arXiv subjects

Fiona Abney-McPeek

Publications and source records attributed to Fiona Abney-McPeek.

4 recordsLinked to original sources

arXiv2026

Entanglement and information scrambling in long-range measurement-only circuits

Measurement-only circuits provide a minimal setting in which repeated local projections can either generate or suppress many-body entanglement, giving rise to measurement-induced phase transitions and dynamical regimes, that might have no unitary counterpart. Here we investigate entanglement and information transitions in one-dimensional measurement-only Clifford circuits with long-range two-qubit parity checks. By tuning both the measurement range and density per layer, we uncover a broad set of phases whose classification requires probes beyond entanglement entropy, such as mutual information, tripartite mutual information, purification from an ancilla, and Bell-cluster statistics. We map phase diagrams using large-scale Clifford simulations for two protocols: a random-basis design in which each measurement is randomly chosen from $\lbrace XX,YY,ZZ \rbrace$, and a single-basis design in which the basis is fixed within each layer but varies between layers, hence introducing more structure to the circuit. We map the trajectory-averaged entanglement entropy to a two-dimensional statistical mechanics model by extending a replica-based method to random-basis measurement-only circuits, and show that a continuous-time limit yields an effective long-range XX hamiltonian in the steady state. This connection links the observed volume-law to sub-volume-law entanglement transition to the boundary between a continuous symmetry broken phase and a critical XY phase. Strikingly, in structured (single-basis) circuits we find a phase in which volume-law and long-range entanglement coexists with rapid, size-independent purification of an ancilla qubit, and the absence of scrambling, highlighting measurement-only circuits as a promising route to efficiently preparing highly entangled and technologically useful quantum states.

quant-ph↗

arXiv2022

Realizing Artin-Schreier Covers with Minimal $a$-numbers in Positive Characteristic

Suppose $X$ is a smooth projective connected curve defined over an algebraically closed field of characteristic $p>0$ and $B \subset X$ is a finite, possibly empty, set of points. Booher and Cais determined a lower bound for the $a$-number of a $\mathbf{Z}/p \mathbf{Z}$-cover of $X$ with branch locus $B$. For odd primes $p$, in most cases it is not known if this lower bound is realized. In this note, when $X$ is ordinary, we use formal patching to reduce that question to a computational question about $a$-numbers of $\mathbf{Z}/p\mathbf{Z}$-covers of the affine line. As an application, when $p=3$ or $p=5$, for any ordinary curve $X$ and any choice of $B$, we prove that the lower bound is realized for Artin-Schreier covers of $X$ with branch locus $B$.

math.NT↗

arXiv2021

The Stembridge Equality for Skew Stable Grothendieck Polynomials and Skew Dual Stable Grothendieck Polynomials

The Schur polynomials $s_λ$ are essential in understanding the representation theory of the general linear group. They also describe the cohomology ring of the Grassmannians. For $ρ= (n, n-1, \dots, 1)$ a staircase shape and $μ\subseteq ρ$ a subpartition, the Stembridge equality states that $s_{ρ/μ} = s_{ρ/μ^T}$. This equality provides information about the symmetry of the cohomology ring. The stable Grothendieck polynomials $G_λ$, and the dual stable Grothendieck polynomials $g_λ$, developed by Buch, Lam, and Pylyavskyy, are variants of the Schur polynomials and describe the $K$-theory of the Grassmannians. Using the Hopf algebra structure of the ring of symmetric functions and a generalized Littlewood-Richardson rule, we prove that $G_{ρ/μ} = G_{ρ/μ^T}$ and $g_{ρ/μ} = g_{ρ/μ^T}$, the analogues of the Stembridge equality for the skew stable and skew dual stable Grothendieck polynomials.

math.CO↗

arXiv2021

Ehrhart-Equivalence, Equidecomposability, and Unimodular Equivalence of Integral Polytopes

Ehrhart polynomials are extensively-studied structures that interpolate the discrete volume of the dilations of integral $n$-polytopes. The coefficients of Ehrhart polynomials, however, are still not fully understood, and it is not known when two polytopes have equivalent Ehrhart polynomials. In this paper, we establish a relationship between Ehrhart-equivalence and other forms of equivalence: the $\operatorname{GL}_n(\mathbb{Z})$-equidecomposability and unimodular equivalence of two integral $n$-polytopes in $\mathbb{R}^n$. We conjecture that any two Ehrhart-equivalent integral $n$-polytopes $P,Q\subset\mathbb{R}^n$ are $\operatorname{GL}_n(\mathbb{Z})$-equidecomposable into $\frac{1}{(n-1)!}$-th unimodular simplices, thereby generalizing the known cases of $n=1, 2, 3$. We also create an algorithm to check for unimodular equivalence of any two integral $n$-simplices in $\mathbb{R}^n$. We then find and prove a new one-to-one correspondence between unimodular equivalence of integral $2$-simplices and the unimodular equivalence of their $n$-dimensional pyramids. Finally, we prove the existence of integral $n$-simplices in $\mathbb{R}^n$ that are not unimodularly equivalent for all $n \ge 2$.

math.CO↗