61,565 research outputs found
Weakly-coupled systems in quantum control
This paper provides rigorous definitions and analysis of the dynamics of
weakly-coupled systems and gives sufficient conditions for an infinite
dimensional quantum control system to be weakly-coupled. As an illustration we
provide examples chosen among common physical systems
Exploiting Non-Markovianity of the Environment for Quantum Control
When the environment of an open quantum system is non-Markovian, amplitude
and phase flow not only from the system into the environment but also back.
Here we show that this feature can be exploited to carry out quantum control
tasks that could not be realized if the system was isolated. Inspired by recent
experiments on superconducting phase circuits, we consider an anharmonic ladder
with resonant amplitude control only. This restricts realizable operations to
SO(N). The ladder is immersed in an environment of two-level systems. Strongly
coupled two-level systems lead to non-Markovian effects, whereas the weakly
coupled ones result in single-exponential decay. Presence of the environment
allows for implementing diagonal unitaries that, together with SO(N), yield the
full group SU(N). Using optimal control theory, we obtain errors that are
solely -limited
Thermodynamics of Quantum-Jump-Conditioned Feedback Control
We consider open quantum systems weakly coupled to thermal reservoirs and
subjected to quantum feedback operations triggered with or without delay by
monitored quantum jumps. We establish a thermodynamic description of such
system and analyze how the first and second law of thermodynamics are modified
by the feedback. We apply our formalism to study the efficiency of a qubit
subjected to a quantum feedback control and operating as a heat pump between
two reservoirs. We also demonstrate that quantum feedbacks can be used to
stabilize coherences in nonequilibrium stationary states which in some cases
may even become pure quantum states.Comment: 12 pages, 6 figure
Pulsed Laser Cooling for Cavity-Optomechanical Resonators
A pulsed cooling scheme for optomechanical systems is presented that is
capable of cooling at much faster rates, shorter overall cooling times, and for
a wider set of experimental scenarios than is possible by conventional methods.
The proposed scheme can be implemented for both strongly and weakly coupled
optomechanical systems in both weakly and highly dissipative cavities. We study
analytically its underlying working mechanism, which is based on
interferometric control of optomechanical interactions, and we demonstrate its
efficiency with pulse sequences that are obtained by using methods from optimal
control. The short time in which our scheme approaches the optomechanical
ground state allows for a significant relaxation of current experimental
constraints. Finally, the framework presented here can be used to create a rich
variety of optomechanical interactions and hence offers a novel, readily
available toolbox for fast optomechanical quantum control.Comment: 6 pages, 4 figure
Control of free induction decay with quantum state preparation in a weakly coupled multi-spin system
Nuclear magnetic resonance (NMR) has been a widely used tool in various
scientific fields and practical applications, with quantum control emerging as
a promising strategy for synergistic advancements. In this paper, we propose a
novel approach that combines NMR and quantum state preparation techniques to
control free induction decay (FID) signals in weakly coupled spin systems,
specifically Trifluoroiodoethylene . We investigate the FID signal of
the three-spin system and compare the differences between the FID signals in
the thermal state and the pseudo-pure state (PPS), where the latter is
generated using quantum state preparation techniques. Our approach aims to
demonstrate a single exponentially decaying FID in weakly coupled spins, in
which oscillatory FID signals are often observed. We validate our findings
through numerical simulations and experimental measurements, and justify the
validity of the theory. Our method opens a door to advancing spin system
research and extending the capabilities of NMR with current quantum
technologies in various scientific and practical fields.Comment: 6 pages, 4 figures. Comments are welcom
Quantifying spatial correlations of general quantum dynamics
Understanding the role of correlations in quantum systems is both a fundamental challenge as well as of high practical relevance for the control of multi-particle quantum systems. Whereas a lot of research has been devoted to study the various types of correlations that can be present in the states of quantum systems, in this work we introduce a general and rigorous method to quantify the amount of correlations in the dynamics of quantum systems. Using a resource-theoretical approach, we introduce a suitable quantifier and characterize the properties of correlated dynamics. Furthermore, we benchmark our method by applying it to the paradigmatic case of two atoms weakly coupled to the electromagnetic radiation field, and illustrate its potential use to detect and assess spatial noise correlations in quantum computing architectures
Directionality of acoustic phonon emission in weakly-confined semiconductor quantum dots
The direction of propagation of acoustic phonons emitted by electron relaxation in weakly confined, parabolic quantum dots charged with one or two electrons is studied theoretically. The emission angle strongly depends on the energy of the phonon, the dominant electron-phonon scattering mechanism (deformation potential or piezoelectric field), and the orbital symmetries of the initial and final electron states. This leads to different behaviors for phonons emitted by electrons relaxing between levels of single and coupled quantum dots. Our results establish the basis to control the direction of propagation of phonon modes triggered by transitions in quantum dot systems
Perfect quantum transport in arbitrary spin networks
Spin chains have been proposed as wires to transport information between
distributed registers in a quantum information processor. Unfortunately, the
challenges in manufacturing linear chains with engineered couplings has
hindered experimental implementations. Here we present strategies to achieve
perfect quantum information transport in arbitrary spin networks. Our proposal
is based on the weak coupling limit for pure state transport, where information
is transferred between two end-spins that are only weakly coupled to the rest
of the network. This regime allows disregarding the complex, internal dynamics
of the bulk network and relying on virtual transitions or on the coupling to a
single bulk eigenmode. We further introduce control methods capable of tuning
the transport process and achieve perfect fidelity with limited resources,
involving only manipulation of the end-qubits. These strategies could be thus
applied not only to engineered systems with relaxed fabrication precision, but
also to naturally occurring networks; specifically, we discuss the practical
implementation of quantum state transfer between two separated nitrogen vacancy
(NV) centers through a network of nitrogen substitutional impurities.Comment: 5+7 page
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