Papers

Boson sampling arising from multiphoton interference in linear-optical networks is a prominent non-universal model for quantum computation. Here, by encoding the multi-qubit state to bosonic Fock state, we present a scalable quantum-circuit framework for simulating boson sampling on a universal quantum computing platform. Beginning with balanced beam-splitter transformations on the single- and two-photon sectors, we derive equivalent quantum-circuit implementations and unify them within a common Hilbert-space representation using an ancilla-assisted encoding. This construction is then generalized to arbitrary interferometers by replacing each optical beam splitter with a repeating quantum-circuit unit that selectively acts only within the relevant local interference subspace, requiring $N+1$ qubits for a two-photon $N$-mode interferometer and a linear-overhead subspace-identification procedure. Using this framework, gate-based quantum circuit for a four-mode boson-sampling circuit is developed and experimentally implemented on a four-qubit gate-based photonic qubit system. The qubit framework for emulating boson sampling of $n-$photons in $m-$mode will be useful to solve a broad class of sampling complexity problem on a gate-based quantum computers.

The existence of genuinely unextendible product bases (GUPBs), incomplete orthogonal sets of fully product states whose orthogonal complements contain no product vector across any bipartition, has remained an open problem. Here we construct GUPBs for any number $N\geq3$ of parties using classical maximum distance separable (MDS) codes. The MDS property imposes a rigidity on the induced product tiling across every bipartition; combined with Fourier mode deletion and a stopper state, this rigidity enforces genuine unextendibility. Consequently, the orthogonal complement of each GUPB is a genuinely entangled subspace whose normalized projector is invariant under partial transposition across every bipartition, yielding an explicit family of multipartite bound entangled states. We further construct GME witnesses that detect these states even though no fully decomposable witness can do so. Moreover, the resulting indistinguishability persists under arbitrary finite tensor powers and measurements separable across any bipartition. These results establish a direct connection between error-correcting codes and multipartite entanglement and provide an algebraic route to certifying genuinely multipartite bound entanglement.

Accurately determining the ground-state properties of quantum many-body systems remains a central challenge. In this work, we introduce an autoregressive projective quantum Monte Carlo (PQMC) framework that leverages recurrent neural networks (RNNs) to guide the stochastic dynamics. By incorporating autoregressive sampling into PQMC, we demonstrate substantial improvements in accuracy compared to standard unguided PQMC, while retaining polynomial computational cost. We benchmark our approach against conventional variational RNN ansätze and find that the autoregressive PQMC consistently achieves lower energies and higher fidelity, regardless of system size or whether the Hamiltonian is Hermitian or non-Hermitian. Our results highlight the versatility and power of neural-guided PQMC methods, paving the way for promising scalable simulations of low-energy states in complex quantum many-body systems.

Ordered magnets harbor intrinsically squeezed ground states and magnonic excitations characterized by entanglement between spins and nonclassical magnon number composition. A pathway to detecting the superpositions of noneigenmode magnon number states underlying these nonclassical magnetic ground states has recently been demonstrated by utilizing a qubit coupled to the magnon mode via a direct dispersive interaction. Here, we theoretically develop this qubit spectroscopy further delineating the capabilities and limitations of this qubit spectroscopy for sensing the quantum superpositions that underlie the excited states. We demonstrate that the spectroscopy lends itself naturally to unraveling the superpositions that underlie the various quantized squeezed-magnon number states. However, excited states comprising superpositions of multiple squeezed Fock states become increasingly hard due to the large number of possible transitions, and resulting peaks, in the qubit spectroscopy thereby requiring qubits with narrower linewidths. Along the same lines, we theoretically demonstrate the qubit spectroscopy of a low amplitude coherent squeezed-magnon state analyzing the tradeoff between frequency crowding due to multiple transitions and peak linewidths. Our work lays the groundwork and design equations for deploying high-quality qubits towards sensing the composite nature of spin excitations in magnetic systems.

Quantum heat transport for non-equilibrium steady state (NESS) exhibits a characteristic turnover effect, where the heat current reaches a maximum and subsequently declines as system-bath coupling increases. Although numerically exact methods can simulate this non-monotonic behavior, they offer limited information on the thermal state of the heat baths. Here, we introduce a frequency-selective thermometric protocol to probe the baths sustaining an NESS. By extracting a frequency-resolved effective temperature spectrum using a tunable two-level probe, we demonstrate that spectral dispersion serves as a direct witness for the non-equilibrium state of the heat baths. To demonstrate the protocol, we applied the hierarchical equations of motion to spin-boson and two-qubit models, though any exact method can be used. For both models, the turnover effect can be explained by how the thermal state of the heat baths evolves as the system-bath coupling strength increases.

Qubit coherence is an essential figure of merit for quantum information processing applications such as quantum computing, or quantum repeaters. Understanding the coherence properties of the underlying physical qubits that facilitate such applications is therefore are often limited by coupling to lattice phonons, which in turn constrains operation temperature. Here we study phonon induced electronic spin decoherence in group-IV vacancy centers in diamond. We begin by modeling the spin-phonon interaction and then employ the widely used Born-Markov approximation, highlighting its inconsistencies in this setting and its deviations from experimental observations. To close the gap between theoretical predictions and experimental results, we relax certain approximations, investigate their contributions to the predicted coherence times, and identify the dominant sources of discrepancy. We further demonstrate that experimentally measured electronic spin coherence dynamics are consistently captured within a non-Markovian framework, and we show how the magnetic field orientation influences the qubit coherence time.

We present the concept and development of a novel accelerator-based source of high-intensity quantum-entangled 511 keV gamma-ray pairs produced through positron-electron annihilation. The source leverages the unique capabilities of the proposed Jefferson Lab positron facility to generate polarized, high-current positron beams with a well-defined time structure. These beams enable the production of entangled annihilation photons at intensities far exceeding those available from conventional radioactive sources. The resulting gamma-ray pairs can be characterized using Compton polarimetry techniques, providing a powerful platform for precision studies of quantum entanglement. The combination of high intensity, controllable polarization, and precise timing also opens new opportunities in medical imaging, materials science, quantum information science, and spintronics. Compared with traditional radioactive sources, the proposed system offers orders-of-magnitude higher photon flux, tunable beam parameters, and unprecedented control of the annihilation process. We discuss the source design, methods for entanglement characterization, potential applications, and future development directions.

Mobile nanodiamond quantum sensors in liquids are affected by Brownian rotation, variable photon collection, and perturbations from optical trapping. Here we assemble 40-nm nitrogen-vacancy nanodiamonds on porous, birefringent vaterite microspherulites, creating mobile sensors with a polarization-addressable body frame and a chemically active carbonate interface. Under 976-nm trapping, the sensors retain spin resonance and longitudinal relaxation, with less than 7% variation in contrast and an approximately 1-MHz resonance shift at 0.8 W. Zeeman-split resonances resolve magnetic fields from 0 to 0.8 mT, with a response metric of 78–144 $\mu$T Hz$^{-1/2}$. In cell-culture medium, a 10.7-$\mu$M proton-equivalent dose shortens $T_1$ from $23.4 \pm 2.3$ to $9.0 \pm 1.2$ $\mu$s, yielding concentration and pH sensitivities of $6.46$ $\mu$M Hz$^{-1/2}$ and $6.54$ mpH Hz$^{-1/2}$, respectively. A 500-fold larger proton dose in ethanol produces a weaker response. A grand-canonical charge-regulation model links proton chemical potential to interfacial switching, establishing a route to multimodal quantum sensing in complex liquids.

In this paper we introduce the new version of QTris, a board game designed to teach and learn Quantum Mechanics within the framework of Quantum Information and Computation. The key idea behind the game is that every game sequence simulates a process on a system of qubits. Thus, QTris can be effectively integrated as a pedagogical tool to teach Quantum Mechanics at high-school level following a two-state approach. After arguing in support of this latter approach, we describe QTris' basic rules and some of its possible extensions, emphasizing how the game mechanics puts in clear light key quantum concepts such as incompatibility, probabilistic measurement and unitary transformation. Moreover, we report on the results of a QTris-based educational activity which involved about 150 high-school students and provided encouraging preliminary indications that QTris can be a useful pedagogical platform to promote an immediate understanding of some key concepts of Quantum Mechanics.

We present an analysis on the geometrical and physical nature of the $p_x + ip_y$ superconductor on the square lattice, with an emphasis on the topological phase transition at half-filling. We develop a local topological marker from specific Dirac points within the Brillouin zone, which is introduced via the addition of two one-dimensional (1D) $\mathbb{Z}$ $(\mathbb{Z}_2$) invariants defined on the Bloch sphere. We relate this topological marker to the electron spectral function integrated on frequency through the local momentum-resolved electron density, which may be measured via Angle Resolved Photoemission Spectroscopy (ARPES), and show that it remains well-protected including temperature effects. Integrating on a small area around a specific point in momentum space associated to the measure uncertainty, this also reveals the Van Hove logarithmic profile of the density of states in the derivative of the local marker while preserving the topological information. Topological transitions correspond to a protected semi-metal. We analyse the real space representation of this topological marker from correlation functions. We present physical responses such as the topological superfluid density.

We derive the four principal asymptotic rate-distance tradeoffs for binary codes—Plotkin, Elias–Bassalygo, and the two McEliece–Rodemich–Rumsey–Welch (MRRW) bounds—from one theorem, the “pretty good criterion.” If the bit error rate under the pretty good measurement (PGM)—the quantum analog of posterior sampling—of a binary-input output-symmetric classical–quantum (cq) channel lies below $\delta$, then every length-$n$ binary code, linear or nonlinear, of relative distance $\delta$ has rate at most the channel's capacity, up to an $O(n^{-1/2})$ correction. Rate–distance bounds thereby reduce to a channel design problem, wherein the task is to minimize channel capacity subject to the posterior bit error rate constraint. Via the pretty good criterion, the binary erasure channel (BEC) yields Plotkin, the binary symmetric channel (BSC) yields Elias–Bassalygo, the pure-state channel (PSC) yields the first MRRW bound, and a masked PSC yields the second MRRW bound exactly. This framework is then instantiated with new channels to improve upon the MRRW bounds. Specifically, the mixed-qubit channel (MQC), a mixed-state version of PSC, strictly improves the first MRRW bound at every $0 < \delta < \frac{1}{2}$, while the masked mixed-qubit channel (2MQC) strictly improves the second MRRW bound throughout the same interval.

In this work, we demonstrate a quantum pulse gate (QPG) in thin-film lithium niobate. QPGs enable the selective manipulation and detection of temporal modes of quantum light and form the basis of numerous applications in photonic quantum technologies. To date, their widespread adaption is held back by two main limitations: restricted wavelength and polarization combinations of the involved fields and low normalized conversion efficiencies. We overcome these limitations through developing a QPG in thin-film lithium niobate. We design a waveguide geometry that provides the required dispersion properties for a highly efficient type-0 sum-frequency generation.We verify our design through mapping of the phase matching intensity, and demonstrate high-quality QPG operation by measuring a temporal-mode selectivity of (96.8$\pm$1.7)% on par with existing QPGs. Thanks to the strong confinement in thin-film lithium niobate, we succeed in demonstrating an internal conversion efficiency of (89.6$\pm$0.1)% for a pump power of only 20mW in front of our sample. This yields a lower-bound estimate for the normalized conversion efficiency of (1810$\pm$10)$\mathrm{W}^{-1}\mathrm{cm}^{-2}$, three orders of magnitude higher than in previous QPGs. Our results establish thin-film lithium niobate as ideal platform for high-performance QPGs and are a major step towards practical QPGs for photonic quantum technologies.

We investigate the implementation of controlled-phase (CP) gates with quantum walks in a dual-rail encoding through the use of interacting particles. While previous proposals have focused on indistinguishable particles (bosons or fermions) to achieve unitary fidelity for plane-wave scattering, practical implementations require finite-size wavepackets and routing through single-particle gates, both factors that introduce unavoidable fidelity losses. We show that extending the interaction range beyond on-site or first-neighbor terms provides sufficient control over the scattering potential to engineer CP gates with distinguishable particles that match the ideal bosonic/fermionic performance. For finite Gaussian wavepackets, we derive analytical approximations for the gate fidelity in terms of the transmission coefficient's magnitude and phase derivatives. We find that while distinguishable-particle scattering alone exhibits slightly lower fidelity than the indistinguishable case, the overall architecture that we propose avoids the additional single-particle gates required for routing indistinguishable particles. The roundabout gates needed for the latter indeed introduce fidelity losses approximately one order of magnitude larger than the interaction-induced losses, making the distinguishable-particle approach competitive for practical implementations. Our results establish multi-neighbor interactions as a tool for quantum information processing with continuous-time quantum walks and provide quantitative guidelines for optimizing gate fidelities in finite-size systems.

We develop a classical model-theoretic representation of partial Boolean algebras and use it to formulate quantum-like uncertainty without abandoning classical propositional logic. Given a surjection from the initial formulæ\ of a propositional language onto a partial Boolean algebra $(\mathcal V,\Pi)$, we construct a consistent theory $\mathcal T_g$ whose core—the ordered set of equivalence classes of initial formulæ—is isomorphic to $(\mathcal V,\Pi)$. Its models are characterized as upward-closed clusters, yielding a model-theoretic formulation of KS-colourability: an $n$-dimensional partial Boolean algebra is KS-colourable exactly when the induced theory has a model meeting every pre-frame in one primitive formula. For finite-spectrum observables, uncertainty is defined by the number of locally admissible atomic outcomes. Dispersion-free models are characterized by the singleton pre-frame condition. With an additional measurement-update postulate, a finite example shows how measurement of an incompatible observable can destroy sharpness, providing a model-theoretic form of back-action. A $12$-vertex partial Boolean algebra is KS-colourable, whereas a rigorously constructed $140$-vertex, four-dimensional partial Boolean algebra is not, as shown by a parity argument; its incidence structure is isomorphic to the Peres $24$-ray, $24$-basis configuration in $\mathbb R^4$. Macroscopic interpretations show that these phenomena arise from the organization of propositions and models rather than from nonclassical deduction. Finally, we relate certain models to the probability-one propositions of pure states and density operators, while emphasizing that such certainty models do not determine the full quantum state.

We formulate and exactly solve a model for coherent association and dissociation of fermionic heteronuclear dimers in the deep-lattice Mott regime. Starting from the onsite three-component atom–molecule Hamiltonian, we show how the single-site model maps to the paradigmatic Jaynes–Cummings Hamiltonian from quantum optics. In this mapping, the fermionic molecular/free-atom sector forms an effective two-level system, while the bosonic atomic mode plays the role of the oscillator degree of freedom. We fix the conserved number of fermionic constituent atoms to one but allow an arbitrary conserved number $N$ of bosonic constituent atoms. The accessible doublet is then $|e,N-1\rangle\leftrightarrow|g,N\rangle$, and the coherent conversion coupling is bosonically enhanced to $\chi\sqrt{N}$. Exact analytic expressions are derived for molecular dissociation, atom-pair association, mode populations, and boson–fermion correlation dynamics. The model provides a transparent matter-wave realization of Jaynes–Cummings physics in a heteronuclear Bose–Fermi system and an exactly solvable setting for understanding coherent atom–molecule conversion and bosonic enhancement in lattice systems.

Architectural specialization and distribution can help scale fault-tolerant quantum computers, but may also introduce substantial overheads from communication, routing, and resource duplication. We introduce a heterogeneous distributed architecture in which a magic core is connected to an extensible storage system composed of one-dimensional lanes of specialized cold-storage nodes. The storage system supports parallel random access to Pauli string parities. This organization is particularly well suited to fermionic quantum simulation, enabling parallel execution of the highly non-local Pauli strings arising from these systems. We evaluate the architecture on fault-tolerant simulations of the dynamics of the Fermi-Hubbard and sparse Sachdev-Ye-Kitaev (SYK) models on systems of up to 450 logical qubits. These workloads exhibit complementary communication structures: Fermi-Hubbard produces a spectrum of interactions from local to non-local shaped by lattice geometry, whereas sparse SYK produces highly non-local and overlapping Pauli operators. For a Trotter step of a 450-logical-qubit Fermi-Hubbard workload, a six-lane system with 30 T-state factories is within approximately $1.4\times$ the wall-clock time of a homogeneous distributed architecture with 4 times as many T-state factories and substantially greater connectivity and sites for injecting magic. For matched T-factory counts, our architecture is $\sim 2\times$ faster.

Nitrogen vacancy centers in diamond have established themselves as good sensing element for various type of sensors. In particular magnetometers based on diamond impurities are quickly developing and are already on the market. Yet, optical readout in these systems complicates system design. Recently schemes of dispersive readout of nitrogen vacancy spin state using high finesse dielectric cavities for microwave field were proposed, which do not use the optical readout scheme. However, only shot noise based estimates were so far done for sensitivity of these devices. Here we provide detailed analysis of various practically relevant noise and loss sources for such a system. Furthermore, we consider the possibility of using the squeezing quantum state of the probing microwave field and show it allows to improve the device performance even at room temperature.

Physical conservation laws, such as those of energy and momentum, are generally believed to hold exactly and locally in spacetime, including in quantum phenomena. Yet Aharonov, Popescu, and Rohrlich (APR) recently argued, on the basis of a thought experiment, that individual quantum events, unlike ensemble averages, may occasionally violate local conservation laws. Their argument relies on the wave phenomenon known as "superoscillations", which APR themselves discovered more than 30 years ago. Here we provide experimental evidence for such a violation. We extract photons from a small superoscillatory region near the core of an optical vortex and show that their mean transverse momentum is statistically incompatible with a general bound implied by local momentum conservation. The derivation of this bound requires only the theoretically well-supported assumption that the extraction mechanism does not alter the photons' mean transverse momentum. We also detect photons with high transverse momentum at a rate significantly exceeding that predicted by a model assuming local momentum conservation. Because this violation can be established only counterfactually and through postselection, it does not conflict with relativistic causality. Our results may represent the first example of a distinct form of quantum nonlocality that does not explicitly rely on entanglement.

One of the obstacles to the widespread adoption of quantum computing is the problem of efficient circuit synthesis. Current quantum hardware has limited connections between qubits, with each qubit connected to only a few others. This means that the circuit has to be transformed to accommodate this. In this paper, we present an algorithm that converts a circuit containing a sequence of CNOT gates into a form that is suitable for arbitrary quantum computer architectures. Although we demonstrate the algorithm only in the context of quantum fingerprinting, similar gate sequences are prevalent in quantum algorithms; for instance, they are present in the textbook quantum Fourier transform. We present a quantum circuit implementation of the quantum hashing algorithm (quantum fingerprinting algorithm) for a quantum device with restrictions on the application of two-qubit gates that are expressed as a qubit connectivity graph. As an example of usage of the technique, we apply it to quantum finite automata recognizing the unary $MOD_p=\{a^\ell: \ell \bmod p=0\}$ language, and the $EQ_p=\{a^\ell b^r: \ell \equiv r \pmod p\}$ language. Given the enhancements that our algorithm provides~– for instance, in one case it achieves a 16%–17% decrease in CNOT circuit cost~– we believe it could also be useful in a broader quantum compilation context.

Hole-phonon interactions play an important role in transport and decoherence processes in semiconductor quantum dots. Here we investigate hole-phonon coupling in a gate-defined GaAs double quantum dot integrated with a quantum point contact charge sensor. Under finite source-drain bias, pronounced oscillatory stripe patterns appear near specific charge transition regions in the charge stability diagram. We attribute these oscillations to phonon emission during inelastic interdot tunneling. A theoretical model including piezoelectric hole-phonon coupling reproduces the observed patterns. Furthermore, our analysis shows that the oscillations emerge only in particular charge configurations. Our results provide direct insight into phonon-assisted transport and coherent hole-phonon interactions in semiconductor quantum dots.

Bicycle (two-block circulant) quantum low-density parity-check (LDPC) codes include some of the best known small quantum codes, yet their design has relied on group-algebra formulations in which the dimension and distance are accessible only through matrix computation. We show that in the cyclic case the construction collapses into the polynomial ring $\F_2[x]/(x^{l}-1)$: self-orthogonality is automatic, the quantum dimension is read off from a polynomial gcd, and the minimum distance is certified exactly through the Calderbank correspondence to additive codes over $\F_4$, turning code search into an algebraically pre-filtered enumeration that reaches parameter regimes poorly covered by existing tables. A computer search based on this framework recovers the short codes $[[42,12,4]]_2$ and $[[62,12,4]]_2$ and produces a family of codes with competitive figure of merit $kd^2/n$, including $[[66,20,7]]_2$ with $kd^2/n=14.85$, above the bivariate bicycle code $[[144,12,12]]_2$ ($kd^2/n=12$) at less than half the block length, together with $[[46,2,8]]_2$, $[[66,2,9]]_2$, $[[66,4,8]]_2$, $[[66,6,8]]_2$ and, at $n=90$, $[[90,16,6]]_2$, $[[90,18,6]]_2$, $[[90,20,6]]_2$. An exhaustive census at $n=48$ delineates the boundary of this picture: we exhibit a $[[48,10,6]]_2$ code from a minimal $48$-element group (the Aydin–Tamo–Barg realization uses $72$ elements), and prove that distance $5$ forces a stabilizer-rank loss, which excludes $[[48,10,5]]_2$ from the weight-$8$ symmetric coset family. The framework thus opens a systematic route to bicycle-type quantum LDPC codes beyond the reach of group-theoretic searches, and identifies exactly where genuinely coset-theoretic phenomena begin.

Multipartite entanglement is conventionally classified by state families viz. family of GHZ and W class of states, with each family expected to behave differently under measurement. We show that, at least for the question of how entanglement splits after a single-particle measurement, this is not the division that matters for qutrits. Extending the Aravind's correspondence (which models entanglement as topological linking, and projective measurement as physically cutting a ring from an interlinked configuration\cite{aravind1997}) from qubits to qutrits, we derive the complete measurement-induced entanglement splitting of the GHZ type qutrit state i.e |GHZ_3> and of the full family of symmetric W class qutrit states, six two same - one different states i.e |{W_{p,p,q}^{sym}}> and one all - different state i.e. |W_{0,1,2}>, under both the computational basis (CB) and the mutually unbiased bases (MUBs), obtaining exact eigenvalues and Schmidt ranks for every outcome in every case. We see that the |W_{0,1,2}> state behaves similarly as |GHZ_3> state, a single, outcome-independent residual rank in each basis, while the |{W_{p,p,q}^{sym}> states alone show probability-weighted, outcome-dependent behaviour. The relevant structural line is therefore repeated-index versus all-different-index bag structure, not GHZ class versus $W$ class. We express this classification using a two-strand cabling extension of Aravind's ring-and-link picture. This is needed because the qutrit residual Schmidt rank (R) takes three values, R belonging to {1,2,3}, rather than the qubit binary (i.e. R belonging to {1,2}). We are explicit throughout that this cabling dictionary is a labeling convention built to reproduce an independently computed Schmidt rank, not a topological invariant derived from the link diagrams themselves, and we discuss what would be needed to close that gap

Electron-phonon coupling has been a central topic in condensed matter physics for decades, and firstprinciples methods have demonstrated remarkable success in quantitatively capturing its role in a wide variety of physical phenomena and materials. Conventional calculations of electron-phonon coupling typically assume that phonons have infinite lifetimes, but phonons can exhibit finite lifetimes due to anharmonic phonon-phonon interactions. In this work, we derive an expression for the electron-phonon coupling scattering rates including the effects of anharmonic three-phonon interactions, which lead to phonon dephasing and finite phonon lifetimes. We also describe a first-principles implementation of this anharmonic electron-phonon coupling which can be seamlessly integrated within existing workflows for the evaluation of electron-phonon and phonon-phonon coupling interactions. Finally, we present calculations of electron-phonon scattering rates including phonon dephasing in a range of materials, and discuss the different microscopic mechanisms by which anharmonic phonons influence electron-phonon coupling. This study establishes the importance of finite phonon lifetimes in the evaluation of electron-phonon coupling, and provides a platform to explore these effects in a wide range of materials and phenomena.

Multiple quantum computing platforms across neutral atoms [1], nitrogen vacancy centres [2, 3], gate-defined dots [4-6] and 14|15 phosphorus atom qubits [7, 8] in silicon are experimentally exploring the use of high connectivity qubits, beyond that of nearest-neighbour planar lattices. Theoretical works consider modifications to fault-tolerant codes to leverage this higher qubit connectivity, such as non-local LDPC codes [9], inspiring superconducting [10] and photonic [11] platforms to also seek non-planar connectivity. In addition, separate theoretical works consider biased noise, where bit- and phase-flip errors are not equally likely. In this work, we present efficient methods for implementing 6.6.6 and 4.8.8 colour codes, as well as bilayer and folded surface codes, using two-qubit registers. We also leverage noise bias to avoid hook errors, demonstrating comparable performance to the surface code. By combining colour and bilayer codes, we show how magic state cultivation procedures [12-14] can be improved, in a procedure we refer to as the Magic Scroll. Not only does the Magic Scroll escape to a standard surface code, it also improves cultivation volumes by 3x and supports magic $|T\rangle$ state fidelities as low as $10^{-9}$. We show that this technique can be further leveraged to improve distillation performance, showing a 3x improvement to distillation volumes for error rates of $\sim 10^{-15}$. Through these constructions, we demonstrate techniques to leverage noise bias and high qubit connectivity, showing how register-based architectures can improve error rates and reduce quantum volumes in fault-tolerant quantum computing.

Programmable microcavities support grand-canonical photon gases. We show that bosonic state counting creates an entropic staircase of most-probable total occupations. For detuning density continuous and nonzero at the chemical-potential threshold, the active-cell fraction is asymptotically linear at low temperature and the conditional law has a universal limit; for uniform disorder the law is exact over a finite temperature interval. For two modes it is the Gauss–Kuzmin distribution, linking photonic thermodynamics and metric number theory. We outline finite-array and dye-microcavity tests.

Quantum low-density parity-check (qLDPC) codes can encode multiple logical qubits using sparse parity checks, yet searching for useful finite-length instances remains a challenging design problem because code performance must be optimized while satisfying practical constraints. Motivated by recent advances in artificial-intelligence agents for scientific discovery, we develop a multi-agent framework for discovering practical qLDPC codes. The framework combines specialist proposal and review, persistent scientific memory, long-horizon evolution of executable programs, and deterministic construction and evaluation within a closed-loop search. These programs instantiate coset-orbit balanced-product codes, providing a search space that includes bicycle and lifted-product constructions as well as non-normal subgroup actions. To incorporate practical constraints, we restrict the search to binary CSS codes with block length $n\leq400$ and overall weight $w\leq10$. Within this regime, the framework discovers codes with leading or competitive rate–distance performance in every weight class considered, with representative instances including $[[288,16,18]]$ at $w=7$, $[[288,18,18]]$ at $w=9$, and $[[234,28,18]]$ at $w=10$. The search also uncovers structurally distinct, high-performing constructions, including a $[[336,12,\leq24]]$ candidate and a $[[368,18,16]]$ code, both of which are genuine balanced-product constructions with non-normal subgroup actions. When evaluated under code-capacity depolarizing noise using a common BP-OSD decoding protocol, the discovered codes also exhibit low logical failure rates. Together, these results provide hardware-relevant finite-length candidates for further experimental evaluation and show how structured agentic search can contribute to scientific discovery.

A sodium laser guide star operated as a mesospheric magnetometer modulates a 589 nm laser at the local Larmor frequency and usually diverts a fraction of its power to a repumping light that recovers atoms lost to the dark ground state.The polarization, read out for the most strongly driven velocity group, calls for 2.8 times the flux optimal fraction, and a shot noise figure of merit combining the two observables for 2 times, beyond the range commercial guide star lasers provide.

Autonomous quantum thermal machines have recently been proposed as physics-based computing substrates where logical inputs and outputs are encoded in temperature gradients. While such “thermodynamic neurons” exhibit a clear trade-off between computational fidelity and heat dissipation, the fundamental information-theoretic limits of temperature-encoded computation remain uncharacterized. Here, we derive rigorous bounds linking average error probability, channel capacity, and entropy production for finite-capacity thermal reservoirs operating far from equilibrium. We prove that the minimal dissipation required to achieve a target average error probability $\langle \xi \rangle$ diverges as $\langle \xi \rangle$ approaches a fundamental minimum error floor $\epsMin$ imposed by finite-reservoir thermal fluctuations. We further establish a thermodynamic channel capacity that saturates at high dissipation, and quantify the minimal dissipation required for cascaded networks to maintain target fidelity. We demonstrate that the required dissipation grows linearly $\mathcal{O}(L)$ with network depth for shallow networks, but diverges as the network depth $L$ approaches a fundamental maximum limit $L_{\max} = \epsNet/\epsMin$ imposed by the minimum error floor. Furthermore, under strong noise amplification conditions, the required dissipation can grow up to $\mathcal{O}(L^3)$. Our framework bridges stochastic thermodynamics, finite-time information theory, and autonomous computation, providing rigorous design principles for energy-efficient analog thermodynamic hardware.

Quantum mechanics is difficult to teach because its conceptual content and mathematical notation usually arrive together. Rudolph's misty-state language was designed to decouple those burdens; basis states are visual objects, clouds represent superposition, gates act by elementary replacement rules, and destructive interference appears as cancellation rather than as matrix calculation. An elementary “misty-state” language can make quantum circuits accessible to students before they master complex linear algebra. Development presented here was initiated/led by the first author. The contribution is not a replacement for complete graphical calculi such as ZX or sum-over-paths. It is a source-specific bridge from an intuitive educational notation to a mathematically explicit, executable, and falsifiable semantics.

Phase singularities are topological defects around which the phase winds by an integer multiple of $2\pi$. In entangled multiphoton states, they can emerge nonlocally in the joint wavefunction rather than in the field of either subsystem alone. Here we show that the quantum Gouy phase generates nonlocal phase singularities (NPSs) in the two-dimensional longitudinal propagation space of entangled photon pairs. We consider photon pairs produced via spontaneous parametric down-conversion pumped by a Laguerre–Gaussian beam, with the signal and idler photons propagating independently over different longitudinal distances. The accumulated radial-mode-dependent Gouy phases induce destructive interference among biphoton spatial-mode components, producing isolated intensity nulls with quantized phase winding. For a pump with radial mode number $p$, the NPS topological charges have magnitude $p$, whereas their propagation positions and charge signs are governed by the Rayleigh ranges of the pump and phase-matching functions. We further identify the radial-mode structure required for their formation, showing that separable biphoton states cannot support isolated longitudinal NPSs. Our results extend nonlocal singular optics from transverse spatial correlations to longitudinal propagation dynamics and establish propagation distance as a coordinate space for topological structures in entangled photon pairs.