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Chinese Physics B

Coupling and characterization of a Si/SiGe triple quantum dot array with a microwave resonator

Shun-Li Jiang, Tian-Yi Jiang, Yong-Qiang Xu, Rui 睿 Wu 吴, Tian-Yue Hao, Shu-Kun Ye, Ran-Ran 冉冉 Cai 蔡, Bao‐Chuan Wang, Hai-Ou Li, Gang Cao, Guo‐Ping Guo

Published Aug 20, 2024• 2 citations
Publisher

Abstract

Abstract Scaling up spin qubits in silicon-based quantum dots is one of the pivotal challenges in achieving large-scale semiconductor quantum computation. To satisfy the connectivity requirements and reduce the lithographic complexity, utilizing the qubit array structure and the circuit quantum electrodynamics (cQED) architecture together is expected to be a feasible scaling scheme. A triple-quantum dot (TQD) coupled with a superconducting resonator is regarded as a basic cell to demonstrate this extension scheme. In this article, we investigate a system consisting of a silicon TQD and a high-impedance TiN coplanar waveguide (CPW) resonator. The TQD can couple to the resonator via the right double-quantum dot (RDQD), which reaches the strong coupling regime with a charge–photon coupling strength of g 0/(2π) = 175 MHz. Moreover, we illustrate the high tunability of the TQD through the characterization of stability diagrams, quadruple points (QPs), and the quantum cellular automata (QCA) process. Our results contribute to fostering the exploration of silicon-based qubit integration.

DOI
10.1088/1674-1056/ad711d

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Cavity coupled flopping-mode spin qubit is considered as a promising scheme for enabling long-range qubit interactions in large-scale semiconductor quantum computation. In this work, we fabricate a linear Si/SiGe triple quantum dot (TQD) array coupled with a high-impedance TiN coplanar waveguide cavity via the gate of outer quantum dot. By utilizing two adjacent dots within the TQD, we sequentially encode two flopping-mode qubits at different positions, whether with or without gate connection, which exhibit strong coupling to the cavity. Furthermore, we demonstrate the qubit manipulation with the help of dispersive readout, achieving Rabi oscillation frequencies of 16.9 and 13.7 MHz at zero detuning. These results expand the spatial range of qubit coupling and readout via the cavity, enhancing the operational efficiency of cavity-quantum dot array coupled system.
Abstract One major challenge to scaling quantum dot qubits is the dense wiring requirements, making it difficult to envision fabricating large 2D arrays of nearest-neighbor-coupled qubits necessary for error correction. We describe a method to ameliorate this issue by spacing out the qubits using superconducting resonators facilitated by 3D integration. To prove the viability of this approach, we use integration to couple an off-chip high-impedance TiN resonator to a double quantum dot in a Si/SiGe heterostructure. Using the resonator as a dispersive gate sensor, we tune the device down to the single electron regime with an SNR = 5.36. Characterizing the individual systems shows 3D integration can be done while maintaining low-charge noise for the quantum dots and high-quality factors for the superconducting resonator (single photon QL = 2.14 × 104 with Qi ≈ 3 × 105), necessary for readout and high-fidelity two-qubit gates.
Coherent spin-photon coupling is believed to play a significant role in silicon-based quantum computation. The resonant exchange (RX) qubit, formed in a triple quantum dot, is a promising platform for spin-photon coupling and qubit scaling due to the large electric dipole moment and full electrical control without auxiliary micromagnets. However, there has been no experimental demonstration of silicon RX qubits and their strong coupling to microwave photons to date. In this work, we report the strong coupling between an RX qubit and a high-impedance resonator on a Si/SiGe heterostructure with coupling strength g_{s}/(2π)=65.8 MHz and decoherence rate γ_{s}/(2π)=21.4 MHz. Furthermore, the dependence of decoherence rate on detuning is measured and analyzed using a phenomenological model, indicating that the charge noise is the main source of decoherence. Our results demonstrate the viability of RX qubits in silicon, highlighting their crucial role of large-scale qubit integration for silicon quantum computation and opening new possibilities for quantum network.
Spins in semiconductor quantum dots are a candidate for cryogenic quantum processors due to their exceptionally long coherence times. One major challenge to scaling quantum dot spin qubits is the dense wiring requirements, making it difficult to envision fabricating large arrays of nearest-neighbor-coupled qubits necessary for error correction. We describe a method to solve this problem by spacing the qubits out using high-impedance superconducting resonators with a 2D grid unit cell area of 0.16 mm20.16~\text{mm}^20.16 mm2 using 3D integration. To prove the viability of this approach, we demonstrate 3D integration of a high-impedance TiN resonator coupled to a double quantum dot in a Si/SiGe heterostructure. Using the resonator as a dispersive gate sensor, we tune the device down to the single electron regime with an SNR = 5.36 limited by the resonator-dot capacitance. Characterization of the dot and resonator systems shows such integration can be done while maintaining low charge noise metrics for the quantum dots and with improved loaded quality factors for the superconducting resonator (QL=2.14×104Q_L = 2.14 \times 10^4QL​=2.14×104), allowing for high-sensitivity charge detection and the potential for high fidelity 2-qubit gates. This work paves the way for 2D quantum dot qubit arrays with cavity mediated interactions.
Semiconductor quantum dots in silicon demonstrate exceptionally long spin lifetimes as qubits and are therefore promising candidates for quantum information processing. However, control and readout techniques for these devices have thus far employed low frequency electrons, in contrast to high speed temperature readout techniques used in other qubit architectures, and coupling between multiple quantum dot qubits has not been satisfactorily addressed.This dissertation presents the design and characterization of a semiconductor charge qubit based on double quantum dot in silicon with an integrated microwave resonator for control and readout. The 6 GHz resonator is designed to achieve strong coupling with the quantum dot qubit, allowing the use of circuit QED control and readout techniques which have not previously been applicable to semiconductor qubits. To achieve this coupling, this document demonstrates successful operation of a novel silicon double quantum dot design with a single active metallic layer and a coplanar stripline resonator with a bias tee for dc excitation.Experiments presented here demonstrate quantum localization and measurement of both electrons on the quantum dot and photons in the resonator. Further, it is shown that the resonator-qubit coupling in these devices is sufficient to reach the strong coupling regime of circuit QED. The details of a measurement setup capable of performing simultaneous low noise measurements of the resonator and quantum dot structure are also presented here.The ultimate aim of this research is to integrate the long coherence times observed in electron spins in silicon with the sophisticated readout architectures available in circuit QED based quantum information systems. This would allow superconducting qubits to be coupled directly to semiconductor qubits to create hybrid quantum systems with separate quantum memory and processing components.
Abstract The hybrid circuit quantum electrodynamics architecture integrated quantum dots with a microwave resonator results in the creation of a controllable artificial system and enriches its physics through electron–photon interaction. In this study, a hybrid device is investigated, wherein a triple quantum dot (TQD) is dipole coupled with electric field of a superconducting quantum interference device array resonator. The quantum cellular automata (QCA) process of TQD, related to charge reconfiguration as a result of Coulomb interaction between each dot, is observed by probing reflectance of the resonator. The suppressed cavity reflectance signal of the QCA process may experimentally provide the evidence for the different measurement mechanism of the cavity from external electrometers like quantum point contact. Furthermore, on careful tuning of multiple energy level differences of the TQD to match the cavity photon frequency, four tunneling processes assisted by the absorption of the cavity photons occur simultaneously, contributing to “photon‐assisted” quadruple point. Consequently, these two specific phenomena are found to be closely dependent on the relationship between the various Coulomb energy in TQD and the cavity photon energy. The results are consistent with the theoretical model presented and imply that this hybrid system has the potential for investigating exotic many‐body effects and matter–light interaction.