text: 223,137,1389878084543860736,513464916,Carlos Sánchez Muñoz,"New paper on the arxiv today, in colaboration with G. Frascella and Frank Schlawin: ""Quantum metrology of two-photon absorption"" <LINK> What is this about? A short thread 👇🧵 The simultaneous absorption of 2 photons by a quantum system is very important tool for spectroscopy and microscopy. E.g., 2-photon microscopy in life sciences allows to get images with higher spatial resolution, deeper tissue penetration, and less damage to the sample! 💥💥 <LINK> Here we tackle the following question: if we use light to shine a system that absorbs photons in pairs, and analyse the resulting state of the light, how much can we learn about that system? Is our learning much better if we drive the system with *quantum* states of light? <LINK> To answer this, we computed the precision of estimation of two-photon absorption cross sections. In the limit of very small cross sections, we find that squeezed states have no fundamental limits to the precision you can achieve! 🤯 (In more technical words, the quantum Fisher information diverges). We can’t get too excited about this though, since the measurement one would need to do to achieve this precision is not realizable in practice, at least not easily 😅 Nevertheless, looking at the precision you achieve by standard homodyne measurements, we find that squeezed yield an inverse quadratic scaling of precision with photon number 1/N²! (some might call this super-Heisenberg scaling). 🚀🚀 <LINK> This is much better than coherent states, that scale as 1/N^(3/2) (which is not bad either).",https://arxiv.org/abs/2105.01561,"Two-photon absorption (TPA) is of fundamental importance in super-resolution imaging and spectroscopy. Its nonlinear character allows for the prospect of using quantum resources, such as entanglement, to improve measurement precision or to gain new information on, e.g., ultrafast molecular dynamics. Here, we establish the metrological properties of nonclassical squeezed light sources for precision measurements of TPA cross sections. We find that there is no fundamental limit for the precision achievable with squeezed states in the limit of very small cross sections. Considering the most relevant measurement strategies -- namely photon counting and quadrature measurements -- we determine the quantum advantage provided by squeezed states as compared to coherent states. We find that squeezed states outperform the precision achievable by coherent states when performing quadrature measurements, which provide improved scaling of the Fisher information with respect to the mean photon number $\sim n^4$. Due to the interplay of the incoherent nature and the nonlinearity of the TPA process, unusual scaling can also be obtained with coherent states, which feature a $\sim n^3$ scaling in both quadrature and photon-counting measurements. ",Quantum metrology of two-photon absorption,7,"['New paper on the arxiv today, in colaboration with G. Frascella and Frank Schlawin:\n\n""Quantum metrology of two-photon absorption""\n<LINK>\n\nWhat is this about? A short thread 👇🧵', 'The simultaneous absorption of 2 photons by a quantum system is very important tool for spectroscopy and microscopy. E.g., 2-photon microscopy in life sciences allows to get images with higher spatial resolution, deeper tissue penetration, and less damage to the sample! 💥💥 https://t.co/RnXXtp6OrN', 'Here we tackle the following question: if we use light to shine a system that absorbs photons in pairs, and analyse the resulting state of the light, how much can we learn about that system?  Is our learning much better if we drive the system with *quantum* states of light? https://t.co/fR8lNrjk0x', 'To answer this, we computed the precision of estimation of two-photon absorption cross sections. In the limit of very small cross sections, we find that squeezed states have no fundamental limits to the precision you can achieve! 🤯', '(In more technical words, the quantum Fisher information diverges). We can’t get too excited about this though, since the measurement one would need to do to achieve this precision is not realizable in practice, at least not easily 😅', 'Nevertheless, looking at the precision you achieve by standard homodyne measurements, we find that squeezed yield an inverse quadratic scaling of precision with photon number 1/N²! (some might call this super-Heisenberg scaling). 🚀🚀 https://t.co/zW3fVFGC5h', 'This is much better than coherent states, that scale as 1/N^(3/2) (which is not bad either).']",21,05,1534