arXiv subjects

D. Segal

Publications and source records attributed to D. Segal.

6 recordsLinked to original sources

arXiv2018

Studying fundamental physics using quantum enabled technologies with trapped molecular ions

The text below was written during two visits that Daniel Segal made at Universit{é} Paris 13. Danny stayed at Laboratoire de Physique des Lasers the summers of 2008 and 2009 to participate in the exploration of a novel lead in the field of ultra-high resolution spectroscopy. Our idea was to probe trapped molecular ions using Quantum Logic Spectroscopy (QLS) in order to advance our understanding of a variety of fundamental processes in nature. At that time, QLS, a ground-breaking spectroscopic technique, had only been demonstrated with atomic ions. Our ultimategoals were new approaches to the observation of parity violation in chiral molecules and tests of time variations of the fundamental constants. This text is the original research proposal written eight years ago. We have added a series of notes to revisit it in the light of what has been since realized in the field.

physics.atom-ph↗

arXiv2013

Qubit-mediated energy transfer between thermal reservoirs: beyond Markovian Master equation

We study qubit-mediated energy transfer between two electron reservoirs by adopting a numerically-exact influence functional path-integral method. This non-perturbative technique allows us to study the system's dynamics beyond the weak coupling limit. Our simulations for the energy current indicate that perturbative-Markovian Master equation predictions significantly deviate from exact numerical results already at intermediate coupling, $πρα_{j,j'}\gtrsim 0.4$, where $ρ$ is the metal (Fermi sea) density of states, taken as a constant, and $α_{j,j'}$ is the scattering potential energy of electrons, between the $j$ and $j'$ states. Markovian Master equation techniques should be therefore used with caution beyond the strictly weak subsystem-bath coupling limit, especially when a quantitative knowledge of transport characteristics is desired.

cond-mat.mes-hall↗

arXiv2012

Vibrational cooling, heating, and instability in molecular conducting junctions: Full counting statistics analysis

We study current-induced vibrational cooling, heating, and instability in a donor-acceptor rectifying molecular junction using a full counting statistics approach. In our model, electron-hole pair excitations are coupled to a given molecular vibrational mode which is either harmonic or highly anharmonic. This mode may be further coupled to a dissipative thermal environment. Adopting a master equation approach, we confirm the charge and heat exchange fluctuation theorem in the steady-state limit, for both harmonic and anharmonic models. Using simple analytical expressions, we calculate the charge current and several measures for the mode effective temperature. At low bias, we observe the effect of bias-induced cooling of the vibrational mode. At higher bias, the mode effective temperature is higher than the environmental temperature, yet the junction is stable. Beyond that, once the vibrational mode (bias-induced) excitation rate overcomes its relaxation rate, instability occurs. We identify regimes of instability as a function of voltage bias and coupling to an additional phononic thermal bath. Interestingly, we observe a reentrant behavior where an unstable junction can properly behave at a high enough bias. The mechanism for this behavior is discussed.

cond-mat.mes-hall↗

arXiv2011

Quantum fluctuation theorem for heat exchange in the strong coupling regime

We study quantum heat exchange in a multi-state impurity coupled to two thermal reservoirs. Allowing for strong system-bath interactions, we show that a steady-state heat exchange fluctuation theorem holds, though the dynamical processes nonlinearly involve the two reservoirs. We accomplish a closed expression for the cumulant generating function, and use it obtain the heat current and its cumulants in a nonlinear thermal junction, the two-bath spin-boson model.

cond-mat.stat-mech↗

arXiv2008

Double wells, scalar fields and quantum phase transitions in ions traps

Since Hund's work on the ammonia molecule, the double well potential has formed a key paradigm in physics. Its importance is further underlined by the central role it plays in the Landau theory of phase transitions. Recently, the study of entanglement properties of many-body systems has added a new angle to the study of quantum phase transitions of discrete and continuous degrees of freedom, i.e., spin and harmonic chains. Here we show that control of the radial degree of freedom of trapped ion chains allows for the simulation of linear and non-linear Klein-Gordon fields on a lattice, in which the parameters of the lattice, the non-linearity and mass can be controlled at will. The system may be driven through a phase transition creating a double well potential between different configurations of the ion crystal. The dynamics of the system are controllable, local properties are measurable and tunnelling in the double well potential would be observable.

quant-ph↗

arXiv2001

Steady state quantum mechanics of thermally relaxing systems

A theoretical description of quantum mechanical steady states is developed. Applications for simple quantum mechanical systems described in terms of coupled level structures yield a formulation equivalent to time independent scattering theory. Applications to steady states of thermally relaxing systems leads to time independent scattering theory in Liouville space that is equivalent to the tetradic Green's function formalism. It provides however a direct route to derive particular forms of the Liouville equation applicable in steady state situations. The theory is applied to study the conduction properties in the super-exchange model of a metal-molecule-metal contact weakly coupled to the thermal environment. The energy resolved temperature dependent transmission probability, as well as its coherent (tunneling) and incoherent (activated) parts, are calculated using the Redfield approximation. These components depend differently on the energy gap (or barrier), on the temperature and on the bridge length. The coherent component is most important at low temperatures, large energy gaps and small chain lengths. The incoherent component dominates in the opposite limits. The integrated transmission provides a generalization of the Landauer conduction formula for small junctions in the presence of thermal relaxation.

cond-mat↗