Papers

Quantum machine learning is rapidly emerging as a promising and potentially more sustainable approach that can complement traditional, energy-hungry HPC, AI, and GPU resources-particularly for the demanding global challenges the world urgently needs to address. In recent years, the first prototypes of quantum processors have reached the market, are sometimes available via the cloud, and distributed quantum computing is beginning to move from a largely theoretical concept to a demonstrated reality. However, these devices are still noisy and qubit-limited. Therefore, it is desirable to design quantum machine learning models with a reduced quantum register and a limited number of quantum gates, avoiding overly deep and wide quantum circuits. Here, we explore this idea by proposing a novel divide-et-impera-based training protocol that splits quantum neural networks into smaller components and better governs their optimization. We benchmark our approach on real data and real-world prediction tasks in intertwined energy and environmental domains, such as the status of charging stations for electric vehicles and the global air quality index. Our results suggest a design principle for quantum machine learning algorithms across a wide range of applications, which can be more feasibly tested on state-of-the-art quantum processors or within modular quantum architectures being developed for future hybrid infrastructures interconnected via high-speed communication links.

Predicting anharmonic vibrational spectra is a complex computational task, which becomes quickly infeasible as molecular size and the number of vibrational basis functions increase, leading to an exponential growth of the underlying Hilbert space. Here, we employ a sample-based quantum diagonalization (SQD) framework to compute anharmonic vibrational energies and spectra. The approach combines quantum state preparation and sampling with configuration recovery, diagonalization of the Hamiltonian projected in a subspace of basis configurations, and calculation of transition-dipole moments to obtain both vibrational energies and infrared spectra. We investigate two approaches for sampling, namely, vib-LUCJ and vib-SqDRIFT and apply the method to study the polyyne molecules C$_2$H$_2$ and C$_4$H$_2$, reaching representations requiring up to 104 qubits. Beyond energies, transition-dipole calculations reveal that infrared intensities and excited-state composition continue to evolve with basis size through anharmonic mixing and intensity redistribution, even when low-energy eigenvalues appear converged. These results show that sample-based quantum subspace methods can capture spectroscopic information in vibrational spaces far beyond the regime of full diagonalization. Moreover, our simulation identify multi-state recovery and scalable projected-space treatment as central challenges for further scaling sample-based approaches.

Classical approximation complexity asks what solution quality can be guaranteed with polynomial-time computation. The classes APX, PTAS, and FPTAS distinguish a fixed approximation ratio, approximation to any fixed accuracy, and approximation schemes whose running time is also polynomial in inverse accuracy. Their randomized counterparts are R-APX, R-PTAS, and R-FPTAS. We define bounded-error quantum counterparts BQ-APX, BQ-PTAS, and BQ-FPTAS. Membership requires a uniform quantum algorithm that, on every input, returns a feasible classical solution achieving at least the claimed approximation ratio with probability at least 2/3. Scores (objective values) must be efficiently classically computable. Running time includes parameter selection, preparation, measurement, decoding, and repetition. Many quantum optimization methods are used heuristically, and high benchmark scores alone do not establish these guarantees. We further establish a conditional hierarchy for logarithmic, polynomial, and exponential approximation factors. Assuming NP $\nsubseteq$ BQP, the quantum classes form a strict hierarchy. Problems based on prime factorization and discrete logarithms give conditional quantum-classical separations. Certified Maximum Order has an exact quantum algorithm, while any randomized polynomial-time algorithm guaranteeing at least an inverse-polynomial approximation ratio on every input would yield efficient factoring. Discrete-Logarithm Fitting has an exact quantum algorithm and a deterministic one-half approximation, but any fixed improvement over one half would give a randomized polynomial-time algorithm for the safe-prime discrete logarithm problem. Our results show, under explicit complexity assumptions, that quantum computation can improve worst-case approximation guarantees. A quantum-classical gap for common problems such as MaxCut or MaxSAT remains open.

We produce degenerate photon pairs called signal and idler via parametric down-conversion (PDC) in a Fabry-Pérot waveguide resonator having close to a 2GHz bandwidth in the telecom C-band. Our PDC source is based on a type-II periodically-poled Lithium Niobate waveguide with high-reflecting end facets forming the resonator. We measure the strength of the photon-pair correlation between signal and idler after selecting a single resonator mode from the multimode PDC emission. Thereafter, we investigate their sub-nanosecond long pulse shapes, in other words the time bins, with standard photon counting. We find that the time-bin durations vary significantly from each other, which can be predicted by the different optical losses of the cross-polarized signal and idler. Further, we simulate the temporal properties of signal and idler via the Fourier transform of their joint spectral characteristics. Our results deliver empiric insight about the time bins of photon pairs and are relevant for driving future quantum networks at the edge to narrow bandwidths but nevertheless in the pulsed regime.

We extend sample-based quantum diagonalization (SQD) to anharmonic vibrational spectra and use it to benchmark how vibrational ansätze scale on present-day hardware under a direct one-hot encoding (up to 72 qubits). Five particle-conserving circuits are warm-started through vibrational coupled-cluster (VCC) t1, t2 amplitudes: UVCCSD, the compact heuristic circuit (CHC), and three unitary-cluster-Jastrow ansätze introduced here, VLUCJ, Vg-uCJ, and VIm-uCJ. A self-consistent configuration-recovery loop reconstructs correlated states from hardware samples in the low-retention regime where naïve post-selection breaks down, enabling the calculation of ground-state energies for H$_2$O, CH$_2$O, and CH$_2$ClF (3-9 modes). We compare harmonic-oscillator and vibrational self-consistent-field (VSCF, "modal") reference bases. In the small-modal-basis regime relevant for near-term devices, the modal basis is typically more accurate than the harmonic-oscillator representation; empirically, it also yields substantially better-converged hardware sampling for deep circuits at these qubit counts. Across ansätze, we find a clear retention/accuracy tradeoff when scaling: the new VLUCJ circuit is the most hardware-robust, retaining the largest fraction of physically valid one-hot outcomes, whereas the more expressive uCJ variants and UVCCSD can recover more correlation when retention is sufficient. Finally, we extend the recovery protocol to excited states by targeting a chosen per-mode VSCF occupation and warm-starting it with a state-specific VCC calculation, and we demonstrate the calculation of one representative fundamental vibrational frequency per molecule on IBM QPUs.

Interactive quantum circuit simulators are increasingly used to support introductory quantum computing education for learners from varied disciplinary backgrounds. These environments can also generate detailed response logs of submitted circuits, but such data are rarely transformed into evidence that instructors can use for course redesign and development. We present a learning analytics framework for quantum circuit simulator tasks and report its task-level branch on anonymised logs from an introductory quantum computing course delivered in the TIM learning environment. The task branch characterises exercises through participation, completion, first-attempt accuracy, valid-attempt counts, sessionised active time, and observed answer-space reporting of common correct and incorrect constructions. The dataset covers the 2024-2025 cohort of 492 learners, 47,533 valid submissions, and 21 obligatory quantum circuit exercises. The framework identifies bottleneck tasks, broad solution spaces, and recurring wrong-answer patterns that are not visible from final scores alone. Its most distinctive output is a plain-text representation of the observed answer space, designed to make open-ended circuit submissions directly interpretable to instructors. We show how response logs can reveal actionable task-design issues and support concrete course redesign. A learner-level branch is retained only as an ongoing research extension and is not a central empirical contribution of the present paper.

We provide a geometric description of Lee-Yang tensors, building upon several recent results of Bravyi, Gosset, Liu, and Wong. By applying tools from complex Perron-Frobenius theory, we generalize one of their key lemmas to bound the spectral ratio of non-normal operators with Lee-Yang radius greater than one. As a direct consequence, we provide a local-to-global principle for bounding spectral gaps of Suzuki-Fisher Hamiltonians, a family of $2$-local Hamiltonians, using only the Lee-Yang radius of each local operator to bound the gap from below. On the other hand, we develop a simple perturbative technique to show that the Gibbs states of $k$-local Hamiltonians, $k \geq 3$, cannot have Lee-Yang radius at least one for all inverse temperatures $\beta \geq 0$. We apply this same method to conclude that Suzuki-Fisher Hamiltonians are precisely those Hamiltonians whose Gibbs states are Lee-Yang at all inverse temperatures $\beta \geq 0$.

Several published comparisons of variational quantum optimizers time only runs that reach a target loss, or read the verdict at a single target. Either convention could decide whether an optimizer's costlier steps pay off. We measure how much each convention changes verdicts among Adam, simultaneous perturbation stochastic approximation (SPSA) and quantum natural gradient (QNG), on initializations held out from the selection of settings. We compute the exact metric that preconditions QNG, price every step in circuit evaluations and give every method the same budget. In a median pooled over circuit widths, cost families and a sweep of settings with common misses, SPSA needs more than twice Adam's evaluations to reach a loose target. Dropping the censored runs that miss the target hides this gap. On the global-cost family we hold fixed the settings selected for a strict target. QNG then usually reaches the loose target after Adam but the strict target first. QNG's strict-target lead disappears when the metric's simulator price, linear in the number of parameters, is replaced by an assumed hardware count quadratic in that number. We recommend charging every miss the budget and reporting verdicts across targets.

Conventional Chern insulators rely on breaking time-reversal symmetry via magnetic fields or synthetic gauge fields. Here we introduce a fundamentally different paradigm: a static lattice without any gauge field becomes a Chern insulator solely through the cooperation of two non-Hermitian ingredients: on-site loss and non-reciprocal coupling. Neither effect alone suffices; only their synergy opens a topological gap and gives rise to robust chiral edge states with a nonzero Chern number. The underlying mechanism originates from a non-Hermitian chiral molecule formed by the lossy sites, whose dynamically dominant mode carries an orbital angular momentum that effectively generates a synthetic flux after the fast-decaying degrees of freedom are eliminated. Our results establish non-Hermitian cooperation as a versatile resource for inducing Chern topology without external fields or temporal modulations, opening a new route to topological phases in open classical and quantum systems.

Non-reciprocal lattices offer a flexible setting for directional wave transport, raising the question of how enhanced internal scattering translates into transmission between fixed external ports. We address this question for non-reciprocal Su–Schrieffer–Heeger (SSH) chains with staggered gain and loss by relating the reference-dependent insertion kernel $K_p=VG_pV$ to the coherent transmission intensity $T$. On a fixed finite graph, a strong-insertion expansion gives a contribution proportional to $\gamma^{1-d}$, whose coefficient is the signed sum of shortest directed paths of length $d$. When this sum is nonzero, it sets the leading behavior independently of fixed diagonal losses; when it cancels, those losses can enter the first surviving higher-order term. For a fixed cross-sublattice endpoint channel, transmission has a strictly negative slope at every nonzero differentiable stationary point of the kernel magnitude. In the weak-insertion regime, the reference-system coefficient $\chi=-\mathrm{Re}\,\mathrm{Tr}[(G_{0p}Z)^2]$ predicts the initial transmission change for symmetric SSH ports, and $\chi>0$ together with a strictly stable baseline guarantees local stable enhancement. Finite-chain calculations and driven dynamics connect these results to observable response and distinguish asymptotic convergence from transient settling. A strictly dissipative short-chain example exhibits local enhancement without net power gain. Together, these results separate graph-path structure, coherent port response, and dynamical establishment, providing channel-specific criteria for interpreting internal scattering.

We develop an end-to-end framework for estimating canonical thermal properties of particle-number-conserving second-quantized Hamiltonians using quantum simulations. The framework integrates initial state preparation with mixed Dicke states, particle-number-preserving Trotterized simulation, and generalized quantum signal processing to estimate canonical partition functions and observables. Building on this canonical scheme, we introduce a grand-canonical reconstruction scheme in which the same quantum measurement data can be reused for arbitrary chemical potentials through classical reweighting, thereby avoiding repeated quantum circuit executions as the chemical potential is varied. We prove the existence of system-size-independent temperature regimes in which both the canonical and reconstructed grand-canonical schemes have lower asymptotic time complexity than classical Lanczos methods, up to polynomial factors, for physically relevant Hamiltonians. We numerically validate our theoretical results for the two-dimensional Hubbard model in both weak- and intermediate-coupling regimes.

We introduce a non-orthogonal amplitude amplification (NOAA) method for hybrid continuous-variable- discrete-variable (CV-DV) quantum processors, where the available CV-assisted projector is not perfectly se- lective for the target state. We establish a bound on the achievable target-state fidelity, which is determined by the initial target-state amplitude and the selectivity of the accessible reflection operator. This bound limits the performance of NOAA in hybrid CV-DV systems. To mitigate this limitation, we propose using a squeezed CV ancilla to reduce the overlap between relevant CV states and a hybrid quantum signal processing (HQSP) filter to suppress errors arising from imperfect knowledge of the target eigenenergy. Numerical simulations show that, for small initial target-state amplitudes, our protocol achieves higher fidelity and efficiency than the repeat-until-success (RUS) method despite the presence of non-orthogonality. For large initial amplitudes, RUS is already efficient, and amplitude amplification provides little additional advantage.

We construct CSS codes with three logical qubits whose logical CCZ gate is implemented by transversal physical $T/T^{\dagger}$ gates and whose distance is at least $3$. These codes start with $8$-divisible $X$-stabilizers defined by projective geometry, which guarantees $d_Z\geq 3$. A SAT solver then finds three $X$-logical operators compatible with the transversal CCZ. We build codes at thirteen block lengths from $n=48$ to $n=496$, with $d_Z=3$ or $4$, and illustrate the method with the $[[48,3,3]]$ code $Q_{48}$. Additionally, we prove that no CSS code with three logical qubits, $Z$-distance at least $3$, and a quasi-transversal CCZ gate (transversal $T$ with a diagonal Clifford correction) exists below $n=39$. The $[[47,3,3]]$ code of Jacinto et al. serves as an upper bound, leaving $39\leq n\leq46$ open.

We present a comparative analysis of two open-source quantum network simulators, QuISP and SeQUeNCe, focusing on cross-validation of basic networking tasks to ensure consistency and accuracy in simulation outputs. Although both simulators are designed to study quantum network management policies and their dynamics under complex noise models, their differing underlying assumptions can lead to variations in simulation results. We highlight the discrepancies in how the two simulators handle connections, internal network node processing time, and classical communication, resulting in significant quantitative and qualitative differences in the time required to perform basic network tasks such as entanglement generation, purification, and swapping. We simulate common scenarios between the simulators to compare both the latency of resource distribution and the fidelity of the distributed resources. Our findings indicate that while the simulators differ in the time required to complete network tasks—a constant factor difference attributable to their respective connection models—they agree on the fidelity of the distributed resources under identical error parameters. This work demonstrates a crucial first step towards enhancing the reliability and reproducibility of quantum network simulations, as well as leading to full protocol development. Furthermore, our benchmarking methodology establishes a foundational set of tasks for the cross-validation of simulators to study future quantum networks.

Can an agent's predictions reveal whether its reasoning is based on a classical or a quantum model? Using known results on matrix factorizations, here we show that quantum Bayesian retrodiction can produce one-step-ahead forecasts incompatible with every classical Bayesian explanation based on learning about a fixed but unknown sampling law from conditionally independent observations. The separation has a sharp threshold in the number of outcomes: for any measurement with at most four outcomes, the quantum predictions admit a classical realization, irrespective of the prior state and the finite Hilbert-space dimension, whereas a five-outcome measurement on a single qubit already violates an explicit classical bound. This bound holds for arbitrary classical latent states, prior probabilities, and sampling laws, and involves only the agent's initial and updated predictions. Thus, in this setting, quantum Bayesian retrodiction is strictly more expressive than classical Bayesian learning, and this difference can be witnessed without observing or specifying the agent's internal description.

We present a hybrid quantum-classical framework that detects affinity and romance-investment fraud by modelling the cognitive biases in a manipulative conversation. In our proposed framework, cognitive biases central to this fraud class are carried by dedicated qubits in a structured parameterized quantum circuit, together with a frame qubit makes the encoding sensitive to the temporal order of manipulative reframing, and a narrative qubit that aggregates co-occurrence through a trainable entanglement layer. The circuit parameters are trained jointly with a classical reinforcement-learning agent that decides, turn by turn, whether to flag the conversation, modeled as an optimal stopping problem. We evaluate the model's performance on synthetic conversations that include hard negatives, legitimate but urgent, and legitimate but pushy sales conversations.

Eve receives two average photon counts, while a monitor watching for external leakage may register nothing. Can she conclude that Alice and Bob's opaque cavity devices did not communicate? We give a constructive counterexample: two independently operated controls activate a shared beam-splitter interaction after the inputs arrive. The parties report genuine sample averages, and a fixed local threshold converts these reports into a CHSH game with expected score $S=13/4$ for four repetitions per block, approaching $4$ for large blocks in the ideal model. This exceeds the usual $2\sqrt2$ quantum benchmark because the devices interact during their response. A separate dispersive-bus model explains how substantial exchange can coexist with a small probability of a click in a specified leakage monitor; an illustrative open-system calculation exhibits both effects without postselection. The output marginals nevertheless reveal signalling. The example separates three questions: whether the reports are honest, whether a monitored port is quiet, and whether the devices are physically isolated.

In a thermally occupied multimode trapped ensemble, mode-dependent detunings can strongly suppress Ramsey contrast even when the underlying dynamics remains coherent. We develop a weak-axis-resolved Hamiltonian theory in which collective mode spins experience longitudinal detunings and overlap-dependent exchange interactions. Without exchange, the distribution of detunings across thermally occupied modes produces coherent phase mixing and an algebraically decaying Ramsey-contrast envelope in the many-mode continuum regime. At the mean-field level, exchange generates a self-consistent restoring field that reduces phase dispersion and restores collective contrast. The crossover is governed by the competition between the collective exchange scale and the thermally induced detuning spread: when the late-time contrast is expressed in terms of their ratio, results at different temperatures collapse onto a common trend, and the crossover coupling follows the predicted inverse-square thermal scaling, with a numerical exponent of 2.06. Weak irreversible pure dephasing limits, but does not eliminate, this recovery, demonstrating that exchange refocuses coherent inhomogeneous phase mixing but cannot reverse irreversible phase noise.

Geometric heat pumping is the transfer of energy between reservoirs at equal temperature where the heat exchanged in an adiabatic cycle depends only on the driving contour in parameter space. We implement this mechanism on a superconducting quantum processor using a collision model, where a driven qubit interacts repeatedly with two ancilla qubits that are prepared in thermal states and emulate the reservoirs. Energy measurements before and after each interaction provide a calorimetric record of the heat exchanged with each reservoir. By reversing the driving contour, we extract a heat contribution associated with pumping. Its dependence on the period and on the contour follows exact simulations of the collision model, without adjustable parameters, and approaches in the slow-driving regime the geometric limit of the corresponding Lindblad dynamics.

The motion of a particle in a finite-depth confining potential, such as that of an electromagnetically trapped atom or ion, is approximately harmonic at low energy and softens as the escape energy is approached. When the particle is driven by a stochastic force, the heating and escape times depend sensitively on the noise power spectrum. We study escape times of particles in softening potentials driven by power-law colored noise. We identify two nested conditions for weak noise: the particle must execute many oscillations before escape, and noise forces must be small relative to forces exerted by the trap so as not to tilt the potential appreciably. In this regime, we derive expressions for the mean escape time using stochastic averaging techniques and compare them with Monte Carlo simulations of the full equations of motion. We also examine the crossover to regimes where these conditions are not met and large quasi-static forces give rise to additional escape mechanisms. Applying these results to an experimental measurement of lifetimes in a microfabricated ion trap, we find that spectral color alone cannot account for the rapid escape rates observed, whereas quasi-static barrier tilting by a stray field of plausible magnitude could. These results are relevant to the heating and escape of trapped atoms due to noisy force fields, as well as to other nonlinear oscillators subject to colored noise.

Organisations deciding which assets to migrate to post-quantum cryptography first, and how that work competes with a backlog of classical findings, lack a common unit: post-quantum scores are dimensionless and quantum-only, while classical risk is annualised loss. We express both threats as a cost of delay in currency per year on the same asset. The quantum term is the rate at which deferring migration commits irreversible harvest-now-decrypt-later loss, computed from required confidentiality duration, recordable traffic share and data turnover, using a quantum-arrival law fitted in closed form to published expert anchors. A competing-risks factor couples the two terms so the same loss is not counted twice. We prove that the construction is not a weighted sum of a classical and a quantum score, give a dominance threshold on the classical hazard that is independent of asset value, and show that the induced order is optimal for sequencing work under constant loss rates. We verify the implementation by simulation, adaptive quadrature and a second implementation. On four public systems with parameters assumed from public documentation, the quantum term reorders the asset list beyond input uncertainty for one system only (signal-to-noise 1.36 against 0.14-0.46), moves specific long-lived, quiet, recordable assets decisively, and otherwise changes magnitudes. Asset value and turnover explain 73-91% of the uncertainty in the quantum term; the arrival date explains 3-17%. The case studies are illustrative and are not validated against outcomes.

Alice and Bob each have a qubit, and they would like to perform a two-qubit gate on them with the assistance of Charlie. The action of this gate depends on a parameter, which either Charlie knows, will receive later as classical information, or is encoded in a program state. We discuss both the case in which Alice and Bob send Charlie their qubits, which he entangles with his state, and the case where Alice and Bob use teleportation to entangle their states with Charlie's state. All of these procedures depend on the ability of Alice and Bob to apply local correction operations that depend on the results of measurements that Charlie makes, and we discuss under what conditions such operations are possible.

Valley excitations are considered one of the biggest challenges for a coherent spin shuttling in Si/SiGe heterostructures. In this work we theoretically investigate the valley dynamics during spin shuttling in a Si/SiGe heterostructure by considering a two-level system given by the two low-lying valley states of the mobile quantum dot. We assume that the electron is initially in the valley ground state and analyze the evolution of this state during shuttling. We find that, depending on the shuttling velocity, the system can be in three distinct regimes. In one of these regimes, the quantum information is preserved even in the presence of the valley excitations, allowing for coherent spin shuttling independently of the shuttling distance. This regime is obtained for a shuttling velocity of tens of m/s, a desired regime where dephasing mechanisms, such as spin-valley hotspots and spatially varying spin splitting, can be suppressed. This result is in accordance with recent experimental work that obtained a high spin shuttling fidelity after a fast and long shuttling. We also propose strategies based on the Partial Landau-Zener model to enhance the valley shuttling fidelity, which was found to be much more efficient than previously proposed strategies based on the standard Landau-Zener model.

We investigate the effects of initial states on the dynamics of a quantum spin-boson model using an efficient variational polaron master equation approach. The transformation of a factorized system-environment initial state into the variational polaron frame introduces inhomogeneous terms in the master equation, essential for accurately describing non-Markovian dynamics beyond the weak coupling regime. To efficiently account for these effects, we formulate the dynamics in an extended auxiliary Liouville space, converting the resulting integro-differential equations into coupled ordinary differential equations. We further introduce a simplified variational polaron technique for computing the time evolution of expectation values of general observables, including those that do not commute with the polaron transformation, overcoming a major limitation of previous approaches and enabling the unified treatment of coherence and population dynamics. The effects of transformed initial states generated from arbitrary factorized initial states are systematically characterized through expectation values and trace-distance analysis, providing insight into the associated bath-relaxation dynamics over a broad range of tunneling amplitudes, temperatures, and coupling strengths. Comparison with the weak-coupling master equation reveals a delay phenomenon associated with multi-bath-quanta processes, pronounced at intermediate coupling strengths and tunneling amplitudes. We further show that coherent superposition initial states induce stronger nonequilibrium effects than localized states, with inhomogeneous terms playing a crucial role in the short-time dynamics. The proposed formalism applies to both undriven and resonantly driven spin-boson models, providing a computationally efficient framework for open quantum-system dynamics with arbitrary factorized initial states and general physical observables.

In quantum reading, classical messages are encoded in sequences of quantum channels and recovered by probing the channels and processing their outputs. We study the reading capacity of a finite family of finite-dimensional channels under an average constraint on the probing energy, allowing arbitrary adaptive operations between channel uses. Using an input-dependent chain rule for the Belavkin-Staszewski relative entropy, we derive a converse bound expressed as an optimization involving channel Choi operators and the operator relative entropy. This formulation admits semidefinite approximations and reduces, without an energy constraint, to a channel information radius. To obtain achievable rates, we construct bilinear semidefinite lower approximations to a standard non-adaptive reading bound. Alternating optimization produces feasible probe states and encoding distributions, whose Holevo information gives a directly evaluable achievable rate. For jointly classical-quantum channels, we derive a separate converse based on the Umegaki relative entropy. Without an energy constraint, this converse matches a non-adaptive achievable rate, recovering a recent result of Pascual Abraldes and Winter: non-adaptive protocols suffice to achieve the unconstrained reading capacity of jointly classical-quantum channels.

While a Fabry-Perot (FP) cavity interferometer is a standard tool in modern optics, analogous physics can also be observed with matter waves such as Bose-Einstein condensates (BECs). Interatomic collisions in BECs can induce nonlinear features such as multi-valued transmission spectra for interferometry experiments. Observation of interaction effects in the matter-wave analogue of FP interferometry has not yet been experimentally achieved, mostly due to broadening of transmission peaks by interaction-induced shifts of cavity resonances. In this work, we theoretically show that this limitation can be overcome by engineering a momentum chirp in a BEC wavepacket. By balancing this chirp against the dynamical mean-field energy shift of the cavity during transmission, we predict enhanced resonant spectra and bistability features due to interaction-assisted tunneling that would be otherwise inaccessible. We show that this physics is readily observable with quasi-one-dimensional BECs of cold atoms colliding with a pair of light-induced Gaussian potential barriers forming the cavity. We also benchmark the requisite optimum chirp needed and characterize the contrast of near-discontinuous FP transmission spectra at an interacting resonance. Our findings enable the realization of technologies like matter-wave switching protocols, and high-precision velocity measurements; estimates of achievable sensitivity for the latter are provided.

Recently, neutral atom arrays have become known for their promising potential in quantum information processing. High-fidelity entangling operations are typically achieved by exciting atoms to high-lying Rydberg states through two-photon processes. To improve the performance of these systems at the hardware level, dual-species strategies have been applied to enhance readout, error correction, and reloading in neutral atom systems. However, the influence of laser crosstalk arising from two-photon excitation for dual-species systems has remained largely unexplored in the literature. Here, we develop a model that incorporates the influence of crosstalk in inter-species Rydberg gates with two-photon driving. We demonstrate that the influence of this crosstalk can be suppressed to arbitrarily small levels through appropriate gate design, with gate fidelities greater than $99.8\%$ achievable with conservative experimental parameters in the near-detuned case of an $^{85}$Rb/$^{87}$Rb system. We also outline how this fidelity can be further enhanced through improvements to the Rydberg excitation.

We study zero modes bound to charge-conjugation defects in fractional quantum Hall-superconductor (FQH-SC) heterostructures built from Abelian and non-Abelian FQH states. Although the associated defects are well described by $G$-crossed braided tensor categories, a local operator description of their zero modes is not generally known. We generalize the bulk-to-boundary construction of localized zero mode operators to FQH-SCs with non-Abelian parent topological orders, mapping bulk Wilson operators in the folded theory to localized zero mode operators in the one-dimensional FQH-SC theory. This construction distinguishes zero mode anyons from the local zero mode operators that act on the defect Hilbert space and yields a generalized zero mode algebra. It also determines the fusion-channel dependence of tunneling: tunneling of zero mode operators probes bulk monodromy, while direct zero mode anyon transfer probes $G$-crossed associativity data. Applying this framework, we recover the $\mathbb{Z}_{2m}$ parafermion zero mode structure of fermionic Laughlin FQH-SCs at filling $\nu=1/m$, obtain a $\mathbb{Z}_2^{(n)}\times\mathbb{Z}_N$ structure for generalized Moore-Read states at filling $\nu=1/m$, with $N=2m$ for fermionic states and $N=m$ for bosonic states, and find a $\mathrm{Fib}\times\mathbb{Z}_N$ structure for the $k=3$ Read-Rezayi state at filling $\nu=3/(3M+2)$, with $N=2(3M+2)$ for fermionic states and $N=(3M+2)/2$ for bosonic states. In the Read-Rezayi case, zero mode operator tunneling and direct zero mode anyon transfer yield distinct universal amplitude ratios between the neutral fusion channels, providing a characteristic signature of the underlying Fibonacci defect structure.

I propose a simple visualization for pure two-qubit states, constructed from three components: two Bloch balls for the marginal qubits (the mixed states obtained by ignoring the other qubit, respectively) and an entanglement component consisting of a rotoreflection and a contraction. I prove that this picture accurately captures the local and global structure of the relevant state space without gaps or degeneracies: the underlying parametrization is a global diffeomorphism onto the state space. Finally, I use this picture to visualize conditional states, the entanglement degree(s) of freedom, and single qubit rotations.

Quantum numerical algorithms often encode a positive solution $q$ in the amplitudes of a quantum state, while the required scientific output is a normalized linear functional of $q$. Basis measurements produce probabilities determined by squared solution values, while the functional uses the solution values themselves. We study the complexity of this output-interface problem for $F_\phi(q)=\int\phi q\,\mathrm d\nu/\int q\,\mathrm d\nu$ and identify a target-dependent susceptibility $\chi_\phi$ that governs the amount of copies of the solution state needed. For a fixed positive reference state and a neighborhood around it, the optimal number of unknown-state copies is $\Theta\!\left(\chi_0\varepsilon^{-2}\log(1/\beta)\right)$, where $\varepsilon$ is the absolute error tolerance and $\beta$ is the allowed failure probability. We show that two fixed single-copy measurements attain the same rate. We then analyze how this baseline changes when the interface retains classical information, uses adaptive allocation, supplies coherent access, or restricts the allowed solution family. Therefore $\chi_\phi$ quantifies a central cost of using a solution encoded in an $L^2$-normalized quantum state to estimate an $L^1$-normalized linear observable.