Hi all,
today Ralph will tell us what he's been up to lately. See below for more details. Note that the theory colloquium follows immediately afterward and will likely be of interest to many of you. Naftali Tishby from the Hebrew University of Jerusalem will give a talk "The Information Theory of Deep Neural Networks: The statistical physics perspective". See http://www.theorycolloquium.phys.ethz.ch/ for more info.
Best,
-joe
Title: Unifying paradigms of quantum refrigeration: how resource-control determines fundamental limits.
Description: I'll speak about recent work (https://arxiv.org/abs/1710.11624, although there are significant updates that I will talk about). We wanted to compare different descriptions of cooling quantum systems, ranging from "incoherent" control, where one has thermal baths and energy preserving operations, to "coherent" control, where one has access to a perfect battery, and arbitrary unitaries.
Starting from the single shot case for the smallest possible thermal machine that cools a qubit, we determine the minimum achievable temperatures, and the work cost vs temperature. Interestingly, although coherent control always gets cooler, incoherent protocols appears to be more efficient for small temperature changes. For repeated operations, we recover autonomous thermal machines for the incoherent case, and algorithmic cooling for the coherent case.
In addition, for more general machines, we demonstrate a simple equivalence between the coherent and incoherent case, and from this prove that 1) every incoherent machine can approach the temperature and work cost of a coherent one arbitrarily close, and thus 2) For unbounded machine size, both types of control saturate the second law of thermodynamics.
Finally, we demonstrate that the bounds on cooling qubits determine most interesting properties for higher-dimensional systems as well.