashed lines show the area corresponding to the experimental result. [2] J. Schliemann and D. Loss, PRB 68, 165311 (2003). This work was supported by JSPS. Fig. 1 Schematic top view of the sample.

Abstract: Floriana Lombardi

Nanoscale High critical Temperature Superconductors for fundamental studies and hybrid devices

D. Gustafsson, R. Baghadi, R. Arpaia, D. Golubev*, M. Fogelstöm, S. Kubatkin, T. Claeson, T. Bauch and F. Lombardi Quantum Device Physics Laboratory, Microtechnology and Nanoscience, Chalmers University of Technology, SE-41296, Göteborg, Sweden *Aalto University, Finland Floriana.Lombardi@chalmers.se The phase diagram of the High-Tc Superconductors (HTS) is shaped by the spontaneous emergence of various ordered states, tuned by doping and driven by the many competing degree of freedom where not only charge and spin are of relevance, but also lattice and orbitals have an active role in building up the ground state. The identification of the ordered states, like the charge stripes recently discovered in all cuprates families, is crucial for understanding high-temperature superconductivity. This is a very complicated task which could come to a turning point by studying the transport properties of HTS devices at nanoscale, on dimensions comparable with the characteristic lengths of the local orders. The idea here is that in HTS in low-dimensional form, like nanodots and nanowires, the locality of charge/spin arrangement is highly enhanced, which might lead to more dramatic effects on the transport properties of mesoscopic systems. This can be instrumental in getting new insights into the still unknown microscopic mechanism at the origin of the superconducting phenomenon in cuprates. In the first part of my contribution, I report on our recent progress in realizing a spectroscopic technique based on an HTS nanoscale device that allows an unprecedented energy resolution, thanks to Coulomb blockade effects, a regime practically inaccessible up to now in these materials [1]. An all YBa2Cu3O7-x (YBCO) Single Electron Transistor (SET) has been fabricated by using biepitaxial grain boundaries as tunnel barriers. In such a devices we find that the energy required to add an extra electron to a nanometer size YBCO island depends on the parity (odd/even) of the excess electrons on the island itself and increases with magnetic field. This is inconsistent with a pure dx

2−y

2-wave symmetry and demonstrates a complex order parameter component on the island that needs to be incorporated into any theoretical model of HTS. By using both a semiclassical and tight binding model calculation for the island I we will also discuss the most probable symmetry for the subdominant imaginary order parameter. In the second part of my talk I will present our recent results on the realization of YBCO nanogaps for hybrid devices. Indeed the engineering of interfaces involving HTS materials and two dimensional systems like Topological Insulator (TIs) or Graphene could present several advantages, when compare to conventional superconductors, in revealing the new physics due to the proximity of a superconductor and a material with Dirac dispersion. Here I report on a novel fabrication technique which uses Au encapsulation to achieve YBCO nanogaps as small as 35 nm [2]. To demonstrated the feasibility of the YBCO nanogaps for hybrid devices we have bridged the nanogap with a thin Au layer. In several devices we have observed a critical current up to 80 K. Such structures were characterized by record values of the Jc up to 107A/cm2 at T=4.2 K. To prove the Josephson nature of the weak coupling through the nanogap we have measured the magnetic field patterns demonstrating almost ideal Fraunhofer-like dependence of the critical current Moreover the detected Shapiro steps, observed by irradiating the junction with microwaves, also support the existence of Josephson effect through the Au film.𝜈For some devices we have detected the formation of half-integer Shapiro steps at low temperatures, which might be attributed to a non-sinisuoidal current phase relation of the YBCO-Au-YBCO junction and/or of the d-wave symmetry of the YBCO order parameter. Our study clearly shows that these YBCO nanogaps can represent a novel platform for realizing hybrid devices beyond the present state of the art. [1] D. Gustafsson, D. Golubev, M. Fögelstrom, T. Claeson, S. Kubatkin, T. Bauch and F. Lombardi Nature Nanotechnology 8, 25 (2013) [2] R. Baghdadi, R. Arpaia, S.Charpentier, D. Golubev, T. Bauch and F. Lombardi Phys. Rev. Applied (2015).

Abstract: Masaaki Tanaka

Ferromagnetic semiconductors and heterostructures for semiconductor spintronics: Wavefunction engineering using n-type electron-induced ferromagnetic semiconductor (In,Fe)As

Masaaki Tanaka1,2, Le Duc Anh1, Pham Nam Hai1,3

1 Department of Electrical Engineering & Information Systems, The University of Tokyo 2 Institute for Nano-Quantum Information Electronics, The University of Tokyo 3 Department of Physical Electronics, Tokyo Institute of Technology Ferromagnetic semiconductors (FMSs) have been intensively studied for decades as they have novel functionalities that cannot be achieved with conventional metallic materials, such as the ability to control magnetism by electrical gating or light irradiation [1][2]. Prototype FMSs such as (Ga,Mn)As, however, are always p-type, making it difficult to be used in real spin devices. Here, we demonstrate that by introducing iron (Fe) to InAs, it is possible to fabricate a new n-type electron-induced FMS with the ability to control ferromagnetism by both Fe and independent carrier doping. The studied (In1-x,Fex)As layers were grown by low-temperature molecular beam epitaxy on semi-insulating GaAs substrates. Electron carriers in these layers are generated by independent chemical doping of donors. The ferromagnetism was investigated by magnetic circular dichroism (MCD), superconducting quantum interference device (SQUID), and anomalous Hall effect (AHE) measurements. With increasing the electron density concentration (n = 1.8×1018 cm-3 to 2.7×1019 cm-3) and Fe concentration (x = 5 - 8%), the MCD intensity shows strong enhancement at optical critical point energies E1 (2.61 eV), E1 + Δ1 (2.88 eV), E0’ (4.39 eV) and E2 (4.74 eV) of InAs, indicating that the band structure of (In,Fe)As is spin-split due to sp-d exchange interaction between the localized d states of Fe and the electron sea. SQUID and AHE measurements are also consistent with the MCD results. The Hall and Seebeck effects confirm the n-type conductivity of our (In,Fe)As samples. The electron effective mass is estimated to be as small as 0.03-0.175m0, depending on the electron concentration. These reveal that the electrons are in the InAs conduction band rather than in the impurity band, making it easy to understand (In,Fe)As by conventional Zener-model of carrier-induced ferromagnetism [3]. This band picture is different from that of GaMnAs [4][5]. Our results open the way to implement novel spin-devices such as spin light-emitting diodes or spin field-effect transistors, as well as help understand the mechanism of carrier-mediated ferromagnetism in FMSs [6-12].

Furthermore, we demonstrate new phenomena in (In,Fe)As and its hetrerostructures: Novel crystalline anisotropic magnetoresistance with two fold and eight fold symmetry [7], and control of ferromagnetism by strain, quantum confinement, gate electric field and wavefunction engineering in quantum heterostructures with a (In,Fe)As quantum well [9-11].

This work was partly supported by Grant-in-Aids for Scientific Research including Specially Promoted Research and Project for Developing Innovation Systems of MEXT.

References [1] S. Koshihara, A. Oiwa, M. Hirasawa, S. Katsumoto, Y. Iye, C. Urano, H. Takagi and H. Munekata, Phys. Rev. Lett. 78, 4617 (1997). [2] H. Ohno, D. Chiba, F. Matsukura, T. Ohmiya, E. Abe, T. Dietl, Y. Ohno and K. Ohtani, Nature 408, 944 (2000). [3] T. Dietl, H. Ohno, F. Matsukura, J. Cibert and D. Ferrand, Science 287, 1019 (2000). [4] S. Ohya, I. Muneta, P. N. Hai, and M. Tanaka, Phys. Rev. Lett. 104, 167204 (2010). [5] S. Ohya, K. Takata, and M. Tanaka, Nature Phys. 7, 342 (2011). [6] P. N. Hai, L. D. Anh and M. Tanaka, cond-mat, arXiv:1106.0561v3 (2011); P. N. Hai, L. D. Anh, S. Mohan, T. Tamegai, M. Kodzuka, T. Ohkubo, K. Hono, and M. Tanaka, Appl. Phys. Lett. 101, 182403 (2012). [7] P. N. Hai, D. Sasaki, L. D. Anh, and M. Tanaka, Appl. Phys. Lett. 100, 262409 (2012). [8] P. N. Hai, L. D. Anh, and M. Tanaka, Appl. Phys. Lett. 101, 252410 (2012). [9] L. D. Anh, P. N. Hai, and M. Tanaka, Appl. Phys. Lett. 104, 042404 (2014). [10] D. Sasaki, L. D. Anh, P. N. Hai, and M. Tanaka, Appl. Phys. Lett. 104, 142406 (2014). [11] L. D. Anh, P. N. Hai, Y. Kasahara, Y. Iwasa, and M. Tanaka, arXiv 1503.02174 (2015). [12] M. Tanaka, S. Ohya, and P. N. Hai (invited), Appl. Phy. Rev., 1, 011102 (2014).

Abstract: Mikael Fogelström Spontaneously broken time-reversal symmetry in d-wave superconductors Conventional superconductors are strong diamagnets that through the Meissner effect expel magnetic fields. It would therefore be surprising if a superconducting ground state would support spontaneous magnetics fields. Such time-reversal symmetry broken states have been proposed for the high-temperature superconductors, but their identification remains experimentally controversial. Here we show a route to a low-temperature superconducting state with broken time-reversal symmetry that may accommodate currently conflicting experiments. This state is characterised by an unusual vortex pattern in the form of a necklace of fractional vortices around the perimeter of the material, where neighbouring vortices have opposite current circulation. This vortex pattern is a result of a spectral rearrangement of current carrying states near the surfaces.

Abstract: Yoshiro Hirayama Nuclear spin polarization and detection in quantum Hall systems Yoshiro Hirayama(1),(2),(3)

1Department of Physics, Tohoku University, Sendai 980-8578, Japan

2Graduate Program in Spintronics, Sendai 980-8578i, Japan

3WPI-AIMR, Tohoku University, Sendai 980-8577, Japan

Dynamic nuclear polarization and resistive detection of nuclear polarization open us highly-sensitive resistively-detected NMR (nuclear magnetic resonance) in quantum-Hall systems, unveiling many interesting physics of two-dimensional (2D) systems, especially GaAs 2D systems.

Nuclear spins can be dynamically polarized in GaAs quantum well by using several different methods. The spin phase transition (SPT) characteristics at n = 2/3 allows us a sensitive detection of nuclear polarization. We found that nuclear polarization induced by circularly polarized optical illumination results in spatially uniform nuclear polarization [1]. The nuclear spin polarization is induced by the flip-flop interaction when the optically accumulated electron spins return to the equilibrium condition. Reflecting the selection rule of light absorption in the quantum well, nuclear polarization is well controlled by irradiation wavelength and polarity [2]. The filling-factor dependence is non-monotonic and can be explained by not fractional quantum Hall states but the effect of electron spin polarization through excitons and trions [3].

On the other hand, dynamic nuclear polarization by a large current flow at n = 2/3 SPT results in spatially inhomogeneous nuclear polarization reflecting domain structures formed at SPT [4]. Although inhomogeneity complicates experimental results, this inhomogeneity helps us to understand some physics. The selective nuclear polarization in one of the bilayer quantum wells enables us to study nuclear spin diffusion both parallel and perpendicular to the quantum well. We found asymmetric nuclear spin diffusion and a strong suppression of diffusion in the perpendicular direction through the barrier [5]. Furthermore, sudden change in nuclear polarization distribution appeared by one-second exposure to the electron-spin Goldstone mode provides us a hint to consider the novel corrective phenomena including both electron and nuclear spins [6]. 1. K. Akiba, S. Kanasugi, K. Nagase, and Y. Hirayama, Appl. Phys. Lett., 99, 112106 (2011). 2. K. Akiba, T. Yuge, S. Kanasugi, K. Nagase, and Y. Hirayama, Phys. Rev. B87, 235309 (2013). 3. K. Akiba, S. Kanasugi, T. Yuge, K. Nagase, and Y. Hirayama, Phys. Rev. Lett. 115, 026804 (2015). 4. M. H. Fauzi, S. Watanabe, N. Kumada, and Y. Hirayama, J. Korean Phys. Soc., 60, 1676 (2012). 5. T. Hatano, W. Kume, S. Watanabe, K. Akiba, K. Nagase, and Y. Hirayama, Phys. Rev. B91, 115318

(2015). 6. M. H. Fauzi, S. Watanabe, and Y. Hirayama, Phys. Rev. B90, 235308 (2014).

Abstract: Sergey Kubatkin Weak localization in epitaxial graphene on SiC: influence of impurity spin dynamics. Sergey Kubatkin Department of Microtechnology and Nanoscience, Chalmers University of Technology We have performed magnetotransport measurements on monolayer epitaxial graphene and analyzed them in the framework of the disordered Fermi liquid theory. We have separated the electron-electron and weak-localization contributions to resistivity and demonstrated the phase coherence over a micrometer length scale, setting the limit of at least 50 ps on the spin relaxation time in this material [1]. By magnetotransport studies of epitaxial graphene on SiC in a vector magnetic field we have demonstrated that spin relaxation, detected using weak localisation analysis, is suppressed by an in-plane magnetic field, B∥∥, and thereby proving a proof that it is caused, at least in part, by spinful scatterers. A non-monotonic dependence of effective decoherence rate on B∥∥ reveals the intricate role of scatterer’s spin dynamics in forming the interference correction to conductivity [2], an effect that has gone unnoticed in earlier weak localization studies; the effect is general and not limited only to magnetotransport in graphene. 1. S. Lara-Avila. et al., Disordered Fermi Liquid in Epitaxial Graphene from Quantum Transport Measurements, Phys. Rev. Lett. 107, 166602 (2011) 2. S. Lara-Avila. et al., Influence of impurity spin dynamics on weak localization in epitaxial graphene on SiC, Phys. Rev. Lett. (2015), accepted.

Abstract: Hideo Ohno Spintronics Nano-Devices for Nonvolatile VLSIs Hideo Ohno1, 2, 3, 4

1Laboratory for Nanoelectronics and Spintronics, RIEC, Tohoku University, Sendai, Japan 2Center for Spintronics Integrated Systems, Tohoku University, Sendai, Japan 3Center for Innovative Integrated Electronics, Tohoku University, Japan 4WPI Advanced Institute for Materials Research, Tohoku University, Sendai, Japan I review physics and materials science of nanoscale spintronic devices being developed for nonvolatile VLSI [1]. VLSIs can be made high performance and yet standby-power free by using magnetic tunnel junction, a two-terminal spintronic device, in combination with current CMOS technology. The scalability of perpendicular magnetic tunnel junctions utilizing CoFeB-MgO [2] is passing the 20 nm dimension; the smallest and well characterized ones now reaching 11 nm [3, 4]. Another important entity is three terminal devices utilizing current-induced domain wall motion [4] and its recent variants using spin-orbit torque [5-7]. If time allows, I will discuss electric-field switching of magnetization in perpendicular CoFeB-MgO magnetic tunnel junctions [8]. [1] H. Ohno, International Electron Device Meeting (IEDM) (invited) 9.4.1 (2010). [2] S. Ikeda, et al. Nature Materials, 9, 721 (2010). [3] H. Sato, et al. IEDM 2013 and Appl. Phys. Lett. 105, 062403 (2014). [4] S. Fukami, et al. IEDM 2013; Nature Comm. 4:2293 doi: 10.1038/ncomms3293 (2013); IEEE Tras. Mag. 50, 34106 (2014); Phys. Rev. B 91, 235401 (2015). [5] M. Yamanouchi, et al. Appl. Phys. Lett. 102, 212408 (2013). [6] C. Zhang, et al. Appl. Phys. Lett. 107, 012401 (2015). [7] S. Fukami, et al. arXiv:1507.00888. [8] S. Kanai, et al. Appl. Phys. Lett. 101, 122403 (2012); 103, 072408 (2013); 104, 212406 (2014)

Abstract: Markus Hennrich

Rydberg excitation of trapped strontium ions

G. Higgins1,2, F. Pokorny1,2, F. Kress1, J. Haag1, C. Maier1, Y. Colombe1, M. Hennrich1,2

1 Institute for Experimental Physics, University of Innsbruck, 6020 Innsbruck, Austria 2 Department of Physics, Stockholm University, 10691 Stockholm, Sweden E-mail: markus.hennrich@fysik.su.se

Trapped Rydberg ions are a novel approach for quantum information processing [1,2]. This idea joins the advanced quantum control of trapped ions with the strong dipolar interaction between Rydberg atoms. For trapped ions this method promises to speed up entangling interactions [3] and to enable such operations in larger ion crystals [4].

We report on the first experimental realization of trapped strontium Rydberg ions. A single ion was confined in a linear Paul trap and excited to Rydberg states (25S to 37S) using a two-photon excitation with 243nm and 308nm laser light. The transitions we observed are narrow and the excitation can be performed repeatedly which indicates that the Rydberg ions are stable in the ion trap. Similar results have been recently reported on a single photon Rydberg excitation of trapped calcium ions [5].

The tunability of the 304-309nm laser should enable us to excite our strontium ions to even higher Rydberg levels. Such highly excited levels are required to achieve a strong interaction between neighboring Rydberg ions in the trap as will be required for quantum gates using the Rydberg interaction.

References

[1] M. Müller, L. Liang, I. Lesanovsky, P. Zoller, New J. Phys. 10, 093009 (2008).

[2] F. Schmidt-Kaler, et al., New J. Phys. 13, 075014 (2011).

[3] W. Li, I. Lesanovsky, Appl. Phys. B 114, 37-44 (2014).

[4] W. Li, A.W. Glaetzle, R. Nath, I. Lesanovsky, Phys. Rev. A 87, 052304 (2013).

[5] T. Feldker, et al., arXiv:1506.05958.

Abstract: Lars Samuelson New approaches to nanowire-based technologies and applications Lars Samuelson NanoLund and Solid State Physics, Lund University, LUND, Sweden also CSO for QuNano AB, Glo AB and Sol Voltaics AB The field of nanowires is today becoming quite mature with the build-up of rather strong expectations for applications and commercialization break-through in fields ranging from electronics to energy harvesting and lighting. Still today, quite new approaches for growth and utilization of nanowire-technologies emerge. I will describe a few such cases, for instance the development of the “flying-wire” growth occurring in the aerosol phase (“Aerotaxy”) without the use of any substrate, and the related challenge of bridging the gap in assembly from the nano-scale to the meter-scale. I will also describe our recent efforts in the use of nanowires as seeds for development of dislocation-free platelets of GaN and InGaN, for optics as well as for electronics applications.

Abstract: Ian Davidson Photonic quantum information The interdisciplinary field of quantum information processing and communication connects quantum mechanics/optics/electronics with classical information theory to achieve tasks in information and communication that are impossible with classical methods. This fusion has led to new concepts such as the qubit and quantum teleportation, and new applications, such as quantum cryptography (the only unconditionally secure secret key distribution method known), and quantum computing. Quantum information science has also revitalized the discussions about the foundations of quantum theory. The field is currently very active and is driving for progress in both physics and information technology. Photons, or light quanta, are the best choice for quantum communication as they can be transported with low loss, both in optical fibers and in free space. Using photons, more advanced building blocks of quantum information theory can be produced; complex superpositions and entangled states can be generated and manipulated using linear optics. These building blocks can then be used in quantum communication and quantum cryptography. I will review our effort generation and characterisation of bright single photon and multipartite photon polarization entanglement sources; superconducting nanowires single-photon detector (SSPD) and femtosecond laser integrated optics circuits. In quantum communication and cryptography we have demonstrated different protocols such as multiparty secret sharing, communication complexity, clock synchronization, and random access code.

Abstract: Susumu Noda Recent Progress in Photonic Crystals and Their Applications So far, we have developed a variety of photonic nano-structures and devices based on photonic crystals for next-generation communication, information processing, and energy applications. Among them, I will discuss about following three topics in this workshop: 1) Broad-area coherent photonic-crystal lasers for evolution of semiconductor lasers, 2) thermal-emission control for renovation of thermal-emission devices, and 3) advanced photon manipulation based on ultra-high-Q nanocavities, which includes all-silicon nano-Raman lasers, integration of high-Q nanocavities and on-chip photon transfer.

Abstract: Fredrik Karlsson

InGaN quantum dots as polarized photon emitters

K. F. Karlsson1, A. Lundskog, C. W. Hsu, S. Amloy, U. Forsberg, T. Jemsson, H. Machhadani, E. Janzén and P. O. Holtz

Semiconductor Materials, IFM, Linköping University, SE-581 83 Linköping, Sweden

III-nitride based quantum dots (QDs) have attracted much attention as efficient light emitters, offering deeper confinement potentials and a wider range of photon energies than provided by the conventional III-arsenide system. Moreover, the unique valence band structure with small split-off energy makes the semiconducting nitrides particularly useful for emission of polarized light [1].

We utilize the apexes of hexagonal GaN micropyramids as preferential nucleation sites for InGaN QDs. The structures are fabricated by low-pressure hot-wall MOCVD, and the micropyramids are obtained by selective area growth on photolithography-defined SiN patterns. Optimized growth conditions result in the formation of single QDs, as evidenced by photoluminescence (PL) spectroscopy, and the photon energy can be tuned by about 400 meV in the indigo and violet part of the visible spectrum by controlling the growth temperature of the InGaN layer [2]. It is demonstrated that the top (0001) facet on slightly truncated pyramids is essential for QD formation.

The optical spectra of the pyramids reveal sharp sub-meV emission lines [2], typical for QDs, and signatures of a charged exciton complex have been identified [3]. An ultimate proof of QD formation is provided by the photon antibuching characteristics of the emission [4-5]. All pyramids exhibit a strongly linearly polarized emission from the QDs, implying that the dots possess a significant degree of asymmetry [1].

We have developed a novel concept based on elongated pyramids for controlling the polarization direction (see Fig. 1), by which the predefined elongation determines the polarization vectors of the emitted photons from the QDs [6]. The resulting QDs have a high degree of linear polarization (average 84 percent), with a high probability to be well aligned with the axis of elongation (up to about 90 percent for one micron elongation). Best polarization alignment is obtained for elongations parallel with the principal axes of the crystal, arranged with multiples of 60o angle with respect to each other, but some degree of polarization control in 30o steps is also shown possible (see Fig. 2). This growth scheme should allow fabrication of compact arrays of photon emitters, with a controlled polarization direction for each individual emitter.

[1] S. Amloy et al., arXiv: 1311.5731: http://arxiv.org/abs/1311.5731. [2] C. W. Hsu et al., Nano Letters 11 2415 (2011). [3] C. W. Hsu et al., Applied Physics Letters 103, 013109 (2013). [4] T. Jemsson et al., Applied Physics Letters 105, 081901 (2014) [5] T. Jemsson et al., Nanotechnology 26, 065702 (2015). [6] A. Lundskog et al., Light: Science & Applications 3, e139 (2014).

1 Corresponding author: freka@ifm.liu.se

Fig. 1: (a) SEM image showing uniform growth of GaN pyramids with the elongation parallel with

2110éë ùû (𝛼=0o). (b,c) Close up SEM images of individual pyramids with various elongation directions (𝛼=n⋅30o, n = 0, 1 … 5).

Fig. 2: (left) Histograms of the measured polarization direction for QDs on pyramids with various elongation directions. (right) Polar plot of the PL intensity versus the angle of the linear polarizer analyzer for elongated pyramids with 𝛼=0o.

Abstract: Kaz Hirakawa Terahertz spectroscopy of quantum nanostructures far beyond the diffraction limit K. Hirakawa Institute of Industrial Science and Institute for Nano Quantum Information Electronics, University of Tokyo, 4-6-1 Komaba, Tokyo 153-8585, Japan Characteristic energy scales in extremely small quantum nanostrucures such as quantum dots and single molecules lie mostly in the terahertz (THz) range and interactions between THz fields and nm-scale systems lead to intriguing phenomena. However, the THz wavelength is about 100 mm and orders of magnitude longer than the size of such nm-scale systems. This large mismatch between the size of nanostructures and the wavelength of THz radiation gives extremely small interaction cross sections, making THz measurements on nm-scale systems extremely difficult. In this presentation, we report on the intersublevel transition spectroscopy on single InAs QDs [1-3]. Metal nanogap electrodes integrated with a bow-tie antenna allow us to go much beyond the diffraction limit and can focus the THz radiation on the nanostructures. We used a single electron transistor (SET) geometry that consisted of an InAs QD and nanogap metal electrodes as a sensitive THz detector and detected intersublevel transition as a photocurrent induced in the SET. By using Fourier transform spectrometry, we determined the intersublevel transition spectra in single QDs even in the few electron regime. Furthermore, we have investigated electron transport in single C60 molecule transistors under the illumination of monochromatic THz radiation at 2.5 THz [4]. We have observed photon-assisted tunneling in SMTs. Furthermore, we have found that the THz field induced at the molecule is dramatically enhanced by the plasmonic effect of the nanogap electrodes and exceeds 100 kV/cm. [1] Y. Zhang, K. Shibata, N. Nagai, C. Ndebeka-Bandou, G. Bastard, and K. Hirakawa, Nano Letters 15, 1166 (2015). [2] Y. Zhang, K. Shibata, N. Nagai, C. Ndebeka-Bandou, G. Bastard, and K. Hirakawa, Phys. Rev. B 91, 241301(R) (2015). [3] Y. Zhang, K. Shibata, N. Nagai, C. Ndebeka-Bandou, G. Bastard, and K. Hirakawa, Appl. Phys. Lett., in press. [4] K. Yoshida, K. Shibata, and K. Hirakawa, submitted.

Abstract: Göran Johansson Artificial atoms in an open transmission line In this talk, I’ll discuss the physics of microwave photons moving in a coplanar waveguide (1D transmission line) interacting with one or more artificial atoms. Compared to the optical regime, the microwave regime allows for strong and stable coupling of the photons to (artificial) atoms. Using a mirror, it is also possible to modify the mode structure of the vacuum fluctuations at the atom, i.e. to control the spontaneous emission rate. I’ll also briefly discuss the possibility of generating and detecting single microwave photons in this setup. The presentation is primarily based on the following references: * "Probing the quantum vacuum with an artificial atom in front of a mirror", I.-C. Hoi, A. F. Kockum, L. Tornberg, A. Pourkabirian, G. Johansson, P. Delsing, C. M. Wilson e-print arXiv:1410.8840, to appear in Nature Physics (2015). * "Detecting itinerant single microwave photons", Sankar Raman Sathyamoorthy, Thomas M. Stace, Göran Johansson e-print arXiv:1504.04979 * "Non-absorbing high-efficiency counter for itinerant microwave photons", Bixuan Fan, Göran Johansson, Joshua Combes, G. J. Milburn, Thomas M. Stace, Phys. Rev. B 90, 035132 (2014). * "Quantum nondemolition detection of a propagating microwave photon", Sankar R. Sathyamoorthy, L. Tornberg, Anton F. Kockum, Ben Q. Baragiola, Joshua Combes, C.M. Wilson, Thomas M. Stace, G. Johansson Phys. Rev. Lett. 112, 093601 (2014). • "Scattering of coherent pulses on a two-level system”, Joel Lindkvist, Göran Johansson New J. Phys. 16, 055018 (2014).

Abstract: Katsuhiro Tomioka Vertical III-V nanowire transistors for future low-power switches Katsuhiro Tomioka and Takashi Fukui Graduate School of Information Science and Technology, and Research Center for Integrated Quantum Electronics, Hokkaido University tomioka@rciqe.hokudai.ac.jp

Huge power dissipation is a serious problem for future integrated circuits. The main issue facing

next-generation nanoelectronic switches is how to achieve ultralow power consumption while enhancing performance. Silicon-based CMOS technologies are striving to suppress the short-channel effect and enhanced OFF-state leakage current by changing their gate architecture. Moreover, they are expected to change channel materials and transport mechanism in order to enhance the ON-state current under a lower supply voltage and to minimize the subthreshold slope for low power consumption. These distinct concerns need to be mutually addressed in extending CMOS technologies. In this regard, nm-scaled heteroepitaxy of III-V nanowires on Si and unique III-V/Si heterojunctions would assist accelerate the innovations.

Here we report the position-controlled growth of III-V nanowires on Si without any buffering technique, demonstration of surrounding-gate transistors using III-V core–multishell nanowires as modulation-doped channels on Si, and challenges in steep subthreshold-slope switches using III-V nanowire/Si heterjunction as building-blocks for low power circuits.

Vertical surrounding-gate transistors using III-V core–multishell nanowire channels has a six-sided, modulation-doping structure. The nanowire channel offered by the 2DEG in core-multishell nanowire greatly enhances the on-state current while keeping good gate controllability [1]. These devices provide a route to making vertically-oriented high-performance transistors for the next generation of field-effect transistors.

Next, we demonstrate tunneling field-effect transistors (TFETs) using III-V nanowire/Si heterojunctions and experimentally demonstrate steep-slope switching behaviors using III-V NW/Si heterojunction TFETs with surrounding-gate architecture [2]. Control of resistances in this vertical TFET structure is important for achieving steep-slope switching, and specific doping to form intrinsic layer in nanowire plays key role to improve electrostatic behavior of the TFETs [3]. A minimum subthreshold slope (SS) of the TFET is 21 mV/dec at VDS of 0.10 – 1.00 V [2]. Serious issues in TFETs is low ON-state current because of high-series resistance and minor phenomenon compared with thermal diffusion process. Finally, we demonstrate new device concept to solve the issues in TFETs. The device shows a steep SS (40 mV/dec) with rapid enhancement of the ON-state current.

References [1] K.Tomioka, M.Yoshimura and T.Fukui, Nature 488, 189(2012). [2] K.Tomioka, M.Yoshimura and T.Fukui, IEEE VLSI symposia Tech. Dig. 47 (2011) [3] K.Tomioka, M. Yoshimura and T. Fukui, Nano Lett. 13, 5822 (2013).

Abstract: Martin Leijnse Making Majoranas talk to charge: A realistic platform for topological quantum information processing Majorana bound states (MBS) are special zero-energy modes predicted to appear in exotic spin-polarized p-wave superconductors. MBS satisfy non-Abelian statistics and, in addition, encode quantum information in a topologically protected manner, which makes them highly interesting for quantum computation applications. The required p-wave superconductivity seems to be hard to find in nature, but recent theoretical works have shown that it can instead be artificially engineered, for example in a semiconductor nanowire with strong spin-orbit coupling which is covered by a superconductor and exposed to a magnetic field. Following the theoretical predictions, a number of experimental groups took on the challenge to create MBS and over the last few years tentative signatures of Majorana bound states have indeed been observed. The next generation of experiments must now go beyond merely detecting the existance of MBS and instead probe their exotic properties, such as the (hopefully) exceptionally long coherence times and non-Abelian statistics. To accomplish this, one must create controllable ways to initialize, manipulate, and read out the quantum information encoded in MBS. In this talk, I will discuss one possible platform for this next generation of Majorana experiments, which is based on coupling the quantum information encoded in MBS to charge degrees of freedom, which provides convenient ways both of coupling different MBS qubits to each other (for manipulation), and of coupling to the outside world (for initialization and readout). I will explain how MBS-charge couplings can be controllably switched on and off in a setup where small superconducting islands are coupled to each other and to a macrosopic superconductor through gate-controlled Josephson junctions. Based on this control, we will see how the most important milestones on the way to topological quantum information processing can be achieved, and what the associated experimental requirements are.

Abstract: Toshiro Hiramoto Characteristics of Silicon Nanowire Transistors for Integration with Room-Temperature Operating Silicon Single-Electron Transistors Toshiro Hiramoto Institute of Industrial Science, The University of Tokyo 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan, Email: hiramoto@nano.iis.u-tokyo.ac.jp As the conventional MOSFET is approaching to its scaling and performance limit, the great expectations for so-called “Beyond CMOS” devices have been raised. One of the promising approaches is, instead of the integration of only Beyond CMOS devices, the integration of Beyond CMOS into the conventional CMOS platform to add new functionality to the present CMOS [1]. The silicon single-electron transistor (SET) is among such Beyond CMOS devices. In our group, SETs and CMOS devices have been integrated onto a single chip and the operation of SET/CMOS integrated circuits has been demonstrated at room temperature [2]. CMOS analog selectors, which will be the building blocks of multibit address decoders, are combined with SETs, and the circuit operation has been demonstrated. In this talk, characteristics of silicon nanowire transistors for low-voltage SET/CMOS integrated circuits will be presented. Special emphasis will be placed on the mobility enhancement [3] and threshold voltage variability [4] in silicon nanowire transistors with width less than 10nm. The minimum nanowire width is as narrow as 2nm. Acknowledgement: This work was partly supported by a Grant-in-Aid for Scientific Research and by Project for Developing Innovation Systems of MEXT, Japan. References: [1] Emerging Research Devices (ERD) Chapter, The International Technology Roadmap for Semiconductors (ITRS), 2013 Edition. [2] R. Suzuki, M. Nozue, T. Saraya, and T. Hiramoto, Jpn. J. Appl. Phys. 52, 04CJ05, 2013. [3] J. Chen, T. Saraya, and T. Hiramoto, VLSI Symposium on Technology, p. 175, 2010. [4] T. Mizutani, Y. Tanahashi, R. Suzuki, T. Saraya, M. Kobayashi, and T. Hiramoto, Silicon Nanoelectronics Workshop, p. 21, 2015.

Abstract: David Haviland Intermodulation in frequency combs for sensitive measurement at the quantum and nano scale. Prof. David Haviland Nanostructure Physics Royal Institute of Technology (KTH), Stockholm, Sweden. High quality factor resonators are excellent for detecting very weak signals. When driven near resonance, the response amplitude and phase of the resonator become extremely sensitive to small perturbations. These perturbations often give rise to nonlinear dynamics of the resonator, where the perturbing force is a nonlinear function of the resonators dynamic state variables (e.g. position and momentum). Yet in most applications of resonant detection, analysis of the perturbation is based on linearization of the dynamics (i.e. shift of resonance frequency). This talk will describe an alternative way of analyzing the resonator dynamics based on a phase-coherent measurement of intermodulation, or frequency mixing. The resonator is probed by excitation with many tones in a frequency comb. These applied tones intermodulate to generate a response comb that is measured with a multifrequency lockin amplifier. Analysis of the response comb allows one to reconstruct the perturbing nonlinearity with remarkable speed and accuracy. Application of this technique to Atomic Force Microscopy will be described. The potential to use this method to study quantum correlations in a microwave frequency comb will be discussed.

Abstract: Yoshihiro Iwasa Memristive switching in transition metal dichalcogenide 2D Crystals Yoshihiro Iwasa QPEC & Department of Applied Physics, University of Tokyo and RIKEN Center for Emergent Matter Science Scaling down materials to an atomic-layer level produces rich physical and chemical properties as exemplified in various two-dimensional (2D) crystals extending from graphene, transition metal dichalcogenides to black phosphorous. These include Dirac physics, quantum Hall physics, and valleytronic functions, which are caused by the dramatic modification of electronic band structures, simply by thinning. In the case of transition metal dichalcogenides (TMDs), the band gap becomes direct in monolayers, and the broken inversion symmetry and the strong spin-orbit interaction causes peculiar valley-dependent spin polarization in zero-magnetic field [1], as well as peculiar opto-valleytronics [2, 3]. In reduced dimensions, on the other hand, the electron correlation effects and their consequence, electronic phase transitions, are also significantly changed from bulk systems, and thus result in new properties and functions. Here we address unique physical properties of correlated 2D electron system 1T-TaS2, which was achieved simply by thinning. The ordering kinetics of the charge density wave transition was revealed to become extremely slow with reduction of thickness [4], resulting in an emergence of metastable states [5]. Furthermore, we realized the unprecedented memristive switching to multi-step non-volatile states by applying in-plane electric field. [1] R. Suzuki et al, Nat. Nano. 9, 611 (2014). [2] Y. J. Zhang et al., Nano Lett. 12, 1136 (2012), ibid. 13, 3023 (2013). [3] Y. J. Zhang et al., Science 344, 725 (2014). [4] M. Yoshida et al., Sci. Rep. 4, 7302 (2014). [5] M. Yoshida et al., Sci. Adv. in press

Abstract: Per Delsing Interaction between propagating phonons and a superconducting qubit M.V. Gustafsson, T. Aref, A. Frisk-Kockum, M. Ekström, G. Johansson and P. Delsing Chalmers University of Technology, 41296 Göteborg, Sweden We present a new type of mechanical quantum device, where propagating surface acoustic wave (SAW) phonons serve as carriers for quantum information. At the core of our device is a superconducting qubit, designed to couple to SAW waves in the underlying substrate through the piezoelectric effect. This type of coupling can be very strong, and in our case exceeds the coupling to any external electromagnetic mode. The SAW waves propagate freely on the surface of the substrate, and we use a remote electro-acoustic transducer to address the qubit acoustically. Three different experiments are presented: i) Exciting the qubit with an electromagnetic signal we can “listen” to the SAW phonons emitted by the qubit. The low speed of sound also allows us to observe the emission of the qubit in the time domain, which gives clear proof that the dominant coupling is acoustic. ii) Reflecting a SAW wave off the qubit, we observe a nonlinear reflection with strong reflection at low power and low reflection at high power. iii) Exciting the qubit with both an electromagnetic signal and with a SAW signal, we can do two tone spectroscopy on the qubit In all of these experiments we find a good agreement between experiment and theory. [1] M.V. Gustafsson et al., Nature Physics, 8, 338 (2012) [2] M.V.et al., Science 346, 207 (2014) [3] A. Frisk-Ko et al., Phys. Rev. A, 90, 013837 (2014) [4] T. Aref et al., arXiv:1506.01631 (2015)