383 research outputs found
Gaussian processes for choosing laser parameters for driven, dissipative Rydberg aggregates
To facilitate quantum simulation of open quantum systems at finite
temperatures, an important ingredient is to achieve thermalization on a given
time-scale. We consider a Rydberg aggregate (an arrangement of Rydberg atoms
that interact via long-range interactions) embedded in a laser-driven atomic
environment. For the smallest aggregate (two atoms), suitable laser parameters
can be found by brute force scanning of the four tunable laser parameters. For
more atoms, however, such parameter scans are too computationally costly. Here
we apply Gaussian processes to predict the thermalization performance as a
function of the laser parameters for two-atom and four-atom aggregates. These
predictions perform remarkably well using just 1000 simulations, demonstrating
the utility of Gaussian processes in an atomic physics setting. Using this
approach, we find and present effective laser parameters for generating
thermalization, the robustness of these parameters to variation, as well as
different thermalization dynamics
Hierarchy of stochastic pure states for open quantum system dynamics
We derive a hierarchy of stochastic evolution equations for pure states
(quantum trajectories) to efficiently solve open quantum system dynamics with
non-Markovian structured environments. From this hierarchy of pure states
(HOPS) the exact reduced density operator is obtained as an ensemble average.
We demonstrate the power of HOPS by applying it to the Spin-Boson model, the
calculation of absorption spectra of molecular aggregates and energy transfer
in a photosynthetic pigment-protein complex
Non-Markovian Dynamics in Ultracold Rydberg Aggregates
We propose a setup of an open quantum system in which the environment can be
tuned such that either Markovian or non-Markovian system dynamics can be
achieved. The implementation uses ultracold Rydberg atoms, relying on their
strong long-range interactions. Our suggestion extends the features available
for quantum simulators of molecular systems employing Rydberg aggregates and
presents a new test bench for fundamental studies of the classification of
system-environment interactions and the resulting system dynamics in open
quantum systems.Comment: 13 pages, 4 figure
Flexible scheme to truncate the hierarchy of pure states
The hierarchy of pure states (HOPS) is a wavefunction-based method which can
be used for numerically modeling open quantum systems. Formally, HOPS recovers
the exact system dynamics for an infinite depth of the hierarchy. However,
truncation of the hierarchy is required to numerically implement HOPS. We want
to choose a 'good' truncation method, where by 'good' we mean that it is
numerically feasible to check convergence of the results. For the truncation
approximation used in previous applications of HOPS, convergence checks are
numerically challenging. In this work we demonstrate the application of the
'-particle approximation' (PA) to HOPS. We also introduce a new
approximation, which we call the '-mode approximation' (MA). We then
explore the convergence of these truncation approximations with respect to the
number of equations required in the hierarchy. We show that truncation
approximations can be used in combination to achieve convergence in two
exemplary problems: absorption and energy transfer of molecular aggregates.Comment: 8 pages, 3 figure
Quantum simulation of energy transport with embedded Rydberg aggregates
We show that an array of ultracold Rydberg atoms embedded in a laser driven
background gas can serve as an aggregate for simulating exciton dynamics and
energy transport with a controlled environment. Spatial disorder and
decoherence introduced by the interaction with the background gas atoms can be
controlled by the laser parameters. This allows for an almost ideal realization
of a Haken-Reineker-Strobl type model for energy transport. Physics can be
monitored using the same mechanism that provides control over the environment.
The degree of decoherence is traced back to information gained on the
excitation location through the monitoring, turning the setup into an
experimentally accessible model system for studying the effects of quantum
measurements on the dynamics of a many-body quantum system.Comment: 5 pages, 4 figures, 3 pages supp. in
Simulation of absorption spectra of molecular aggregates: A hierarchy of stochastic pure state approach
Simulation of spectroscopic observables for molecular aggregates with strong and structured coupling of electronic excitation to vibrational degrees of freedom is an important but challenging task. The Hierarchy of Pure States (HOPS) provides a formally exact solution based on local, stochastic trajectories. Exploiting the localization of HOPS for the simulation of absorption spectra in large aggregates requires a formulation in terms of normalized trajectories. Here, we provide a normalized dyadic equation where the ket- and bra-states are propagated in different electronic Hilbert spaces. This work opens the door to applying adaptive HOPS methods for the simulation of absorption spectra. (C) 2022 Author(s)
Optomechanical interactions in non-Hermitian photonic molecules
We study optomechanical interactions in non-Hermitian photonic molecules that support two photonic states and one acoustic mode. The nonlinear steady-state solutions and their linear stability landscapes are investigated as a function of the system\u27s parameters and excitation power levels. We also examine the temporal evolution of the system and uncover different regimes of nonlinear dynamics. Our analysis reveals several important results: (1) parity-time () symmetry is not necessarily the optimum choice for maximum optomechanical interaction. (2) Stable steady-state solutions are not always reached under continuous wave optical excitations. (3) Accounting for gain saturation effects can regulate the behavior of the otherwise unbounded oscillation amplitudes. Our study provides a deeper insight into the interplay between optical non-Hermiticity and optomechanical coupling and can thus pave the way for new device applications
On-chip non-reciprocal optical devices based on quantum inspired photonic lattices
We propose a novel geometry for integrated photonic devices that can be used
as isolators and polarization splitters based on engineered photonic lattices.
Starting from optical waveguide arrays that mimic Fock space representation of
a non-interacting two-site Bose Hubbard Hamiltonian, we show that introducing
magneto-optic nonreciprocity to these structures leads to a superior optical
isolation performance. In the forward propagation direction, an input TM
polarized beam experiences a perfect state transfer between the input and
output waveguide channels while surface Bloch oscillations block the backward
transmission between the same ports. Our analysis indicates a large isolation
ratio of 75 dB after a propagation distance of 8 mm inside seven coupled
waveguides. Moreover, we demonstrate that, a judicious choice of the
nonreciprocity in this same geometry can lead to perfect polarization
splitting.Comment: 13 pages 3 figure
Light transport in PT-invariant photonic structures with hidden symmetries
We introduce a recursive bosonic quantization technique for generating
classical PT photonic structures that possess hidden symmetries and higher
order exceptional points. We study light transport in these geometries and we
demonstrate that perfect state transfer is possible only for certain initial
conditions. Moreover, we show that for the same propagation direction, left and
right coherent transports are not symmetric with field amplitudes following two
different trajectories. A general scheme for identifying the conservation laws
in such PT-symmetric photonic networks is also presented
Dynamics of a nano-scale rotor driven by single-electron tunneling
We investigate theoretically the dynamics and the charge transport properties
of a rod-shaped nano-scale rotor, which is driven by a similar mechanism as the
nanomechanical single-electron transistor (NEMSET). We show that a static
electric potential gradient can lead to self-excitation of oscillatory or
continuous rotational motion. The relevant parameters of the device are
identified and the dependence of the dynamics on these parameters is studied.
We further discuss how the dynamics is related to the measured current through
the device. Notably, in the oscillatory regime, we find a negative differential
conductance. The current-voltage characteristics can be used to infer details
of the surrounding environment which is responsible for damping
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