In briefWeak measurement of polarization qubits using a partially coherent temporal pointer
SummaryThis paper studies weak measurement of polarization qubits using a temporal pointer, aiming to characterize weak values even when the pointer is only partially coherent. The authors derive a closed-form expression for the post-selected temporal shift that interpolates between incoherent and ideal coherent limits via a single visibility parameter. Experiments on polarization states along three trajectories on the Poincaré sphere show that two trajectories give parameter-free benchmarks, while the third is sensitive to incoherence and is well described by the single-parameter model.
In briefA complete classification of operator controllability for three-level quantum systems driven by one control
SummaryThis paper studies whether closed finite-dimensional quantum systems driven by a single coherent control can achieve operator controllability. It proves two general Lie-algebraic results: conditions under which controllability survives controlled energy-level shifts, and a basis-element condition ensuring the dynamical Lie algebra contains su(N). Combined with known results, these yield a complete classification for all three-level systems in terms of Hamiltonian matrix elements, with necessary and sufficient conditions in each case.
In briefSpiral edge states in topological 2D Sb2Te3 crystals
SummaryThis paper studies how edge states conduct electricity in twinned and spiral two-dimensional Sb2Te3 topological insulator crystals. The authors report spatially continuous edge states along two spiral, knotted edge channels that are joined by a topological defect. Using electron energy loss spectroscopy, magnetic force microscopy and carrier transport measurements, they identify a 0.155 eV excitation in the spiral, linked to two isolated states in the gap and localized at the crystal edges.
Timothy Carlson, Daniel Lazega, Scott McGuire et al.
In briefGenerating entanglement by breaking degeneracy of superradiant steady states with local operations
SummaryThe paper studies many-body entanglement in superradiance. It shows that adding incoherent local processes, normally considered harmful, can produce high levels of entanglement between emitters. Using degenerate non-Hermitian perturbation theory, the authors analyze steady-state degeneracy breaking from a few emitters up to the thermodynamic limit. When pumping dominates, population accumulates in maximally entangled minimal pseudo-spin states, which correspond to multi-emitter singlet states.
In briefClassical communication lets single-shot quantum compression need fewer qubits
SummaryThe paper asks whether free classical communication reduces the quantum resources needed for single-shot quantum compression. The authors show that at any fixed error in (0,1), some sources need arbitrarily large compression cost without assistance, while one qubit suffices with classical communication and no preshared entanglement. For i.i.d. sources, the first three asymptotic terms of the two costs coincide, while for nonlattice spectra classical communication saves asymptotically log2(e)−1 bits per block.
In briefDefect-avoidance method for heavy-hexagon quantum chip layouts
SummaryThis paper addresses defective superconducting qubits that disrupt error correction, proposing a defect-avoidance scheme for the heavy-hexagon architecture, which has lower connectivity of 2 to 3. The scheme measures all gauge operators of a super-stabilizer in two cycles, compared with four in earlier methods. Experiments on IBM quantum hardware show that avoiding the defect reduces the logical error rate per cycle for both logical X and Z errors by about 10%.
In briefClifford invariants and three-copy quantum tests: a study of symmetry-based checks for qutrit systems
SummaryThe paper analyzes the third tensor power of the Clifford representation on n qutrits, for n≥2, and reduces the Clifford-twirled three-copy tensor to four real parameters. Two parameters are spectral moments of the input, and two are cubic invariants built from the Weyl characteristic and discrete Wigner functions. For pure inputs a single parameter suffices, and the authors bound stabilizer fidelity and derive criteria for complex projective 3-designs. They also give explicit copy and query bounds for stabilizer testing and for testing unknown observables.
In briefUsing AI to lower the trust cost of quantum application development
SummaryThis paper proposes a development method that combines generative AI with formal verification to reduce the human effort needed to confirm that generated quantum circuits realize the intended computation, which the authors call "trust cost." The implementation is split into a mathematical specification, a quantum circuit, and a correspondence theorem with its proof showing the two agree. Humans check the specification and theorem statement, while the proof is left to mechanical checking. The authors describe a concrete example implementing time evolution of a stochastic particle system and report its results.
In briefScalability and performance metrics for boson sampling devices: how large boson sampling systems can practically grow and how to measure them
SummaryThis paper examines theoretical scalability limits of boson sampling systems on linear-optical platforms under practical conditions such as photon loss, mode mismatch, and input state error. The authors use non-negativity conditions of phase-space quasiprobability distributions to analyze these effects. They also introduce two device-level metrics, the boson sampling score and the boson sampling volume, for comparing platforms.
In briefDynamical quantum phase transitions via the dynamical phase accumulated at an equilibrium critical point
SummaryThis paper studies dynamical quantum phase transitions produced by a two-step linear quench with a finite waiting time at the equilibrium critical point. The waiting stage accumulates a dynamical phase that depends on the waiting time and reflects the critical spectral structure. In the transverse Ising chain, this phase shifts the critical structure from a single-critical-mode regime to a multiple-critical-mode regime, and the boundary between them is determined analytically and numerically.
In briefEntanglement-aware circuit cutting that splits quantum circuits across devices to reduce reconstruction cost
SummaryThe paper presents SACE, a framework for partitioning quantum circuits so they can run across resource-limited components in distributed quantum computing. It screens partitions with an entanglement-capability proxy and native implementation cost (EP-Cost), then refines choices using finite-bond MPS simulations. On small-scale benchmarks such as QFT and QAOA circuits, the method reports lower quasiprobability decomposition overhead and improved reconstruction accuracy.
In briefQuantum Machine Learning for Higgs Boson Event Classification: Sample Size and Representation Study
SummaryThis paper examines how a quantum support vector machine and a variational quantum classifier perform at separating Higgs boson signal from background, using simulated events from the ATLAS Higgs Machine Learning Challenge. The authors vary training set sizes from 250 to 4000 events and test principal component analysis and autoencoder input representations. At larger training sizes, the QSVM outperformed the VQC but remained below the best optimized classical classifiers.
In briefFast, low-excitation ion transport through X-junctions for QCCD quantum processors
SummaryThis paper presents a waveform design method for moving trapped ions through 90-degree X-junctions in QCCD quantum architectures, combining multi-RF low-barrier channels, shortcut-to-adiabaticity dynamics, and constrained DC voltage optimization. In experiments, a single 171Yb+ ion made a 90-degree turn in 5 μs at an average speed of 14.6 m/s, with final equivalent coherent phonon number staying below 0.001 over 50 round trips. System-level evaluations report a roughly 30% reduction in median execution cycle duration, with the transport share of execution time falling from about 70% to 55%.
In briefSimplifying spin-coupled Grover walks on hypercubes using harmonic subspaces
SummaryThis paper studies spin-coupled Grover walks on hypercubes within the quantum Bernoulli noise framework. The authors find parity-dependent harmonic subspaces generated by central Hamming layers: a fixed-point subspace in even dimension, and an explicit eight-dimensional reduced dynamics in odd dimension. Using symmetric-group representation theory, they characterize the isotypic structure and determine the reduced spectrum, and they derive long-time probability behavior showing the states can occupy an asymptotically vanishing fraction of the hypercube while spanning its full Hamming diameter.
In briefQuantum reservoir optimized via quantum Fisher information outperforms tuned classical reservoirs
SummaryThe paper shows that a quantum reservoir computer whose quantum parameters are optimized using the quantum Fisher information (QFI) metric achieves an advantage over a classical reservoir with equal readout cost. On Mackey-Glass forecasting, a driven Jaynes-Cummings reservoir with one to three atoms beats a tuned echo-state network at every size from 4 to 30 trained weights, with 25-69% lower held-out error. After grid and Bayesian searches saturate, the QFI-aware stage further lowers error by 29-51% at 12-30 weights.
WhyUses quantum Fisher information to optimize a quantum reservoir, beating tuned classical baselines across sizes with a derived bound and fairly thorough held-out evaluation.
In briefQuadrature-detected zero-to-ultralow-field NMR: a sign-resolving magnetic resonance method
SummaryThe paper introduces quadrature-detected zero-to-ultralow-field NMR, which uses two orthogonal atomic optically pumped magnetometers to detect separate components of sample magnetization and combine them into a quadrature signal. This lets the method distinguish positive from negative resonance frequencies, so the signs of gyromagnetic ratios can be determined. Compared with single-axis detection, it reduces peak density and overlap. Experimental J-spectra of thermally polarized [13C]-formic acid and [13C]-methanol are shown, along with a theoretical framework for the signals.
Anne M. Fabricant, Florin Teleanu, Adam Ortmeier et al.
In briefMolecular magnetic amplifier using hyperpolarized molecules for weak field boosting.
SummaryThe authors use SABRE parahydrogen hyperpolarization to keep nuclear spins in liquid molecules in non-equilibrium order at zero field, creating a frequency-selective gain medium. By feeding the collective magnetic field back to the spins, they raise the susceptibility to about 80. Near threshold, a weak 20 pT field at 3.37 Hz is amplified roughly fourfold.
In briefExponential Quantum Advantage in Stationary Signal Sensing: entangled probes learn a signal's time statistics exponentially faster than local protocols.
SummaryThis paper studies how quantum entanglement can help learn the temporal statistics of a stationary classical signal. The authors propose an entanglement-assisted scheme using two-mode squeezed probes and local Bell measurements, which achieves polynomial acquisition time at inverse-polynomial accuracy. They also prove that any local idler-free protocol requires acquisition time exponential in the number of temporal modes per window.
WhyProves exponential acquisition-time advantage of entanglement-assisted sensing over local idler-free protocols, with matching lower bound.
In briefThe GHZ Game in Black and White: a real-valued version of a three-party quantum game
SummaryThe paper shows that three players can win the GHZ game using only the standard real-valued misty state formalism, provided each party holds two balls instead of one, six in total. The author notes that complex numbers can generally be replaced by tagging them with a qubit, but a single shared tagging qubit would allow the parties to pass information, so one ball per party is replaced by three locally accessed balls.
In briefCompetitive scaling of small-subsystem optimization heuristics for the LABS problem
SummaryThe paper studies the low autocorrelation binary sequences (LABS) problem, a combinatorial optimization task with a very rugged energy landscape. The authors optimize small subsystems of n spins that are decoupled from the rest of the system and report that this reaches global optima. With n = 4, the time-to-solution scales as O(1.333^N) for N in [27, 60], which is competitive with current classical and quantum heuristics.
In briefSeparating emission-stage entanglement from femtoscopic correlations
SummaryThis paper studies how femtoscopic correlations change the relation between the spin entanglement of emitted particle pairs and that of pairs selected at a given relative momentum. For two spin-1/2 particles, the momentum-selected spin state can be entangled even when the state at emission is separable. The authors derive a momentum-dependent separability criterion and apply it to identical Λ hyperon pairs, where quantum statistics and final-state interactions affect singlet and triplet channels differently at low relative momentum.
In briefA method for factorizing quantum signal processing phase factors using logarithmic derivatives
SummaryThis paper improves the computation of phase factors for quantum signal processing. Instead of using Prony's method, it uses the logarithmic derivative of an associated polynomial, whose Fourier coefficients give the power sums of roots inside the unit disk. The Newton–Girard identities then recover the polynomial coefficients without root finding. The algorithm runs in O(d log² d) time and achieves maximum errors around 10⁻¹² in numerical tests.
In briefFault-tolerant ripple-carry adder runs below threshold on a trapped-ion quantum computer
SummaryThe researchers deployed a universal fault-tolerant quantum computing architecture built on [[8,3,2]] and [[4,2,2]] error-detecting codes on Quantinuum's Helios-1 trapped-ion quantum computer. They ran ripple-carry adder circuits for classical inputs up to five bits. Combining an uncomputing-based algorithmic check with the error-detecting codes, one-bit addition showed a single logical failure after burst-error filtering, giving an estimated logical failure rate of (6.0 ± 5.9) × 10⁻⁵, below the (3.5 ± 1.3) × 10⁻³ observed for unencoded one-bit addition on the same hardware. Two- and three-bit adders also improved, while four- and five-bit adders ran just above threshold.
Jacob S. Nelson, Andrew J. Landahl, and Andrew D. Baczewski
In briefLifting a classical binary linear code to a quantum stabilizer code
SummaryThis paper studies when an arbitrary [n,k,d] classical binary linear code can be turned into an [[n,k,d]] quantum stabilizer code using the codeword stabilized (CWS) framework. The authors analyze random CWS codes built from the classical code and an Erdős-Rényi random graph G(n,1/2). They give a lower bound on the probability that the minimum distance d is preserved. This yields a Gilbert-Varshamov-type condition on n, k, d that guarantees a graph producing a quantum code with the same parameters.
In briefCompass in the Mirror: Quantum Backpropagation with Hopf-Ansatz Gradients
SummaryThe paper presents a method for computing the full gradient of a variational quantum state using the Hopf ansatz, which builds states from nested magnitude splits and phases. A phase-calibrated controlled reflection and a separate signed leaf record let shared finite-shot measurements yield every gradient component. It also gives execution-count bounds for a global method and a layer-wise checkpoint schedule.
In briefSemiclassical states and time-reversal symmetry for observable algebras in de Sitter space
SummaryThis paper studies gauge-invariant observables in de Sitter static patch holography, obtained by coupling bulk quantum fields to an observer's dynamical clock. The authors introduce heavy-clock states and show that, in the heavy-clock limit, correlation functions of dressed observables reproduce bulk de Sitter quantum field correlators. They also consider a generalized observer Hamiltonian covering both clock orientations and construct a time-reversal-invariant observable algebra.}
In briefObserving Higgs oscillations and their power-law decay in a cavity QED quantum simulator
SummaryResearchers used cold rubidium-87 atoms coupled to an optical cavity to simulate fermionic superfluids and study how pairing evolves after a quench. They observed transient oscillations of the order parameter linked to a collective amplitude (Higgs) mode. Oscillations decay as a power law with exponent 0.65(8) in the weak-pairing regime, but decay faster, with exponent above 1, in the strong-pairing regime. The oscillation frequency is set by the minimum quasiparticle excitation energy.
Chitose Maruko, Haoqing Zhang, Eliot A. Bohr et al.
In briefCategorifying quantum spin systems: a homotopical framework using topological n-nets
SummaryThe authors build a homotopical framework that assigns associative unital algebras to local regions of n-dimensional space using topological n-nets, capturing the locality structure of lattice theories. This net-theoretic view categorifies to a higher Morita category. The paper shows that the group of locality-preserving symmetries of (3+1)-dimensional quantum spin systems is isomorphic to the full Witt group of nondegenerate braided fusion categories, answering a question posed by Haah.
WhyIdentifies locality-preserving symmetries of (3+1)D spin systems with the Witt group of braided fusion categories, answering Haah's question; a strong theoretical result.
In briefQuantum-chip experiment colliding Hubbard quasiparticles to create entanglement
SummaryThe authors ran a quasiparticle scattering experiment on IBM's ibm_boston digital quantum processor, colliding a doublon and a holon in a 21-site half-filled chain encoded on 42 qubits. The measured transmission probability matches the Bethe-ansatz scattering matrix without free parameters. The collision also creates entanglement by superposing transmitted and reflected components, inferred from particle-number fluctuations. A control collision between two doublons showed neither effect.
WhyFirst measurement of Hubbard quasiparticle transmission on quantum hardware, matching Bethe-ansatz predictions without free parameters, with entanglement inferred from number fluctuations.
In briefA Warped Born Rule That Makes Observation Act Like a Maxwell's Demon in Quantum Gases
SummaryThe paper replaces the standard Born rule with a warped version raised to a power b and studies many-body systems with conserved particle number under repeated local particle measurements. For b greater than 1, the gas tends to collect into nearly frozen configurations, so observation appears to extract entropy from a closed system. For b less than 1, long-wavelength fluctuations are suppressed, producing a hyperuniform gas. Both phases are derived analytically for a one-dimensional quantum gas and checked with matrix product state simulations.
In briefA scalable GPU solver for finding quantum system ground states in large subspaces
SummaryThis paper presents a scalable ground-state solver for sample-based quantum diagonalization (SQD), built on the JAX API for GPU and multi-GPU computing platforms. It can perform subspace diagonalization in subspaces of up to 2^30 dimensions and describes its general-purpose eigensolver and SQD-specific matrix-vector operation. A simple physics model demonstrates its GPU memory efficiency, and the eigensolver shows good strong scaling across many GPUs.
In briefQuantum query complexity of maximum degree problems and generalizations
SummaryThe paper studies the quantum query complexity of basic graph problems. It proves a tight Θ(n^{3/2}) bound for finding a maximum-out-degree vertex in an n-vertex tournament, and gives a direct proof that finding a maximum-degree vertex in an undirected graph also requires Θ(n^{3/2}) queries. It also presents an O(n^{2-1/(k+1)})-query quantum algorithm for Maximum (k,n-k)-Cut and reduces k-Graph Collision to it, yielding unconditional lower bounds with exponents strictly above 3/2 for k≥3.
WhyProves tight Θ(n^{3/2}) quantum query bounds for maximum degree, resolving a conjecture, and gives new strictly larger lower bounds.
Amin Shiraz Gilani, Nikhil S. Mande, Subhasree Patro et al.
In briefMaximally antiflat fermionic states at fixed particle number
SummaryThis paper studies maximally antiflat pure number-conserving fermionic states, which are extremal cases for measuring non-Gaussian structure relative to the covariance matrix. The authors show that at fixed particle number, maximal first antiflatness is equivalent to a completely flat one-body reduced density matrix, and they provide an existence classification with explicit constructions. They also analyze connected four-point correlations beyond the covariance level and derive an upper bound on this quartic structure in terms of first antiflatness.
In briefA quantum neural network using annealing and wavelet transforms to forecast air pollution
SummaryThis paper proposes a scalable hybrid framework combining variational quantum circuits with quantum annealing to model fine particulate matter (PM2.5) in UK urban data. The authors report that their quantum neural networks outperform classical baselines such as MLP and LSTM on raw, high-entropy environmental data. They also scale the model to 172 qubits and report improved predictive accuracy when combined with wavelet decomposition.
Otto Menegasso Pires, Andr\'e Saimon, Daniela Herrmann et al.
In briefBicycle Race: small two-block codes on the Pareto frontier
SummaryThe paper systematically searches group-algebra two-block quantum LDPC codes, enumerating about 10^8 codes with up to 320 qubits on a laptop. Several exhaustive censuses yield complete statements about optimal codes, such as the Gross code's uniqueness at a given parameter. The authors also analyze where good codes concentrate and report new codes, all made available in a public database.
WhySystematic exhaustive census of two-block group codes yields complete optimality statements and new strong small codes, substantively advancing understanding of small quantum LDPC codes.
In briefGPU-parallel BP decoding for quantum LDPC memory: a faster decoder for error correction in quantum memory.
SummaryThe paper extends BP-SF, a belief-propagation decoder guided by oscillation with independent syndrome-flip trials, adding windowed and streaming operations in a CUDA implementation. In circuit-level simulations of the [[144,12,12]] bivariate bicycle code at physical error rate 0.002, parallel BP-SF cut 99.9th-percentile call latency by 13.15 times versus an eight-chain Relay-BP GPU baseline. Windowed BP-SF keeps the logical error rate flat and per-round compute nearly constant over 512 rounds, with a 17.1-fold speedup over monolithic decoding.
In briefClassical help does not raise limits for energy-limited bosonic dephasing channels
SummaryThis paper proves that four capacities of single-mode bosonic dephasing channels are equal under an average photon-number constraint. These are the unassisted quantum and private capacities, and the two-way classically assisted quantum and private capacities. The result holds even when parties exchange classical messages between channel uses and adapt later inputs accordingly. For each finite constraint value, the common capacity equals the coherent information optimized over Fock-diagonal input states meeting the constraint.
WhyProves equality of four capacities for bosonic dephasing channels via rigorous chain rules; a strong theoretical advance with a narrow subfield impact.
In briefBoosting analogue quantum computing with a logically encoded XX gadget
SummaryThis paper introduces the truss gadget, an exact construction that produces two-body XX interactions using only one-body X and Z fields and two-body ZZ interactions available on superconducting quantum annealers. The authors validate it by reproducing the dynamics of a target XX Hamiltonian on a trapped-ion quantum processor. Applied to weighted maximum-independent-set instances on a superconducting annealer, the gadget empirically yields about a thousand-fold higher probability of finding a near-ground state than implementations without XX interactions.
Robert J. Banks, Natasha Feinstein, Roopayan Ghosh et al.
In briefA hardware-native instruction set for hybrid trapped-ion qudit and oscillator processors
SummaryThis paper introduces a hardware-native instruction set for trapped-ion processors that uses the multilevel internal states of each ion, rather than adding more ions, to enlarge the computational space. The authors prove that three native operation families suffice for universality of one qudit coupled to several bosonic modes, and adding inter-ion entangling operations extends this to multi-qudit registers. The architecture is implemented in the open-source HybridLane framework and applied to simulating vibronic dynamics of a three-chromophore complex, projecting about tenfold faster Trotter steps on a 40Ca+ qudit processor with about 1.1% average RMSE against a published reference.
In briefQTestBench: A Framework for Testing LLM-Generated Quantum Code Tests
SummaryThis paper introduces QTestBench, a framework that evaluates test suites generated by large language models for quantum software. It has models produce syntactic, semantic, and behavioral tests, then compares each test's verdict with independent benchmark checkers. Experiments on PennyLane QHack and Qiskit HumanEval tasks show that generated tests almost always execute, but their ability to tell correct from faulty implementations lags behind, so executability alone overstates test quality.
In briefCombining quantum and classical models by diversity for better classification
SummaryThis paper asks whether the structural diversity of quantum circuit designs can be combined through model fusion to improve predictions. The authors apply Combinatorial Fusion Analysis to a pool of 29 classical models and quantum circuits, selecting maximally diverse subsets to combine. On four binary classification benchmarks, the hybrid fusion outperforms the best single model on every dataset, with accuracy gains of up to 6.03%.
Jingyan Xu, Yuanhong Wu, Samuel Yen-Chi Chen et al.
In briefReplica transition in measurement-altered Ising criticality
SummaryThis paper studies the ensemble of post-measurement states that arises when measurements are performed on the critical Ising chain. It shows that the replicated ensemble undergoes a phase transition exactly at the replica limit Q→1 relevant for Born-averaged observables, which blocks standard replica treatments. Using boundary conformal field theory, the authors explain the mechanism and analytically compute the universal O(1) constant in the Shannon entropy of the measurement record, previously known only numerically.
In briefLocality–preparation time tradeoffs in dissipative quantum systems: how the spatial range of dissipation limits how fast many-body states can be prepared, illustrated with the Kitaev chain.
SummaryThe paper studies how the spatial locality of dissipation constrains the time needed to prepare quantum many-body states as steady states of open-system dynamics. For quadratic fermionic systems, the authors derive an exact locality–preparation time relation and a construction that optimizes locality while preserving the target state. Applied to the Kitaev chain, the framework shows that critical and gapped regimes have different tradeoffs: at criticality, suppressing algebraic tails forces preparation time to grow algebraically with system size, whereas trivial and topological gapped phases allow exponentially localized dissipation with finite preparation time in the thermodynamic limit.
In briefDynamical Lie algebras for fixed-gate quantum ansätze: a method for analyzing circuits used in quantum machine learning
SummaryThis paper addresses parameterized quantum circuits, a central framework for variational quantum algorithms in the NISQ era with uses in quantum simulation, combinatorial optimization, and quantum machine learning. The authors develop a new approach for computing the dynamical Lie algebras of circuits that combine parametrized gates with non-parametrized entangling gates. The aim is to extend recent algebraic results to the architectures actually used in quantum machine learning.
