报告题目 (Title)：Shortcuts to adiabaticity for longitudinal spin-photon interfaces in quantum dots（量子点中纵向自旋声子界面的量子绝热捷径）

报告人 (Speaker)：陈玺 教授（马德里材料科学研究所）

报告时间 (Time)：2026年5月29日（周五）下午2:00-5:00

报告地点 (Place)：校本部G601

邀请人 (Inviter)：张永平

主办部门：理学院物理系

摘要 (Abstract)：

Longitudinal spin--photon coupling in semiconductor quantum dots provides a promising route toward fast and flexible quantum control. In particular, hole-spin qubits in Si and Ge quantum dots exhibit strong electrically tunable spin-orbit interaction and anisotropic g-tensors, enabling the spin-photon interaction to be tuned from transverse to longitudinal by adjusting the magnetic-field orientation. In the longitudinal regime, the resonator field modulates the qubit energy splitting without inducing spin flips, which naturally suppresses unwanted excitation exchange and enables quantum nondemolition operations, fast entangling gates, and reduced backaction.

Here we develop a unified framework based on shortcuts to adiabaticity (STA) to engineer time-dependent longitudinal spin--photon interfaces for semiconductor spin qubits. By combining inverse engineering with an exact polaron-like unitary transformation, we derive analytical control protocols that map target quantum operations directly onto experimentally tunable longitudinal couplings. The key idea is to design an auxiliary trajectory that enforces closed-loop displacements of the resonator in phase space, so that the cavity returns to its vacuum state at the end of the protocol while the qubit system accumulates the desired phase. For a single qubit, the method realizes fast and high-fidelity phase gates through qubit-state-dependent cavity displacements. The resonator is displaced along a closed trajectory and brought back to vacuum at the final time, thereby eliminating residual qubit--photon entanglement. For two qubits coupled to a common resonator mode, the same strategy produces an effective controllable ZZ interaction and enables fast entangling gates such as the controlled-$Z$ gate. In contrast to conventional modulated-pulse protocols, where gate times are restricted by resonance conditions required to close the cavity trajectory, the STA construction imposes the closed-loop condition by design and therefore allows gate implementation at arbitrary final times. The framework further extends naturally to multi-qubit systems, where it generates programmable Ising-type interaction graphs and supports multipartite entanglement generation, including GHZ states.

We also analyze the effects of realistic imperfections, including low-frequency qubit dephasing, cavity dissipation, and residual transverse coupling. The results show that fast STA protocols strongly suppress dephasing-induced errors, while smooth pulse shaping mitigates photon-loss-induced residual cavity displacement. Residual transverse terms can be treated perturbatively and remain small in the dispersive regime with bounded pulse derivatives. These results establish STA-engineered longitudinal coupling as a scalable and versatile paradigm for quantum control in solid-state platforms. The approach provides a unified route to fast single-qubit gates, cavity-mediated entangling gates, robust readout, and programmable multi-qubit interactions in semiconductor spin-qubit architectures.