Raoul Dillenschneider

Experimental verification of Landauer/'s principle linking information and thermodynamics

In 1961, Rolf Landauer argued that the erasure of information is a dissipative process. A minimal quantity of heat, proportional to the thermal energy and called the Landauer bound, is necessarily produced when a classical bit of information is deleted. A direct consequence of this logically irreversible transformation is that the entropy of the environment increases by a finite amount. Despite its fundamental importance for information theory and computer science, the erasure principle has not been verified experimentally so far, the main obstacle being the difficulty of doing single-particle experiments in the low-dissipation regime. Here we experimentally show the existence of the Landauer bound in a generic model of a one-bit memory. Using a system of a single colloidal particle trapped in a modulated double-well potential, we establish that the mean dissipated heat saturates at the Landauer bound in the limit of long erasure cycles. This result demonstrates the intimate link between information theory and thermodynamics. It further highlights the ultimate physical limit of irreversible computation.

Quantum discord and quantum phase transition in spin chains

Quantum phase transitions of the transverse Ising and antiferromagnetic

Energetics of quantum correlations

XXZ

Memory erasure in small systems.

spin

Exciton formation in graphene bilayer

S=1/2

Quantum Smoluchowski equation for driven systems

chains are studied using quantum discord. Quantum discord allows the measure of quantum correlations present in many-body quantum systems. It is shown that the amount of quantum correlations increases close to the critical points. The observations are in agreement with the information provided by the concurrence, which measures the entanglement of the many-body system.

Supersolid phase transitions for hard-core bosons on a triangular lattice

We consider a photo-Carnot engine that consists of a single-mode radiation field in an optical cavity. One the heat reservoirs is made of a beam of thermally entangled pairs of two-level atoms that interact resonantly with the cavity. We express the thermodynamic efficiency of the engine in terms of the quantum discord of the atomic pair and find that it can exceed its classical value. Our results show that useful work can be extracted from quantum correlations, indicating that the latter are a valuable resource in quantum thermodynamics.

Site-occupation constraints in mean-field approaches to quantum spin systems at finite temperature

We consider an overdamped nanoparticle in a driven double-well potential as a generic model of an erasable 1-bit memory. We study in detail the statistics of the heat dissipated during an erasure process and show that full erasure may be achieved by dissipating less heat than the Landauer bound. We quantify the occurrence of such events and propose a single-particle experiment to verify our predictions. Our results show that Landauers principle has to be generalized at the nanoscale to accommodate heat fluctuations.

Kekule-distortion-induced exciton instability in graphene

Exciton instability in graphene bilayer systems is studied in the case of a short-ranged Coulomb interaction and a finite voltage difference between the layers. Self-consistent exciton gap equations are derived and solved numerically and analytically under controlled approximation. We obtain that a critical strength of the Coulomb interaction exists for the formation of excitons. The critical strength depends on the amount of voltage difference between the layers and on the interlayer hopping parameter.

Chiral symmetry restoration in (2+1)-dimensional QED with a Maxwell-Chern-Simons term at finite temperature

We consider a driven quantum harmonic oscillator strongly coupled to a heat bath. Starting from the exact quantum Langevin equation, we use a Greens function approach to determine the corresponding semiclassical equation for the Wigner phase space distribution. In the limit of high friction and high temperature, we apply Brinkmans method to derive the quantum Smoluchowski equation for the probability distribution in position space. We further determine the range of validity of the equation and discuss the special case of a Brownian parametric oscillator.