We study spin transport in the one- and two-electron regimes of parallel-coupled double quantum dots (DQDs). The DQDs are formed in InAs nanowires by a combination of crystal-phase engineering and electrostatic gating, with an interdot tunnel coupling ($t$) tunable by one order of magnitude. Large single-particle energy separations (up to 10 meV) and $|g^{*}|$ factors ($\sim 10$) enable detailed studies of the $B$-field-induced transition from a singlet-to-triplet ground state as a function of $t$. In particular, we investigate how the magnitude of the spin-orbit-induced singlet-triplet anticrossing depends on $t$. For cases of strong coupling, we find values of $230\mu \mathrm{eV}$ for the anticrossing using excited-state spectroscopy. Experimental results are reproduced by calculations based on rate equations and a DQD model including a single orbital in each dot.

The superconducting pairing in ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$ is widely considered to be chiral $p$ wave with ${\overrightarrow{d}}_{\mathit{k}}\sim (k_x+i{k}_y)\widehat{z}$, which belongs to the $E_u$ representation of the crystalline $D_{4h}$ group. However, this superconducting order appears hard to reconcile with a number of key experiments. In this Letter, based on symmetry analysis we discuss the possibility of odd-parity pairing with inherent three-dimensional character enforced by the interorbital interlayer coupling and the sizable spin-orbit coupling in the material. We focus on a yet unexplored $E_u$ pairing, which contains finite ($k_z\widehat{x}$, $k_z\widehat{y}$) component in the gap function. Under appropriate circumstances a novel time-reversal invariant nematic pairing can be realized. This nematic superconducting state could make contact with some puzzling observations on ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$, such as the absence of spontaneous edge current and no evidence of split transitions under uniaxial strains.

Traditionally, in three dimensions, the only symmetries essential for superconductivity are time reversal ($\mathcal{T}$) and inversion ($\mathcal{I}$). Here, we examine superconductivity in two dimensions and find that $\mathcal{T}$ and $\mathcal{I}$ are not required, and having a combination of either symmetry with a mirror operation ($M_z$) on the basal plane is sufficient. By combining energetic and topological arguments, we classify superconducting states when $\mathcal{T}$ and $\mathcal{I}$ are not present, a situation encountered in several experimentally relevant systems, such as transition metal dichalcogenides or a two-dimensional Rashba system, when subject to an applied field, and in superconducting monolayer FeSe with Néel antiferromagnetic order. Energetic arguments suggest interesting superconducting states arise. For example, we find a unique pure intraband pairing state with Majorana chiral edge states in Néel-ordered FeSe. Employing topological arguments, we find when the only symmetry is the combination of $\mathcal{I}$ with $M_z$, the superconducting states are generically fully gapped and can have topologically protected chiral Majorana edge modes. In all other cases, there are no chiral Majorana edge states, but the superconducting bulk can have point nodes with associated topologically protected flatband Majorana edge modes. Our analysis provides guidance on the design and search for novel two-dimensional superconductors and superconducting heterostructures.

Nuclear magnetic resonance measurements were performed on ${\mathrm{CeCu}}_2{\mathrm{Si}}_2$ in the presence of a magnetic field close to the upper critical field ${\mu }_0{H}_{\mathrm{c}2}$ in order to investigate its superconducting (SC) properties near pair-breaking fields. In lower fields, the Knight shift and nuclear spin-lattice relaxation rate divided by temperature $1/T_{1}T$ abruptly decreased below the SC transition temperature $T_{\mathrm{c}}(H)$, a phenomenon understood within the framework of conventional spin-singlet superconductivity. In contrast, $1/T_{1}T$ was enhanced just below $T_{\mathrm{c}}(H)$ and exhibited a broad maximum when magnetic fields close to ${\mu }_0{H}_{\mathrm{c}2}(0)$ were applied parallel or perpendicular to the $c$ axis; although the Knight shift decreased just below $T_{\mathrm{c}}(H)$. This enhancement of $1/T_{1}T$, which was recently observed in the organic superconductor $\kappa \text{−}(\mathrm{BEDT}\text{−}\mathrm{TTF}{)}_2\mathrm{Cu}(\mathrm{NCS}{)}_2$, suggests the presence of high-density Andreev bound states in the inhomogeneous SC region, a hallmark of the Fulde-Ferrell-Larkin-Ovchinnikov phase.

We present the quantum critical theory of an interacting nodal Fermi liquid of quasirelativistic pseudospin-$3/2$ fermions that have a noninteracting birefringent spectrum with two distinct Fermi velocities. When such quasiparticles interact with gapless bosonic degrees of freedom that mediate either the long-range Coulomb interaction or its short range component (responsible for spontaneous symmetry breaking), in the deep infrared or quantum critical regime in two dimensions, the system is, respectively, described by a marginal- or a non-Fermi liquid of relativistic spin-$1/2$ fermions (possessing a unique velocity), and is always a marginal Fermi liquid in three dimensions. We consider a possible generalization of these scenarios to fermions with an arbitrary half-odd-integer spin, and conjecture that critical spin-$1/2$ excitations represent a superuniversal description of the entire family of interacting quasirelativistic fermions.

We present a new class of tunable light-driven oscillators based on mm-scale objects adsorbed at fluid interfaces. A fixed light source induces photothermal surface tension gradients (Marangoni stresses) that drive nanocomposite hydrogel discs away from a stable apex position atop a drop of water. The capillary forces on the disc increase with surface curvature; thus, they act to restore the disc to its original position. As the disc reenters the light source it again experiences Marangoni propulsion, leading to sustained oscillation for appropriate conditions. Propulsive forces can be modulated with incident light intensity, while the restoring force can be tuned via surface curvature—i.e., drop volume—providing highly tunable oscillatory behaviors. To our knowledge, this is the first example where Marangoni and capillary forces combine to incite sustained motion. As such, a model was developed that describes this behavior and provides key insights into the underlying control parameters. We expect that this simple approach will enable the study of more complex and coupled oscillatory systems.

Chemically active droplets are nonequilibrium systems that combine phase separation with chemical reactions. We here investigate how the activity introduced by the chemical reactions influences solid particles inside such droplets. We find that passive particles are centered in active droplets governed by first-order reactions. In autocatalytic active droplets, only catalytically active particles can be centered. An example of such systems in biology are centrosomes. Our study can account for the observed positioning of centrioles and provides a general mechanism to control the position of particles within chemically active droplets.

We demonstrate dynamical control of the superradiant transition of cavity-BEC system via periodic driving of the pump laser. We show that the dominant density wave order of the superradiant state can be suppressed, and that the subdominant competing order of Bose-Einstein condensation emerges in the steady state. Furthermore, we show that additional, nonequilibrium density wave orders, which do not exist in equilibrium, can be stabilized dynamically. Finally, for strong driving, chaotic dynamics emerge.

We demonstrate that, by changing the direction of the chirp in vacuum-ultraviolet pulses, one can switch between excitation and ionization with very high contrast, if the carrier frequency of the light is resonant with two bound states. This is a surprising consequence of rapid adiabatic passage if extended to include transitions to the continuum. The chirp phase locks the linear combination of the two resonantly coupled bound states whose ionization amplitudes interfere constructively or destructively depending on the chirp direction under suitable conditions. We derive the phenomenon in a minimal model and verify the effect with calculations for helium as a realistic example.

It is known that the long-time energy-resolved photofragment state distribution produced upon photodissociation of a molecule cannot be modified in the weak-field limit for a fixed pump pulse spectral profile. This work, however, demonstrates both computationally and mathematically that the above limitation can be circumvented in practice when the molecule presents overlapping resonances. It is shown that when two or more energies where the resonances overlap are excited by different laser pulses delayed in time, interference is induced between the product fragment states associated with the different energies populated. The occurrence of interference is found to be independent of the delay time between the pulses exciting the different energies. Thus, as demonstrated, this finding makes it possible to modify the fragment distribution at a given energy, as far in time and as many times as desired.

The semimetal ${\mathrm{MoTe}}_2$ is studied by spin- and angle-resolved photoemission spectroscopy across the centrosymmetry-breaking structural transition temperature of the bulk. A three-dimensional spin-texture is observed in the bulk Fermi surface in the low temperature, noncentrosymmetric phase that is consistent with first-principles calculations. The spin texture and two types of surface Fermi arc are not completely suppressed above the bulk transition temperature. The lifetimes of quasiparticles forming the Fermi arcs depend on thermal history and lengthen considerably upon cooling toward the bulk structural transition. The results indicate that a new form of polar instability exists near the surface when the bulk is largely in a centrosymmetric phase.

Nonequilibrium quasiparticle excitations degrade the performance of a variety of superconducting circuits. Understanding the energy distribution of these quasiparticles will yield insight into their generation mechanisms, the limitations they impose on superconducting devices, and how to efficiently mitigate quasiparticle-induced qubit decoherence. To probe this energy distribution, we systematically correlate qubit relaxation and excitation with charge-parity switches in an offset-charge-sensitive transmon qubit, and find that quasiparticle-induced excitation events are the dominant mechanism behind the residual excited-state population in our samples. By itself, the observed quasiparticle distribution would limit $T_1$ to $\approx 200\mu \mathrm{s}$, which indicates that quasiparticle loss in our devices is on equal footing with all other loss mechanisms. Furthermore, the measured rate of quasiparticle-induced excitation events is greater than that of relaxation events, which signifies that the quasiparticles are more energetic than would be predicted from a thermal distribution describing their apparent density.

We report the realization of a robust and highly controllable two-dimensional (2D) spin-orbit (SO) coupling with a topological nontrivial band structure. By applying a retro-reflected 2D optical lattice, phase tunable Raman couplings are formed into the antisymmetric Raman lattice structure, and generate the 2D SO coupling with precise inversion and $C_4$ symmetries, leading to considerably enlarged topological regions. The lifetime of the 2D SO coupled Bose-Einstein condensate reaches several seconds, which enables exploring fine-tuning interaction effects. These essential advantages of the present new realization open the door to explore exotic quantum many-body effects and nonequilibrium dynamics with novel topology.

We present a violation of the Clauser-Horne-Shimony-Holt inequality without the fair sampling assumption with a continuously pumped photon pair source combined with two high efficiency superconducting detectors. Because of the continuous nature of the source, the choice of the duration of each measurement round effectively controls the average number of photon pairs participating in the Bell test. We observe a maximum violation of $S=2.01602(32)$ with an average number of pairs per round of $\approx 0.32$, compatible with our system overall detection efficiencies. Systems that violate a Bell inequality are guaranteed to generate private randomness, with the randomness extraction rate depending on the observed violation and on the repetition rate of the Bell test. For our realization, the optimal rate of randomness generation is a compromise between the observed violation and the duration of each measurement round, with the latter realistically limited by the detection time jitter. Using an extractor composably secure against quantum adversary with quantum side information, we calculate an asymptotic rate of $\approx 1300\mathrm{random}\mathrm{bits}/\mathrm{s}$. With an experimental run of 43 min, we generated 617 920 random bits, corresponding to $\approx 240\mathrm{random}\mathrm{bits}/\mathrm{s}$.

For copper-based superconductors, the maximum superconducting transition temperature $T_{c,\max }$ of different families measured from experiment can vary from 38 K in ${\mathrm{La}}_2{\mathrm{CuO}}_4$ to 135 K in ${\mathrm{HgBa}}_2{\mathrm{Ca}}_2{\mathrm{Cu}}_3{\mathrm{O}}_8$ at the optimal hole doping concentration. We demonstrate herein, using ab initio computations, a new trend suggesting that the cuprates with stronger out-of-${\mathrm{CuO}}_2$-plane chemical bonding between the apical anion (O, Cl) and apical cation (e.g., La, Hg, Bi, Tl) are generally correlated with higher $T_{c,\max }$ in experiments. We then show the underlying fundamental phenomena of coupled apical charge flux and lattice dynamics when the apical oxygen oscillates vertically. This triggers the charge flux among the apical cation, apical anion, and the in-plane ${\mathrm{CuO}}_4$ unit. The effect not only dynamically modulates the site energy of the hole at a given Cu site to control the in-plane charge transfer energy, but also can modulate the in-plane hole hopping integral simultaneously in a dynamic way by the cooperative apical charge fluxes.

Here we present a $\mathrm{Rb}\text{−}{}^{129}\mathrm{Xe}$ spin-exchange optical pumping polarizer capable of rapid generation of large volumes of highly polarized ${}^{129}\mathrm{Xe}$ gas. Through modeling and measurements we maximize the ${}^{129}\mathrm{Xe}$ nuclear spin polarization output to enable the generation of polarized ${}^{129}\mathrm{Xe}$ gas imaging volumes ($300{\mathrm{cm}}^3$) every 5 min within a clinical setting. Our model is verified by experiment to correctly predict the optimum Rb vapor density for maximum ${}^{129}\mathrm{Xe}$ nuclear polarization for a flux $3.4\mathrm{W}/{\mathrm{cm}}^2$ of circularly polarized Rb $D_1$ photons incident on an 80 cm long cylindrical optical cell. We measure a ${}^{129}\mathrm{Xe}$ magnetization production efficiency of ${\eta }_{\mathrm{pr}}=1.8\%$, which approaches the photon efficiency limit ${\eta }_{\gamma }=3.3\%$ of this system and enables the polarization of $2.72\times {10}^{22}$ ${}^{129}\mathrm{Xe}$ spins per hour, corresponding to $1013{\mathrm{cm}}^3$ of 100% polarized ${}^{129}\mathrm{Xe}$ at STP. This magnetization production rate is threefold higher than the highest previously published ${}^{129}\mathrm{Xe}$ magnetization production rate and has enabled routine clinical lung magnetic resonance imaging (MRI) with hyperpolarized ${}^{129}\mathrm{Xe}$ doses available on demand at run time, as well as high-SNR ${}^{129}\mathrm{Xe}$ MRI of the human brain and kidneys.

Atomic magnetometry is one of the most sensitive ways to measure magnetic fields. We present a method for converting a naturally scalar atomic magnetometer into a vector magnetometer by exploiting the polarization dependence of hyperfine transitions in rubidium atoms. First, we fully determine the polarization ellipse of an applied microwave field using a self-calibrating method, i.e., a method in which the light-atom interaction provides everything required to know the field in an orthogonal laboratory frame. We then measure the direction of an applied static field using the polarization ellipse as a three-dimensional reference defined by Maxwell’s equations. Although demonstrated with trapped atoms, this technique could be applied to atomic vapors, or a variety of atomlike systems.