1,337 research outputs found
The Glassy Wormlike Chain
We introduce a new model for the dynamics of a wormlike chain in an
environment that gives rise to a rough free energy landscape, which we baptise
the glassy wormlike chain. It is obtained from the common wormlike chain by an
exponential stretching of the relaxation spectrum of its long-wavelength
eigenmodes, controlled by a single stretching parameter. Predictions for
pertinent observables such as the dynamic structure factor and the
microrheological susceptibility exhibit the characteristics of soft glassy
rheology and compare favourably with experimental data for reconstituted
cytoskeletal networks and live cells. We speculate about the possible
microscopic origin of the stretching, implications for the nonlinear rheology,
and the potential physiological significance of our results.Comment: 12 pages, 8 figures. Minor correction
Chaos and Complexity of quantum motion
The problem of characterizing complexity of quantum dynamics - in particular
of locally interacting chains of quantum particles - will be reviewed and
discussed from several different perspectives: (i) stability of motion against
external perturbations and decoherence, (ii) efficiency of quantum simulation
in terms of classical computation and entanglement production in operator
spaces, (iii) quantum transport, relaxation to equilibrium and quantum mixing,
and (iv) computation of quantum dynamical entropies. Discussions of all these
criteria will be confronted with the established criteria of integrability or
quantum chaos, and sometimes quite surprising conclusions are found. Some
conjectures and interesting open problems in ergodic theory of the quantum many
problem are suggested.Comment: 45 pages, 22 figures, final version, at press in J. Phys. A, special
issue on Quantum Informatio
Spectral signatures of many-body localization with interacting photons
Statistical mechanics is founded on the assumption that a system can reach
thermal equilibrium, regardless of the starting state. Interactions between
particles facilitate thermalization, but, can interacting systems always
equilibrate regardless of parameter values\,? The energy spectrum of a system
can answer this question and reveal the nature of the underlying phases.
However, most experimental techniques only indirectly probe the many-body
energy spectrum. Using a chain of nine superconducting qubits, we implement a
novel technique for directly resolving the energy levels of interacting
photons. We benchmark this method by capturing the intricate energy spectrum
predicted for 2D electrons in a magnetic field, the Hofstadter butterfly. By
increasing disorder, the spatial extent of energy eigenstates at the edge of
the energy band shrink, suggesting the formation of a mobility edge. At strong
disorder, the energy levels cease to repel one another and their statistics
approaches a Poisson distribution - the hallmark of transition from the
thermalized to the many-body localized phase. Our work introduces a new
many-body spectroscopy technique to study quantum phases of matter
Theoretical study of stimulated and spontaneous Hawking effects from an acoustic black hole in a hydrodynamically flowing fluid of light
We propose an experiment to detect and characterize the analog Hawking
radiation in an analog model of gravity consisting of a flowing
exciton-polariton condensate. Under a suitably designed coherent pump
configuration, the condensate features an acoustic event horizon for sound
waves that at the semiclassical level is equivalent to an astrophysical black
hole horizon. We show that a continuous-wave pump-and-probe spectroscopy
experiment allows to measure the analog Hawking temperature from the dependence
of the stimulated Hawking effect on the pump-probe detuning. We anticipate the
appearance of an emergent resonant cavity for sound waves between the pump beam
and the horizon, which results in marked oscillations on top of an overall
exponential frequency dependence. We finally analyze the spatial correlation
function of density fluctuations and identify the hallmark features of the
correlated pairs of Bogoliubov excitations created by the spontaneous Hawking
process, as well as novel signatures characterizing the emergent cavity
Photon Statistics; Nonlinear Spectroscopy of Single Quantum Systems
A unified description of multitime correlation functions, nonlinear response
functions, and quantum measurements is developed using a common generating
function which allows a direct comparison of their information content. A
general formal expression for photon counting statistics from single quantum
objects is derived in terms of Liouville space correlation functions of the
material system by making a single assumption that spontaneous emission is
described by a master equation
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