51
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Bednarek S, Szafran B, Dudek RJ, Lis K. Induced quantum dots and wires: electron storage and delivery. PHYSICAL REVIEW LETTERS 2008; 100:126805. [PMID: 18517899 DOI: 10.1103/physrevlett.100.126805] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/24/2007] [Indexed: 05/26/2023]
Abstract
We show that quantum dots and quantum wires are formed underneath metal electrodes deposited on a planar semiconductor heterostructure containing a quantum well. The confinement is due to the self-focusing mechanism of an electron wave packet interacting with the charge induced on the metal surface. Induced quantum wires guide the transfer of electrons along metal paths and induced quantum dots store the electrons in specific locations of the nanostructure. Induced dots and wires can be useful for devices operating on the electron spin. An application for a spin readout device is proposed.
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Affiliation(s)
- S Bednarek
- Faculty of Physics and Applied Computer Science, AGH University of Science and Technology, al. Mickiewicza 30, 30-059 Kraków, Poland
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52
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Amasha S, Maclean K, Radu IP, Zumbühl DM, Kastner MA, Hanson MP, Gossard AC. Electrical control of spin relaxation in a quantum dot. PHYSICAL REVIEW LETTERS 2008; 100:046803. [PMID: 18352316 DOI: 10.1103/physrevlett.100.046803] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/13/2007] [Indexed: 05/26/2023]
Abstract
We demonstrate electrical control of the spin relaxation time T1 between Zeeman-split spin states of a single electron in a lateral quantum dot. We find that relaxation is mediated by the spin-orbit interaction, and by manipulating the orbital states of the dot using gate voltages we vary the relaxation rate W identical withT1(-1) by over an order of magnitude. The dependence of W on orbital confinement agrees with theoretical predictions, and from these data we extract the spin-orbit length. We also measure the dependence of W on the magnetic field and demonstrate that spin-orbit mediated coupling to phonons is the dominant relaxation mechanism down to 1 T, where T1 exceeds 1 s.
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Affiliation(s)
- S Amasha
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
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53
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Abstract
Semiconductor spintronicsSpintronics refers commonly to phenomena in which the spin of electrons in a solid state environment plays the determining role. In a more narrow sense spintronics is an emerging research field of electronics: spintronics devices are based on a spin control of electronics, or on an electrical and optical control of spin or magnetism. While metal spintronics has already found its niche in the computer industry—giant magnetoresistance systems are used as hard disk read heads—semiconductor spintronics is yet to demonstrate its full potential. This review presents selected themes of semiconductor spintronics, introducing important concepts in spin transport, spin injection, Silsbee-Johnson spin-charge coupling, and spin-dependent tunneling, as well as spin relaxation and spin dynamics. The most fundamental spin-dependent interaction in nonmagnetic semiconductors is spin-orbit coupling. Depending on the crystal symmetries of the material, as well as on the structural properties of semiconductor based heterostructures, the spin-orbit coupling takes on different functional forms, giving a nice playground of effective spin-orbit Hamiltonians. The effective Hamiltonians for the most relevant classes of materials and heterostructures are derived here from realistic electronic band structure descriptions. Most semiconductor device systems are still theoretical concepts, waiting for experimental demonstrations. A review of selected proposed, and a few demonstrated devices is presented, with detailed description of two important classes: magnetic resonant tunnel structures and bipolar magnetic diodes and transistors. In view of the importance of ferromagnetic semiconductor materials, a brief discussion of diluted magnetic semiconductors is included. In most cases the presentation is of tutorial style, introducing the essential theoretical formalism at an accessible level, with case-study-like illustrations of actual experimental results, as well as with brief reviews of relevant recent achievements in the field.
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54
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Pfund A, Shorubalko I, Ensslin K, Leturcq R. Suppression of spin relaxation in an InAs nanowire double quantum dot. PHYSICAL REVIEW LETTERS 2007; 99:036801. [PMID: 17678307 DOI: 10.1103/physrevlett.99.036801] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/03/2007] [Indexed: 05/16/2023]
Abstract
We investigate the triplet-singlet relaxation in a double quantum dot defined by top gates in an InAs nanowire. In the Pauli spin blockade regime, the leakage current can be mainly attributed to spin relaxation. While at weak and strong interdot coupling relaxation is dominated by two individual mechanisms, the relaxation is strongly reduced at intermediate coupling and finite magnetic field. In addition we observe a characteristic bistability of the spin-nonconserving current as a function of magnetic field. We propose a model where these features are explained by the polarization of nuclear spins enabled by the interplay between hyperfine and spin-orbit mediated relaxation.
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Affiliation(s)
- A Pfund
- Solid State Physics Laboratory, ETH Zürich, 8093 Zürich, Switzerland
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55
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Meunier T, Vink IT, van Beveren LHW, Tielrooij KJ, Hanson R, Koppens FHL, Tranitz HP, Wegscheider W, Kouwenhoven LP, Vandersypen LMK. Experimental signature of phonon-mediated spin relaxation in a two-electron quantum dot. PHYSICAL REVIEW LETTERS 2007; 98:126601. [PMID: 17501146 DOI: 10.1103/physrevlett.98.126601] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/19/2006] [Indexed: 05/15/2023]
Abstract
We observe an experimental signature of the role of phonons in spin relaxation between triplet and singlet states in a two-electron quantum dot. Using both the external magnetic field and the electrostatic confinement potential, we change the singlet-triplet energy splitting from 1.3 meV to zero and observe that the spin relaxation time depends nonmonotonously on the energy splitting. A simple theoretical model is derived to capture the underlying physical mechanism. The present experiment confirms that spin-flip energy is dissipated in the phonon bath.
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Affiliation(s)
- T Meunier
- Kavli Institute of Nanoscience, Delft University of Technology, P.O. Box 5046, 2600 GA Delft, The Netherlands
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56
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Hanson R, Burkard G. Universal set of quantum gates for double-dot spin qubits with fixed interdot coupling. PHYSICAL REVIEW LETTERS 2007; 98:050502. [PMID: 17358835 DOI: 10.1103/physrevlett.98.050502] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/18/2006] [Revised: 10/17/2006] [Indexed: 05/14/2023]
Abstract
We propose a set of universal gate operations for the singlet-triplet qubit realized by two-electron spins in a double quantum dot, in the presence of a fixed inhomogeneous magnetic field. All gate operations are achieved by switching the potential offset between the two dots with an electrical bias, and do not require time-dependent control of the tunnel coupling between the dots. We analyze the two-electron dynamics and calculate the effective qubit rotation angle as a function of the applied electric bias. We present explicit gate sequences for single-qubit rotations about two orthogonal axes, and a CNOT gate sequence, completing the universal gate set.
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Affiliation(s)
- Ronald Hanson
- Center for Spintronics and Quantum Computation, University of California, Santa Barbara, California 93106, USA
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57
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Kataoka M, Schneble RJ, Thorn AL, Barnes CHW, Ford CJB, Anderson D, Jones GAC, Farrer I, Ritchie DA, Pepper M. Single-electron population and depopulation of an isolated quantum dot using a surface-acoustic-wave pulse. PHYSICAL REVIEW LETTERS 2007; 98:046801. [PMID: 17358796 DOI: 10.1103/physrevlett.98.046801] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/30/2006] [Indexed: 05/14/2023]
Abstract
We use a pulse of surface acoustic waves (SAWs) to control the electron population and depopulation of a quantum dot. The barriers between the dot and reservoirs are set high to isolate the dot. Within a time scale of approximately 100 s the dot can be set to a nonequilibrium charge state, where an empty (occupied) level stays below (above) the Fermi energy. A pulse containing a fixed number of SAW periods is sent through the dot, controllably changing the potential, and hence the tunneling probability, to add (remove) an electron to (from) the dot.
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Affiliation(s)
- M Kataoka
- Cavendish Laboratory, J.J. Thompson Avenue, Cambridge CB3 0HE, United Kingdom
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58
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Sigrist M, Ihn T, Ensslin K, Reinwald M, Wegscheider W. Coherent probing of excited quantum dot states in an interferometer. PHYSICAL REVIEW LETTERS 2007; 98:036805. [PMID: 17358712 DOI: 10.1103/physrevlett.98.036805] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/30/2006] [Indexed: 05/14/2023]
Abstract
Measurements of elastic and inelastic cotunneling currents are presented on a two-terminal Aharonov-Bohm interferometer with a Coulomb-blockaded quantum dot embedded in each arm. Coherent current contributions, even in a magnetic field, are found in the nonlinear regime of inelastic cotunneling at a finite-bias voltage. The phase of the Aharonov-Bohm oscillations in the current exhibits phase jumps of pi at the onsets of inelastic processes. We suggest that additional coherent elastic processes occur via the excited state. Our measurement technique allows the detection of such processes on a background of other inelastic current contributions and contains qualitative information about the ratio of transport and inelastic relaxation rates.
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Affiliation(s)
- Martin Sigrist
- Solid State Physics Laboratory, ETH Zürich, 8093 Zürich, Switzerland
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59
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Simon P, Feinberg D. Electronic spin precession and interferometry from spin-orbital entanglement in a double quantum dot. PHYSICAL REVIEW LETTERS 2006; 97:247207. [PMID: 17280318 DOI: 10.1103/physrevlett.97.247207] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/17/2006] [Indexed: 05/13/2023]
Abstract
A double quantum dot inserted in parallel between two metallic leads can entangle the electron spin with the orbital (dot index) degree of freedom. An Aharonov-Bohm orbital phase can be transferred to the spinor wave function, providing a geometrical control of the spin precession around a fixed magnetic field. A fully coherent behavior occurs in a mixed orbital-spin Kondo regime. Evidence for the spin precession can be obtained, either using spin-polarized metallic leads or by placing the double dot in one branch of a metallic loop.
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Affiliation(s)
- P Simon
- Laboratoire de Physique et Modélisation des Milieux Condensés, CNRS and Université Joseph Fourier, BP 166, 38042 Grenoble, France
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60
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Koppens FHL, Buizert C, Tielrooij KJ, Vink IT, Nowack KC, Meunier T, Kouwenhoven LP, Vandersypen LMK. Driven coherent oscillations of a single electron spin in a quantum dot. Nature 2006; 442:766-71. [PMID: 16915280 DOI: 10.1038/nature05065] [Citation(s) in RCA: 316] [Impact Index Per Article: 17.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2006] [Accepted: 07/06/2006] [Indexed: 11/09/2022]
Abstract
The ability to control the quantum state of a single electron spin in a quantum dot is at the heart of recent developments towards a scalable spin-based quantum computer. In combination with the recently demonstrated controlled exchange gate between two neighbouring spins, driven coherent single spin rotations would permit universal quantum operations. Here, we report the experimental realization of single electron spin rotations in a double quantum dot. First, we apply a continuous-wave oscillating magnetic field, generated on-chip, and observe electron spin resonance in spin-dependent transport measurements through the two dots. Next, we coherently control the quantum state of the electron spin by applying short bursts of the oscillating magnetic field and observe about eight oscillations of the spin state (so-called Rabi oscillations) during a microsecond burst. These results demonstrate the feasibility of operating single-electron spins in a quantum dot as quantum bits.
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Affiliation(s)
- F H L Koppens
- Kavli Institute of NanoScience, Delft University of Technology, PO Box 5046, 2600 GA, Delft, The Netherlands.
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61
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Laird EA, Petta JR, Johnson AC, Marcus CM, Yacoby A, Hanson MP, Gossard AC. Effect of exchange interaction on spin dephasing in a double quantum dot. PHYSICAL REVIEW LETTERS 2006; 97:056801. [PMID: 17026127 DOI: 10.1103/physrevlett.97.056801] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/03/2005] [Indexed: 05/12/2023]
Abstract
We measure singlet-triplet dephasing in a two-electron double quantum dot in the presence of an exchange interaction which can be electrically tuned from much smaller to much larger than the hyperfine energy. Saturation of dephasing and damped oscillations of the spin correlator as a function of time are observed when the two interaction strengths are comparable. Both features of the data are compared with predictions from a quasistatic model of the hyperfine field.
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Affiliation(s)
- E A Laird
- Department of Physics, Harvard University, Cambridge, MA 02138, USA
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62
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63
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Sapmaz S, Meyer C, Beliczynski P, Jarillo-Herrero P, Kouwenhoven LP. Excited state spectroscopy in carbon nanotube double quantum dots. NANO LETTERS 2006; 6:1350-5. [PMID: 16834409 DOI: 10.1021/nl052498e] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
We report on low-temperature measurements in a fully tunable carbon nanotube double quantum dot. A new fabrication technique has been used for the top-gates in order to avoid covering the whole nanotube with an oxide layer as in previous experiments. The top-gates allow us to form single dots and control the coupling between them, and we observe 4-fold shell filling. We perform inelastic transport spectroscopy via the excited states in the double quantum dot, a necessary step toward the implementation of new microwave-based experiments.
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Affiliation(s)
- Sami Sapmaz
- Kavli Institute of Nanoscience, Delft University of Technology, The Netherlands.
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64
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de Visser RL, Blaauboer M. Deterministic teleportation of electrons in a quantum dot nanostructure. PHYSICAL REVIEW LETTERS 2006; 96:246801. [PMID: 16907265 DOI: 10.1103/physrevlett.96.246801] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/10/2006] [Indexed: 05/11/2023]
Abstract
We present a proposal for deterministic quantum teleportation of electrons in a semiconductor nanostructure consisting of a single and a double quantum dot. The central issue addressed in this Letter is how to design and implement the most efficient--in terms of the required number of single and two-qubit operations--deterministic teleportation protocol for this system. Using a group-theoretical analysis, we show that deterministic teleportation requires a minimum of three single-qubit rotations and two entangling (square root SWAP) operations. These can be implemented for spin qubits in quantum dots using electron-spin resonance (for single-spin rotations) and exchange interaction (for square root SWAP operations).
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Affiliation(s)
- R L de Visser
- Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands
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65
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Atatüre M, Dreiser J, Badolato A, Högele A, Karrai K, Imamoglu A. Quantum-Dot Spin-State Preparation with Near-Unity Fidelity. Science 2006; 312:551-3. [PMID: 16601152 DOI: 10.1126/science.1126074] [Citation(s) in RCA: 114] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
We have demonstrated laser cooling of a single electron spin trapped in a semiconductor quantum dot. Optical coupling of electronic spin states was achieved using resonant excitation of the charged quantum dot (trion) transitions along with the heavy-light hole mixing, which leads to weak yet finite rates for spin-flip Raman scattering. With this mechanism, the electron spin can be cooled from 4.2 to 0.020 kelvin, as confirmed by the strength of the induced Pauli blockade of the trion absorption. Within the framework of quantum information processing, this corresponds to a spin-state preparation with a fidelity exceeding 99.8%.
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Affiliation(s)
- Mete Atatüre
- Institute of Quantum Electronics, ETH Zurich, CH-8093 Zurich, Switzerland.
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66
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Hu X, Das Sarma S. Charge-fluctuation-induced dephasing of exchange-coupled spin qubits. PHYSICAL REVIEW LETTERS 2006; 96:100501. [PMID: 16605716 DOI: 10.1103/physrevlett.96.100501] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/26/2005] [Revised: 09/30/2005] [Indexed: 05/08/2023]
Abstract
Exchange-coupled spin qubits in semiconductor nanostructures are shown to be vulnerable to dephasing caused by charge noise invariably present in the semiconductor environment. This decoherence of exchange gate by environmental charge fluctuations arises from the fundamental Coulombic nature of the Heisenberg coupling and presents a serious challenge to the scalability of the widely studied exchange gate solid state spin quantum computer architectures. We estimate dephasing times for coupled spin qubits in a wide range (from 1 ns up to >1 micros) depending on the exchange coupling strength and its sensitivity to charge fluctuations.
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Affiliation(s)
- Xuedong Hu
- Department of Physics, University at Buffalo, The State University of New York, 239 Fronczak Hall, Buffalo, New York 14260-1500, USA
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67
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Wu Y, Li X, Duan LM, Steel DG, Gammon D. Density matrix tomography through sequential coherent optical rotations of an exciton qubit in a single quantum dot. PHYSICAL REVIEW LETTERS 2006; 96:087402. [PMID: 16606223 DOI: 10.1103/physrevlett.96.087402] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/15/2005] [Indexed: 05/08/2023]
Abstract
We demonstrate single qubit density matrix tomography in a single semiconductor quantum dot system through consecutive phase sensitive rotations of the qubit via ultrafast coherent optical excitations. The result is important for quantifying gate operations in quantum information processing in the quantum dot systems as well as demonstrating consecutive arbitrary qubit rotations.
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Affiliation(s)
- Yanwen Wu
- The H.M. Randall Laboratory of Physics, The University of Michigan, Ann Arbor, Michigan 48109, USA
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68
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Paladino E, Sassetti M, Falci G, Weiss U. Pure dephasing due to damped bistable quantum impurities. Chem Phys 2006. [DOI: 10.1016/j.chemphys.2005.08.065] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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69
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Tokura Y, van der Wiel WG, Obata T, Tarucha S. Coherent single electron spin control in a slanting Zeeman field. PHYSICAL REVIEW LETTERS 2006; 96:047202. [PMID: 16486882 DOI: 10.1103/physrevlett.96.047202] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/14/2005] [Indexed: 05/06/2023]
Abstract
We consider a single electron in a 1D quantum dot with a static slanting Zeeman field. By combining the spin and orbital degrees of freedom of the electron, an effective quantum two-level (qubit) system is defined. This pseudospin can be coherently manipulated by the voltage applied to the gate electrodes, without the need for an external time-dependent magnetic field or spin-orbit coupling. Single-qubit rotations and the controlled-NOT operation can be realized. We estimated the relaxation (T1) and coherence (T2) times and the (tunable) quality factor. This scheme implies important experimental advantages for single electron spin control.
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Affiliation(s)
- Yasuhiro Tokura
- NTT Basic Research Laboratories, NTT Corporation, Atsugi-shi, Kanagawa 243-0198, Japan
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70
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Sasaki S, Fujisawa T, Hayashi T, Hirayama Y. Electrical pump-and-probe study of spin singlet-triplet relaxation in a quantum dot. PHYSICAL REVIEW LETTERS 2005; 95:056803. [PMID: 16090902 DOI: 10.1103/physrevlett.95.056803] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/09/2005] [Indexed: 05/03/2023]
Abstract
Spin relaxation from a triplet excited state to a singlet ground state in a semiconductor quantum dot is studied by employing an electrical pump-and-probe method. Spin relaxation occurs via co-tunneling when the tunneling rate is relatively large, confirmed by a characteristic square dependence of the relaxation rate on the tunneling rate. When co-tunneling is suppressed by reducing the tunneling rate, the intrinsic spin relaxation is dominated by spin-orbit interaction. We discuss a selection rule of the spin-orbit interaction based on the observed double-exponential decay of the triplet state.
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Affiliation(s)
- S Sasaki
- NTT Basic Research Laboratories, NTT Corporation, Atsugi-shi, Kanagawa 243-0198, Japan.
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