I invented a new method to numerically compute quantum Cramer-Rao bounds for semiparametric problems. I was hoping that it'd give tighter bounds than an old method, but I can't help but laugh when I see the result.

Easy to keep gravity classical in a consistent quantum model—assume it *measures* the rest of universe to estimate the stress-energy tensor. Hard part is narrow down the measurement model; any backaction probably too weak to observe experimentally in our lifetime (fig from a 2014 talk)

arxiv.org/abs/2606.18025 On-sky demo of SPADE for binary-source hypothesis testing. They introduced a 1-cm aperture to reduce turbulence effect, but clear advantage observed and an encouraging step.

Tentative schedule of the 3rd Workshop on Quantum Metrology and Quantum-Inspired Superresolution is posted at blog.nus.edu.sg/mankei/qisr26/. Stellar list of invited speakers from theory to experiments in microscopy and astronomy. Still a few slots for contributed talks on 4 Aug.

The first startup based on quantum-inspired superresolution? "rather than treating the scene as a blurry picture on a sensor, Guha’s method treats the arriving light itself as the ‘thing’ to be measured via quantum mathematics." www.defenseone.com/technology/2...

Kudos to the experimentalists.

I'm deeply saddened that, when I google "BCH", it's now full of results about bitcoin cash and not Baker–Campbell–Hausdorff.

arxiv.org/abs/2605.10767 A new review paper on quantum-inspired superresolution. Thanks to my co-authors, who did all the heavy lifting.

blog.nus.edu.sg/mankei/qisr26/ The 3rd Workshop on Quantum Metrology and Quantum-Inspired Superresolution will be held tentatively on 4-7 Aug over Zoom. The present edition will broaden the scope to encompass the general field of Quantum Metrology. Please register and share.

quantumzeitgeist.com/quantum-nois... Surprised that this website chooses to feature this paper of ours. Anyway I'd like to clarify that the improvement of spectral photon counting over homodyne is not limited to 30%, as claimed there. Not sure where they got that number from. (1/2)

I wrote a blog post explaining my recent preprint. I wonder if it is now a waste of time to write these myself and AI may do a better job, but writing from scratch is still more enjoyable than proof-reading someone else's writing. blog.nus.edu.sg/mankei/2026/...

doi.org/10.1073/pnas... With all due respect to Sir John Pendry and I've only glanced at the paper, but this is just spontaneous parametric down conversion.

Dirac visited Singapore (then part of Malaysia; the now-NUS campus was part of U. of Malaya) on 2nd March 1955. Our physics department treats this photo as a treasure, but for him it's not the most pleasant trip. [excerpt from Dirac's biography by Farmelo]

More than two decades after Google introduced a game called Google Scholar that has taken the academia by storm, we finally have a winner.

arxiv.org/abs/2604.00413 Following the on-sky demo of superresolution by SPADE last year, there's now a demo using fluorophores by Warwick Bowen's group, achieving 40nm resolution. Still early days, but amazing experimental progress in both telescopy and microscopy.

To achieve the ultimate Holevo-Nagaoka bound for quantum multiparameter estimation, people have used a lot of fancy math to describe the measurement, but it offers little clue what the experiment would look like. This work proposes a more physical scheme. arxiv.org/abs/2603.17955

www.nature.com/articles/s41... I've been saying that entanglement-assisted stellar interferometry is unlikely to become practical in my lifetime, but that won't stop me from shamelessly claiming a little bit of credit every time others make heroic progress in this direction.

www.science.org/doi/10.1126/..., www.science.org/doi/10.1126/... STO has a Pockels coefficient >30x that of lithium niobate at cryogenic temperature. Sounds like a miracle.

Is QCMC dead as well?

"This theory is going to revolutionize the car industry... We assume that the road is a frictionless plane and we won't study what happens when there is friction. We also perform a demo using superfluids." This is what a lot of quantum metrology papers look like to me.

If only everyone were this honest [Stroock, Gaussian Measures]

Thank you for your invitation. I am intrigued by paper, but unfortunately it is against my principles---and indeed common sense---to provide free service for a for-profit company. It is nothing personal and it has nothing to do with the quality of the paper. I appreciate your understanding.

No-cloning theorem in a tweet: define the tensor-product map f(rho)=rho x rho, plug in rho(X) as a function of unknown X, and observe that your favorite info measure (mine is quantum Fisher info) has increased. Since a physical channel can't increase info, f cannot be physical.

For those looking forward to the next edition of the Workshop on Quantum-Inspired Superresolution, previously held in 2021 and 2023 by Zoom (blog.nus.edu.sg/mankei/2nd-w...), sorry that I have not been able to host one this year, but I hope to do it again next summer.

"On-sky Demonstration of Subdiffraction-limited Astronomical Measurement Using a Photonic Lantern." I haven't read the paper yet, but this sounds exciting. iopscience.iop.org/article/10.3... newsroom.ucla.edu/releases/tel...

When I review a bad paper but try to stay diplomatic

www.youtube.com/watch?v=MLh0... Stunning experiment of macroscopic quantum tunneling at room temperature! Widespread applications as well. (not trying to belittle the amazing Nobel achievement at all, just fun to point out)

SQUID and superconducting circuits are cool, but with all due respect the benefit of quantum computing to mankind is not even net positive yet.

The AI has spoken

x.com/arxiv/status... We have this curious phenomenon that the number of papers is exploding in recent years, but Nobel prizes are more often going to older people and older work. What if quantity is negatively correlated with quality?

Putting my thoughts together. Why networks beat "hero" sensors and what birds can teach us. quantum-noise.ghost.io/quantum-sens...

doi.org/10.1109/MSP.... Sad to learn that Van Trees passed away in 2023. His books are for me the perfect balance of principles and practice. For many years they were my secret recipe for my research—just pick a chapter and generalize to quantum.

Quantum Optics Lecture Notes v0.5: the main addition is Appendices K and L on the classical "semiparametric Cramer-Rao bound." (1/2) www.ece.nus.edu.sg/stfpage/tmk/... www.ece.nus.edu.sg/stfpage/tmk/...

A random memory: when I was an undergrad I went to an optics professor for advice; one question I asked was whether I could do research in theoretical optics. He looked at me with disgust and said, "there's nothing left to do in theoretical optics."

Quantum Optics Lecture Notes v0.4: A4 size: www.ece.nus.edu.sg/stfpage/tmk/... Letter size: www.ece.nus.edu.sg/stfpage/tmk/... Added some appendices on open quantum systems and classical statistics. Updated the appendix on probability.

www.physics.nus.edu.sg/faculty/lo-h... Singapore is the hottest place to do physics now!

I heard many talks recently about bounds, and people would just write down inequalities and pretend that they are cool. One famous example is the Cramer-Rao bound for biased estimators en.wikipedia.org/wiki/Cram%C3.... (1/n)

Forgive me if I prefer quantum thermodynamics in the 70's [Lindblad (1975)]

Stop treating the academia like a game; it ends up embarrassing everyone at the institution and not just the offenders. Reputation is hard to build and easy to destroy.

I heard people are interested in quantum sensing of time-varying signals again, so it's time for yet another round of shameless self-promotion: doi.org/10.1103/Phys... doi.org/10.1103/Phys... doi.org/10.1088/1367... doi.org/10.1103/Phys... doi.org/10.1103/Phys... (1/2)

Three recent experimental demonstrations of quantum-inspired superresolution spectroscopy: arxiv.org/abs/2506.20514 arxiv.org/abs/2506.20416 arxiv.org/abs/2506.22767

This will be handy for the new pope

Quantum Optics Lecture Notes v0.3.1 A4 size: www.ece.nus.edu.sg/stfpage/tmk/... Letter size: www.ece.nus.edu.sg/stfpage/tmk/... Updates after teaching PC4246 this semester. Clarifications of common issues, various improvements, and many bug fixes; see cover page for details.

Cool doi.org/10.1038/s413...

Two pandemic-era papers I neglected to promote earlier: (1) For quantum objects that arrive randomly and rarely, the Poisson state is an approximation that leads to neat formulas for many information quantities. doi.org/10.22331/q-2... (1/n)

Talagrand, Quantum Field Theory, Appendix I on Gupta–Bleuler

New application of quantum-inspired superresolution!

An underappreciated invention by Horace Yuen and Vincent Chan: the balanced homodyne detector [ opg.optica.org/ol/abstract.... ], which I covered today in a Quantum Optics class. Simple, elegant, works in practice.