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SUMMARY:Quantum first detection time
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UID:indico-contribution-6-148@zakopane.if.uj.edu.pl
DESCRIPTION:Speakers: Eli Barkai (Bar-Ilan University\, Israel)\nWe invest
igate the quantum first detection problem for a quantum walk \nusing proje
ctive measurement postulates. \nA simple relation between the measurement
free state function |psi> and |phi>_n is obtained\, \nthe latter\nis the
first detection amplitude at the n-th attempt. This relation is the quantu
m renewal equation\, its classical counter part is widely used to find sta
tistics of first passage time for random walks and Brownian motion. We inv
estigate statistics of first detection for open and closed systems (first
arrival or passage is not well defined in quantum theory). For closed sys
tems\, like a ring\, with a\ntranslation invariant Hamiltonian\, we find Z
eno physics\, optimum sampling times\, critical sampling effect related to
revivals\, dark states\, and quantisation of the mean detection time. For
a quantum walk on the line\, with particle starting on |x_i> and detected
on the origing |0>\, with a tight-binding Hamiltonian with hops to neares
t neighbours\, we find the detection probability decays like (time)^(-3) w
ith super imposed quantum oscillation\, thus the quantum exponent is doubl
e its classical counter part. The Polya problem is discussed\, and it is f
ound that in one dimension the total detection probability\, does not depe
nd on the initial distance of the particle from detector\, though survival
of the particle is not unity. There is an optimal sampling time which max
imises the\ntotal detection probability. \n\n$ $\n\nJoint work with Harel
Fridman\, David Kessler\, and Felix Thiel.\n\nhttps://zakopane.if.uj.edu.p
l/event/4/contributions/148/
LOCATION:
URL:https://zakopane.if.uj.edu.pl/event/4/contributions/148/
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SUMMARY:Dynamics of classical isolated disordered systems
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UID:indico-contribution-6-145@zakopane.if.uj.edu.pl
DESCRIPTION:Speakers: Leticia\, F Cugliandolo (Universite Pierre et Marie
Curie)\nWe study the dynamics of classical disordered macroscopic models\n
completely isolated from the environment reproducing\, in a classical\nset
ting\, the ‘quantum quench’ protocol. We use two classes of models\,\n
distinguished by the complexity of their energy landscape. We identify\nqu
enches after which the evolution approaches a stationary state that can\nb
e associated to equilibrium at a single temperature (related to the\nenerg
y change during the quench)\, cases in which an ageing asymptotic\ndynamic
s persists asymptotically\, and quenches in which a steady state\ncharacte
rised by a Generalised Gibbs Ensemble is found. In the latter case\nwe sho
w that all the GGE effective temperatures can be obtained from the\nstanda
rd fluctuation dissipation relation\, in the frequency domain. The\nparame
ter dependence of the asymptotic states is rationalised in terms of\ndynam
ic phase diagrams.\n\n$\\\;$\n\n[1] Leticia F. Cugliandolo\, Gustavo S. Lo
zano\, Nicolas Nessi J. Stat. Mech. (2017) 083301.\n\n[2] Laura Foini\, An
drea Gambassi\, Robert Konik\, Leticia F. Cugliandolo\nPhys. Rev. E 95\, 0
52116 (2017)\n\nhttps://zakopane.if.uj.edu.pl/event/4/contributions/145/
LOCATION:
URL:https://zakopane.if.uj.edu.pl/event/4/contributions/145/
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SUMMARY:Mesoscopic and metastable quantum systems
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DTSTAMP;VALUE=DATE-TIME:20220928T134917Z
UID:indico-contribution-6-18@zakopane.if.uj.edu.pl
DESCRIPTION:Speakers: Bernardo Spagnolo (University of Palermo)\nWe shortl
y review the transient dynamics of mesoscopic systems\, such as Josephson
junctions\, in noisy environments. The role of noise induced solitons and
breathers on the mean switching time from the superconducting metastable s
tate to the resistive state\, in the presence of an external noise source
modeled by α-stable Lévy distributions\, will be outlined.\nThereafter\,
the dissipative dynamics of a particle moving in a strongly asymmetric do
uble well potential\, interacting with a thermal bath will be considered.
Common wisdom is that quantum fluctuations enhance the escape rate from me
tastable states in the presence of dissipation. We show that dissipation c
an enhance the stability of a quantum metastable system. We find that the
escape time from the metastable region has a nonmonotonic behavior\, with
a maximum\, versus the system-bath coupling\, and with a minimum versus th
e temperature\, thus producing a stabilizing effect. Therefore\, as the te
mperature increases\, an enhancement of the escape time is observed\, incr
easing the stability of the metastable state. These results shed new light
on the role of the environmental fluctuations in stabilizing quantum meta
stable systems. \n We will show then\, how the combined effects of strong
Ohmic dissipation and monochromatic driving affect the stability of a quan
tum system with a metastable state. We find that\, by increasing the coupl
ing with the environment\, the escape time makes a transition from a regim
e in which it is substantially controlled by the driving\, displaying reso
nant peaks and dips\, to a regime of frequency-independent escape time wit
h a peak followed by a steep fall off. The quantum noise enhanced stabilit
y phenomenon is observed in the system investigated. Resonant activation\,
the presence of a minimum in the mean escape time\, occurs when the time
scale of the modulations is the same as the characteristic time scale of t
he system’s dynamics. The simple quantum system considered displays as w
ell the general features that at slow modulations the mean escape time is
dominated by the slowest configuration assumed by he system\, while at fas
t modulations the escape dynamics is determined by the average configurati
on. \n\n$ $\n\n[1] D. Valenti\, C. Guarcello\, and B. Spagnolo\, Phys. Rev
. B **89**\, 214510 (2014).\n\n[2] C. Guarcello\, D. Valenti\, and B. Spag
nolo\, Phys. Rev. B **92**\, 174519 (2015).\n\n[3] C. Guarcello\, D. Valen
ti\, B. Spagnolo\, V. Pierro and G. Filatrella\, Nanotechnology\, **28**\,
134001 (2017).\n\n[4] D. Valenti\, L. Magazzù\, P. Caldara\, and B. Spag
nolo\, “Stabilization of quantum metastable states by dissipation”\, P
hysical Review B **91**\, 235412 (7) (2015).\n\n[5] Luca Magazzù\, Angelo
Carollo\, Bernardo Spagnolo\, Davide Valenti\, “Quantum dissipative dyn
amics of a bistable system in the sub-Ohmic to super-Ohmic regime”\, Jou
rnal of Statistical Mechanics: Theory and Experiment 054016 (2016).\n\n[6]
B. Spagnolo\, C. Guarcello\, L. Magazzù\, A. Carollo\, D. Persano Adorno
\, D. Valenti\, “Nonlinear Relaxation Phenomena in Metastable Condensed
Matter Systems”\, Entropy\, 19 (1)\, 20 (2017).
\n\n[7] L. Magazzù\,
P. Hänggi\, B. Spagnolo\, and D. Valenti\, “Quantum Resonant Activation
”\, Physical Review E 95 (13)\, 042104 (2017).\n\nhttps://zakopane.if.uj
.edu.pl/event/4/contributions/18/
LOCATION:
URL:https://zakopane.if.uj.edu.pl/event/4/contributions/18/
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