7,808 research outputs found
Floquet time-crystals as sensors of AC fields
Get PDFThe long range spatial and temporal ordering displayed by discrete time
crystals, can become advantageous properties when used for sensing extremely
weak signals. Here, we investigate their performance as quantum sensors of weak
AC-fields and demonstrate, using the quantum Fisher information measure, that
they can overcome the shot noise limit while allowing long interrogation times.
In such systems, collective interactions stabilize their dynamics against noise
making them robust enough to protocol imperfections.Comment: 6 + 6 pages, 5 + 5 figure
Dissipative topological superconductors in number-conserving systems
Get PDFWe discuss the dissipative preparation of p-wave superconductors in number-conserving one-dimensional fermionic systems. We focus on two setups: the first one entails a single wire coupled to a bath, whereas in the second one the environment is connected to a two-leg ladder. Both settings lead to stationary states which feature the bulk properties of a p-wave superconductor, identified in this number-conserving setting through the long-distance behavior of the proper p-wave correlations. The two schemes differ in the fact that the steady state of the single wire is not characterized by topological order, whereas the two-leg ladder hosts Majorana zero modes, which are decoupled from damping and exponentially localized at the edges. Our analytical results are complemented by a numerical study based both on an exact representation of the density matrix and on a matrix-product-density-operator one. With these tools we characterize the steady-state properties of the protocols, their asymptotic decay rate, and their robustness
Sobre as práticas e reflexões publicitárias de Fernando Pessoa
Get PDFNeste texto, a autora analisa alguns trabalhos publicitários de Fernando Pessoa, bem
como algumas das suas reflexões sobre esta actividade. É dada especial atenção ao slogan
“Primeiro estranha-se. Depois entranha-se”, analisado sobre a perspectiva das funções
e propriedades deste constituinte da mensagem publicitária. Por fim, recorda-se
um recente slogan que recupera o clássico de Fernando Pessoa.
On this article, the author analyses some advertising texts created by Fernando Pessoa and
some of his thoughts about this activity. The main attention goes to the famous slogan “Primeiro
estranha-se. Depois entranha-se”, analysed through the principles of the functions
and proprieties of this element of advertisements. Finally, the author presents a recent slogan, constructed through the slogan of the Portuguese writer
Localized Majorana-Like Modes in a Number-Conserving Setting: An Exactly Solvable Model
Get PDFIn this Letter we present, in a number conserving framework, a model of interacting fermions in a two-wire geometry supporting nonlocal zero-energy Majorana-like edge excitations. The model has an exactly solvable line, on varying the density of fermions, described by a topologically nontrivial ground state wave function. Away from the exactly solvable line we study the system by means of the numerical density matrix renormalization group. We characterize its topological properties through the explicit calculation of a degenerate entanglement spectrum and of the braiding operators which are exponentially localized at the edges. Furthermore, we establish the presence of a gap in its single particle spectrum while the Hamiltonian is gapless, and compute the correlations between the edge modes as well as the superfluid correlations. The topological phase covers a sizable portion of the phase diagram, the solvable line being one of its boundaries
Signatures of many-body localization in the dynamics of two-site entanglement
Get PDFWe are able to detect clear signatures of dephasing—a distinct trait of many-body localization (MBL)—via the dynamics of two-site entanglement, quantified through the concurrence. Using the protocol implemented by M. Schreiber et al. [Science 349, 842 (2015)], we show that in the MBL phase the average two-site entanglement decays in time as a power law, while in the Anderson localized phase it tends to a plateau. The power-law exponent is not universal and displays a clear dependence on the interaction strength. This behavior is also qualitatively different from the ergodic phase, where the two-site entanglement decays exponentially. All the results are obtained by means of time-dependent density matrix renormalization-group simulations and further corroborated by analytical calculations on an effective model. Two-site entanglement has been measured in cold atoms: our analysis paves the way for the first direct experimental test of many-body dephasing in the MBL phase
From localization to anomalous diffusion in the dynamics of coupled kicked rotors
Get PDFWe study the effect of many-body quantum interference on the dynamics of coupled periodically kicked systems whose classical dynamics is chaotic and shows an unbounded energy increase. We specifically focus on an N -coupled kicked rotors model: We find that the interplay of quantumness and interactions dramatically modifies the system dynamics, inducing a transition between energy saturation and unbounded energy increase. We discuss this phenomenon both numerically and analytically through a mapping onto an N -dimensional Anderson model. The thermodynamic limit N → ∞, in particular, always shows unbounded energy growth. This dynamical delocalization is genuinely quantum and very different from the classical one: Using a mean-field approximation, we see that the system self-organizes so that the energy per site increases in time as a power law with exponent smaller than 1. This wealth of phenomena is a genuine effect of quantum interference: The classical system for N >= 2 always behaves ergodically with an energy per site linearly increasing in time. Our results show that quantum mechanics can deeply alter the regularity or ergodicity properties of a many-body-driven system
Floquet time crystals in clock models
Get PDFWe construct a class of period-n-tupling discrete time crystals based on Zn clock variables, for all the integers n. We consider two classes of systems where this phenomenology occurs: disordered models with short-range interactions and fully connected models. In the case of short-range models, we provide a complete classification of time-crystal phases for generic n. For the specific cases of n=3 and n=4, we study in detail the dynamics by means of exact diagonalization. In both cases, through an extensive analysis of the Floquet spectrum, we are able to fully map the phase diagram. In the case of infinite-range models, the mapping onto an effective bosonic Hamiltonian allows us to investigate the scaling to the thermodynamic limit. After a general discussion of the problem, we focus on n=3 and n=4, representative examples of the generic behavior. Remarkably, for n=4 we find clear evidence of a crystal-to-crystal transition between period n-tupling and period n/2-tupling
Determination of the critical exponents in dissipative phase transitions: Coherent anomaly approach
No full textScrambling and entanglement spreading in long-range spin chains
Get PDFWe study scrambling in connection with multipartite entanglement dynamics in regular and chaotic long-range spin chains, characterized by a well-defined semi-classical limit. For regular dynamics, scrambling and entanglement dynamics are found to be very different: up to the Ehrenfest time, they rise side by side, departing only afterward. Entanglement saturates and becomes extensively multipartite, while scrambling, characterized by the dynamic of the square commutator of initially commuting variables, continues its growth up to the recurrence time. Remarkably, the exponential growth of the latter emerges not only in the chaotic case but also in the regular one, when the dynamics occurs at a dynamical critical point
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