Tight uniform continuity bounds for quantum entropies: conditional entropy, relative entropy distance and energy constraintsResearch Paper
Motivation
We present a bouquet of continuity bounds for quantum entropies, falling broadly into two classes: First, a tight analysis of the Alicki-Fannes continuity bounds for the conditional von Neumann entropy, reaching almost the best possible form that depends only on the system dimension and the trace distance of the states. Almost the same proof can be used to derive similar continuity bounds for the relative entropy distance from a convex set of states or positive operators. As applications we give new proofs, with tighter bounds, of the asymptotic continuity of the relative entropy of entanglement, , and its regularization , as well as of the entanglement of formation, . Using a novel "quantum coupling" of density operators, which may be of independent interest, we extend the latter to an asymptotic continuity bound for the regularized entanglement of formation, aka entanglement cost, . Second, analogous continuity bounds for the von Neumann entropy and conditional entropy in infinite dimensional systems under an energy constraint, most importantly systems of multiple quantum harmonic oscillators. While without an energy bound the entropy is discontinuous, it is well-known to be continuous on states of bounded energy. However, a quantitative statement to that effect seems not to have been known. Here, under some regularity assumptions on the Hamiltonian, we find that, quite intuitively, the Gibbs entropy at the given energy roughly takes the role of the Hilbert space dimension in the finite-dimensional Fannes inequality.
This mission is the statement-level formalization of Tight uniform continuity bounds for quantum entropies: conditional entropy, relative entropy distance and energy constraints (arXiv:1507.07775v6). Every numbered result of the paper was scanned. The results stated here are open sorry goals, ready for solvers to prove.
What is formalized
7 statements of the paper are in Lean 4 (Mathlib 0df444a). The goal theorem is Remark 3: explicit near-tightness example for Lemma 2 (Remark 3: explicit near-tightness example for Lemma 2, PDF p. 3). The milestones are the other numbered results, in the paper's order, each quoting the paper.
The paper's own objects are the definition item of this mission. Objects shared across papers come from the prove2quantum library and from earlier papers' missions, listed as references.
Provenance: prove2quantum's pipeline drafted each statement (gpt-6.1-sol on Stanford's Sherlock cluster). A blind read-back, written without seeing the paper, is attached to every item. An independent moderator compared each statement against the paper and passed the whole paper without edits.
Deferred results
12 results of the paper are not stated yet, because the library lacks an interface they need:
- Lemma 2: almost tight conditional entropy continuity (paper headline): Normalized trace-class bipartite states, partial traces, extended conditional entropy, common-basis qc/cq predicates (hard)
- Corollary 4: continuity of entanglement of formation and entanglement cost: Countable exact pure-state ensembles, entanglement of formation, and its tensor-power regularization with an infinite factor (hard)
- Remark 6: separable infinite-dimensional extension of Proposition 5: Trace-class tensor-square states, Hilbert-Schmidt vectorization, marginals, basis transpose and root fidelity (hard)
- Corollary 8: continuity of relative entropy of entanglement and its regularization: Infinite-factor Umegaki relative entropy, closed separable-state set, E_R and E_R-infinity (hard)
- Proposition 14: quantum coupling with large operator norm: Arbitrary separable trace-class couplings, tensor marginals and operator norm (hard)
- Lemma 15: energy-constrained entropy continuity by coupling: Arbitrary finite-energy trace-class states, full spectral entropy, trace distance and quadratic-form energy (hard)
- Meta-Lemma 16: adjustable-cutoff energy-constrained entropy continuity: Arbitrary finite-energy trace-class states and their spectral entropy and trace distance (hard)
- Meta-Lemma 17: energy-constrained conditional entropy continuity: Infinite-dimensional bipartite trace-class states with finite-A-entropy conditional extension and A-only form energy (hard)
- Eq. (19): oscillator Gibbs entropy bound and equal-allocation maximization: A correct optimizing equality for the unequal-frequency allocation simplex (source-ambiguity)
- Lemma 18: explicit harmonic-oscillator entropy and conditional entropy bounds: Full Fock trace-class input states, oscillator quadratic-form energy, and arbitrary-ancilla conditional entropy (hard)
- Remark 19: large-energy sharpness of oscillator leading coefficients: Actual mixed Fock witnesses, Gibbs purification, trace distance and conditional entropy, plus large-energy comparison (hard)
- Unnumbered consequence: uniform continuity at each fixed energy: A trace-distance state domain of arbitrary bounded-energy densities and uniform-in-B conditional entropy (hard)
Selected references
- Tight uniform continuity bounds for quantum entropies: conditional entropy, relative entropy distance and energy constraints, arXiv:1507.07775v6, https://arxiv.org/abs/1507.07775v6