arXiv subjects

Peter Hänggi

Publications and source records attributed to Peter Hänggi.

At least 55 records · Page 3Linked to original sources

arXiv2014

Quantum fluctuation theorems and generalized measurements during the force protocol

Generalized measurements of an observable performed on a quantum system during a force protocol are investigated and conditions that guarantee the validity of the Jarzynski equality and the Crooks relation are formulated. In agreement with previous studies by Campisi {\it et al.} [M. Campisi, P. Talkner, and P. Hänggi, Phys. Rev. Lett. {\bf 105}, 140601 (2010); Phys. Rev. E {\bf 83}, 041114 (2011)], we find that these fluctuation relations are satisfied for projective measurements; however, for generalized measurements special conditions on the operators determining the measurements need to be met. For the Jarzynski equality to hold, the measurement operators of the forward protocol must be normalized in a particular way. The Crooks relation additionally entails that the backward and forward measurement operators depend on each other. Yet, quite some freedom is left as to how the two sets of operators are interrelated. This ambiguity is removed if one considers selective measurements, which are specified by a {\it joint} probability density function of work and measurement results of the considered observable. We find that the respective forward and backward joint probabilities satisfy the Crooks relation only if the measurement operators of the forward and backward protocols are the time-reversed adjoints of each other. In this case, the work probability density function {\it conditioned} on the measurement result satisfies a modified Crooks relation. The modification appears as a protocol-dependent factor that can be expressed by the information gained by the measurements during the forward and backward protocols. Finally, detailed fluctuation theorems with an arbitrary number of intervening measurements are obtained.

cond-mat.stat-mech↗

arXiv2014

Anomalous Heat Diffusion

Consider anomalous energy spread in solid phases, i.e., $MSD= \int (x -{\langle x \rangle}_E)^2 ρ_E(x,t)dx \propto t^β$, as induced by a small initial excess energy perturbation distribution $ρ_{E}(x,t=0)$ away from equilibrium. The associated total thermal equilibrium heat flux autocorrelation function $C_{JJ}(t)$ is shown to obey rigorously the intriguing relation, $d^2 MSD/dt^2 = 2C_{JJ}(t)/(k_BT^2c)$, where $c$ is the specific volumetric heat capacity. Its integral assumes a time-local Helfand-moment relation; i.e. $ dMSD/dt|_{t=t_s} = 2/(k_BT^2c)\int_0^{t_s} C_{JJ}(s)ds$, where the chosen cut-off time $t_s$ is determined by the maximal signal velocity for heat transfer. Given the premise that the averaged nonequilibrium heat flux is governed by an anomalous heat conductivity, energy diffusion scaling determines a corresponding anomalous thermal conductivity scaling behaviour.

cond-mat.stat-mech↗

arXiv2013

Entanglement creation in a quantum dot-nanocavity system

We explore the possibility to entangle an excitonic two-level system in a semiconductor quantum dot (QD) with a cavity defined on a photonic crystal by sweeping the cavity frequency across its resonance with the exciton transition. The dynamic cavity detuning is established by a radio frequency surface acoustic wave (SAW). It induces Landau-Zener (LZ) transitions between the excitonic and the photonic degrees of freedom and thereby creates a superposition state. We optimize this scheme by using tailored Fourier-synthesized SAW pulses with up to five harmonics. The theoretical study is performed with a master equation approach for present state-of-the-art setups. Assuming experimentally demonstrated system parameters, we demonstrate that the composed pulses increase both the maximum entanglement and its persistence. The latter is only limited by the dominant dephasing mechanism; i.e., the photon loss from the cavity.

cond-mat.mes-hall↗

arXiv2013

Reduced density matrix for nonequilibrium steady states: A modified Redfield solution approach

We describe a method to obtain the reduced density matrix (RDM) correct up to second order in system-bath coupling in \emph{nonequilibrium} steady state situations. The RDM is obtained via a scheme based on analytic continuation, using the time-local Redfield-like quantum master equation, which was earlier used by the same authors [J. Chem. Phys. \textbf{136}, 194110 (2012)] to obtain the correct thermal equilibrium description. This nonequilibrium modified Redfield solution is then corroborated with the exact RDM obtained via the nonequilibrium Green's function technique for the quantum harmonic oscillator. Lastly, the scheme is compared to different quantum master equations (QMEs), namely the time-local Redfield-like and the Lindblad-like QMEs, in order to illustrate the differences between each of these approaches.

cond-mat.stat-mech↗

arXiv2013

Employing Circuit QED to Measure Nonequilibrium Work Fluctuations

We study an interferometric method for the measurement of the statistics of work performed on a driven quantum system, which has been put forward recently [Dorner et al., Phys. Rev. Lett. 110 230601 (2013), Mazzola et al., Phys. Rev. Lett. 110 230602 (2013)]. The method allows replacing two projective measurements of the energy of the driven system with qubit tomography of an ancilla that is appropriately coupled to it. We highlight that this method could be employed to obtain the work statistics of closed as well as open driven system, even in the strongly dissipative regime. We then illustrate an implementation of the method in a circuit QED set-up, which allows one to experimentally obtain the work statistics of a parametrically driven harmonic oscillator. Our implementation is an extension of the original method, in which two ancilla-qubits are employed and the work statistics is retrieved through two-qubit state tomography. Our simulations demonstrate the experimental feasibility.

quant-ph↗

arXiv2013

Power spectrum of electronic heat current fluctuations

We analyze the fluctuations of an electronic thermal current across an idealized molecular junction. The focus here will be on the spectral features of the resulting heat fluctuations. By use of the Green functionmethod we derive an explicit expression for the frequency-dependent power spectral density of the emerging energy fluctuations. The complex expression simplifies considerably in the limit of zero frequency, yielding the noise intensity of the heat current. The spectral density for the electronic heat fluctuations still depends on the frequency in the zero-temperature limit, assuming different asymptotic behaviours in the low- and high-frequency regions. We further address subtleties and open problems from an experimental viewpoint for measurements of frequency-dependent power spectral densities.

cond-mat.mes-hall↗

arXiv2012

On the origin of power-laws in equilibrium

A particle in the attractive Coulomb field has an interesting property: its specific heat is constant and negative. We show, both analytically and numerically, that when a classical Hamiltonian system stays in weak contact with one such negative specific heat object, its statistics conforms to a fat-tailed power-law distribution with power index given by $C/k_B-1$, where $k_B$ is Boltzmann constant and $C$ is the heat capacity.

cond-mat.stat-mech↗

arXiv2012

Geometric magnetism in open quantum systems

An isolated classical chaotic system, when driven by the slow change of several parameters, responds with two reaction forces: geometric friction and geometric magnetism. By using the theory of quantum fluctuation relations we show that this holds true also for open quantum systems, and provide explicit expressions for those forces in this case. This extends the concept of Berry curvature to the realm of open quantum systems. We illustrate our findings by calculating the geometric magnetism of a damped charged quantum harmonic oscillator transported along a path in physical space in presence of a magnetic field and a thermal environment. We find that in this case the geometric magnetism is unaffected by the presence of the heat bath.

cond-mat.stat-mech↗

arXiv2012

Reply to M. Meléndez and W. G. Hoover [arXiv:1206.0188v2]

In response to the recent critical comment by M. Meléndez and W. G. Hoover [arXiv:1206.0188v2] on our work [M. Campisi et al., Phys. Rev. Lett. 108, 250601 (2012)], we show that their molecular dynamics simulations do not disprove our theory but in fact convincingly corroborate it.

cond-mat.stat-mech↗

arXiv2012

Logarithmic oscillators: ideal Hamiltonian thermostats

A logarithmic oscillator (in short, log-oscillator) behaves like an ideal thermostat because of its infinite heat capacity: when it weakly couples to another system, time averages of the system observables agree with ensemble averages from a Gibbs distribution with a temperature T that is given by the strength of the logarithmic potential. The resulting equations of motion are Hamiltonian and may be implemented not only in a computer but also with real-world experiments, e.g., with cold atoms.

cond-mat.stat-mech↗

arXiv2012

Deterministic transport of particles in a micro-pump

We study the drift of suspended micro-particles in a viscous liquid pumped back and forth through a periodic lattice of pores (drift ratchet). In order to explain the particle drift observed in such an experiment, we present an one-dimensional deterministic model of Stokes' drag. We show that the stability of oscillations of particle is related to their amplitude. Under appropriate conditions, particles may drift and two mechanisms of transport are pointed out. The first one is due to an spatio-temporal synchronization between the fluid and particle motions. As results the velocity is locked by the ratio of the space periodicity over the time periodicity. The direction of the transport may switch by tuning the parameters. Noteworthy, its emergence is related to a lattice of 2-periodic orbits but not necessary to chaotic dynamics. The second mechanism is due to an intermittent bifurcation and leads to a slow transport composed by long time oscillations following by a relative short transport to the next pore. Both steps repeat in a quasi-periodic manner. The direction of this last transport is strongly dependent on the pore geometry.

physics.flu-dyn↗

arXiv2012

Nonequilibrium phases in hybrid arrays with flux qubits and NV centers

We propose a startling hybrid quantum architecture for simulating a localization-delocalization transition. The concept is based on an array of superconducting flux qubits which are coupled to a diamond crystal containing nitrogen-vacancy (NV) centers. The underlying description is a Jaynes-Cummings-lattice in the strong-coupling regime. However, in contrast to well-studied coupled cavity arrays the interaction between lattice sites is mediated here by the qubit rather than by the oscillator degrees of freedom. Nevertheless, we point out that a transition between a localized and a delocalized phase occurs in this system as well. We demonstrate the possibility of monitoring this transition in a non-equilibrium scenario, including decoherence effects. The proposed scheme allows the monitoring of localization-delocalization transitions in Jaynes-Cummings-lattices by use of currently available experimental technology. Contrary to cavity-coupled lattices, our proposed recourse to stylized qubit networks facilitates (i) to investigate localization-delocalization transitions in arbitrary dimensions and (ii) to tune the inter-site coupling in-situ.

quant-ph↗

arXiv2012

Non-Markovian qubit decoherence during dispersive readout

We study qubit decoherence under generalized dispersive readout, i.e., we investigate a qubit coupled to a resonantly driven dissipative harmonic oscillator. We provide a complete picture by allowing for arbitrarily large qubit-oscillator detuning and by considering also a coupling to the square of the oscillator coordinate, which is relevant for flux qubits. Analytical results for the decoherence time are obtained by a transformation of the qubit-oscillator Hamiltonian to the dispersive frame and a subsequent master equation treatment beyond the Markov limit. We predict a crossover from Markovian decay to a decay with Gaussian shape. Our results are corroborated by the numerical solution of the full qubit-oscillator master equation in the original frame.

cond-mat.mes-hall↗

arXiv2012

Generalized Gibbs state with modified Redfield solution: Exact agreement up to second order

A novel scheme for the steady state solution of the standard Redfield quantum master equation is developed which yields agreement with the exact result for the corresponding reduced density matrix up to second order in the system-bath coupling strength. We achieve this objective by use of an analytic continuation of the off-diagonal matrix elements of the Redfield solution towards its diagonal limit. Notably, our scheme does not require the provision of yet higher order relaxation tensors. Testing this modified method for a heat bath consisting of a collection of harmonic oscillators we assess that the system relaxes towards its correct coupling-dependent, generalized quantum Gibbs state in second order. We numerically compare our formulation for a damped quantum harmonic system with the nonequilibrium Green's function formalism: we find good agreement at low temperatures for coupling strengths that are even larger than expected from the very regime of validity of the second-order Redfield quantum master equation. Yet another advantage of our method is that it markedly reduces the numerical complexity of the problem; thus allowing to study efficiently large-sized \emph{system} Hilbert spaces.

cond-mat.stat-mech↗

arXiv2012

Reply to W. G. Hoover [arXiv:1204.0312v2]

In response to W. G. Hoover's comment [arXiv:1204.0312v2] on our work [arXiv:1203.5968], we show explicitly that the divergence of the velocity field associated with the Nosé-Hoover equations is nonzero, implying that those equations are not volume preserving, and hence, as often stated in the literature, are not Hamiltonian. We further elucidate that the trajectories {q(t)} generated by the Nosé-Hoover equations are generally not identical to those generated by Dettmann's Hamiltonian. Dettmann's Hamiltonian produces the same trajectories as the Nosé-Hoover equations only on a specific energy shell, but not on the neighboring ones. This fact explains why the Nosé-Hoover equations are not volume preserving. The Hamiltonian that we put forward with [arXiv:1203.5968] instead produces thermostated dynamics irrespective of the energy value. The main advantage of our Hamiltonian thermostat over previous ones is that it contains kinetic energy terms that are of standard form with coordinate-independent masses and consequently is readily matched in laboratory experiments.

cond-mat.stat-mech↗

arXiv2012

Phononics: Manipulating heat flow with electronic analogs and beyond

The form of energy termed heat that typically derives from lattice vibrations, i.e. the phonons, is usually considered as waste energy and, moreover, deleterious to information processing. However, with this colloquium, we attempt to rebut this common view: By use of tailored models we demonstrate that phonons can be manipulated like electrons and photons can, thus enabling controlled heat transport. Moreover, we explain that phonons can be put to beneficial use to carry and process information. In a first part we present ways to control heat transport and how to process information for physical systems which are driven by a temperature bias. Particularly, we put forward the toolkit of familiar electronic analogs for exercising phononics; i.e. phononic devices which act as thermal diodes, thermal transistors, thermal logic gates and thermal memories, etc.. These concepts are then put to work to transport, control and rectify heat in physical realistic nanosystems by devising practical designs of hybrid nanostructures that permit the operation of functional phononic devices and, as well, report first experimental realizations. Next, we discuss yet richer possibilities to manipulate heat flow by use of time varying thermal bath temperatures or various other external fields. These give rise to a plenty of intriguing phononic nonequilibrium phenomena as for example the directed shuttling of heat, a geometrical phase induced heat pumping, or the phonon Hall effect, that all may find its way into operation with electronic analogs.

cond-mat.mes-hall↗

arXiv2012

Relativistic Brownian motion on a graphene chip

Relativistic Brownian motion can be inexpensively demonstrated on a graphene chip. The interplay of stochastic and relativistic dynamics, governing the transport of charge carrier in graphene, induces noise-controlled effects such as (i) a stochastic effective mass, detectable as a suppression of the particle mobility with increasing the temperature; (ii) a transverse ratchet effect, measurable as a net current orthogonal to an ac drive on an asymmetric substrate, and (iii) a chaotic stochastic resonance. Such properties can be of practical applications in the emerging graphene technology.

cond-mat.stat-mech↗

arXiv2011

Rayleigh and depinning instabilities of forced liquid ridges on heterogeneous substrates

Depinning of two-dimensional liquid ridges and three-dimensional drops on an inclined substrate is studied within the lubrication approximation. The structures are pinned to wetting heterogeneities arising from variations of the strength of the short-range polar contribution to the disjoining pressure. The case of a periodic array of hydrophobic stripes transverse to the slope is studied in detail using a combination of direct numerical simulation and branch-following techniques. Under appropriate conditions the ridges may either depin and slide downslope as the slope is increased, or first breakup into drops via a transverse instability, prior to depinning. The different transition scenarios are examined together with the stability properties of the different possible states of the system.

nlin.PS↗