301
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Dzhioev RI, Korenev VL. Stabilization of the electron-nuclear spin orientation in quantum dots by the nuclear quadrupole interaction. PHYSICAL REVIEW LETTERS 2007; 99:037401. [PMID: 17678325 DOI: 10.1103/physrevlett.99.037401] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/05/2007] [Indexed: 05/16/2023]
Abstract
The nuclear quadrupole interaction eliminates the restrictions imposed by hyperfine interaction on the spin coherence of an electron and nuclei in a quantum dot. The strain-induced nuclear quadrupole interaction suppresses the nuclear spin flip and makes possible the zero-field dynamic nuclear polarization in self-organized InP/InGaP quantum dots. The direction of the effective nuclear magnetic field is fixed in space, thus quenching the magnetic depolarization of the electron spin in the quantum dot. The quadrupole interaction suppresses the zero-field electron spin decoherence also for the case of nonpolarized nuclei. These results provide a new vision of the role of the nuclear quadrupole interaction in nanostructures: it elongates the spin memory of the electron-nuclear system.
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Affiliation(s)
- R I Dzhioev
- A.F. Ioffe Physical Technical Institute, St. Petersburg, 194021 Russia
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302
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Rudner MS, Levitov LS. Self-polarization and dynamical cooling of nuclear spins in double quantum dots. PHYSICAL REVIEW LETTERS 2007; 99:036602. [PMID: 17678304 DOI: 10.1103/physrevlett.99.036602] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/18/2006] [Indexed: 05/16/2023]
Abstract
The spin-blockade regime of double quantum dots features coupled dynamics of electron and nuclear spins resulting from the hyperfine interaction. We explain observed nuclear self-polarization via a mechanism based on feedback of the Overhauser shift on electron energy levels, and propose to use the instability toward self-polarization as a vehicle for controlling the nuclear spin distribution. In the dynamics induced by a properly chosen time-dependent magnetic field, nuclear spin fluctuations can be suppressed significantly below the thermal level.
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Affiliation(s)
- M S Rudner
- Department of Physics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA
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303
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Angus SJ, Ferguson AJ, Dzurak AS, Clark RG. Gate-defined quantum dots in intrinsic silicon. NANO LETTERS 2007; 7:2051-5. [PMID: 17567176 DOI: 10.1021/nl070949k] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
We report the fabrication and measurement of silicon quantum dots with tunable tunnel barriers in a narrow-channel field-effect transistor. Low-temperature transport spectroscopy is performed in both the many-electron ( approximately 100 electrons) regime and the few-electron ( approximately 10 electrons) regime. Excited states in the bias spectroscopy provide evidence of quantum confinement. These results demonstrate that depletion gates are an effective technique for defining quantum dots in silicon.
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Affiliation(s)
- Susan J Angus
- Australian Research Council Centre of Excellence for Quantum Computer Technology, University of New South Wales, Sydney, Australia.
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304
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Simon P, Loss D. Nuclear spin ferromagnetic phase transition in an interacting two dimensional electron gas. PHYSICAL REVIEW LETTERS 2007; 98:156401. [PMID: 17501366 DOI: 10.1103/physrevlett.98.156401] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/10/2006] [Indexed: 05/15/2023]
Abstract
Electrons in a two-dimensional semiconducting heterostructure interact with nuclear spins via the hyperfine interaction. Using a a Kondo lattice formulation of the electron-nuclear-spin interaction, we show that the nuclear-spin system within an interacting two-dimensional electron gas undergoes a ferromagnetic phase transition at finite temperatures. We find that electron-electron interactions and non-Fermi liquid behavior substantially enhance the nuclear-spin Curie temperature into the mK range with decreasing electron density.
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Affiliation(s)
- Pascal Simon
- Department of Physics and Astronomy, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
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305
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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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306
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Oulton R, Greilich A, Verbin SY, Cherbunin RV, Auer T, Yakovlev DR, Bayer M, Merkulov IA, Stavarache V, Reuter D, Wieck AD. Subsecond spin relaxation times in quantum dots at zero applied magnetic field due to a strong electron-nuclear interaction. PHYSICAL REVIEW LETTERS 2007; 98:107401. [PMID: 17358564 DOI: 10.1103/physrevlett.98.107401] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/21/2006] [Indexed: 05/14/2023]
Abstract
A key to ultralong electron spin memory in quantum dots (QDs) at zero magnetic field is the polarization of the nuclei, such that the electron spin is stabilized along the average nuclear magnetic field. We demonstrate that spin-polarized electrons in n-doped (In,Ga)As/GaAs QDs align the nuclear field via the hyperfine interaction. A feedback onto the electrons occurs, leading to stabilization of their polarization due to formation of a nuclear spin polaron [I. A. Merkulov, Phys. Solid State 40, 930 (1998)]. Spin depolarization of both systems is consequently greatly reduced, and spin memory of the coupled electron-nuclear spin system is retained over 0.3 sec at temperature of 2 K.
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Affiliation(s)
- R Oulton
- Experimentelle Physik II, Universität Dortmund, D-44221 Dortmund, Germany
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307
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Yao W, Liu RB, Sham LJ. Restoring coherence lost to a slow interacting mesoscopic spin bath. PHYSICAL REVIEW LETTERS 2007; 98:077602. [PMID: 17359060 DOI: 10.1103/physrevlett.98.077602] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/17/2006] [Indexed: 05/14/2023]
Abstract
For a two-state quantum object interacting with a slow mesoscopic interacting spin bath, we show that a many-body solution of the bath dynamics conditioned on the quantum-object state leads to an efficient control scheme to recover the lost quantum-object coherence through disentanglement. We demonstrate the theory with the realistic problem of one electron spin in a bath of many interacting nuclear spins in a semiconductor quantum dot. The spin language can be easily generalized to a quantum object in contact with a bath of interacting multilevel quantum units with the caveat that the bath is mesoscopic and its dynamics is slow compared with the quantum object.
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Affiliation(s)
- Wang Yao
- Department of Physics, University of California San Diego, La Jolla, California 92093-0319, USA
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308
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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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309
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MacLean K, Amasha S, Radu IP, Zumbühl DM, Kastner MA, Hanson MP, Gossard AC. Energy-dependent tunneling in a quantum dot. PHYSICAL REVIEW LETTERS 2007; 98:036802. [PMID: 17358709 DOI: 10.1103/physrevlett.98.036802] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/02/2006] [Indexed: 05/14/2023]
Abstract
We present measurements of the rates for an electron to tunnel on and off a quantum dot, obtained using a quantum point contact charge sensor. The tunnel rates show exponential dependence on drain-source bias and plunger gate voltages. The tunneling process is shown to be elastic, and a model describing tunneling in terms of the dot energy relative to the height of the tunnel barrier quantitatively describes the measurements.
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Affiliation(s)
- K MacLean
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
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310
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Quantum Entanglement and Teleportation of Quantum-Dot States in Microcavities. E-JOURNAL OF SURFACE SCIENCE AND NANOTECHNOLOGY 2007. [DOI: 10.1380/ejssnt.2007.51] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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311
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Popa I, Gaebel T, Neumann P, Jelezko F, Wrachtrup J. Spin Polarization in Single Spin Experiments on Defects in Diamond. Isr J Chem 2006. [DOI: 10.1560/ijc_46_4_393] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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312
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Yang A, Steger M, Karaiskaj D, Thewalt MLW, Cardona M, Itoh KM, Riemann H, Abrosimov NV, Churbanov MF, Gusev AV, Bulanov AD, Kaliteevskii AK, Godisov ON, Becker P, Pohl HJ, Ager JW, Haller EE. Optical detection and ionization of donors in specific electronic and nuclear spin States. PHYSICAL REVIEW LETTERS 2006; 97:227401. [PMID: 17155840 DOI: 10.1103/physrevlett.97.227401] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/30/2006] [Indexed: 05/12/2023]
Abstract
We resolve the remarkably sharp bound exciton transitions of highly enriched 28Si using a single-frequency laser and photoluminescence excitation spectroscopy, as well as photocurrent spectroscopy. Well-resolved doublets in the spectrum of the 31P donor reflect the hyperfine coupling of the electronic and nuclear donor spins. The optical detection of the nuclear spin state, and selective pumping and ionization of donors in specific electronic and nuclear spin states, suggests a number of new possibilities which could be useful for the realization of silicon-based quantum computers.
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Affiliation(s)
- A Yang
- Department of Physics, Simon Fraser University, Burnaby, British Columbia, V5A 1S6 Canada
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313
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Morello A, Stamp PCE, Tupitsyn IS. Pairwise decoherence in coupled spin qubit networks. PHYSICAL REVIEW LETTERS 2006; 97:207206. [PMID: 17155713 DOI: 10.1103/physrevlett.97.207206] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/31/2006] [Indexed: 05/12/2023]
Abstract
Experiments involving phase coherent dynamics of networks of spins, such as echo experiments, will only work if decoherence can be suppressed. We show here, by analyzing the particular example of a crystalline network of Fe8 molecules, that most decoherence typically comes from pairwise interactions (particularly dipolar interactions) between the spins, which cause "correlated errors." However, at very low T these are strongly suppressed. These results have important implications for the design of quantum information processing systems using electronic spins.
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Affiliation(s)
- Andrea Morello
- Department of Physics and Astronomy, University of British Columbia, Vancouver BC V6T 1Z1, Canada
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314
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Berezovsky J, Mikkelsen MH, Gywat O, Stoltz NG, Coldren LA, Awschalom DD. Nondestructive Optical Measurements of a Single Electron Spin in a Quantum Dot. Science 2006; 314:1916-20. [PMID: 17095655 DOI: 10.1126/science.1133862] [Citation(s) in RCA: 162] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Kerr rotation measurements on a single electron spin confined in a charge-tunable semiconductor quantum dot demonstrate a means to directly probe the spin off-resonance, thus minimally disturbing the system. Energy-resolved magneto-optical spectra reveal information about the optically oriented spin polarization and the transverse spin lifetime of the electron as a function of the charging of the dot. These results represent progress toward the manipulation and coupling of single spins and photons for quantum information processing.
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Affiliation(s)
- J Berezovsky
- Center for Spintronics and Quantum Computation, University of California, Santa Barbara, CA 93106, USA
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315
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Huang Z, Sadiek G, Kais S. Time evolution of a single spin inhomogeneously coupled to an interacting spin environment. J Chem Phys 2006; 124:144513. [PMID: 16626220 DOI: 10.1063/1.2192778] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We study the time evolution of a single spin coupled by exchange interaction to an environment of interacting spin bath modeled by the XY Hamiltonian. By evaluating the spin correlator of the single spin, we observed that the decay rate of the spin oscillations strongly depends on the relative magnitude of the exchange coupling between the single spin and its nearest neighbor J(') and coupling among the spins in the environment J. The decoherence time varies significantly based on the relative coupling magnitudes of J and J('). The decay rate law has a Gaussian profile when the two exchange couplings are of the same order J(') approximately J but converts to exponential and then a power law as we move to the regimes of J(')>J and J(')<J. We also show that the spin oscillations propagate from the single spin to the environmental spins with a certain speed. The effect of varying the anisotropic parameter, external magnetic field, and temperature on the decaying rate of the spin state is also discussed.
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Affiliation(s)
- Zhen Huang
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, USA
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316
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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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317
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Tang JM, Levy J, Flatté ME. All-electrical control of single ion spins in a semiconductor. PHYSICAL REVIEW LETTERS 2006; 97:106803. [PMID: 17025843 DOI: 10.1103/physrevlett.97.106803] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/09/2006] [Indexed: 05/12/2023]
Abstract
We propose a method for all-electrical manipulation of single ion spins substituted into a semiconductor. Mn ions with a bound hole in GaAs form a natural example. Direct electrical manipulation of the ion spin is possible, because electric fields manipulate the orbital wave function of the hole, and through the spin-orbit coupling the spin is reoriented as well. Coupling ion spins can be achieved using gates to control the size of the hole wave function. Coherent manipulation of ionic spins may find applications in high-density storage and in scalable coherent or quantum information processing.
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Affiliation(s)
- Jian-Ming Tang
- Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242-1479, USA
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318
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San-Jose P, Zarand G, Shnirman A, Schön G. Geometrical spin dephasing in quantum dots. PHYSICAL REVIEW LETTERS 2006; 97:076803. [PMID: 17026261 DOI: 10.1103/physrevlett.97.076803] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/13/2006] [Indexed: 05/12/2023]
Abstract
We study spin-orbit mediated relaxation and dephasing of electron spins in quantum dots. We show that higher order contributions provide a relaxation mechanism that dominates for low magnetic fields and is of geometrical origin. In the low-field limit relaxation is dominated by coupling to electron-hole excitations and possibly 1/f noise rather than phonons.
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Affiliation(s)
- Pablo San-Jose
- Institut für Theoretische Festkörperphysik and DFG-Center for Functional Nanostructures (CFN), Universität Karlsruhe, D-76128 Karlsruhe, Germany
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319
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Krenner HJ, Clark EC, Nakaoka T, Bichler M, Scheurer C, Abstreiter G, Finley JJ. Optically probing spin and charge interactions in a tunable artificial molecule. PHYSICAL REVIEW LETTERS 2006; 97:076403. [PMID: 17026254 DOI: 10.1103/physrevlett.97.076403] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/28/2006] [Indexed: 05/12/2023]
Abstract
We optically probe and electrically control a single artificial molecule containing a well defined number of electrons. Charge and spin dependent interdot quantum couplings are probed optically by adding a single electron-hole pair and detecting the emission from negatively charged exciton states. Coulomb- and Pauli-blockade effects are directly observed, and tunnel coupling and electrostatic charging energies are independently measured. The interdot quantum coupling is shown to be mediated by electron tunneling. Our results are in excellent accord with calculations that provide a complete picture of negative excitons and few-electron states in quantum dot molecules.
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Affiliation(s)
- H J Krenner
- Walter Schottky Institut and Physik Department, Technische Universität München, Am Coulombwall 3, D-85748 Garching, Germany
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320
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Akimov IA, Feng DH, Henneberger F. Electron spin dynamics in a self-assembled semiconductor quantum dot: the limit of low magnetic fields. PHYSICAL REVIEW LETTERS 2006; 97:056602. [PMID: 17026126 DOI: 10.1103/physrevlett.97.056602] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/27/2006] [Indexed: 05/12/2023]
Abstract
Using the trion as an optical probe, we uncover novel electron spin dynamics in CdSe/ZnSe Stranski-Krastanov quantum dots. The longitudinal spin lifetime obeys an inverse power law associated with recharging processes in the dot ensemble. No hint at spin-orbit mediated spin relaxation is found. At very weak magnetic fields (< 50 mT), electron spin dynamics related to the hyperfine interaction with the lattice nuclei is uncovered. A strong Knight field gives rise to nuclear ordering and formation of dynamical polarization on a 100-micros time scale under continuous electron spin pumping. The associated spin transients are temperature robust and can be observed up to 100 K.
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Affiliation(s)
- I A Akimov
- Institut für Physik, Humboldt Universität zu Berlin, Newtonstrasse 15, 12489 Berlin, Germany
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321
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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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322
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323
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Greilich A, Yakovlev DR, Shabaev A, Efros AL, Yugova IA, Oulton R, Stavarache V, Reuter D, Wieck A, Bayer M. Mode Locking of Electron Spin Coherences in Singly Charged Quantum Dots. Science 2006; 313:341-5. [PMID: 16857937 DOI: 10.1126/science.1128215] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The fast dephasing of electron spins in an ensemble of quantum dots is detrimental for applications in quantum information processing. We show here that dephasing can be overcome by using a periodic train of light pulses to synchronize the phases of the precessing spins, and we demonstrate this effect in an ensemble of singly charged (In,Ga)As/GaAs quantum dots. This mode locking leads to constructive interference of contributions to Faraday rotation and presents potential applications based on robust quantum coherence within an ensemble of dots.
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Affiliation(s)
- A Greilich
- Experimentelle Physik II, Universität Dortmund, D-44221 Dortmund, Germany
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324
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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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325
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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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326
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Greilich A, Oulton R, Zhukov EA, Yugova IA, Yakovlev DR, Bayer M, Shabaev A, Efros AL, Merkulov IA, Stavarache V, Reuter D, Wieck A. Optical control of spin coherence in singly charged (In,Ga)As/GaAs quantum dots. PHYSICAL REVIEW LETTERS 2006; 96:227401. [PMID: 16803342 DOI: 10.1103/physrevlett.96.227401] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/15/2005] [Indexed: 05/10/2023]
Abstract
Electron spin coherence has been generated optically in n-type modulation doped (In,Ga)As/GaAs quantum dots (QDs) which contain on average a single electron per dot. The coherence arises from resonant excitation of the QDs by circularly polarized laser pulses, creating a coherent superposition of an electron and a trion. Time dependent Faraday rotation is used to probe the spin precession of the optically oriented electrons about a transverse magnetic field. The coherence generation can be controlled by pulse intensity, being most efficient for (2n+1)pi pulses.
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Affiliation(s)
- A Greilich
- Experimentelle Physik II, Universität Dortmund, D-44221 Dortmund, Germany
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327
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Stano P, Fabian J. Theory of phonon-induced spin relaxation in laterally coupled quantum dots. PHYSICAL REVIEW LETTERS 2006; 96:186602. [PMID: 16712384 DOI: 10.1103/physrevlett.96.186602] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/30/2005] [Indexed: 05/09/2023]
Abstract
Phonon-induced spin relaxation in coupled lateral quantum dots in the presence of spin-orbit coupling is calculated. The calculation for single dots is consistent with experiment. Spin relaxation in double dots at useful interdot couplings is dominated by spin-hot spots that are strongly anisotropic. Spin-hot spots are ineffective for a diagonal crystallographic orientation of the dots with a transverse in-plane field. This geometry is proposed for spin-based quantum information processing.
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Affiliation(s)
- Peter Stano
- Institute for Theoretical Physics, University of Regensburg, 93040 Regensburg, Germany
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328
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Onac E, Balestro F, van Beveren LHW, Hartmann U, Nazarov YV, Kouwenhoven LP. Using a quantum dot as a high-frequency shot noise detector. PHYSICAL REVIEW LETTERS 2006; 96:176601. [PMID: 16712318 DOI: 10.1103/physrevlett.96.176601] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/26/2005] [Indexed: 05/09/2023]
Abstract
We present the experimental realization of a quantum dot (QD) operating as a high-frequency noise detector. Current fluctuations produced in a nearby quantum point contact (QPC) ionize the QD and induce transport through excited states. The resulting transient current through the QD represents our detector signal. We investigate its dependence on the QPC transmission and voltage bias. We observe and explain a quantum threshold feature and a saturation in the detector signal. This experimental and theoretical study is relevant in understanding the backaction of a QPC used as a charge detector.
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Affiliation(s)
- E Onac
- Kavli Institute of Nanoscience Delft, Delft University of Technology, The Netherlands.
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329
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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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330
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Le Hur K, Recher P, Dupont E, Loss D. Mesoscopic resonating valence bond system on a triple dot. PHYSICAL REVIEW LETTERS 2006; 96:106803. [PMID: 16605773 DOI: 10.1103/physrevlett.96.106803] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/21/2005] [Indexed: 05/08/2023]
Abstract
We theoretically introduce a mesoscopic pendulum from a triple dot. The pendulum is fastened through a singly occupied dot (spin qubit). Two other strongly capacitively coupled islands form a double-dot charge qubit with one electron in excess oscillating between the two low-energy charge states (1,0) and (0,1). The triple dot is placed between two superconducting leads. Under realistic conditions, the main proximity effect stems from the injection of resonating singlet (valence) bonds on the triple dot. This gives rise to a Josephson current that is charge- and spin-dependent and, as a consequence, exhibits a distinct resonance as a function of the superconducting phase difference.
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Affiliation(s)
- Karyn Le Hur
- Département de Physique et RQMP, Université de Sherbrooke, Sherbrooke, Québec, Canada, J1K 2R1
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331
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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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332
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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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333
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Gustavsson S, Leturcq R, Simovic B, Schleser R, Ihn T, Studerus P, Ensslin K, Driscoll DC, Gossard AC. Counting statistics of single electron transport in a quantum dot. PHYSICAL REVIEW LETTERS 2006; 96:076605. [PMID: 16606120 DOI: 10.1103/physrevlett.96.076605] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/11/2005] [Indexed: 05/08/2023]
Abstract
We have measured the full counting statistics of current fluctuations in a semiconductor quantum dot (QD) by real-time detection of single electron tunneling with a quantum point contact. This method gives direct access to the distribution function of current fluctuations. Suppression of the second moment (related to the shot noise) and the third moment (related to the asymmetry of the distribution) in a tunable semiconductor QD is demonstrated experimentally. With this method we demonstrate the ability to measure very low current and noise levels.
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Affiliation(s)
- S Gustavsson
- Solid State Physics Laboratory, ETH Zürich, CH-8093 Zürich, Switzerland.
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334
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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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335
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Barrett SD, Stace TM. Continuous measurement of a microwave-driven solid state qubit. PHYSICAL REVIEW LETTERS 2006; 96:017405. [PMID: 16486516 DOI: 10.1103/physrevlett.96.017405] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/09/2004] [Indexed: 05/06/2023]
Abstract
We analyze the dynamics of a continuously observed, damped, microwave-driven solid state charge qubit, consisting of a single electron in a double well potential. The microwave field induces transitions between the qubit eigenstates, which have a profound effect on the detector output current. Useful information about the qubit dynamics, such as dephasing and relaxation rates, and the Rabi frequency, can be extracted from the detector conductance and output noise power spectrum. We also propose a technique for single-shot electron spin readout, for spin based quantum information processing, which has a number of practical advantages over existing schemes.
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Affiliation(s)
- S D Barrett
- Hewlett-Packard Laboratories, Filton Road, Stoke Gifford, Bristol BS34 8QZ, United Kingdom.
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336
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García CP, Pellegrini V, Pinczuk A, Rontani M, Goldoni G, Molinari E, Dennis BS, Pfeiffer LN, West KW. Evidence of correlation in spin excitations of few-electron quantum dots. PHYSICAL REVIEW LETTERS 2005; 95:266806. [PMID: 16486387 DOI: 10.1103/physrevlett.95.266806] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/06/2005] [Indexed: 05/06/2023]
Abstract
We report inelastic light scattering measurements of spin and charge excitations in nanofabricated AlGaAs/GaAs quantum dots with few electrons. A narrow spin excitation peak is observed and assigned to the intershell triplet-to-singlet monopole mode of dots with four electrons. Configuration-interaction theory provides precise quantitative interpretations that uncover large correlation effects that are comparable to exchange Coulomb interactions.
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337
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Oestreich M, Römer M, Haug RJ, Hägele D. Spin noise spectroscopy in GaAs. PHYSICAL REVIEW LETTERS 2005; 95:216603. [PMID: 16384167 DOI: 10.1103/physrevlett.95.216603] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/18/2005] [Indexed: 05/05/2023]
Abstract
We observe the noise spectrum of electron spins in bulk GaAs by Faraday-rotation noise spectroscopy. The experimental technique enables the undisturbed measurement of the electron-spin dynamics in semiconductors. We measure exemplarily the electron-spin relaxation time and the electron Landé g factor in -doped GaAs at low temperatures and find good agreement of the measured noise spectrum with a theory based on Poisson distribution probability.
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Affiliation(s)
- M Oestreich
- Institut für Festkörperphysik, Universität Hannover, Appelstrasse 2, D-30167 Hannover, Germany
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338
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Anders FB, Schiller A. Real-time dynamics in quantum-impurity systems: a time-dependent numerical renormalization-group approach. PHYSICAL REVIEW LETTERS 2005; 95:196801. [PMID: 16384007 DOI: 10.1103/physrevlett.95.196801] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/29/2005] [Indexed: 05/05/2023]
Abstract
We develop a general approach to the nonequilibrium dynamics of quantum-impurity systems for arbitrary coupling strength. The numerical renormalization group is used to generate a complete basis set necessary for the correct description of the time evolution. We benchmark our method with the exact analytical solution for the resonant-level model. As a first application, we investigate the equilibration of an ultrasmall quantum dot subject to a sudden change of gate voltage and external magnetic field. Two distinct relaxation times are identified for the spin and charge dynamics.
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Affiliation(s)
- Frithjof B Anders
- Department of Physics, Universität Bremen, P.O. Box 330 440, D-28334 Bremen, Germany
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339
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Blaauboer M, Divincenzo DP. Detecting entanglement using a double-quantum-dot turnstile. PHYSICAL REVIEW LETTERS 2005; 95:160402. [PMID: 16241775 DOI: 10.1103/physrevlett.95.160402] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/10/2004] [Indexed: 05/05/2023]
Abstract
We propose a scheme based on using the singlet ground state of an electron spin pair in a double-quantum-dot nanostructure as a suitable setup for detecting entanglement between electron spins via the measurement of an optimal entanglement witness. Using time-dependent gate voltages and magnetic fields the entangled spins are separated and coherently rotated in the quantum dots and subsequently detected at spin-polarized quantum point contacts. We analyze the coherent time evolution of the entangled pair and show that by counting coincidences in the four exits an entanglement test can be done. This setup is close to present-day experimental possibilities and can be used to produce pairs of entangled electrons "on demand."
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Affiliation(s)
- M Blaauboer
- Kavli Institute of Nanoscience, Delft University of Technology, The Netherlands
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340
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Petta JR, Johnson AC, Taylor JM, Laird EA, Yacoby A, Lukin MD, Marcus CM, Hanson MP, Gossard AC. Coherent Manipulation of Coupled Electron Spins in Semiconductor Quantum Dots. Science 2005; 309:2180-4. [PMID: 16141370 DOI: 10.1126/science.1116955] [Citation(s) in RCA: 710] [Impact Index Per Article: 37.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
We demonstrated coherent control of a quantum two-level system based on two-electron spin states in a double quantum dot, allowing state preparation, coherent manipulation, and projective readout. These techniques are based on rapid electrical control of the exchange interaction. Separating and later recombining a singlet spin state provided a measurement of the spin dephasing time, T2*, of approximately 10 nanoseconds, limited by hyperfine interactions with the gallium arsenide host nuclei. Rabi oscillations of two-electron spin states were demonstrated, and spin-echo pulse sequences were used to suppress hyperfine-induced dephasing. Using these quantum control techniques, a coherence time for two-electron spin states exceeding 1 microsecond was observed.
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Affiliation(s)
- J R Petta
- Department of Physics, Harvard University, Cambridge, MA 02138, USA
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341
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Koppens FHL, Folk JA, Elzerman JM, Hanson R, van Beveren LHW, Vink IT, Tranitz HP, Wegscheider W, Kouwenhoven LP, Vandersypen LMK. Control and Detection of Singlet-Triplet Mixing in a Random Nuclear Field. Science 2005; 309:1346-50. [PMID: 16037418 DOI: 10.1126/science.1113719] [Citation(s) in RCA: 477] [Impact Index Per Article: 25.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
We observed mixing between two-electron singlet and triplet states in a double quantum dot, caused by interactions with nuclear spins in the host semiconductor. This mixing was suppressed when we applied a small magnetic field or increased the interdot tunnel coupling and thereby the singlet-triplet splitting. Electron transport involving transitions between triplets and singlets in turn polarized the nuclei, resulting in marked bistabilities. We extract from the fluctuating nuclear field a limitation on the time-averaged spin coherence time T2* of 25 nanoseconds. Control of the electron-nuclear interaction will therefore be crucial for the coherent manipulation of individual electron spins.
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Affiliation(s)
- F H L Koppens
- Kavli Institute of Nanoscience, Delft University of Technology, Post Office Box 5046, 2600 GA Delft, Netherlands
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342
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Fal'ko VI, Altshuler BL, Tsyplyatyev O. Anisotropy of spin splitting and spin relaxation in lateral quantum dots. PHYSICAL REVIEW LETTERS 2005; 95:076603. [PMID: 16196808 DOI: 10.1103/physrevlett.95.076603] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/04/2005] [Indexed: 05/04/2023]
Abstract
Inelastic spin relaxation and spin splitting epsilon(s) in lateral quantum dots are studied in the regime of strong in-plane magnetic field. Because of both the g-factor energy dependence and spin-orbit coupling, epsilon(s) demonstrates a substantial nonlinear magnetic field dependence similar to that observed by Hanson et al. [Phys. Rev. Lett. 91, 196802 (2003)]. It also varies with the in-plane orientation of the magnetic field due to crystalline anisotropy of the spin-orbit coupling. The spin relaxation rate is also anisotropic, the anisotropy increasing with the field. When the magnetic length is less than the "thickness" of the GaAs dot, the relaxation can be an order of magnitude faster for B ||[100] than for B || [110].
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343
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Bulaev DV, Loss D. Spin relaxation and decoherence of holes in quantum dots. PHYSICAL REVIEW LETTERS 2005; 95:076805. [PMID: 16196813 DOI: 10.1103/physrevlett.95.076805] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/08/2005] [Indexed: 05/04/2023]
Abstract
We investigate heavy-hole spin relaxation and decoherence in quantum dots in perpendicular magnetic fields. We show that at low temperatures the spin decoherence time is 2 times longer than the spin relaxation time. We find that the spin relaxation time for heavy holes can be comparable to or even longer than that for electrons in strongly two-dimensional quantum dots. We discuss the difference in the magnetic-field dependence of the spin relaxation rate due to Rashba or Dresselhaus spin-orbit coupling for systems with positive (i.e., GaAs quantum dots) or negative (i.e., InAs quantum dots) g factor.
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Affiliation(s)
- Denis V Bulaev
- Department of Physics and Astronomy, University of Basel, Switzerland
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344
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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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345
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Affiliation(s)
- J Carlos Egues
- Department of Physics and Informatics, Institute of Physics of São Carlos, University of São Paulo, São Carlos 13560-970, Brazil.
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346
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Abstract
We propose a protocol and physical implementation for partial Bell-state measurements of Fermionic qubits, allowing for deterministic quantum computing in solid-state systems without the need for two-qubit gates. Our scheme consists of two spin qubits in a double quantum dot where the two dots have different Zeeman splittings and resonant tunneling between the dots is only allowed when the spins are antiparallel. This converts spin parity into charge information by means of a projective measurement and can be implemented with established technologies. This measurement-based qubit scheme greatly simplifies the experimental realization of scalable quantum computers in electronic nanostructures.
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Affiliation(s)
- Hans-Andreas Engel
- Lyman Laboratory, Department of Physics, Harvard University, Cambridge, MA 02138, USA
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347
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Dutt MVG, Cheng J, Li B, Xu X, Li X, Berman PR, Steel DG, Bracker AS, Gammon D, Economou SE, Liu RB, Sham LJ. Stimulated and spontaneous optical generation of electron spin coherence in charged GaAs quantum dots. PHYSICAL REVIEW LETTERS 2005; 94:227403. [PMID: 16090438 DOI: 10.1103/physrevlett.94.227403] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/03/2004] [Indexed: 05/03/2023]
Abstract
We report on the coherent optical excitation of electron spin polarization in the ground state of charged GaAs quantum dots via an intermediate charged exciton (trion) state. Coherent optical fields are used for the creation and detection of the Raman spin coherence between the spin ground states of the charged quantum dot. The measured spin decoherence time, which is likely limited by the nature of the spin ensemble, approaches 10 ns at zero field. We also show that the Raman spin coherence in the quantum beats is caused not only by the usual stimulated Raman interaction but also by simultaneous spontaneous radiative decay of either excited trion state to a coherent combination of the two spin states.
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Affiliation(s)
- M V Gurudev Dutt
- The H. M. Randall Laboratory of Physics, The University of Michigan, Ann Arbor, MI 48109, USA
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348
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Johnson AC, Petta JR, Taylor JM, Yacoby A, Lukin MD, Marcus CM, Hanson MP, Gossard AC. Triplet–singlet spin relaxation via nuclei in a double quantum dot. Nature 2005; 435:925-8. [PMID: 15944715 DOI: 10.1038/nature03815] [Citation(s) in RCA: 434] [Impact Index Per Article: 22.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2005] [Accepted: 05/19/2005] [Indexed: 11/10/2022]
Abstract
The spin of a confined electron, when oriented originally in some direction, will lose memory of that orientation after some time. Physical mechanisms leading to this relaxation of spin memory typically involve either coupling of the electron spin to its orbital motion or to nuclear spins. Relaxation of confined electron spin has been previously measured only for Zeeman or exchange split spin states, where spin-orbit effects dominate relaxation; spin flips due to nuclei have been observed in optical spectroscopy studies. Using an isolated GaAs double quantum dot defined by electrostatic gates and direct time domain measurements, we investigate in detail spin relaxation for arbitrary splitting of spin states. Here we show that electron spin flips are dominated by nuclear interactions and are slowed by several orders of magnitude when a magnetic field of a few millitesla is applied. These results have significant implications for spin-based information processing.
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Affiliation(s)
- A C Johnson
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
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349
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Hanson R, van Beveren LHW, Vink IT, Elzerman JM, Naber WJM, Koppens FHL, Kouwenhoven LP, Vandersypen LMK. Single-shot readout of electron spin states in a quantum dot using spin-dependent tunnel rates. PHYSICAL REVIEW LETTERS 2005; 94:196802. [PMID: 16090196 DOI: 10.1103/physrevlett.94.196802] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/31/2004] [Indexed: 05/03/2023]
Abstract
We present a method for reading out the spin state of electrons in a quantum dot that is robust against charge noise and can be used even when the electron temperature exceeds the energy splitting between the states. The spin states are first correlated to different charge states using a spin dependence of the tunnel rates. A subsequent fast measurement of the charge on the dot then reveals the original spin state. We experimentally demonstrate the method by performing readout of the two-electron spin states, achieving a single-shot visibility of more than 80%. We find very long triplet-to-singlet relaxation times (up to several milliseconds), with a strong dependence on the in-plane magnetic field.
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Affiliation(s)
- R Hanson
- Kavli Institute of Nanoscience, Delft University of Technology, GA Delft, The Netherlands
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350
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Ortner G, Bayer M, Lyanda-Geller Y, Reinecke TL, Kress A, Reithmaier JP, Forchel A. Control of vertically coupled InGaAs/GaAs quantum dots with electric fields. PHYSICAL REVIEW LETTERS 2005; 94:157401. [PMID: 15904185 DOI: 10.1103/physrevlett.94.157401] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/29/2003] [Indexed: 05/02/2023]
Abstract
Controllable interactions that couple quantum dots are a key requirement in the search for scalable solid state implementations for quantum information technology. From optical studies of excitons and corresponding calculations, we demonstrate that an electric field on vertically coupled pairs of In(0.6)Ga(0.4)As/GaAs quantum dots controls the mixing of the exciton states on the two dots and also provides controllable coupling between carriers in the dots.
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Affiliation(s)
- G Ortner
- Experimentelle Physik II, Universität Dortmund, D-44221 Dortmund, Germany
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