In briefHigh-sensitivity 10 MHz radio field sensing using Rydberg atoms
SummaryThis paper proposes and demonstrates a quantum sensing scheme for radio frequency electric fields in the 3-30 MHz shortwave band, using cesium Rydberg states and electromagnetically induced transparency. It uses an all-infrared optical setup with 852 nm, 1470 nm, and 780 nm lasers to prepare the 49P3/2 Rydberg state in a room-temperature cesium vapor cell. The state is then probed non-destructively through ladder-type four-level EIT spectroscopy.
In briefRobust universal geometric quantum gates using shortened composite pulses on superconducting circuits
SummaryThe paper proposes a scheme for universal robust nonadiabatic geometric quantum gates built from shortened composite pulses. It uses simple pulse control and extra evolution parameters to reduce sensitivity to universal systematic errors. Numerical simulations show its gate set is more error-resilient than conventional single-loop geometric gates. The robustness advantage is also verified on realistic superconducting quantum circuits.
In briefSolution size growth in iterative refinement for linear optimization
SummaryIterative refinement boosts solution precision by solving a sequence of related problems. This paper studies how the solution sizes produced by this process grow when applied to linear programs. It exhibits a class of problems where solution size can grow exponentially with the number of refinement iterations. The authors also show that avoiding this requires a black-box solver to be "lucky", and that simplex with Bland's rule exhibits the exponential growth.
In briefIndustrial-scale growth of ultra-pure silicon-28 layers for more reliable electron spin qubits
SummaryThis paper reports growing high-purity silicon-28 epitaxial layers on float-zone silicon using an industrial reduced-pressure chemical vapor deposition system. Mass spectrometry shows 99.997% isotopic purity with 29Si below 30 ppm. Vacuum annealing between 850 and 1150 C identified a thermal window below 950 C where the thin layer structure remains intact. Measurements at 1.5 K and a double quantum dot device report a Hahn-echo coherence time of 28.8 microseconds and single-qubit gate fidelities up to 99.9%.
In briefGenerating High-Dimensional Maximally Entangled OAM States via Joint Pump and Modal-Space Engineering
SummaryThis paper studies high-dimensional entanglement of photon pairs produced by spontaneous parametric down-conversion in orbital angular momentum (OAM) modes. Prior pump-beam engineering was limited to low-dimensional subspaces, so the authors examine how the spatial pump structure and the chosen OAM subspace interact. They show how to generate maximally entangled states in d×d subspaces for arbitrary d and determine the pump profile required for a target state.
Richard Bernecker, Baghdasar Baghdasaryan, Fabian Steinlechner et al.
In briefInformation-control limits for resetting a monitored qubit while keeping its measurement record indistinguishable
SummaryThe paper studies how much control is needed to reset a continuously monitored qubit, prepared in its excited state, to its ground state while keeping its measurement record statistically close to that of an undriven ground-state qubit. Distinguishability is measured by the Kullback–Leibler divergence of the record law, and control cost by the integrated squared Rabi frequency. The authors prove a lower bound on their product, give an exact constant for the high-effort regime, and show that a two-phase feedback policy attains it.</summary>
In briefWhat an observer reads from a holographic screen
SummaryThe paper asks what an observer can read from a holographic screen made of an array of qubits. Within the generalized holographic principle, the interaction between two separable systems is written as a weighted sum of commuting observables, and the authors characterize when a readout carries a spectral profile depending on the weights. They prove that such a profile appears at every weighting exactly when the distinct nonzero traces of the qubits are linearly independent over the field with two elements.
In briefErgotropy as a measure of distance from equilibrium
SummaryThe paper shows that the ergotropy (available energy) of a thermally isolated system equals the 1-Wasserstein distance between two energy probability density functions. These are the energy profile of the system's state and the energy profile of its associated passive state. The result is proven for both classical and quantum systems and illustrated with examples. It formalises the idea that ergotropy quantifies distance from equilibrium.
In briefUnbounded benefit of adaptive quantum measurements in entanglement-assisted communication
SummaryThis paper studies how shared entanglement can cut the classical communication needed for distributed computation. It shows tasks that adaptive protocols solve with just three messages, while non-adaptive quantum receivers need unboundedly many. The authors also prove two complementary limits relating adaptive and non-adaptive protocols.
WhyThe authors prove the advantage of adaptivity in entanglement-assisted communication is unbounded and give two complementary simulation limits.
In briefHardware-efficient continuous-variable quantum computing using non-Gaussian gates in a Floquet-engineered BEC cavity
SummaryThis paper proposes a continuous-variable quantum computing scheme that uses a single-cavity 87Rb Bose-Einstein condensate as a macroscopic bosonic mode. It describes deterministic, post-selection-free non-Gaussian gates built from Floquet-engineered two-axis twisting, which generate Wigner negativity in the over-squeezed regime. A numerical benchmark with N=50 atoms reports a minimum Wigner function value of about -0.214.
In briefCoherent conversion of an interacting polariton condensate into a photonic Bose-Einstein condensate
SummaryThis paper studies a multimode-cavity scheme that coherently converts an interacting dark-state-polariton condensate into a confined photonic Bose-Einstein condensate when the atom-cavity coupling is removed. It shows that polariton mass, matter fraction, and particle number control the condensate occupation during preparation, and that changing mass alters the response to repulsion through orbital overlap even with a fixed single-particle spectrum. After decoupling from matter, the photons evolve under the free cavity Hamiltonian while retaining correlations acquired in the interacting gas.
G. D. de Moraes Neto, M. A. de Ponte, N. G. de Almeida et al.
In briefQuantum entanglement as a resource for building lasting order
SummaryThis paper studies whether local quantum entanglement in a driven-dissipative bosonic lattice can create large-scale patterns that persist after the entanglement disappears. The authors derive finite-time bounds on pattern intensity for separable evolutions and show that quantum dynamics exceeds these bounds during formation and noisy stabilization. They also add an environment that suppresses local coherence and activates classical transport, so the patterns remain after local entanglement is lost.
In briefAdaptive quantum sensing scheme for detecting gravitational waves
SummaryThis paper proposes a feedback-controlled quantum metrology scheme for detecting weak gravitational waves through their direct energy exchange with light. The method adaptively adjusts the SU(2) control direction based on current estimates of the wave's frequency and phase, so frequency shifts add up across intervals and are read out as an optical phase difference. It extends to elliptically polarized waves by using two sensing channels at 45 degrees to measure the plus and cross components separately. In the ideal coherent regime, the quantum Fisher information scales as T_int²T_ph², and for fixed photon number the ideal sensitivity shows Heisenberg-like 1/n scaling.
In briefA criterion for judging spectrally pure photon-pair generation in coupled waveguides without periodic poling
SummaryThis paper proposes a reachability criterion for determining whether coupled waveguides can produce spectrally pure photon pairs by spontaneous parametric down-conversion without periodic poling. The criterion uses a nonlinear main guide and a linear auxiliary guide, linking phase closure to material and mode selection. A full-vector AlN/TiO$_2$ example reports a calculated unfiltered Schmidt purity of 0.789 over 5 mm.
In briefLarge-scale quantum molecular dynamics using sampling-based quantum diagonalization
SummaryThis paper introduces SqDRIFT-AIMD, which combines randomized sample-based Krylov quantum diagonalization with analytical nuclear gradients for ab initio molecular dynamics. For a 40-qubit active space, it reports more accurate ground-state energies than CCSD-driven simulations. The authors apply the method to proton transfer dynamics in the Zundel cation using IBM Heron r3 quantum processors.
Ankit Khandelwal, Nirmal M R, Aaryav Mishra et al.
In briefTensor-network proof of uniform gaps in spin chains and ladders
SummaryThe paper verifies and formalizes a computer-assisted proof by OpenAI of a uniform gap in the periodic spin-1 Heisenberg chain, using tensor-network diagrams and Lean 4. Reading the partition-function network along space and imaginary time shows how finite-ring bounds propagate to longer even rings. This sharpens the spin-1 bound by a factor of 19 to Δ_L > 0.0729 for all even L ≥ 36. The authors identify reflection positivity as the general condition behind the proof and certify uniform gaps in seven additional spin chains and ladders.
In briefExact sampling for photon inputs beyond single photons and linear optics
SummaryThe paper extends an exact boson sampling algorithm for single photons to other input states and to adaptive and non-linear circuits. It builds four exact samplers, covering superpositions of vacuum and one photon, photonic matrix-product states, adaptive linear optics, and a single-mode non-linear phase. The samplers match strong simulation on small instances, and cost models suggest near single-photon cost in some cases.
Jean Senellart, Stephen Wein, Pierre-Emmanuel Emeriau
In briefA Witness for Quantum Correlations via Nonlinear Spectroscopy
SummaryThis paper shows that signals from existing spectroscopic techniques can be used to witness entanglement in molecular systems. The approach uses a spectroscopic map from admissible quantum states to a finite-dimensional space of signal coefficients, defining joint expectation value sets compatible with all admissible states and their separable subset. The authors illustrate the construction with rotational invariants and the spectral structure of optical signals, and add fluorescence dynamics and photon coincidences as a complementary example.
In briefSingle-photon sources at telecom C-band made by precisely placing quantum dots in circular grating cavities
SummaryThis work integrates MOVPE-grown C-band InAs/InP quantum dots deterministically into circular Bragg grating resonators to create single-photon sources for fiber-based quantum networks. The emitters show a radiative lifetime of (1400 ± 50) ps and a spectral linewidth of (41.0 ± 4.0) μeV. Under non-resonant excitation, the post-selected single-photon purity is (0.95 ± 0.02), and the raw two-photon interference visibility is (35 ± 2)%, rising to (70 ± 18)% with temporal post-selection.
Monica Pengerla, Yury Berdnikov, Alexander Kosarev et al.
In briefImaging spin entanglement with a scanning tunneling microscope
SummaryThis paper examines how spin inelastic electron tunneling spectroscopy (IETS) can quantify and image quantum entanglement in spin-1/2 systems assembled on surfaces. It links spectral moments of the tunneling conductance to one-tangle, nearest-neighbor concurrence, internal energy and magnetic specific heat. The approach is applied to experimental IETS data from nanographene spin chains, showing good agreement with theory.
J. C. G. Henriques, B. Vi\~na-Baus\'a, I. Brihuega et al.
In briefQubit encoding of the mass observable in quantized Schwarzschild interior
SummaryThis paper presents a quantum-computing framework for the mass observable of the Wheeler–DeWitt quantized Schwarzschild black-hole interior. The authors build finite-dimensional representations of the mass operator in the physical sector of correlated two-mode oscillator states and map them to qubit operators via Pauli decomposition. They analytically establish how the number of nonvanishing Pauli terms and independent measurement settings scale with truncation size. A two-qubit variational quantum eigensolver for the smallest nontrivial truncation agrees well with the exact spectrum.
In briefBias-free superconducting microwave nonreciprocity from a passive nonlinear resonator
SummaryThis paper demonstrates a bias-free microwave nonreciprocal device on a superconducting chip, made from a single nonlinear superconducting resonator without Josephson junctions. Unequal coupling to the two feeding ports makes the resonance shift depending on direction, and its sharp Fano lineshape turns this asymmetry into a large transmission contrast. The niobium nitride (NbN) device reaches a directional contrast of 53.0 dB at 4.6 dB insertion loss, exceeding 20 dB over 9.7 MHz.
Brendan MacKay, Abdul Mohamed, Andrea Al\`u et al.
In briefOne Measurement Triggering Multiple Fronts in Kitaev and Cluster Chains
SummaryThe paper studies how a projective measurement on one site of a quantum chain's ground state changes distant quadratic observables. The authors solve exactly for the Kitaev chain, the cluster chain in a transverse field, and the Kitaev chain with power-law couplings. They find that far-away observables respond through fronts whose position and width depend only on the quasiparticle dispersion, while strength depends on the measured and observed operators.
In briefPeriodic readout causes a first-order generalization transition in a quantum perceptron
SummaryThis paper studies a quantum perceptron whose readout is a square-wave periodic function of weighted inputs, analyzing its typical generalization in the thermodynamic limit with a teacher-student replica-symmetric theory. Above a critical oscillation frequency, increasing the training load triggers a first-order transition from weakly to strongly teacher-aligned phases, producing a discontinuous jump in generalization. At fixed load, raising the frequency drives the equilibrium generalization error to chance level even when all training examples are classified perfectly.
Fabio Benatti, Masoud Gharahi, Giovanni Gramegna et al.
In briefSpin asymmetries in thermal neutron capture by polarized helium-3 with twisted neutron beams
SummaryThis paper theoretically analyzes a nuclear reaction induced by twisted neutrons carrying extra orbital angular momentum along their direction of travel. It derives angular momentum selection rules for thermal neutron capture on spin-polarized helium-3 nuclei. The authors find that the new spin effects from orbital angular momentum are confined to a region about the size of the de Broglie wavelength around the beam's phase singularity. Spin asymmetries are predicted across a range of experimental conditions.
In briefExtending MEAT to source and detector correlations
SummaryThis paper proves variants of the marginal-constrained entropy accumulation theorem (MEAT) for finite-size security analysis of quantum key distribution with correlated sources and detectors. The source results allow a round's state to depend on the current setting and a finite number of earlier choices, while the detector results require memory effects to persist for finite rounds after a click with all detectors off. Combined, the approach handles both kinds of imperfections jointly and yields key rates on qubit BB84 that remain competitive.
In briefWhat a Quantum Layer Adds: An Ablation Study of Hybrid Models for Stock Cross-Sectional Ranking
SummaryThis paper studies a hybrid quantum-classical temporal convolutional network that ranks 2000 Tokyo Stock Exchange equities daily. It compares six conditions, including a trained, frozen, or absent quantum circuit and a parameter-matched classical surrogate, using walk-forward folds, bootstrap intervals, and deflated Sharpe ratios. The trained and frozen circuits are statistically equivalent, and no condition's deflated Sharpe ratio is distinguishable from zero. The authors report the same pattern on 2000 US equities.
In briefBP-based quantum LDPC decoding under long-range correlated noise and prior mismatch
SummaryThe paper tests two BP-based quantum LDPC decoders, Relay-BP and beam search, which were designed for independent noise, on spatially correlated noise with unchanged single-error probabilities. Correlated errors are generated from a hidden Gaussian Markov random field that controls correlation strength and range. The authors find that correlation can change logical error rates by orders of magnitude and alter how the decoders rank against BP-OSD. They also report that correlation mainly raises the chance of known trapping configurations, and that supplying marginals conditioned on the hidden field recovers most lost performance, pointing to prior mismatch as a major cause.
In briefTrade-off between trainability and classical simulability in IQP-based RL policies
SummaryThis paper studies reinforcement learning policies built from parameterized IQP quantum circuits, whose measurement outcomes are mapped to a smaller action space by a classical decoder. The authors analyze this trade-off through the decoder's Fourier-Pauli expansion and derive an exact expression for policy variance under uniform initialization. They introduce a majority decoder that aims to avoid initialization concentration while remaining hard to simulate classically. In ten-qubit CartPole experiments, the majority decoder achieved higher returns than the tested alternatives.
