Universal quantum control of two-electron spin quantum bits using dynamic nuclear polarization

Foletti, Sandra; Bluhm, Hendrik; Mahalu, D.; Umansky, V.; Yacoby, Amir

doi:10.1038/nphys1424

Cited by 422 publications

(626 citation statements)

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“…We choose the inter-dot distance to be 40 nm in order to have distinct dots that still have appreciable tunnel coupling and exchange. This is a smaller interdot distance than is typical for experiments, [3][4][5] but that is simply because the dots themselves are smaller here. The qualitative behavior should be similar.…”

Section: B Parameter Choicesmentioning

confidence: 82%

“…2,3 Recent experiments have made tremendous advances along these lines, demonstrating single-qubit initialization, arbitrary manipulation, and single-shot readout, all within a fraction of the coherence time of the qubit. [3][4][5][6][7] Preliminary steps toward an entangling two-qubit gate have also been reported. 8 In principle, successful completion of that program leaves the (admittedly enormous) challenge of scaling up to large numbers of qubits as the last remaining hurdle in the fabrication of a practical quantum computer.…”

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confidence: 99%

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Screening of charged impurities with multielectron singlet-triplet spin qubits in quantum dots

et al. 2011

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Charged impurities in semiconductor quantum dots comprise one of the main obstacles to achieving scalable fabrication and manipulation of singlet-triplet spin qubits. We theoretically show that using dots that contain several electrons each can help to overcome this problem through the screening of the rough and noisy impurity potential by the excess electrons. We demonstrate how the desired screening properties turn on as the number of electrons is increased, and we characterize the properties of a double quantum dot singlet-triplet qubit for small odd numbers of electrons per dot. We show that the sensitivity of the multi-electron qubit to charge noise may be an order of magnitude smaller than that of the two-electron qubit.One of the most promising paths to scalable quantum computation is to use laterally defined double quantum dots (DQDs) in semiconductor heterostructures. The qubit is formed by the spin states of the two-electron DQD with total spin projection zero along the z axis. 1,2 Such a qubit is insensitive to spatially uniform magnetic field fluctuations, and, most importantly, amenable to fast electrical manipulation. 2,3 Recent experiments have made tremendous advances along these lines, demonstrating single-qubit initialization, arbitrary manipulation, and single-shot readout, all within a fraction of the coherence time of the qubit. 3-7 Preliminary steps toward an entangling two-qubit gate have also been reported. 8 In principle, successful completion of that program leaves the (admittedly enormous) challenge of scaling up to large numbers of qubits as the last remaining hurdle in the fabrication of a practical quantum computer.However, a practical issue has emerged which threatens to be a crippling impediment to continued rapid progress. The semiconductor samples used to create quantum dots invariably contain a number of charge impurity centers, perhaps 10 10 cm −2 in GaAs systems. 9 Even if the charge on these centers can be frozen to avoid switching noise, their presence inhibits access to the oneelectron-per-dot regime since the lowest energy states of the dot may be fragmented due to the roughened potential landscape. [10][11][12][13] This makes it difficult to find samples suitable for spin qubit realization. Furthermore, typically the impurities do introduce some switching noise, [14][15][16][17] so that even in samples in which the impurities are all far enough from the DQD that a two-electron singlettriplet qubit can be accessed, the interdot exchange energy is still subject to random fluctuation, leading to gate errors and decoherence. [18][19][20] This necessitates operating in a parameter regime such that the sensitivity of the exchange energy to the charge noise is minimized, a so-called "sweet spot". 21 In general, the charge noise problem is even more pernicious when performing twoqubit operations directly mediated by the Coulomb interaction, and one must again seek a sweet spot. 22,23 However, in practice, this strategy may not be sufficient since one typically cannot optimize ov...

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Section: B Parameter Choicesmentioning

confidence: 82%

mentioning

confidence: 99%

Screening of charged impurities with multielectron singlet-triplet spin qubits in quantum dots

et al. 2011

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“…[2][3][4] In GaAs-based qubits, which are the state of the art, the essential gate operations 1, 5,6 for quantum computation 7,8 have been demonstrated. [9][10][11][12][13][14][15][16][17][18] But GaAs possesses a serious handicap for coherent spin manipulations-the nuclear spins. 19,20 Controlling this source of decoherence is of major interest and an active field of research.…”

Section: Introductionmentioning

confidence: 99%

“…19,20 Controlling this source of decoherence is of major interest and an active field of research. 18,[21][22][23][24][25][26] Alternatives to III-V semiconductors with inherent nuclear spins are systems composed of atoms without nuclear magnetic moments, such as Si and C. [27][28][29] Natural silicon consists of three isotopes: 28 Si (92.2%), 29 Si (4.7%), and 30 Si (3.1%). 30 Hereof only 29 Si has nonzero nuclear spin (I = 1/2), and purification can further reduce its abundance down to 0.05%.…”

Section: Introductionmentioning

confidence: 99%

Theory of spin relaxation in two-electron laterally coupled Si/SiGe quantum dots

2012

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Highly accurate numerical results of phonon-induced two-electron spin relaxation in silicon double quantum dots are presented. The relaxation, enabled by spin-orbit coupling and the nuclei of 29 Si (natural or purified abundance), is investigated for experimentally relevant parameters, the interdot coupling, the magnetic field magnitude and orientation, and the detuning. We calculate relaxation rates for zero and finite temperatures (100 mK), concluding that our findings for zero temperature remain qualitatively valid also for 100 mK. We confirm the same anisotropic switch of the axis of prolonged spin lifetime with varying detuning as recently predicted in GaAs. Conditions for possibly hyperfine-dominated relaxation are much more stringent in Si than in GaAs. For experimentally relevant regimes, the spin-orbit coupling, although weak, is the dominant contribution, yielding anisotropic relaxation rates of at least two orders of magnitude lower than in GaAs.

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“…A high quality two-dimensional electron gas is induced by a field-effect and is tunable over a wide range of density. Device design, fabrication, and low temperature (T= 0.3K) transport data are reported.Nanostructures such as quantum point contacts and quantum dots fabricated on modulation-doped AlGaAs/GaAs heterostructures are widely used to explore nanoscale electron transport and are utilized extensively in spin-based approaches to quantum computing [1][2][3][4][5][6][7][8]. Modulation-doped GaAs/AlGaAs heterostructures possess several desirable attributes including very high mobility of the underlying two-dimensional electron gas (2DEG) and the relative ease of nanostructure fabrication.…”

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confidence: 99%

Field-effect-induced two-dimensional electron gas utilizing modulation-doped ohmic contacts

Mondal

Gardner

Watson

et al. 2014

Solid State Communications

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Modulation-doped AlGaAs/GaAs heterostructures are utilized extensively in the study of quantum transport in nanostructures, but charge fluctuations associated with remote ionized dopants often produce deleterious effects. Electric field-induced carrier systems offer an attractive alternative if certain challenges can be overcome. We demonstrate a field-effect transistor in which the active channel is locally devoid of modulation-doping, but silicon dopant atoms are retained in the ohmic contact region to facilitate reliable lowresistance contacts. A high quality two-dimensional electron gas is induced by a field-effect and is tunable over a wide range of density. Device design, fabrication, and low temperature (T= 0.3K) transport data are reported.Nanostructures such as quantum point contacts and quantum dots fabricated on modulation-doped AlGaAs/GaAs heterostructures are widely used to explore nanoscale electron transport and are utilized extensively in spin-based approaches to quantum computing [1][2][3][4][5][6][7][8]. Modulation-doped GaAs/AlGaAs heterostructures possess several desirable attributes including very high mobility of the underlying two-dimensional electron gas (2DEG) and the relative ease of nanostructure fabrication. However, the presence of ionized dopants inherent to modulationdoping can have adverse effects on the behavior of nanostructures and are a possible source of decoherence for spin-qubits [9,10]. Ionized dopants can act as active trapping sites for electrons injected from the metal surface gate through the Schottky barrier [11], giving rise to random switching of the charge state of the impurities. These fluctuations cause instability through a time-dependent potential landscape [10][11][12][13]. Methods such as 'bias cooling' in which nanostructures are cooled while a positive bias applied to the gates aid in reducing fluctuations [11], but charge noise is still believed to a dominant mechanism limiting gate fidelities in spin qubits [9].

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Universal quantum control of two-electron spin quantum bits using dynamic nuclear polarization

Abstract: . 2009. Universal quantum control of two-electron spin quantum bits using dynamic nuclear polarization. Nature Physics 5(12): 903-908.Published Version

Cited by 422 publications

References 30 publications

Screening of charged impurities with multielectron singlet-triplet spin qubits in quantum dots

Screening of charged impurities with multielectron singlet-triplet spin qubits in quantum dots

Theory of spin relaxation in two-electron laterally coupled Si/SiGe quantum dots

Field-effect-induced two-dimensional electron gas utilizing modulation-doped ohmic contacts

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