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1. Optimising Perfect Quantum State Transfer for Timing Insensitivity

   Kay, Alastair; Kim, Sooyeong; Tamon, Christino (July 2025, arxiv.org (quant-ph))

   When studying the perfect transfer of a quantum state from one site to another, it is typically assumed that one can receive the arriving state at a specific instant in time, with perfect accuracy. Here, we study how sensitive perfect state transfer is to that timing. We design engineered spin chains which reduce their sensitivity, proving that this construction is asymptotically optimal. The same construction is applied to the task of creating superpositions, also known as fractional revival. 

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2. Single-ancilla ground state preparation via Lindbladians

   https://doi.org/10.1103/PhysRevResearch.6.033147  

   Ding, Zhiyan; Chen, Chi-Fang; Lin, Lin (August 2024, Physical Review Research)

   We design a quantum algorithm for ground state preparation in the early fault tolerant regime. As a Monte Carlo style quantum algorithm, our method features a Lindbladian where the target state is stationary. The construction of this Lindbladian is algorithmic and should not be seen as a specific approximation to some weakly coupled system-bath dynamics in nature. Our algorithm can be implemented using just one ancilla qubit and efficiently simulated on a quantum computer. It can prepare the ground state even when the initial state has zero overlap with the ground state, bypassing the most significant limitation of methods like quantum phase estimation. As a variant, we also propose a discrete-time algorithm, demonstrating even better efficiency and providing a near-optimal simulation cost depending on the desired evolution time and precision. Numerical simulations using Ising and Hubbard models demonstrate the efficacy and applicability of our method. Published by the American Physical Society2024 

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3. How excitation wavelength affects excited state dynamics in o -nitrophenol: A theoretical perspective

   https://doi.org/10.1063/5.0274633  

   Abeygunewardane, Dakshitha; Weinacht, Thomas; Matsika, Spiridoula (July 2025, The Journal of Chemical Physics)

   The excited-state dynamics of o-nitrophenol have been explored using trajectory surface hopping nonadiabatic dynamics combined with floating occupation molecular orbital complete active space configuration interaction. We focus on the effect of excitation energy on the subsequent dynamics. The absorption spectrum of o-nitrophenol has two peaks, centered at 3.9 eV (∼320 nm) and 5.1 eV (∼240 nm), and we performed dynamics starting from each of these peaks. The results show that even though the relaxation time constants are similar for the two excitation windows, the underlying dynamics are different. When exciting to the low energy peak, the dynamics are dominated by intramolecular proton transfer followed by internal conversion to the ground state, while exciting to the high-energy peak leads to fast internal conversion to the first excited state and slower decay to the ground state. In this case, intramolecular proton transfer does not occur as frequently, and many trajectories decay to the ground state through conical intersections without proton transfer. By calculating spin–orbit coupling values along the trajectories, we also show that intersystem crossing is possible. Based on the Landau–Zener probability formula, we estimate that there is about a 30%–40% probability that intersystem crossing will occur within 1 ps. 

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4. Adiabatic quantum state transfer in a semiconductor quantum-dot spin chain

   https://doi.org/10.1038/s41467-021-22416-5  

   Kandel, Yadav P.; Qiao, Haifeng; Fallahi, Saeed; Gardner, Geoffrey C.; Manfra, Michael J.; Nichol, John M. (December 2021, Nature Communications)

   null (Ed.)

   Abstract Semiconductor quantum-dot spin qubits are a promising platform for quantum computation, because they are scalable and possess long coherence times. In order to realize this full potential, however, high-fidelity information transfer mechanisms are required for quantum error correction and efficient algorithms. Here, we present evidence of adiabatic quantum-state transfer in a chain of semiconductor quantum-dot electron spins. By adiabatically modifying exchange couplings, we transfer single- and two-spin states between distant electrons in less than 127 ns. We also show that this method can be cascaded for spin-state transfer in long spin chains. Based on simulations, we estimate that the probability to correctly transfer single-spin eigenstates and two-spin singlet states can exceed 0.95 for the experimental parameters studied here. In the future, state and process tomography will be required to verify the transfer of arbitrary single qubit states with a fidelity exceeding the classical bound. Adiabatic quantum-state transfer is robust to noise and pulse-timing errors. This method will be useful for initialization, state distribution, and readout in large spin-qubit arrays for gate-based quantum computing. It also opens up the possibility of universal adiabatic quantum computing in semiconductor quantum-dot spin qubits. 

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5. Excited State Structural Evolution of a GFP Single-Site Mutant Tracked by Tunable Femtosecond-Stimulated Raman Spectroscopy

   https://doi.org/10.3390/molecules23092226  

   Tang, Longteng; Zhu, Liangdong; Taylor, Miles; Wang, Yanli; Remington, S.; Fang, Chong (September 2018, Molecules)

   Tracking vibrational motions during a photochemical or photophysical process has gained momentum, due to its sensitivity to the progression of reaction and change of environment. In this work, we implemented an advanced ultrafast vibrational technique, femtosecond-stimulated Raman spectroscopy (FSRS), to monitor the excited state structural evolution of an engineered green fluorescent protein (GFP) single-site mutant S205V. This mutation alters the original excited state proton transfer (ESPT) chain. By strategically tuning the Raman pump to different wavelengths (i.e., 801, 539, and 504 nm) to achieve pre-resonance with transient excited state electronic bands, the characteristic Raman modes of the excited protonated (A*) chromophore species and intermediate deprotonated (I*) species can be selectively monitored. The inhomogeneous distribution/population of A* species go through ESPT with a similar ~300 ps time constant, confirming that bridging a water molecule to protein residue T203 in the ESPT chain is the rate-limiting step. Some A* species undergo vibrational cooling through high-frequency motions on the ~190 ps time scale. At early times, a portion of the largely protonated A* species could also undergo vibrational cooling or return to the ground state with a ~80 ps time constant. On the photoproduct side, a ~1330 cm−1 delocalized motion is observed, with dispersive line shapes in both the Stokes and anti-Stokes FSRS with a pre-resonance Raman pump, which indicates strong vibronic coupling, as the mode could facilitate the I* species to reach a relatively stable state (e.g., the main fluorescent state) after conversion from A*. Our findings disentangle the contributions of various vibrational motions active during the ESPT reaction, and offer new structural dynamics insights into the fluorescence mechanisms of engineered GFPs and other analogous autofluorescent proteins. 

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