We present a simple method for obtaining reliable angular and energy distributions of electrons ejected from arbitrary condensed biomaterials by proton impact. Relying on a suitable description of the electronic excitation spectrum and a physically motivated relation between the ion and electron scattering angles, it yields cross sections in rather good agreement with experimental data in a broad range of ejection angles and energies, by only using as input the target composition and density. The versatility and simplicity of the method, which can be also extended to other charged particles, make it especially suited for obtaining ionization data for any complex biomaterial present in realistic cellular environments.

The Heisenberg-Robertson uncertainty relation expresses a limitation in the possible preparations of the system by giving a lower bound to the product of the variances of two observables in terms of their commutator. Notably, it does not capture the concept of incompatible observables because it can be trivial; i.e., the lower bound can be null even for two noncompatible observables. Here we give two stronger uncertainty relations, relating to the sum of variances, whose lower bound is guaranteed to be nontrivial whenever the two observables are incompatible on the state of the system.

It has recently been shown that probabilistic protocols based on postselection boost the performances of the replication of quantum clocks and phase estimation. Here we demonstrate that the improvements in these two tasks have to match exactly in the macroscopic limit where the number of clones grows to infinity, preserving the equivalence between asymptotic cloning and state estimation for arbitrary values of the success probability. Remarkably, the cloning fidelity depends critically on the number of rationally independent eigenvalues of the clock Hamiltonian. We also prove that probabilistic metrology can simulate cloning in the macroscopic limit for arbitrary sets of states when the performance of the simulation is measured by testing small groups of clones.

We study the ground state phase diagram of a one-dimensional hard-core bosonic model with nearest-neighbor interactions ($XXZ$ model) where every site is coupled Ohmically to an independent but identical reservoir, hereby generalizing spin-boson models to interacting spin-boson systems. We show that a bath-induced Bose liquid phase can occur in the ground state phase diagram away from half filling. This phase is compressible, gapless, and conducting but not superfluid. At half filling, only a Luttinger liquid and a charge density wave are found. The phase transition between them is of Kosterlitz-Thouless type where the Luttinger parameter takes a nonuniversal value. The applied quantum Monte Carlo method can be used for all open bosonic and unfrustrated spin systems, regardless of their dimension, filling factor, and spectrum of the dissipation as long as the quantum system couples to the bath via the density operators.

We consider error suppression schemes in which quantum information is encoded into the ground subspace of a Hamiltonian comprising a sum of commuting terms. Since such Hamiltonians are gapped, they are considered natural candidates for protection of quantum information and topological or adiabatic quantum computation. However, we prove that they cannot be used to this end in the two-local case. By making the favorable assumption that the gap is infinite, we show that single-site perturbations can generate a degeneracy splitting in the ground subspace of this type of Hamiltonian which is of the same order as the magnitude of the perturbation, and is independent of the number of interacting sites and their Hilbert space dimensions, just as in the absence of the protecting Hamiltonian. This splitting results in decoherence of the ground subspace, and we demonstrate that for natural noise models the coherence time is proportional to the inverse of the degeneracy splitting. Our proof involves a new version of the no-hiding theorem which shows that quantum information cannot be approximately hidden in the correlations between two quantum systems. The main reason that two-local commuting Hamiltonians cannot be used for quantum error suppression is that their ground subspaces have only short-range (two-body) entanglement.

We discuss the thermodynamics of closed quantum systems driven out of equilibrium by a change in a control parameter and undergoing a unitary process. We compare the work actually done on the system with the one that would be performed along ideal adiabatic and isothermal transformations. The comparison with the latter leads to the introduction of irreversible work, while that with the former leads to the introduction of inner friction. We show that these two quantities can be treated on an equal footing, as both can be linked with the heat exchanged in thermalization processes and both can be expressed as relative entropies. Furthermore, we show that a specific fluctuation relation for the entropy production associated with the inner friction exists, which allows the inner friction to be written in terms of its cumulants.

Many of the technical complications associated with the general theory of relativity ultimately stem from the nonlinearity of Einstein’s equation. It is shown here that an appropriate choice of dynamical variables may be used to eliminate all such nonlinearities beyond a particular order: Both Landau-Lifshitz and tetrad formulations of Einstein’s equation are obtained that involve only finite products of the unknowns and their derivatives. Considerable additional simplifications arise in physically interesting cases where metrics become approximately Kerr or, e.g., plane waves, suggesting that the variables described here can be used to efficiently reformulate perturbation theory in a variety of contexts. In all cases, these variables are shown to have simple geometrical interpretations that directly relate the local causal structure associated with the metric of interest to the causal structure associated with a prescribed background. A new method to search for exact solutions is outlined as well.

In this Letter, we consider the collinear limit of gluon scattering amplitudes in planar $\mathcal{N}=4$ super-Yang-Mills theory at strong coupling. We argue that in this limit scattering amplitudes map into correlators of twist fields in the two dimensional nonlinear $O(6)$ sigma model, similar to those appearing in recent studies of entanglement entropy. We provide evidence for this assertion by combining the intuition springing from the string world-sheet picture and the predictions coming from the operator product expansion series. One of the main implications of these considerations is that scattering amplitudes receive equally important contributions at strong coupling from both the minimal string area and its fluctuations in the sphere.

Doing a double Wick rotation in the world sheet theory of the light cone ${\mathrm{AdS}}_5\times {\text{S}}^5$ superstring results in an inequivalent, so-called mirror theory that plays a central role in the field of integrability in the AdS-CFT correspondence. We show that this mirror theory can be interpreted as the light cone theory of a free string on a different background. This background is related to ${\mathrm{dS}}_5\times {\mathrm{H}}^5$ by a double $T$-duality, and has hidden supersymmetry. The geometry can also be extracted from an integrable deformation of the ${\mathrm{AdS}}_5\times {\text{S}}^5$ sigma model, and we prove the observed mirror duality of these deformed models at the bosonic level as a byproduct. While we focus on ${\mathrm{AdS}}_5\times {\text{S}}^5$, our results apply more generally.

We report a measurement of single top quark production in proton-antiproton collisions at a center-of-mass energy of $\sqrt{s}=1.96\mathrm{TeV}$ using a data set corresponding to $7.5{\mathrm{fb}}^{-1}$ of integrated luminosity collected by the Collider Detector at Fermilab. We select events consistent with the single top quark decay process $t\to Wb\to \ell \nu b$ by requiring the presence of an electron or muon, a large imbalance of transverse momentum indicating the presence of a neutrino, and two or three jets including at least one originating from a bottom quark. An artificial neural network is used to discriminate the signal from backgrounds. We measure a single top quark production cross section of $3.04_{-0.53}^{+0.57}\mathrm{pb}$ and set a lower limit on the magnitude of the coupling between the top quark and bottom quark $|V_{\mathit{t}\mathit{b}}|>0.78$ at the 95% credibility level.

We report on a complete calculation of electroweak production of top-quark pairs in $e^{+}{e}^{-}$ annihilation at next-to-next-to-leading order in quantum chromodynamics. Our setup is fully differential in phase space and can be used to calculate any infrared-safe observable. Especially we calculated the next-to-next-to-leading-order corrections to the top-quark forward-backward asymmetry and found sizable effects. Our results show a large reduction of the theoretical uncertainties in predictions of the forward-backward asymmetry, and allow for a precision determination of the top-quark electroweak couplings at future $e^{+}{e}^{-}$ colliders.

The ratio between the prompt $\psi (2S)$ and $J/\psi$ yields, reconstructed via their decays into ${\mu }^{+}{\mu }^{-}$, is measured in Pb-Pb and $p$-$p$ collisions at $\sqrt{s_{NN}}=2.76\mathrm{TeV}$. The analysis is based on Pb-Pb and $p$-$p$ data samples collected by CMS at the Large Hadron Collider, corresponding to integrated luminosities of $150\mu {\mathrm{b}}^{-1}$ and $5.4{\mathrm{pb}}^{-1}$, respectively. The double ratio of measured yields $(N_{\psi (2S)}/N_{J/\psi }{)}_{\mathrm{Pb}\text{−}\mathrm{Pb}}/(N_{\psi (2S)}/N_{J/\psi }{)}_{p\text{−}p}$ is computed in three Pb-Pb collision centrality bins and two kinematic ranges: one at midrapidity, $|y|<1.6$, covering the transverse momentum range $6.5<p_T<30\mathrm{GeV}/c$, and the other at forward rapidity, $1.6<|y|<2.4$, extending to lower $p_T$ values, $3<p_T<30\mathrm{GeV}/c$. The centrality-integrated double ratio changes from $0.45\pm 0.13(\text{stat})\pm 0.07(\text{syst})$ in the first range to $1.67\pm 0.34(\text{stat})\pm 0.27(\text{syst})$ in the second. This difference is most pronounced in the most central collisions.

The electromagnetic polarizabilities of the nucleon are fundamental properties that describe its response to external electric and magnetic fields. They can be extracted from Compton-scattering data—and have been, with good accuracy, in the case of the proton. In contradistinction, information for the neutron requires the use of Compton scattering from nuclear targets. Here, we report a new measurement of elastic photon scattering from deuterium using quasimonoenergetic tagged photons at the MAX IV Laboratory in Lund, Sweden. These first new data in more than a decade effectively double the world data set. Their energy range overlaps with previous experiments and extends it by 20 MeV to higher energies. An analysis using chiral effective field theory with dynamical $\mathrm{\Delta }(1232)$ degrees of freedom shows the data are consistent with and within the world data set. After demonstrating that the fit is consistent with the Baldin sum rule, extracting values for the isoscalar nucleon polarizabilities, and combining them with a recent result for the proton, we obtain the neutron polarizabilities as ${\alpha }_n=[11.55\pm 1.25(\text{stat})\pm 0.2(\mathrm{BSR})\pm 0.8(\mathrm{th})]\times {10}^{-4}{\mathrm{fm}}^3$ and ${\beta }_n=[3.65\mp 1.25(\text{stat})\pm 0.2(\mathrm{BSR})\mp 0.8(\mathrm{th})]\times {10}^{-4}{\mathrm{fm}}^3$, with ${\chi }^2=45.2$ for 44 degrees of freedom.

We investigate photon-momentum sharing between an electron and an ion following different photoionization regimes. We find very different partitioning of the photon momentum in one-photon ionization (the photoelectric effect) as compared to multiphoton processes. In the photoelectric effect, the electron acquires a momentum that is much greater than the single photon momentum $\hslash \omega /c$ [up to ($8/5$) $\hslash \omega /c$] whereas in the strong-field ionization regime, the photoelectron only acquires the momentum corresponding to the photons absorbed above the field-free ionization threshold plus a momentum corresponding to a fraction ($3/10$) of the ionization potential $I_p$. In both cases, due to the smallness of the electron-ion mass ratio, the ion takes nearly the entire momentum of all absorbed $N$ photons (via the electron-ion center of mass). Additionally, the ion takes, as a recoil, the photoelectron momentum resulting from mutual electron-ion interaction in the electromagnetic field. Consequently, the momentum partitioning of the photofragments is very different in both regimes. This suggests that there is a rich, unexplored physics to be studied between these two limits which can be generated with current ultrafast laser technology.

Investigations of $CP$ violation in the hadron sector may be done using measurements in the ThO molecule. Recent measurements in this molecule improved the limit on the electron electric dipole moment (EDM) by an order of magnitude. Another time-reversal ($T$) and parity ($P$)-violating effect in ${}^{229}\mathrm{ThO}$ is induced by the nuclear magnetic quadrupole moment. We perform nuclear and molecular calculations to express this effect in terms of the strength constants of $T$, $P$-odd nuclear forces, neutron EDM, QCD vacuum angle $\theta$, quark EDM, and chromo-EDM.

The fine structure and ionization energy of the $1s2s2p$ ${}^{4}P$ state of the helium negative ion ${\mathrm{He}}^{-}$ are calculated in Hylleraas coordinates, including relativistic and QED corrections up to $O({\alpha }^{4}m{c}^2)$, $O\mathbf{(}(\mu /M){\alpha }^{4}m{c}^2\mathbf{)}$, $O({\alpha }^{5}m{c}^2)$, and $O\mathbf{(}(\mu /M){\alpha }^{5}m{c}^2\mathbf{)}$. Higher order corrections are estimated for the ionization energy. A comparison is made with other calculations and experiments. We find that the present results for the fine structure splittings agree with experiment very well. However, the calculated ionization energy deviates from the experimental result by about 1 standard deviation. The estimated theoretical uncertainty in the ionization energy is much less than the experimental accuracy.

High-order harmonic generation (HHG) is investigated in rare-gas clusters as a function of the cluster size using 0.8 and $1.3\mu \mathrm{m}$ femtosecond lasers. A characteristic, species-dependent knee structure in the single particle response is observed. A 1D recollision model qualitatively reproduces this behavior and associates it to the degree of delocalization of the initial wave function. Small clusters are observed to have a higher efficiency than monomers but rapidly lose this advantage as the size increases. The implications of these findings on the HHG mechanism in clusters are discussed.

The scattering of a flying photon by a two-level system ultrastrongly coupled to a one-dimensional photonic waveguide is studied numerically. The photonic medium is modeled as an array of coupled cavities and the whole system is analyzed beyond the rotating wave approximation using matrix product states. It is found that the scattering is strongly influenced by the single- and multiphoton dressed bound states present in the system. In the ultrastrong coupling regime a new channel for inelastic scattering appears, where an incident photon deposits energy into the qubit, exciting a photon-bound state, and escaping with a lower frequency. This single-photon nonlinear frequency conversion process can reach up to 50% efficiency. Other remarkable features in the scattering induced by counterrotating terms are a blueshift of the reflection resonance and a Fano resonance due to long-lived excited states.

We investigate the reduction of the electromagnetic field fluctuations in resonance fluorescence from a single emitter coupled to an optical nanostructure. We find that such hybrid systems can lead to the creation of squeezed states of light, with quantum fluctuations significantly below the shot-noise level. Moreover, the physical conditions for achieving squeezing are strongly relaxed with respect to an emitter in free space. A high degree of control over squeezed light is feasible both in the far and near fields, opening the pathway to its manipulation and applications on the nanoscale with state-of-the-art setups.