The intrinsic presence of ghosts in the symmetric teleparallel framework is elucidated. We illustrate our general arguments in $f(\mathbb{Q})$ theories by studying perturbations in the three inequivalent spatially flat cosmologies. Two of these branches exhibit reduced linear spectra, signalling they are infinitely strongly coupled. For the remaining branch we unveil the presence of seven gravitational degrees of freedom and show that at least one of them is a ghost. Our results rule out $f(\mathbb{Q})$ cosmologies and clarify the number of propagating degrees of freedom in these theories.

We compute the complete set of two-loop master integrals for the scattering of four massless particles and a massive one. Our results are ready for phenomenological applications, removing a major obstacle to the computation of complete next-to-next-to-leading order QCD corrections to processes such as the production of a $H/Z/W$ boson in association with two jets at the LHC. Furthermore, they open the door to new investigations into the structure of quantum-field theories and provide precious analytic data for studying the mathematical properties of Feynman integrals.

Recent experiments on kagome metals ${\mathrm{AV}}_3{\mathrm{Sb}}_5$ ($\mathrm{A}=\mathrm{Cs},\mathrm{Rb},\mathrm{K}$) indicated spontaneous time-reversal symmetry breaking in the charge density wave state in the absence of static magnetization. The loop current order (LCO) is proposed as its cause, but a microscopic model explaining the emergence of LCO through electronic correlations has not been firmly established. We show that the coupling between van Hove singularities with distinct mirror symmetries is a key ingredient to generate LCO ground state. By constructing an effective model, we find that when multiple van Hove singularities with opposite mirror eigenvalues are close in energy, the nearest-neighbor electron repulsion favors a ground state with coexisting LCO and charge bond order. It is then demonstrated that this mechanism applies to the kagome metals ${\mathrm{AV}}_3{\mathrm{Sb}}_5$. Our findings provide an intriguing mechanism of LCO and pave the way for a deeper understanding of complex quantum phenomena in kagome systems.

Time-resolved multiterahertz (THz) spectroscopy is used to observe an ultrafast, nonthermal electronic phase change in SnSe driven by interband photoexcitation with 1.55 eV pump photons. The transient THz photoconductivity spectrum is found to be Lorentzian-like, indicating charge localization and phase segregation. The rise of photoconductivity is bimodal in nature, with both a fast and slow component due to excitation into multiple bands and subsequent intervalley scattering. The THz conductivity magnitude, dynamics, and spectra show a drastic change in character at a critical excitation fluence of approximately $6\mathrm{mJ}/{\mathrm{cm}}^2$ due to a photoinduced phase segregation and a macroscopic collapse of the band gap.

Universality of local unitary transformations is one of the cornerstones of quantum computing with many applications and implications that go beyond this field. However, it has recently been shown that this universality does not hold in the presence of continuous symmetries: generic symmetric unitaries on a composite system cannot be implemented, even approximately, using local symmetric unitaries on the subsystems. In this Letter, we show that, despite these constraints, any SU(2) rotationally invariant unitary can be realized with the Heisenberg exchange interaction, which is 2-local and rotationally invariant, provided that the system interacts with a pair of ancilla qubits. We also show that a single ancilla is not enough to achieve universality. Furthermore, we study qubit circuits formed from $k$-local rotationally invariant unitaries and fully characterize the constraints imposed by locality on the realizable unitaries. We also find an interpretation of these constraints in terms of the average energy of states with a fixed angular momentum.

The Gottesman-Kitaev-Preskill (GKP) code may be used to overcome noise in continuous variable quantum systems. However, preparing GKP states remains experimentally challenging. We propose a method for preparing GKP states by engineering a time-periodic Hamiltonian whose Floquet states are GKP states. This Hamiltonian may be realized in a superconducting circuit comprising a SQUID shunted by a superinductor and a capacitor, with a characteristic impedance twice the resistance quantum. The GKP Floquet states can be prepared by adiabatically tuning the frequency of the external magnetic flux drive. We predict that highly squeezed $>11.9\mathrm{dB}$ (10.8 dB) GKP magic states can be prepared on a microsecond timescale, given a quality factor of ${10}^6$ (${10}^5$) and flux noise at typical rates.

In a system with one conserved charge the charge diffusion is modified by nonlinear self-interactions within an effective field theory (EFT) of diffusive fluctuations. We include the slowest ultraviolet (UV) mode, constructing a UV-regulated EFT. The relaxation time of this UV mode is protected from renormalization, as supported by experimental data in a bad metal system. Furthermore, the retarded density-density Green’s function acquires four branch points, eventually increasing the range of applicability. We discuss the fate of long time tails as well as implications for the quark gluon plasma.

We perform for the first time an amplitude analysis of the decay $D^{+}\to K_S^0{\pi }^{+}\eta$ and report the observation of the decay $D^{+}\to K_S^0{a}_0(980{)}^{+}$ using $2.93{\mathrm{fb}}^{-1}$ of $e^{+}{e}^{-}$ collision data taken at a center-of-mass energy of 3.773 GeV with the BESIII detector. As the only $W$-annihilation-free decay among $D$ to $a_0(980)$ pseudoscalar, $D^{+}\to K_S^0{a}_0(980{)}^{+}$ is the ideal decay in extracting the contributions of the $W$-emission amplitudes involving $a_0(980)$ and to study the final-state interactions. The absolute branching fraction of $D^{+}\to K_S^0{\pi }^{+}\eta$ is measured to be $(1.27\pm 0.04_{\mathrm{stat}}\pm 0.03_{\mathrm{syst}})\%$. The branching fractions of intermediate processes $D^{+}\to K_S^0{a}_0(980{)}^{+}$ with $a_0(980{)}^{+}\to {\pi }^{+}\eta$ and $D^{+}\to {\pi }^{+}{\overline{K}}_0^{*}(1430{)}^0$ with ${\overline{K}}_0^{*}(1430{)}^0\to K_S^0\eta$ are measured to be $(1.33\pm 0.05_{\mathrm{stat}}\pm 0.04_{\mathrm{syst}})\%$ and $(0.14\pm 0.03_{\mathrm{stat}}\pm 0.01_{\mathrm{syst}})\%$, respectively.

We report the optical trapping of multiple ions localized at individual lattice sites of a one-dimensional optical lattice. We observe a fivefold increased range of axial dc-electric field strength for which ions can be optically trapped with high probability and an increase of the axial eigenfrequency by 2 orders of magnitude compared to an optical dipole trap without interference but of similar intensity. Our findings motivate an alternative pathway to extend arrays of trapped ions in size and dimension, enabling quantum simulations with particles interacting at long range.

We investigate the electronic structure of $2H\text{−}\mathrm{Nb}{\mathrm{S}}_2$ and $h$-BN by angle-resolved photoemission spectroscopy (ARPES) and photoemission intensity calculations. Although in bulk form, these materials are expected to exhibit band degeneracy in the $k_z=\pi /c$ plane due to screw rotation and time-reversal symmetries, we observe gapped band dispersion near the surface. We extract from first-principles calculations the near-surface electronic structure probed by ARPES and find that the calculated photoemission spectra from the near-surface region reproduce the gapped ARPES spectra. Our results show that the near-surface electronic structure can be qualitatively different from the bulk electronic structure due to partially broken nonsymmorphic symmetries.

The iron-based superconductor ${\mathrm{FeSe}}_{1-x}{\mathrm{Te}}_x$ has recently gained significant attention as a host of two distinct physical phenomena: (i) Majorana zero modes that can serve as potential topologically protected qubits, and (ii) a realization of the orbital-selective Mott transition. In this Letter, we connect these two phenomena and provide new insights into the interplay between strong electronic correlations and nontrivial topology in ${\mathrm{FeSe}}_{1-x}{\mathrm{Te}}_x$. Using linearized quasiparticle self-consistent $GW$ plus dynamical mean-field theory, we show that the topologically protected Dirac surface state has substantial $\mathrm{Fe}(d_{xy})$ character. The proximity to the orbital-selective Mott transition plays a dual role: it facilitates the appearance of the topological surface state by bringing the Dirac cone close to the chemical potential but destroys the $Z_2$ topological superconductivity when the system is too close to the orbital-selective Mott phase. We derive a reduced effective Hamiltonian that describes the topological band. Its parameters capture all the chemical trends found in the first principles calculation. Our findings provide a framework for further study of the interplay between strong electronic correlations and nontrivial topology in other iron-based superconductors.

Sensing a classical signal using a linear quantum device is a pervasive application of quantum-enhanced measurement. The fundamental precision limits of linear waveform estimation, however, are not fully understood. In certain cases, there is an unexplained gap between the known waveform-estimation quantum Cramér-Rao bound and the optimal sensitivity from quadrature measurement of the outgoing mode from the device. We resolve this gap by establishing the fundamental precision limit, the waveform-estimation Holevo Cramér-Rao bound, and how to achieve it using a nonstationary measurement. We apply our results to detuned gravitational-wave interferometry to accelerate the search for postmerger remnants from binary neutron-star mergers. If we have an unequal weighting between estimating the signal’s power and phase, then we propose how to further improve the signal-to-noise ratio by a factor of $\sqrt{2}$ using this nonstationary measurement.