The lifetime of the ${}^{3}P_0$ state of ${\mathrm{Bi}}^{-}$ has been measured by selective photodetachment in a cryogenic ion-beam storage ring. By measuring the lifetime as a function of applied laser powers and extrapolating to zero laser power, a lifetime of $16.0\pm 0.5$ s is deduced for electric quadrupole decay of the excited state to the ground sate. The result provides a stringent test of recent state-of-the art theoretical calculations.

Measurements of the phase of two-photon matrix elements are presented for resonant and antiresonant two-color ionization of helium. A tunable, narrow-bandwidth, near-infrared (NIR) laser source is used for extreme ultraviolet (XUV) high-harmonic generation (HHG). The 15th harmonic of the laser is used within ($1+1^{\prime }$) $\mathrm{XUV}+\mathrm{NIR}$ two-photon ionization and tuned in and out of resonance with members of the $1snp{}^{1}P_1$ ($n=3,4,5$) Rydberg series, covering a broad spectral range with high spectral resolution. The technique allows us to observe characteristic rapid changes in the phase of the two-photon matrix elements around the resonances and at the antiresonances between the resonances. Similar effects are observed for ($1+2^{\prime }$) $\mathrm{XUV}+\mathrm{NIR}$ three-photon ionization. The experimental results are compared to a perturbative model and to numerical solutions of the time-dependent Schrödinger equation in the single-active-electron approximation, elucidating the origin and dependences of the observed phenomena.

By representing an event as the joint state of a detector-timer couple that interacts with a system, we recover the familiar tensor product structure, used to describe spatially separated systems, in the context of timelike events. Furthermore, with this approach, we extend the superposition principle to the moment of occurrence of events. We then outline quantum signatures of causality that manifest through coherence in the detector state and correlation functions of time operators. Finally, we expand the scope of quantum information theoretic measures of state discrimination and information content, commonly used to characterize spatially separated systems, to events in spacetime. For causally connected events, we illustrate a deterministic relationship between events (akin to spatially entangled physical systems) where observing a previous event (one subsystem) enables us to delineate a later event (the other subsystem).

We show that the cross sections for a broad range of resonant inelastic processes accompanied by excitation exchange (such as spin exchange, Förster resonance, or angular momentum exchange) exhibit a near-threshold scaling $E^{\mathrm{\Delta }{m}_{12}}$, where $E$ is the collision energy, $\mathrm{\Delta }{m}_{12}=m_1^{\prime }+m_2^{\prime }-m_1-m_2$, and $m_i$ and $m_i^{\prime }$ are the initial and final angular momentum projections of the colliding species ($i=1,2$). In particular, the inelastic cross sections for $\mathrm{\Delta }{m}_{12}=0$ transitions display an unconventional $E^0$ scaling similar to that of elastic cross sections, and their rates vanish as $T^{\mathrm{\Delta }{m}_{12}+1/2}$. For collisions dominated by even partial waves (such as those of identical bosons in the same internal state) the scaling is modified to ${\sigma }_{\text{inel}}\propto E^{\mathrm{\Delta }{m}_{12}+1}$ if $\mathrm{\Delta }{m}_{12}$ is odd. We present accurate quantum scattering calculations that illustrate these modified threshold laws for resonant spin exchange in ultracold $\text{Rb}+\text{Rb}$ and ${\mathrm{O}}_2+{\mathrm{O}}_2$ collisions. Our results illustrate that the well-known $k^{-1}$ threshold scaling of inelastic cross sections only applies to exothermic, rather than resonant, inelastic processes.

We investigate the delocalization of operators in nonchaotic quantum systems whose interactions are encoded in an underlying graph or network. In particular, we study how fast operators of different sizes delocalize as the network connectivity is varied. We argue that these delocalization properties are well captured by Krylov complexity and show, numerically, that efficient delocalization of large operators can only happen within sufficiently connected network topologies. Finally, we demonstrate how this can be used to furnish a deeper understanding of the quantum charging advantage of a class of Sachdev-Ye-Kitaev (SYK)-like quantum batteries.

Fluctuating electric fields emanating from surfaces are a major possible source of decoherence in a number of quantum applications, including trapped ions and near-surface nitrogen-vacancy diamond qubits. Here, we show that at low temperatures, due to superradiant decay, phonon-induced excitation exchange between adsorbed atoms can counterintuitively mitigate the electric field noise. We derive an exact mapping between the noise spectrum of $N$ interacting fluctuators with $M$ vibrational levels to $\left(\genfrac{}{}{0pt}{}{N+M-1}{N}\right)$-1 noninteracting two-level dipoles. The anharmonic interaction of the fluctuators with the surface is semiempirical and physically motivated. This anharmonicity affects the noise spectral power intensity at higher temperatures. We describe conditions for which the ubiquitous $1/f$ noise emerges naturally from the coupled dynamics of identical fluctuators and whose behavior depends critically on correlation among the fluctuators.

We consider a cryptographically motivated framework for quantum metrology in the presence of a malicious adversary. We begin by devising an estimation strategy for a (potentially) altered resource (due to a malicious adversary) and quantify the amount of bias and the loss in precision as a function of the introduced uncertainty in the resource. By incorporating an appropriate cryptographic protocol, the uncertainty in the resource can be bounded with respect to the soundness of the cryptographic protocol. Thus the effectiveness of the quantum metrology problem can be directly related to the effectiveness of the cryptography protocol. As an example, we consider a quantum metrology problem in which resources are exchanged through an unsecured quantum channel. We then construct two protocols for this task which offer a trade-off between difficulty of implementation and efficiency.

We study a system of 2D trapped bosons in a quasiperiodic potential via ab initio path integral Monte Carlo simulations, focusing on its finite-temperature properties, which have not yet been explored. Alongside the superfluid, normal fluid, and insulating phases, we demonstrate the existence of a Bose glass phase, which is found to be robust to thermal fluctuations, up to about half of the critical temperature of the noninteracting system. Local quantities in the trap are characterized by employing zonal estimators, allowing us to trace a phase diagram; we do so for a set of parameters within reach of current experiments with quasi-2D optical confinement.

To capture a three-dimensional (3D) image, conventional methods often require multiple two-dimensional images of the scene from different perspectives. Here we show the reconstruction of a 3D scene with a fixed camera using quantum correlated photon pairs from a single source. Correlated photon pairs are effectively mirror images of each other so, by measuring the emission position of one photon, and the emission angle of the other, the entire propagation trajectory of the pair, and, subsequently, the 3D scene, can be reconstructed. The high photon correlation and low photon flux from a quantum source also makes it well suited for 3D imaging of light sensitive samples.

We combine experimental and theoretical approaches to explore excited rotational states of molecules embedded in helium nanodroplets using ${\mathrm{CS}}_2$ and ${\mathrm{I}}_2$ as examples. Laser-induced nonadiabatic molecular alignment is employed to measure spectral lines for rotational states extending beyond those initially populated at the 0.37 K droplet temperature. We construct a simple quantum-mechanical model, based on a linear rotor coupled to a single-mode bosonic bath, to determine the rotational energy structure in its entirety. The calculated and measured spectral lines are in good agreement. We show that the effect of the surrounding superfluid on molecular rotation can be rationalized by a single quantity, the angular momentum, transferred from the molecule to the droplet.

We demonstrate a method of qubit state preparation and measurement (SPAM) based on a weakly open quantum channel that achieves a higher fidelity than previous demonstrations, even with low detection efficiency. The trapped-ion qubit SPAM infidelity ($2.1_{-0.4}^{+0.5}\times {10}^{-4}$) is limited by setup-specific errors from ion loss and imperfect population transfer between qubit eigenstates, and we show that full transfer would yield an inaccuracy less than $8\times {10}^{-5}$. The high precision of this method revealed errors caused by a rare ($\approx {10}^{-4}$ likelihood) magnetic-dipole decay that we measure and correct by driving an additional transition. Since this scheme allows fluorescence collection for effectively unlimited periods, high fidelity is achievable even with limited optical access and low quantum efficiency photon detectors.

Complications in preparing and preserving quantum correlations stimulate recycling of a single quantum resource in information processing and communication tasks multiple times. Here, we consider a scenario involving multiple independent pairs of observers acting with unbiased inputs on a single pair of spatially separated qubits sequentially. In this scenario, we address whether more than one pair of observers can demonstrate quantum advantage in some specific $2\to 1$ and $3\to 1$ random access codes. Interestingly, we not only address these in the affirmative but also illustrate that unbounded pairs can exhibit quantum advantage. Furthermore, these results remain valid even when all observers perform suitable projective measurements and an appropriate separable state is initially shared.

We report on a surprisingly efficient acceleration of ambient gas ions in the presence of a laser-irradiated nanoparticle. Near-infrared laser pulses with an intensity of $2\times {10}^{15}\mathrm{W}{\mathrm{cm}}^{-2}$ are used to irradiate a single CsCl nanoparticle surrounded by a helium gas with a density of around ${10}^{15}{\mathrm{cm}}^{-3}$. In this interaction ${\mathrm{He}}^{+}$ ions gain higher maximum kinetic energy than ${\mathrm{Cs}}^{+}$ and ${\mathrm{Cl}}^{+}$ ions. We suggest that ${\mathrm{He}}^{+}$ ions are accelerated by a positive charge at the nanoparticle surface whereas the movement of ${\mathrm{Cs}}^{+}$ and ${\mathrm{Cl}}^{+}$ ions is interlinked to the expansion of the nanoplasma electrons. Our results reveal an essential contribution of the environment to the interaction of intense light with dense matter.

Decoherence affects all quantum systems, natural or artificial, and is the primary obstacle impeding quantum technologies. We show theoretically that for a Rydberg qubit in a Bose condensed environment, experiments can image the system-environment interface that is central for decoherence. High-precision absorption images of the condensed environment will be able to capture transient signals that show the real-time buildup of a mesoscopic entangled state in the environment. This is possible before decoherence sources other than the condensate itself can kick in, since qubit decoherence timescales can be tuned from the order of nanoseconds to microseconds by a choice of the excited Rydberg principal quantum number $\nu$. Imaging the interface will allow detailed explorations of open quantum system concepts and may offer guidance for coherence protection in challenging scenarios with non-Markovian environments.

Vortex solitons (dark solitons) are described in self-defocusing Kerr media whose phase line singularity is not parallel to the propagation direction, but is perpendicular or tilted almost arbitrary angles, depending on the medium linear dispersion. These solitons broaden the so-called spatiotemporal optical vortices recently observed in experiments to the nonlinear realm, opening alternative perspectives in practical applications of optical vortices.

We study theoretically the deformation of the Fermi surface (FS) of a three-dimensional gas of Rydberg-dressed ${}^6\mathrm{Li}$ atoms. The laser dressing to high-lying Rydberg $D$ states results in angle-dependent soft-core-shaped interactions whose anisotropy is described by multiple spherical harmonics. We show that this can drastically modify the shape of the FS and that its deformation depends on the interplay between the Fermi momentum $k_F$ and the reciprocal momentum $\overline{k}$ corresponding to the characteristic soft-core radius of the dressing-induced potential. When $k_F<\overline{k}$, the dressed interaction stretches a spherical FS into an ellipsoid. When $k_F\gtrsim \overline{k}$, complex deformations are encountered which exhibit multipolar characteristics. We analyze the formation of Cooper pairs around the deformed FS and show that they occupy large orbital angular momentum states ($p, f$, and $h$ wave) coherently. Our study demonstrates that Rydberg dressing to high angular momentum states may pave a route toward the investigation of unconventional Fermi gases and multiwave superconductivity.

We used a direct laser writing technique to build annular waveguides inside a glassy blade. These waveguides have shown the capability of generating orbital angular momentum beams with different topological charges in the same structure. Here we demonstrate that, after choosing suitable waveguide parameters, one may tune the topological charge of a beam just by tilting the input wavefront. This work opens opportunities for optical communications using spatial degrees of freedom multiplexed beams and for generation of tunable angular momentum at the microscale for integrability of lab on chips.

We study the ability to implement unitary maps on states of the $I=9/2$ nuclear spin in ${}^{87}\mathrm{Sr}$, a $d=10$ dimensional (qudecimal) Hilbert space, using quantum optimal control. Through a combination of nuclear spin resonance and a tensor ac Stark shift, by solely modulating the phase of a radio-frequency magnetic field, the system is quantum controllable. Alkaline-earth-metal atoms, such as ${}^{87}\mathrm{Sr}$, have a very favorable figure of merit for such control due to narrow intercombination lines and the large hyperfine splitting in the excited states. We numerically study the quantum speed limit, optimal parameters, and the fidelity of arbitrary state preparation and full SU(10) maps, including the presence of decoherence due to optical pumping induced by the light-shifting laser. We also study the use of robust control to mitigate some dephasing due to inhomogeneities in the light shift. We find that with an rf Rabi frequency of ${\mathrm{\Omega }}_{\text{rf}}$ and 0.5% inhomogeneity in the the light shift we can prepare an arbitrary Haar-random state in a time $T=4.5\pi /{\mathrm{\Omega }}_{\text{rf}}$ with average fidelity $\langle {\mathcal{F}}_{\psi }\rangle =0.9992$, and an arbitrary Haar-random SU(10) map in a time $T=24\pi /{\mathrm{\Omega }}_{\text{rf}}$ with average fidelity $\langle {\mathcal{F}}_U\rangle =0.9923$.

We consider rotating finite-size vortex arrays in Bose-Einstein condensates that are confined by cylindrically symmetric external potentials. We show that such systems possess two exact Nambu-Goldstone zero modes associated with two spontaneously broken continuous symmetries of the system. We verify our analytical result via direct numerical diagonalizations of the Bogoliubov–de Gennes equations. We conclude by comparing rotating vortex lattices in superfluids to supersolids and discrete time crystals.