The Berry connection describes transformations induced by adiabatically varying Hamiltonians. We study how zero modes of the modular Hamiltonian are affected by varying the region that supplies the modular Hamiltonian. In the vacuum of a 2D conformal field theory, global conformal symmetry singles out a unique modular Berry connection, which we compute directly and in the dual three-dimensional anti–de Sitter (${\mathrm{AdS}}_3$) picture. In certain cases, Wilson loops of the modular Berry connection compute lengths of curves in ${\mathrm{AdS}}_3$, reproducing the differential entropy formula. Modular Berry transformations can be measured by bulk observers moving with varying accelerations.

A recent measurement of the hyperfine splitting in the ground state of Li-like ${{}^{208}\mathrm{Bi}}^{80+}$ has established a “hyperfine puzzle”—the experimental result exhibits a $7\sigma$ deviation from the theoretical prediction [J. Ullmann et al., Nat. Commun. 8, 15484 (2017); J. P. Karr, Nat. Phys. 13, 533 (2017)]. We provide evidence that the discrepancy is caused by an inaccurate value of the tabulated nuclear magnetic moment (${\mu }_I$) of ${}^{209}\mathrm{Bi}$. We perform relativistic density functional theory and relativistic coupled cluster calculations of the shielding constant that should be used to extract the value of ${\mu }_I({}^{209}\mathrm{Bi})$ and combine it with nuclear magnetic resonance measurements of $\mathrm{Bi}({\mathrm{NO}}_3{)}_3$ in nitric acid solutions and of the hexafluoridobismuthate(V) ${\mathrm{BiF}}_6^{-}$ ion in acetonitrile. The result clearly reveals that ${\mu }_I({}^{209}\mathrm{Bi})$ is much smaller than the tabulated value used previously. Applying the new magnetic moment shifts the theoretical prediction into agreement with experiment and resolves the hyperfine puzzle.

We show the existence of a flatband consisting of photonic zero modes in a gain and loss modulated lattice system as a result of the underlying non-Hermitian particle-hole symmetry. This general finding explains the previous observation in parity-time symmetric systems where non-Hermitian particle-hole symmetry is hidden. We further discuss the defect states in these systems, whose emergence can be viewed as an unconventional alignment of a pseudospin under the influence of a complex-valued pseudomagnetic field. These defect states also behave as a chain with two types of links, one rigid in a unit cell and one soft between unit cells, as the defect states become increasingly localized with the gain and loss strength.

Crystal structures and the Bloch theorem play a fundamental role in condensed matter physics. We extend the static crystal to the dynamic “space-time” crystal characterized by the general intertwined space-time periodicities in $D+1$ dimensions, which include both the static crystal and the Floquet crystal as special cases. A new group structure dubbed a “space-time” group is constructed to describe the discrete symmetries of a space-time crystal. Compared to space and magnetic groups, the space-time group is augmented by “time-screw” rotations and “time-glide” reflections involving fractional translations along the time direction. A complete classification of the 13 space-time groups in one-plus-one dimensions ($1+1\mathrm{D}$) is performed. The Kramers-type degeneracy can arise from the glide time-reversal symmetry without the half-integer spinor structure, which constrains the winding number patterns of spectral dispersions. In $2+1\mathrm{D}$, nonsymmorphic space-time symmetries enforce spectral degeneracies, leading to protected Floquet semimetal states. We provide a general framework for further studying topological properties of the ($D+1$)-dimensional space-time crystal.

The ground state of nanowires of single-crystalline pyrochlore ${\mathrm{Y}}_2{\mathrm{Ir}}_2{\mathrm{O}}_7$ is a density wave. The application of a transverse magnetic field increases the threshold electric field for the collective depinning of the density wave state at a low temperature, leading to colossal magnetoresistance for voltages around the depinning threshold. This is in striking contrast to the case where even a vanishingly small longitudinal magnetic field sharply reduces the depinning threshold voltage, resulting in negative magnetoresistance. Ruling out several other possibilities, we argue that this phenomenon is likely to be a consequence of the chiral anomaly in the gapped out Weyl semimetal phase in ${\mathrm{Y}}_2{\mathrm{Ir}}_2{\mathrm{O}}_7$.

Single monolayer FeSe film grown on a Nb-doped ${\mathrm{SrTiO}}_3(001)$ substrate shows the highest superconducting transition temperature ($T_C\sim 100\mathrm{K}$) among the iron-based superconductors (iron pnictides), while the $T_C$ value of bulk FeSe is only $\sim 8\mathrm{K}$. Although bulk FeSe does not show antiferromagnetic order, calculations suggest that the parent $\mathrm{FeSe}/\mathrm{SrTi}{\mathrm{O}}_3$ films are antiferromagnetic. Experimentally, because of a lack of a direct probe, the magnetic state of $\mathrm{FeSe}/\mathrm{SrTi}{\mathrm{O}}_3$ films remains mysterious. Here, we report direct evidence of antiferromagnetic order in the parent $\mathrm{FeSe}/\mathrm{SrTi}{\mathrm{O}}_3$ films by the magnetic exchange bias effect measurements. The magnetic blocking temperature is $\sim 140\mathrm{K}$ for a single monolayer film. The antiferromagnetic order disappears after electron doping.

We explore a method to probe new long- and intermediate-range interactions using precision atomic isotope shift spectroscopy. We develop a formalism to interpret linear King plots as bounds on new physics with minimal theory inputs. We focus only on bounding the new physics contributions that can be calculated independently of the standard model nuclear effects. We apply our method to existing ${\mathrm{Ca}}^{+}$ data and project its sensitivity to conjectured new bosons with spin-independent couplings to the electron and the neutron using narrow transitions in other atoms and ions, specifically, Sr and Yb. Future measurements are expected to improve the relative precision by 5 orders of magnitude, and they can potentially lead to an unprecedented sensitivity for bosons within the 0.3 to 10 MeV mass range.

The azimuthal anisotropy Fourier coefficients ($v_n$) in 8.16 TeV $p+\mathrm{Pb}$ data are extracted via long-range two-particle correlations as a function of the event multiplicity and compared to corresponding results in $pp$ and PbPb collisions. Using a four-particle cumulant technique, $v_n$ correlations are measured for the first time in $pp$ and $p+\mathrm{Pb}$ collisions. The $v_2$ and $v_4$ coefficients are found to be positively correlated in all collision systems. For high-multiplicity $p+\mathrm{Pb}$ collisions, an anticorrelation of $v_2$ and $v_3$ is observed, with a similar correlation strength as in PbPb data at the same multiplicity. The new correlation results strengthen the case for a common origin of the collectivity seen in $p+\mathrm{Pb}$ and PbPb collisions in the measured multiplicity range.

Using time- and spatially resolved hard x-ray diffraction microscopy, the striking structural and electrical dynamics upon optical excitation of a single crystal of ${\mathrm{BaTiO}}_3$ are simultaneously captured on subnanoseconds and nanoscale within individual ferroelectric domains and across walls. A large emergent photoinduced electric field of up to $20\times {10}^6\mathrm{V}/\mathrm{m}$ is discovered in a surface layer of the crystal, which then drives polarization and lattice dynamics that are dramatically distinct in a surface layer versus bulk regions. A dynamical phase-field modeling method is developed that reveals the microscopic origin of these dynamics, leading to gigahertz polarization and elastic waves traveling in the crystal with sonic speeds and spatially varying frequencies. The advances in spatiotemporal imaging and dynamical modeling tools open up opportunities for disentangling ultrafast processes in complex mesoscale structures such as ferroelectric domains.

We investigate an operational description of identical noninteracting particles in multiports. In particular, we look for physically motivated restrictions that explain their bunching probabilities. We focus on a symmetric 3-port in which a triple of superquantum particles admitted by our generalized probabilistic framework would bunch with a probability of $\frac{3}{4}$. The bosonic bound of $\frac{2}{3}$ can then be restored by imposing the additional requirement of product evolution of certain input states. These states are characterized by the fact that, much like product states, their entropy equals the sum of entropies of their one-particle substates. This principle is, however, not enough to exclude the possibility of superquantum particles in higher-order multiports.

The eigenstate thermalization hypothesis (ETH), which dictates that all diagonal matrix elements within a small energy shell be almost equal, is a major candidate to explain thermalization in isolated quantum systems. According to the typicality argument, the maximum variations of such matrix elements should decrease exponentially with increasing the size of the system, which implies the ETH. We show, however, that the typicality argument does not apply to most few-body observables for few-body Hamiltonians when the width of the energy shell decreases at most polynomially with increasing the size of the system.

In various dimensions, we can sometimes compute observables of interacting conformal field theories (CFTs) that are connected to free theories via the renormalization group (RG) flow by computing protected quantities in the free theories. On the other hand, in two dimensions, it is often possible to algebraically construct observables of interacting CFTs using free fields without the need to explicitly construct an underlying RG flow. In this Letter, we begin to extend this idea to higher dimensions by showing that one can compute certain observables of an infinite set of unitary strongly interacting four-dimensional $\mathcal{N}=2$ superconformal field theories (SCFTs) by performing simple calculations involving sets of nonunitary free four-dimensional hypermultiplets. These free fields are distant cousins of the Majorana fermion underlying the two-dimensional Ising model and are not obviously connected to our interacting theories via an RG flow. Rather surprisingly, this construction gives us Lagrangians for particular observables in certain subsectors of many “non-Lagrangian” SCFTs by sacrificing unitarity while preserving the full $\mathcal{N}=2$ superconformal algebra. As a by-product, we find relations between characters in unitary and nonunitary affine Kac-Moody algebras. We conclude by commenting on possible generalizations of our construction.

It is generally believed that when Cooper pairing occurs between two different species of fermions, their Fermi surfaces become locked together so that the resultant state remains “neutral,” with equal number densities of the two species, even when subjected to a chemical potential that couples to the difference in number densities. This belief is based on mean-field calculations in models with a zero-range interaction, where the anomalous self-energy is independent of energy and momentum. Following up on an early report of a deviation from neutrality in a Dyson-Schwinger calculation of color-flavor-locked quark matter, we investigate the neutrality of a two-species condensate using a Yukawa model which has a finite-range interaction. In a mean field calculation we obtain the full energy-momentum dependence of the self-energy and find that the energy dependence leads to a population imbalance in the Cooper-paired phase when it is stressed by a species-dependent chemical potential. This gives some support to the suggestion that the color-flavor-locked phase of quark matter might not be an insulator.

We study interaction of generic asymmetric molecules with laser fields having twisted polarization, using a pair of strong time-delayed short laser pulses with crossed linear polarizations as an example. We show that such an excitation not only provides unidirectional rotation of the most polarizable molecular axis, but also induces a directed torque along this axis, which results in a transient orientation of the molecules. The asymmetric molecules are chiral in nature and different molecular enantiomers experience the orienting action in opposite directions causing out-of-phase oscillations of their dipole moments. The resulting microwave radiation was recently suggested to be used for analysis or discrimination of chiral molecular mixtures. We reveal the mechanism behind this laser-induced orientation effect, show that it is classical in nature, and envision further applications of light with twisted polarization.

The generation of laserlike narrow bandwidth emissions from nitrogen molecular ions ($N_2^{+}$) generated in intense near- and mid infrared femtosecond laser fields has aroused much interest because of the mysterious physics underlying such a phenomenon. Here, we perform a pump-probe measurement on the nonlinear interaction of rotational quantum wave packets of $N_2^{+}$ generated in midinfrared (e.g., at a wavelength centered at 1580 nm) femtosecond laser fields with an ultrashort probe pulse whose broad spectrum overlaps both $P$- and $R$-branch rotational transition lines between the electronic states $N_2^{+}(B^2{\mathrm{\Sigma }}_u^{+},v^{\prime }=0)$ and $N_2^{+}(X^2{\mathrm{\Sigma }}_g^{+},v=0)$. The results indicate the occurrence of highly efficient near-resonant stimulated Raman scattering in the quantum wave packets of $N_2^{+}$ ions generated in strong laser fields in the midinfrared region, of which the underlying mechanism is different from that of the air lasers generated in atmospheric environment when pumping with 800 nm intense pulses.

Quantum networks will enable extraordinary capabilities for communicating and processing quantum information. These networks require a reliable means of storage, retrieval, and manipulation of quantum states at the network nodes. A node receives one or more coherent inputs and sends a conditional output to the next cascaded node in the network through a quantum channel. Here, we demonstrate this basic functionality by using the quantum interference mechanism of electromagnetically induced transparency in a transmon qubit coupled to a superconducting resonator. First, we apply a microwave bias, i.e., drive, to the qubit-cavity system to prepare a $\mathrm{\Lambda }$-type three-level system of polariton states. Second, we input two interchangeable microwave signals, i.e., a probe tone and a control tone, and observe that transmission of the probe tone is conditional upon the presence of the control tone that switches the state of the device with up to 99.73% transmission extinction. Importantly, our electromagnetically induced transparency scheme uses all dipole allowed transitions. We infer high dark state preparation fidelities of $>99.39\%$ and negative group velocities of up to $-0.52\pm 0.09\mathrm{km}/\mathrm{s}$ based on our data.

Superradiance in an ensemble of atoms leads to the collective enhancement of radiation in a particular mode shared by the atoms in their spontaneous decay from an excited state. The quantum aspects of this phenomenon are highlighted when such collective enhancement is observed in the emission of a single quantum of light. Here we report a further step in exploring experimentally the nonclassical features of superradiance by implementing the process not only with single excitations, but also in a two-excitation state. Particularly, we measure and theoretically model the wave packets corresponding to superradiance in both the single-photon and two-photon regimes. Such progress opens the way to the study and future control of the interaction of nonclassical light modes with collective quantum memories at higher photon numbers.