We propose a concept for a cryogenic source of atomic tritium at sub-Kelvin temperatures and energies suitable for magnetic trapping. The source is based on the dissociation of solid molecular ${\mathrm{T}}_2$ films below 1 K by electrons from a pulsed rf discharge, a technique recently demonstrated for atomic hydrogen, combined with buffer-gas cooling and magnetic confinement. We analyze the key processes limiting the source performance, adsorption, spin exchange, and recombination, and show that atomic tritium fluxes exceeding ${10}^{15} {\mathrm{s}}^{-1}$ at temperature of $\sim 200$ mK can be achieved. Such a source would enable Doppler-free two-photon $1S$–$2S$ spectroscopy in atomic tritium for high-precision measurements of the triton charge radius, providing a crucial benchmark for bound-state QED and improving the comparison between electronic, muonic, and scattering determinations of nuclear sizes in light systems. Beyond spectroscopy, using atomic tritium source avoids molecular final-state broadening in $\beta$ decay and is therefore necessary for next-generation neutrino-mass measurements; combined with detector technologies such as sub-eV resolution quantum sensors or cyclotron radiation emission spectroscopy, it enables an order-of-magnitude improvement compared to the current best experimental limit. Additionally, the source can be used to generate a beam of low-field-seeking deuterium atoms for loading magnetic traps, an important benchmark before trapping tritium atoms, which is useful for precision spectroscopy.

We explore the feasibility of realizing Dicke states in qubit arrays with always-on isotropic Heisenberg coupling between adjacent qubits, assuming a single Zeeman-type control acting in the $z$ direction on an actuator qubit. The Lie-algebraic criteria of controllability imply that such an array is not completely controllable, but satisfies the conditions for subspace controllability on any subspace with a fixed number of excitations. Therefore, a qubit array described by the model under consideration is state-to-state controllable for an arbitrary choice of initial and final states that have the same Hamming weight. This limited controllability is exploited here for the time-efficient dynamical generation of an $a$-excitation Dicke state $|D_a^N\rangle$ ($a=1,2,...,N-1$) in a linear array with $N$ qubits starting from a generic Hamming-weight-$a$ product state. To dynamically generate the desired Dicke states—including $W$ states $|W_N\rangle$ as their special ($a=1$) case—in the shortest possible time with a single local $Z$ control, we employ an optimal-control scheme based on the dressed chopped random basis (dCRAB) algorithm. We optimize the target-state fidelity over the expansion coefficients of smoothly varying control fields in a truncated random Fourier basis; this is done by combining Nelder-Mead-type local optimizations with the multistart-based clustering algorithm that facilitates searches for global extrema. In this manner, we obtain the optimal-control fields for Dicke-state preparation in arrays with up to nine qubits. Based on our numerical results, we find that the shortest possible state-preparation times scale as $\mathcal{O}\left(N^{2.08}\right)$ for $W$ states and $\mathcal{O}\left(N^{1.78}\right)$ for $a=2$ Dicke states. Finally, we demonstrate the robustness of our dCRAB-based state-engineering scheme against various types of imperfections of relevance for its anticipated experimental implementation.

We investigate the electronic structure of ${\mathrm{AgF}}_2, {\mathrm{AgFBF}}_4$, AgF, and ${\mathrm{Ag}}_2\mathrm{O}$ using x-ray absorption spectroscopy (XAS) and resonant inelastic x-ray scattering (RIXS) at the Ag $L_3$ edge. XAS results were compared with density functional theory computations of the spectra, allowing an identification of main features and an assessment of the theoretical approximations. Our RIXS measurements reveal that ${\mathrm{AgF}}_2$ exhibits charge-transfer (CT) excitations and $dd$ excitations, analogous to those observed in ${\mathrm{La}}_2{\mathrm{CuO}}_4$. We propose to use the ratio of $dd$ to CT spectral weight as a measure of the covalence of the compounds and provide explicit equations for the weights as a function of the scattering geometry for crystals and powders. The measurements at the metal site $L_3$ edge and previous measurement in the ligand $K$ edge reveal a striking similarity between the fluoride and cuprate materials, with fluorides somewhat more covalent than cuprates. These findings support the hypothesis that silver fluorides are an excellent platform to mimic the physics of cuprates, providing a promising avenue for exploring high-$T_c$ superconductivity and exotic magnetism in quasi-two-dimensional (${\mathrm{AgF}}_2$) and quasi-one-dimensional (${\mathrm{AgFBF}}_4$) materials.

By means of cellular dynamical mean-field theory (CDMFT), we study how short-range correlations drive the breakdown of the self-consistent perturbation theory in two-dimensional systems and the most relevant physical consequences associated with it, such as the CDMFT Mott transition. To this aim, we first derive in a structured and consistent way the Bethe-Salpeter equation (BSE) formalism at the CDMFT level in all physical channels, explicitly addressing the important aspect of the related Ward identities. In this context, we perform systematic calculations of the BSE for the two-dimensional Hubbard model at half filling at intermediate coupling. Our study illustrates how the divergence of a fundamental building block of the BSE in the charge channel, the two-particle irreducible vertex, systematically occurs at lower interactions than in the (purely local) DMFT case. We establish that these divergences are a prerequisite for the CDMFT Mott instability in two dimensions, which occurs at larger interaction values, and explicitly demonstrate that both are driven by short-ranged antiferromagnetic spin fluctuations.

Global gyrokinetic simulations are performed for the first time to investigate cross-scale interactions between electromagnetic ion temperature gradient (ITG) turbulence and fishbone instability in tokamak plasmas. The investigation of fluctuation response in the multiscale simulation including both instabilities indicates a strong impact of fishbone on ITG turbulence. Detailed analysis reveals that fishbone-driven zonal radial electric fields at nonlinear saturation significantly suppress electromagnetic ITG turbulence, reducing ion thermal transport close to the neoclassical level. The simulation results agree well with experimental observations of turbulence suppression during fishbone bursts. These findings advance understanding of multiscale interactions that enhance thermal confinement in fusion plasmas.

Quantum phase estimation is a cornerstone algorithm for fault-tolerant quantum computation, especially for electronic structure calculations of chemical systems. Optimal simulation relies on a complex trade-offs across many parameters including Hamiltonian simulation techniques, basis sets, and the fermion-to-qubit encodings. Here, we characterize the trade-offs and quantify the quantum resource costs of the sorted-list encoding as a particle-conserving, low-qubit alternative to the Jordan-Wigner encoding. We identify specific regimes, across different simulation techniques and basis sets, where the sorted-list encoding would be favorable compared to existing methods. Our findings are further supported through numerical benchmarks of real-world chemical systems. We found the sorted-list encoding to be a viable alternative to the Jordan-Wigner encoding for the compact molecular orbital basis when the electron-filling ratio is low, which typically occurs when high-precision results are required. In the plane-wave basis, we found similar asymptotic gate and qubit scaling between the sorted-list and the first-quantized encoding, although the first-quantized encoding still retains lower constant factors.

We propose a scheme to realize nonreciprocal multiphoton bundle emission in a spinning resonator. The system consists of a rotating two-mode cavity directly coupled to a two-level atom, enabling efficient excitation of the desired multiphoton bundle states. These photon bundles originate from leapfrog transitions between dressed states, established through the coherent atom-cavity coupling under multiphoton resonance conditions. When the rotating resonator is driven in different directions, it generates opposite Sagnac-Fizeau shifts, making the resonant conditions dependent on the direction. As a consequence, distinct multiphoton transition channels can be selectively activated by tuning the driving direction and frequency. The nonreciprocal two-photon or three-photon bundle emission with the same and different modes can be implemented with a high tunability. This scheme provides a feasible route toward direction-controlled multiphoton emitters with potential applications in chiral quantum information processing.

Rydberg atoms efficiently link photons between the radio-frequency (rf) and optical domains. They furnish a medium in which the presence of an rf field imprints on the transmission of a probe laser beam by altering the coherent coupling between atomic quantum states. The immutable atomic energy structure underpins quantum-metrological rf-field measurements and has driven intensive efforts to realize inherently self-calibrated sensing devices. Here, we investigate spectroscopic signatures owing to the quantization of atomic angular momentum. Using an electromagnetically induced transparency (EIT) sensing scheme, specific combinations of atomic terms are shown to give rise to universal, distinctive fingerprints in the detected optical fields upon rotating a linearly polarized rf field. Employing a dressed state picture, we identify two types of atomic angular momentum ladders that display strikingly disparate spectroscopic characteristics, including the distinctive absence or presence of a central spectral EIT peak. Our study adds important insights into the prospects of Rydberg atomic gases for quantum-metrological electric field characterization including polarimetry. In particular, it calls into question prevailing interpretations of SI-traceable Rydberg atom electrometers.

We develop an analytical approach for steady-state normal-ordered magnon moments (NOMMs) in a driven-dissipative magnon-qubit system with coherent and dissipative couplings, and further benchmark it against the full quantum master-equation simulations of mean magnon number and second-order intensity correlation function, $g^{\left(2\right)}\left(0\right)$. Specifically, we first show that strong coherent coupling alone can produce an intermediate-pump magnon-lasing-like emission window, identified by a small-signal stability criterion and characterized by near-Poissonian statistics $[g^{\left(2\right)}\left(0\right)\simeq 1]$ and pronounced linewidth narrowing. For dissipative coupling alone, the magnon emission exhibits nonclassical antibunching $[g^{\left(2\right)}\left(0\right)<1]$ at the optimal mean magnon number and features a large pump-tunable spectral linewidth. In the hybrid dissipative and weak-coherent-coupling regime, the dissipative channel can substantially enhance the steady-state mean magnon number while simultaneously inducing strong magnon antibunching, with $g^{\left(2\right)}\left(0\right)\ll 1$. The results obtained here may find potential applications in microwave-magnonic and related hybrid quantum platforms, and the analytical NOMM method could also provide a route to treating other driven open boson-fermion systems.

We introduce a reinforcement-learning algorithm designed to identify the fixed points of a given quantum operation. The method iteratively constructs the unitary transformation that maps the computational basis onto the basis of fixed points through a reward-penalty scheme based on quantum measurements. In cases where the operation corresponds to a Hamiltonian evolution, this task reduces to determining the Hamiltonian eigenstates. The algorithm is first benchmarked on random Hamiltonians acting on two and three qubits and then applied to many-body systems of up to six qubits, including the transverse-field Ising model and the all-to-all pairing Hamiltonian. In both cases, the algorithm is demonstrated to perform successfully; in the pairing model, it can also reveal hidden symmetries that can be exploited to restrict learning to specific symmetry sectors. Finally, we discuss the possibility of postselecting high-fidelity states even when full convergence has not been reached.

We present a rigorous derivation of the matrix elements of the orbital magnetic moment (OMM) of Bloch states. Our calculations include the Berry connection term in the $k$-derivatives of Bloch states, which was omitted in previous works. The resulting formula for the OMM matrix elements applies to any nondegenerate Bloch states within Hilbert space. We identify two new contributions: The first restores gauge covariance for nondegenerate states, while the second, being itself gauge covariant, can provide significant quantitative corrections depending on the system under study. We examine their impact on the orbital Hall effect in two bilayer systems: a 2H transition metal dichalcogenide bilayer and a biased bilayer graphene. In both cases, these new terms reduce the orbital Hall conductivity plateau compared with results that neglect them, suggesting that multilayered van der Waals materials may be particularly susceptible to the derived OMM corrections. Our findings may contribute to the formal understanding of electronic OMM transport and to the conceptual foundations of the emerging field of orbitronics.

Runtime optimization of the quantum computing within a given computational resource is important to achieve practical quantum advantage. In this paper, we propose a runtime reduction protocol for the lattice surgery, which utilizes the soft information corresponding to the logical measurement error. Our proposal is a simple two-step protocol: operating the lattice surgery with the small number of syndrome-measurement cycles and reexecuting it with full syndrome-measurement cycles in cases where the timelike soft information suggests the presence of logical errors. We first discuss basic features of the timelike complementary gap as the concrete example of the timelike soft information based on numerical results. Then, we study average runtime of sequences of commutable logical Pauli measurements. We find that our protocol surpasses an existing runtime reduction protocol called temporally encoded lattice surgery (TELS) when the length of the sequence is small. In addition, we confirm that the combination of our protocol and the TELS protocol can reduce the runtime further, over 50% in comparison to the naive serial execution of the lattice surgery. The proposed protocol in this paper can be applied to any quantum computing architecture based on the lattice surgery, and we expect that this will be one of the fundamental building blocks of runtime optimization to achieve practical scale quantum computing.

Multistable structures can reconfigure and passively maintain their geometry, enabling adaptive materials with tunable properties and performance tailored to changes in conditions. This work presents a theoretical and an experimental framework for designing and analyzing two-dimensional multistable structures composed of interconnected elastically buckled beams in different arrangements. First, we develop an analytical model and use numerical continuation to identify stable and unstable equilibrium configurations. Then, experimental samples validate the analytically predicted stable states, yielding structures with asymmetric energy potentials and reconfigurable effective stiffness. This approach provides a foundation for programmable, modular mechanical metamaterials assembled from bistable building blocks.

Non-Hermitian (NH) quantum systems demonstrate striking differences from their Hermitian counterparts, leading to claims of NH advantage in areas ranging from metrology to entanglement generation. We show that in the context of quantum computation, any such NH advantage is unlikely to be scalable as an efficient computational resource: If coherent nonunitary evolution with renormalization could be realized with only polynomial overhead, then the resulting model could implement postselection, implying implausibly strong complexity-theoretic power under standard assumptions. We define $\mathrm{NHBQP}\left(U\right)$ as the computational power of polynomial-size quantum circuits that, in addition to a standard universal unitary gate set, may apply a fixed gate $U$ on $O\left(1\right)$ qubits that is not proportional to a unitary, with the state renormalized after each use of $U$. We prove that this model is powerful enough to decide every language in $\mathrm{PostBQP}$ (equivalently $\mathrm{PP}$). Moreover, in the standard uniform circuit-family model, this characterization is tight: For any fixed such nonunitary gate $U, \mathrm{NHBQP}\left(U\right)=\mathrm{PostBQP}=\mathrm{PP}$. $\mathrm{PostBQP}$ is believed intractable, so this suggests that any scalable NH computational advantage must come with a compensating cost limiting its efficiency. Additionally, we study simulation complexity of restricted classes of nonunitary systems by purifying them to postselected unitary evolution in a form preserving system locality. Using this framework, we show that unitary gates with postselection can simulate not only evolution under NH Hamiltonians but arbitrary quantum trajectories. Any NH model whose purification lies in a strongly simulable unitary family (e.g., Clifford, matchgate, or low-bond-dimension tensor-network circuits) remains efficiently classically simulable, provided the relevant postselected events occur with probability $\mathrm{\Omega }\left(2^{-\mathrm{poly}\left(n\right)}\right)$. Thus, adding non-Hermiticity to a universal unitary system makes it infeasibly computationally powerful, while adding it to a strongly simulable system adds no computational power in this setting.

Stochastic exponential growth is nearly ubiquitous across cellular life, but how its microscopic noise structure shapes population growth remains poorly understood. Here, we introduce an exactly solvable population model in which cells grow exponentially with fluctuations that scale with the square root of cell size and divide according to general size-control mechanisms. Our first result is that the population growth rate is exactly equal to the mean single-cell growth rate, for all noise strengths and for all division and size-regulation schemes that maintain size homeostasis. Thus, square-root growth noise does not affect long-term fitness, in sharp contrast to models with size-independent stochastic growth rates. Second, we derive an exact solution for the steady-state distribution of cell sizes in the population and show that it is broadened by growth fluctuations. Third, the mean-rescaled population size $N_t/\langle N_t\rangle$ converges to a stationary compound Poisson-exponential distribution that depends only on growth noise. This distribution, and hence the long-time shape of population-size fluctuations, is unchanged by division-size noise or asymmetric partitioning. These results identify Feller-type exponential growth with square-root noise as an exactly solvable benchmark for stochastic growth in size-controlled populations and provide concrete signatures that distinguish it from models with size-independent growth-rate noise.