Impact of valley phase and splitting on readout of silicon spin qubits

Tagliaferri, Marco; Bavdaz, P. L.; Huang, W.; Dzurak, A. S.; Culcer, Dimitrie; Veldhorst, Menno

doi:10.1103/physrevb.97.245412

Cited by 19 publications

(16 citation statements)

References 78 publications

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“…14 illustrates how the ancilla dot may be used to implement a valley-to-charge conversion, such that the spin state of the ground valley is unaffected after postselection. We neglect the valley phase here as analyzing its effect in readout is not the present focus, although it certainly will affect readout quality [111]. We make use of Eq.…”

Section: Valley Projective Measurementmentioning

confidence: 99%

Multicore Quantum Computing

Jnane,

Undseth,

Cai

et al. 2022

Preprint

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Any architecture for practical quantum computing must be scalable. An attractive approach is to create multiple cores, computing regions of fixed size that are well-spaced but interlinked with communication channels. This exploded architecture can relax the demands associated with a single monolithic device: the complexity of control, cooling and power infrastructure as well as the difficulties of cross-talk suppression and near-perfect component yield. Here we explore interlinked multicore architectures through analytic and numerical modelling. While elements of our analysis are relevant to diverse platforms, our focus is on semiconductor electron spin systems in which numerous cores may exist on a single chip. We model shuttling and microwave-based interlinks and estimate the achievable fidelities, finding values that are encouraging but markedly inferior to intra-core operations. We therefore introduce optimsed entanglement purification to enable highfidelity communication, finding that 99.5% is a very realistic goal. We then assess the prospects for quantum advantage using such devices in the NISQ-era and beyond: we simulate recently proposed exponentially-powerful error mitigation schemes in the multicore environment and conclude that these techniques impressively suppress imperfections in both the inter-and intra-core operations.

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Section: Valley Projective Measurementmentioning

confidence: 99%

Multicore Quantum Computing

Jnane,

Undseth,

Cai

et al. 2022

Preprint

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“…Bulk silicon has six-fold degenerate conduction band minima referred to as valleys. In a Si/SiO 2 hetero-structure, strong confinement along the vertical (ẑ) direction and strain at the Si/SiO 2 interface raises the energy of the four in-plane valleys, leaving a 2-fold degeneracy of the out-of-plane [27,28]. Disorder at the Si/SiO 2 interface can cause |∆| and φ to vary randomly between QDs [29,30].…”

Section: A Valley-orbit Hamiltonianmentioning

confidence: 99%

Simulated coherent electron shuttling in silicon quantum dots

2020

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Shuttling of single electrons in gate-defined silicon quantum dots is numerically simulated. A minimal gate geometry without explicit tunnel barrier gates is introduced, and used to define a chain of accumulation mode quantum dots, each controlled by a single gate voltage. One-dimensional potentials are derived from a three-dimensional electrostatic model, and used to construct an effective Hamiltonian for efficient simulation. Control pulse sequences are designed by maintaining a fixed adiabaticity, so that different shuttling conditions can be systematically compared. We first use these tools to optimize the device geometry for maximum transport velocity, considering only orbital states and neglecting valley and spin degrees of freedom. Taking realistic geometrical constraints into account, charge shuttling speeds up to ∼ 300 m/s preserve adiabaticity. Coherent spin transport is simulated by including spin-orbit and valley terms in an effective Hamiltonian, shuttling one member of a singlet pair and tracking the entanglement fidelity. With realistic device and material parameters, shuttle speeds in the range 10 − 100 m/s with high spin entanglement fidelities are obtained when the tunneling energy exceeds the Zeeman energy. High fidelity also requires the inter-dot valley phase difference to be below a threshold determined by the ratio of tunneling and Zeeman energies, so that spin-valley-orbit mixing is weak. In this regime, we find that the primary source of infidelity is a coherent spin rotation that is correctable, in principle. The results pertain to proposals for large-scale spin qubit processors in isotopically purified silicon that rely on coherent shuttling of spins to rapidly distribute quantum information between computational nodes.

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“…with the complex quantity ∆ j = E j V e iφ j consisting of the valley splitting E j V and valley phase φ j in dot j = L, C, R. Because of atomistic defects at the silicon interface the valley pseudo-vector can have a different phase in each dot [36,11,42,22]. The valley Hamiltonian in the valley eigenbasis of each dot can be written as…”

Section: Hamiltonianmentioning

confidence: 99%

Theory of valley-resolved spectroscopy of a Si triple quantum dot coupled to a microwave resonator

Russ

Péterfalvi

Burkard

2020

J. Phys.: Condens. Matter

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We theoretically study a silicon triple quantum dot (TQD) system coupled to a superconducting microwave resonator. The response signal of an injected probe signal can be used to extract information about the level structure by measuring the transmission and phase shift of the output field. This information can further be used to gain knowledge about the valley splittings and valley phases in the individual dots. Since relevant valley states are typically split by several µeV, a finite temperature or an applied external bias voltage is required to populate energetically excited states. The theoretical methods in this paper include a capacitor model to fit experimental charging energies, an extended Hubbard model to describe the tunneling dynamics, a rate equation model to find the occupation probabilities, and an input-output model to determine the response signal of the resonator.

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Impact of valley phase and splitting on readout of silicon spin qubits

Cited by 19 publications

References 78 publications

Multicore Quantum Computing

Multicore Quantum Computing

Simulated coherent electron shuttling in silicon quantum dots

Theory of valley-resolved spectroscopy of a Si triple quantum dot coupled to a microwave resonator

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