1,720,992 research outputs found
Interactions and integrability in weakly monitored Hamiltonian systems
Full text linkInterspersing unitary dynamics with local measurements results in
measurement-induced phases and transitions in many-body quantum systems. When
the evolution is driven by a local Hamiltonian, two types of transitions have
been observed, characterized by an abrupt change in the system size scaling of
entanglement entropy. The critical point separates the strongly monitored
area-law phase from a volume law or a sub-extensive, typically logarithmic-like
one at low measurement rates. Identifying the key ingredients responsible for
the entanglement scaling in the weakly monitored phase is the key purpose of
this work. For this purpose, we consider prototypical one-dimensional spin
chains with local monitoring featuring the presence/absence of U(1) symmetry,
integrability, and interactions. Using exact numerical methods, the system
sizes studied reveal that the presence of interaction is always correlated to a
volume-law weakly monitored phase. In contrast, non-interacting systems present
sub-extensive scaling of entanglement. Other characteristics, namely
integrability or U(1) symmetry, do not play a role in the character of the
entanglement phase.Comment: 4 pages, 4 figure
Measurement-induced criticality as a data-structure transition
Full text linkWe 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
Code for "Hilbert space delocalisation under random unitary circuits"
No full text<p>Unitary dynamics of a quantum system initialized in a selected basis state yields, generically, a state that is a superposition of all the basis states. This process, associated with the quantum information scrambling and intimately tied to the resource theory of coherence, may be viewed as a gradual delocalization of the system's state in the Hilbert space. <br>This work analyzes the Hilbert space delocalization under dynamics of random quantum circuits, which serve as a minimal model of chaotic dynamics of quantum many-body systems. We employ analytical methods based on the replica trick and Weingarten calculus to investigate the time evolution of the participation entropies which quantify the Hilbert space delocalization. We demonstrate that the participation entropies approach, up to a fixed accuracy, their long-time saturation value in times that scale logarithmically with the system size. Exact numerical simulations and tensor network techniques corroborate our findings. </p>
Error-resilience Phase Transitions in Encoding-Decoding Quantum Circuits
Full text linkUnderstanding 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
subject to local coherent and incoherent errors. We analytically demonstrate
the existence of a phase transition from an error-protecting phase to an
error-vulnerable phase occurring when the error strength is increased. This
transition is accompanied by R\'enyi entropy transitions and by onset of
multifractal features in the system. Our results provide a new perspective on
storing and processing quantum information, while the introduced framework
enables an analytic understanding of a dynamical critical phenomenon in a
many-body system.Comment: Revised version, incoherent and site-dependent errors included, 4+14
pages, comments welcome
Entanglement and Correlation Spreading in non-Hermitian Spin Chains
No full text4.5 + 11 pagWe study a driven-dissipative Bose-Hubbard model in presence of two-particle losses and an incoherent single-particle drive on each lattice site, leading to a finite-density stationary state. Using dynamical mean-field theory (DMFT) and an impurity solver based on exact diagonalization of the associated Lindbladian, we investigate the regime of strong two-particle losses. Here, a stationarystate quantum Zeno effect emerges, as can be seen in the on-site occupation and spectral function. We show that DMFT captures this effect through its self-consistent bath. We show that, in the deep Zeno regime, the bath structure simplifies, with the occupation of all bath sites except one becoming exponentially suppressed. As a result, an effective dissipative hard-core Bose-Hubbard dimer model emerges, where the auxiliary bath site has single-particle dissipation controlled by the Zeno dissipative scale
Controlling entanglement at absorbing state phase transitions in random circuits
Full text linkMany-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
Quantum information spreading in random spin chains
Full text linkWe study the spreading of quantum correlations and information in a
one-dimensional quantum spin chain with critical disorder as encoded in an
infinite randomness fixed point. Specifically, we focus on the dynamics after a
quantum quench of the R\'enyi entropies, of the mutual information and of the
entanglement negativity in the prototypical XXZ spin chain with random bonds
and anisotropy parameters. We provide analytic predictions in the scaling
regime based on real-space renormalization group methods. We support these
findings through numerical simulations in the non-interacting limit, where we
can access the scaling regime.Comment: 15 pages, 7 figure
Entanglement Transitions from Stochastic Resetting of Non-Hermitian Quasiparticles
Full text linkWe put forward a phenomenological theory for entanglement dynamics in
monitored quantum many-body systems with well-defined quasiparticles. Within
this theory entanglement is carried by ballistically propagating non-Hermitian
quasiparticles which are stochastically reset by the measurement protocol with
rate given by their finite inverse lifetime. We write down a renewal equation
for the statistics of the entanglement entropy and show that depending on the
spectrum of quasiparticle decay rates different entanglement scaling can arise
and even sharp entanglement phase transitions. When applied to a Quantum Ising
chain where the transverse magnetization is measured by quantum jumps, our
theory predicts a critical phase with logarithmic scaling of the entanglement,
an area law phase and a continuous phase transition between them, with an
effective central charge vanishing as a square root at the transition point. We
compare these predictions with with exact numerical calculations on the same
model and find an excellent agreement.Comment: 5+7 pages, 3 figures + Erratu
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