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Microwave driven geometric quantum computation on semiconductor charge qubits

Chengxian Zhang, Tao Chen, Xin Wang, Zheng‐Yuan Xue

Published Apr 1, 2020• 0 citations
OpenAlex

Abstract

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.

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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.
Abstract A semiconductor‐based charge qubit, confined in double quantum dots, can be a platform to implement quantum computing. However, it suffers severely from charge noises. Here, a theoretical framework to implement universal geometric quantum gates in this system is provided. It is found that, while the detuning noise can be suppressed by operating near its corresponding sweet spot, the tunneling noise, on the other hand, is amplified and becomes the dominant source of error for single‐qubit gates, a fact previously insufficiently appreciated. It is demonstrated, through numerical simulation, that the geometric gates outperform the dynamical gates across a wide range of tunneling noise levels, making them particularly suitable to be implemented in conjunction with microwave driving. To obtain a nontrivial two‐qubit gate, a hybrid system is introduced with charge qubits coupled by a superconducting resonator. When each charge qubit is in resonance with the resonator, it is possible to construct an entangling geometric gate with fidelity higher than that of the dynamical gate for experimentally relevant noise levels. Therefore, the results suggest that geometric quantum gates are powerful tools to achieve high‐fidelity manipulation for the charge qubit.
Semiconductor double quantum-dot hybrid qubits are promising candidates for high-fidelity quantum computing. However, their performance is limited by charge noise, which is ubiquitous in solid-state devices, and phonon-induced dephasing. Here we explore methods for improving the quantum operations of a hybrid qubit, using strong microwave driving to enable gate operations that are much faster than decoherence processes. Using numerical simulations and a theoretical method based on a cumulant expansion, we analyze qubit dynamics in the presence of 1/f1/f1/f charge noise, which forms the dominant decoherence mechanism in many solid-state devices. We show that, while strong-driving effects and charge noise both reduce the quantum gate fidelity, simple pulse-shaping techniques effectively suppress the strong-driving effects. Moreover, a broad AC sweet spot emerges when the detuning parameter and the tunneling coupling are driven simultaneously. Taking into account phonon-mediated noise, we find that it should be possible to achieve ${X}_{\ensuremath{\pi}}$ gates with fidelities higher than 99.999.9%99.9.
High-Fidelity Single-Qubit Gates Via Strongly Driving of a Double Quantum Dot Hybrid Qubit with 1/f1/f1/f Charge Noise
Semiconductor double quantum dot hybrid qubits are promising candidates for high-fidelity quantum computing. However, their performance is limited by charge noise, which is ubiquitous in solid-state devices, and phonon-induced dephasing. Here we explore methods for improving the quantum operations of a hybrid qubit, using strong microwave driving to enable gate operations that are much faster than decoherence processes. Using numerical simulations and a theoretical method based on a cumulant expansion, we analyze qubit dynamics in the presence of 1/f1/f1/f charge noise, which forms the dominant decoherence mechanism in many solid-state devices. We show that, while strong-driving effects and charge noise both reduce the quantum gate fidelity, simple pulse-shaping techniques effectively suppress the strong-driving effects. Moreover, a broad AC sweet spot emerges when the detuning parameter and the tunneling coupling are driven simultaneously. Taking into account phonon-mediated noise, we find that it should be possible to achieve XπX_{\pi}Xπ​ gates with fidelities higher than 99.9%99.9\%99.9%.
The charge and spin degrees of freedom of an electron constitute natural bases for constructing quantum two level systems, or qubits, in semiconductor quantum dots. The quantum dot charge qubit offers a simple architecture and high-speed operation, but generally suffers from fast dephasing due to strong coupling of the environment to the electron’s charge. On the other hand, quantum dot spin qubits have demonstrated long coherence times, but their manipulation is often slower than desired for important future applications. This talk will present experimental progress of a ‘hybrid’ qubit, formed by three electrons in a Si/SiGe double quantum dot, which combines desirable characteristics (speed and coherence) in the past found separately in qubits based on either charge or spin degrees of freedom. Using resonant microwaves, we first discuss qubit operations near the ‘sweet spot’ for charge qubit operation. Along with fast ( >GHz) manipulation rates for any rotation axis on the Bloch sphere, we implement two independent tomographic characterization schemes in the charge qubit regime: traditional quantum process tomography (QPT) and gate set tomography (GST). We also present resonant qubit operations of the hybrid qubit performed on the same device, DC pulsed gate operations of which were recently demonstrated. We demonstrate three-axis control and the implementation of dynamic decoupling pulse sequences. Performing QPT on the hybrid qubit, we show that AC gating yields π rotation process fidelities higher than 93% for X-axis and 96% for Z-axis rotations, which demonstrates efficient quantum control of semiconductor qubits using resonant microwaves. We discuss a path forward for achieving fidelities better than the threshold for quantum error correction using surface codes.
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.
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.