708 research outputs found
Decoherence in adiabatic quantum evolution - application to Cooper pair pumping
One of the challenges of adiabatic control theory is the proper inclusion of
the effects of dissipation. Here, we study the adiabatic dynamics of an open
two-level quantum system deriving a generalized master equation to consistently
account for the combined action of the driving and dissipation. We demonstrate
that in the zero temperature limit the ground state dynamics is not affected by
environment. As an example, we apply our theory to Cooper pair pumping which
demonstrates the robustness of ground state adiabatic evolution.Comment: 7 pages, derivation of the master equation in the appendi
Work and its fluctuations in a driven quantum system
We analyze work done on a quantum system driven by a control field. The
average work depends on the whole dynamics of the system, and is obtained as
the integral of the average power operator. As a specific example we focus on a
superconducting Cooper-pair box forming a two-level system. We obtain
expressions for the average work and work distribution in a closed system, and
discuss control field and environment contributions to the average work for an
open system.Comment: 8 pages, 3 figure
Calorimetric measurement of work in a quantum system
We propose a calorimetric measurement of work in a quantumsystem. As a physical realization, we consider a superconducting two-levelsystem, a Cooper-pair box, driven by a gate voltage past an avoided levelcrossing at charge degeneracy. We demonstrate that, with realistic experimentalparameters, the temperature measurement of a resistor (environment) can detectsingle microwave photons emitted or absorbed by the two-level system. Thismethod would thus be a way to measure the full distribution of work in repeatedmeasurements, and to assess the quantum fluctuation relations.Peer reviewe
Measurement scheme for the Lamb shift in a superconducting circuit with broadband environment
Motivated by recent experiments on quantum mechanical charge pumping in a
Cooper pair sluice, we present a measurement scheme for observing shifts of
transition frequencies in two-level quantum systems induced by broadband
environmental fluctuations. In contrast to quantum optical and related set-ups
based on cavities, the impact of a thermal phase reservoir is considered. A
thorough analysis of Lamb and Stark shifts within weak-coupling master
equations is complemented by non-perturbative results for the model of an
exactly solvable harmonic system. The experimental protocol to measure the Lamb
shift in experimentally feasible superconducting circuits is analysed in detail
and supported by numerical simulations.Comment: 8 pages, 4 figure
Brownian refrigeration by hybrid tunnel junctions
Voltage fluctuations generated in a hot resistor can cause extraction of heat
from a colder normal metal electrode of a hybrid tunnel junction between a
normal metal and a superconductor. We extend the analysis presented in [Phys.
Rev. Lett. 98, 210604 (2007)] of this heat rectifying system, bearing
resemblance to a Maxwell's demon. Explicit analytic calculations show that the
entropy of the total system is always increasing. We then consider a single
electron transistor configuration with two hybrid junctions in series, and show
how the cooling is influenced by charging effects. We analyze also the cooling
effect from nonequilibrium fluctuations instead of thermal noise, focusing on
the shot noise generated in another tunnel junction. We conclude by discussing
limitations for an experimental observation of the effect.Comment: 16 pages, 16 figure
Compressive Sensing-Based Harmonic Sources Identification in Smart Grids
Identifying the prevailing polluting sources would help the distribution system operators in acting directly on the cause of the problem, thus reducing the corresponding negative effects. Due to the limited availability of specific measurement devices, ad hoc methodologies must be considered. In this regard, compressive sensing (CS)-based solutions are perfect candidates. This mathematical technique allows recovering sparse signals when a limited number of measurements are available, thus overcoming the lack of power quality meters. In this article, a new formulation of the ell _{1} -minimization algorithm for CS problems, with quadratic constraint, has been designed and investigated in the framework of the identification of the main polluting sources in smart grids. A novel whitening transformation is proposed for this context. This specific transformation allows the energy of the measurement errors to be appropriately estimated, and thus, better identification results are obtained. The validity of the proposal is proven by means of several simulations and tests performed on two distribution networks for which suitable measurement systems are considered along with a realistic quantification of the uncertainty sources
Cooper pair current in the presence of flux noise
We study the effect of the flux noise on the Cooper pair current and pumping.
We generalize the definition of the current in order to take into account the
contribution induced by the environment. It turns out that this dissipative
current vanishes for charge noise but it is finite in general for noise
operators that do not commute with the charge operator. We discuss in a generic
framework the effect of flux noise and present a way to engineer it by coupling
the system to an additional external circuit. We calculate numerically the
pumped charge through the device by solving the master equation for the reduced
density matrix of the system and show how it depends on the coupling to the
artificial environment.Comment: 10 pages, 6 figure
PO-0785: Improvement strategies and performance enhancement in Healthcare: the reorganisation of Radiotherapy
- âŠ