In this Letter, we introduce the concept of in-trap nuclear decay spectroscopy of highly charged radioactive ions and describe its successful application as a novel spectroscopic tool. This is demonstrated by a measurement of the decay properties of radioactive mass $A=124$ ions (here, ${}^{124}\mathrm{In}$ and ${}^{124}\mathrm{Cs}$) in the electron-beam ion trap of the TITAN facility at TRIUMF. By subjecting the trapped ions to an intense electron beam, the ions are charge bred to high charge states (i.e., equivalent to the removal of $N$-shell electrons), and an increase of storage times to the level of minutes without significant ion losses is achieved. The present technique opens the venue for precision spectroscopy of low branching ratios and is being developed in the context of measuring electron-capture branching ratios needed for determining the nuclear ground-state properties of the intermediate odd-odd nuclei in double-beta ($\beta \beta$) decay.

The molecular Schrödinger equation is rewritten in terms of nonunitary equations of motion for the nuclei (or electrons) that depend parametrically on the configuration of an ensemble of generally defined electronic (or nuclear) trajectories. This scheme is exact and does not rely on the tracing out of degrees of freedom. Hence, the use of trajectory-based statistical techniques can be exploited to circumvent the calculation of the computationally demanding Born-Oppenheimer potential-energy surfaces and nonadiabatic coupling elements. The concept of the potential-energy surface is restored by establishing a formal connection with the exact factorization of the full wave function. This connection is used to gain insight from a simplified form of the exact propagation scheme.

We propose a superradiant metrology technique to achieve the Heisenberg limit superresolving displacement measurement by encoding multiple light momenta into a three-level atomic ensemble. We use $2N$ coherent pulses to prepare a single excitation superradiant state in a superposition of two timed Dicke states that are $4N$ light momenta apart in momentum space. The phase difference between these two states induced by a uniform displacement of the atomic ensemble has $1/4N$ sensitivity. Experiments are proposed in crystals and in ultracold atoms.

We introduce the concept of a driven quantum walk. This work is motivated by recent theoretical and experimental progress that combines quantum walks and parametric down-conversion, leading to fundamentally different phenomena. We compare these striking differences by relating the driven quantum walks to the original quantum walk. Next, we illustrate typical dynamics of such systems and show that these walks can be controlled by various pump configurations and phase matchings. Finally, we end by proposing an application of this process based on a quantum search algorithm that performs faster than a classical search.

High resolution measurements reveal that condensation isotherms of ${}^4\mathrm{He}$ in high porosity silica aerogel become discontinuous below a critical temperature. We show that this behavior does not correspond to an equilibrium phase transition modified by the disorder induced by the aerogel structure, but to the disorder-driven critical point predicted for the athermal out-of-equilibrium dynamics of the random-field Ising model. Our results evidence the key role of nonequilibrium effects in the phase transitions of disordered systems.

We compute the free energy minimizing structures of particle monolayers in the presence of enthalpic barriers of a finite height $\beta V_{\mathrm{ext}}$ using classical density functional theory and Monte Carlo simulations. We show that a periodic square template with dimensions up to at least 10 times the particle diameter disrupts the formation of the entropically favored hexagonally close-packed 2D lattice in favor of a square lattice. The results illustrate how graphoepitaxy can successfully order nanoparticulate films into desired patterns many times smaller than those of the prepatterned template.

The nature of the Mott transition in the absence of any symmetry breaking remains a matter of debate. We study the correlation-driven insulator-to-metal transition in the prototypical 3D Mott system ${\mathrm{GaTa}}_4{\mathrm{Se}}_8$, as a function of temperature and applied pressure. We report novel experiments on single crystals, which demonstrate that the transition is of first order and follows from the coexistence of two states, one insulating and one metallic, that we toggle with a small bias current. We provide support for our findings by contrasting the experimental data with calculations that combine local density approximation with dynamical mean-field theory, which are in very good agreement.

The spin-orbit interaction (SOI) of a two-dimensional hole gas in the inversion symmetric semiconductor Ge is studied in a strained-$\mathrm{Ge}/\mathrm{SiGe}$ quantum well structure. We observe weak antilocalization (WAL) in the magnetoconductivity measurement, revealing that the WAL feature can be fully described by the $k$-cubic Rashba SOI theory. Furthermore, we demonstrate electric field control of the Rashba SOI. Our findings reveal that the heavy hole (HH) in strained Ge is a purely cubic Rashba system, which is consistent with the spin angular momentum $m_j=\pm 3/2$ nature of the HH wave function.

We consider 2D Heisenberg antiferromagnets on a triangular lattice with spatially anisotropic interactions in a high magnetic field close to the saturation. We show that this system possesses a rich phase diagram in a field or anisotropy plane due to competition between classical and quantum orders: an incommensurate noncoplanar spiral state, which is favored classically, and a commensurate coplanar state, which is stabilized by quantum fluctuations. We show that the transformation between these two states is highly nontrivial and involves two intermediate phases—the phase with coplanar incommensurate spin order and the one with noncoplanar double-$\mathbf{Q}$ spiral order. The transition between the two coplanar states is of commensurate-incommensurate type, not accompanied by softening of spin-wave excitations. We show that a different sequence of transitions holds in triangular antiferromagnets with exchange anisotropy, such as ${\mathrm{Ba}}_3{\mathrm{CoSb}}_2{\mathrm{O}}_9$.

We introduce the concept of a bosonic spin liquid condensate (SLC), where spinful bosons in a lattice form a zero-temperature spin disordered charge condensate that preserves the spin rotation symmetry, but breaks the U(1) symmetry due to a spinless order parameter with charge one. It has an energy gap to all the spin excitations. We show that such SLC states can be realized in a system of spin $S\ge 2$ bosons. In particular, we analyze the SLC phase diagram in the spin 2 case using a mean-field variational wave function method. We show there is a direct analogy between the SLC and the resonating-valence-bond state.

Steane’s 7-qubit quantum error-correcting code admits a set of fault-tolerant gates that generate the Clifford group, which in itself is not universal for quantum computation. The 15-qubit Reed-Muller code also does not admit a universal fault-tolerant gate set but possesses fault-tolerant $T$ and control-control-$Z$ gates. Combined with the Clifford group, either of these two gates generates a universal set. Here, we combine these two features by demonstrating how to fault-tolerantly convert between these two codes, providing a new method to realize universal fault-tolerant quantum computation. One interpretation of our result is that both codes correspond to the same subsystem code in different gauges. Our scheme extends to the entire family of quantum Reed-Muller codes.

We analyze primordial non-Gaussianity in single-field inflationary models when the tensor-to-scalar ratio is large. Our results show that detectable levels of non-Gaussianity $f_{NL}\sim 50$ are still possible in the simplest class of models described by the effective theory of inflation. However, the shape is very tightly constrained, making a sharp prediction that could be confirmed or falsified by a future detection of non-Gaussianity.

We propose a scale-invariant chiral perturbation theory of the pseudo-Nambu-Goldstone bosons of chiral symmetry (pion $\pi$) as well as the scale symmetry (dilaton $\varphi$) for large $N_f$ QCD. The resultant dilaton mass $M_{\varphi }$ reads $M_{\varphi }^2=m_{\varphi }^2+\frac{1}{4}(3-{\gamma }_m)(1+{\gamma }_m)(2N_f{F}_{\pi }^2/F_{\varphi }^2)m_{\pi }^2+(\mathrm{chiral}\log \mathrm{corrections})$, where $m_{\varphi }$, $m_{\pi }$, ${\gamma }_m$, $F_{\pi }$, and $F_{\varphi }$ are the dilaton mass in the chiral limit, the pion mass, the mass anomalous dimension, and the decay constants of $\pi$ and $\varphi$, respectively. The chiral extrapolation of the lattice data, when plotted as $M_{\varphi }^2$ versus $m_{\pi }^2$, then simultaneously determines ($m_{\varphi }$, $F_{\varphi }$) of the technidilaton in walking technicolor with ${\gamma }_m\simeq 1$. The chiral logarithmic corrections are explicitly given.

The difference in the angular distributions between beauty quarks and antiquarks, referred to as the charge asymmetry, is measured for the first time in $b\overline{b}$ pair production at a hadron collider. The data used correspond to an integrated luminosity of $1.0{\text{fb}}^{-1}$ collected at 7 TeV center-of-mass energy in proton-proton collisions with the LHCb detector. The measurement is performed in three regions of the invariant mass of the $b\overline{b}$ system. The results obtained are $A_{\mathrm{C}}^{b\overline{b}}(40<M_{b\overline{b}}<75\mathrm{GeV}/c^2)=0.4\pm 0.4\pm 0.3\%$, $A_{\mathrm{C}}^{b\overline{b}}(75<M_{b\overline{b}}<105\mathrm{GeV}/c^2)=2.0\pm 0.9\pm 0.6\%$, $A_{\mathrm{C}}^{b\overline{b}}(M_{b\overline{b}}>105\mathrm{GeV}/c^2)=1.6\pm 1.7\pm 0.6\%$, where $A_{\mathrm{C}}^{b\overline{b}}$ is defined as the asymmetry in the difference in rapidity between jets formed from the beauty quark and antiquark, where in each case the first uncertainty is statistical and the second systematic. The beauty jets are required to satisfy $2<\eta <4$, $E_{\mathrm{T}}>20\mathrm{GeV}$, and have an opening angle in the transverse plane $\mathrm{\Delta }\varphi >2.6\mathrm{rad}$. These measurements are consistent with the predictions of the standard model.

The Bénard–von Kármán vortex shedding instability in the wake of a cylinder is perhaps the best known example of a supercritical Hopf bifurcation in fluid dynamics. However, a simplified physical description that accurately accounts for the saturation amplitude of the instability is still missing. Here, we present a simple self-consistent model that provides a clear description of the saturation mechanism and quantitatively predicts the saturated amplitude and flow fields. The model is formally constructed by a set of coupled equations governing the mean flow together with its most unstable eigenmode with finite size. The saturation amplitude is determined by requiring the mean flow to be neutrally stable. Without requiring any input from numerical or experimental data, the resolution of the model provides a good prediction of the amplitude and frequency of the vortex shedding as well as the spatial structure of the mean flow and the Reynolds stress.

Pressure dependence of the Ce valence in ${\mathrm{CeCu}}_2{\mathrm{Ge}}_2$ has been measured up to 24 GPa at 300 K and to 17 GPa at 18–20 K using x-ray absorption spectroscopy in the partial fluorescence yield. A smooth increase of the Ce valence with pressure is observed across the two superconducting (SC) regions without any noticeable irregularity. The chemical pressure dependence of the Ce valence was also measured in ${\mathrm{Ce}({\mathrm{Cu}}_{1-x}{\mathrm{Ni}}_x)}_2{\mathrm{Si}}_2$ at 20 K. A very weak, monotonic increase of the valence with $x$ was observed, without any significant change in the two SC regions. Within experimental uncertainties, our results show no evidence for the valence transition with an abrupt change in the valence state near the SC II region, challenging the valence-fluctuation mediated superconductivity model in these compounds at high pressure and low temperature.

The isolation of energetically persistent scattering pathways from the resonant manifold of an open electron billiard in the deep quantum regime is demonstrated. This enables efficient conductance switching at varying temperature and Fermi velocity, using a weak magnetic field. The effect relies on the interplay between magnetic focusing and soft-wall confinement, which rescale the scattering pathways and decouple quasibound states from the attached leads, the field-free motion being forwardly collimated. The mechanism proves robust against billiard shape variations and qualifies as a nanoelectronic current control element.

The phonon modes of individual ultrathin CdSe nanoplatelets are investigated using surface-enhanced Raman scattering in a tightly confined plasmonic geometry. The surface-enhanced Raman scattering spectra, taken on single nanoplatelets sandwiched between a gold nanoparticle and a gold surface, reveal a phonon doublet arising from oscillations perpendicular to and within the platelet plane. The out-of-plane mode cannot be observed with conventional Raman spectroscopy. The resulting strong electric field enhancements and the field vector reorientation within such nanometer-sized plasmonic gaps reveal otherwise hidden information deep into the Brillouin zone illuminating the vibrational properties of ultrathin materials.