Fluctuations of the optical length induced by fundamental thermal noise are known to set the ultimate phase resolution of fiber-based interferometers. Although this noise has been studied in detail for optical fibers made of solid glass material, its impact on the performance of hollow-core optical fibers has not yet been assessed. In such fibers, the guided light interacts only weakly with the glass material whose thermal and thermo-optic properties normally determine the thermal noise level, suggesting that a difference in performance should be expected. Based on the comparison of several interferometers optimized for phase sensitivity, we present measurements of thermal noise in the 20 to 200 kHz range in hollow-core nested antiresonant nodeless fibers (NANF) with their core filled with air at different pressures. In this frequency range, our measurements are in good agreement with the adapted thermoconductive noise model we introduce, suggesting that the thermo-optic contribution from the gas that fills the core is generally dominant, regardless of the exact hollow-core fiber design. While we show that an antiresonant hollow-core fiber filled with air at atmospheric pressure is noisier at 1550 nm than a silica fiber of equal optical length and mode-field area, we also demonstrate the lowest thermal noise power per unit optical length ever measured in a fiber ($\approx 1.3\times {10}^{-17}({\mathrm{rad}}^2/\mathrm{Hz})/\mathrm{m}$ at 30 kHz) using a large-mode-area NANF evacuated and sealed at 0.15 atm. In addition to lowering the internal pressure, we predict that the noise density in this spectral range can be reduced by filling the core with a low-polarizability noble gas. Our results indicate that low-loss antiresonant hollow-core fibers can compete with ultrastable cavities for the purpose of laser frequency stabilization; when evacuated, such fibers should constitute the best option to significantly decrease the fundamental noise floor in interferometric applications currently based on conventional solid-core fibers.

We uncover current-bias characteristics of superfluid-normal state junctions with weakly-interacting Bose gases. It is shown that in the presence of a chemical potential bias the characteristics can strongly be asymmetric for origin. The salient feature that is absent in the fermionic counterpart arises from a tunneling process associated with a condensate and a bosonic Andreev reflection process. It turns out that such processes are intrinsically nonlinear and therefore do not obey Ohm's law even at a low bias. In addition, the remaining processes are found to obey Ohm's law and become dominant for transport driven by a temperature bias.

In certain instances, the particle paths predicted by Bohmian mechanics are thought to be at odds with classical intuition. A striking illustration arises in the interference experiments envisaged by Englert, Scully, Süssmann, and Walther, which lead the authors to claim that the Bohmian trajectories cannot be real and so must be “surreal.” Through a combined experimental and numerical study, we here demonstrate that individual trajectories in the hydrodynamic pilot-wave system exhibit the key features of their surreal Bohmian counterparts. These real surreal classical trajectories are rationalized in terms of the system's non-Markovian pilot-wave dynamics. Our study thus makes clear that the designation of Bohmian trajectories as surreal is based on misconceptions concerning the limitations of classical dynamics and a lack of familiarity with pilot-wave hydrodynamics.

The standard dynamical approach to quantum thermodynamics is based on Markovian master equations describing the thermalization of a system weakly coupled to a large environment, and on tools such as entropy production relations. Here we develop a framework overcoming the limitations that the current dynamical and information theory approaches encounter when applied to this setting. More precisely, we introduce the notion of continuous thermomajorization and employ it to obtain necessary and sufficient conditions for the existence of a Markovian thermal process transforming between given initial and final energy distributions of the system. These lead to a complete set of generalized entropy production inequalities including the standard one as a special case. Importantly, these conditions can be reduced to a finitely verifiable set of constraints governing nonequilibrium transformations under master equations. What is more, the framework is also constructive, i.e., it returns explicit protocols realizing any allowed transformation. These protocols use as building blocks elementary thermalizations, which we prove to be universal controls. Finally, we also present an algorithm constructing the full set of energy distributions achievable from a given initial state via Markovian thermal processes and provide a Mathematica implementation solving $d=6$ on a laptop computer in minutes.

We propose a quantum Fourier transform on photons in which a single atom-coupled cavity system mediates the photon-photon interactions. Our protocol utilizes time-delay feedback of photons and requires no active feedforward control. The time-delay feedback enables a single atom-cavity system to implement a quantum Fourier transform on an arbitrary number of photonic qubits on-the-fly, while rapid tuning of the atomic transition implements arbitrary controlled-phase gates. We analyze the performance of the protocol numerically and show that it can implement quantum Fourier transforms with tens of photons using state-of-the-art cavity quantum electrodynamics.

Third-order parametric down-conversion describes a class of nonlinear processes in which a pump photon can be down-converted into triplets of photons. It has been identified as a source of nonclassical light, with capabilities beyond those offered by better-established processes such as spontaneous four-wave mixing. Here we discuss the implementation of third-order parameter down-conversion (TOPDC) in integrated photonic systems. We derive equations for the rates of TOPDC in a nonresonant (waveguide) and resonant (microring) platform, such that the scaling with experimental parameters can be plainly seen. We find that generally nonresonant platforms should be pursued for spontaneous TOPDC (SpTOPDC), whereas resonant platforms are more suitable for stimulated TOPDC (StTOPDC). We present a sample calculation for TOPDC rates in sample systems with conservative and accessible parameters. We find that StTOPDC should be observable with the current fabrication technology, and that with some progress in the design of TOPDC platforms, integrated SpTOPDC too could be demonstrated in the near term.

We present a semianalytical framework for computing the coupling of radiative and guided waves in slowly varying (nearly uniform or nearly periodic) surfaces, which is especially relevant to the exploitation of nonlocal effects in large-area metasurfaces. Our framework bridges a gap in the theory of slowly varying surfaces: aside from brute-force numerical simulations, current approximate methods can model either guided $\mathit{or}$ radiative waves but cannot easily model their coupling. We solve this problem by combining two methods: the locally periodic approximation, which approximates radiative scattering by composing a set of periodic scattering problems, and spatial coupled-wave theory, which allows the perturbative modeling of guided waves using an eigenmode expansion. We derive our framework for both nearly uniform and nearly periodic surfaces, and we validate each case against brute-force finite-difference time-domain simulations, which show increasing agreement as the surface varies more slowly.

In general, the optical binding force between identical particles is thought to be symmetric. However, we demonstrate analytically a counterintuitively asymmetric longitudinal optical binding force between two identical electric and magnetic dipolar dielectric particles. This homodimer is confined in two counterpropagating incoherent plane waves along the dimer's axis. The force consists of the electric dipolar, magnetic dipolar, and electric-magnetic dipolar coupling interactions. The combined effect of these interactions is markedly different than the expected behavior in the Rayleigh approximation. The asymmetric force is a result of the asymmetric forward and backward scattering of the particles due to the dipolar hybridization and coupling interactions. Consequently, it leads to a harmonic driving force on the pair, which decays with the interparticle distance to the first power. We show the rich nonequilibrium dynamics of the dimer and of the two particles impelled by the driving and binding forces and discuss the ranges of particle refractive index and size in which the asymmetric binding force arises. Our results open perspectives for nonequilibrium light-driven multiparticle transport and self-assembly.

Many-body systems driven out of equilibrium can exhibit scaling flows of the quantum state. For a sudden quench to resonant interactions between particles we construct a class of analytical scaling solutions for the time evolved wave function with a complex scale parameter. These solutions determine the exact dynamical scaling of observables such as the pair correlation function, the contact and the fidelity. We give explicit examples of the nonequilibrium dynamics for two trapped fermions or bosons quenched to unitarity, for ideal Bose polarons, and for resonantly interacting, Borromean three-body systems. These solutions reveal universal scaling properties of interacting many-body systems that arise from the buildup of correlations at short times after the quench.

Triple-NOON states are superpositions of the form $e^{i{\phi }_1}|N,0,0\rangle +e^{i{\phi }_2}|0,N,0\rangle +e^{i{\phi }_3}|0,0,N\rangle$ involving $N$ bosonic quanta distributed over three modes. We theoretically show how such highly entangled states can be generated with interacting ultracold bosonic atoms in a symmetric three-site lattice. The basic protocol consists in preparing all atoms on one site of the lattice and then letting the system evolve during a specific time such that collective tunneling of the atoms to the other two sites takes place. The key point put forward here is that this evolution time can be reduced by several orders of magnitude via the application of a periodic driving of the lattice, thereby rendering this protocol feasible in practice. This driving is suitably tuned such that classical chaos is generated in the entire accessible phase space except for the Planck cells that host the states participating at the above triple-NOON superposition. Chaos-assisted tunneling can then give rise to a dramatic speedup of this collective tunneling process, without significantly affecting the purity of this superposition. A triple-NOON state containing $N=5$ particles can thereby be realized with ${}^{87}\mathrm{Rb}$ atoms on timescales of the order of a few seconds.

Efficient transduction devices that reversibly convert optical and microwave quantum signals into each other are essential for integrating different technologies. Rare-earth ions in solids, and in particular erbium ions, with both optical and microwave addressable transitions are promising candidates for designing transducers. We propose a microwave-to-optical quantum transducer scheme based on the dark state protocol in ${}^{167}\mathrm{Er}$ doped into yttrium orthosilicate (YSO) at zero external magnetic fields. Zero-field operation is beneficial for superconducting resonators that can incur extra losses in magnetic fields. By calculating the fidelity and efficiency of the transducer, considering the most important imperfections, we show that an efficient conversion is possible with a high fidelity. We also investigate the microwave transitions of ${}^{167}\mathrm{Er}$:YSO that can be used for the transducer protocol.

We compare recent experimental results [Science 375, 528 (2022)] of the superfluid unitary Fermi gas near the critical temperature with a thermodynamic model based on the elementary excitations of the system. We find good agreement between experimental data and our theory for several quantities such as first sound, second sound, and superfluid fraction. We also show that mode mixing between first and second sound occurs. Finally, we characterize the response amplitude to a density perturbation: Close to the critical temperature both first and second sound can be excited through a density perturbation, whereas at lower temperatures only the first sound mode exhibits a significant response.

We present our model of the $e+{\mathrm{CO}}_2$ system that has been used to calculate the two-dimensional electron energy-loss spectrum of ${\mathrm{CO}}_2$ for incoming electron energies up to 5 eV reported in our Letter [Phys. Rev. Lett. 129, 013401 (2022)]. We derive the effective Hamiltonian that describes the nonlocal dynamics of ${\mathrm{CO}}_2^{-}$ within the full vibrational space and in the presence of the ${}^2{\mathrm{\Sigma }}_g^{+}$ virtual state and the Renner-Teller coupled ${}^2{\mathrm{\Pi }}_u$ shape resonance. The electronic states are represented by three discrete states that interact directly with each other and also indirectly through the electronic continuum that consists of $s$ and $p$ partial waves. Based on our ab initio fixed-nuclei $R$-matrix calculations, parameters of the model are determined using a fitting procedure that utilizes the high symmetry of the system. The topology of the resulting complex potential energy surfaces is discussed. The model is constructed in such a way that the Hamiltonian expressed in a harmonic vibrational basis of the neutral molecule is a sparse matrix which enabled us to solve the multidimensional dynamics of vibrational excitation using iterative methods based on Krylov subspaces.

We report on a twofold increase of the ${}^{39}\mathrm{Ar}$ loading rate in an atom trap by enhancing the generation of metastable atoms in a discharge source. Additional atoms in the metastable $1s_5$ level (Paschen notation) are obtained via optically pumping both the $1s_4\text{−}2p_6$ transition at 801 nm and the $1s_2\text{−}2p_6$ transition at 923 nm. By solving the master equation for the corresponding six-level system, we identify these two transitions to be the most suitable ones and encounter a transfer process between $1s_2$ and $1s_4$ when pumping both transitions simultaneously. We calculate the previously unknown frequency shifts of the two transitions in ${}^{39}\mathrm{Ar}$ and confirm the results with trap loading measurements. The demonstrated increase in the loading rate enables a corresponding decrease in the required sample size, uncertainty, and measurement time for ${}^{39}\mathrm{Ar}$ dating, a significant improvement for applications such as dating of ocean water and alpine ice cores.

We investigate linear optical noiseless quantum amplifiers driven by auxiliary Fock states and photon number measurements. We seek optimal interferometric schemes that maximize the probability of success of such noiseless quantum amplifiers and we focus on fixed linear optical interferometric setups that do not involve feed-forward. We first investigate noiseless amplifiers based on the quantum-scissors scheme and then extend our analysis to general interferometric couplings. We find that the more general interferometric couplings can outperform the quantum scissors. For noiseless amplifiers driven by an auxiliary single-photon state we recover the single-photon catalysis as an efficient noiseless amplification configuration for setups without feed-forward. We complement our analysis of linear optical noiseless quantum amplifiers by discussion of the general form of single-mode linear optical quantum operations driven by auxiliary $N$-photon state.

We realize the first magneto-optical trap of an atom in main group III of the Periodic Table. Our atom of choice (indium) does not have a transition out of its ground state suitable for laser cooling; therefore, laser cooling is performed on the $|5P_{3/2},F=6\rangle \to |5D_{5/2},F=7\rangle$ transition, where $|5P_{3/2},F=6\rangle$ is a long-lived metastable state. Optimization of our trap parameters results in atoms numbers as large as $5\times {10}^8$ atoms with temperatures of order 1 mK. Additionally, through trap decay measurements, we infer a one-body trap lifetime of $12.3\mathrm{s}$. This lifetime is consistent with background gas collisions and indicates that our repumpers have closed all leakage pathways. We also infer a two-body loss rate of $1.6\times {10}^{-11}{\mathrm{cm}}^3/\mathrm{s}$, which is comparable to those measured in alkali atoms. The techniques demonstrated in this Letter can be straightforwardly applied to other group-III atoms, and our results pave the way for realizing quantum degenerate gases of these particles.

We have performed a comprehensive numerical investigation of the scattering of antihydrogen ($\overline{\mathrm{H}}$) and positronium (Ps) atoms, at collision energies just above the threshold for the rearrangement reaction resulting in ${\overline{\mathrm{H}}}^{+}$ ions. Formation of ${\overline{\mathrm{H}}}^{+}$ in $\overline{\mathrm{H}} +\mathrm{Ps}$ collisions is of vivid interest for experiments with $\overline{\mathrm{H}}$ at CERN. We treat all open channels below the threshold for the rearrangement into $\overline{\mathrm{H}} +\mathrm{Ps}$ (which includes elastic scattering, excitation and deexcitation of positronium to and from the excited states with $n=2,3$, polarization and depolarization of $\mathrm{Ps}(n,l)$, rearrangement into ${\overline{\mathrm{H}}}^{+}+e^{-}$, and formation of Ps and $\overline{\mathrm{H}}$ in the reverse reaction). Our method is a combination of the variational calculation with the coupled rearrangement channel method. The four-body solutions of the Schrödinger equation, obtained via diagonalization of the full Hamiltonian, are combined with the channel functions that satisfy the correct asymptotic boundary conditions, in a procedure that delivers the scattering matrix $S$. The complete set of $S$-matrix elements for all allowed scattering processes is calculated (both in forward and reverse directions, without assumption of the detailed balance). The scattering cross sections are obtained from the $S$-matrix elements calculated for the total angular momenta $J=0–6$, and for the positronic spin $S=0$, required for the formation of ${\overline{\mathrm{H}}}^{+}$. The numerical accuracy of the calculation is checked using the criterion of unitarity of the $S$ matrix. Convergence of the cross section is examined with respect to the partial wave contributions, under the constraint of conservation of total angular momentum and parity. We show that the energy behavior of the cross sections near thresholds is consistent with the Wigner laws. The cross sections for processes that compete with ${\overline{\mathrm{H}}}^{+}$ formation are presented.

We theoretically propose a synthetic frequency dimension scheme to control the spectrum of a light beam propagating through an array of evanescently coupled waveguides modulated in time by a propagating sound wave via the acousto-optical effect. Configurations are identified where the emerging two-dimensional synthetic space-frequency lattice displays a nontrivial topological band structure. The corresponding chiral edge states can be exploited to manipulate the frequency spectrum of an incident beam in a robust way. In contrast to previous works, our proposal is not based on discrete high-Q cavity modes and can be applied to the manipulation of broadband signals with arbitrary spectra.

Scaling a trapped-ion based quantum simulator to a large number of ions creates a fully controllable quantum system that becomes inaccessible to numerical methods. When highly anisotropic trapping potentials are used to confine the ions in the form of a long linear string, several challenges have to be overcome to achieve high-fidelity coherent control of a quantum system extending over hundreds of micrometers. In this paper, we describe a setup for carrying out many-ion quantum simulations including single-ion coherent control that we use for demonstrating entanglement in 50-ion strings. Furthermore, we present a set of experimental techniques probing ion qubits by Ramsey and Carr-Purcell-Meiboom-Gill pulse sequences that enable detection (and compensation) of power-line-synchronous magnetic-field variations, measurement of path-length fluctuations, and detection of the wavefronts of elliptical laser beams coupling to the ion string.

We prove that a classical computer can efficiently sample from the photon-number probability distribution of a Gaussian state prepared by using an optical circuit that is shallow and local. Our paper generalizes previous known results for qubits to the continuous-variable domain. The key to our proof is the observation that the adjacency matrices characterizing the Gaussian states generated by shallow and local circuits have small bandwidth. To exploit this structure, we devise fast algorithms to calculate loop Hafnians of banded matrices. Since sampling from deep optical circuits with exponential-scaling photon loss is classically simulable, our results pose a challenge to the feasibility of demonstrating quantum supremacy on photonic platforms with local interactions.