Dresden 2026 – scientific programme

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QI: Fachverband Quanteninformation

QI 7: Quantum Thermodynamics

QI 7.2: Talk

Tuesday, March 10, 2026, 09:45–10:00, BEY/0E17

Exploring Noisy Quantum Thermodynamical Processes via Global Depolarizing Approximation — Jian Li¹, Xiaoyang Wang², Marcus Huber¹, Nicolai Friis¹, and •Pharnam Bakhshinezhad¹ — ¹Atominstitut, TU Wien, Stadionallee 2, 1020 Vienna, Austria — ²RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS), Wako 351-0198, Japan

Noise is an unavoidable challenge for quantum thermodynamical protocols in deep circuits [1]. To overcome the difficulty of analytically characterizing cumulative, gate-dependent errors, we introduce the Global Depolarizing Approximation (GDA), a scalable framework. The GDA approximates complex local noise channels with a single, system-wide depolarizing channel, requiring only a moderate circuit depth that approximates a unitary 2-design [2].

Applying the GDA to the Two-Sort Algorithmic Cooling (TSAC) protocol [3], we derive a novel analytical expression for its asymptotic cooling limit under realistic noise. This analysis reveals a fundamental noise-induced trade-off: the ideal exponential gain from increasing the qubit number is counteracted by an exponential increase in noise accumulation, which dictates an optimal qubit number and a sharp upper bound on the achievable cooling performance. We validate the GDA's accuracy against detailed physical noise simulations for both TSAC and Dynamic Cooling (DC) protocols [4]. Our framework offers a powerful tool for quantifying the thermodynamic cost of imperfect control in noisy quantum systems.

Keywords: Quantum Thermodynamics; Algorithmic Cooling; Quantum Noise; Global Depolarizing Approximation; Imperfect control