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Exact prediction of the lambda point of liquid helium-4 from information causality

Jiaxuan Yang

Published Mar 8, 2026• 0 citations
Publisher

Abstract

We derive a universal upper bound on the temperature of macroscopic quantum coherence, based on information causality and quantum speed limits. The bound, \( T_c \leq \frac{\hbar}{2k_B} \cdot \frac{v_{\text{LR}}}{\xi_0} \), arises from the interplay between the Lieb-Robinson information speed and the energy-time uncertainty principle. Without any fitting parameters, it accurately predicts the superfluid transition temperature of $^4$He (2.185 K vs. experimental 2.172 K) when geometric effects are included. The bound applies across diverse systems—from superconductors to black holes—suggesting a fundamental connection between quantum coherence, causality, and information propagation. This work highlights information causality as a foundational constraint on macroscopic quantum phenomena. The manuscript has been submitted to Physical Review Letters.

DOI
10.5281/zenodo.18906653

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We derive a universal upper bound on the temperature of macroscopic quantum coherence, based on information causality and quantum speed limits. The bound, ( T_c \leq \frac{\hbar}{2k_B} \cdot \frac{v_{\text{LR}}}{\xi_0} ), arises from the interplay between the Lieb-Robinson information speed and the energy-time uncertainty principle. Without any fitting parameters, it accurately predicts the superfluid transition temperature of 4^44He (2.185 K vs. experimental 2.172 K) when geometric effects are included. The bound applies across diverse systems—from superconductors to black holes—suggesting a fundamental connection between quantum coherence, causality, and information propagation. This work highlights information causality as a foundational constraint on macroscopic quantum phenomena. The manuscript has been submitted to Physical Review Letters.
The Lieb-Robinson bound (LRB) states that the range and strength of interactions between the constituents of a complex many-body system impose upper limits to how fast the signal can propagate. It manifests in a light conelike growth of correlation function connecting two distant subsystems. Here, we employ the techniques of quantum information to demonstrate that the LRB can be determined from local measurements performed on a single qubit that is connected to a many-body system. This formulation provides an operational recipe for estimating the LRB in complex systems, replacing the measurement of the correlation function with simple single-particle manipulations. We demonstrate the potency of this approach by deriving the upper limit to the speed of signal propagation in the XY spin chain.
Speed of state transitions in macroscopic systems is a crucial concept for foundations of nonequilibrium statistical mechanics as well as various applications in quantum technology represented by optimal quantum control.While extensive studies have made efforts to obtain rigorous constraints on dynamical processes since Mandelstam and Tamm, speed limits that provide tight bounds for macroscopic transitions have remained elusive.Here, by employing the local conservation law of probability, the fundamental principle in physics, we develop a general framework for deriving qualitatively tighter speed limits for macroscopic systems than many conventional ones.We show for the first time that the speed of the expectation value of an observable defined on an arbitrary graph, which can describe general many-body systems, is bounded by the "gradient" of the observable, in contrast with conventional speed limits depending on the entire range of the observable.This framework enables us to derive novel quantum speed limits for macroscopic unitary dynamics.Unlike previous bounds, the speed limit decreases when the expectation value of the transition Hamiltonian increases; this intuitively describes a new trade-off relation between time and the quantum phase difference.Our bound is dependent on instantaneous quantum states and thus can achieve the equality condition, which is conceptually distinct from the Lieb-Robinson bound.We also find that, beyond expectation values of macroscopic observables, the speed of macroscopic quantum coherence can be bounded from above by our general approach.The newly obtained bounds are verified in transport phenomena in particle systems and nonequilibrium dynamics in many-body spin systems.We also demonstrate that our strategy can be applied for finding new speed limits for macroscopic transitions in stochastic systems, including quantum ones, where the bounds are expressed by the entropy production rate.Our work elucidates novel speed limits on the basis of local conservation law, providing fundamental limits to various types of nonequilibrium quantum macroscopic phenomena.
Abstract We establish a universal bound on entanglement dynamics, proving that for any quantum system with energy E, the rate of entanglement entropy change is limited by ∣dSdt∣≤2Eπℏ\left |\frac{dS}{dt}\right | \leq \frac{2E}{\pi \hbar}​dtdS​​≤πℏ2E​ | d S d t | ≤ 2 E π ħ . This bound, which can be saturated by specific protocols, emerges from a framework treating entanglement rate as a physical observable and connects directly to quantum circuit complexity. When extended to quantum field theory, we demonstrate that the maximum entanglement propagation velocity equals the speed of light, revealing a fundamental connection between quantum information constraints and relativistic causality. We propose experimental tests on quantum computing platforms and explore implications for quantum computing efficiency and spacetime structure. Our results suggest that information-theoretic principles may be more fundamental than spacetime concepts, unifying quantum information, computational complexity, and relativistic physics.
We prove that the time required for sustained information scrambling in any Hamiltonian quantum system is universally at least logarithmic in the entanglement entropy of scrambled states. This addresses two foundational problems in nonequilibrium quantum dynamics. (1) It sets the earliest possible time for the applicability of equilibrium statistical mechanics in a quantum system coupled to a bath at a finite temperature. (2) It proves a version of the fast scrambling conjecture, originally motivated in models associated with black holes, as a fundamental property of quantum mechanics itself. Our result builds on a refinement of the energy-time uncertainty principle in terms of the infinite temperature spectral form factor in quantum chaos. We generalize this formulation to arbitrary initial states of the bath, including finite temperature states, by mapping Hamiltonian dynamics with any initial state to nonunitary dynamics at infinite temperature. A regularized spectral form factor emerges naturally from this procedure, whose decay is universally constrained by analyticity in complex time. This establishes an exact speed limit on information scrambling by the most general quantum mechanical Hamiltonian without any restrictions on locality or the nature of interactions.
Uncertainty relations represent a foundational principle in quantum mechanics, imposing inherent limits on the precision with which \textit{mechanically} conjugate variables such as position and momentum can be simultaneously determined. This work establishes analogous relations for \textit{thermodynamically} conjugate variables -- specifically, a classical intensive parameter θθθ and its corresponding extensive quantum operator O^\hat{O}O^ -- in equilibrium states. We develop a framework to derive a rigorous thermodynamic uncertainty relation for such pairs, where the uncertainty of the classical parameter θθθ is quantified by its quantum Fisher information Fθ\mathcal{F}_θFθ​. The framework is based on an exact integral representation that relates Fθ\mathcal{F}_θFθ​ to the autocorrelation function of operator O^\hat{O}O^. From this representation, we derive a tight upper bound for the quantum Fisher information, which yields a thermodynamic uncertainty relation: Δθ ΔO‾≥kBTΔθ\,\overline{ΔO} \ge k_\text{B}TΔθΔO≥kB​T with ΔO‾≡∂θ⟨O^⟩ Δθ\overline{ΔO}\equiv\partial_θ\langle\hat{O}\rangle\,ΔθΔO≡∂θ​⟨O^⟩Δθ and TTT is the system temperature. The result establishes a fundamental precision limit for quantum sensing and metrology in thermal systems, directly connecting it to the thermodynamic properties of linear response and fluctuations.
The Lieb-Robinson bound shows the existence of a maximum speed of signal propagation in discrete quantum mechanical systems with local interactions. This generalizes the concept of relativistic causality beyond field theory, and provides a powerful tool in theoretical condensed matter physics and quantum information science. Here, we extend the scope of this seminal result by considering general markovian quantum evolution, where we prove that an equivalent bound holds. In addition, we use the generalized bound to demonstrate that correlations in the stationary state of a Markov process decay on a length scale set by the Lieb-Robinson velocity and the system's relaxation time.