<p>In recent years, the tunable coupling scheme of controlling qubit-qubit coupling by modulating coupler frequency has gradually become the mainstream scheme for designing superconducting quantum circuits. Here, we propose a tunable coupling scheme based on fluxonium-transmon-transmon (FTT), this asymmetric structure composed of fluxonium and transmon will optimize the frequency space of the system. In this system, both qubits and coupler are capacitively coupled, and the coupler is a frequency tunable transmon qubit. By decoupling the coupler from the system, the effective coupling strength can be easily adjusted to zero to close the net coupling between qubits. We study the performance of this scheme by simulating the general single-qubit <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12648_2025_3598_Article_IEq1.gif" Format="GIF" Height="23" Rendition="HTML" Resolution="72" Type="Linedraw" Width="51" /> </InlineMediaObject> <EquationSource Format="TEX">$\left( X_{{\pi }/{2}}\right)$</EquationSource> <EquationSource Format="MATHML"><math> <mfenced close=")" open="("> <msub> <mi>X</mi> <mrow> <mi>π</mi> <mo stretchy="false">/</mo> <mn>2</mn> </mrow> </msub> </mfenced> </math></EquationSource> </InlineEquation> gate and two-qubit <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12648_2025_3598_Article_IEq2.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="75" /> </InlineMediaObject> <EquationSource Format="TEX">$\left( iSWAP\right)$</EquationSource> <EquationSource Format="MATHML"><math> <mfenced close=")" open="("> <mi>i</mi> <mi>S</mi> <mi>W</mi> <mi>A</mi> <mi>P</mi> </mfenced> </math></EquationSource> </InlineEquation> gate. How to achieve a high fidelity and strong robustness of universal quantum gate operations is the key to achieving large-scale fault-tolerant quantum computing. In the bias point of the qubits, we achieved a single qubit gate with 99.91<InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12648_2025_3598_Article_IEq3.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="15" /> </InlineMediaObject> <EquationSource Format="TEX">$\%$</EquationSource> <EquationSource Format="MATHML"><math> <mo>%</mo> </math></EquationSource> </InlineEquation> fidelity and a two-qubit gate with 99.02<InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12648_2025_3598_Article_IEq3.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="15" /> </InlineMediaObject> <EquationSource Format="TEX">$\%$</EquationSource> <EquationSource Format="MATHML"><math> <mo>%</mo> </math></EquationSource> </InlineEquation> fidelity through numerical simulation. Our approach effectively addresses the frequency crowding issue, establishing stable two-qubit gates between qubits with large detuning.</p>

Realization of two-qubit gates operations in asymmetric superconducting circuits

期刊论文
发表日期：

2025年4月24日

查看全文

Tao Zhang,
Chaoying Zhao

摘要

In recent years, the tunable coupling scheme of controlling qubit-qubit coupling by modulating coupler frequency has gradually become the mainstream scheme for designing superconducting quantum circuits. Here, we propose a tunable coupling scheme based on fluxonium-transmon-transmon (FTT), this asymmetric structure composed of fluxonium and transmon will optimize the frequency space of the system. In this system, both qubits and coupler are capacitively coupled, and the coupler is a frequency tunable transmon qubit. By decoupling the coupler from the system, the effective coupling strength can be easily adjusted to zero to close the net coupling between qubits. We study the performance of this scheme by simulating the general single-qubit $\left( X_{{\pi }/{2}}\right)$ $(X_{π / 2})$ gate and two-qubit $\left( iSWAP\right)$ $(i, S, W, A, P)$ gate. How to achieve a high fidelity and strong robustness of universal quantum gate operations is the key to achieving large-scale fault-tolerant quantum computing. In the bias point of the qubits, we achieved a single qubit gate with 99.91 $\%$ $%$ fidelity and a two-qubit gate with 99.02 $\%$ $%$ fidelity through numerical simulation. Our approach effectively addresses the frequency crowding issue, establishing stable two-qubit gates between qubits with large detuning.