Coherent multi-spin exchange coupling in a quantum-dot spin chain

Qiao, Haifeng; Kandel, Yadav P.; Deng, Kuangyin; Fallahi, Saeed; Gardner, Geoffrey C.; Manfra, Michael J.; Barnes, Edwin; Nichol, John M.

doi:10.48550/arxiv.2001.02277

Cited by 3 publications

(5 citation statements)

References 32 publications

(50 reference statements)

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“…As our calculations will show, barrier modulation (e.g., forward biasing an X gate) increases J in silicon dots primarily by softening the potential to reduce the electron separation, enhancing their Coulomb interaction, rather than by simply increasing the tunnel coupling through a fixed barrier, as might be intuited from simple FH models. Our observations in simulations are consistent with recent experiments showing the importance of electron displacement in modulating simultaneous exchange in GaAs [41]; as discussed in section 4, such effects are even stronger in silicon owing to its larger mass.…”

Section: Simultaneous Exchange Operation In Si/sige Tqds From Fcisupporting

confidence: 92%

Resonant exchange operation in triple-quantum-dot qubits for spin–photon transduction

Pan

Keating²,

Gyure³

et al. 2020

Quantum Sci. Technol.

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Triple quantum dots (TQDs) are promising semiconductor spin qubits because of their all-electrical control via fast, tunable exchange interactions and immunity to global magnetic fluctuations. These qubits couple to photons in the resonant exchange (RX) regime, when exchange is simultaneously active on both qubit axes. However, most theoretical work has been based on phenomenological Fermi-Hubbard models, which may not fully capture the complexity of the qubit spin-charge states in this regime. Here we investigate exchange in Si/SiGe and GaAs TQDs using full configuration interaction (FCI) calculations which better describe practical device operation. We show that high exchange operation in general, and the RX regime in particular, can differ significantly from simple models, presenting new challenges and opportunities for spin-photon coupling. We highlight the impact of device electrostatics and effective mass on exchange and identify a new operating point (XRX) where strong spin-photon coupling is most likely to occur in Si/SiGe TQDs. Based on our numerical results, we analyze the feasibility of a remote entanglement cavity iSWAP protocol and discuss design pathways for improving fidelity. Our analysis provides insight into the requirements for TQD spin-photon transduction and demonstrates more generally the necessity of accurate modeling of exchange in spin qubits. ‡ Present address:

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Section: Simultaneous Exchange Operation In Si/sige Tqds From Fcisupporting

confidence: 92%

Resonant exchange operation in triple-quantum-dot qubits for spin–photon transduction

Pan

Keating²,

Gyure³

et al. 2020

Quantum Sci. Technol.

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“…B z i includes both a large 0.5-T external magnetic field and the smaller hyperfine field. The exchange couplings J 1 , J 2 , and J 3 are controlled by pulsing virtual barrier gate voltages [30]. We model the dependence of the exchange couplings on the virtual barrier gate voltages in the Heitler-London framework [30,31].…”

Section: Device and Hamiltonianmentioning

confidence: 99%

“…The exchange couplings J 1 , J 2 , and J 3 are controlled by pulsing virtual barrier gate voltages [30]. We model the dependence of the exchange couplings on the virtual barrier gate voltages in the Heitler-London framework [30,31]. The model allows us to predict the required barrier gate voltages for a set of desired exchange couplings.…”

Section: Device and Hamiltonianmentioning

confidence: 99%

“…In the experimental data, however, the periodicity is slightly larger than 1, and the strongest quality-factor enhancement occurs at J 2 τ ≈ 0.57. This is due to the imperfect calibration of the exchange coupling J 2 [30]. In particular, the presence of the hyperfine field gradient makes it difficult to measure and control the exchange couplings with sub-MHz resolution.…”

Section: Floquet-enhanced Spin Swapsmentioning

confidence: 99%

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Floquet-Enhanced Spin Swaps

Qiao,

Kandel,

Van Dyke

et al. 2020

Preprint

Self Cite

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The transfer of information between quantum systems is essential for quantum communication and computation. In quantum computers, high connectivity between qubits can improve the efficiency of algorithms, assist in error correction, and enable high-fidelity readout. However, as with all quantum gates, operations to transfer information between qubits can suffer from errors associated with spurious interactions and disorder between qubits, among other things. Here, we harness interactions and disorder between qubits to boost the fidelity of a swap operation for spin eigenstates in semiconductor gate-defined quantum-dot spin qubits. We use a system of four single-spin qubits, which we configure as two Ising-coupled singlet-triplet qubits. Our approach, which relies on the physics underlying discrete time crystals, enhances the quality factor of spin-eigenstate swaps by up to an order of magnitude. Our results show how interactions and disorder in multi-qubit systems can stabilize non-trivial quantum operations and suggest potential uses for non-equilibrium quantum phenomena, like time crystals, in quantum information processing applications.

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“…Achieving this regime can be challenging and often leads to a nonlinear dependence of the exchange on the external gate voltages. 54,55 As a result, it may be difficult in practice to realize the ideally shaped Gaussian pulses considered in the previous section. Fortunately, the adiabatic nature of the control scheme renders spin-CTAP largely insensitive to these effects.…”

Section: Imperfections In Ac Exchange Drivingmentioning

confidence: 99%

Coherent transport of spin by adiabatic passage in quantum dot arrays

Gullans,

Petta

2020

Preprint

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We introduce an adiabatic transfer protocol for spin states in large quantum dot arrays that is based on time-dependent modulation of the Heisenberg exchange interaction in the presence of a magnetic field gradient. We refer to this protocol as spin-CTAP (coherent transport by adiabatic passage) in analogy to a related protocol developed for charge state transfer in quantum dot arrays. The insensitivity of this adiabatic protocol to pulse imperfections has potential advantages for reading out extended spin qubit arrays. When the static exchange interaction varies across a spinqubit array, a quantum-controlled version of spin-CTAP is possible, where the transfer process is conditional on the spin states in the middle of the array. This conditional operation can be used to generate N -qubit entangled GHZ states. Using a realistic noise model, we analyze the robustness of the spin-CTAP operations and find that high-fidelity (>95%) spin eigenstate transfer and GHZ state preparation is feasible in current devices.

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Coherent multi-spin exchange coupling in a quantum-dot spin chain

Cited by 3 publications

References 32 publications

Resonant exchange operation in triple-quantum-dot qubits for spin–photon transduction

Resonant exchange operation in triple-quantum-dot qubits for spin–photon transduction

Floquet-Enhanced Spin Swaps

Coherent transport of spin by adiabatic passage in quantum dot arrays

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