Measurement-induced criticality as a data-structure transition

We employ unsupervised learning tools to identify different phases and their transition in quantum systems subject to the combined action of unitary evolution and stochastic measurements. Specifically, we consider principal component analysis and intrinsic dimension estimation to reveal a measurement-induced structural transition in the data space. We test our approach on a 1+1D stabilizer circuit and find the quantities of interest furnish novel order parameters defined directly in the raw data space. Our results provide a first use of unsupervised tools in dynamical quantum phase transitions.Comment: 7 pages, 5 figure

Crimes against Environment in Albania and the European Union's Approach to the Protection of Environment through Criminal Law

The protection of environment is of particular importance for Albania in its integration process to the European Union (EU), which considers it to be one of the “essential objectives of the Community” as highlighted in the case-law of the European Court of Justice. Taking into consideration the requirements of the specific EU directives on the protection of environment through criminal law, one of the expected legal reforms in the approximation process will be the adaption of the Albanian substantive environmental criminal law to the requirements of the Environmental Crime Directives. The need for aligning the Albanian criminal law with these directives has been highlighted by the Commission in the 2014 Progress Report on Albania. This paper examines the Albanian substantive environmental criminal law and its application in practice in the last ten years, aiming to identify the main challenges it faces in the context of the required transposition of EU Environmental Crime Directives, while also making suggestions on how to better respond to these issues. For this purpose, the paper will also refer to the experience of other countries with the implementation process in this field, highlighting the main problems encountered and the impacts of the Environmental Crime Directives transposition

Controlling entanglement at absorbing state phase transitions in random circuits

Many-body unitary dynamics interspersed with repeated measurements display a rich phenomenology hallmarked by measurement-induced phase transitions. Employing feedback-control operations that steer the dynamics toward an absorbing state, we study the entanglement entropy behavior at the absorbing state phase transition. For short-range control operations, we observe a transition between phases with distinct sub-extensive scalings of entanglement entropy. In contrast, the system undergoes a transition between volume-law and area-law phases for long-range feedback operations. The fluctuations of entanglement entropy and of the order parameter of the absorbing state transition are fully coupled for sufficiently strongly entangling feedback operations. In that case, entanglement entropy inherits the universal dynamics of the absorbing state transition. This is, however, not the case for arbitrary control operations, and the two transitions are generally distinct. We quantitatively support our results by introducing a framework based on stabilizer circuits with classical flag labels. Our results shed new light on the problem of observability of measurement-induced phase transitions.Comment: 4+6pp, comments welcome

Entanglement guided search for parent Hamiltonians

We introduce a method for the search of parent Hamiltonians of input wave-functions based on the structure of their reduced density matrix. The two key elements of our recipe are an ansatz on the relation between reduced density matrix and parent Hamiltonian that is exact at the field theory level, and a minimization procedure on the space of relative entropies, which is particularly convenient due to its convexity. As examples, we show how our method correctly reconstructs the parent Hamiltonian correspondent to several non-trivial ground state wave functions, including conformal and symmetry-protected-topological phases, and quantum critical points of two-dimensional antiferromagnets described by strongly coupled field theories. Our results show the entanglement structure of ground state wave-functions considerably simplifies the search for parent Hamiltonians.Comment: 5 pages, 5 figures, supplementary materia

Universal behavior beyond multifractality of wave-functions at measurement--induced phase transitions

We investigate the structure of many-body wave functions of 1D quantum circuits with local measurements employing the participation entropies. The leading term in system size dependence of participation entropy indicates a model dependent multifractal scaling of the wave-functions at any non-zero measurement rate. The sub-leading term contains universal information about measurement-induced phase transitions and plays the role of an order parameter, being constant non-zero in the error correcting phase and vanishing in the quantum Zeno phase. We provide robust numerical evidence investigating a variety of quantum many-body systems, and provide an analytical interpretation of this behavior expressing the participation entropy in terms of partition functions of classical statistical models in 2D.Comment: 4+16 pages, added new results on universality and extended discussions, comments welcom

Volume-to-Area Law Entanglement Transition in a non-Hermitian Free Fermionic Chain

We consider the dynamics of the non-Hermitian Su-Schrieffer-Heeger model arising as the no-click limit of a continuously monitored free fermion chain where particles and holes are measured on two sublattices. The model has $\mathcal{PT}$-symmetry, which we show to spontaneously break as a function of the strength of measurement backaction, resulting in a spectral transition where quasiparticles acquire a finite lifetime in patches of the Brillouin zone. We compute the entanglement entropy's dynamics in the thermodynamic limit and demonstrate an entanglement transition between volume-law and area-law scaling, which we characterize analytically. Interestingly we show that the entanglement transition and the $\mathcal{PT}$-symmetry breaking do not coincide, the former occurring when the entire decay spectrum of the quasiparticle becomes gapped.Comment: version 2 , 4 figures, minor adjustments and clarifications in section I

Error-resilience Phase Transitions in Encoding-Decoding Quantum Circuits

Understanding how errors deteriorate the information encoded in a many-body quantum system is a fundamental problem with practical implications for quantum technologies. Here, we investigate a class of encoding-decoding random circuits with coherent errors. The existence of a phase transition separating an error-protecting phase at weak error strength from an error-vulnerable phase is analytically demonstrated. We derive exact expressions showing that this transition is accompanied by an area-to-volume law entanglement transition and a localization transition in the computational basis. The emergence of multifractal features in the considered system is highlighted.Comment: 4+9 pages, comments welcome