Davide Chiuchiù (University of Perugia)

Abstract:
Starting from the birth of statistical mechanics, the linkage between thermodynamics and information is a field alive with many discussions and a large variety of (discording) interpretations. The most accepted framework is the one formulated by Bennett which states a one-to-one relationship between thermodynamic and logic reversibility. In this talk, critical failures of this relationship are analyzed by using arguments taken from recent papers by Sagawa. In particular it will be proven that thermodynamic entropy and information are not interchangeable. Some other critical points of Bennett claims will also be presented as the basic ideas behind an experiment now performed in Perugia.

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Date & time: 03/03/2015 at 10:00.

Location: Room V1.33, Civil Engineering Building, Instituto Superior Técnico, Lisbon.

Seth Lloyd (Massachusetts Institute of Technology)

Abstract:
Machine learning algorithms look for patterns in data. Frequently, that data comes in the form of large arrays of high-dimensional vectors. Quantum computers are adept at manipulating large arrays of high-dimensional vectors. This talk presents a series of quantum algorithms for big data analysis. The ability of quantum computers to perform Fourier transforms, find eigenvectors and eigenvalues, and invert matrices translates into quantum algorithms for clustering, principal component analysis, and for identifying topological features such as numbers of connected components, holes and voids. These quantum algorithms are exponentially faster than their classical counterparts: complex patterns in datasets of size N can be identified in time O(logN). The talk will discuss methods for implementing quantum machine learning algorithms on the current generation of quantum information processors.


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Date & time: 10/12/2014 at 15:00.

Location: Amphitheatre VA1, Civil Engineering Building, Instituto Superior Técnico, Lisbon.

Note: Joint session with Physics of Information Colloquium.

Hamed Mohammady (Physics of Information Group - IT)

Abstract:
A promising platform for quantum information processing is that of silicon impurities, where the quantum states are manipulated by magnetic resonance. Such systems, in abstraction, can be considered as a nucleus of arbitrary spin coupled to an electron of spin one-half via an isotropic hype rfine interaction. We therefore refer to them as "nuclear-electronic spin systems". The traditional example, being subject to intensive experimental studies, is that of phosphorus doped silicon (Si:P) which couples a spin one-half electron to a nucleus of the same spin, with a hyperfine strength of 117.5 MHz. More recently, bismuth doped silicon (Si:Bi) has been suggested as an alternative instantiation of nuclear-electronic spin systems, differing from Si:P by its larger nuclear spin and hyperfine strength of 9/2 and 1.4754 GHz respectively. Here we develop a model that is capable of predicting the magnetic resonance properties of nuclear-electronic spin systems, which has proven to be in good agreement with experiments. Furthermore, we show that the larger nuclear spin and hyperfine strength of Si:Bi, compared with that of Si:P, offer advantages for quantum information processing by providing magnetic field-dependent two-dimensional decoherence free subspaces, called optimal working points or clock transitions, which have been identified to exist in Si:Bi, but not Si:P.


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Date & time: 06/06/2014 at 16:15.

Location: Room P3.10, Mathematics Building, Instituto Superior Técnico, Lisbon.

Note: Joint session with Quantum Computation and Information Seminar.

Lev Murokh (Queens College of the City University of New York)

Abstract:
Living objects at the nanoscale can be viewed as molecular complexes, whose dynamics is often controlled by the transfer of single charges or single-photon absorption events. In many senses, it is similar to the principles of operation of semiconductor nanostructures and elements of molecular electronics. Correspondingly, the methods of condensed matter and statistical physics can be applied.

In this talk, I address proton-pumping complexes and proton-driven nanomotor of the mitochondria membranes. These systems convert the energy obtained from the food to the proton gradient across the membrane, to the mechanical rotation of the nanomotor, and, finally, to the energy of chemical compounds. We propose simple physical models for these complexes which not only allow the quantitative description but can inspire the implementations in nanoelectronics as well.


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Date & time: 14/04/2014 at 10:30.

Location: Seminar Room (2.8.3), Physics Department, Instituto Superior Técnico, Lisbon.

Patrícia Figueiredo (ISR, IST, University of Lisbon)

Abstract:
Current neuroimaging techniques allow the noninvasive mapping of human brain networks, with progressively better temporal and spatial resolution. In this talk, I will address the critical problem of relating the electrophysiological and haemodynamic correlates of such networks that are mapped using different techniques. I will first overview my research on the combination of multiple functional magnetic resonance imaging (fMRI) methodologies for obtaining physiologically meaningful and reliable haemodynamic measures. I will then talk about the simultaneous acquisition of the electroencephalogram (EEG) with fMRI, with the aim of directly relating electrophysiological and haemodynamic measures of brain function. Overall, these developments should not only help elucidate healthy brain networks, but also contribute to the identification of biomarkers for specific neurological and psychiatric diseases.


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Date & time: 04/04/2014 at 15:00.

Location: Seminar Room (2.8.3), Physics Department, Instituto Superior Técnico, Lisbon.

César Rodríguez-Rosario (University of Bremen)

Abstract:
Quantum decoherence is seen as an undesired source of irreversibility that destroys quantum resources. Quantum coherences are a property that vanishes at thermodynamic equilibrium. Away from equilibrium, quantum coherences challenge the classical notions of a thermodynamic bath in a Carnot engines, affect the efficiency of quantum transport, lead to violations of Fourier's law, and can be used to dynamically control the temperature of a state. However, the role of quantum coherence in thermodynamics is not fully understood.

We will show that the relative entropy of a state with quantum coherence with respect to its decohered state captures its deviation from thermodynamic equilibrium. As a result, changes in quantum coherence can lead to a heat flow with no associated temperature, and affect the entropy production rate. From this, we derive a quantum version of the Onsager reciprocal relations that shows that there is a reciprocal relation between thermodynamic forces from coherence and quantum transport. Quantum decoherence can be useful and offers new possibilities of thermodynamic control for quantum transport and to understand transport in photosynthetic complexes.


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Date & time: 27/02/2014 at 10:30.

Location: Seminar Room (2.8.3), Physics Department, Instituto Superior Técnico, Lisbon.

Note: Joint session with Quantum Computation and Information Seminar.

Igor Neri (University of Perugia)

Abstract:
Maximum energy efficiency in computation is bound both by technological and physical limits. The ultimate limit in computation is a consequence of thermodynamics and was first argued in 1961 by Rolf Landauer from which it takes the name. This limit can be beaten by trading the dissipated energy with the uncertainty in the distinguishability of switch logic states.

In this seminar the exploitation of faulty logic gates to save energy will be considered. A logic gate simulator, considering hardware prone to errors (i.e. operating the switches below the Landauer limit), within the stochastic logic gate model used, will be presented.

Simulated results of sorting algorithms based on faulty hardware will then be presented and discussed. The computation error will then be related to the energy saving in respect to the correct computation assuming to operate the logic gates switches at the Landauer limit.

The presented results highlight that accepting a small error in computation it is possible to save energy, correlating accuracy to energy saving in respect to the Landauer limit. However an effort have to be made from different fields of engineering and science in order to exploit at the best the potential of approximate computation.

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Date & time: 30/01/2014 at 10:30.

Location: Seminar Room (2.8.3), Physics Department, Instituto Superior Técnico, Lisbon.

Marco Pezzutto (University of Trieste)

Abstract:
Under certain assumptions, it is possible to define for an open quantum system many key thermodynamic quantities, such as the internal energy, entropy, exchanged heat and work. By means of these quantities, the zeroth, first and second law of thermodynamics can also be given a consistent formulation. 

A brief introduction on the dynamics of open quantum systems will be given, together with a review of the concepts of positivity and complete positivity in relation with entanglement. 

Afterwards, it will be shown how to define the law of thermodynamics, and specifically the second one in terms of positivity of the internal entropy production, and the connections with complete positivity of the dynamics.
Such techniques have been applied to a concrete case, namely a model for a quantum pumping process in a noisy environment. The master equation originally proposed for this model turns out to provide a non-completely positive dynamics, and it was found that, in certain conditions, this fact can lead to consequences from a thermodynamical point of view, such as violations of the second law. 

Complete positivity, beside guaranteeing a physically consistent description when entanglement is taken into account, seems then to gain an important role in relation to thermodynamics.

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Date & time: 13/12/2013 at 16:15.

Location: Room P3.10, Mathematics Building, Instituto Superior Técnico, Lisbon.

Note: Joint session with Quantum Computation and Information Seminar.

Kerstin Eder (University of Bristol)

Abstract:
Energy efficiency is now a major (if not the major) concern in electronic systems engineering. While hardware can be designed to save a modest amount of energy, the potential for savings are far greater at the higher levels of abstraction in the system stack. The greatest savings are expected from energy consumption-aware software.

In this seminar I will focus on the importance of energy transparency from hardware to software as a foundation for energy-aware system design. Energy transparency enables a deeper understanding of how algorithms and coding impact on the energy consumption of a computation when executed on hardware. It is a key prerequisite for informed design space exploration and helps system designers to find the optimal tradeoff between performance, accuracy and energy consumption of a computation. Promoting energy efficiency to a first class software design goal is therefore an urgent research challenge.

I will give insights into my research agenda towards energy-aware software design, and show initial, very encouraging results in static analysis for energy consumption of programs based on energy consumption models for state-of-the-art hardware.

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Date & time: 27/09/2013 at 10:00.

Location: Seminar Room (2.8.3), Physics Department, Instituto Superior Técnico, Lisbon.

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Support: Supported by Phys-Info (IT), with funding from FCT, FEDER and EU FP7, specifically through FCT strategic project FCT PEst-OE/EEI/LA0008/2013 and the FP7 projects Landauer (GA 318287) and PAPETS (GA 323901).