Simulation of open quantum dynamics and investigation of quantum correlations in finite systems

Federico Gallina, Matteo Bruschi, Barbara Fresch

Abstract The unraveling of open quantum system dynamics in terms of stochastic quantum trajectories offers a picture of open system dynamics that consistently considers memory effects stemming from the finite correlation time of environment fluctuations. These fluctuations significantly influence the coherence and energy transport properties of excitonic systems. When their correlation time is comparable to the timescale of the Hamiltonian evolution, it leads to the departure of open system dynamics from the Markovian limit. In this work, we leverage the unraveling of exciton dynamics through stochastic Hamiltonian propagators to design quantum circuits that simulate exciton transport, capturing finite memory effects. In addition to enabling the synthesis of parametrizable quantum circuits, stochastic unitary propagators provide a transparent framework for investigating non-Markovian effects on exciton transport. Our analysis reveals a nuanced relationship between environment correlation time and transport efficiency, identifying a regime of ‘memory-assisted’ quantum transport where time-correlated fluctuations allow the system to reach higher efficiency. However, this property is not universal and can only be realized in conjunction with specific features of the system Hamiltonian.

Jacek Okołowicz, Marek Płoszajczak, I. Rotter

Ángel S. Sanz, Salvador Miret-Artés

Samarth Lamba, Aleksandra A. Ziółkowska

Abstract Hamiltonian simulation is one of the main proposed applications of near-term quantum computers, but its practical value depends on whether real hardware can preserve intended Hamiltonian dynamics once sampling limits, gate noise, decoherence, and circuit depth are taken into account. This study investigates whether the IBM quantum backend \texttt{ibm\_marrakesh} can reproduce the many-body dynamics shown by ideal simulation, using a 15-qubit one-dimensional tilted-field Ising chain as the benchmark system. The system was initialized with all qubits spin-up except for a localized spin-down excitation at the central qubit, $q_8$, and evolved using a second-order Trotterized circuit with timestep $\Delta t=0.1$. The reference case, $h_z=0$, was compared with the tilted-field case, $h_z=h_x=0.35625$, across three interaction regimes: $J=0.90h_x$, $J=h_x$, and $J=1.40h_x$. Local magnetization, total magnetization, and connected spin correlations were used to track magnetization memory and finite-speed correlation spreading from the central excitation. The ideal simulation shows clear local and total magnetization evolution, as well as connected-correlation spreading outward from $q_8$, giving a baseline for the intended Hamiltonian dynamics. The IBM hardware results reproduce the broad early-time magnetization trend but show compressed local-magnetization values, reduced separation between qubits, and weaker long-range connected-correlation structure. These differences indicate that the open-access quantum hardware preserves some early-time features of the intended dynamics, while longer-time correlation spreading is increasingly obscured by finite sampling, two-qubit gate errors, readout error, decoherence, and circuit depth. Overall, the study uses this spin-chain system as a direct benchmark for testing how much physically meaningful many-body behavior can still be extracted from noisy open-access quantum hardware.

Dmitry Mozyrsky

Samarth Lamba, Aleksandra A. Ziółkowska

Abstract Hamiltonian simulation is one of the main proposed applications of near-term quantum computers, but its practical value depends on whether real hardware can preserve intended Hamiltonian dynamics once sampling limits, gate noise, decoherence, and circuit depth are taken into account. This study investigates whether the IBM quantum backend \texttt{ibm\_marrakesh} can reproduce the many-body dynamics shown by ideal simulation, using a 15-qubit one-dimensional tilted-field Ising chain as the benchmark system. The system was initialized with all qubits spin-up except for a localized spin-down excitation at the central qubit, $q_8$, and evolved using a second-order Trotterized circuit with timestep $\Delta t=0.1$. The reference case, $h_z=0$, was compared with the tilted-field case, $h_z=h_x=0.35625$, across three interaction regimes: $J=0.90h_x$, $J=h_x$, and $J=1.40h_x$. Local magnetization, total magnetization, and connected spin correlations were used to track magnetization memory and finite-speed correlation spreading from the central excitation. The ideal simulation shows clear local and total magnetization evolution, as well as connected-correlation spreading outward from $q_8$, giving a baseline for the intended Hamiltonian dynamics. The IBM hardware results reproduce the broad early-time magnetization trend but show compressed local-magnetization values, reduced separation between qubits, and weaker long-range connected-correlation structure. These differences indicate that the open-access quantum hardware preserves some early-time features of the intended dynamics, while longer-time correlation spreading is increasingly obscured by finite sampling, two-qubit gate errors, readout error, decoherence, and circuit depth. Overall, the study uses this spin-chain system as a direct benchmark for testing how much physically meaningful many-body behavior can still be extracted from noisy open-access quantum hardware.