51
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Fink T, Bluhm H. Noise spectroscopy using correlations of single-shot qubit readout. PHYSICAL REVIEW LETTERS 2013; 110:010403. [PMID: 23383763 DOI: 10.1103/physrevlett.110.010403] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/25/2012] [Indexed: 06/01/2023]
Abstract
A better understanding of the noise causing qubit decoherence is crucial for improving qubit performance. The noise spectrum affecting the qubit may be extracted by measuring dephasing under the application of pulse sequences but requires accurate qubit control and sufficiently long relaxation times, which are not always available. Here, we describe an alternative method to extract the spectrum from correlations of single-shot measurement outcomes of successive free induction decays. This method only requires qubit initialization and readout with a moderate fidelity and also allows independent tuning of both the overall sensitivity and the frequency region over which it is sensitive. Thus, it is possible to maintain a good detection contrast over a very wide frequency range. We discuss using our method for measuring both 1/f noise and the fluctuation spectrum of the nuclear bath of GaAs spin qubits.
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Affiliation(s)
- T Fink
- 2nd Institute of Physics C, RWTH Aachen University, D-52074 Aachen, Germany and JARA-Fundamentals of Future Information Technology, D-52425 Jülich, Germany
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52
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Frolov SM, Danon J, Nadj-Perge S, Zuo K, van Tilburg JWW, Pribiag VS, van den Berg JWG, Bakkers EPAM, Kouwenhoven LP. Suppression of Zeeman gradients by nuclear polarization in double quantum dots. PHYSICAL REVIEW LETTERS 2012; 109:236805. [PMID: 23368241 DOI: 10.1103/physrevlett.109.236805] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/07/2012] [Indexed: 06/01/2023]
Abstract
We use electric dipole spin resonance to measure dynamic nuclear polarization in InAs nanowire quantum dots. The resonance shifts in frequency when the system transitions between metastable high and low current states, indicating the presence of nuclear polarization. We propose that the low and the high current states correspond to different total Zeeman energy gradients between the two quantum dots. In the low current state, dynamic nuclear polarization efficiently compensates the Zeeman gradient due to the g-factor mismatch, resulting in a suppressed total Zeeman gradient. We present a theoretical model of electron-nuclear feedback that demonstrates a fixed point in nuclear polarization for nearly equal Zeeman splittings in the two dots and predicts a narrowed hyperfine gradient distribution.
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Affiliation(s)
- S M Frolov
- Kavli Institute of Nanoscience, Delft University of Technology, 2600 GA Delft, The Netherlands
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53
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54
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Raith M, Stano P, Baruffa F, Fabian J. Theory of spin relaxation in two-electron lateral coupled quantum dots. PHYSICAL REVIEW LETTERS 2012; 108:246602. [PMID: 23004302 DOI: 10.1103/physrevlett.108.246602] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/29/2011] [Indexed: 06/01/2023]
Abstract
A global quantitative picture of the phonon-induced two-electron spin relaxation in GaAs double quantum dots is presented using highly accurate numerics. Wide regimes of interdot coupling, magnetic field magnitude and orientation, and detuning are explored in the presence of a nuclear bath. Most important, the giant magnetic anisotropy of the singlet-triplet relaxation can be controlled by detuning switching the principal anisotropy axes: a protected state becomes unprotected upon detuning and vice versa. It is also established that nuclear spins can dominate spin relaxation for unpolarized triplets even at high magnetic fields, contrary to common belief.
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Affiliation(s)
- Martin Raith
- Institute for Theoretical Physics, University of Regensburg, D-93040 Regensburg, Germany
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55
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Nadj-Perge S, Pribiag VS, van den Berg JWG, Zuo K, Plissard SR, Bakkers EPAM, Frolov SM, Kouwenhoven LP. Spectroscopy of spin-orbit quantum bits in indium antimonide nanowires. PHYSICAL REVIEW LETTERS 2012; 108:166801. [PMID: 22680747 DOI: 10.1103/physrevlett.108.166801] [Citation(s) in RCA: 77] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/09/2012] [Indexed: 06/01/2023]
Abstract
A double quantum dot in the few-electron regime is achieved using local gating in an InSb nanowire. The spectrum of two-electron eigenstates is investigated using electric dipole spin resonance. Singlet-triplet level repulsion caused by spin-orbit interaction is observed. The size and the anisotropy of singlet-triplet repulsion are used to determine the magnitude and the orientation of the spin-orbit effective field in an InSb nanowire double dot. The obtained results are confirmed using spin blockade leakage current anisotropy and transport spectroscopy of individual quantum dots.
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Affiliation(s)
- S Nadj-Perge
- Kavli Institute of Nanoscience, Delft University of Technology, 2600 GA Delft, The Netherlands
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56
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Medford J, Cywiński Ł, Barthel C, Marcus CM, Hanson MP, Gossard AC. Scaling of dynamical decoupling for spin qubits. PHYSICAL REVIEW LETTERS 2012; 108:086802. [PMID: 22463554 DOI: 10.1103/physrevlett.108.086802] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/18/2011] [Indexed: 05/31/2023]
Abstract
We investigate the scaling of coherence time T(2) with the number of π pulses n(π) in a singlet-triplet spin qubit using Carr-Purcell-Meiboom-Gill (CPMG) and concatenated dynamical decoupling (CDD) pulse sequences. For an even numbers of CPMG pulses, we find a power law T(2) is proportional to (n(π))(γ(e)), with γ(e)=0.72±0.01, essentially independent of the envelope function used to extract T(2). From this surprisingly robust value, a power-law model of the noise spectrum of the environment, S(ω)~ω(-β), yields β=γ(e)/(1-γ(e))=2.6±0.1. Model values for T(2)(n(π)) using β=2.6 for CPMG with both even and odd n(π) up to 32 and CDD orders 3 through 6 compare very well with the experiment.
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Affiliation(s)
- J Medford
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
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57
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Prance JR, Shi Z, Simmons CB, Savage DE, Lagally MG, Schreiber LR, Vandersypen LMK, Friesen M, Joynt R, Coppersmith SN, Eriksson MA. Single-shot measurement of triplet-singlet relaxation in a Si/SiGe double quantum dot. PHYSICAL REVIEW LETTERS 2012; 108:046808. [PMID: 22400879 DOI: 10.1103/physrevlett.108.046808] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/02/2011] [Indexed: 05/31/2023]
Abstract
We investigate the lifetime of two-electron spin states in a few-electron Si/SiGe double dot. At the transition between the (1,1) and (0,2) charge occupations, Pauli spin blockade provides a readout mechanism for the spin state. We use the statistics of repeated single-shot measurements to extract the lifetimes of multiple states simultaneously. When the magnetic field is zero, we find that all three triplet states have equal lifetimes, as expected, and this time is ~10 ms. When the field is nonzero, the T(0) lifetime is unchanged, whereas the T- lifetime increases monotonically with the field, reaching 3 sec at 1 T.
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Affiliation(s)
- J R Prance
- University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
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58
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Coupling artificial molecular spin states by photon-assisted tunnelling. Nat Commun 2011; 2:556. [PMID: 22109530 PMCID: PMC3483534 DOI: 10.1038/ncomms1561] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2011] [Accepted: 10/20/2011] [Indexed: 11/17/2022] Open
Abstract
Artificial molecules containing just one or two electrons provide a powerful platform
for studies of orbital and spin quantum dynamics in nanoscale devices. A well-known
example of these dynamics is tunnelling of electrons between two coupled quantum
dots triggered by microwave irradiation. So far, these tunnelling processes have
been treated as electric-dipole-allowed spin-conserving events. Here we report that
microwaves can also excite tunnelling transitions between states with different
spin. We show that the dominant mechanism responsible for violation of spin
conservation is the spin–orbit interaction. These transitions make it
possible to perform detailed microwave spectroscopy of the molecular spin states of
an artificial hydrogen molecule and open up the possibility of realizing full
quantum control of a two-spin system through microwave excitation. Tunnelling transitions triggered by microwave irradiation between
coupled quantum dots have generally been assumed to be spin-conserving. This study shows
that this condition is violated in the presence of spin–orbit coupling, thus
opening new possibilities for manipulating a two–spin qubit system by
microwave irradiation.
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59
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Kobayashi T, Hitachi K, Sasaki S, Muraki K. Observation of hysteretic transport due to dynamic nuclear spin polarization in a GaAs lateral double quantum dot. PHYSICAL REVIEW LETTERS 2011; 107:216802. [PMID: 22181907 DOI: 10.1103/physrevlett.107.216802] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/28/2011] [Indexed: 05/31/2023]
Abstract
We report a new transport feature in a GaAs lateral double quantum dot that emerges for magnetic-field sweeps and shows hysteresis due to dynamic nuclear spin polarization (DNP). This DNP signal appears in the Coulomb blockade regime by virtue of the finite interdot tunnel coupling and originates from the crossing between ground levels of the spin triplet and singlet extensively used for nuclear spin manipulations in pulsed-gate experiments. The magnetic-field dependence of the current level is suggestive of unbalanced DNP between the two dots, which opens up the possibility of controlling electron and nuclear spin states via dc transport.
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Affiliation(s)
- Takashi Kobayashi
- NTT Basic Research Laboratories, NTT Corporation, Morinosato-Wakamiya, Atsugi, Japan
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60
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Leijnse M, Flensberg K. Quantum information transfer between topological and spin qubit systems. PHYSICAL REVIEW LETTERS 2011; 107:210502. [PMID: 22181866 DOI: 10.1103/physrevlett.107.210502] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/28/2011] [Indexed: 05/31/2023]
Abstract
We propose a method to coherently transfer quantum information, and to create entanglement, between topological qubits and conventional spin qubits. Our suggestion uses gated control to transfer an electron (spin qubit) between a quantum dot and edge Majorana modes in adjacent topological superconductors. Because of the spin polarization of the Majorana modes, the electron transfer translates spin superposition states into superposition states of the Majorana system, and vice versa. Furthermore, we show how a topological superconductor can be used to facilitate long-distance quantum information transfer and entanglement between spatially separated spin qubits.
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Affiliation(s)
- Martin Leijnse
- Nano-Science Center & Niels Bohr Institute, University of Copenhagen, Denmark
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61
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Sasaki A, Kojo M, Hirose K, Goto H. Real-space finite-difference approach for multi-body systems: path-integral renormalization group method and direct energy minimization method. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2011; 23:434001. [PMID: 21998159 DOI: 10.1088/0953-8984/23/43/434001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
The path-integral renormalization group and direct energy minimization method of practical first-principles electronic structure calculations for multi-body systems within the framework of the real-space finite-difference scheme are introduced. These two methods can handle higher dimensional systems with consideration of the correlation effect. Furthermore, they can be easily extended to the multicomponent quantum systems which contain more than two kinds of quantum particles. The key to the present methods is employing linear combinations of nonorthogonal Slater determinants (SDs) as multi-body wavefunctions. As one of the noticeable results, the same accuracy as the variational Monte Carlo method is achieved with a few SDs. This enables us to study the entire ground state consisting of electrons and nuclei without the need to use the Born-Oppenheimer approximation. Recent activities on methodological developments aiming towards practical calculations such as the implementation of auxiliary field for Coulombic interaction, the treatment of the kinetic operator in imaginary-time evolutions, the time-saving double-grid technique for bare-Coulomb atomic potentials and the optimization scheme for minimizing the total-energy functional are also introduced. As test examples, the total energy of the hydrogen molecule, the atomic configuration of the methylene and the electronic structures of two-dimensional quantum dots are calculated, and the accuracy, availability and possibility of the present methods are demonstrated.
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Affiliation(s)
- Akira Sasaki
- Department of Precision Science and Technology, Graduate School of Engineering, Osaka University, Suita, Osaka, Japan
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62
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Kiss A, Pályi A, Ihara Y, Wzietek P, Simon P, Alloul H, Zólyomi V, Koltai J, Kürti J, Dóra B, Simon F. Enhanced NMR relaxation of Tomonaga-Luttinger liquids and the magnitude of the carbon hyperfine coupling in single-wall carbon nanotubes. PHYSICAL REVIEW LETTERS 2011; 107:187204. [PMID: 22107670 DOI: 10.1103/physrevlett.107.187204] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/08/2011] [Indexed: 05/31/2023]
Abstract
Recent transport measurements [Churchill et al. Nature Phys. 5, 321 (2009)] found a surprisingly large, 2-3 orders of magnitude larger than usual (13)C hyperfine coupling (HFC) in (13)C enriched single-wall carbon nanotubes. We formulate the theory of the nuclear relaxation time in the framework of the Tomonaga-Luttinger liquid theory to enable the determination of the HFC from recent data by Ihara et al. [Europhys. Lett. 90, 17,004 (2010)]. Though we find that 1/T(1) is orders of magnitude enhanced with respect to a Fermi-liquid behavior, the HFC has its usual, small value. Then, we reexamine the theoretical description used to extract the HFC from transport experiments and show that similar features could be obtained with HFC-independent system parameters.
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Affiliation(s)
- A Kiss
- Budapest University of Technology and Economics, Institute of Physics and Condensed Matter Research Group of the Hungarian Academy of Sciences, H-1521 Budapest, Hungary
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63
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Schroer MD, Petersson KD, Jung M, Petta JR. Field tuning the g factor in InAs nanowire double quantum dots. PHYSICAL REVIEW LETTERS 2011; 107:176811. [PMID: 22107563 DOI: 10.1103/physrevlett.107.176811] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/07/2011] [Indexed: 05/31/2023]
Abstract
We study the effects of magnetic and electric fields on the g factors of spins confined in a two-electron InAs nanowire double quantum dot. Spin sensitive measurements are performed by monitoring the leakage current in the Pauli blockade regime. Rotations of single spins are driven using electric-dipole spin resonance. The g factors are extracted from the spin resonance condition as a function of the magnetic field direction, allowing determination of the full g tensor. Electric and magnetic field tuning can be used to maximize the g-factor difference and in some cases altogether quench the electric-dipole spin resonance response, allowing selective single spin control.
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Affiliation(s)
- M D Schroer
- Department of Physics, Princeton University, Princeton, New Jersey 08544, USA
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64
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Pauli spin blockade in a highly tunable silicon double quantum dot. Sci Rep 2011; 1:110. [PMID: 22355627 PMCID: PMC3216592 DOI: 10.1038/srep00110] [Citation(s) in RCA: 75] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2011] [Accepted: 09/22/2011] [Indexed: 11/16/2022] Open
Abstract
Double quantum dots are convenient solid-state platforms to encode quantum information. Two-electron spin states can be detected and manipulated using quantum selection rules based on the Pauli exclusion principle, leading to Pauli spin blockade of electron transport for triplet states. Coherent spin states would be optimally preserved in an environment free of nuclear spins, which is achievable in silicon by isotopic purification. Here we report on a deliberately engineered, gate-defined silicon metal-oxide-semiconductor double quantum dot system. The electron occupancy of each dot and the inter-dot tunnel coupling are independently tunable by electrostatic gates. At weak inter-dot coupling we clearly observe Pauli spin blockade and measure a large intra-dot singlet-triplet splitting > 1 meV. The leakage current in spin blockade has a peculiar magnetic field dependence, unrelated to electron-nuclear effects and consistent with the effect of spin-flip cotunneling processes. The results obtained here provide excellent prospects for realising singlet-triplet qubits.
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65
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Brunner R, Shin YS, Obata T, Pioro-Ladrière M, Kubo T, Yoshida K, Taniyama T, Tokura Y, Tarucha S. Two-qubit gate of combined single-spin rotation and interdot spin exchange in a double quantum dot. PHYSICAL REVIEW LETTERS 2011; 107:146801. [PMID: 22107226 DOI: 10.1103/physrevlett.107.146801] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/18/2011] [Indexed: 05/31/2023]
Abstract
A crucial requirement for quantum-information processing is the realization of multiple-qubit quantum gates. Here, we demonstrate an electron spin-based all-electrical two-qubit gate consisting of single-spin rotations and interdot spin exchange in a double quantum dot. A partially entangled output state is obtained by the application of the two-qubit gate to an initial, uncorrelated state. We find that the degree of entanglement is controllable by the exchange operation time. The approach represents a key step towards the realization of universal multiple-qubit gates.
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Affiliation(s)
- R Brunner
- Quantum Spin Information Project, ICORP, Japan Science and Technology Agency, Atsugi-shi, Kanagawa, 243-0198, Japan.
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66
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Makhonin MN, Kavokin KV, Senellart P, Lemaître A, Ramsay AJ, Skolnick MS, Tartakovskii AI. Fast control of nuclear spin polarization in an optically pumped single quantum dot. NATURE MATERIALS 2011; 10:844-848. [PMID: 21874005 DOI: 10.1038/nmat3102] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/04/2011] [Accepted: 07/19/2011] [Indexed: 05/31/2023]
Abstract
Highly polarized nuclear spins within a semiconductor quantum dot induce effective magnetic (Overhauser) fields of up to several Tesla acting on the electron spin, or up to a few hundred mT for the hole spin. Recently this has been recognized as a resource for intrinsic control of quantum-dot-based spin quantum bits. However, only static long-lived Overhauser fields could be used. Here we demonstrate fast redirection on the microsecond timescale of Overhauser fields on the order of 0.5 T experienced by a single electron spin in an optically pumped GaAs quantum dot. This has been achieved using coherent control of an ensemble of 10(5) optically polarized nuclear spins by sequences of short radiofrequency pulses. These results open the way to a new class of experiments using radiofrequency techniques to achieve highly correlated nuclear spins in quantum dots, such as adiabatic demagnetization in the rotating frame leading to sub-μK nuclear spin temperatures, rapid adiabatic passage, and spin squeezing.
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67
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Abstract
Scaling down the size of computing circuits is about to reach the limitations imposed by the discrete atomic structure of matter. Reducing the power requirements and thereby dissipation of integrated circuits is also essential. New paradigms are needed to sustain the rate of progress that society has become used to. Single-atom transistors, SATs, cascaded in a circuit are proposed as a promising route that is compatible with existing technology. We demonstrate the use of quantum degrees of freedom to perform logic operations in a complementary-metal-oxide-semiconductor device. Each SAT performs multilevel logic by electrically addressing the electronic states of a dopant atom. A single electron transistor decodes the physical multivalued output into the conventional binary output. A robust scalable circuit of two concatenated full adders is reported, where by utilizing charge and quantum degrees of freedom, the functionality of the transistor is pushed far beyond that of a simple switch.
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68
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Takahashi R, Kono K, Tarucha S, Ono K. Voltage-selective bidirectional polarization and coherent rotation of nuclear spins in quantum dots. PHYSICAL REVIEW LETTERS 2011; 107:026602. [PMID: 21797631 DOI: 10.1103/physrevlett.107.026602] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/03/2011] [Indexed: 05/31/2023]
Abstract
We propose and demonstrate that the nuclear spins of the host lattice in GaAs double quantum dots can be polarized in either of two opposite directions, parallel or antiparallel to an external magnetic field. The direction is selected by adjusting the dc voltage. This nuclear polarization manifests itself by repeated controlled electron-nuclear spin scattering in the Pauli spin-blockade state. Polarized nuclei are also controlled by means of nuclear magnetic resonance. This Letter confirms that the nuclear spins in quantum dots are long-lived quantum states with a coherence time of up to 1 ms, and may be a promising resource for quantum-information processing such as quantum memories for electron spin qubits.
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Affiliation(s)
- R Takahashi
- Low Temperature Physics Laboratory, RIKEN, Wako, Saitama 351-0198, Japan
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69
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Shakouri K, Esmaeilzadeh M, Szafran B, Salehani HK. Electronic properties of a defected ring-shaped quantum dot array. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2011; 23:225801. [PMID: 21572222 DOI: 10.1088/0953-8984/23/22/225801] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
In this paper we present a theoretical study of an array of circularly arranged quantum dots with a rectangular Kronig-Penney potential in the presence of a perpendicular magnetic field. For a perfect array of dots, an analytical formula for energy dispersion is derived. We also study the effects of disorder on the energy spectrum and persistent tunneling current. The effects of electron-electron interaction are then investigated for both perfect and defected arrays. We show that the period of Aharonov-Bohm oscillations is fractional for interacting electrons confined in a perfect array. In contrast, for a defected array, we find a critical value of electron-electron interaction strength at which a transition occurs from an integer to a fractional period of Aharonov-Bohm oscillations. Moreover, it is shown that the persistent current of weakly interacting electrons confined in a defected array is greater than the current of non- or strongly interacting electrons.
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Affiliation(s)
- Kh Shakouri
- Department of Physics, Iran University of Science and Technology, Narmak, Tehran, Iran
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70
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Nadj-Perge S, Frolov SM, Bakkers EPAM, Kouwenhoven LP. Spin–orbit qubit in a semiconductor nanowire. Nature 2010; 468:1084-7. [DOI: 10.1038/nature09682] [Citation(s) in RCA: 532] [Impact Index Per Article: 38.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2010] [Accepted: 11/10/2010] [Indexed: 11/09/2022]
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71
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Ladd TD, Press D, De Greve K, McMahon PL, Friess B, Schneider C, Kamp M, Höfling S, Forchel A, Yamamoto Y. Pulsed nuclear pumping and spin diffusion in a single charged quantum dot. PHYSICAL REVIEW LETTERS 2010; 105:107401. [PMID: 20867546 DOI: 10.1103/physrevlett.105.107401] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/29/2009] [Indexed: 05/29/2023]
Abstract
We report the observation of a feedback process between the nuclear spins in a single charged quantum dot under coherently pulsed optical excitation and its trion transition. The optical pulse sequence intersperses resonant narrow-band pumping for spin initialization with off-resonant ultrafast pulses for coherent electron-spin rotation. A hysteretic sawtooth pattern in the free-induction decay of the single electron spin is observed; a mathematical model indicates a competition between optical nuclear pumping and nuclear spin-diffusion. This effect allows dynamic tuning of the electron Larmor frequency to a value determined by the pulse timing, potentially allowing more complex coherent control operations.
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Affiliation(s)
- Thaddeus D Ladd
- E. L. Ginzton Laboratory, Stanford University, Stanford, California 94305, USA.
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72
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Rudner MS, Levitov LS. Dynamical cooling of nuclear spins in double quantum dots. NANOTECHNOLOGY 2010; 21:274016. [PMID: 20571203 DOI: 10.1088/0957-4484/21/27/274016] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
Electrons trapped in quantum dots can exhibit quantum-coherent spin dynamics over long timescales. These timescales are limited by the coupling of electron spins to the disordered nuclear spin background, which is a major source of noise and dephasing in such systems. We propose a scheme for controlling and suppressing fluctuations of nuclear spin polarization in double quantum dots, which uses nuclear spin pumping in the spin-blockade regime. We show that nuclear spin polarization fluctuations can be suppressed when electronic levels in the two dots are properly positioned near resonance. The proposed mechanism is analogous to that of optical Doppler cooling. The Overhauser shift due to fluctuations of nuclear polarization brings electron levels in and out of resonance, creating internal feedback to suppress fluctuations. Estimates indicate that a better than 10-fold reduction of fluctuations is possible.
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Affiliation(s)
- M S Rudner
- Department of Physics, Harvard University, 17 Oxford Street, Cambridge, MA 02138, USA
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73
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Lupton JM, McCamey DR, Boehme C. Coherent Spin Manipulation in Molecular Semiconductors: Getting a Handle on Organic Spintronics. Chemphyschem 2010; 11:3040-58. [DOI: 10.1002/cphc.201000186] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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74
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Reilly DJ, Taylor JM, Petta JR, Marcus CM, Hanson MP, Gossard AC. Exchange control of nuclear spin diffusion in a double quantum dot. PHYSICAL REVIEW LETTERS 2010; 104:236802. [PMID: 20867261 DOI: 10.1103/physrevlett.104.236802] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/20/2009] [Indexed: 05/25/2023]
Abstract
The influence of gate-controlled two-electron exchange on the relaxation of nuclear polarization in small ensembles (N∼10(6)) of nuclear spins is examined in a GaAs double quantum dot system. Waiting in the (2,0) charge configuration, which has large exchange splitting, reduces the nuclear diffusion rate compared to that of the (1,1) configuration. Matching exchange to Zeeman splitting significantly increases the nuclear diffusion rate.
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Affiliation(s)
- D J Reilly
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
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75
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McCamey DR, van Schooten KJ, Baker WJ, Lee SY, Paik SY, Lupton JM, Boehme C. Hyperfine-field-mediated spin beating in electrostatically bound charge carrier pairs. PHYSICAL REVIEW LETTERS 2010; 104:017601. [PMID: 20366393 DOI: 10.1103/physrevlett.104.017601] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/16/2009] [Indexed: 05/29/2023]
Abstract
Organic semiconductors offer a unique environment to probe the hyperfine coupling of electronic spins to a nuclear spin bath. We explore the interaction of spins in electron-hole pairs in the presence of inhomogeneous hyperfine fields by monitoring the modulation of the current through an organic light emitting diode under coherent spin-resonant excitation. At weak driving fields, only one of the two spins in the pair precesses. As the driving field exceeds the difference in local hyperfine field experienced by electron and hole, both spins precess, leading to pronounced spin beating in the transient Rabi flopping of the current. We use this effect to measure the magnitude and spatial variation in hyperfine field on the scale of single carrier pairs, as required for evaluating models of organic magnetoresistance, improving organic spintronics devices, and illuminating spin decoherence mechanisms.
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Affiliation(s)
- D R McCamey
- Department of Physics and Astronomy, University of Utah, 115 South 1400 East, Salt Lake City, Utah 84112, USA
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76
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Bodoky F, Gühne O, Blaauboer M. Modeling the decay of entanglement for electron spin qubits in quantum dots. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2009; 21:395602. [PMID: 21832394 DOI: 10.1088/0953-8984/21/39/395602] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
We investigate the time evolution of entanglement under various models of decoherence: a general heuristic model based on local relaxation and dephasing times, and two microscopic models describing decoherence of electron spin qubits in quantum dots due to the hyperfine interaction with the nuclei. For each of the decoherence models, we investigate and compare how long the entanglement can be detected. We also introduce filtered witness operators, which extend the available detection time and investigate this detection time for various multipartite entangled states. By comparing the time required for detection with the time required for generation and manipulation of entanglement, we estimate for a range of different entangled states how many qubits can be entangled in a one-dimensional array of electron spin qubits.
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Affiliation(s)
- F Bodoky
- Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands
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77
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Trif M, Simon P, Loss D. Relaxation of hole spins in quantum dots via two-phonon processes. PHYSICAL REVIEW LETTERS 2009; 103:106601. [PMID: 19792331 DOI: 10.1103/physrevlett.103.106601] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/23/2009] [Indexed: 05/28/2023]
Abstract
We investigate theoretically spin relaxation in heavy-hole quantum dots in low external magnetic fields. We demonstrate that two-phonon processes and spin-orbit interaction are experimentally relevant and provide an explanation for the recently observed saturation of the spin-relaxation rate in heavy-hole quantum dots with vanishing magnetic fields. We propose further experiments to identify the relevant spin-relaxation mechanisms in low magnetic fields.
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Affiliation(s)
- Mircea Trif
- Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
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78
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Yokoshi N, Imamura H, Kosaka H. Electrical measurement of a two-electron spin state in a double quantum dot. PHYSICAL REVIEW LETTERS 2009; 103:046806. [PMID: 19659384 DOI: 10.1103/physrevlett.103.046806] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/20/2009] [Indexed: 05/28/2023]
Abstract
We propose a scheme for electrical measurement of two-electron spin states in a semiconductor double quantum dot. We calculated the adiabatic charge transfer when surface gates are modulated in time. Because of spin-orbit coupling in the semiconductor, spatial displacement of the electrons causes a total spin rotation. It follows that the expectation value of the transferred charge reflects the relative phase as well as the total spin population of a prepared singlet-triplet superposition state. The precise detection of the charge transfer serves to identify the quantum superposition.
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79
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Danon J, Vink IT, Koppens FHL, Nowack KC, Vandersypen LMK, Nazarov YV. Multiple nuclear polarization States in a double quantum dot. PHYSICAL REVIEW LETTERS 2009; 103:046601. [PMID: 19659378 DOI: 10.1103/physrevlett.103.046601] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/16/2009] [Indexed: 05/28/2023]
Abstract
We observe multiple stable states of nuclear polarization and nuclear self-tuning over a large range of fields in a double quantum dot under conditions of electron spin resonance. The observations can be understood within an elaborated theoretical rate equation model for the polarization in each of the dots, in the limit of strong driving. This model also captures unusual features of the data, such as fast switching and a "wrong" sign of polarization. The results reported enable applications of this polarization effect, including accurate manipulation and control of nuclear fields.
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Affiliation(s)
- J Danon
- Kavli Institute of NanoScience, Delft University of Technology, 2628 CJ Delft, The Netherlands
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80
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Wang L, Rastelli A, Kiravittaya S, Benyoucef M, Schmidt OG. Self-Assembled Quantum Dot Molecules. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2009; 21:2601-2618. [PMID: 36751061 DOI: 10.1002/adma.200803109] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/22/2008] [Revised: 03/02/2009] [Indexed: 06/18/2023]
Abstract
Semiconductor quantum dot molecules (QDMs) are systems composed of two or more closely spaced and interacting QDs. QDMs are receiving much attention both as playground for studying coupling and energy transfer processes between "artificial atoms" and as new systems, which substantially extend the range of possible applications of QDs. QDMs can be conveniently fabricated by self-assembly either through chemical synthesis or epitaxial growth. Although QDMs relying on the random occurrence of nearby QDs can be used for fundamental studies, special fabrication protocols must be used to create QDMs with well-defined properties. In this article, we focus on self-assembled QDMs obtained by epitaxial growth and embedded in a semiconductor matrix, which are appealing for the possible realization of quantum gates based on two-level systems defined in QDs. We provide a comprehensive overview of the development and current stage of the research on QDMs composed of vertically (in the growth direction) or laterally (in the growth plane) aligned QDs. The review highlights some recent milestone works and points out the challenges and future directions in the field.
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Affiliation(s)
- Lijuan Wang
- Max-Planck-Institut für Festkörperforschung Heisenbergstr. 1, 70569 Stuttgart (Germany)
| | - Armando Rastelli
- Institute for Integrative Nanosciences, IFW Dresden Helmholtzstr. 20, 01069 Dresden (Germany)
| | - Suwit Kiravittaya
- Max-Planck-Institut für Festkörperforschung Heisenbergstr. 1, 70569 Stuttgart (Germany)
| | - Mohamed Benyoucef
- Max-Planck-Institut für Festkörperforschung Heisenbergstr. 1, 70569 Stuttgart (Germany)
- Institute for Integrative Nanosciences, IFW Dresden Helmholtzstr. 20, 01069 Dresden (Germany)
| | - Oliver G Schmidt
- Institute for Integrative Nanosciences, IFW Dresden Helmholtzstr. 20, 01069 Dresden (Germany)
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81
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Optically controlled locking of the nuclear field via coherent dark-state spectroscopy. Nature 2009; 459:1105-9. [DOI: 10.1038/nature08120] [Citation(s) in RCA: 191] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2008] [Accepted: 05/05/2009] [Indexed: 11/08/2022]
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82
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Cappellaro P, Jiang L, Hodges JS, Lukin MD. Coherence and control of quantum registers based on electronic spin in a nuclear spin bath. PHYSICAL REVIEW LETTERS 2009; 102:210502. [PMID: 19519089 DOI: 10.1103/physrevlett.102.210502] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/06/2009] [Indexed: 05/27/2023]
Abstract
We consider a protocol for the control of few-qubit registers comprising one electronic spin embedded in a nuclear spin bath. We show how to isolate a few proximal nuclear spins from the rest of the bath and use them as building blocks for a potentially scalable quantum information processor. We describe how coherent control techniques based on magnetic resonance methods can be adapted to these solid-state spin systems, to provide not only efficient, high fidelity manipulation but also decoupling from the spin bath. As an example, we analyze feasible performances and practical limitations in the realistic setting of nitrogen-vacancy centers in diamond.
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Affiliation(s)
- P Cappellaro
- Harvard-Smithsonian Center for Astrophysics, Physics Department, Harvard University, Cambridge, Massachusetts 02138, USA
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83
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Qassemi F, Coish WA, Wilhelm FK. Stationary and transient leakage current in the Pauli spin blockade. PHYSICAL REVIEW LETTERS 2009; 102:176806. [PMID: 19518811 DOI: 10.1103/physrevlett.102.176806] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/15/2008] [Indexed: 05/27/2023]
Abstract
We study the effects of cotunneling and a nonuniform Zeeman splitting on the stationary and transient leakage current through a double quantum dot in the Pauli spin blockade regime. We find that the stationary current due to cotunneling vanishes at low temperature and large applied magnetic field, allowing for the dynamical (rapid) preparation of a pure spin ground state, even at large voltage bias. Additionally, we analyze current that flows between blocking events, characterized, in general, by a fractional effective charge e*. This charge can be used as a sensitive probe of spin-relaxation mechanisms and can be used to determine the visibility of Rabi oscillations.
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Affiliation(s)
- F Qassemi
- Institute for Quantum Computing and Department of Physics and Astronomy, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
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84
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Kodera T, Ono K, Kitamura Y, Tokura Y, Arakawa Y, Tarucha S. Quantitative estimation of exchange interaction energy using two-electron vertical double quantum dots. PHYSICAL REVIEW LETTERS 2009; 102:146802. [PMID: 19392466 DOI: 10.1103/physrevlett.102.146802] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/26/2009] [Indexed: 05/27/2023]
Abstract
We use Pauli-spin blockade in two-electron vertical double quantum dots to quantitatively estimate the exchange energy J in a wide range of interdot level detuning Delta and fully compare it with calculations. Pauli-spin blockade is lifted via a singlet- (S-)triplet (T) transition mediated by hyperfine coupling, which abruptly occurs in our devices when the S-T transition energy or J is compensated by the Zeeman energy. We use this feature to derive J depending on Delta between the S-S and T-T resonances. The obtained J versus Delta including the resonance effect is perfectly reproduced by Hubbard model calculations.
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Affiliation(s)
- T Kodera
- Institute for Nano Quantum Information Electronics, the University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan.
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85
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Reilly DJ, Taylor JM, Laird EA, Petta JR, Marcus CM, Hanson MP, Gossard AC. Measurement of temporal correlations of the overhauser field in a double quantum dot. PHYSICAL REVIEW LETTERS 2008; 101:236803. [PMID: 19113577 DOI: 10.1103/physrevlett.101.236803] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/24/2007] [Indexed: 05/27/2023]
Abstract
In quantum dots made from materials with nonzero nuclear spins, hyperfine coupling creates a fluctuating effective Zeeman field (Overhauser field) felt by electrons, which can be a dominant source of spin qubit decoherence. We characterize the spectral properties of the fluctuating Overhauser field in a GaAs double quantum dot by measuring correlation functions and power spectra of the rate of singlet-triplet mixing of two separated electrons. Away from zero field, spectral weight is concentrated below 10 Hz, with approximately 1/f2 dependence on frequency f. This is consistent with a model of nuclear spin diffusion, and indicates that decoherence can be largely suppressed by echo techniques.
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Affiliation(s)
- D J Reilly
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
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86
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Lin ZR, Guo GP, Tu T, Zhu FY, Guo GC. Generation of quantum-dot cluster States with a superconducting transmission line resonator. PHYSICAL REVIEW LETTERS 2008; 101:230501. [PMID: 19113532 DOI: 10.1103/physrevlett.101.230501] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/20/2008] [Indexed: 05/27/2023]
Abstract
We propose an efficient method to generate cluster states in spatially separated double quantum dots with a superconducting transmission line resonator. When the detuning between the double-dot qubit transition frequency and the frequency of the full wave mode in the transmission line resonator satisfies some conditions, an Ising-like operator between an arbitrary two separated qubits can be achieved. Even including the main noise sources, it is shown that the high fidelity cluster states could be generated in this solid system in just one step.
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Affiliation(s)
- Zhi-Rong Lin
- Key Laboratory of Quantum Information, University of Science and Technology of China, Chinese Academy of Sciences, Hefei 230026, People's Republic of China
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87
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Sadiek G, Huang Z, Aldossary O, Kais S. Nuclear-induced time evolution of entanglement of two-electron spins in anisotropically coupled quantum dot. Mol Phys 2008. [DOI: 10.1080/00268970802290313] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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88
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Prezhdo OV. Multiple excitons and the electron–phonon bottleneck in semiconductor quantum dots: An ab initio perspective. Chem Phys Lett 2008. [DOI: 10.1016/j.cplett.2008.03.099] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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89
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90
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Koppens FHL, Nowack KC, Vandersypen LMK. Spin echo of a single electron spin in a quantum dot. PHYSICAL REVIEW LETTERS 2008; 100:236802. [PMID: 18643533 DOI: 10.1103/physrevlett.100.236802] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/03/2007] [Indexed: 05/26/2023]
Abstract
We report a measurement of the spin-echo decay of a single electron spin confined in a semiconductor quantum dot. When we tip the spin in the transverse plane via a magnetic field burst, it dephases in 37 ns due to the Larmor precession around a random effective field from the nuclear spins in the host material. We reverse this dephasing to a large extent via a spin-echo pulse, and find a spin-echo decay time of about 0.5 micros at 70 mT. These results are in the range of theoretical predictions of the electron spin coherence time governed by the electron-nuclear dynamics.
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Affiliation(s)
- F H L Koppens
- Kavli Institute of NanoScience Delft, Delft, The Netherlands
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91
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Stopa M, Marcus CM. Magnetic field control of exchange and noise immunity in double quantum dots. NANO LETTERS 2008; 8:1778-1782. [PMID: 18494532 DOI: 10.1021/nl801282t] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
We employ density functional calculated eigenstates as a basis for exact diagonalization studies of semiconductor double quantum dots, with two electrons, through the transition from the symmetric bias regime to the regime where both electrons occupy the same dot. We calculate the singlet-triplet splitting J(epsilon) as a function of bias detuning epsilon and explain its functional shape with a simple, double anticrossing model. A voltage noise suppression "sweet spot," where d J(epsilon)/d(epsilon) = 0 with nonzero J(epsilon), is predicted and shown to be tunable with a magnetic field B.
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Affiliation(s)
- M Stopa
- Center for Nanoscale Systems, and Department of Physics, Harvard University, Cambridge, MA 02138, USA.
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92
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Petta JR, Taylor JM, Johnson AC, Yacoby A, Lukin MD, Marcus CM, Hanson MP, Gossard AC. Dynamic nuclear polarization with single electron spins. PHYSICAL REVIEW LETTERS 2008; 100:067601. [PMID: 18352516 DOI: 10.1103/physrevlett.100.067601] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/06/2007] [Indexed: 05/26/2023]
Abstract
We polarize nuclear spins in a GaAs double quantum dot by controlling two-electron spin states near the anticrossing of the singlet (S) and m(S)= +1 triplet (T+) using pulsed gates. An initialized S state is cyclically brought into resonance with the T+ state, where hyperfine fields drive rapid rotations between S and T+, "flipping" an electron spin and "flopping" a nuclear spin. The resulting Overhauser field approaches 80 mT, in agreement with a simple rate-equation model. A self-limiting pulse sequence is developed that allows the steady-state nuclear polarization to be set using a gate voltage.
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Affiliation(s)
- J R Petta
- Department of Physics, Harvard University, 17 Oxford St., Cambridge, Massachusetts 02138, USA
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93
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Danon J, Nazarov YV. Nuclear tuning and detuning of the electron spin resonance in a quantum dot: theoretical consideration. PHYSICAL REVIEW LETTERS 2008; 100:056603. [PMID: 18352405 DOI: 10.1103/physrevlett.100.056603] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/04/2007] [Indexed: 05/26/2023]
Abstract
We study nuclear spin dynamics in a quantum dot close to the conditions of electron spin resonance. We show that at a small frequency mismatch, the nuclear field detunes the resonance. Remarkably, at larger frequency mismatch, its effect is opposite: The nuclear system is bistable, and in one of the stable states, the field accurately tunes the electron spin splitting to resonance. In this state, the nuclear field fluctuations are strongly suppressed, and nuclear spin relaxation is accelerated.
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Affiliation(s)
- Jeroen Danon
- Kavli Institute of NanoScience, Delft University of Technology, 2628 CJ Delft, The Netherlands
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94
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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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95
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Optical pumping of a single hole spin in a quantum dot. Nature 2008; 451:441-4. [DOI: 10.1038/nature06472] [Citation(s) in RCA: 338] [Impact Index Per Article: 21.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2007] [Accepted: 11/06/2007] [Indexed: 11/09/2022]
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96
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Rudner MS, Levitov LS. Electrically driven reverse overhauser pumping of nuclear spins in quantum dots. PHYSICAL REVIEW LETTERS 2007; 99:246602. [PMID: 18233468 DOI: 10.1103/physrevlett.99.246602] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/04/2007] [Indexed: 05/25/2023]
Abstract
We propose a new mechanism for polarizing nuclear spins in quantum dots, based on periodic modulation of the hyperfine coupling by electric driving at the electron spin resonance frequency. Dynamical nuclear polarization results from resonant excitation rather than hyperfine relaxation mediated by a thermal bath, and thus is not subject to Overhauser-like detailed balance constraints. This allows polarization in the direction opposite to that expected from the Overhauser effect. Competition of the electrically driven and bath-assisted mechanisms can give rise to spatial modulation and sign reversal of polarization on a scale smaller than the electron confinement radius in the dot.
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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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97
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Laird EA, Barthel C, Rashba EI, Marcus CM, Hanson MP, Gossard AC. Hyperfine-mediated gate-driven electron spin resonance. PHYSICAL REVIEW LETTERS 2007; 99:246601. [PMID: 18233467 DOI: 10.1103/physrevlett.99.246601] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/03/2007] [Indexed: 05/25/2023]
Abstract
An all-electrical spin resonance effect in a GaAs few-electron double quantum dot is investigated experimentally and theoretically. The magnetic field dependence and absence of associated Rabi oscillations are consistent with a novel hyperfine mechanism. The resonant frequency is sensitive to the instantaneous hyperfine effective field, and the effect can be used to detect and create sizable nuclear polarizations. A device incorporating a micromagnet exhibits a magnetic field difference between dots, allowing electrons in either dot to be addressed selectively.
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Affiliation(s)
- E A Laird
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
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98
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Nowack KC, Koppens FHL, Nazarov YV, Vandersypen LMK. Coherent Control of a Single Electron Spin with Electric Fields. Science 2007; 318:1430-3. [PMID: 17975030 DOI: 10.1126/science.1148092] [Citation(s) in RCA: 246] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Affiliation(s)
- K C Nowack
- Kavli Institute of Nanoscience, Delft University of Technology, Post Office Box 5046, 2600 GA Delft, the Netherlands.
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99
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Greilich A, Shabaev A, Yakovlev DR, Efros AL, Yugova IA, Reuter D, Wieck AD, Bayer M. Nuclei-Induced Frequency Focusing of Electron Spin Coherence. Science 2007; 317:1896-9. [PMID: 17901328 DOI: 10.1126/science.1146850] [Citation(s) in RCA: 198] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The hyperfine interaction of an electron with the nuclei is considered as the primary obstacle to coherent control of the electron spin in semiconductor quantum dots. We show, however, that the nuclei in singly charged quantum dots act constructively by focusing the electron spin precession about a magnetic field into well-defined modes synchronized with a laser pulse protocol. In a dot with a synchronized electron, the light-stimulated fluctuations of the hyperfine nuclear field acting on the electron are suppressed. The information about electron spin precession is imprinted in the nuclei and thereby can be stored for tens of minutes in darkness. The frequency focusing drives an electron spin ensemble into dephasing-free subspaces with the potential to realize single frequency precession of the entire ensemble.
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Affiliation(s)
- A Greilich
- Experimentelle Physik II, Universität Dortmund, D-44221 Dortmund, Germany
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100
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Koppens FHL, Klauser D, Coish WA, Nowack KC, Kouwenhoven LP, Loss D, Vandersypen LMK. Universal phase shift and nonexponential decay of driven single-spin oscillations. PHYSICAL REVIEW LETTERS 2007; 99:106803. [PMID: 17930403 DOI: 10.1103/physrevlett.99.106803] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/24/2007] [Indexed: 05/25/2023]
Abstract
We study, both theoretically and experimentally, driven Rabi oscillations of a single electron spin coupled to a nuclear-spin bath. Because of the long correlation time of the bath, two unusual features are observed in the oscillations. The decay follows a power law, and the oscillations are shifted in phase by a universal value of approximately pi/4. These properties are well understood from a theoretical expression that we derive here in the static limit for the nuclear bath. This improved understanding of the coupled electron-nuclear system is important for future experiments using the electron spin as a qubit.
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Affiliation(s)
- F H L Koppens
- Kavli Institute of NanoScience Delft, P.O. Box 5046, 2600 GA Delft, The Netherlands
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