Quantum dot spin cellular automata for realizing a quantum processor

Bayat, Abolfazl; Creffield, Charles E.; Jefferson, J. H.; Pepper, M.; Bose, Sougato

doi:10.1088/0268-1242/30/10/105025

Cited by 15 publications

(7 citation statements)

References 32 publications

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“…The logical charge states of a CQ qubit are protected from uniform electric field fluctuations because their charge distributions have the same centre of mass (in other words, no dipole moment). It is interesting to note that several related systems also propose to use dipole-free geometries, including the zero-detuning sweet spot of a conventional charge qubit 17 24 25 , which we analyse below, a three-island transmon qubit 26 , and quantum cellular automata 27 28 29 .…”

Section: Resultsmentioning

confidence: 99%

A decoherence-free subspace in a charge quadrupole qubit

et al. 2017

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Quantum computing promises significant speed-up for certain types of computational problems. However, robust implementations of semiconducting qubits must overcome the effects of charge noise that currently limit coherence during gate operations. Here we describe a scheme for protecting solid-state qubits from uniform electric field fluctuations by generalizing the concept of a decoherence-free subspace for spins, and we propose a specific physical implementation: a quadrupole charge qubit formed in a triple quantum dot. The unique design of the quadrupole qubit enables a particularly simple pulse sequence for suppressing the effects of noise during gate operations. Simulations yield gate fidelities 10–1,000 times better than traditional charge qubits, depending on the magnitude of the environmental noise. Our results suggest that any qubit scheme employing Coulomb interactions (for example, encoded spin qubits or two-qubit gates) could benefit from such a quadrupolar design.

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Section: Resultsmentioning

confidence: 99%

A decoherence-free subspace in a charge quadrupole qubit

et al. 2017

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“…Their implementation, however, requires a method of manipulating the spin of individual electrons. This can be done by using micromagnets [2][3][4][5][6], but it is difficult to confine magnetic fields to the small volumes occupied by the qubits and obtain the necessary level of control. A method of addressing spin by applying local gating potentials would thus be greatly preferable.…”

Section: Introductionmentioning

confidence: 99%

Controlling spin without magnetic fields: The Bloch-Rashba rotator

Creffield

2020

Phys. Rev. B

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We consider the dynamics of a quantum particle held in a lattice potential and subjected to a time-dependent spin-orbit coupling. Tilting the lattice causes the particle to perform Bloch oscillations, and by suitably changing the Rashba interaction during its motion, the spin of the particle can be gradually rotated. Even if the Rashba coupling can only be altered by a small amount, large spin rotations can be obtained by accumulating the rotation from successive oscillations. We show how the time dependence of the spin-orbit coupling can be chosen to maximize the rotation per cycle, and thus how this method can be used to produce a precise and controllable spin rotator, which we term the Bloch-Rashba rotator, without requiring an applied magnetic field.

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“…This charge separation provides an additional degree of freedom which might potentially be exploited for quantum information manipulation. It was shown in several papers 1,9,10 that the spin properties of charge-separated Wigner molecules affect the time dynamics of state evolution: in the absence of magnetic field, the singlet state's charge will oscillate while the triplet state will be stationary. The dynamics can be reversed by the application of magnetic flux through the dot.…”

Section: Introductionmentioning

confidence: 99%

“…The dynamics can be reversed by the application of magnetic flux through the dot. If singlet and triplet states are regarded as qubit states |0 and |1 , this devices enables a simple, controlled qubit transformation 1 .…”

Section: Introductionmentioning

confidence: 99%

Rashba controlled two-electron spin-charge qubits as building blocks of a quantum computer

Kregar,

Ramsak

2020

Preprint

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The spin-sensitive charge oscillation, controlled by an external magnetic field, was recently proposed as a mechanism of transformations of qubits, defined as two-electron spin-charge Wannier molecules in a square quantum dot 1 . The paper expands this idea by including the effects of Rashba type spin-orbit coupling. The problem is studied theoretically by mapping the system to an analytic effective Hamiltonian for 8 low energy states, comprising singlet and triplet on each dot diagonal. The validity of the mapping is confirmed by comparing the energy and spin of full and mapped system, and also by the reproduction of charge-oscillation dynamics in the presence of magnetic flux. The newly introduced Rashba coupling significantly enriches the system dynamics, affecting the magnitude of charge oscillations and allowing the controlled transitions between singlet and triplet states due to the spin rotations, induced by spin-orbit coupling. The results indicate the possibility for use of the studied system for quantum information processing, while possible extensions of the system to serve as a qubit in a universal quantum computer, fulfilling all five DiVincenzo criteria, are also discussed.

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Quantum dot spin cellular automata for realizing a quantum processor

Cited by 15 publications

References 32 publications

A decoherence-free subspace in a charge quadrupole qubit

A decoherence-free subspace in a charge quadrupole qubit

Controlling spin without magnetic fields: The Bloch-Rashba rotator

Rashba controlled two-electron spin-charge qubits as building blocks of a quantum computer

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