Multimode cavity quantum electrodynamics—where a two-level system interacts simultaneously with many cavity modes—provides a versatile framework for quantum information processing and quantum optics. Because of the combination of long coherence times and large interaction strengths, one of the leading experimental platforms for cavity QED involves coupling a superconducting circuit to a 3D microwave cavity. In this work, we realize a 3D multimode circuit QED system with single photon lifetimes of 2 ms across 9 modes of a novel seamless cavity. We demonstrate a variety of protocols for universal single-mode quantum control applicable across all cavity modes, using only a single drive line. We achieve this by developing a straightforward flute method for creating monolithic superconducting microwave cavities that reduces loss while simultaneously allowing control of the mode spectrum and mode-qubit interaction. We highlight the flexibility and ease of implementation of this technique by using it to fabricate a variety of 3D cavity geometries, providing a template for engineering multimode quantum systems with exceptionally low dissipation. This work is an important step towards realizing hardware efficient random access quantum memories and processors, and for exploring quantum many-body physics with photons.

Limited-valency colloidal particles can self-assemble into polymeric structures analogous to molecules. While their structural equilibrium properties have attracted wide attention, insight into their dynamics has proven challenging. Here, we investigate the polymerization dynamics of semiflexible polymers in 2D by direct observation of assembling divalent particles, bonded by critical Casimir forces. The reversible critical Casimir force creates living polymerization conditions with tunable chain dissociation, association, and bending rigidity. We find that unlike dilute polymers that show exponential size distributions in excellent agreement with Flory theory, concentrated samples exhibit arrest of rotational and translational diffusion due to a continuous isotropic-to-nematic transition in 2D, slowing down the growth kinetics. These effects are circumvented by the addition of higher-valency particles, cross linking the polymers into networks. Our results connecting polymer flexibility, polymer interactions, and the peculiar isotropic-nematic transition in 2D offer insight into the polymerization processes of synthetic two-dimensional polymers and biopolymers at membranes and interfaces.

Encoding classical data into quantum states is considered a quantum feature map to map classical data into a quantum Hilbert space. This feature map provides opportunities to incorporate quantum advantages into machine learning algorithms to be performed on near-term intermediate-scale quantum computers. The crucial idea is using the quantum Hilbert space as a quantum-enhanced feature space in machine learning models. Although the quantum feature map has demonstrated its capability when combined with linear classification models in some specific applications, its expressive power from the theoretical perspective remains unknown. We prove that the machine learning models induced from the quantum-enhanced feature space are universal approximators of continuous functions under typical quantum feature maps. We also study the capability of quantum feature maps in the classification of disjoint regions. Our work enables an important theoretical analysis to ensure that machine learning algorithms based on quantum feature maps can handle a broad class of machine learning tasks. In light of this, one can design a quantum machine learning model with more powerful expressivity.

The control of many-body quantum dynamics in complex systems is a key challenge in the quest to reliably produce and manipulate large-scale quantum entangled states. Recently, quench experiments in Rydberg atom arrays [Bluvstein et al. Science 371, 1355 (2021)] demonstrated that coherent revivals associated with quantum many-body scars can be stabilized by periodic driving, generating stable subharmonic responses over a wide parameter regime. We analyze a simple, related model where these phenomena originate from spatiotemporal ordering in an effective Floquet unitary, corresponding to discrete time-crystalline behavior in a prethermal regime. Unlike conventional discrete time crystals, the subharmonic response exists only for Néel-like initial states, associated with quantum scars. We predict robustness to perturbations and identify emergent timescales that could be observed in future experiments. Our results suggest a route to controlling entanglement in interacting quantum systems by combining periodic driving with many-body scars.

Inflation solves several cosmological problems at the classical and quantum level, with a strong agreement between the theoretical predictions of well-motivated inflationary models and observations. In this Letter, we study the corrections induced by dynamical collapse models, which phenomenologically solve the quantum measurement problem, to the power spectrum of the comoving curvature perturbation during inflation and the radiation-dominated era. We find that the corrections are strongly negligible for the reference values of the collapse parameters.

We construct a class of interacting ($d-2$)-form theories in $d$ dimensions that are “third-way” consistent. This refers to the fact that the interaction terms in the $p$-form field equations of motion neither come from the variation of an action nor are they off-shell conserved on their own. Nevertheless, the full equation is still on-shell consistent. Various generalizations, e.g., coupling them to ($d-3$)-forms, where three algebras play a prominent role, are also discussed. The method to construct these models also easily recovers the modified three-dimensional Yang-Mills theory obtained earlier and straightforwardly allows for higher derivative extensions.

The $\mathrm{SU}(N)$ Yang-Mills matrix model admits self-dual and anti-self-dual instantons. When coupled to $N_f$ flavors of massless quarks, the Euclidean Dirac equation in an instanton background has $n_{+}$ positive and $n_{-}$ negative chirality zero modes. The vacua of the gauge theory are $N$-dimensional representations of SU(2), and the (anti-) self-dual instantons tunnel between two commuting representations, the initial one composed of $r_0^{(1)}$ irreps and the final one with $r_0^{(2)}$ irreps. We show that the index ($n_{+}-n_{-}$) in such a background is equal to a new instanton charge ${\mathcal{T}}_{\mathrm{new}}=\pm [r_0^{(2)}-r_0^{(1)}]$. Thus ${\mathcal{T}}_{\mathrm{new}}=(n_{+}-n_{-})$ is the matrix model version of the Atiyah-Singer index theorem. Further, we show that the path integral measure is not invariant under a chiral rotation, and relate the noninvariance of the measure to the index of the Dirac operator. Axial symmetry is broken anomalously, with the residual symmetry being a finite group. For $N_f$ fundamental fermions, this residual symmetry is ${\mathbb{Z}}_{2N_f}$, whereas for adjoint quarks it is ${\mathbb{Z}}_{4N_f}$.

The event-by-event correlations between three flow amplitudes are measured for the first time in Pb-Pb collisions, using higher-order symmetric cumulants. We find that different three-harmonic correlations develop during the collective evolution of the medium when compared to correlations that exist in the initial state. These new results cannot be interpreted in terms of previous lower-order flow measurements since contributions from two-harmonic correlations are explicitly removed in the new observables. A comparison to Monte Carlo simulations provides new and independent constraints for the initial conditions and system properties of nuclear matter created in heavy-ion collisions.

In a recent breakthrough in first-principles calculations of two-electron systems, Patkóś, Yerokhin, and Pachucki [Phys. Rev. A 103, 042809 (2021)] have performed the first complete calculation of the Lamb shift of the helium $2{}^3{\mathrm{S}}_1$ and $2{}^3{\mathrm{P}}_J$ triplet states up to the term in ${\alpha }^{7}m$. Whereas their theoretical result of the frequency of the $2{}^3\mathrm{P}\leftarrow 2{}^3\mathrm{S}$ transition perfectly agrees with the experimental value, a more than $10\sigma$ discrepancy was identified for the $3{}^3\mathrm{D}\leftarrow 2{}^3\mathrm{S}$ and $3{}^3\mathrm{D}\leftarrow 2{}^3\mathrm{P}$ transitions, which hinders the determination of the ${\mathrm{He}}^{2+}$ charge radius from atomic spectroscopy. We present here a new measurement of the ionization energy of the $2{}^1{\mathrm{S}}_0$ state of He [960 332 040.491(32) MHz] which we use in combination with the $2{}^3{\mathrm{S}}_1\leftarrow 2{}^1{\mathrm{S}}_0$ interval measured by Rengelink et al. [Nat. Phys. 14, 1132 (2018).] and the $2{}^3\mathrm{P}\leftarrow 2{}^3{\mathrm{S}}_1$ interval measured by Zheng et al. [Phys. Rev. Lett. 119, 263002 (2017)] and Cancio Pastor et al. [Phys. Rev. Lett. 92, 023001 (2004)] to derive experimental ionization energies of the $2{}^3{\mathrm{S}}_1$ state [1152 842 742.640(32) MHz] and the $2{}^3\mathrm{P}$ centroid energy [876 106 247.025(39) MHz]. These values reveal disagreements with the ${\alpha }^{7}m$ Lamb shift prediction by $6.5\sigma$ and $10\sigma$, respectively, and support the suggestion by Patkóš et al. of an unknown theoretical contribution to the Lamb shifts of the $2{}^3\mathrm{S}$ and $2{}^3\mathrm{P}$ states of He.

The interaction of intense femtosecond x-ray pulses with molecules sensitively depends on the interplay between multiple photoabsorptions, Auger decay, charge rearrangement, and nuclear motion. Here, we report on a combined experimental and theoretical study of the ionization and fragmentation of iodomethane (${\mathrm{CH}}_3\mathrm{I}$) by ultraintense ($\sim {10}^{19}\mathrm{W}/{\mathrm{cm}}^2$) x-ray pulses at 8.3 keV, demonstrating how these dynamics depend on the x-ray pulse energy and duration. We show that the timing of multiple ionization steps leading to a particular reaction product and, thus, the product’s final kinetic energy, is determined by the pulse duration rather than the pulse energy or intensity. While the overall degree of ionization is mainly defined by the pulse energy, our measurement reveals that the yield of the fragments with the highest charge states is enhanced for short pulse durations, in contrast to earlier observations for atoms and small molecules in the soft x-ray domain. We attribute this effect to a decreased charge transfer efficiency at larger internuclear separations, which are reached during longer pulses.

Franson interferometry is a well-known quantum measurement technique for probing photon-pair frequency correlations that is often used to certify time-energy entanglement. We demonstrate, for the first time, the complementary technique in the time basis called conjugate-Franson interferometry. It measures photon-pair arrival-time correlations, thus providing a valuable addition to the quantum toolbox. We obtain a conjugate-Franson interference visibility of $96\pm 1\%$ without background subtraction for entangled photon pairs generated by spontaneous parametric down-conversion. Our measured result surpasses the quantum-classical threshold by 25 standard deviations and validates the conjugate-Franson interferometer (CFI) as an alternative method for certifying time-energy entanglement. Moreover, the CFI visibility is a function of the biphoton’s joint temporal intensity, and is therefore sensitive to that state’s spectral phase variation: something that is not the case for Franson interferometry or Hong-Ou-Mandel interferometry. We highlight the CFI’s utility by measuring its visibilities for two different biphoton states: one without and the other with spectral phase variation, observing a 21% reduction in the CFI visibility for the latter. The CFI is potentially useful for applications in areas of photonic entanglement, quantum communications, and quantum networking.

Optical nonlinearities are known to coherently couple amplitude and phase of light, which can result in the formation of periodic waveforms. Such waveforms are referred to as optical frequency combs. Here we show that Bloch gain—a nonclassical phenomenon that was first predicted in the 1930s—can play an essential role in comb formation. We develop a self-consistent theoretical model that considers all aspects of comb dynamics: band structure, electron transport, and cavity dynamics. In quantum cascade lasers, Bloch gain gives rise to a giant Kerr nonlinearity, which enables frequency modulated combs and serves as the physical origin of the linewidth enhancement factor. Bloch gain also triggers the formation of solitonlike structures in ring resonators, paving the way toward electrically driven Kerr combs.

Speckle patterns are ubiquitous in optics and have multiple applications for which the control of their spatial correlations is essential. Here, we report on a method to engineer speckle correlations behind a scattering medium through the singular value decomposition of the transmission matrix. We not only demonstrate control over the speckle grain size and shape but also realize patterns with nonlocal correlations. Moreover, we show that the reach of our method extends also along the axial dimension, allowing volumetric speckle engineering behind scattering layers.

Nonlinear waves become asymmetric when asymmetric physical effects are present within the system. One example is the self-steepening effect. When exactly balanced with dispersion, it leads to a fully integrable system governed by the Chen-Lee-Liu equation. The latter provides a natural basis for the analysis of asymmetric wave dynamics just as nonlinear Schrödinger or Korteweg–de Vries equations provide the basis for analyzing solitons with symmetric profile. In this work, we found periodic wave trains of the Chen-Lee-Liu equation evolved from fully developed modulation instability and analyzed a highly nontrivial spectral evolution of such waves in analytic form that shows strong asymmetry of its components. We present the conceptual basis for finding such spectra that can be used in analyzing asymmetric nonlinear waves in other systems.

QED cascades play an important role in extreme astrophysical environments like magnetars. They can also be produced by passing a relativistic electron beam through an intense laser field. Signatures of collective pair plasma effects in these QED cascades are shown to appear, in exquisite detail, through plasma-induced frequency upshifts in the laser spectrum. Remarkably, these signatures can be detected even in small plasma volumes moving at relativistic speeds. Strong-field quantum and collective pair plasma effects can thus be explored with existing technology, provided that ultradense electron beams are colocated with multipetawatt lasers.

We study the critical energy dissipation in an atomic superfluid gas with two symmetric spin components by an oscillating magnetic obstacle. Above a certain critical oscillation frequency, spin-wave excitations are generated by the magnetic obstacle, demonstrating the spin superfluid behavior of the system. When the obstacle is strong enough to cause density perturbations via local saturation of spin polarization, half-quantum vortices (HQVs) are created for higher oscillation frequencies, which reveals the characteristic evolution of critical dissipative dynamics from spin-wave emission to HQV shedding. Critical HQV shedding is further investigated using a pulsed linear motion of the obstacle, and we identify two critical velocities to create HQVs with different core magnetization.

We have performed density-matrix renormalization group studies of a square lattice $t\text{−}J$ model with small hole doping, $\delta \ll 1$, on long four and six-leg cylinders. We include frustration in the form of a second-neighbor exchange coupling, $J_2=J_1/2$, such that the undoped ($\delta =0$) “parent” state is a quantum spin liquid. In contrast to the relatively short range superconducting (SC) correlations that have been observed in recent studies of the six-leg cylinder in the absence of frustration, we find power-law SC correlations with a Luttinger exponent, $K_{\mathrm{SC}}\approx 1$, consistent with a strongly diverging SC susceptibility, $\chi \sim T^{-(2-K_{\mathrm{SC}})}$ as the temperature $T\to 0$. The spin-spin correlations—as in the undoped state—fall exponentially suggesting that the SC “pairing” correlations evolve smoothly from the insulating parent state.