In briefQuantum channel tomography: optimal query bounds near the boundary
SummaryThis paper studies quantum channel tomography, which learns the full description of an unknown quantum channel from black-box queries. It resolves the open query complexity in the near-boundary regime, where the dilation rate is slightly above 1, and gives tight bounds for both diamond norm and Choi trace norm error. The results show that the transition from Heisenberg to classical scaling occurs abruptly for diamond norm error but gradually for Choi trace norm error.
WhyThe authors close the near-boundary gap, reporting matching tight bounds for diamond and Choi trace norm tomography, revealing two distinct Heisenberg-to-classical transitions.
In briefFull-order mutual information from modular flow, without replicas
SummaryThe paper derives an all-orders long-distance expansion of vacuum mutual information between two disjoint balls in generic d-dimensional CFTs. It uses a radial sewing expansion, a modular response formula for relative entropy, and geometric modular flow, avoiding replica-number analytic continuation. In the two-dimensional Ising CFT, the first ten radial orders are computed and show good agreement with lattice data at finite separation.
In briefLee-Yang theorems for q-deformed oscillators and doubly-scaled SYK
SummaryThe paper proves that the vacuum partition function of the q-deformed oscillator has all its zeros on the imaginary axis (the Lee-Yang property) for every q in [-1,1), confirming conjectures by Okuyama from 2023. Using the link between q-deformed oscillators and the doubly-scaled SYK Hamiltonian, the authors show that the annealed SYK partition function has the same property in the thermodynamic limit. They conclude that the quenched SYK partition function has a zero-free strip of constant width with high probability.
WhyThe authors prove the q-deformed oscillator partition function has Lee-Yang zeros and extend this to doubly-scaled SYK.
In briefSpacetime Structure Emerging in a Learning Agent's Memory
SummaryThis paper studies whether the causal structure of spacetime can appear inside the memory of an agent performing a quantum information task. A model-based reinforcement-learning agent was trained to maximize quantum mutual information between localized probes and a quantum field in Minkowski spacetime, without being given the metric or causal structure. The agent's internal predictive model developed null structure in its planner, from which the Minkowski causal structure was reconstructed with high accuracy.
In briefSingle-pass stochastic cooling for electron microscopy: a theoretical study on reducing electron beam energy spread via strong electron-light coupling in nanophotonic structures
SummaryThe paper addresses the brightness limits of electron sources in electron microscopes by proposing single-pass stochastic cooling inside the microscope, using strong electron-light coupling in nanophotonic structures. The approach is laser-free, compatible with continuous-wave operation, and aims to improve longitudinal emittance without loss. The authors develop a fully quantum mechanical model valid in the strong coupling regime and derive an analytic asymptotic formula for the optimal cooled energy spread. Numerical simulations show that reduced energy spread corresponds to higher electron quantum state purity and smaller longitudinal phase space area.
In briefUnifying entanglement and nonclassicality through the Narcowich-Wigner spectrum
SummaryThis paper studies the relationship between quantum entanglement and nonclassicality, which is known to be linked through two-mode mixing. The authors extend this connection to arbitrary multimode Gaussian evolutions. They use the Narcowich-Wigner spectrum to quantify single-mode phase-space nonclassicality and derive sufficient conditions for a single-mode state to generate NPT entanglement after a multimode Gaussian unitary evolution. These conditions tighten and generalize existing criteria.
Massimo Frigerio, Zacharie Van Herstraeten, Hania Herbi et al.
In briefQuantum tomography in Schwartz space, a function-space framework for reconstructing quantum states
SummaryThis paper shows that standard quantum tomography results, usually proven in Hilbert spaces, can also be established within the theory of Schwartz spaces. It shows that quantum states are equivalently characterized by their Wigner function, the characteristic function of that Wigner function, and the probability distributions of linear combinations of position and momentum. The techniques are presented in a form more accessible to physicists.
Tobias Thrien, Gabriele Carcassi, David Carf\`i et al.
In briefFailure odds of quantum hashing when some seeds are bad
SummaryThis paper studies hashing used to extract secure randomness against quantum adversaries, as in quantum random number generation and key distribution. It bounds the probability of failure in practical settings where a seed may be reused across rounds and may not be ideal. The authors show that randomness extraction against quantum side information yields near-uniform random numbers except with a bounded failure probability. They extend this guarantee to blockwise hashing over multiple rounds and relax the almost two-universality assumption.
Asker Friis Bach, Isabel Moreno Babuglia, Jonatan Bohr Brask
In briefExceptional points and optimized encoding in qubit stabilizer codes
SummaryThis paper studies stabilizer codes under continuous blind stabilizer measurements, casting error correction as a Liouvillian spectral problem where Hamiltonian terms compete with dissipative error channels. The authors show this competition generically produces Liouvillian exceptional points, whose occurrence at weak error rates is limited by the code distance, and that these points accelerate the decay of encoded coherences. They then optimize the logical qubit encoding using Lindblad operator eigenmodes and apply it to the [[5,1,3]] code, where it outperforms naive encoding near the exceptional point.
Yves Rottstaedt, Andrei I. Pavlovm Alexander Shnirman, Yuval Gefen et al.
In briefSurface charges and quantum reflection of hydrogen-isotope beams at grazing incidence
SummaryThis paper theoretically studies how trapped electric charges on dielectric mirrors affect the specular reflection and diffuse scattering of hydrogen, deuterium, and tritium atoms at grazing incidence on SiO2/Si and MgF2 surfaces. The authors show that the charge distribution determines the polarization potential seen by the atoms, which changes the threshold behavior of reflection. At a surface charge density of 10^12 cm^-2, absorption increases by up to 26% for SiO2/Si and by two to three times for MgF2.
In briefLossless propagation bounds for long-range fermionic interactions
SummaryThis paper proves propagation estimates for extensive fermionic many-body interactions with polynomial time growth, no loss of spatial decay, and an optimal threshold for the polynomial spatial exponent. The authors construct local representatives of evolved interactions on metric spaces with polynomial volume growth. The threshold a > d_vol is shown to be optimal in general. The results yield dynamical estimates for perturbation theory with extensive perturbations.
WhyThe authors give lossless propagation bounds for fermionic interactions with polynomial growth and prove the threshold a>d_vol is optimal, with applications to gap stability and adiabatic theory.
In briefFaster thermalization of 1D noncommuting Hamiltonians using system-bath interactions with linearly many ancillas
SummaryThe paper proves rapid convergence of a system-bath algorithm that prepares Gibbs states of one-dimensional noncommuting Hamiltonians at any fixed positive temperature. For a chain of n qudits, it reaches trace-norm error ε in expected total evolution time Õ(n/ε). This improves the previously proved Õ(n^6/ε) bound for single-ancilla samplers, up to logarithmic factors.
WhyThe authors improve the bound for single-ancilla system-bath Gibbs samplers from O(n^6) to linear system-size dependence, with theoretical analysis.
In briefQuartet state of the neutral nitrogen-vacancy center in diamond and optimized near-infrared spin readout
SummaryAfter photoionization, the nitrogen-vacancy center in diamond leaves a neutral defect in a metastable quartet state of unknown energy. Using tunable femtosecond two-photon optically detected magnetic resonance, the authors find the spin-contrast onset at 1.23 ± 0.02 eV and place the quartet 0.54 ± 0.04 eV above the neutral ground state. This threshold makes 1060–1075 nm the optimal excitation for spin readout, giving 26–37% higher shot-noise-limited sensitivity than 1030–1040 nm.
Nikoletta Jegenyes, P\'al Ma\'ak, Vladimir Verkhovlyuk et al.
In briefAgentic Pipeline Verifying Topological Code Mapping to Quantum Hardware via Lean
SummaryThis paper presents an AI-agent-assisted workflow that uses the Lean proof assistant to check whether an effective device Hamiltonian preserves the intended low-energy subspace of a target many-body Hamiltonian. It applies the method to topological quantum error correction, building the ideal Hamiltonian from qubits and parity checks and comparing three bounds on unwanted energy shifts. In an eight-qubit toric-code array on a superconducting device, an AI agent finds device parameters within a leakage budget, and Lean verifies four isolated low-energy states close to the ideal code space.
In briefLearning stabilizer structure under global depolarizing noise with polynomial copies
SummaryThe paper studies how to learn the stabilizer structure of an unknown pure n-qubit state observed through global depolarizing noise of unknown strength, using destructive two-copy Bell measurements. It gives a learner that uses polynomially many copies and 2^t times polynomial classical time, for any fixed noise bound below one. This answers an open question from Tang and Steckmann by exceeding their earlier noise threshold of about 0.16.
WhyThe authors extend the noise threshold from about 0.16 to any fixed global depolarizing bound below one, with polynomial copies and 2^t time.
In briefControlling phase between cores of multi-core fiber inline using a commercial polarization controller
SummaryPhase control between cores is needed for interferometry in multi-core fiber, but no compact inline device exists for this. The authors show that a commercial, low-loss inline polarization controller can work as an inline inter-core phase shifter. In two-core interferometry on a four-core patchcord, one device gave a reversible phase of 0.95 ± 0.02 rad, with a lower bound of 0.38 rad independent of operating point.
In briefQyantram: A Transparent and Verifiable Quantum Computing Platform
SummaryThis paper presents Qyantram, an open quantum computing platform with four subsystems: a staged compilation pipeline, a router, an error identification engine, and a machine-learning engine. Its verification exploits inactive qubits remaining in the |0> state, reducing complexity from 2^N to 2^k and achieving about 10,000x speed-ups on 127- and 156-qubit layouts. The router publishes rejected SWAP candidates and their scores, but introduces about 1.27x more SWAP gates than Qiskit's SABRE.
Sharyu Kekane, Sadique Khatib, Abhushan Bokade et al.
