Péter Lévay, Szilvia Nagy, János Pipek
An elementary formula for the von Neumann and Renyi entropies describing quantum correlations in two-fermionic systems having four single particle states is presented. An interesting geometric structure of fermionic entanglement is revealed. A connection with the generalized Pauli principle is established.
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Recently, there has been a surge of interest in using Rényi entropies as quantifiers of correlations in many-body quantum systems. However, it is well known that in general these entropies do not satisfy the strong subadditivity inequality, which is a central property ensuring the positivity of correlation measures. In fact, in many cases they do not even satisfy the weaker condition of subadditivity. In the present paper we shed light on this subject by providing a detailed survey of Rényi entropies for bosonic and fermionic Gaussian states. We show that for bosons the Rényi entropies always …
We explore the relation between the von Neumann entropy and the Renyi entropies of integer orders for shift-invariant quasi-free Fermionic lattice systems. We investigate approximating the von Neumann entropy by a combination of integer-order Renyi entropies and give an estimate for the quality of such an approximation.
Notions of Fermionic Entropies of a Causal Fermion System
本文针对因果费米子系统定义了三种费米子熵，利用准自由态熵公式结合约化单粒子密度算符，通过多场景例子阐释定义，回顾面积定律并关联模理论计算相对熵。
Symmetry-driven correlation patterns in one-dimensional periodic fermionic systems: closed-form expressions and exact selection rules for correlation functions, entanglement entropies and mutual information
本文利用循环对称性，将费米子关联函数表示为傅里叶求和，推导出闭式表达式和精确选择定则，揭示一维周期系统中关联的非均匀结构，为理解关联模式提供普适参考。
Entanglement Rényi Entropies from Ballistic Fluctuation Theory: the free fermionic case
本研究借助纠缠熵与大偏差理论的关联，将弹道涨落理论（BFT）应用于分支点扭场关联函数，在自由费米子系统中证明BFT可推导Rényi纠缠熵的平衡行为与动力学，解释量子猝灭后的纠缠增长，揭示纠缠大尺度行为源于流体力学涨落。
An elementary collision model of a molecular reservoir is considered upon which an external field is applied and the work is dissipated into heat. To realize macroscopic irreversibility at the microscopic level, we introduce a ``graceful'' irreversible map which randomly mixes the identities of the molecules. This map is expected to generate informatic entropy exactly equal to the independently calculable irreversible thermodynamic entropy.
We compute the quantum Renyi relative entropies in an infinite spinless fermionic chain with a defect. Doing a numerical analysis we will show that the resulting quantity depends non trivially on the effective central charge of the theory. Moreover, we will see that an explicit analytic expression can be written for all of them and from that, one can read the quantum fidelity and the relative entropy.
We revisit statistical wavefunction properties of finite systems of interacting fermions in the light of strength functions and their participation ratio and information entropy. For weakly interacting fermions in a mean-field with random two-body interactions of increasing strength $λ$, the strength functions $F_k(E)$ are well known to change, in the regime where level fluctuations follow Wigner's surmise, from Breit-Wigner to Gaussian form. We propose an ansatz for the function describing this transition which we use to investigate the participation ratio $ξ_2$ and the information entropy $S…
We consider the symmetry resolved Rényi entropies in the one dimensional tight binding model, equivalent to the spin-1/2 XX chain in a magnetic field. We exploit the generalised Fisher-Hartwig conjecture to obtain the asymptotic behaviour of the entanglement entropies with a flux charge insertion at leading and subleading orders. The o(1) contributions are found to exhibit a rich structure of oscillatory behaviour. We then use these results to extract the symmetry resolved entanglement, determining exactly all the non-universal constants and logarithmic corrections to the scaling that are not …
We show that any quantum information theory based on anticommuting operators must be supplemented by a superselection rule deeply rooted in relativity to establish a reasonable notion of entanglement. While quantum information may be encoded in the fermionic Fock space, the unrestricted theory has a peculiar feature: The marginals of bipartite pure states need not have identical entropies, which leads to an ambiguous definition of entanglement. We solve this problem, by proving that it is removed by relativity, i.e., by the parity superselection rule that arises from Lorentz invariance via the…
We derive a general relation between the bosonic and fermionic entanglement in the ground states of supersymmetric quadratic Hamiltonians. For this, we construct canonical identifications between bosonic and fermionic subsystems. Our derivation relies on a unified framework to describe both, bosonic and fermionic Gaussian states in terms of so-called linear complex structures $J$. The resulting dualities apply to the full entanglement spectrum between the bosonic and the fermionic systems, such that the von Neumann entropy and arbitrary Renyi entropies can be related. We illustrate our finding…
We derive the monotonicity of the quantum relative entropy by an elementary operational argument based on Stein's lemma in quantum hypothesis testing. For the latter we present an elementary and short proof that requires the law of large numbers only. Joint convexity of the quantum relative entropy is proven too, resulting in a self-contained elementary version of Tropp's approach to Lieb's concavity theorem, according to which the map tr(exp(h+log a)) is concave in a on positive operators for self-adjoint h.
In this paper we present a protocol for the implementation of a positive-operator-valued measure (POVM) on massive fermionic qubits. We present methods for implementing non-dispersive qubit transport, spin rotations and spin polarizing beam-splitter operations. Our scheme attains linear optics-like control of the spatial extent of the qubits by considering groundstate electrons trapped in the minima of surface acoustic waves in semiconductor heterostructures. Furthermore, we numerically simulate a high-fidelity POVM that carries out Procrustean entanglement distillation in the framework of our…
In this paper we study the time evolution of (Renyi) entanglement entropies for locally excited states in four dimensional free massless fermionic field theory. Locally excited states are defined by being acted by various local operators on the ground state. Their excesses are defined by subtracting (Renyi) entanglement entropy for the ground state from those for locally excited states. They finally approach some constant if the subsystem is given by half of the total space. They have spin dependence. They can be interpreted in terms of quasi-particles.
In this work we consider the time evolution of charged Renyi entanglement entropies after exciting the vacuum with local fermionic operators. In order to explore the information contained in charged Renyi entropies, we perform computations of their excess due to the operator excitation in 2d CFT, free fermionic field theories in various dimensions as well as holographically. In the analysis we focus on the dependence on the entanglement charge, the chemical potential and the spacetime dimension. We find that excesses of charged (Renyi) entanglement entropy can be interpreted in terms of charge…
Pauli spectrum and nonstabilizerness of random fermionic Gaussian states
本文刻画了随机费米子高斯态的魔法性，推导了其Pauli谱与稳定化熵的精确表达式，发现冻结现象，并证明典型态在丢弃一定比例模式后仍保持魔法性。
The non-stabilizerness of fermionic Gaussian states
本文提出一种高效方法量化费米子高斯态的非稳定化性，揭示其与Haar随机态的相似行为，并通过计算稳定性Renyi熵和参与熵，展示了在高维拓扑模型中非稳定化性的相变特性。
Williamson majorization theory of fermionic non-Gaussianity
本文建立费米子非高斯性的威廉姆森 majorization 定律，将相关量化指标转化为强单调量，推导态转换条件，且理论可在现有量子设备上验证。
Recent advances in the field of strongly correlated electron systems allow to access the entanglement properties of interacting fermionic models, by means of Monte Carlo simulations. We briefly review the techniques used in this context to determine the entanglement entropies and correlations of the entanglement Hamiltonian. We further apply these methods to compute the spin two-point function of entanglement Hamiltonian for a stripe embedded into a correlated topological insulator. Further we discuss a recent method that allows an unbiased, numerically exact, direct determination of the entan…
We have recently shown that the entanglement entropy of any bipartition of a quantum state can be approximated as the sum of certain link strengths connecting internal and external sites. The representation is useful to unveil the geometry associated with the entanglement structure of a quantum many-body state which may occasionally differ from the one suggested by the Hamiltonian of the system. Yet, the obtention of these entanglement links is a complex mathematical problem. In this work, we address this issue and propose several approximation techniques for matrix product states, free fermio…
Recent numerical advances in the field of strongly correlated electron systems allow the calculation of the entanglement spectrum and entropies for interacting fermionic systems. An explicit determination of the entanglement (modular) Hamiltonian has proven to be a considerably more difficult problem, and only a few results are available. We introduce a technique to directly determine the entanglement Hamiltonian of interacting fermionic models by means of auxiliary field quantum Monte Carlo simulations. We implement our method on the one-dimensional Hubbard chain partitioned into two segments…
Entanglement capacity of fermionic Gaussian states
该研究针对费米子高斯态的量子两体系统，提出以纠缠容量替代纠缠熵估算纠缠程度，推导了带/不带粒子数约束两种情形下平均纠缠容量的精确与渐近公式，推广了已有结果，核心工具是费米子高斯态纠缠熵研究中最新发展的有限求和简化方法。
The recent direct experimental measurement of quantum entanglement paves the way towards a better understanding of many-body quantum systems and their correlations. Nevertheless, the experimental and theoretical advances had so far been predominantly limited to bosonic systems. Here, we study fermionic systems. Using experimental setups where multiple copies of the same state are prepared, arbitrary order Renyi entanglement entropies and entanglement negativities can be extracted by utilizing spatially-uniform beam splitters and on-site occupation measurement. As an example, we simulate the us…
Symmetry Resolved Entanglement of Excited States in Quantum Field Theory III: Bosonic and Fermionic Negativity
本文扩展了量子场论中准粒子激发态对称性分辨纠缠的研究，通过解析和数值方法证明对称性分辨负性具有普适行为，并发现费米子与玻色子负性矩比值在激发态与基态间相同。
Entanglement is considered a fundamental ingredient for quantum technologies and condensed matter systems are among the good candidates for quantum devices. For bipartite pure states the von Neumann entropy is a proper measure of entanglement, while the linear entropy, associated to the mixedness of the reduced density matrices, is a simpler quantity to be obtained and is considered to be qualitatively equivalent to the von Neumann. Here we investigate both linear and von Neumann entropies for quantifying entanglement in homogeneous, superlattice and disordered Hubbard chains. We find regimes …
Topological phases of matter possess intricate correlation patterns typically probed by entanglement entropies or entanglement spectra. In this work, we propose an alternative approach to assessing topologically induced edge states in free and interacting fermionic systems. We do so by focussing on the fermionic covariance matrix. This matrix is often tractable either analytically or numerically and it precisely captures the relevant correlations of the system. By invoking the concept of monogamy of entanglement we show that highly entangled states supported across a system bi-partition are la…
Symmetry-twisted multi-entropies: Order parameters for 2D SPT phases
研究如何从期望值提取二维玻色SPT信息，提出基于部分对称和置换操作期望值的非局部序参量，对应对称扭曲多熵，能检测四体和六体纠缠，限制虚假贡献，有望推广到费米子和高维系统。
Non-Local Magic Resources for Fermionic Gaussian States
本文提出非局域稳定izer熵的闭式表达式，用于高效计算费米子高斯态的非局域魔力，揭示了随机态、XY模型临界点及非平衡淬火过程中的魔力行为。
We investigate the crossover of the entanglement entropy towards its thermal value in nearly integrable systems. We employ equation of motion techniques to study the entanglement dynamics in a lattice model of weakly interacting spinless fermions after a quantum quench. For weak enough interactions we observe a two-step relaxation of the entanglement entropies of finite subsystems. Initially the entropies follow a nearly integrable evolution, approaching the value predicted by the Generalized Gibbs Ensemble (GGE) of the unperturbed model. Then, they start a slow drift towards the thermal stati…
We report a non-trivial feature of the vacuum structure of free massive or massless Dirac fields in the hyperbolic de Sitter spacetime. Here we have two causally disconnected regions, say $R$ and $L$ separated by another region, $C$. We are interested in the field theory in $R\cup L$ to understand the long range quantum correlations between $R$ and $L$. There are local modes of the Dirac field having supports individually either in $R$ or $L$, as well as global modes found via analytically continuing the $R$ modes to $L$ and vice versa. However, we show that unlike the case of a scalar field, …
Explicit Pfaffian Formula for Amplitudes of Fermionic Gaussian Pure States in Arbitrary Pauli Bases
本文提出显式普法夫公式和递归关系，用于计算任意泡利基下费米子高斯纯态的振幅，从而支持全局纠缠、Shannon-Rényi熵、形成概率研究及高效量子层析成像，并用于分析测量后纠缠熵。
Analytical solutions of the Schrödinger equation for the one-dimensional quantum well with all possible permutations of the Dirichlet and Neumann boundary conditions (BCs) in perpendicular to the interfaces uniform electric field $\mathscr{E}$ are used for the comparative investigation of their interaction and its influence on the properties of the system. Limiting cases of the weak and strong voltages allow an easy mathematical treatment and its clear physical explanation; in particular, for the small $\mathscr{E}$, the perturbation theory derives for all geometries a linear dependence of the…
Total and Symmetry resolved Entanglement spectra in some Fermionic CFTs from the BCFT approach
本文使用BCFT方法研究了某些2维费米子CFT中单个区间的全纠缠谱与对称性分辨纠缠谱，发现模不变Dirac费米子的全纠缠谱与对偶半径处紧致玻色子结果匹配，且U(1)对称性的特征loglog(ℓ/ε)项在对称性分辨纠缠谱中与M成正比。
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