Everything in quantum, reported daily.

Researchers found that 405-nanometer light can temporarily reduce a quantum transmitter’s modulation variance, creating a calibration mismatch after the variance recovers. Their calculations show the mismatch can produce a falsely positive estimated key rate, not demonstrated secret-key generation.

A paper posted by Peixue Wu on October 29, 2026, proves that entangling codewords does not increase classical communication rates for phase-covariant channels in any dimension. It also establishes strong additivity for qubit-to-qubit channels and identifies questions that remain open for other channel classes.

A theoretical comparison finds that quantum-dot sources can outperform optimized weak coherent laser pulses in modeled MDI-QKD key rates, assuming perfect photon indistinguishability for that comparison. A separate analysis finds that imperfect indistinguishability sharply limits the modeled transmission range for both source types.

A neural decoder called Triage cuts reported decoding time for two high-rate quantum LDPC codes in simulations. The October 29 preprint reports speedups of 28× and 343×, but compares GPU batch processing with CPU baselines.

The Hong Kong Monetary Authority announced a post-quantum cryptography toolkit on November 2, while a July survey found that 32% of respondent banks had not begun transition work. The HKMA says the toolkit offers a framework and practical tools for banks’ transition; the survey’s first readiness score was 2.3 out of 10.

A paper describes a protocol for estimating the inner product of continuous-variable quantum states using local homodyne measurements at shared phase settings. Its sufficient bounds show improved accuracy scaling for Gaussian states, while simulations illustrate how estimation error varies with mode count and state family.

A new neural-network study compares fractional quantum Hall states across filling factors while including Landau-level mixing. Its highest reported overlaps belong to specific small-system comparisons; the candidate-state overlaps fall as mixing increases.

A Gross–Pitaevskii simulation finds that sound can leave a superfluid vortex with more Kelvin waves even as those waves lose energy. In a reflecting cavity, shifting the initial sound phase reverses the transfer, while the paper’s example rate for spontaneous splitting is extremely small.

Tanay Roy’s protocol distributes encoded shares of a quantum gate resource to candidate nodes before the recipient is selected. A later key release lets one chosen node complete the gate, subject to the protocol’s stated conditions.

A paper by Hengyue Li and colleagues describes a compiled approach to probabilistic imaginary-time evolution whose circuit size per attempt stays fixed as evolution time changes. Benchmarks show that its cost per accepted output depends on postselection and the comparison method, with grouped filtering outperforming it on the reported XYZ example.

Linjing Jiang and Pengfei Zhang of Fudan University introduce fermionic relative Rényi negativities to detect mixed-state entanglement in Sachdev–Ye–Kitaev models. Their large-N calculations reveal first-order transitions that simple observables miss, including two transitions in a weakly coupled model.

Researchers present an exactly solvable Ising model as a benchmark for quantum and classical optimization, finding recurring system-size fluctuations in quantum annealing and QAOA. Tests on a D-Wave processor and simulations also show how the model’s structure and hardware constraints shape the results.

A theoretical study finds that cavity-assisted stabilization of periodically driven quantum states depends not only on resonance but also on the strengths of competing transitions. The authors’ simulations show that those channels can cooperate, produce mixed steady states or prevent stabilization near Floquet-zone hybridization.

A photon-pairing method reconstructed intensity spectra over a 400-kilometer fiber link, with a signal-to-noise ratio above 23.5 decibels at very low receiving power. The study reports that second-order photon correlations avoid interferogram phase alignment and may support long-haul spectroscopy.

Surabhi Luthra and Alex Owens report a hardware demonstration of individually addressed logical Pauli measurements using QLDPC surgery on Quantinuum’s H2-2 trapped-ion processor. Their experiments use a seven-qubit gadget to measure one logical qubit in a two-qubit code block while preserving the spectator qubit.

A study describes dynamical quantum phase transitions that occur in open chains but not under periodic boundary conditions. The authors connect the effect to memory, complex momenta and a winding number, and propose a particle-counting test.