Decoherence of floating qubits due to capacitive coupling

Quantum Annealing Machine based on Floating Gate Array

Quantum annealing machines based on superconducting qubits, which have the potential to solve optimization problems faster than digital computers, are of great interest not only to researchers but also to the general public. Here, we propose a quantum annealing machine based on a semiconductor floating gate (FG) array. We use the same device structure as that of the commercial FG NAND flash memory except for small differences such as thinner tunneling barrier. We theoretically derive an Ising Hamiltonian from the FG system in its single-electron region. Recent high-density NAND flash memories …

实现无偏置空闲与高保真 CZ 门的电容并联双 Transmon 耦合器

Capacitively Shunted Double-Transmon Coupler Realizing Bias-Free Idling and High-Fidelity CZ Gate

提出并实验验证零磁通偏置的电容并联双 transmon 耦合器，在实现高保真 CZ 门的同时消除空闲直流偏置并拓宽磁通工作范围。

耦合到高阻抗谐振器的半导体电荷量子比特的频率分辨退相干光谱

Frequency-resolved decoherence spectroscopy of a semiconductor charge qubit coupled to a high-impedance resonator

通过将GaAs双量子点电荷量子比特耦合到高阻抗SQUID阵列谐振器，进行频率分辨退相干光谱研究，揭示了弛豫和纯退相干的分离及不同频率下的主导机制，观察到弛豫率的三次方标度，归因于压电声子耦合。

利用零磁通甜点的电容性短路双转子耦合器实现参数驱动的iSWAP门

Parametrically Driven iSWAP Gate Using a Capacitively Shunted Double-Transmon Coupler at the Zero-Flux Sweet Spot

研究通过电容性短路双转子耦合器在零磁通点实现高保真度的参数驱动iSWAP门，避免了大幅值基带磁通脉冲带来的退相干问题，验证了理论模型在频域和时域动态中的适用性。

Quantum Computing with Atomic Josephson Junction Arrays

We present a quantum computing scheme with atomic Josephson junction arrays. The system consists of a small number of atoms with three internal states and trapped in a far-off resonant optical lattice. Raman lasers provide the "Josephson" tunneling, and the collision interaction between atoms represent the "capacitive" couplings between the modes. The qubit states are collective states of the atoms with opposite persistent currents. This system is closely analogous to the superconducting flux qubit. Single qubit quantum logic gates are performed by modulating the Raman couplings, while two-qub…

High coherence hybrid superconducting qubit

We measure the coherence of a new superconducting qubit, the {\em low-impedance flux qubit}, finding $T_2^* \sim T_1 \sim 1.5μ$s. It is a three-junction flux qubit, but the ratio of junction critical currents is chosen to make the qubit's potential have a single well form. The low impedance of its large shunting capacitance protects it from decoherence. This qubit has a moderate anharmonicity, whose sign is reversed compared with all other popular qubit designs. The qubit is capacitively coupled to a high-Q resonator in a $λ/2$ configuration, which permits the qubit's state to be read out disp…

梯度计量型、完全可调的电容并联磁通量子比特

Gradiometric, Fully Tunable C-Shunted Flux Qubits

本文提出一种梯度计量型完全可调电容并联磁通量子比特，在磁通不敏感点实现25 μs弛豫时间和约20 GHz调谐范围，并用于跨倍频程检测两能级隧穿缺陷。

臂量子比特：一种为相干性与耦合协同设计的超导量子比特

The Arm Qubit: A Superconducting Qubit Co-Designed for Coherence and Coupling

本文提出臂量子比特，通过数据存储与耦合双模式协同设计，实现高速高保真纠缠门和读出，仅靠电容耦合即可扩展，为容错量子计算提供有前景的构建模块。

Scalable nonadiabatic holonomic quantum computation on a superconducting qubit lattice

Geometric phase is an indispensable element for achieving robust and high-fidelity quantum gates due to its built-in noise-resilience feature. However, due to the complexity of manipulation and the intrinsic leakage of the encoded quantum information to non-logical-qubit basis, the experimental realization of universal nonadiabatic holonomic quantum computation is very difficult. Here, we propose to implement scalable nonadiabatic holonomic quantum computation with decoherence-free subspace encoding on a two-dimensional square superconducting transmon-qubit lattice, where only the two-body int…

Spin-based quantum computing using electrons on liquid helium

Numerous physical systems have been proposed for constructing quantum computers, but formidable obstacles stand in the way of making even modest systems with a few hundred quantum bits (qubits). Several approaches utilize the spin of an electron as the qubit. Here it is suggested that the spin of electrons floating on the surface of liquid helium will make excellent qubits. These electrons can be electrostatically held and manipulated much like electrons in semiconductor heterostructures, but being in a vacuum the spins on helium suffer much less decoherence. In particular, the spin orbit inte…

弱磁场下超导量子比特中$1/f$磁通噪声的演化

Evolution of $1/f$ Flux Noise in Superconducting Qubits with Weak Magnetic Fields

针对超导电路$1/f$磁通噪声微观起源不明的问题，研究人员通过对电容分流磁通量子比特施加弱面内磁场，观测到退相时间和噪声谱的特殊变化，提出该现象与自旋团簇尺寸随磁场增大相关，为构建完整的磁通噪声微观理论提供了依据。

CZ门保真度高于$99.8\\%$的长距离transmon耦合器

Long-distance transmon coupler with CZ gate fidelity above $99.8\%$

本研究提出基于悬浮transmon的可调长距离量子比特耦合器，通过波导介导耦合实现2毫米间距下50MHz以上耦合，降低串扰并预留读出器件空间，达成99.81%保真度的CZ门，助力可扩展量子处理器研发。