Project acronym COSPSENA
Project Coherence of Spins in Semiconductor Nanostructures
Researcher (PI) Dominik Max Zumbühl
Host Institution (HI) UNIVERSITAT BASEL
Call Details Starting Grant (StG), PE3, ERC-2007-StG
Summary Macroscopic control of quantum states is a major theme in much of modern physics because quantum coherence enables study of fundamental physics and has promising applications for quantum information processing. The potential significance of quantum computing is recognized well beyond the physics community. For electron spins in GaAs quantum dots, it has become clear that decoherence caused by interactions with the nuclear spins is a major challenge. We propose to investigate and reduce hyperfine induced decoherence with two complementary approaches: nuclear spin state narrowing and nuclear spin polarization. We propose a new projective state narrowing technique: a large, Coulomb blockaded dot measures the qubit nuclear ensemble, resulting in enhanced spin coherence times. Further, mediated by an interacting 2D electron gas via hyperfine interaction, a low temperature nuclear ferromagnetic spin state was predicted, which we propose to investigate using a quantum point contact as a nuclear polarization detector. Estimates indicate that the nuclear ferromagnetic transition occurs in the sub-Millikelvin range, well below already hard to reach temperatures around 10 mK. However, the exciting combination of interacting electron and nuclear spin physics as well as applications in spin qubits give ample incentive to strive for sub-Millikelvin temperatures in nanostructures. We propose to build a novel type of nuclear demagnetization refrigerator aiming to reach electron temperatures of 0.1 mK in semiconductor nanostructures. This interdisciplinary project combines Microkelvin and nanophysics, going well beyond the status quo. It is a challenging project that could be the beginning of a new era of coherent spin physics with unprecedented quantum control. This project requires a several year commitment and a team of two graduate students plus one postdoctoral fellow.
Summary
Macroscopic control of quantum states is a major theme in much of modern physics because quantum coherence enables study of fundamental physics and has promising applications for quantum information processing. The potential significance of quantum computing is recognized well beyond the physics community. For electron spins in GaAs quantum dots, it has become clear that decoherence caused by interactions with the nuclear spins is a major challenge. We propose to investigate and reduce hyperfine induced decoherence with two complementary approaches: nuclear spin state narrowing and nuclear spin polarization. We propose a new projective state narrowing technique: a large, Coulomb blockaded dot measures the qubit nuclear ensemble, resulting in enhanced spin coherence times. Further, mediated by an interacting 2D electron gas via hyperfine interaction, a low temperature nuclear ferromagnetic spin state was predicted, which we propose to investigate using a quantum point contact as a nuclear polarization detector. Estimates indicate that the nuclear ferromagnetic transition occurs in the sub-Millikelvin range, well below already hard to reach temperatures around 10 mK. However, the exciting combination of interacting electron and nuclear spin physics as well as applications in spin qubits give ample incentive to strive for sub-Millikelvin temperatures in nanostructures. We propose to build a novel type of nuclear demagnetization refrigerator aiming to reach electron temperatures of 0.1 mK in semiconductor nanostructures. This interdisciplinary project combines Microkelvin and nanophysics, going well beyond the status quo. It is a challenging project that could be the beginning of a new era of coherent spin physics with unprecedented quantum control. This project requires a several year commitment and a team of two graduate students plus one postdoctoral fellow.
Max ERC Funding
1 377 000 €
Duration
Start date: 2008-06-01, End date: 2013-05-31
Project acronym LASER-ARPES
Project Laser based photoemission: revolutionizing the spectroscopy of correlated electrons
Researcher (PI) Felix Baumberger
Host Institution (HI) UNIVERSITE DE GENEVE
Call Details Starting Grant (StG), PE3, ERC-2007-StG
Summary It is proposed to develop a novel instrument for angular resolved photoelectron spectroscopy (ARPES) by combining a laser based ultraviolet light source with a state-of-the-art electron spectrometer. This combination will be unique in Europe and will push this important technique to an entirely new level of resolution, comparable to the thermal broadening at 1 K and nearly an order of magnitude lower than the resolution achievable in practical ARPES experiments with the latest synchrotron light sources. The low photon energy of this new source will also markedly enhance the bulk sensitivity of ARPES and thus enable the investigation of interesting materials that were not accessible so far. These new capabilities will be used to study the subtle quantum many-body states of correlated electrons in transition metal oxides, a frontier topic in condensed-matter physics. Specifically, we will focus on electronic instabilities in perovskites and elucidate how different degrees of freedom play together to determine the often vastly different properties of chemically closely related materials. Moreover, we will apply modern electron spectroscopy to correlated molecular solids with complex phase diagrams that challenge existing theory for satisfactory explanations. This field is largely unexplored but is fundamental for advances in molecular electronics.
Summary
It is proposed to develop a novel instrument for angular resolved photoelectron spectroscopy (ARPES) by combining a laser based ultraviolet light source with a state-of-the-art electron spectrometer. This combination will be unique in Europe and will push this important technique to an entirely new level of resolution, comparable to the thermal broadening at 1 K and nearly an order of magnitude lower than the resolution achievable in practical ARPES experiments with the latest synchrotron light sources. The low photon energy of this new source will also markedly enhance the bulk sensitivity of ARPES and thus enable the investigation of interesting materials that were not accessible so far. These new capabilities will be used to study the subtle quantum many-body states of correlated electrons in transition metal oxides, a frontier topic in condensed-matter physics. Specifically, we will focus on electronic instabilities in perovskites and elucidate how different degrees of freedom play together to determine the often vastly different properties of chemically closely related materials. Moreover, we will apply modern electron spectroscopy to correlated molecular solids with complex phase diagrams that challenge existing theory for satisfactory explanations. This field is largely unexplored but is fundamental for advances in molecular electronics.
Max ERC Funding
1 450 825 €
Duration
Start date: 2008-08-01, End date: 2013-07-31
Project acronym MASPIC
Project Spin currents in magnetic nanostructures
Researcher (PI) Mathias Kläui
Host Institution (HI) JOHANNES GUTENBERG-UNIVERSITAT MAINZ
Call Details Starting Grant (StG), PE3, ERC-2007-StG
Summary MaSpic will create an autonomous team at the University of Konstanz to investigate the interaction between magnetization, spin - polarized and pure diffusive spin currents using novel instrumentation and innovative theoretical approaches. A thorough understanding of the fundamental charge and spin transport interaction mechanisms, key to use of the spin degree of freedom for Spintronics, will be developed. To understand the interplay between spin-polarized charge currents and magnetization configurations (adiabatic vs. non-adiabatic electron transport), the reciprocal effects of magnetization on the current (magnetoresistance) and of the current on magnetization (spin transfer torque) will be correlated for the same spin structures. Non-intrusive high resolution imaging at variable temperature will be used to probe the non-adiabaticity and help understand the hotly debated influence of thermal excitations on transport. Pure diffusive spin currents will be efficiently generated and used to manipulate magnetization with ultra-low power dissipation. The poorly understood spin current generation by the Spin Hall Effect and spin current propagation will be probed by direct imaging and the sign of the spin accumulation and influence of scattering determined to separate intrinsic and extrinsic effects. For the measurements a unique variable temperature high resolution SEMPA imaging system will be acquired and further developed including ultra-fast electrical contacts. Theoretical modelling using an atomistic Heisenberg approach will go beyond the conventional micromagnetic calculations that are limited to 0K. To understand thermal transport effects, temperature dependent simulations with adiabatic and non-adiabatic spin torque terms will accompany experiments. Realistic lattice structures and heterostructures will be modelled to simulate the influence of the pure spin currents on the magnetization using spatially varying interface torque terms, not previously possible.
Summary
MaSpic will create an autonomous team at the University of Konstanz to investigate the interaction between magnetization, spin - polarized and pure diffusive spin currents using novel instrumentation and innovative theoretical approaches. A thorough understanding of the fundamental charge and spin transport interaction mechanisms, key to use of the spin degree of freedom for Spintronics, will be developed. To understand the interplay between spin-polarized charge currents and magnetization configurations (adiabatic vs. non-adiabatic electron transport), the reciprocal effects of magnetization on the current (magnetoresistance) and of the current on magnetization (spin transfer torque) will be correlated for the same spin structures. Non-intrusive high resolution imaging at variable temperature will be used to probe the non-adiabaticity and help understand the hotly debated influence of thermal excitations on transport. Pure diffusive spin currents will be efficiently generated and used to manipulate magnetization with ultra-low power dissipation. The poorly understood spin current generation by the Spin Hall Effect and spin current propagation will be probed by direct imaging and the sign of the spin accumulation and influence of scattering determined to separate intrinsic and extrinsic effects. For the measurements a unique variable temperature high resolution SEMPA imaging system will be acquired and further developed including ultra-fast electrical contacts. Theoretical modelling using an atomistic Heisenberg approach will go beyond the conventional micromagnetic calculations that are limited to 0K. To understand thermal transport effects, temperature dependent simulations with adiabatic and non-adiabatic spin torque terms will accompany experiments. Realistic lattice structures and heterostructures will be modelled to simulate the influence of the pure spin currents on the magnetization using spatially varying interface torque terms, not previously possible.
Max ERC Funding
1 610 786 €
Duration
Start date: 2008-08-01, End date: 2014-04-30
Project acronym OPTNANO
Project Quantum optics in nanostructures
Researcher (PI) Stephanie Reich
Host Institution (HI) FREIE UNIVERSITAET BERLIN
Call Details Starting Grant (StG), PE3, ERC-2007-StG
Summary Nanomaterials are intriguing structures for quantum optics. Their color depends on their size and shape; they are very selective in the wavelengths they absorb and emit. Although nanostructures have been used to color windows and surfaces since the Middle Ages, we lack the understanding how size, shape, and microscopic structure control the optical properties of nanomaterials. In this project, we plan to develop a fundamental description of quantum optics in one-dimensional nanosystems. Core concepts will be quantum confinement and electron interactions when carriers are forced into a small space. The proposed work will focus on carbon nanotubes as a model nanosystem. The tubes show pronounced confinement effects; they emit and absorb light in the near infrared and visible. We will measure optical transitions, quantum cross sections, and electron interaction using luminescence, Raman scattering, and photoconductivity. The optical properties will be tailored by selecting specific tube types and changing the tube environment. A description of optical processes is incomplete without considering defects in real nanostructures. We will develop techniques to study and introduce imperfections. Their optical signatures and their effect on light emission will be determined on individual tubes. The experiments will be complemented by materials modeling. We will describe confinement effects and Coulomb interaction in semiempirical calculations of nanotube light absorption. The knowledge gained on carbon nanotubes will be applied to predict and study the optical properties of other one-dimensional systems. The goal is to obtain a robust and transferable model of quantum optics in nanostructures. This project will also advance characterization of nanomaterials by optical spectroscopy and applications of nanotubes as light detectors and emitters. We plan to develop tools for nanotube population analysis (tube type) and to test carbon tubes as wavelength-selective photodetectors
Summary
Nanomaterials are intriguing structures for quantum optics. Their color depends on their size and shape; they are very selective in the wavelengths they absorb and emit. Although nanostructures have been used to color windows and surfaces since the Middle Ages, we lack the understanding how size, shape, and microscopic structure control the optical properties of nanomaterials. In this project, we plan to develop a fundamental description of quantum optics in one-dimensional nanosystems. Core concepts will be quantum confinement and electron interactions when carriers are forced into a small space. The proposed work will focus on carbon nanotubes as a model nanosystem. The tubes show pronounced confinement effects; they emit and absorb light in the near infrared and visible. We will measure optical transitions, quantum cross sections, and electron interaction using luminescence, Raman scattering, and photoconductivity. The optical properties will be tailored by selecting specific tube types and changing the tube environment. A description of optical processes is incomplete without considering defects in real nanostructures. We will develop techniques to study and introduce imperfections. Their optical signatures and their effect on light emission will be determined on individual tubes. The experiments will be complemented by materials modeling. We will describe confinement effects and Coulomb interaction in semiempirical calculations of nanotube light absorption. The knowledge gained on carbon nanotubes will be applied to predict and study the optical properties of other one-dimensional systems. The goal is to obtain a robust and transferable model of quantum optics in nanostructures. This project will also advance characterization of nanomaterials by optical spectroscopy and applications of nanotubes as light detectors and emitters. We plan to develop tools for nanotube population analysis (tube type) and to test carbon tubes as wavelength-selective photodetectors
Max ERC Funding
1 097 820 €
Duration
Start date: 2008-08-01, End date: 2013-07-31
Project acronym SULIWA
Project Deeply Supercooled Liquid Water
Researcher (PI) Thomas Loerting
Host Institution (HI) UNIVERSITAET INNSBRUCK
Call Details Starting Grant (StG), PE3, ERC-2007-StG
Summary "Water is ubiquitous and so an understanding of water’s anomalous liquid state is crucial for such diverse fields as protein biochemistry, meteorology or astrophysics. A postulated first order phase transition between two distinct one-component liquids at low temperatures is believed to be the key to many riddles in contemporary science: a “fragile” liquid of high density and a “strong” liquid of low density. At higher temperatures the phase boundary might end in a speculative second critical point in supercooled water. Unfortunately it has not been possible so far to support/falsify these hypotheses with direct experiments because of fast crystallization of the liquid(s) in the relevant portion of the phase diagram, which is called ""no man's land"". Therefore, experiments to test the hypothesis were previously done in the non-crystalline, solid state (“amorphous water”) at temperatures well below the ""no man's land"". More than 20 years ago liquid-like relaxation was measured on heating glassy water at 1 bar to 136 - 150 K, i.e., to temperatures slightly below crystallization, which is still discussed controversially. Recently we managed to observe liquid-like properties on heating high density amorphous ice (HDA) under isobaric conditions at pressures up to 1 GPa above its glass-liquid transition at a temperature slightly below the ""no man's land"" without observing significant crystallization. These findings open the exciting possibility to characterize (e.g., by dilatometry, thermal analysis and dielectric spectroscopy) deeply supercooled liquid water both at ambient and high pressure conditions and to check if water indeed shows a first order liquid-liquid phase transition between two distinct liquids. This will unravel the question how many liquids and how many corresponding amorphous states there are in water, and if VHDA discovered by us in 2001 shows a polyamorphic transition to HDA, or if it is simply annealed HDA."
Summary
"Water is ubiquitous and so an understanding of water’s anomalous liquid state is crucial for such diverse fields as protein biochemistry, meteorology or astrophysics. A postulated first order phase transition between two distinct one-component liquids at low temperatures is believed to be the key to many riddles in contemporary science: a “fragile” liquid of high density and a “strong” liquid of low density. At higher temperatures the phase boundary might end in a speculative second critical point in supercooled water. Unfortunately it has not been possible so far to support/falsify these hypotheses with direct experiments because of fast crystallization of the liquid(s) in the relevant portion of the phase diagram, which is called ""no man's land"". Therefore, experiments to test the hypothesis were previously done in the non-crystalline, solid state (“amorphous water”) at temperatures well below the ""no man's land"". More than 20 years ago liquid-like relaxation was measured on heating glassy water at 1 bar to 136 - 150 K, i.e., to temperatures slightly below crystallization, which is still discussed controversially. Recently we managed to observe liquid-like properties on heating high density amorphous ice (HDA) under isobaric conditions at pressures up to 1 GPa above its glass-liquid transition at a temperature slightly below the ""no man's land"" without observing significant crystallization. These findings open the exciting possibility to characterize (e.g., by dilatometry, thermal analysis and dielectric spectroscopy) deeply supercooled liquid water both at ambient and high pressure conditions and to check if water indeed shows a first order liquid-liquid phase transition between two distinct liquids. This will unravel the question how many liquids and how many corresponding amorphous states there are in water, and if VHDA discovered by us in 2001 shows a polyamorphic transition to HDA, or if it is simply annealed HDA."
Max ERC Funding
1 389 238 €
Duration
Start date: 2008-08-01, End date: 2013-07-31
