Isotopically enhanced triple-quantum-dot qubit

Eng, Kevin; Ladd, Thaddeus D.; Smith, Aaron; Borselli, Matthew; Kiselev, A. A.; Fong, Bryan H.; Holabird, K.S.; Hazard, Thomas; Huang, Biqin; Deelman, Peter W.; Milosavljevic, I.; Schmitz, A.; Ross, Richard S.; Gyure, Mark F.; Hunter, A. T.

doi:10.1126/sciadv.1500214

Cited by 226 publications

(240 citation statements)

References 31 publications

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“…This technique is routinely used for read out in spin qubits [60][61][62]. Quantum-dot charge sensors have also been implemented in nanowires, obtaining couplings similar to the GaAs case [63,64].…”

Section: Read Out Methodsmentioning

confidence: 99%

Milestones Toward Majorana-Based Quantum Computing

et al. 2016

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We introduce a scheme for preparation, manipulation, and read out of Majorana zero modes in semiconducting wires with mesoscopic superconducting islands. Our approach synthesizes recent advances in materials growth with tools commonly used in quantum-dot experiments, including gate control of tunnel barriers and Coulomb effects, charge sensing, and charge pumping. We outline a sequence of milestones interpolating between zero-mode detection and quantum computing that includes (1) detection of fusion rules for non-Abelian anyons using either proximal charge sensors or pumped current, (2) validation of a prototype topological qubit, and (3) demonstration of non-Abelian statistics by braiding in a branched geometry. The first two milestones require only a single wire with two islands, and additionally enable sensitive measurements of the system's excitation gap, quasiparticle poisoning rates, residual Majorana zero-mode splittings, and topological-qubit coherence times. These pre-braiding experiments can be adapted to other manipulation and read out schemes as well.

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Section: Read Out Methodsmentioning

confidence: 99%

Milestones Toward Majorana-Based Quantum Computing

et al. 2016

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“…"singlet-triplet") [7][8][9][10], 3-DFS (a.k.a. "exchange-only") [11][12][13][14], or 4-DFS qubits [15] of various implementations are possible. The DFS gives some immunity to global field fluctuations, but more importantly it allows for gate operations via a sequence of pair-wise exchange interactions between spins with fast, baseband voltage control on the metallic top-gates, obviating the need for RF pulses.…”

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confidence: 99%

Charge-noise-insensitive gate operations for always-on, exchange-only qubits

2016

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We introduce an always-on, exchange-only qubit made up of three localized semiconductor spins that offers a true "sweet spot" to fluctuations of the quantum dot energy levels. Both single-and two-qubit gate operations can be performed using only exchange pulses while maintaining this sweet spot. We show how to interconvert this qubit to other three-spin encoded qubits as a new resource for quantum computation and communication.Semiconductor qubits [1,2] are a leading candidate technology for quantum information processing [3]. Spins can have extremely long quantum coherence due to a decoupling of spin information from charge noise in many materials, and they are small, enabling high density. But these strengths pose a challenge for control as microwave pulses generally result in slow gates with significant potential for crosstalk to nearby qubits. The exchange interaction on the other hand provides a natural and fast method for entangling semiconductor qubits: it can be used to perform two-spin entangling operations with a finite-length voltage pulse or to couple spins with a constant interaction. Exchange also provides a solution to the control problem by allowing a two-level system to be encoded into the greater Hilbert space of multiple physical spins. Following work on decoherence free subspaces and subsystems (DFS) [4][5][6], many multi-spinbased qubits have been proposed and demonstrated with various desirable properties for quantum computing: as examples, 2-DFS (a.k.a. "singlet-triplet") [7][8][9][10], 3-DFS (a.k.a. "exchange-only") [11][12][13][14], or 4-DFS qubits [15] of various implementations are possible. The DFS gives some immunity to global field fluctuations, but more importantly it allows for gate operations via a sequence of pair-wise exchange interactions between spins with fast, baseband voltage control on the metallic top-gates, obviating the need for RF pulses. However, charge noise likely limits gate fidelity [16,17] as charge and spin are coupled while spins undergo exchange.The effects of charge (or other) noise on memory or gate fidelity can be suppressed to a certain extent by taking advantage of natural or engineered "sweet" spots: a spot in parameter space where critical system properties are minimally effected by certain environmental changes. Sweet spots have been an effective tool to increase the coherence of superconducting qubits [18,19] and more recently have been applied to exchange-only qubits [20][21][22][23][24]. For example, in the "resonant exchange" (RX) qubit-an encoded qubit made out of 3 quantum dot qubits with "always-on" exchange interactions and a much higher chemical potential for the middle dot than the outer dots-a partial sweet spot is maintained while microwave control allows for single qubit operations [20,21] "resonant" with the gap of the 3-spin system. The first derivative of the RX qubit frequency vanishes for one of the two detuning parameters that are affected by charge noise. For two qubit gates, the RX qubit offers a relatively large transition dipole...

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“…1,2 Recent progress in semiconductor quantum-dot structures have shown long single-spin coherence times and high-fidelity coherent operations. [3][4][5][6][7] Furthermore, linear arrays have been successfully scaled to triple and quadruple dots, [8][9][10][11][12] and 2 × 2 arrays have been demonstrated as well. 13 However, there are practical limitations to the size of tunnel-coupled quantum dot arrays in one or two dimensions.…”

Section: Introductionmentioning

confidence: 99%

Coherent shuttle of electron-spin states

et al. 2017

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We demonstrate a coherent spin shuttle through a GaAs/AlGaAs quadruple-quantum-dot array. Starting with two electrons in a spin-singlet state in the first dot, we shuttle one electron over to either the second, third, or fourth dot. We observe that the separated spin-singlet evolves periodically into the m = 0 spin-triplet and back before it dephases due to nuclear spin noise. We attribute the time evolution to differences in the local Zeeman splitting between the respective dots. With the help of numerical simulations, we analyze and discuss the visibility of the singlet-triplet oscillations and connect it to the requirements for coherent spin shuttling in terms of the inter-dot tunnel coupling strength and rise time of the pulses. The distribution of entangled spin pairs through tunnel coupled structures may be of great utility for connecting distant qubit registers on a chip. 13 However, there are practical limitations to the size of tunnel-coupled quantum dot arrays in one or two dimensions. Integrating larger numbers of qubits can be achieved by coherently connecting distant qubit registers on a chip.14-17 Such coherent links could also serve to connect different functions such as memory and processor units.2 As an alternative to coherent spin-spin coupling at a distance, the physical transfer of electrons across the chip while preserving the spin information can serve as an interface between separated quantum dot arrays. 2,18 This is similar in spirit to experiments with trapped ions that were shuttled around through segmented ion traps. 19,20 To our knowledge, there are no demonstrations of the transfer of single electron spins coherently through arrays of three or more coupled quantum dots. (A closely related work appeared subsequent to our submission. H. Flentje et al., Coherent long-distance displacement of individual electron spins. arXiv:1701.01279) Various physical mechanisms have been proposed to controllably transfer single charges through confined structures, including Thouless pumps, 21, 22 charge pumps 23 , and surface acoustic waves, 24 and several of these approaches have been experimentally demonstrated with quantum dot devices. 12,25,26 Furthermore, charge transfer with preservation of spin projection was shown using surface acoustic waves 27 and charge pumps.

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Isotopically enhanced triple-quantum-dot qubit

Abstract: Three coupled quantum dots in isotopically purified silicon enable all-electrical qubit control with long coherence time.

Cited by 226 publications

References 31 publications

Milestones Toward Majorana-Based Quantum Computing

Milestones Toward Majorana-Based Quantum Computing

Charge-noise-insensitive gate operations for always-on, exchange-only qubits

Coherent shuttle of electron-spin states

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