arXiv subjects

Massimiliano Di Ventra

Publications and source records attributed to Massimiliano Di Ventra.

At least 109 records · Page 6Linked to original sources

arXiv2013

Tunable Quantum Temperature Oscillations in Graphene and Carbon Nanoribbons

We investigate the local electron temperature distribution in carbon nano-ribbon (CNR) and graphene junctions subject to an applied thermal gradient. Using a realistic model of a scanning thermal microscope, we predict quantum temperature oscillations whose wavelength is related to that of Friedel oscillations. Experimentally, this wavelength can be tuned over several orders of magnitude by gating/doping, bringing quantum temperature oscillations within reach of the spatial resolution of existing measurement techniques.

cond-mat.mes-hall↗

arXiv2013

Quantum Analogies in Ionic Transport Through Nanopores

Ionic transport in nanopores or nanochannels is key to many cellular processes and is now being explored as a method for DNA/polymer sequencing and detection. Although apparently simple in its scope, the study of ionic dynamics in confined geometries has revealed interesting new phenomena that have an almost one-to-one correspondence with the quantum regime. The picture that emerges is that ions can form two `quasi-particle' states, one in which they surround themselves with other ions of opposite charge - ionic atmosphere - and one in which semi-bound water molecules form layers at different distances from the ions - hydration layers. The second state gives rise to two additional effects. In the first, which is a single quasi-particle effect, the ionic conductance through a nanopore is predicted to be `quantized' as a function of pore radius, with the corresponding `quantization units' not related to universal constants - like the Plank constant and the elementary charge - but rather to the radii of the hydration layers. The second effect instead involves the many-body interaction among ionic quasi-particles of the same sign, and occurs when the pore has a finite capacitance to accommodate ions so that there is a threshold concentration beyond which ions of the same sign are not energetically allowed to enter the pore. Similar to the electron transport case, the ionic counterpart appears only in the `quantum' regime, when the hydration layers forming the ionic quasi-particles need to break in order to pass through the pore. Here, we review all these phenomena, and discuss the conditions under which they may be detected making the analogy with the electronic transport case. Since nanopores are being considered for a host of technological applications in DNA sequencing and detection, we expect these phenomena will become very relevant and their understanding paramount to progress.

cond-mat.mes-hall↗

arXiv2013

Foundations of stochastic time-dependent current-density functional theory for open quantum systems: Potential pitfalls and rigorous results

We clarify some misunderstandings on the time-dependent current density functional theory for open quantum systems we have recently introduced [M. Di Ventra and R. D'Agosta, Phys. Rev. Lett. {\bf 98}, 226403 (2007)]. We also show that some of the recent formulations attempting to improve on this theory suffer from some inconsistencies, especially in establishing the mapping between the external potential and the quantities of interest. We offer a general argument about this mapping, showing that it must fulfill certain "dimensionality" requirements.

cond-mat.mtrl-sci↗

arXiv2013

Memory models of adaptive behaviour

Adaptive response to a varying environment is a common feature of biological organisms. Reproducing such features in electronic systems and circuits is of great importance for a variety of applications. Here, we consider memory models inspired by an intriguing ability of slime molds to both memorize the period of temperature and humidity variations, and anticipate the next variations to come, when appropriately trained. Effective circuit models of such behavior are designed using i) a set of LC-contours with memristive damping, and ii) a single memcapacitive system-based adaptive contour with memristive damping. We consider these two approaches in detail by comparing their results and predictions. Finally, possible biological experiments that would discriminate between the models are discussed. In this work, we also introduce an effective description of certain memory circuit elements.

q-bio.CB↗

arXiv2013

Generalized Floquet theory: application to dynamical systems with memory and Bloch's theorem for nonlocal potentials

Floquet theory is a powerful tool in the analysis of many physical phenomena, and extended to spatial coordinates provides the basis for Bloch's theorem. However, in its original formulation it is limited to linear systems with periodic coefficients. Here, we extend the theory by proving a theorem for the general class of systems including linear operators commuting with the period-shift operator. The present theorem greatly expands the range of applicability of Floquet theory to a multitude of phenomena that were previously inaccessible with this type of analysis, such as dynamical systems with memory. As an important extension, we also prove Bloch's theorem for nonlocal potentials.

math.DS↗

arXiv2013

Kondo memory in driven strongly-correlated quantum dots

We investigate the real-time current response of strongly-correlated quantum dot systems under sinusoidal driving voltages. By means of an accurate hierarchical equations of motion approach, we demonstrate the presence of prominent memory effects induced by the Kondo resonance on the real-time current response. These memory effects appear as distinctive hysteresis line shapes and self-crossing features in the dynamic current-voltage characteristics, with concomitant excitation of odd-number overtones. They emerge as a cooperative effect of quantum coherence - due to inductive behavior - and electron correlations - due to the Kondo resonance. We also show the suppression of memory effects and the transition to classical behavior as a function of temperature. All these phenomena can be observed in experiments and may lead to novel quantum memory applications.

cond-mat.str-el↗

arXiv2013

Self-organization and solution of shortest-path optimization problems with memristive networks

We show that memristive networks-namely networks of resistors with memory-can efficiently solve shortest-path optimization problems. Indeed, the presence of memory (time non-locality) promotes self organization of the network into the shortest possible path(s). We introduce a network entropy function to characterize the self-organized evolution, show the solution of the shortest-path problem and demonstrate the healing property of the solution path. Finally, we provide an algorithm to solve the traveling salesman problem. Similar considerations apply to networks of memcapacitors and meminductors, and networks with memory in various dimensions.

cs.ET↗

arXiv2013

Electrochemical response of biased nanoelectrodes in solution

Novel approaches to DNA sequencing and detection require the measurement of electrical currents between metal probes immersed in ionic solution. Here, we experimentally demonstrate that these systems maintain large background currents with a transient response that decays very slowly in time and noise that increases with ionic concentration. Using a non-equilibrium stochastic model, we obtain an analytical expression for the ionic current that shows these results are due to a fast electrochemical reaction at the electrode surface followed by the slow formation of a diffusion layer. During the latter, ions translocate in the weak electric field generated after the initial rapid screening of the strong fields near the electrode surfaces. Our theoretical results are in very good agreement with experimental findings.

cond-mat.mes-hall↗

arXiv2013

Reading, writing and squeezing the entangled states of two nanomechanical resonators coupled to a SQUID

We study a system of two nanomechanical resonators embedded in a dc SQUID. We show that the inductively-coupled resonators can be treated as two entangled quantum memory elements with states that can be read from, or written on by employing the SQUID as a displacement detector or switching additional external magnetic fields, respectively. We present a scheme to squeeze the even modeof the state of the resonators and consequently reduce the noise in the measurement of the magnetic flux threading the SQUID. Wefinally analyze the effect of dissipation on the squeezing using the quantum master equation, and show the qualitatively differentbehavior for the weak and strong damping regimes. Our predictions can be tested using current experimental capabilities.

cond-mat.mes-hall↗

arXiv2012

Controlling Transport of Ultra-Cold Atoms in 1D Optical Lattices with Artificial Gauge Fields

We show that the recently developed optical lattices with Peierls substitution -- which can be modeled as a lattice with a complex tunneling coefficient -- may be used to induce controllable quantum transport of ultra-cold atoms. In particular, we show that by ramping up the phase of the complex tunneling coefficient in a spatially uniform fashion, a finite quasi steady-state current (QSSC) ensues from the exact dynamics of non-interacting fermions. The direction and magnitude of the current can be controlled by the overall phase difference but not the details of the ramp. The entanglement entropy does not increase when the QSSC lasts. Due to different spin statistics, condensed non-interacting bosons do not support a finite QSSC under the same setup. We also find that an approximate form of the QSSC survives when perturbative effects from interactions, weak harmonic background traps, and finite-temperature are present, which suggests that our findings should be observable with available experimental capabilities.

cond-mat.quant-gas↗

arXiv2012

Memristive properties of single-molecule magnets

Single-molecule magnets weakly coupled to two ferromagnetic leads act as memory devices in electronic circuits---their response depends on history, not just on the instantaneous applied voltage. We show that magnetic anisotropy introduces a wide separation of timescales between fast and slow relaxation processes in the system, which leads to a pronounced memory dependence in a wide intermediate time regime. We study the response to a harmonically varying bias voltage from slow to rapid driving within a master-equation approach. The system is not purely memristive but shows a partially capacitive response on short timescales. In the intermediate time regime the molecular spin can be used as the state variable in a two-terminal molecular memory device.

cond-mat.mes-hall↗

arXiv2012

Photoactivation of neurons by laser-generated local heating

We present a method for achieving temporally and spatially precise photoactivation of neurons without the need for genetic expression of photosensitive proteins. Our method depends upon conduction of thermal energy via absorption by a dye or carbon particles and does not require the presence of voltage-gated channels to create transmembrane currents. We demonstrate photothermal initiation of action potentials in Hirudo verbana neurons and of transmembrane currents in Xenopus oocytes. Thermal energy is delivered by focused 50 ms, 650 nm laser pulses with total pulse energies between 250 and 3500 \muJ. We document an optical delivery system for targeting specific neurons that can be expanded for multiple target sites. Our method achieves photoactivation reliably (70 - 90% of attempts) and can issue multiple pulses (6-9) with minimal changes to cellular properties as measured by intracellular recording. Direct photoactivation presents a significant step towards all-optical analysis of neural circuits in animals such as Hirudo verbana where genetic expression of photosensitive compounds is not feasible.

physics.bio-ph↗

arXiv2012

Dynamical crossover between the infinite-volume and empty-lattice limits of ultra-cold fermions in 1D optical lattices

Unlike typical condensed-matter systems, ultra-cold atoms loaded into optical lattices allow separate control of both the particle number and system size. As a consequence, there are two distinct "thermodynamic" limits that can be defined for these systems: i) "infinite-volume limit" at constant finite density, and ii) "empty-lattice limit" at constant particle number. To probe the difference between these two limits and their crossover, we consider a partially occupied lattice and study the transport of non-interacting fermions and fermions interacting at the mean-field level into the unoccupied region. In the infinite-volume limit, a finite steady-state current emerges. On the other hand, in the empty-lattice limit there is no finite steady-state current. By changing the initial filling, we find a smooth crossover between the two limits. Our predictions may be verified using available experimental tools and demonstrate a fundamental difference between isolated small systems such as ultra-cold atoms and conventional condensed-matter systems.

cond-mat.quant-gas↗

arXiv2012

Second and higher harmonics generation with memristive systems

We show that memristive systems can be used very efficiently to generate passively both double and higher frequency harmonics. A technique for maximizing the power conversion efficiency into any given harmonic is developed and applied to a single memristive system and memristive bridge circuits. We find much higher rates of power conversion compared to the standard diode bridge, with the memristive bridge more efficient for second and higher harmonics generation compared to the single memristive system. The memristive bridge circuit optimized for second harmonic generation behaves as a two-quarter-wave rectifier.

cond-mat.mes-hall↗

arXiv2012

Bosonic and fermionic transport phenomena of ultra-cold atoms in 1D optical lattices

Using the micro-canonical picture of transport -- a framework ideally suited to describe the dynamics of closed quantum systems such as ultra-cold atom experiments -- we show that the exact dynamics of non-interacting fermions and bosons exhibit very different transport properties when the system is set out of equilibrium by removing the particles from half of the lattice. We find that fermions rapidly develop a finite quasi steady-state current reminiscent of electronic transport in nanoscale systems. This result is robust -- it occurs with or without a harmonic confining potential and at zero or finite temperature. The zero-temperature bosonic current instead exhibits strong oscillatory behavior that decays into a steady-state of zero current only in the thermodynamic limit. These differences appear most strikingly in the different particle number fluctuations on half of the lattice as a consequence of the spin statistics. These predictions can be readily verified experimentally.

cond-mat.quant-gas↗

arXiv2012

Stochastic memory: memory enhancement due to noise

There are certain classes of resistors, capacitors and inductors that, when subject to a periodic input of appropriate frequency, develop hysteresis loops in their characteristic response. Here, we show that the hysteresis of such memory elements can also be induced by white noise of appropriate intensity even at very low frequencies of the external driving field. We illustrate this phenomenon using a physical model of memory resistor realized by $\mathrm{TiO_2}$ thin films sandwiched between metallic electrodes, and discuss under which conditions this effect can be observed experimentally. We also discuss its implications on existing memory systems described in the literature and the role of colored noise.

cond-mat.mes-hall↗

arXiv2011

Neuromorphic, Digital and Quantum Computation with Memory Circuit Elements

Memory effects are ubiquitous in nature and the class of memory circuit elements - which includes memristors, memcapacitors and meminductors - shows great potential to understand and simulate the associated fundamental physical processes. Here, we show that such elements can also be used in electronic schemes mimicking biologically-inspired computer architectures, performing digital logic and arithmetic operations, and can expand the capabilities of certain quantum computation schemes. In particular, we will discuss few examples where the concept of memory elements is relevant to the realization of associative memory in neuronal circuits, spike-timing-dependent plasticity of synapses, digital and field-programmable quantum computing.

cond-mat.mes-hall↗

arXiv2011

Current oscillations in Vanadium Dioxide: evidence for electrically triggered percolation avalanches

In this work, we experimentally and theoretically explore voltage controlled oscillations occurring in micro-beams of vanadium dioxide. These oscillations are a result of the reversible insulator to metal phase transition in vanadium dioxide. Examining the structure of the observed oscillations in detail, we propose a modified percolative-avalanche model which allows for voltage-triggering. This model captures the periodicity and waveshape of the oscillations as well as several other key features. Importantly, our modeling shows that while temperature plays a critical role in the vanadium dioxide phase transition, electrically induced heating cannot act as the primary instigator of the oscillations in this configuration. This realization leads us to identify electric field as the most likely candidate for driving the phase transition.

cond-mat.mes-hall↗