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Implementation of high-fidelity geometric singlet-triplet qubits operating near the transverse sweet spot

Wen-Xin Xie, Chengxian Zhang, Zheng‐Yuan Xue

Published Jan 31, 2021• 0 citations
OpenAlex

Abstract

The key to realizing fault-tolerant quantum computation for semiconductor quantum-dot singlet-triplet (ST) qubits is to operate both the single- and two-qubit gates with high fidelity. The feasible way includes operating the qubit near the transverse sweet spot (TSS) to reduce the leading order of the noise, as well as adopting the merit of the global property of the geometric phase. Here, we propose the implementation of the universal geometric gates for the ST qubits in the double quantum dot (DQD). The single-qubit non-cyclic geometric gate which is using the non-cyclic evolution path of the state to obtain the geometric phase can be achieved via introducing the AC-driven detuning operating near the TSS. We perform numerical simulation under the realistic $1/f$ noise environment in DQD. We find that the non-cyclic geometric gate can surpass its dynamical counterpart with a relatively high fidelity of 99.81\%. Meanwhile, we have used the dipole coupling between the DQDs and the cavity resonator which is maximized at the TSS to construct the geometric (holonomic) entangling geometric gate. We have shown that the fidelity for this two-qubit gate can be as high as 99.63\%. Our results suggests that taking advantage of the non-cyclic geometric gates together with using the TSS can be effective to obtain high-fidelity ST qubits.

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Universal Singlet‐Triplet Qubits Implemented Near the Transverse Sweet Spot

Wen‐Xin Xie, Chengxian Zhang, Zheng‐Yuan Xue

Abstract The key to realizing fault‐tolerant quantum computation for singlet‐triplet (ST) qubits in semiconductor double quantum dot (DQD) is to operate both the single‐ and two‐qubit gates with high fidelity. The feasible way includes operating the qubit near the transverse sweet spot (TSS) to reduce the leading order of the noise, as well as adopting the proper pulse sequences which are immune to noise. The single‐qubit gates can be achieved by introducing an AC drive on the detuning near the TSS. The large dipole moment of the DQDs at the TSS has enabled strong coupling between the qubits and the cavity resonator, which leads to two‐qubit entangling gates. When operating in the proper region and applying modest pulse sequences, both single‐ and two‐qubit gates have fidelity higher than 99%. The results in this paper suggest that taking advantage of the appropriate pulse sequences near the TSS can be effective to obtain high‐fidelity ST qubits.

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Fast high-fidelity geometric gates for singlet-triplet qubits

Meiya Chen, Chengxian Zhang, Zheng‐Yuan Xue

Geometric gates that use the global property of the geometric phase is believed to be a powerful tool to realize fault-tolerant quantum computation. However, for singlet-triplet qubits in semiconductor quantum dot, the low Rabi frequency of the microwave control leads to overly long gating time, and thus the constructing geometric gate suffers more from the decoherence effect. Here we investigate the key issue of whether the fast geometric gate can be realized for singlet-triplet qubits without introducing an extra microwave-driven pulse, while maintaining the high-fidelity gate operation at the same time. We surprisingly find that both the single- and two-qubit geometric gates can be implemented via only modulating the time-dependent exchange interaction of the Hamiltonian, which can typically be on the order of $\ensuremath{\sim}\mathrm{GHz}$, and thus the corresponding gate time is of several nanoseconds. Furthermore, the obtained geometric gates are superior to their counterparts, i.e., the conventional dynamical gates for singlet-triplet qubits, with a relatively high fidelity surpassing 99%. Therefore our scheme is particularly applied to singlet-triplet qubits to obtain fast and high-fidelity geometric gates. Our scheme can also be extended to other systems without a microwave drive.

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A fundamental challenge for quantum dot spin qubits is to extend the strength and range of qubit interactions while suppressing their coupling to the environment, since both effects have electrical origins. Key tools include the ability to take advantage of physical resources in different regimes, and to access optimal working points, sweet spots, where dephasing is minimized. Here, we explore an important resource for singlet-triplet qubits: a transverse sweet spot (TSS) that enables transitions between qubit states, a strong dipolar coupling, and leading-order protection from electrical fluctuations. Of particular interest is the possibility of transitioning between the TSS and symmetric operating points while remaining continuously protected. This arrangement is ideal for coupling qubits to a microwave cavity, because it combines tunability of the coupling with noise insensitivity. We perform simulations with [Formula: see text]-type electrical noise, demonstrating that two-qubit gates mediated by a resonator can achieve fidelities >99% under realistic conditions.

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Enhancing the dipolar coupling of a S-T0 qubit with a transverse sweet spot

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Abstract A fundamental challenge for quantum dot spin qubits is to extend the strength and range of qubit interactions while suppressing their coupling to the environment, since both effects have electrical origins. Key tools include the ability to take advantage of physical resources in different regimes, and to access optimal working points, sweet spots, where dephasing is minimized. Here, we explore an important resource for singlet-triplet qubits: a transverse sweet spot (TSS) that enables transitions between qubit states, a strong dipolar coupling, and leading-order protection from electrical fluctuations. Of particular interest is the possibility of transitioning between the TSS and symmetric operating points while remaining continuously protected. This arrangement is ideal for coupling qubits to a microwave cavity, because it combines tunability of the coupling with noise insensitivity. We perform simulations with $$1/f$$1∕f-type electrical noise, demonstrating that two-qubit gates mediated by a resonator can achieve fidelities >99% under realistic conditions.

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Singlet-triplet qubits in lateral quantum dots in semiconductor heterostructures exhibit high-fidelity single-qubit gates via exchange interactions and magnetic field gradients. High-fidelity two-qubit entangling gates are challenging to generate since weak interqubit interactions result in slow gates that accumulate error in the presence of noise. However, the interqubit electrostatic interaction also produces a shift in the local double well detunings, effectively changing the dependence of exchange on the gate voltages. We consider an operating point where the effective exchange is first-order insensitive to charge fluctuations while maintaining nonzero interactions. This ``sweet spot'' exists only in the presence of interactions. We show that working at the interacting sweet spot can directly produce maximally entangling gates, and we simulate the gate evolution under realistic $1/f$ noise. We report theoretical two-qubit gate fidelities above 99% in GaAs and Si systems.

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Microwave driven geometric quantum computation on semiconductor charge qubits

Chengxian Zhang, Tao Chen, Xin Wang +1 more

The charge qubit based on semiconductor double quantum dots is promising to realize fast and scalable quantum information processing. However, due to its strong coupling to charge noise, experimental realization of two-qubit gates has fidelities below 90%. Here, we provide a theoretical framework to achieve precise gate operations on a charge qubit using geometric quantum phase, namely geometric quantum gates. Single-qubit operations are implemented using the microwave-driven X-Y interacting Hamiltonian near certain sweet spots, where the charge noise is effectively suppressed. Meanwhile, we find that the performance of the geometric gates can be further improved up to 99.86% using composite pulses. In addition, to obtain a nontrivial two-qubit gate, we introduce a hybrid system which consists of charge qubits interacting with a high-impedance superconducting resonator. We find that when the individual charge qubit is in resonance with the resonator, it is possible to construct a SWAP-like gate with fidelity over 97%. Therefore, our results suggest that the geometric quantum gates in combination with the microwave-driven fields are powerful tools to achieve high-fidelity manipulation for the charge qubit.

•Apr 1, 2020•0 citations
The key to realizing fault-tolerant quantum computation for semiconductor quantum-dot singlet-triplet (ST) qubits is to operate both the single- and two-qubit gates with high fidelity. The feasible way includes operating the qubit near the transverse sweet spot (TSS) to reduce the leading order of the noise, as well as adopting the merit of the global property of the geometric phase. Here, we propose the implementation of the universal geometric gates for the ST qubits in the double quantum dot (DQD). The single-qubit non-cyclic geometric gate which is using the non-cyclic evolution path of the state to obtain the geometric phase can be achieved via introducing the AC-driven detuning operating near the TSS. We perform numerical simulation under the realistic 1/f1/f1/f noise environment in DQD. We find that the non-cyclic geometric gate can surpass its dynamical counterpart with a relatively high fidelity of 99.81%. Meanwhile, we have used the dipole coupling between the DQDs and the cavity resonator which is maximized at the TSS to construct the geometric (holonomic) entangling geometric gate. We have shown that the fidelity for this two-qubit gate can be as high as 99.63%. Our results suggests that taking advantage of the non-cyclic geometric gates together with using the TSS can be effective to obtain high-fidelity ST qubits.
Abstract The key to realizing fault‐tolerant quantum computation for singlet‐triplet (ST) qubits in semiconductor double quantum dot (DQD) is to operate both the single‐ and two‐qubit gates with high fidelity. The feasible way includes operating the qubit near the transverse sweet spot (TSS) to reduce the leading order of the noise, as well as adopting the proper pulse sequences which are immune to noise. The single‐qubit gates can be achieved by introducing an AC drive on the detuning near the TSS. The large dipole moment of the DQDs at the TSS has enabled strong coupling between the qubits and the cavity resonator, which leads to two‐qubit entangling gates. When operating in the proper region and applying modest pulse sequences, both single‐ and two‐qubit gates have fidelity higher than 99%. The results in this paper suggest that taking advantage of the appropriate pulse sequences near the TSS can be effective to obtain high‐fidelity ST qubits.
Geometric gates that use the global property of the geometric phase is believed to be a powerful tool to realize fault-tolerant quantum computation. However, for singlet-triplet qubits in semiconductor quantum dot, the low Rabi frequency of the microwave control leads to overly long gating time, and thus the constructing geometric gate suffers more from the decoherence effect. Here we investigate the key issue of whether the fast geometric gate can be realized for singlet-triplet qubits without introducing an extra microwave-driven pulse, while maintaining the high-fidelity gate operation at the same time. We surprisingly find that both the single- and two-qubit geometric gates can be implemented via only modulating the time-dependent exchange interaction of the Hamiltonian, which can typically be on the order of $\ensuremath{\sim}\mathrm{GHz}$, and thus the corresponding gate time is of several nanoseconds. Furthermore, the obtained geometric gates are superior to their counterparts, i.e., the conventional dynamical gates for singlet-triplet qubits, with a relatively high fidelity surpassing 99%. Therefore our scheme is particularly applied to singlet-triplet qubits to obtain fast and high-fidelity geometric gates. Our scheme can also be extended to other systems without a microwave drive.
A fundamental challenge for quantum dot spin qubits is to extend the strength and range of qubit interactions while suppressing their coupling to the environment, since both effects have electrical origins. Key tools include the ability to take advantage of physical resources in different regimes, and to access optimal working points, sweet spots, where dephasing is minimized. Here, we explore an important resource for singlet-triplet qubits: a transverse sweet spot (TSS) that enables transitions between qubit states, a strong dipolar coupling, and leading-order protection from electrical fluctuations. Of particular interest is the possibility of transitioning between the TSS and symmetric operating points while remaining continuously protected. This arrangement is ideal for coupling qubits to a microwave cavity, because it combines tunability of the coupling with noise insensitivity. We perform simulations with [Formula: see text]-type electrical noise, demonstrating that two-qubit gates mediated by a resonator can achieve fidelities >99% under realistic conditions.
Abstract A fundamental challenge for quantum dot spin qubits is to extend the strength and range of qubit interactions while suppressing their coupling to the environment, since both effects have electrical origins. Key tools include the ability to take advantage of physical resources in different regimes, and to access optimal working points, sweet spots, where dephasing is minimized. Here, we explore an important resource for singlet-triplet qubits: a transverse sweet spot (TSS) that enables transitions between qubit states, a strong dipolar coupling, and leading-order protection from electrical fluctuations. Of particular interest is the possibility of transitioning between the TSS and symmetric operating points while remaining continuously protected. This arrangement is ideal for coupling qubits to a microwave cavity, because it combines tunability of the coupling with noise insensitivity. We perform simulations with 1/f1/f1/f1∕f-type electrical noise, demonstrating that two-qubit gates mediated by a resonator can achieve fidelities >99% under realistic conditions.
Singlet-triplet qubits in lateral quantum dots in semiconductor heterostructures exhibit high-fidelity single-qubit gates via exchange interactions and magnetic field gradients. High-fidelity two-qubit entangling gates are challenging to generate since weak interqubit interactions result in slow gates that accumulate error in the presence of noise. However, the interqubit electrostatic interaction also produces a shift in the local double well detunings, effectively changing the dependence of exchange on the gate voltages. We consider an operating point where the effective exchange is first-order insensitive to charge fluctuations while maintaining nonzero interactions. This ``sweet spot'' exists only in the presence of interactions. We show that working at the interacting sweet spot can directly produce maximally entangling gates, and we simulate the gate evolution under realistic 1/f1/f1/f noise. We report theoretical two-qubit gate fidelities above 99% in GaAs and Si systems.
The charge qubit based on semiconductor double quantum dots is promising to realize fast and scalable quantum information processing. However, due to its strong coupling to charge noise, experimental realization of two-qubit gates has fidelities below 90%. Here, we provide a theoretical framework to achieve precise gate operations on a charge qubit using geometric quantum phase, namely geometric quantum gates. Single-qubit operations are implemented using the microwave-driven X-Y interacting Hamiltonian near certain sweet spots, where the charge noise is effectively suppressed. Meanwhile, we find that the performance of the geometric gates can be further improved up to 99.86% using composite pulses. In addition, to obtain a nontrivial two-qubit gate, we introduce a hybrid system which consists of charge qubits interacting with a high-impedance superconducting resonator. We find that when the individual charge qubit is in resonance with the resonator, it is possible to construct a SWAP-like gate with fidelity over 97%. Therefore, our results suggest that the geometric quantum gates in combination with the microwave-driven fields are powerful tools to achieve high-fidelity manipulation for the charge qubit.