We introduce a generalized Hamiltonian mean field model—an $XY$ model with both linear and quadratic coupling between spins and explicit Hamiltonian dynamics. In addition to the usual paramagnetic and ferromagnetic phases, this model also possesses a nematic phase. The generalized Hamiltonian mean field model can be solved explicitly using Boltzmann-Gibbs statistical mechanics, in both canonical and microcanonical ensembles. However, when the resulting microcanonical phase diagram is compared with the one obtained using molecular dynamics simulations, it is found that the two are very different. We will present a dynamical theory which allows us to explicitly calculate the phase diagram obtained using molecular dynamics simulations without any adjustable parameters. The model illustrates the fundamental role played by dynamics as well the inadequacy of Boltzmann-Gibbs statistics for systems with long-range forces in the thermodynamic limit.

Possible effects of Chern-Simons (CS) gravity on a quantum interferometer turn out to be dependent on the latitude and direction of the interferometer on Earth in orbital motion around the Sun. Daily and seasonal variations in phase shifts are predicted with an estimate of the size of the effects, wherefore neutron interferometry with $\sim 5\mathrm{m}$ arm length and $\sim {10}^{-4}$ phase measurement accuracy would place a bound on a CS parameter comparable to the Gravity Probe B satellite.

Fluctuations in the solar wind fields tend to not only have velocities and magnetic fields correlated in the sense consistent with Alfvén waves traveling from the Sun, but they also have the magnitude of the magnetic field remarkably constant despite their being broadband. This Letter provides, for the first time, a method for constructing fields with nearly constant magnetic field, zero divergence, and with any specified power spectrum for the fluctuations of the components of the field. Every wave vector, $\mathbf{k}$, is associated with two polarizations; the relative phases of these can be chosen to minimize the variance of the field magnitude while retaining the “random” character of the fields. The method is applied to a case with one spatial coordinate that demonstrates good agreement with observed time series and power spectra of the magnetic field in the solar wind, as well as with the distribution of the angles of rapid changes (“discontinuities”), thus showing a deep connection between two seemingly unrelated issues. It is suggested that using this construction will lead to more realistic simulations of solar wind turbulence and of the propagation of energetic particles.

A power expansion scheme is set up to determine the Wigner function that satisfies the quantum kinetic equation for spin-$1/2$ charged fermions in a background electromagnetic field. Vector and axial-vector current induced by magnetic field and vorticity are obtained simultaneously from the Wigner function. The chiral magnetic and vortical effect and chiral anomaly are shown as natural consequences of the quantum kinetic equation. The axial-vector current induced by vorticity is argued to lead to a local polarization effect along the vorticity direction in heavy-ion collisions.

The ground state of ${}^{10}\mathrm{He}$ was populated using a $2p2n$-removal reaction from a $59\mathrm{MeV}/\mathrm{u}$ ${}^{14}\mathrm{Be}$ beam. The decay energy of the three-body system, ${}^8\mathrm{He}+n+n$, was measured and a resonance was observed at $E=1.60(25)\mathrm{MeV}$ with a 1.8(4) MeV width. This result is in agreement with previous invariant mass spectroscopy measurements, using the ${}^{11}\mathrm{Li}(-p)$ reaction, but is inconsistent with recent transfer reaction results. The proposed explanation that the difference, about 500 keV, is due to the effect of the extended halo nature of ${}^{11}\mathrm{Li}$ in the one-proton knockout reaction is no longer valid as the present work demonstrates that the discrepancy between the transfer reaction results persists despite using a very different reaction mechanism, ${}^{14}\mathrm{Be}(-2p2n)$.

The ${}^{13}\mathrm{C}(\alpha ,n){}^{16}\mathrm{O}$ reaction is the neutron source for the main component of the $s$-process, responsible for the production of most nuclei in the mass range $90\lesssim A\lesssim 204$. It is active inside the helium-burning shell in asymptotic giant branch stars, at temperatures $\lesssim {10}^8\mathrm{K}$, corresponding to an energy interval where the ${}^{13}\mathrm{C}(\alpha ,n){}^{16}\mathrm{O}$ is effective from 140 to 230 keV. In this region, the astrophysical $S(E)$-factor is dominated by the $-3\mathrm{keV}$ subthreshold resonance due to the 6.356 MeV level in ${}^{17}\mathrm{O}$, giving rise to a steep increase of the $S(E)$-factor. Notwithstanding that it plays a crucial role in astrophysics, no direct measurements exist inside the $s$-process energy window. The magnitude of its contribution is still controversial as extrapolations, e.g., through the $R$ matrix and indirect techniques, such as the asymptotic normalization coefficient (ANC), yield inconsistent results. The discrepancy amounts to a factor of 3 or more right at astrophysical energies. Therefore, we have applied the Trojan horse method to the ${}^{13}\mathrm{C}({}^6\mathrm{Li},n{}^{16}\mathrm{O})d$ quasifree reaction to achieve an experimental estimate of such contribution. For the first time, the ANC for the 6.356 MeV level has been deduced through the Trojan horse method as well as the $n$-partial width, allowing to attain an unprecedented accuracy in the ${}^{13}\mathrm{C}(\alpha ,n){}^{16}\mathrm{O}$ study. Though a larger ANC for the 6.356 MeV level is measured, our experimental $S(E)$-factor agrees with the most recent extrapolation in the literature in the 140–230 keV energy interval, the accuracy being greatly enhanced thanks to this innovative approach.

Highly efficient and specific energy transfer mechanisms that involve rotation-rotation, vibration-vibration, and vibration-rotation exchange in diatomic molecules are examined theoretically in ultracold ${\mathrm{H}}_2$, ${\mathrm{D}}_2$, and HD self-collisions as a function of initial vibrational level $v$. The three quasiresonant mechanisms are found to operate for all vibrational levels and yield complex scattering lengths which vary smoothly with $v$. Exceptions to this trend occur at select high values of $v$ where the scattering lengths are modulated by orders of magnitude corresponding to the location of an $s$-wave zero-energy resonance in “vibration space.” The quasiresonant mechanisms, which are not very sensitive to the details of the interaction potential, generally control the final distribution of molecular states for any given initial distribution. The zero-energy resonances are more sensitive to the potential and may be used to vibrationally “tune” the interaction strength, similar to methods which vary applied external fields.

We analyze precision bounds for a local phase estimation in the presence of general, non-Markovian phase noise. We demonstrate that the metrological equivalence of product and maximally entangled states that holds under strictly Markovian dephasing fails in the non-Markovian case. Using an exactly solvable model of a physically realistic finite bandwidth dephasing environment, we demonstrate that the ensuing non-Markovian dynamics enables quantum correlated states to outperform metrological strategies based on uncorrelated states using otherwise identical resources. We show that this conclusion is a direct result of the coherent dynamics of the global state of the system and environment and therefore the obtained scaling with the number of particles, which surpasses the standard quantum limit but does not achieve Heisenberg resolution, possesses general validity that goes beyond specific models. This is in marked contrast with the situation encountered under general Markovian noise, where an arbitrarily small amount of noise is enough to restore the scaling dictated by the standard quantum limit.

We observe and measure dispersive optical nonlinearities in an ensemble of cold Rydberg atoms placed inside an optical cavity. The experimental results are in agreement with a simple model where the optical nonlinearities are due to the progressive appearance of a Rydberg blockaded volume within the medium. The measurements allow a direct estimation of the “blockaded fraction” of atoms within the atomic ensemble.

We propose to use multiphoton interferences from statistically independent light sources in combination with linear optical detection techniques to enhance the resolution in imaging. Experimental results with up to five independent thermal light sources confirm this approach to improve the spatial resolution. Since no involved quantum state preparation or detection is required, the experiment can be considered an extension of the Hanbury Brown–Twiss experiment for spatial intensity correlations of order $N>2$.

Microresonator-based frequency combs (microcombs or Kerr combs) can potentially miniaturize the numerous applications of conventional frequency combs. A priority is the realization of broadband (ideally octave spanning) spectra at detectable repetition rates for comb self-referencing. However, access to these rates involves pumping larger mode volumes and hence higher threshold powers. Moreover, threshold power sets both the scale for power per comb tooth and also the optical pump. Along these lines, it is shown that a class of resonators having surface-loss-limited $Q$ factors can operate over a wide range of repetition rates with minimal variation in threshold power. A new, surface-loss-limited resonator illustrates the idea. Comb generation on mode spacings ranging from 2.6 to 220 GHz with overall low threshold power (as low as 1 mW) is demonstrated. A record number of comb lines for a microcomb (around 1900) is also observed with pump power of 200 mW. The ability to engineer a wide range of repetition rates with these devices is also used to investigate a recently observed mechanism in microcombs associated with dispersion of subcomb offset frequencies. We observe high-coherence phase locking in cases where these offset frequencies are small enough so as to be tuned into coincidence. In these cases, a record-low microcomb phase noise is reported at a level comparable to an open-loop, high-performance microwave oscillator.

Antennas convert propagating radiation to localized electromagnetic energy and to heat. To unambiguously separate between these two aspects, one needs to quantitatively determine the antenna scattering and absorption cross-section spectra. By using a spatial modulation technique combined with a common-path interferometer and lithographically fabricated individual gold nanoantennas, we experimentally determine the scattering and absorption cross-section spectra of different optical antennas simultaneously and quantitatively for the first time.

We study the emission of even and odd high-harmonic orders from oriented OCS molecules. We use an intense, nonresonant femtosecond laser pulse superimposed with its phase-controlled second harmonic field to impulsively align and orient a dense sample of molecules from which we subsequently generate high-order harmonics. The even harmonics appear around the full revivals of the rotational dynamics. We demonstrate perfect coherent control over their intensity through the subcycle delay of the two-color fields. The odd harmonics are insensitive to the degree of orientation, but modulate with the degree of axis alignment, in agreement with calculated photorecombination dipole moments. We further compare the shape of the even and odd harmonic spectra with our calculations and determine the degree of orientation.

We bring the methodology of orienting polar molecules together with the phase sensitivity of high harmonic spectroscopy to experimentally compare the phase difference of attosecond bursts of radiation emitted upon electron recollision from different ends of a polar molecule. This phase difference has an impact on harmonics from aligned polar molecules, suppressing emission from the molecules parallel to the driving laser field while favoring the perpendicular ones. For oriented molecules, we measure the amplitude ratio of even to odd harmonics produced when intense light irradiates CO molecules and determine the degree of orientation and the phase difference of attosecond bursts using molecular frame ionization and recombination amplitudes. The sensitivity of the high harmonic spectrum to subtle phase differences in the emitted radiation makes it a detailed probe of polar molecules and will drive major advances in the theory of high harmonic generation.

Time-varying nonlinear oscillatory systems produce phenomena of resonance crossing and trapping of particles in resonance islands. Traditionally, such processes have been analyzed in terms of adiabatic conditions. Considering, as an example, a simplified one-dimensional model describing the “electron-cloud pinch” during a bunch passage in a particle accelerator, here we present an approach to resonance trapping which does not require any adiabatic condition. Instead we introduce the concept of the attraction point and investigate invariance and scaling properties of motion close to the attraction point, considering a single resonance crossing.

We report on controlled doping of an ultracold Rb gas with single neutral Cs impurity atoms. Elastic two-body collisions lead to a rapid thermalization of the impurity inside the Rb gas, representing the first realization of an ultracold gas doped with a precisely known number of impurity atoms interacting via $s$-wave collisions. Inelastic interactions are restricted to a single three-body recombination channel in a highly controlled and pure setting, which allows us to determine the Rb-Rb-Cs three-body loss rate with unprecedented precision. Our results pave the way for a coherently interacting hybrid system of individually controllable impurities in a quantum many-body system.

We study the Mott transition of a mixed Bose-Fermi system of ultracold atoms in an optical lattice, where the number of (spinless) fermions and bosons adds up to one atom per lattice, $n_F+n_B=1$. For weak interactions, a Fermi surface coexists with a Bose-Einstein condensate while for strong interaction the system is incompressible but still characterized by a Fermi surface of composite fermions. At the critical point, the spectral function of the fermions $A(\mathbf{k},\omega )$ exhibits a pseudogapped behavior, rising as $|\omega |$ at the Fermi momentum, while in the Mott phase it is fully gapped. Taking into account the interaction between the critical modes leads at very low temperatures either to $p$-wave pairing or the transition is driven weakly first order. The same mechanism should also be important in antiferromagnetic metals with a small Fermi surface.

We report the observation of commensurability oscillations of hole-flux composite fermions near a filling factor of $\nu =1/2$ in a high-mobility two-dimensional hole system confined to a GaAs quantum well and subjected to a weak, strain-induced, unidirectional periodic potential modulation. The oscillations, which are consistent with ballistic transport of fully spin-polarized composite fermions in a weak periodic effective magnetic field, are surprisingly strong and exhibit up to third-order minima. We extract a ballistic mean-free path of about $0.1\mu \mathrm{m}$ for the hole-flux composite fermions.

The filled skutterudite compound ${\mathrm{CePt}}_4{\mathrm{Ge}}_{12}$ is situated close to the border between the intermediate valence of Ce and heavy-fermion behavior. Substitution of Ge by Sb drives the system into a strongly correlated and, ultimately, upon further increasing the Sb concentration, an antiferromagnetically ordered state. Our experiments evidence a delicate interplay of emerging Kondo physics and the formation of a local $4f$ moment. An extended non-Fermi-liquid region, which can be understood in the framework of a Kondo-disorder model, is observed. Band-structure calculations support the conclusion that the physical properties are governed by the interplay of electron supply via Sb substitution and the concomitant volume effects.

We compute the bulk photovoltaic effect (BPVE) in ${\mathrm{BiFeO}}_3$ using first-principles shift current theory, finding good agreement with experimental results. Furthermore, we reconcile apparently contradictory observations: by examining the contributions of all photovoltaic response tensor components and accounting for the geometry and ferroelectric domain structure of the experimental system, we explain the apparent lack of BPVE response in striped polydomain samples that is at odds with the significant response observed in monodomain samples. We reveal that the domain-wall-driven response in striped polydomain samples is partially mitigated by the BPVE, suggesting that enhanced efficiency could be obtained in materials with cooperative rather than antagonistic interaction between the two mechanisms.