A novel approach for isomer depletion in ion-atom collisions is proposed and considered theoretically. Analyses are performed for the depletion of the ${}^{93m}\mathrm{Mo}$ isomer for which an unexpectedly large probability was measured in the beam-based experiment of Chiara et al. [Nature (London) 554, 216 (2018)]. The subsequent attempt at a theoretical description based on state-of-the-art atomic theory did not reproduce the experimental result [Wu et al., Phys. Rev. Lett. 122, 212501 (2019)] and showed a dramatic disagreement with the experiment (by many orders of magnitude). This conflict calls for further research on the nature of isomer depletion mechanisms occurring in atomic processes. Here, we propose to consider the ${}^{93m}\mathrm{Mo}$ isomer depletion as the nuclear excitation by electron capture in resonant transfer process taking into account the momentum distribution of the target electrons. Although our results only slightly shift the upper theoretical limit for the total ${}^{93m}\mathrm{Mo}$ isomer depletion probability toward the experimental value, they show the importance of considering the Compton profile in the theoretical description, in particular for the $L$ shell, for which the depletion probability increases by many orders of magnitude.

If a quantum fluid is driven with enough angular momentum, at equilibrium the ground state of the system is given by a lattice of quantized vortices whose density is prescribed by the quantization of circulation. We report on the first experimental study of the Feynman-Onsager relation in a nonequilibrium polariton fluid, free to expand and rotate. Upon initially imprinting a lattice of vortices in the quantum fluid, we track the vortex core positions on picosecond timescales. We observe an accelerated stretching of the lattice and an outward bending of the linear trajectories of the vortices, due to the repulsive polariton interactions. Access to the full density and phase fields allows us to detect a small deviation from the Feynman-Onsager rule in terms of a transverse velocity component, due to the density gradient of the fluid envelope acting on the vortex lattice.

Low-dimensional excitonic materials have inspired much interest owing to their novel physical and technological prospects. In particular, those with strong in-plane anisotropy are among the most intriguing but short of general analyses. We establish the universal functional form of the anisotropic dispersion in the small $k$ limit for 2D dipolar excitonic systems. While the energy is linearly dispersed in the direction parallel to the dipole in plane, the perpendicular direction is dispersionless up to linear order, which can be explained by the quantum interference effect of the interaction among the constituents of 1D subsystems. The anisotropic dispersion results in a $E^{\sim 0.5}$ scaling of the system density of states and predicts unique spectroscopic signatures including: (1) disorder-induced absorption linewidth, $W(\sigma )\sim {\sigma }^{2.8}$, with $\sigma$ the disorder strength, (2) temperature dependent absorption linewidth, $W(T)\sim T^{s+1.5}$, with $s$ the exponent of the environment spectral density, and (3) the out-of-plane angular $\theta$ dependence of the peak splittings in absorption spectra, $\mathrm{\Delta }E(\theta )\propto {\sin }^2\theta$. These predictions are confirmed quantitatively with numerical simulations of molecular thin films and tubules.

In common fluids, viscosity is associated with dissipation. However, when time-reversal symmetry is broken a new type of nondissipative “viscosity” emerges. Recent theories and experiments on classical 2D systems with active spinning particles have heightened interest in “odd viscosity,” but a microscopic theory for it in active materials is still absent. Here, we present such first-principles microscopic Hamiltonian theory, valid for both 2D and 3D, showing that odd viscosity is present in any system, even at zero temperature, with globally or locally aligned spinning components. Our work substantially extends the applicability of odd viscosity into 3D fluids, and specifically to internally driven active materials, such as living matter (e.g., actomyosin gels). We find intriguing 3D effects of odd viscosity such as propagation of anisotropic bulk shear waves and breakdown of Bernoulli’s principle.

Multipartite entanglement is a key resource allowing quantum devices to outperform their classical counterparts, and entanglement certification is fundamental to assess any quantum advantage. The only scalable certification scheme relies on entanglement witnessing, typically effective only for special entangled states. Here, we focus on finite sets of measurements on quantum states (hereafter called quantum data), and we propose an approach which, given a particular spatial partitioning of the system of interest, can effectively ascertain whether or not the dataset is compatible with a separable state. When compatibility is disproven, the approach produces the optimal entanglement witness for the quantum data at hand. Our approach is based on mapping separable states onto equilibrium classical field theories on a lattice and on mapping the compatibility problem onto an inverse statistical problem, whose solution is reached in polynomial time whenever the classical field theory does not describe a glassy system. Our results pave the way for systematic entanglement certification in quantum devices, optimized with respect to the accessible observables.

Tensor network theory and quantum simulation are, respectively, the key classical and quantum computing methods in understanding quantum many-body physics. Here, we introduce the framework of hybrid tensor networks with building blocks consisting of measurable quantum states and classically contractable tensors, inheriting both their distinct features in efficient representation of many-body wave functions. With the example of hybrid tree tensor networks, we demonstrate efficient quantum simulation using a quantum computer whose size is significantly smaller than the one of the target system. We numerically benchmark our method for finding the ground state of 1D and 2D spin systems of up to $8\times 8$ and $9\times 8$ qubits with operations only acting on $8+1$ and $9+1$ qubits, respectively. Our approach sheds light on simulation of large practical problems with intermediate-scale quantum computers, with potential applications in chemistry, quantum many-body physics, quantum field theory, and quantum gravity thought experiments.

We put forward the concept of work extraction from thermal noise by phase-sensitive (homodyne) measurements of the noisy input followed by (outcome-dependent) unitary manipulations of the postmeasured state. For optimized measurements, noise input with more than one quantum on average is shown to yield heat-to-work conversion with efficiency and power that grow with the mean number of input quanta, the efficiency and the inverse temperature of the detector. This protocol is shown to be advantageous compared to common models of information and heat engines.

The self-interacting neutrino hypothesis is well motivated for addressing the tension between the origin of sterile neutrino dark matter and indirect detection constraints. It can also result in a number of testable signals from the laboratories to the cosmos. We show that, in a broad class of models, where the sterile neutrino dark matter relic density is generated by a light neutrinophilic mediator, there must be a lower bound on the amount of extra radiation in early Universe, in particular, $\mathrm{\Delta }{N}_{\mathrm{eff}}>0.12$ at the cosmic microwave background (CMB) epoch. This lower bound will be further strengthened with an improved x-ray search at the Athena observatory. Such an intimate relationship will be unambiguously tested by the upcoming CMB Stage 4 project.

We present the beta functions of gauge and Yukawa couplings in general four-dimensional quantum field theory, at four and three loops, respectively. The essence of our approach is fixing unknown coefficients in the most general ansatz for beta functions by direct calculation in several simplified models. We apply our results to the standard model and its extension with an arbitrary number of Higgs doublets and provide expressions for all four-loop gauge couplings beta functions with matrix Yukawa interactions.

We report on precision spectroscopy of subwavelength confined molecular gases. This was obtained by rovibrational selective reflection of ${\mathrm{NH}}_3$ and ${\mathrm{SF}}_6$ gases using a quantum cascade laser at $\lambda \approx 10.6\mu \mathrm{m}$. Our technique probes molecules at micrometric distances ($\approx \lambda /2\pi$) from the window of a macroscopic cell with submegahertz resolution, allowing molecule-surface interaction spectroscopy. We exploit the linearity and high resolution of our technique to gain novel spectroscopic information on the ${\mathrm{SF}}_6$ greenhouse gas, useful for enriching molecular databases. The natural extension of our work to thin cells will allow compact frequency references and improved measurements of the Casimir-Polder interaction with molecules.

The vibrational motion of molecules represents a fundamental example of an anharmonic oscillator. Using a prototype molecular system, ${\mathrm{HeH}}^{+}$, we demonstrate that appropriate laser pulses make it possible to drive the nuclear motion in the anharmonic potential of the electronic ground state, increasing its energy above the potential barrier and facilitating dissociation by purely vibrational excitation. We find excellent agreement between the frequency-dependent response of the helium hydride molecular cation to both classical and quantum mechanical simulations, thus removing any ambiguities through electronic excitation. Our results provide access to the rich dynamics of anharmonic quantum oscillator systems and pave the way to state-selective control schemes in ground-state chemistry by the adequate choice of the laser parameters.

Two-dimensional quantum systems with competing orders can feature a deconfined quantum critical point, yielding a continuous phase transition that is incompatible with the Landau-Ginzburg-Wilson scenario, predicting instead a first-order phase transition. This is caused by the LGW order parameter breaking up into new elementary excitations at the critical point. Canonical candidates for deconfined quantum criticality are quantum antiferromagnets with competing magnetic orders, captured by the easy-plane ${\mathrm{CP}}^1$ model. A delicate issue however is that numerics indicates the easy-plane ${\mathrm{CP}}^1$ antiferromagnet to exhibit a first-order transition. Here we show that an additional topological Chern-Simons term in the action changes this picture completely in several ways. We find that the topological easy-plane antiferromagnet undergoes a second-order transition with quantized critical exponents. Further, a particle-vortex duality naturally maps the partition function of the Chern-Simons easy-plane antiferromagnet into one of massless Dirac fermions.

We study the ground state of a system of spinless electrons interacting through a screened Coulomb potential in a lattice ring. By using analytical arguments, we show that, when the effective interaction compares with the kinetic energy, the system forms a Wigner crystal undergoing a first-order quantum phase transition. This transition is a condensation in the space of the states and belongs to the class of quantum phase transitions discussed in [M. Ostilli and C. Presilla, J. Phys. A 54, 055005 (2021).]. The transition takes place at a critical value ${r_s}_c$ of the usual dimensionless parameter $r_s$ (radius of the volume available to each electron divided by effective Bohr radius) for which we are able to provide rigorous lower and upper bounds. For large screening length these bounds can be expressed in a closed analytical form. Demanding Monte Carlo simulations allow to estimate ${r_s}_c\simeq 2.3\pm 0.2$ at lattice filling $3/10$ and screening length 10 lattice constants. This value is well within the rigorous bounds $0.7\le {r_s}_c\le 4.3$. Finally, we show that if screening is removed after the thermodynamic limit has been taken, ${r_s}_c$ tends to zero. In contrast, in a bare unscreened Coulomb potential, Wigner crystallization always takes place as a smooth crossover, not as a quantum phase transition.

Threshold photodetachment spectroscopy of the molecular ion ${\mathrm{C}}_3{\mathrm{N}}^{-}$ has been performed at both 16(1) and 295(2) K in a 22-pole ion trap. The 295(2) K spectrum shows a large increase in the cross section with an onset about $200{\mathrm{cm}}^{-1}$ below threshold, which is explained by significant vibrational excitation of the trapped ions at room temperature. This excitation disappears at cryogenic temperatures leading to an almost steplike onset of the cross section at threshold, which cannot be adequately described with a Wigner threshold law. Instead, we show that the model developed by O’Malley for photodetachment from neutrals with large permanent dipoles [Phys. Rev. 137, A1668 (1965)] fits very well to the data. A high-resolution scan of the threshold region yields additional features, which we assign to the rotational $P$ and $R$ branches of an electronic transition to a dipole-bound state with ${}^1{\mathrm{\Sigma }}^{+}$ symmetry. This state is found $2(1){\mathrm{cm}}^{-1}$ below threshold in very good agreement with a recent computational prediction. We furthermore refine the value of the electron affinity of ${\mathrm{C}}_3\mathrm{N}$ to be $34727(1){\mathrm{cm}}^{-1}$.

We describe a technique to measure photon pair joint spectra by detecting the time-correlation beat note when nondegenerate photon pairs interfere at a beam splitter. The technique implements a temporal analog of the Ghosh-Mandel effect with one photon counter and a time-resolved Hong-Ou-Mandel interference with two. It is well suited to characterize pairs of photons, each of which can interact with a single atomic species, as required to study recently predicted photon-photon interaction in subwavelength atomic arrays. With this technique, we characterize photon pairs from cavity-enhanced parametric down-conversion with a bandwidth $\approx 5\mathrm{MHz}$ and frequency separation of $\sim 200\mathrm{MHz}$ near the $D_1$ line of atomic Rb.

The Kitaev model is a remarkable spin model with gapped and gapless spin liquid phases, which are potentially realized in iridates and $\alpha \text{−}{\mathrm{RuCl}}_3$. In the recent experiment of $\alpha \text{−}{\mathrm{RuCl}}_3$, the signature of a nematic transition to the gapped toric code phase, which breaks the $C_3$ symmetry of the system, has been observed through the angle dependence of the heat capacity. We here propose a mechanism by which the nematic transition can be detected electrically. This is seemingly impossible because $J_{\mathrm{eff}}=1/2$ spins do not have an electric quadrupole moment (EQM). However, in the second-order perturbation, the virtual state with a nonzero EQM appears, which makes the nematic order parameter detectable by nuclear magnetic resonance and Mössbauer spectroscopy. The purely magnetic origin of the EQM is different from conventional electronic nematic phases, allowing the direct detection of the realization of Kitaev’s toric error-correction code.