7 research outputs found
Trade-offs between precision and fluctuations in charging finite-dimensional quantum systems
Within quantum thermodynamics, many tasks are modelled by processes that
require work sources represented by out-of-equilibrium quantum systems, often
dubbed quantum batteries, in which work can be deposited or from which work can
be extracted. Here we consider quantum batteries modelled as finite-dimensional
quantum systems initially in thermal equilibrium that are charged via cyclic
Hamiltonian processes. We present optimal or near-optimal protocols for
identical two-level systems and individual -level systems with equally
spaced energy gaps in terms of the charging precision and work fluctuations
during the charging process. We analyze the trade-off between these figures of
merit as well as the performance of local and global operations.Comment: 14+2 pages, 7 figure
Quantum Fokker-Planck Master Equation for Continuous Feedback Control
Measurement and feedback control are essential features of quantum science,
with applications ranging from quantum technology protocols to
information-to-work conversion in quantum thermodynamics. Theoretical
descriptions of feedback control are typically given in terms of stochastic
equations requiring numerical solutions, or are limited to linear feedback
protocols. Here we present a formalism for continuous quantum measurement and
feedback, both linear and nonlinear. Our main result is a quantum Fokker-Planck
master equation describing the joint dynamics of a quantum system and a
detector with finite bandwidth. For fast measurements, we derive a Markovian
master equation for the system alone, amenable to analytical treatment. We
illustrate our formalism by investigating two basic information engines, one
quantum and one classical
Landauer vs. Nernst: What is the True Cost of Cooling a Quantum System?
Thermodynamics connects our knowledge of the world to our capability to
manipulate and thus to control it. This crucial role of control is exemplified
by the third law of thermodynamics, Nernst's unattainability principle, stating
that infinite resources are required to cool a system to absolute zero
temperature. But what are these resources and how should they be utilised? And
how does this relate to Landauer's principle that famously connects information
and thermodynamics? We answer these questions by providing a framework for
identifying the resources that enable the creation of pure quantum states. We
show that perfect cooling is possible with Landauer energy cost given infinite
time or control complexity. However, such optimal protocols require complex
unitaries generated by an external work source. Restricting to unitaries that
can be run solely via a heat engine, we derive a novel Carnot-Landauer limit,
along with protocols for its saturation. This generalises Landauer's principle
to a fully thermodynamic setting, leading to a unification with the third law
and emphasising the importance of control in quantum thermodynamics.Comment: 15 pages, 4 figures, 46 pages of appendice
Landauer Versus Nernst: What is the True Cost of Cooling a Quantum System?
Thermodynamics connects our knowledge of the world to our capability to manipulate and thus to control it. This crucial role of control is exemplified by the third law of thermodynamics, Nernst’s unattainability principle, which states that infinite resources are required to cool a system to absolute zero temperature. But what are these resources and how should they be utilized? And how does this relate to Landauer’s principle that famously connects information and thermodynamics? We answer these questions by providing a framework for identifying the resources that enable the creation of pure quantum states. We show that perfect cooling is possible with Landauer energy cost given infinite time or control complexity. However, such optimal protocols require complex unitaries generated by an external work source. Restricting to unitaries that can be run solely via a heat engine, we derive a novel Carnot-Landauer limit, along with protocols for its saturation. This generalizes Landauer’s principle to a fully thermodynamic setting, leading to a unification with the third law and emphasizes the importance of control in quantum thermodynamics