TY  - JOUR
A1  - Scali, Stefano
A1  - Anders, Janet
A1  - Correa, Luis A.
T1  - Local master equations bypass the secular approximation
JF  - Quantum : the open journal for quantum science
N2  - Master equations are a vital tool to model heat flow through nanoscale thermodynamic systems. Most practical devices are made up of interacting subsystems and are often modelled using either local master equations (LMEs) or global master equations (GMEs). While the limiting cases in which either the LME or the GME breaks down are well understood, there exists a 'grey area' in which both equations capture steady-state heat currents reliably but predict very different transient heat flows. In such cases, which one should we trust? Here we show that, when it comes to dynamics, the local approach can be more reliable than the global one for weakly interacting open quantum systems. This is due to the fact that the secular approximation, which underpins the GME, can destroy key dynamical features. To illustrate this, we consider a minimal transport setup and show that its LME displays exceptional points (EPs). These singularities have been observed in a superconducting-circuit realisation of the model [1]. However, in stark contrast to experimental evidence, no EPs appear within the global approach. We then show that the EPs are a feature built into the Redfield equation, which is more accurate than the LME and the GME. Finally, we show that the local approach emerges as the weak-interaction limit of the Redfield equation, and that it entirely avoids the secular approximation.
Y1  - 2021
U6  - https://doi.org/10.22331/q-2021-05-01-451
SN  - 2521-327X
VL  - 5
PB  - Verein zur Förderung des Open Access Publizierens in den Quantenwissenschaften
CY  - Wien
ER  - 
TY  - JOUR
A1  - Rubio, Jesús
A1  - Anders, Janet
A1  - Correa, Luis A.
T1  - Global quantum thermometry
JF  - Physical review letters / publ. by the American Physical Society
N2  - A paradigm shift in quantum thermometry is proposed. To date, thermometry has relied on local estimation, which is useful to reduce statistical fluctuations once the temperature is very well known. In order to estimate temperatures in cases where few measurement data or no substantial prior knowledge are available, we build instead a method for global quantum thermometry. Based on scaling arguments, a mean logarithmic error is shown here to be the correct figure of merit for thermometry. Its full minimization provides an operational and optimal rule to postprocess measurements into a temperature reading, and it establishes a global precision limit. We apply these results to the simulated outcomes of measurements on a spin gas, finding that the local approach can lead to biased temperature estimates in cases where the global estimator converges to the true temperature. The global framework thus enables a reliable approach to data analysis in thermometry experiments.
Y1  - 2021
U6  - https://doi.org/10.1103/PhysRevLett.127.190402
SN  - 0031-9007
SN  - 1079-7114
VL  - 127
IS  - 19
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Eerqing, Narima
A1  - Subramanian, Sivaraman
A1  - Rubio Jimenez, Jesus
A1  - Lutz, Tobias
A1  - Wu, Hsin-Yu
A1  - Anders, Janet
A1  - Soeller, Christian
A1  - Vollmer, Frank
T1  - Comparing transient oligonucleotide hybridization kinetics using DNA-PAINT and optoplasmonic single-molecule sensing on gold nanorods
JF  - ACS photonics / American Chemical Society
N2  - We report a comparison of two photonic techniques for single-molecule sensing: fluorescence nanoscopy and optoplasmonic sensing. As the test system, oligonucleotides with and without fluorescent labels are transiently hybridized to complementary "docking" strands attached to gold nanorods. Comparing the measured single-molecule kinetics helps to examine the influence of the fluorescent labels as well as factors arising from different sensing geometries. Our results demonstrate that DNA dissociation is not significantly altered by the fluorescent labels and that DNA association is affected by geometric factors in the two techniques. These findings open the door to exploiting plasmonic sensing and fluorescence nanoscopy in a complementary fashion, which will aid in building more powerful sensors and uncovering the intricate effects that influence the behavior of single molecules.
KW  - single-molecule
KW  - plasmonics
KW  - whispering gallery modes
KW  - optoplasmonic
KW  - DNA-PAINT
KW  - fluorescence
KW  - localization microscopy
Y1  - 2021
U6  - https://doi.org/10.1021/acsphotonics.1c01179
SN  - 2330-4022
VL  - 8
IS  - 10
SP  - 2882
EP  - 2888
PB  - American Chemical Society
CY  - Washington
ER  -