5 research outputs found
Energy measurements remain thermometrically optimal beyond weak coupling
We develop a general perturbative theory of finite-coupling quantum thermometry up to second order in probe-sample interaction. By assumption, the probe and sample are in thermal equilibrium, so the probe is described by the mean-force Gibbs state. We prove that the ultimate thermometric precision can be achieved – to second order in the coupling – solely by means of local energy measurements on the probe. Hence, seeking to extract temperature information from coherences or devising adaptive schemes confers no practical advantage in this regime. Additionally, we provide a closed-form expression for the quantum Fisher information, which captures the probe's sensitivity to temperature variations. Finally, we benchmark and illustrate the ease of use of our formulas with two simple examples. Our formalism makes no assumptions about separation of dynamical timescales or the nature of either the probe or the sample. Therefore, by providing analytical insight into both the thermal sensitivity and the optimal measurement for achieving it, our results pave the way for quantum thermometry in setups where finite-coupling effects cannot be ignored
Sovereign Bond Market Reactions to Fiscal Rules and No-Bailout Clauses – The Swiss Experience
Bending the rules of low-temperature thermometry with periodic driving
There exist severe limitations on the accuracy of low-temperature
thermometry, which poses a major challenge for future quantum-technological
applications. Low-temperature sensitivity might be manipulated by tailoring the
interactions between probe and sample. Unfortunately, the tunability of these
interactions is usually very restricted. Here, we focus on a more practical
solution to boost thermometric precision -- driving the probe. Specifically, we
solve for the limit cycle of a periodically modulated linear probe in an
equilibrium sample. We treat the probe-sample interactions \textit{exactly} and
hence, our results are valid for arbitrarily low temperatures and any
spectral density. We find that weak near-resonant modulation strongly enhances
the signal-to-noise ratio of low-temperature measurements, while causing
minimal back action on the sample. Furthermore, we show that near-resonant
driving changes the power law that governs thermal sensitivity over a broad
range of temperatures, thus `bending' the fundamental precision limits and
enabling more sensitive low-temperature thermometry. We then focus on a
concrete example -- impurity thermometry in an atomic condensate. We
demonstrate that periodic driving allows for a sensitivity improvement of
several orders of magnitude in sub-nanokelvin temperature estimates drawn from
the density profile of the impurity atoms. We thus provide a feasible upgrade
that can be easily integrated into low- thermometry experiments.Comment: 9 + 6 pages, 3 figures, accepted versio
Optimal cold atom thermometry using adaptive Bayesian strategies
Precise temperature measurements on systems of few ultracold atoms is of
paramount importance in quantum technology, but can be very resource-intensive.
Here, we put forward an adaptive Bayesian framework that substantially boosts
the performance of cold atom temperature estimation. Specifically, we process
data from release--recapture thermometry experiments on few potassium atoms
cooled down to the microkelvin range in an optical tweezer. We demonstrate that
adaptively choosing the release--recapture times to maximise information gain
does substantially reduce the number of measurements needed for the estimate to
converge to a final reading. Unlike conventional methods, our proposal
systematically avoids capturing and processing uninformative measurements.
Furthermore, we are able to produce much more reliable estimates, especially
when the measured data are scarce and noisy. Likewise, the resulting estimates
converge faster to the real temperature in the asymptotic limit. Our method can
be adapted to enhance the precision and resource-efficiency of many other
techniques running on different experimental setups, thus opening new avenues
in quantum thermometry.Comment: 9 + 3 pages, 7 figures, references update