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[2026-09-05] · src Lu, Lin, Ketterle; Phys. Rev. Lett. (2026-09-02), arXiv:2510.21705 - and companion Lin, Lu, Ketterle, Phys. Rev. Lett. (2026-09-02), arXiv:2510.21692, doi:10.1103/rnx6-wqpf
Jones and Formaggio had proposed (arXiv:2412.11765) that a Bose-Einstein condensate of roughly a million electron-capture ⁸³Rb atoms could go superradiant on its own beta/EC decay, collectively shortening the isotope's 86.2-day half-life to about a minute. Two companion papers from Lu, Lin and Ketterle at MIT now rule that out on two independent grounds. First, emitting a ~MeV neutrino kicks the parent atom at a recoil speed equivalent to Mach 10 - roughly a million times the recoil from an optical photon - which throws the atom out of the coherent mode before any collective phase can build. Second, because neutrinos are fermions, the decay proceeds by destructive interference between the amplitudes for different atoms emitting (equivalently, Pauli blockade of the shared final state): solving the fermionic Dicke problem exactly, they show the total emission rate scales as N rather than the N2 superradiance needs, and that this bound - the jump-rate operator's largest eigenvalue is N times the single-atom rate
holds for the general Hamiltonian, not just this system. The companion
paper quantifies what a real experiment would see: a gain of only 1e-16 or smaller, not the near-complete conversion the original proposal implied, and extends the same conclusion to proposed gamma-ray lasers built on positronium-condensate annihilation.
This is the correction case the brief weights above new results: a specific, recently circulated proposal for an entirely new kind of coherent radiation source is now closed, and closed twice over, by an exact solution rather than a simulation or a rough estimate. The mechanism generalizes past this one scheme - any proposal to get single-fermion emission (neutrinos, but the argument does not care what the fermion is) to go superradiant runs into the same N-scaling bound - so it forecloses a whole category of future proposals rather than just this one BEC. It leaves standing the reason superradiance does work for photons: bosons can pile into one mode, and nothing here touches that.
[2026-09-05] · src Barrier, Peng, Xu, De Beule, Fal'ko, Watanabe, Taniguchi, Geim, Adam, Berdyugin; Phys. Rev. X (2026-09-04), arXiv:2412.01577
Whether magic-angle twisted bilayer graphene's superconductivity comes from phonons or from the electrons' own correlations has been open since the material's 2018 discovery, because the two mechanisms are hard to pull apart in the same sample. The Manchester-led group built two twisted bilayers, each tuned near the magic angle of about 1.1 degrees, separated by less than a nanometer yet electronically decoupled from each other, and used the second layer as a tunable screening gate: raising its carrier density screens Coulomb interactions in the first layer from a distance as short as 0.3 nm. Doing so suppresses both the superconductivity and the correlated- insulator state in the first layer completely, dropping the critical temperature by more than an order of magnitude. Conventional phonon-mediated pairing is not expected to weaken when Coulomb interactions are screened away - if anything it should hold up or strengthen slightly - so the observed collapse points at pairing driven by the electrons' own collective interactions instead.
This does not identify which electronic mechanism does the pairing, but it substantially narrows the field by taking the leading conventional alternative - phonons - off the table for this material, using a technique (a fully independent, in-situ tunable screening layer sitting a few atomic layers away) that is itself the more durable result: it is a way to dial Coulomb screening up and down in a real correlated material without touching the material being measured, which is a tool the next question about magic-angle graphene's pairing mechanism will also need.
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[2026-09-05] · src twelve-keys/src/exercises/bird_blues/exercise.py
Piano gets today's block alone: it carries the longest gap of the three, and alto went yesterday, so the two chops-dependent instruments don't land back to back either way. It's blues family's second lap, and rather than repeat a voicing or a rhythmic pattern this family has already drilled, today's exercise changes the demand entirely — a standard 12-bar major blues with bars 5-8 replaced by a chain of descending chromatic ii-Vs, each one implying a resolution that never arrives until the form lands back home at bar 9. This is the harmonic engine under Charlie Parker's densest bebop blues heads, and it rewards exactly the longer single block piano is due today rather than a quick pass. Key is A major, the most-avoided key on the rotation's ledger so far and the first time this ii-V vocabulary gets played outside a flat spelling.
5 minutes: play the full form once, very slowly (quarter = 50), speaking each chord symbol aloud as you play its root — Amaj7, G#m7b5, C#7, F#m7, B7, Em7, A7, D7, Dm7, G7, C#m7, F#7, Cm7, F7, Bm7, E7, Amaj7, F#7, Bm7, E7. The point isn't the hands yet; it's fixing that bars 6-8 are three ii-Vs that each slide a half step down into the next one rather than resolving, before asking the hands to navigate that at tempo.
Both hands, three keys' worth of tempo cycling isn't today's task — one key, A major, at quarter = 80, LH roots plus RH rootless voicings, four times through the full chorus. Success criterion: four consecutive choruses with no wrong turn at the bar 5-8 chain — every ii-V resolving a half step down into the next rather than by ear-memory jumping to where a normal blues would go, since that's the exact spot this form is built to trip up a player who knows the standard changes too well.
Play the head of "Blues for Alice" over the changes in A, once for notes and once shaping the phrase — the melody's own ii-V cells line up bar for bar with the chord pairs in bars 5-8, so hearing it against today's changes is what makes the harmony click rather than just parse.
Four clean choruses, or fewer if a chorus starts running the chain by guesswork instead of by ear — better to stop with the chain still landing correctly than to keep going until fatigue starts covering for uncertainty and the wrong habit gets the extra reps.
[2026-09-05] · src —
hearCharlie Parker — Blues For Alice · Tidal · Spotify
This is the tune the exercise is named for — the 1951 quintet side that put the descending chromatic ii-V chain into the standard repertoire. Listen to how the rhythm section tracks the chain in bars 5-8 without ever settling, then lands hard on the ii-V-I at bar 9; that release is the payoff the exercise is building hands toward, and it's audible here in a way no amount of slow practice reveals on its own.