Universal quantum computation with electron spins in quantum dots based on superpositions of spacetime paths and Coulomb blockade

Bias-induced chiral current and topological blockadein triple quantum dots

We theoretically investigate the quantum transport properties of a triangular triple quantum dot (TTQD) ring connected with two reservoirs by means of analytical derivation and accurate hierarchical-equations-of-motion calculation. A bias-induced chiral current in the absence of magnetic field is firstly demonstrated, which results from that the coupling between spin gauge field and spin current in the nonequilibrium TTQD induces a scalar spin chirality that lifts the chiral degeneracy and thus the time inversion symmetry. The chiral current is proved to oscillate with bias within the Coulomb …

反对称轨道和电子-电子相互作用对石墨烯双量子点中双粒子自旋和能谷阻塞的作用

The role of antisymmetric orbitals and electron-electron interactions on the two-particle spin and valley blockade in graphene double quantum dots

本文实验研究了双电子双层石墨烯双量子点中的自旋和能谷阻塞，发现该阻塞受反对称轨道、电子-电子相互作用及能谷g因子差异限制，并基于速率方程模拟验证了相关能级跃迁。

Pauli Blockade in Silicon Quantum Dots with Spin-Orbit Control

Quantum computation relies on accurate measurements of qubits not only for reading the output of the calculation, but also to perform error correction. Most proposed scalable silicon architectures utilize Pauli blockade of triplet states for spin-to-charge conversion. In recent experiments, there have been instances when instead of conventional triplet blockade readout, Pauli blockade is sustained only between parallel spin configurations, with $|T_0\rangle$ relaxing quickly to the singlet state and leaving $|T_+\rangle$ and $|T_-\rangle$ states blockaded -- which we call \textit{parity readou…

Spin-Blockade Spectroscopy of Si/SiGe Quantum Dots

We implement a technique for measuring the singlet-triplet energy splitting responsible for spin-to-charge conversion in semiconductor quantum dots. This method, which requires fast, single-shot charge measurement, reliably extracts an energy in the limits of both large and small splittings. We perform this technique on an undoped, accumulation-mode Si/SiGe triple-quantum dot and find that the measured splitting varies smoothly as a function of confinement gate biases. Not only does this demonstration prove the value of having an $in~situ$ excited-state measurement technique as part of a stand…

机器学习揭示双层石墨烯双量子点输运谱中的多重泡利阻塞

Machine learning unveils multiple Pauli blockades in the transport spectroscopy of bilayer graphene double-quantum dots

本文通过建立理论模型并结合机器学习，系统研究了双层石墨烯双量子点中的多重泡利阻塞现象，实现了对泡利阻塞区域的实时自动检测，为二维材料自旋-谷量子比特实验提供了基础。

双层石墨烯双量子点中的三载流子自旋阻塞与耦合

Three-carrier spin blockade and coupling in bilayer graphene double quantum dots

针对静电定义的双层石墨烯量子点，研究其电荷构型$(1,2)\rightleftarrows(0,3)$下的自旋阻塞现象，分析泄漏电流对隧道耦合及磁场的依赖性，揭示了共隧穿、自旋-谷混合等机制的作用。

Pauli Spin Blockade in a Resonant Triple Quantum Dot Molecule

Pauli spin blockade in quantum dot systems occurs when the charge transport is allowed only for some spin states, and it has been an efficient tool in spin-based qubit devices in semiconductors. We theoretically investigate a Pauli spin blockade in a triple quantum dot molecule consisting of three identical quantum dots in a semiconductor in the presence of an external magnetic field through the molecule. When the three-electron state is on resonance with two- or four-electron states, the Aharonov-Bohm oscillation and the Zeeman splitting lead to a periodic spin blockade effect. We focus on th…

粒子-空穴对称性保护石墨烯量子点中的自旋-谷阻塞效应

Particle-hole symmetry protects spin-valley blockade in graphene quantum dots

本研究发现双层石墨烯可实现具有近乎完美粒子-空穴对称性的电子-空穴双量子点，该对称性会产生受保护的单粒子自旋-谷阻塞效应，可用于鲁棒的自旋、谷-电荷转换，支撑自旋与谷量子比特运行。

里德伯封锁中的量子计数

Quantum Counting in the Rydberg Blockade

我们提出一种在中性原子量子计算机上原生近似计数平面2SAT解数量的量子算法，利用里德伯封锁映射约束，通过猝灭产生均匀叠加并采样计数，数值验证其在网格上的准确性与普适性。

Phonon-induced dephasing of singlet-triplet superpositions in double quantum dots without spin-orbit coupling

We show that singlet-triplet superpositions of two-electron spin states in a double quantum dot undergo a phonon-induced pure dephasing which relies only on the tunnel coupling between the dots and on the Pauli exclusion principle. As such, this dephasing process is independent of spin-orbit coupling or hyperfine interactions. The physical mechanism behind the dephasing is elastic phonon scattering, which persists to much lower temperatures than real phonon-induced transitions. Quantitative calculations performed for a lateral GaAs/AlGaAs gate-defined double quantum dot yield micro-second deph…

Valley blockade quantum switching in Silicon nanostructures

In analogy to the Coulomb and the Pauli spin blockade, based on the electrostatic repulsion and the Pauli exclusion principle respectively, the concept of valley blockade in Silicon nanostructures is explored. The valley parity operator is defined. Valley blockade is determined by the parity conservation of valley composition eigenvectors in quantum transport. A Silicon quantum changeover switch based on a triple of donor quantum dots capable to separate electrons having opposite valley parity by virtue of the valley parity conservation is proposed. The quantum changeover switch represents a n…

Dispersive Photon Blockade in a Superconducting Circuit

Mediated photon-photon interactions are realized in a superconducting coplanar waveguide cavity coupled to a superconducting charge qubit. These non-resonant interactions blockade the transmission of photons through the cavity. This so-called dispersive photon blockade is characterized by measuring the total transmitted power while varying the energy spectrum of the photons incident on the cavity. A staircase with four distinct steps is observed and can be understood in an analogy with electron transport and the Coulomb blockade in quantum dots. This work differs from previous efforts in that …