Lorentz Center - Single dopant control from 29 Mar 2010 through 1 Apr 2010
  Current Workshop  |   Overview   Back  |   Home   |   Search   |     

    Single dopant control
    from 29 Mar 2010 through 1 Apr 2010

 
Optical and Electronic Properties of Quantum Dots with Magnetic Impurities

ABSTRACTS

 

Ramon Aguado

“Electronic transport in quantum dots doped with a single Mn-ion”

 

In this talk I will review our work on electrical transport in II–VI semiconductor quantum dots doped with a single-Mn ion [1]. In the few hole/electron regime, these quantum dots behave like a nanomagnet with magnetic properties, such as total spin and magnetic anisotropy, that can be controlled electrically by varying the number of carriers and their orbital nature. Conversely, the electrical properties of these Mn-doped quantum dots depend on the quantum state of the Mn spin, giving rise to spin- dependent charging energies and hysteresis in the Coulomb blockade oscillations of the linear conductance [2]. While dc transport entails considerable information, a complete understanding requires to go beyond and study shot noise, which I will discuss in the second part of the talk. Our results show that hole-Mn exchange anisotropy leads to super-Poissonionan shot noise due to lack of relaxation of the Mn spin. Interestingly, a novel effect at finite frequencies, similar to the Dicke effect in Quantum Optics, allows to separately measure the hole and Mn spin relaxation times [3].

 

[1] "Magnetism and transport in DMS quantum dots", J. Fernández-Rossier and R. Aguado, chapter submitted to the book “Spin Transport and Magnetism in Electronic Systems" Editors: Evgeny Tsymbal and Igor Žutić, Taylor&Francis.

[2] "Single-Electron Transport in Electrically Tunable Nanomagnets", J. Fernández-Rossier and R. Aguado, Physical Review Letters, 98, 106805 (2007).

[3] "Shot noise spectrum of artificial Single Molecule Magnets: measuring spin-relaxation times via the Dicke effect", L. D. Contreras-Pulido and R. Aguado, condmat/09071649.

 

 

---

 

David Awschalom

“Gigahertz coherent control and nanoscale placement of single spins in diamond”

 

Fast quantum control is critical to quantum information processing due to the practical need for fault tolerance.  Resonant spin manipulation is typically performed under the rotating wave approximation (RWA) which assumes that the oscillating driving field can be approximated by a rotating field.  We present high-speed microwave experiments probing the spin dynamics of single nitrogen vacancy (NV) centers in diamond driven by a large amplitude oscillating field where this approximation is no longer valid [1].  Using lithographic coplanar waveguides on diamond we generate a large oscillating magnetic field that induces spin rotations on the same timescale as Larmor precession.  Surprisingly, coherent spin flips still occur under these conditions but on sub-nanosecond timescales - faster than

expected from the RWA. In addition to manipulating the ground state spin, we also apply these techniques to study the spin coherence of single NV centers in their orbital excited state (ES) [2].  We demonstrate ES Rabi oscillations and use multi-pulse resonant control to differentiate between

phonon-induced dephasing, orbital relaxation, and coherent electron-nuclear interactions.  Finally, we present ion implantation techniques demonstrating the ability to spatially position individual NV centers in diamond for a variety of experiments.

 

[1] G. D. Fuchs, V. V. Dobrovitski, D. M. Toyli, F. J. Heremans, D. D.

Awschalom, Science 326, 1520 (2009).

[2] G. D. Fuchs, V. V. Dobrovitski, D. M. Toyli, F. J. Heremans, C. D. Weis,

T. Schenkel, and D.D. Awschalom, submitted (2010).

 

---

 

Lucien Besombes

“Optical detection and dynamics of an individual Mn spin in a quantum dot”

The decrease of the structure size in semiconductor electronic devices and magnetic information storage devices has dramatically reduced the number of atoms necessary to process and store bits of information. Information storage on a single magnetic atom would be an ultimate limit. Diluted magnetic semiconductors systems combining high quality semiconductor structures and the magnetic properties of Mn atoms are good candidates for these ultimate devices. With the development of quantum dots (QDs) doped with Mn atoms, the optical probing of a single atomic spin in a solid state environment became possible using optical micro-spectroscopy techniques: The photon emitted or absorbed by a II-VI semiconductor Mn-doped QD is directly related to the spin state of the Mn atom localized in the dot. This is due to the exchange interaction between a confined electron-hole (e-h) pair and the Mn atom: the e-h pair acts as an effective field along the QDs’ growth axis that lifts up the degeneracy between the six Mn spin states. Depending on the Mn spin projection, the recombination of an injected e-h pair emits a photon with a given energy and polarization. 

In this talk, we will show how the photons emitted by an individual CdTe/ZnTe QD containing a single Mn atom (S=5/2) can be used to probe the dynamics of the Mn spin. We will also discuss how the resonant optical injection of spin polarized carriers can be a tool to control this localized spin. After a description of the spin structure of the system formed by the interaction between a controlled number of confined carriers and a localized Mn spin, we will present photon correlation and time resolved optical pumping experiments on individual QDs allowing probing the dynamics of these few interacting spins.

 

 

---

 

 

Serge Biesemans

"Device Materials and Architecture for the 22nm and beyond"

 

This presentation will provide an overview of recent highlights of scaling Silicon CMOS technology into 32nm node. While the majority of the focus will be on logic processes, also scaling roadmaps in Flash and DRAM will be briefly reviewed. Conventional scaling stopped at the 0.13um node. Strain engineering and noval materials development has fueled Moore's law in 90/65/45/32nm. We will look further into 22/16nm nodes where FinFETs and again new materials may appear. Looking further into the future, new developments like 3D integration and hybrid technologies integration (CMOS + MEMS) are becoming apparent. In the introduction we'll cover the basics of the MOS device operation.

 

 

---

 

 

Martin S. Brandt

“Electrically detected magnetic resonance of few-dopant devices”

 

The combination of magnetic resonance experiments with detection via electronic transport measurements has been used to study defects and dopants in a variety of different devices. The talk will review the state-of-the-art of EDMR allowing the detection of less than 100 dopants in different types of Si nanostructures. Ongoing experiments on few-donor devices in collaboration with the group of Michelle Simmons and the current development of an EDMR microscope will be presented. If time permits, a brief summary of recent progress in the electron paramagnetic resonance of B acceptors will also be given.       

Walter Schottky Institut, Technische Universität München

 

 

---

 

 

María Jose Calderon

“Donors in Si near an interface”

 

Isolated shallow donors in Si constitute the building block for proposed quantum computer architectures [1]. Proposed one and two-qubit logic gates involve manipulating individual electrons or

electron pairs. Electrons may be bound to donors, drawn away towards the interface of Si with a barrier material, or even in a donor-interface superposition of states. A shallow donor, as P or As

in Si, can bind one electron in the neutral state (D0) or two electrons in the negatively charged state (D-). The energies involved in the formation of a negatively charged donor result, within a single

valley effective mass approximation in bulk Si, from rescaling the hydrogenic rydberg to take account of the dielectric constant and effective mass in the semiconductor. In semiconductor devices,

isolated donors are eventually located close to insulating layers which separate them from metallic gates. In this event, the donor energy spectrum can be significantly affected with respect to the

bulk. We analyze, within the effective mass approximation, the effect of nearby insulating and metallic layers on the charging and binding energies of negatively charge donors in Si. We discuss our results in connection to current experiments on the transport properties through

single dopants [2].

 

[1] B. Kane, Nature 393, 133 (1998), and other proposals that followed

this pioneer work.

[2] G. Lansbergen et al, Nature Physics 4, 656 (2008)

 

 

---

 

 

Michael E. Flatté

“Optical and electrical control of single dopants: towards single-dopant devices”

 

Recent advances in quantitatively understanding the electronic and optical properties of single dopants in a variety of local environments (strain, quantum confinement, electric fields, and optical fields) suggest that single dopants may play a central role in new categories of devices. Examples of this emerging field of SOLitary dopant OptoelecTRONICS, or "solotronics" will be provided. These include proposals for all-electrical manipulation of a single Mn spin embedded in GaAs, g-tensor modulation resonance of single donors, the generation of entanglement between individual photons and individual dopant spins, and the use of such entanglement for teleportation. Some key open questions, with an emphasis on theoretical issues, will also be outlined.

 

 

---

 

 

Alexander O. Govorov

“Optical and Electronic Properties of Quantum Dots with Magnetic Impurities”

 

This talk will discuss some of the recent results related to the semiconductor quantum dots doped with magnetic impurities. A single Mn impurity incorporated in a quantum dot strongly modifies the spectrum of optical emission from a quantum-dot system [1-4]. Importantly, a character of Mn-carrier interaction is very different for II-VI and III-V quantum dots (QDs) [1-3]. In the II-VI QDs, a Mn impurity influences mostly the spin-structure of an exciton or exciton [1,2]. In the III-V dots, a spatial localization of a hole by a Mn impurity is very important, and ultimately yields a totally different spin structure [3,4]. Magnetic and spin-orbital interactions in QDs give rise to the coupling between the kinetic motion and spins of electrons. This coupling allows us to manipulate spins of excitons in magnetic and non-magnetic QDs using optical means [1,2] or simply by voltage via the Kondo-type interaction [5,6].

A Mn-doped QD with a variable number of mobile carriers represents an artificial magnetic atom [7]. Due to the Mn-carrier interaction, the order of filling of electronic shells in a magnetic QD can be very different to the case of the real atoms. The “periodic” table of the artificial magnetic atoms can be realized in voltage-tunable transistor structures. For the electron numbers corresponding to the regime of Hund’s rule, the Mn-carrier coupling is especially strong and the magnetic-polaron states are very robust. QD molecules also differ greatly from the real molecules. QD molecules with magnetic impurities may demonstrate the effect of spontaneous breaking of symmetry and corresponding phase transitions [6]. Single QDs and QD molecules can be viewed as voltage-tunable nanoscale memory cells, in which information is stored in the form of robust magnetic-polaron states.

A.O. Govorov: Department of Physics and Astronomy, Ohio University, Athens, Ohio 45701, USA; Govorov@ohiou.edu

 

[1] L. Besombes, Y. Leger, L. Maingault, D. Ferrand, H. Mariette, J. Cibert, Phys. Rev. Lett. 93 (2004) 207403.

[2] A.O. Govorov, A.V. Kalameitsev, Phys. Rev. B 71 (2005) 035338. 

[3] A.O. Govorov, Phys. Rev. B 70 (2004) 035321.

[4] A. Kudelski, A. Lemaitre, A. Miard, P. Voisin, T.C.M. Graham, R.J. Warburton, O. Krebs, Phys. Rev. Lett. 99 (2007) 247209.

[5] A.O. Govorov, K. Karrai, R.J Warburton, R. J, Phys. Rev. B 67, 241307(R) (2003); N.A.J.M. Kleemans, J. van Bree, A. O. Govorov, G. J. Hamhuis, R. Naotzel, A. Yu. Silov and P.M. Koenraad, submitted.

[6] J.M. Smith, P.A. Dalgarno, R.J. Warburton, K. Karrai, B.D. Gerardot, P.M. Petroff, Phys. Rev. Lett. 94 (2005) 197402.

[7] A.O. Govorov, Phys. Rev. B 72 (2005) 075359; W. Zhang, T. Dong, A.O. Govorov, Phys. Rev. B 76 (2007) 075319. 

 

 

---

 

 

Ronald Hanson

“Quantum control of single spins and single photons in diamond”

 

Quantum control of light and matter is an outstanding challenge in modern science. Diamond-based materials have recently emerged as a unique platform for quantum science and engineering [1]. Spins of single Nitrogen-Vacancy (NV) color centers in diamond can be imaged, initialized and read out optically, and show long coherence times even at room temperature. Full control over the spin state and the optical transition may enable exciting applications such as long-distance quantum teleportation and quantum information processing. Moreover, the tunable interactions of the NV center with its environment  also make this system an excellent test bed for fundamental studies on dynamical decoupling, spin-bath interactions [2], and light-matter interactions in engineered nanostructures [3]. For all these applications, high-fidelity control over the optical transition and the spin state of single NV centers is required. In this talk, I will give an overview of our recent work on controlling individual spins and photons using NV centers.

Ronald Hanson, Kavli Institute of Nanoscience, Delft University of Technology, PO Box 5046, 2600 GA Delft, The Netherlands

 

[1]        R. Hanson and D.D. Awschalom, Nature 453, 1043 (2008).

[2]        R. Hanson et al., Science 320, 352 (2008).

[3]        T. van der Sar et al., Appl. Phys. Lett. 94, 173104 (2009).

 

 

---

 

 

Cyrus F. Hirjibehedin

“The impact of the local environment on the Kondo screening of a high-spin atom”

 

Kondo screening is a many-body phenomenon arising from the interaction between a localized magnetic moment and the conduction electrons in a metal.  Spin 1/2 Kondo systems have been investigated extensively in theory and experiments.  However the magnetic atoms that give rise to the Kondo effect in metals often have a larger spin, which makes the properties of the system more complex.  Using a low-temperature scanning tunneling microscope, we explore the Kondo effect of individual high-spin magnetic atoms on surfaces.  Using a combination of elastic and inelastic tunneling spectroscopy, we determine the spin of the atom and explore its impact on the Kondo resonance.  We demonstrate that the local magnetic anisotropy plays a decisive role in the physics of Kondo screening.  In addition, we can tune the Kondo resonance through other parameters, such as coupling to a neighboring unscreened spin and a magnetic field.

 

 

---

 

 

Lloyd Hollenberg

“Mitigation and exploitation of decoherence in silicon and diamond quantum devices”

 

A large part, if not most, of the function and design of a quantum computer is really about the mitigation of the effects of decoherence. The geometric arrangement of qubits, whatever the platform, feeds into the quantum error correction protocol and controls the fault-tolerant error threshold and ultimately the total number of qubits and complexity of the quantum computer at the logical quantum algorithm level. In this talk the situation for silicon donor qubits will be covered, in terms of taking advantage of the evident material properties whilst addressing the many constraints of large scale quantum computer requirements. In an opposite technology direction to quantum computing, the deliberate exposure of a qubit to decoherence may lead to new sensing capabilities which take advantage of the inherent material properties of diamond (e.g. room temperature coherence of the NV system).

 

 

---

 

 

Olivier Krebs

“Magneto-optical properties of singly Mn-doped InAs/GaAs quantum dots”

 

Self-assembled  quantum dots (QDs) doped by a single magnetic ion offers the unique possibility to investigate the sp-d exchange at the microscopy level. In this lecture I will  review our recent results on the optical spectroscopy and theoretical modeling of the spin-related properties in single InAs/GaAs quantum dots (QD) doped by a single Mn atom. In this system the Mn species is a magnetic  impurity of acceptor type. As it  remains in a neutral state at low  temperature, its total spin can be well  described by an effective J=1 spin. This magnetic complex exhibits a strong exchange anisotropy due to  its position inside the QD and to the inhomogeneous strain field typical for self-assembled quantum dots. The very specific spectral signatures of excitons, charged excitons, and biexcitons observed in a charge-tuneable structure and  measured as a function of a magnetic field, reveal many features of the sp-d exchange with the Mn 5/2 spin at the microscopic level. A dominant effect is the magnetic anisotropy induced by the heavy character of holes in  self-assembled quantum dots which is responsible for completely unusual optical selection rules for the QD interband transitions in a transverse magnetic field. These results will be discussed on the basis of a phenomelogical spin Hamiltonian which provides a remarkable agreement for a very large variety of Mn-QD coupling and strain-induced anisotropy.

Laboratoire de Photonique et de Nanostructures, CNRS,  Route de Nozay, 91460 Marcoussis, France

 

 

---

 

 

Mikhail Lukin

“Quantum optical interface for solid-state spin qubits

 

 

We will discuss our efforts to develop quantum  interface between optical photons and long-lived spin memory in solid state. Specifically, we will describe our recent experiments demonstrating  quantum entanglement between single photons and spin qubits associated with Nitrogen Vacancy color centers in diamond.  In addition, we will discuss our recent progress towards implementation of deterministic, cavity QED-based quantum interface for such a system. Finally, new applications of these techniques will be  discussed.

E.Togan, Y.Chu, J.Maze, L.Jiang, A.S.Zibrov and M.D.Lukin

Physics Department, Harvard University

 

 

---

 

 

Andrea Morello

“Single-shot readout of an electron spin in silicon”

 

The electron spin of a donor in silicon is an excellent candidate for a solid-state qubit. It is known to have very long coherence and relaxation times in bulk, and several architectures have been proposed to integrate donor spin qubits with classical silicon microelectronics. Here we show the first experimental proof of single-shot readout of an electron spin in silicon. This breakthrough has been obtained with a device consisting of implanted phosphorus donors, tunnel-coupled to a silicon Single-Electron Transistor (Si-SET), where the SET island is used as a reservoir for spin-to-charge conversion. The charge transfer signals are exceptionally large, and allow time-resolved measurements of spin-dependent tunneling on a ~10 microseconds scale, with a readout fidelity better than 90%. By measuring the occurrence of excited spin states as a function of wait time, we find spin lifetimes up to ~1 s at B=1.75 T, and a magnetic-field dependence consistent with that of phosphorus donors in silicon. Further experiments are underway to integrate this readout method with coherent spin control.

 

---

 

Yukinori Ono

“Single-Dopant Effects in Silicon Nano Transistors”

 

Highly scaled MOSFETs suffer serious problems from the fluctuation of the dopant-atom number but in turn could offer a new concept of an atomic-scale device whose operation is regulated by means of just a single dopant atom. The technology for precisely placing individual atoms is rapidly developing but still premature. Thus, at this early stage of the research, it is crucially important to establish a technology for identifying the position of individual dopant atoms randomly scattered in a transistor. Here, we report our recent work on this matter and explain how individual dopant atoms are identified and how they make an impact on transistor characteristics.

Yukinori Ono, Mohammed A. H. Khalafalla, Katsuhiko Nishiguchi, Akira Fujirawa

NTT Basic Research Laboratories, 3-1 Morinosato Wakamiya, Atsugi, Kanagawa, 243-0198 Japan

email: ono@nttbrl.jp

 

---

 

 

Marc Sanquer

“Detection of single donors effects in ultra-scaled CMOS devices”

 

Variability of threshold voltage is now widely recognized as one of the most critical challenges for the future CMOS technology nodes. In Extremely Thin SOI  transistors (ETSOI) the random fluctuations due to channel doping are suppressed. Still ETSOI devices are sensitive to dopant induced dispersion arising from extensions.  We are able to identify the effect of a single or a few shallow donors coming from extension and demonstrate that these dopants strongly affect  the room temperature transfer characteristics of ultra-scaled NMOSFETs [1].

Low temperature measurements are further used to spatially locate the dopants  responsible for the alteration of the room temperature characteristics.

A large ionization energy is found for donors close to the buried oxide interface, as the result of the dielectric confinement effect [2].

In these studies the drain-source current is via tunneling directly through electronic orbitals associated to a single donor. On the other hand the ionization state (in real time), spin and spatial location of a single donor  can be monitored usinga  nearby single electron transistor used as an electrometer [3].

This permits to sense isolated donors without the strong perturbation by the passing current.

More generally ionization of donors (or offset charges) can strongly affect the transport spectroscopy and the  stability diagrams of SETs [4-5].

*This research has received funding from the EC's

FP7 (2007/2013) under the Grant Agreement Nr: 214989.

Marc Sanquer, CEA-Grenoble INAC

 

1.    M. Pierre , R. Wacquez, X. Jehl, and M. Sanquer,  Vinet and O. Cueto

"Single donor ionization energies in a nanoscale CMOS channel"

Nature Nanotechnology 5, 133 - 137 (2010)

2.    M. Diarra et al., Phys.Rev. B, 75, 045301 (2007).

3.    M. Pierre, M. Hofheinz, X. Jehl, M. Sanquer, G. Molas, M. Vinet, S. Deleonibus

"Background charges and quantum effects in quantum dots transport spectroscopy"

       European Physical Journal B 70, 475 (2009)

4.    M. Hofheinz, X. Jehl, and M. Sanquer G. Molas, M. Vinet, and S. Deleonibus

"Individual charge traps in silicon nanowires:

Measurements of location, spin and occupation number by Coulomb blockade spectroscopy"

European Physical Journal B54, 299-307, (2006).

5.    Hubert C. George,  Mathieu Pierre, Xavier Jehl, Alexei O. Orlov, Marc Sanquer, and Gregory L. Snider 

"Application of negative differential conductance in Al/AlOx single-electron transistors for background charge characterization"

Applied Physics Letters 96, 042114 (2010)

 

---

 

 

Thomas Schenkel

"Ion implantation for spin qubit integration in silicon and diamond - status and prospects"

 

Spins of donors in silicon and of color centers in diamond are promising qubit candidates.  Ion implantation is an established method for controlled doping of materials.  Integration of ion beams with scanning probes for imaging and alignment and the development of single ion detection methods can enable the formation of single qubit devices.  Challenges for reliable single atom placement by ion implantation will be discussed together with progress towards single donor spin readout in silicon and steps towards device integration of color centers in diamond.

 

 

---

 

Michelle Y. Simmons

“Towards Atomically Precise Silicon Devices in all Three Dimensions”

 

Over the past five years we have developed a radical new strategy for the fabrication of atomic-scale devices in silicon [1-4]. Using this process we have recently fabricated conducting nanoscale wires [5] with widths down to ~2nm, tunnel junctions [6], arrays of quantum dots in silicon [7] and in plane gated single electron transistors [8]. We will present an overview of the technology and of the unique devices that have been made [9].

In particular the talk will focus on recent low temperature transport measurements of a few-electron P donor based quantum dot in silicon which shows a surprisingly dense spectrum of excited states with an average energy spacing of 100μV. The energy spacing of these features is much too low to be accounted for by the nm-scale lateral confinement of either the dot or the leads. Instead we can explain these resonant features with lifting of valley degeneracy of the dot orbital states and present effective-mass calculations for this strongly confined Si:P system which are in good agreement with experimental findings. We discuss the role of valley splitting in P-donor based silicon dots and present our latest results towards STM-patterned single donor devices wherein the charging energy and the excited state spectrum are consistent with charge transport through the orbital states of a single P-donor.

Finally we will highlight some of the opportunities ahead for novel single atom device architectures and some of the challenges to achieving truly atomically precise devices in all three spatial dimensions [10].

Centre for Quantum Computer Technology, School of Physics, University of New South Wales,

Sydney, NSW 2052, Australia

 

 

---

 

 

Jörg Wrachtrup

“Diamond defects: Positioning, Control and Physics”

 

Photoactive defects in diamond have generated significant interest over the past couple of years. This is largely due to their facile generation, convenient photophysics and outstanding spin properties. As a result, application in the realm of quantum spintronics, metrology and biophysics have been published. The talk will address the current state-of-the-art in generating diamond defect clusters with high spatial control and efficiency. The spin physics of paramagnetic diamond defects as well as recent advances in generating spin nanostructures will be discussed.

Jörg Wrachtrup, F. Jelezko, P.Neumann, G. Balsubramanian, F. Reinhard, H. Rathgen

University Stuttgart, Institute of Physics, Stuttgart, Germany

 

 

 

 



   [Back]