Controllable exchange coupling between two singlet-triplet qubits

Li, Rui; Hu, Xuedong; You, J. Q.

doi:10.1103/physrevb.86.205306

Cited by 47 publications

(49 citation statements)

References 62 publications

(121 reference statements)

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“…In the framework of solid state physics a rich exploitable platform for universal quantum computation, as witnessed by several experimental [1][2][3][4][5][6] and theoretical [7][8][9] proposals, is represented by the confinement of electron spins in host semiconducting materials. The confinement is achievable following different routes, from electrostatically or self-assembled quantum dots (QDs) [2,10,11] to donor spins in solid matrices [12][13][14] or a combination of them [15][16][17].…”

Section: Introductionmentioning

confidence: 99%

Gate fidelity comparison in semiconducting spin qubit implementations affected by control noises

2018

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A comparison of gate fidelities between different spin qubit types defined in quantum dots and a donor under different control errors is reported. We studied five qubit types, namely the quantum dot spin qubit, the double quantum dot singlet-triplet qubit, the double quantum dot hybrid qubit, the donor qubit and the quantum dot spin-donor qubit. For each one, we derived analytical time sequences that realize single qubit rotations along the principal axis of the Bloch sphere. We estimated the effects of control errors on the gate fidelity by using a Gaussian noise model. Then we compared the gate fidelities among qubit implementations due to pulse timing errors by using a realistic set of values for the error parameters of control amplitudes. E Ferraro et al H J J J J J J J J . ( ) The sequence that realizes R z (θ) is composed by the product of three steps U t U t U t J J J J J J evolution operators are calculated starting from the Hamiltonians H E J J J z z z z i i 3 2 1 , 2 2 J J max max 1 2 1 4 -HQ J J J 1 2 1 4 1 2 -¢ + + ( ) J J 3 4 1 2 --( ) J J J E 2

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Section: Introductionmentioning

confidence: 99%

Gate fidelity comparison in semiconducting spin qubit implementations affected by control noises

2018

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“…We consider the strong repulsion regime with (U − U ′ ) ≫ |t|, |t ′ |, such that each dot contains only one electron. Thus, we can define a projection operator [41] …”

Section: The Anisotropic Exchange Couplingmentioning

confidence: 99%

“…When the Coulomb repulsion in the DQD is so strong that (U − U ′ ) ≫ |t|, |t ′ |, the two electrons in the DQD have a fixed charge configuration; i.e., each dot confines one and only one electron. Thus, we can define a projection operator [41] …”

Section: Appendix A: the Orthonormal Spin-orbit Basismentioning

confidence: 99%

Anisotropic exchange coupling in a nanowire double quantum dot with strong spin-orbit coupling

You

2014

Phys. Rev. B

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A spin-orbit qubit is a hybrid qubit that contains both orbital and spin degrees of freedom of an electron in a quantum dot. Here we study the exchange coupling between two spin-orbit qubits in a nanowire double quantum dot (DQD) with strong spin-orbit coupling (SOC). We find that while the total tunneling in the DQD is irrelevant to the SOC, both the spin-conserved and spin-flipped tunnelings are SOC dependent and can compete with each other in the strong SOC regime. Moreover, the Coulomb repulsion between electrons can combine with the SOC-dependent tunnelings to yield an anisotropic exchange coupling between the two spin-orbit qubits. Also, we give an explicit physical mechanism for this anisotropic exchange coupling.

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“…For a pair of singlet-triplet qubits coupled via tunneling, the effective exchange interaction can be used to carry out two-qubit gates; 7,[24][25][26][27][28] however, this approach typically requires an accompanying mechanism for suppressing errors due to leakage out of the qubit subspace during gate operation. Alternatively, two singlet-triplet qubits in adjacent double dots may be entangled via capacitive coupling.…”

Section: 23mentioning

confidence: 99%

Capacitively coupled singlet-triplet qubits in the double charge resonant regime

Srinivasa

2015

Phys. Rev. B

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We investigate a method for entangling two singlet-triplet qubits in adjacent double quantum dots via capacitive interactions. In contrast to prior work, here we focus on a regime with strong interactions between the qubits. The interplay of the interaction energy and simultaneous large detunings for both double dots gives rise to the "double charge resonant" regime, in which the unpolarized (1111) and fully polarized (0202) four-electron states in the absence of interqubit tunneling are near degeneracy, while being energetically well-separated from the partially polarized (0211 and 1102) states. A rapid controlled-phase gate may be realized by combining time evolution in this regime in the presence of intraqubit tunneling and the interqubit Coulomb interaction with refocusing π pulses that swap the singly occupied singlet and triplet states of the two qubits via, e.g., magnetic gradients. We calculate the fidelity of this entangling gate, incorporating models for two types of noise -charge fluctuations in the single-qubit detunings and charge relaxation within the low-energy subspace via electron-phonon interaction -and identify parameter regimes that optimize the fidelity. The rates of phonon-induced decay for pairs of GaAs or Si double quantum dots vary with the sizes of the dipolar and quadrupolar contributions and are several orders of magnitude smaller for Si, leading to high theoretical gate fidelities for coupled singlet-triplet qubits in Si dots. We also consider the dependence of the capacitive coupling on the relative orientation of the double dots and find that a linear geometry provides the fastest potential gate.

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Controllable exchange coupling between two singlet-triplet qubits

Cited by 47 publications

References 62 publications

Gate fidelity comparison in semiconducting spin qubit implementations affected by control noises

Gate fidelity comparison in semiconducting spin qubit implementations affected by control noises

Anisotropic exchange coupling in a nanowire double quantum dot with strong spin-orbit coupling

Capacitively coupled singlet-triplet qubits in the double charge resonant regime

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