Locality and time irreversibility in quantum processes

Tajima, Hiroyasu, Ryuji Takagi, Yui Kuramochi

Symmetry, irreversibility, and quantum coherence are foundational concepts in physics. Here, we present a universal tradeoff relation between these three concepts. This particularly reveals that (1) under a global symmetry, any attempt to change the local conserved charge causes inevitable irreversibility, and (2) such irreversibility can be mitigated by quantum coherence. Our tradeoff relation follows solely from the unitarity and global symmetry of the total dynamics, allowing for general applicability. For non-equilibrium physics, it relates the coherence cost and the entropy production -- representing thermodynamic irreversibility -- in arbitrary quantum processes. It also provides fundamental limitations on the capability of a number of quantum information processing tasks -- such as gate and measurement implementation and error correction -- that involve symmetry restrictions. Furthermore, it predicts how many bits of classical information thrown into a black hole become unreadable under energy conservation. Our tradeoff relation is based on quantum uncertainty relation, showcasing intimate connections between fundamental physical principles and ultimate operational capability of quantum processes.

Stig Stenholm

Satoshi Uchiyama

Dmitriy Kim

A fundamental hypothesis is proposed in which information is treated as a primary physical quantity, while time is considered a derived characteristic emerging from the ordered accumulation of irreversible interaction events. The concept of an Information-Discrete Quantum Process (IDQP) is introduced as an elementary act of fixing a change in an informational state. Local time is defined as an internal characteristic of a physical system, whereas global time is interpreted as an emergent criterion of consistency among multiple local times. The hypothesis provides a conceptual framework for reexamining causality, time, and matter.

Reddy Govind

We extend Barandes’ indivisible stochastic interpretation of quantum mechanics to address the emergence of classical spacetime and the arrow of time from collective quantum processes. While Barandes (2025) demonstrates that individual quantum sys- tems can be understood as indivisible stochastic processes, we show that when many such systems interact, their collective behavior generates emergent spatial structure through quantum correlations and emergent temporal divisibility through thermody- namic irreversibility. Specifically, we argue that: (1) spatial relations emerge from patterns of quantum entanglement and correlation among multiple actualizations; (2) thermodynamic entropy production in many-body systems creates an irreversible ar- row of time; (3) this irreversibility transforms the fundamentally indivisible quantum process into an apparently divisible classical process; and (4) the time parameter t itself emerges as a bookkeeping device for tracking these irreversible collective changes. This framework provides a unified account of the quantum-to-classical transition, connect- ing quantum foundations, statistical mechanics, and emergent spacetime in a coherent picture where both space and time arise from the collective dynamics of indivisible quantum actualizations.

Guillaume Cœuret Cauquil, Patrice A. Camati, Irénée Frerot +3 more

Entropy production quantifies the amount of irreversibility of a physical process, leading to fundamental bounds for thermodynamic quantities. It captures the inability to run a physical system forward and then backward, bringing it to the same initial state. Considerable research has been carried out in the last decades to extend entropy production to non-equilibrium quantum processes. We experimentally investigate the entropy production of such forward-backward cycles affected by genuinely quantum irreversibility. Namely, we consider processes realized to erase different types of correlations between two interacting systems, from obliterating solely quantum coherence to completely decorrelating local states. This makes the measurement of entropy production experimentally challenging. Addressing this challenge is the purpose of this paper.