Time dependent local potential in a Tomonaga-Luttinger liquid

We study the energy deposition in a one dimensional interacting quantum system with a point like potential modulated in amplitude. The point like potential at position $x=0$ has a constant part and a small oscillation in time with a frequency $\omega$. We use bosonization, renormalization group and linear response theory to calculate the corresponding energy deposition. It exhibits a power law behavior as a function of the frequency that reflects the Tomonaga-Luttinger liquid (TLL) nature of the system. Depending on the interactions in the system, characterized by the TLL parameter $K$ of the system, a crossover between week and strong coupling for the backscattering due to the potential is possible. We compute the frequency scale $\omega_\ast$, at which such crossover exists. We find that the energy deposition due to the backscattering shows different exponent for $K>1$ and $K<1$. We discuss possible experimental consequences, in the context of cold atomic gases, of our theoretical results.Comment: 13 pages, 3 figure

Dynamics of a Mobile Impurity in a Two Leg Bosonic Ladder

We have analyzed the behavior of a mobile quantum impurity in a bath formed by a two-leg bosonic ladder by a combination of field theory (Tomonaga-Luttinger liquid) and numerical (Density Matrix Renormalization Group) techniques. Computing the Green's function of the impurity as a function of time at different momenta, we find a power law decay at zero momentum, which signals the breakdown of any quasi-particle description of the impurity motion. We compute the exponent both for the limits of weak and strong impurity-bath interactions. At small impurity-bath interaction, we find that the impurity experiences the ladder as a single channel one-dimensional bath, but effective coupling is reduced by a factor of $\sqrt 2$, thus the impurity is less mobile in the ladder compared to a one dimensional bath. We compared the numerical results for the exponent at zero momentum with a semi-analytical expression that was initially established for the chain and find excellent agreement without adjustable parameters. We analyze the dependence of the exponent in the transverse hopping in the bath and find surprisingly an increase of the exponent at variance with the naive extrapolation of the single channel regime. We study the momentum dependence of the impurity Green's function and find that, as for the single chain, two different regime of motion exist, one dominated by infrared metatrophy and a more conventional polaronic behavior. We compute the critical momentum between these two regimes and compare with prediction based on the structure factor of the bath. In the polaronic regime we also compute numerically the lifetime of the polaron. Finally we discuss how our results could be measured in cold atomic experiments.Comment: 14 Pages, 13 figure

Mobile Impurity in a Two-Leg Bosonic Ladder

We study the dynamics of a mobile impurity in a two-leg bosonic ladder. The impurity moves both along and across the legs and interacts with a bath of interacting bosonic particles present in the ladder. We use both analytical (Tomonaga-Luttinger liquid - TLL) and numerical (Density Matrix Renormalization Group - DMRG) methods to compute the Green's function of the impurity. We find that for a small impurity-bath interaction, the bonding mode of the impurity effectively couples only to the gapless mode of the bath while the anti-bonding mode of the impurity couples to both gapped and gapless mode of the bath. We compute the time dependence of the Green's function of the impurity, for impurity created either in the anti-bonding or bonding mode with a given momentum. The later case leads to a decay as a power-law below a critical momentum and exponential above, while the former case always decays exponentially. We compare the DMRG results with analytical results using the linked cluster expansion and find a good agreement. In addition we use DMRG to extract the lifetime of the quasi-particle, when the Green's function decays exponentially. We also treat the case of an infinite bath-impurity coupling for which both the bonding and antibonding modes are systematically affected. For this case the impurity Green's function in the bonding mode decays as a power-law at zero momentum.The corresponding exponent increases with increasing transverse-tunneling of the impurity. We compare our results with the other impurity problems for which the motion of either the impurity or the bath is limited to a single chain. Finally we comments on the consequences of our findings for experiments with the ultracold gasses.Comment: 11 pages, 15 figure

Probing non-equilibrium dissipative phase transitions with trapped-ion quantum simulators

Open quantum many-body systems with controllable dissipation can exhibit novel features in their dynamics and steady states. A paradigmatic example is the dissipative transverse field Ising model. It has been shown recently that the steady state of this model with all-to-all interactions is genuinely non-equilibrium near criticality, exhibiting a modified time-reversal symmetry and violating the fluctuation-dissipation theorem. Experimental study of such non-equilibrium steady-state phase transitions is however lacking. Here we propose realistic experimental setups and measurement schemes for current trapped-ion quantum simulators to demonstrate this phase transition, where controllable dissipation is engineered via a continuous weak optical pumping laser. With extensive numerical calculations, we show that strong signatures of this dissipative phase transition and its non-equilibrium properties can be observed with a small system size across a wide range of system parameters. In addition, we show that the same signatures can also be seen if the dissipation is instead achieved via Floquet dynamics with periodic and probabilistic resetting of the spins. Dissipation engineered in this way may allow the simulation of more general types of driven-dissipative systems or facilitate the dissipative preparation of useful many-body entangled states.Comment: 12 pages, 5 figure

Quantum dynamics in one-dimensional and two-leg ladder systems

In this thesis, we work on three problems. In the first problem, we work on a local time-dependent potential in a one-dimensional interacting bath. This work is motivated by cold atomic experiments, where one can shake the ultracold systems by using a time-dependent potential. We use linear response theory, bosonization, and renormalization group to compute the energy deposition in the one-dimensional bath by the time-dependent potential. We find that the energy deposition both for weak and strong coupling regimes shows a power-law behavior on the frequency of oscillation, and shows a different power-law exponent in strong and weak coupling limit. In the second problem, we work on the dynamics of a mobile impurity in a two-leg bosonic ladder. The theoretical and experimental studies of a mobile impurity in a one-dimensional bath in context of ultracold systems motivate this work. We confine the impurity to move in one of the legs of the ladder. We combine bosonization, renormalization group, and density matrix renormalization group to understand the dynamics of the impurity. We compute the Green's function of the impurity both theoretically and numerically. For a small interaction between the impurity and the bath, we find theoretically that the Green's function of the impurity decays as a power-law, and our numerical results show a good agreement with analytical result. Furthermore, we also give an analytical result of the Green's function for an infinite interaction, we find again that the Green's function decays as a power-law, and shows a good agreement with numerical results. Moreover, finally we give a semi-analytical expression for the power-law exponent at zero momentum as a function of interaction, again in good agreement with the numerical results. In the third problem, we are again investigating the dynamics of a mobile impurity in a two-leg bosonic ladder, but in this case, the impurity also tunnels in both longitudinal and transverse directions. We use similar methods than for the second problem. We compute the Green's function in the bonding and the anti-bonding modes of the impurity. The Green's function in the anti-bonding mode decays as power-law at small momentum and small interaction, while the Green's function in the bonding decays exponentially, and our numerical results show a good agreement with analytical ones