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Attosecond noncollinear four wave mixing spectroscopy with one attosecondextreme ultraviolet (XUV) pulse and two few-cycle near-infrared (NIR) pulseswas used to measure the autoionization decay lifetimes of inner valenceelectronic excitations in neon atoms. After a 43-48 eV XUV photon excites a 2selectron into the 2s2p6[np] Rydberg series, broadband NIR pulses couple the2s2p6[3p] XUV-bright state to neighboring 2s2p6[3s] and 2s2p6[3d] XUV-darkstates. Controllable delays of one or both NIR pulses with respect to theattosecond XUV pulse reveal the temporal evolution of either the dark or brightstates, respectively. Experimental lifetimes for the 3s, 3p, and 3d states aremeasured to be 7 +/- 2 fs, 48 +/- 8 fs, and 427 +/- 40 fs, respectively, with95% confidence. Accompanying calculations with two independent ab initiotheoretical methods, NewStock and ASTRA, verify the findings. The resultssupport the expected trend that the autoionization lifetime should be longerfor states that have a smaller penetration in the radial region of the 2s corehole, which in this case is for the higher angular momentum Rydberg orbitals.The underlying theory thus links the lifetime results to electron correlationand provides an assessment of the direct and exchange terms in theautoionization process.

Attosecond four-wave mixing spectroscopy using an XUV pulse and twononcollinear near-infrared pulses is employed to measure Rydberg wavepacketdynamics resulting from extreme ultraviolet excitation of a 3s electron inatomic argon into a series of autoionizing 3s-1np Rydberg states around 29 eV.The emitted signals from individual Rydberg states exhibit oscillatorystructure and persist well beyond the expected lifetimes of the emittingRydberg states. These results reflect substantial contributions of longer-livedRydberg states to the four wave mixing emission signals of each individuallydetected state. A wavepacket decomposition analysis reveals that coherentamplitude transfer occurs predominantly from photoexcited 3s-1(n+1)p states tothe observed 3s-1np Rydberg states. The experimental observations arereproduced by time-dependent Schr\"odinger equation simulations usingelectronic structure and transition moment calculations. The theory highlightsthat coherent amplitude transfer is driven non-resonantly to the 3s-1np statesby the near-infrared light through 3s-1(n+1)s and 3s-1(n-1)d dark states duringthe four-wave mixing process.

A vibrational wavepacket in SF$_6$, created by impulsive stimulated Ramanscattering with a few-cycle infrared pulse, is mapped onto five sulfurcore-excited states using table-top soft X-ray transient absorptionspectroscopy between 170-200 eV. The amplitudes of the X-ray energy shifts ofthe femtosecond oscillations depend strongly on the nature of the state. Theprepared wavepacket is controlled with the pump laser intensity to probe thecore-excited levels for various extensions of the S-F stretching motion. Thisallows the determination of the relative core-level potential energy gradients,in good agreement with TDDFT calculations. This experiment demonstrates a newmeans of characterizing core-excited potential energy surfaces.

Molecular design principles provide guidelines for augmenting a molecule witha smaller group of atoms to realize a desired property or function. Wedemonstrate that these concepts can be used to create an optical cycling centerthat can be attached to a number of aromatic ligands, allowing the scatteringof many photons from the resulting molecules without changing the molecularvibrational states. We provide further design principles that indicate theability to expand this work. This represents a significant step towards aquantum functional group, which may serve as a generic qubit moiety that can beattached to a wide range of molecular structures and surfaces.

Rapid and repeated photon cycling has enabled precision metrology and thedevelopment of quantum information systems using a variety of atoms and simplemolecules. Extending optical cycling to structurally complex molecules wouldprovide new capabilities in these areas, as well as in ultracold chemistry.Increased molecular complexity, however, makes realizing closed opticaltransitions more difficult. Building on the already established strong opticalcycling of diatomic, linear triatomic, and symmetric top molecules, recenttheoretical and experimental work has indicated that cycling will be extendableto phenol containing molecules, as well as other asymmetric species. Theparadigm for these systems is the use of an optical cycling center bonded to amolecular ligand. Theory has suggested that cycling may be extended to evenlarger ligands, like naphthalene, pyrene and coronene. Here, we study theoptical excitation and vibrational branching of the molecules CaO-2-naphthyl,SrO-2-naphthyl and CaO-1-naphthyl and find only weak decay to excitedvibrational states, indicating a promising path to full quantum control andlaser cooling of large arene-based molecules.

D$_2$ molecules, excited by linearly cross-polarized femtosecond extremeultraviolet (XUV) and near-infrared (NIR) light pulses, reveal highlystructured D$^+$ ion fragment momenta and angular distributions that originatefrom two different 4-step dissociative ionization pathways after four photonabsorption (1 XUV + 3 NIR). We show that, even for very low dissociationkinetic energy release $\le$~240~meV, specific electronic excitation pathwayscan be identified and isolated in the final ion momentum distributions. Withthe aid of {\it ab initio} electronic structure and time-dependentSchr\"odinger equation calculations, angular momentum, energy, and parityconservation are used to identify the excited neutral molecular states andmolecular orientations relative to the polarization vectors in these differentphotoexcitation and dissociation sequences of the neutral D$_2$ molecule andits D$_2^+$ cation. In one sequential photodissociation pathway, moleculesaligned along either of the two light polarization vectors are excluded, whileanother pathway selects molecules aligned parallel to the light propagationdirection. The evolution of the nuclear wave packet on the intermediate \Bstateelectronic state of the neutral D$_2$ molecule is also probed in real time.

We investigate the role of nuclear motion and strong-field-induced electroniccouplings during the double ionization of deuterated water usingmomentum-resolved coincidence spectroscopy. By examining the three-bodydicationic dissociation channel, D$^{+}$/D$^{+}$/O, for both few- andmulti-cycle laser pulses, strong evidence for intra-pulse dynamics is observed.The extracted angle- and energy-resolved double ionization yields are comparedto classical trajectory simulations of the dissociation dynamics occurring fromdifferent electronic states of the dication. In contrast with measurements ofsingle photon double ionization, pronounced departure from the expectations forvertical ionization is observed, even for pulses as short as 10~fs in duration.We outline numerous mechanisms by which the strong laser field can modify thenuclear wavefunction en-route to final states of the dication where molecularfragmentation occurs. Specifically, we consider the possibility of acoordinate-dependence to the strong-field ionization rate, intermediate nuclearmotion in monocation states prior to double ionization, and near-resonantlaser-induced dipole couplings in the ion. These results highlight the factthat, for small and light molecules such as D$_2$O, a vertical-transitiontreatment of the ionization dynamics is not sufficient to reproduce thefeatures seen experimentally in the strong field coincidence double-ionizationdata.

Laser induced electronic excitations that spontaneously emit photons and decay directly to the initial ground state ("optical cycling transitions") are used in quantum information and precision measurement for state initialization and readout. To extend this primarily atomic technique to large, organic compounds, we theoretically investigate optical cycling of alkaline earth phenoxides and their functionalized derivatives. We find that optical cycle leakage due to wave function mismatch is low in these species, and can be further suppressed by using chemical substitution to boost the electron-withdrawing strength of the aromatic molecular ligand through resonance and induction effects. This provides a straightforward way to use chemical functional groups to construct optical cycling moieties for laser cooling, state preparation, and quantum measurement.

We report experimental results on three-dimensional momentum-imaging measurements of anions generated via dissociative electron attachment to gaseous formamide. From the momentum images, we analyze the angular and kinetic-energy distributions for NH2-, O-, and H- fragments and discuss the possible electron attachment and dissociation mechanisms for multiple resonances for two ranges of incident electron energies, from 5.3 to 6.8 eV and from 10.0 to 11.5 eV. Ab initio theoretical results for the angular distributions of the NH2- anion for ∼6-eV incident electrons, when compared with the experimental results, strongly suggest that one of the two resonances producing this fragment is a A′′2 Feshbach resonance.

The chaotic nature of x-ray free-electron-laser pulses is a major bottleneck that has limited the joint temporal and spectral resolution of spectroscopic measurements. We show how to use the stochastic x-ray field statistics to overcome this difficulty through correlation signals averaged over independent pulse realizations. No control is required over the spectral phase of the pulse, enabling immediate application of existing, noisy x-ray free-electron-laser pulses. The proposed stimulated Raman technique provides the combined broad observation bandwidth and high time-frequency resolution needed for the observation of elementary molecular events. A model is used to simulate chaotic free-electron-laser pulses and calculate their correlation properties. The resulting joint temporal and spectral resolution is exemplified for a molecular model system with time-dependent frequencies and for the RNA base uracil passing through a conical intersection. Ultrafast coherences, which constitute a direct signature of the nonadiabatic dynamics, are resolved. The detail and depth of physical information accessed by the proposed stochastic signal are virtually identical to those obtained by phase-controlled pulses.

We present state-selective measurements on the NH2+ + H+ and NH+ + H+ + H dissociation channels following single-photon double ionization at 61.5 eV of neutral NH3, where the two photoelectrons and two cations are measured in coincidence using 3D momentum imaging. Three dication electronic states are identified to contribute to the NH2+ + H+ dissociation channel, where the excitation in one of the three states undergoes intersystem crossing prior to dissociation, producing a cold NH2+ fragment. In contrast, the other two states directly dissociate, producing a ro-vibrationally excited NH2+ fragment with roughly 1 eV of internal energy. The NH+ + H+ + H channel is fed by direct dissociation from three intermediate dication states, one of which is shared with the NH2+ + H+ channel. We find evidence of autoionization contributing to each of the double ionization channels. The distributions of the relative emission angle between the two photoelectrons, as well as the relative angle between the recoil axis of the molecular breakup and the polarization vector of the ionizing field, are also presented to provide insight on both the photoionization and photodissociation mechanisms for the different dication states.

We present state-selective measurements on the NH2+ + H+ and NH+ + H+ + H dissociation channels following single-photon double ionization at 61.5 eV of neutral NH3, where the two photoelectrons and two cations are measured in coincidence using 3D momentum imaging. Three dication electronic states are identified to contribute to the NH2+ + H+ dissociation channel, where the excitation in one of the three states undergoes intersystem crossing prior to dissociation, producing a cold NH2+ fragment. In contrast, the other two states directly dissociate, producing a ro-vibrationally excited NH2+ fragment with roughly 1 eV of internal energy. The NH+ + H+ + H channel is fed by direct dissociation from three intermediate dication states, one of which is shared with the NH2+ + H+ channel. We find evidence of autoionization contributing to each of the double ionization channels. The distributions of the relative emission angle between the two photoelectrons, as well as the relative angle between the recoil axis of the molecular breakup and the polarization vector of the ionizing field, are also presented to provide insight on both the photoionization and photodissociation mechanisms for the different dication states.

We present an experimental and theoretical energy- and angle-resolved study on the photoionization dynamics of nonresonant one-color two-photon single-valence ionization of neutral N2 molecules. Using 9.3-eV photons produced via high-order harmonic generation and a three-dimensional momentum imaging spectrometer, we detect the photoelectrons and ions produced from one-color two-photon ionization in coincidence. Photoionization of N2 populates the X ?g+2, A ?u2, and B ?u+2 ionic states of N2+, where the photoelectron angular distributions associated with the X ?g+2 and A ?u2 states both vary with changes in photoelectron kinetic energy of only a few hundred meV. We attribute the rapid evolution in the photoelectron angular distributions to the excitation and decay of dipole-forbidden autoionizing resonances that belong to series of different symmetries, all of which are members of the Hopfield series, and compete with the direct two-photon single ionization.

Dipole-phonon quantum logic (DPQL) leverages the interaction between polar molecular ions and the motional modes of a trapped-ion Coulomb crystal to provide a potentially scalable route to quantum information science. Here, we study a class of candidate molecular ions for DPQL, the cationic alkaline-earth monoxides and monosulfides, which possess suitable structure for DPQL and can be produced in existing atomic ion experiments with little additional complexity. We present calculations of DPQL operations for one of these molecules, CaO+, and discuss progress towards experimental realization. We also further develop the theory of DPQL to include state preparation and measurement and entanglement of multiple molecular ions.

We report measurements on the H++H+ fragmentation channel following direct single-photon double ionization of neutral NH3 at 61.5 eV, where the two photoelectrons and two protons are measured in coincidence using three-dimensional (3D) momentum imaging. We identify four dication electronic states that contribute to H++H+ dissociation, based on our multireference configuration-interaction calculations of the dication potential energy surfaces. The extracted branching ratios between these four dication electronic states are presented. Of the four dication electronic states, three dissociate in a concerted process, while the fourth undergoes a sequential fragmentation mechanism. We find evidence that the neutral NH fragment or intermediate NH+ ion is markedly rovibrationally excited. We also identify differences in the relative emission angle between the two photoelectrons as a function of their energy sharing for the four different dication states, which bare some similarities to previous observations made on atomic targets.

We report measurements on the H++H+ fragmentation channel following direct single-photon double ionization of neutral NH3 at 61.5 eV, where the two photoelectrons and two protons are measured in coincidence using three-dimensional (3D) momentum imaging. We identify four dication electronic states that contribute to H++H+ dissociation, based on our multireference configuration-interaction calculations of the dication potential energy surfaces. The extracted branching ratios between these four dication electronic states are presented. Of the four dication electronic states, three dissociate in a concerted process, while the fourth undergoes a sequential fragmentation mechanism. We find evidence that the neutral NH fragment or intermediate NH+ ion is markedly rovibrationally excited. We also identify differences in the relative emission angle between the two photoelectrons as a function of their energy sharing for the four different dication states, which bare some similarities to previous observations made on atomic targets.

With advent of quantum internet, it becomes crucial to find novel ways toconnect distributed quantum testbeds and develop novel technologies andresearch that extend innovations in managing the qubit performance. Numerousemerging technologies are focused on quantum repeaters and specialized hardwareto extend the quantum distance over special-purpose channels. However, there islittle work that utilizes current network technology, invested in optictechnologies, to merge with quantum technologies. In this paper we argue for anAI-enabled control that allows optimized and efficient conversion between qubitand photon energies, to enable optic and quantum devices to work together. Ourapproach integrates AI techniques, such as deep reinforcement learningalgorithms, with physical quantum transducer to inform real-time conversionbetween the two wavelengths. Learning from simulated environment, the trainedAI-enabled transducer will lead to optimal quantum transduction to maximize thequbit lifetime.

Chiral four-wave mixing signals are calculated using the irreducible tensor formalism. Different polarization and crossing angle configurations allow to single out the magnetic dipole and the electric quadrupole interactions. Other configurations can reveal that the chiral interaction occurs at a given step within the nonlinear interaction pathways. Applications are made to the study of valence excitations of S-ibuprofen by chiral stimulated X-ray Raman signals at the carbon K-edge and by chiral visible 2D electronic spectroscopy.

Hyperfine structure (HFS) of atomic energy levels arises due to interactionsof atomic electrons with a hierarchy of nuclear multipole moments, includingmagnetic dipole, electric quadrupole and higher rank moments. Recently, adetermination of the magnetic octupole moment of the $^{173}\mathrm{Yb}$nucleus was reported from HFS measurements in neutral ${}^{173}\mathrm{Yb}$[PRA 87, 012512 (2013)], and is four orders of magnitude larger than thenuclear theory prediction. Considering this substantial discrepancy between thespectroscopically extracted value and nuclear theory, here we propose to use analternative system to resolve this tension, a singly charged ion of the same$^{173}\mathrm{Yb}$ isotope. Utilizing the substantial suite of tools developedaround $\mathrm{Yb}^+$ for quantum information applications, we propose toextract nuclear octupole and hexadecapole moments from measuring hyperfinesplittings in the extremely long lived first excited state($4f^{13}(^2\!F^{o})6s^2$, $J=7/2$) of $^{173}\mathrm{Yb}^+$. We presentresults of atomic structure calculations in support of the proposedmeasurements.

Hyperfine structure (HFS) of atomic energy levels arises due to interactionsof atomic electrons with a hierarchy of nuclear multipole moments, includingmagnetic dipole, electric quadrupole and higher rank moments. Recently, adetermination of the magnetic octupole moment of the $^{173}\mathrm{Yb}$nucleus was reported from HFS measurements in neutral ${}^{173}\mathrm{Yb}$[PRA 87, 012512 (2013)], and is four orders of magnitude larger than thenuclear theory prediction. Considering this substantial discrepancy between thespectroscopically extracted value and nuclear theory, here we propose to use analternative system to resolve this tension, a singly charged ion of the same$^{173}\mathrm{Yb}$ isotope. Utilizing the substantial suite of tools developedaround $\mathrm{Yb}^+$ for quantum information applications, we propose toextract nuclear octupole and hexadecapole moments from measuring hyperfinesplittings in the extremely long lived first excited state($4f^{13}(^2\!F^{o})6s^2$, $J=7/2$) of $^{173}\mathrm{Yb}^+$. We presentresults of atomic structure calculations in support of the proposedmeasurements.

Noncollinear wave-mixing spectroscopies with attosecond extreme ultraviolet (XUV) pulses provide unprecedented insight into electronic dynamics. In infrared and visible regimes, heterodyne detection techniques utilize a reference field to amplify wave-mixing signals while simultaneously allowing for phase-sensitive measurements. Here, we implement a self-heterodyned detection scheme in noncollinear wave-mixing measurements with a short attosecond XUV pulse train and two few-cycle near infrared (NIR) pulses. The initial spatiotemporally overlapped XUV and NIR pulses generate a coherence of both odd (1snp) and even (1sns and 1snd) parity states within gaseous helium. A variably delayed noncollinear NIR pulse generates angularly-dependent four-wave mixing signals that report on the evolution of this coherence. The diffuse angular structure of the XUV harmonics underlying these emission signals is used as a reference field for heterodyne detection, leading to cycle oscillations in the transient wave-mixing spectra. With this detection scheme, wave-mixing signals emitting from at least eight distinct light-induced, or dressed, states can be observed, in contrast to only one light induced state identified in a similar homodyne wave-mixing measurement. In conjunction with the self-heterodyned detection scheme, the noncollinear geometry permits the conclusive identification and angular separation of distinct wave-mixing pathways, reducing the complexity of transient spectra. These results demonstrate that the application of heterodyne detection schemes can provide signal amplification and phase-sensitivity, while maintaining the versatility and selectivity of noncollinear attosecond XUV wave-mixing spectroscopies. These techniques will be important tools in the study of ultrafast dynamics within complex chemical systems in the XUV regime.

State-specific orbital optimized approaches are more accurate at predictingcore-level spectra than traditional linear-response protocols, but theirutility had been restricted on account of the risk of `variational collapse'down to the ground state. We employ the recently developed square gradientminimization (SGM, J. Chem. Theory Comput. 16, 1699-1710, 2020) algorithm toreliably avoid variational collapse and study the effectiveness of orbitaloptimized density functional theory (DFT) at predicting second period element1s core-level spectra of open-shell systems. Several density functionals(including SCAN, B3LYP and $\omega$B97X-D3) are found to predict excitationenergies from the core to singly occupied levels to high accuracy ($\le 0.3$ eVRMS error), against available experimental data. Higher excited states arehowever more challenging by virtue of being intrinsically multiconfigurational.We thus present a CI inspired route to self-consistently recouple singledeterminant mixed configurations obtained from DFT, in order to obtainapproximate doublet states. This recoupling scheme is used to predict the CK-edge spectra of the allyl radical, the O K-edge spectra of CO$^+$ and the NK-edge of NO$_2$ to high accuracy relative to experiment, indicatingsubstantial promise in using this approach for computation of core-levelspectra for doublet species (vs more traditional time dependent DFT, EOM-CCSDor using unrecoupled mixed configurations). We also present general guidelinesfor computing core-excited states from orbital optimized DFT.

Searching for space-time variations of the constants of Nature is a promising way to search for new physics beyond general relativity and the standard model motivated by unification theories and models of dark matter and dark energy. We propose a new way to search for a variation of the fine-structure constant using measurements of late-type evolved giant stars from the S star cluster orbiting the supermassive black hole in our Galactic Center. A measurement of the difference between distinct absorption lines (with different sensitivity to the fine structure constant) from a star leads to a direct estimate of a variation of the fine structure constant between the star's location and Earth. Using spectroscopic measurements of five stars, we obtain a constraint on the relative variation of the fine structure constant below 10^{-5}. This is the first time a varying constant of nature is searched for around a black hole and in a high gravitational potential. This analysis shows new ways the monitoring of stars in the Galactic Center can be used to probe fundamental physics.

The use of periodic driving for synthesizing many-body quantum states dependscrucially on the existence of a prethermal regime, which exhibits drive-tunableproperties while forestalling the effects of heating. This motivates the searchfor direct experimental probes of the underlying localized nonergodic nature ofthe wave function in this metastable regime. We report experiments on amany-body Floquet system consisting of atoms in an optical lattice subjected toultrastrong sign-changing amplitude modulation. Using a double-quench protocolwe measure an inverse participation ratio quantifying the degree of prethermallocalization as a function of tunable drive parameters and interactions. Weobtain a complete prethermal map of the drive-dependent properties of Floquetmatter spanning four square decades of parameter space. Following the full timeevolution, we observe sequential formation of two prethermal plateaux,interaction-driven ergodicity, and strongly frequency-dependent dynamics oflong-time thermalization. The quantitative characterization of the prethermalFloquet matter realized in these experiments, along with the demonstration ofcontrol of its properties by variation of drive parameters and interactions,opens a new frontier for probing far-from-equilibrium quantum statisticalmechanics and new possibilities for dynamical quantum engineering.

Photodissociation by ultraviolet radiation is the key destruction pathway for CS in photon-dominated regions, such as diffuse clouds. However, the large uncertainties of photodissociation cross sections and rates of CS, resulting from a lack of both laboratory experiments and theoretical calculations, limit the accuracy of calculated abundances of S-bearing molecules by modern astrochemical models. Here we show a detailed ab initio study of CS photodissociation. Accurate potential energy curves of CS electronic states were obtained by choosing an active space CAS(8,10) in MRCI+Q/aug-cc-pV(5+d)Z calculation with additional diffuse functions, with a focus on the B and C 1Σ+ states. Cross sections for both direct photodissociation and predissociation from the vibronic ground state were calculated by applying the coupled-channel method. We found that the C - X (0 - 0) transition has extremely strong absorption due to a large transition dipole moment in the Franck-Condon region, and the upper state is resonant with several triplet states via spin-orbit couplings, resulting in predissociation to the main atomic products C (3 P) and S (1 D). Our new calculations show that the photodissociation rate under the standard interstellar radiation field is 2.9-10-9 s-1, with a 57% contribution from C - X (0 - 0) transition. This value is larger than that adopted by the Leiden photodissociation and photoionization database by a factor of 3.0. Our accurate ab initio calculations will allow more secure determination of S-bearing molecules in astrochemical models.

We demonstrate qubit state measurement for ~160 Cesium atoms in a 3D opticallattice based on coherent spatial splitting of the atoms' wavefunctions. Themeasurement fidelity is 0.9994, essentially independent of the number of qubitsmeasured. The detection scheme is reminiscent of the Stern-Gerlach experiment,but carried out in light traps. The measurement causes no loss, which allows usto demonstrate re-initialization of the 3D qubit array after state measurement,including the replacement of an atom lost to a background gas collision.

We report on the design and performance of a double-sided coincidence velocity map imaging spectrometer optimized for electron-ion and ion-ion coincidence experiments studying inner-shell photoionization of gas-phase molecules with soft X-ray synchrotron radiation. The apparatus employs two microchannel plate detectors equipped with delay-line anodes for coincident, time- and position-resolved detection of photoelectrons and Auger electrons with kinetic energies up to 300 eV on one side of the spectrometer and photoions up to 25 eV per unit charge on the opposite side. We demonstrate its capabilities by measuring valence photoelectrons and ion spectra of neon and nitrogen and by studying channel-resolved photoelectron and Auger spectra along with fragment-ion momentum correlations for chlorine 2p inner-shell ionization of cis- and trans-1,2-dichloroethene.

We report Floquet band engineering of long-range transport and direct imaging of Floquet-Bloch bands in an amplitude-modulated optical lattice. In one variety of Floquet-Bloch bands we observe tunable rapid long-range high-fidelity transport of a Bose condensate across thousands of lattice sites. Quenching into an opposite-parity Floquet-hybridized band allows Wannier-Stark localization to be controllably turned on and off using modulation. A central result of this work is the use of transport dynamics to demonstrate direct imaging of a Floquet-Bloch band structure. These results demonstrate that transport in dynamical Floquet-Bloch bands can be mapped to transport in quasistatic effective bands, opening a path to cold atom quantum emulation of ultrafast multiband electronic dynamics.

In 1872, Maxwell proposed his famous 'demon' thought experiment1. By discerning which particles in a gas are hot and which are cold, and then performing a series of reversible actions, Maxwell's demon could rearrange the particles into a manifestly lower-entropy state. This apparent violation of the second law of thermodynamics was resolved by twentieth-century theoretical work2: the entropy of the Universe is often increased while gathering information3, and there is an unavoidable entropy increase associated with the demon's memory4. The appeal of the thought experiment has led many real experiments to be framed as demon-like. However, past experiments had no intermediate information storage5, yielded only a small change in the system entropy6,7 or involved systems of four or fewer particles8-10. Here we present an experiment that captures the full essence of Maxwell's thought experiment. We start with a randomly half-filled three-dimensional optical lattice with about 60 atoms. We make the atoms sufficiently vibrationally cold so that the initial disorder is the dominant entropy. After determining where the atoms are, we execute a series of reversible operations to create a fully filled sublattice, which is a manifestly low-entropy state. Our sorting process lowers the total entropy of the system by a factor of 2.44. This highly filled ultracold array could be used as the starting point for a neutral-atom quantum computer.

We demonstrate the use of a frequency-doubled optical frequency comb to load, cool, and crystallize trapped atomic ions as an alternative to ultraviolet (UV) or even deep UV continuous-wave lasers. We find that the Doppler shift from the atom's oscillation in the trap, driven by the blue-detuned comb teeth, introduces additional cooling and amplification which gives rise to steady-state phonon lasing of the ion's harmonic motion in the trap. The phonon laser's gain saturation keeps the optical frequency comb from continually adding energy without bound. This protection allows us to demonstrate loading and crystallization of hot ions directly with the comb, eliminating the need for a continuous-wave cooling laser, a technique that is extendable to the deep UV.

We present a simple two-dimensional model of the indirect dissociative recombination process. The model has one electronic and one nuclear degree of freedom and it can be solved to high precision, without making any physically motivated approximations, by employing the exterior complex scaling method together with the finite-elements method and discrete variable representation. The approach is applied to solve a model for dissociative recombination of H2+ in the singlet ungerade channels, and the results serve as a benchmark to test validity of several physical approximations commonly used in the computational modeling of dissociative recombination for real molecular targets. The second, approximate, set of calculations employs a combination of multichannel quantum defect theory and frame transformation into a basis of Siegert pseudostates. The cross sections computed with the two methods are compared in detail for collision energies from 0 to 2 eV.

The complex Kohn variational method for electron-polyatomic-molecule scattering is formulated using an overset-grid representation of the scattering wave function. The overset grid consists of a central grid and multiple dense atom-centered subgrids that allow the simultaneous spherical expansions of the wave function about multiple centers. Scattering boundary conditions are enforced by using a basis formed by the repeated application of the free-particle Green's function and potential Ĝ0+V on the overset grid in a Born-Arnoldi solution of the working equations. The theory is shown to be equivalent to a specific Padé approximant to the T matrix and has rapid convergence properties, in both the number of numerical basis functions employed and the number of partial waves employed in the spherical expansions. The method is demonstrated in calculations on methane and CF4 in the static-exchange approximation and compared in detail with calculations performed with the numerical Schwinger variational approach based on single-center expansions. An efficient procedure for operating with the free-particle Green's function and exchange operators (to which no approximation is made) is also described.

Radio-frequency (rf) Paul traps operated with multifrequency rf trapping potentials provide the ability to independently confine charged particle species with widely different charge-to-mass ratios. In particular, these traps may find use in the field of antihydrogen recombination, allowing antiproton and positron clouds to be trapped and confined in the same volume without the use of large superconducting magnets. We explore the stability regions of two-frequency Paul traps and perform numerical simulations of small samples of multispecies charged-particle mixtures of up to twelve particles that indicate the promise of these traps for antihydrogen recombination.

The fragmentation dynamics of 2,6- and 3,5-difluoroiodobenzene after iodine 4d inner-shell photoionization with soft X-rays are studied using coincident electron and ion momentum imaging. By analyzing the momentum correlation between iodine and fluorine cations in three-fold ion coincidence events, we can distinguish the two isomers experimentally. Classical Coulomb explosion simulations are in overall agreement with the experimentally determined fragment ion kinetic energies and momentum correlations and point toward different fragmentation mechanisms and time scales. While most three-body fragmentation channels show clear evidence for sequential fragmentation on a time scale larger than the rotational period of the fragments, the breakup into iodine and fluorine cations and a third charged co-fragment appears to occur within several hundred femtoseconds.

We used extreme ultraviolet (XUV) transient absorption spectroscopy to study the autoionizing Rydberg states of oxygen in an electronically- and vibrationally-resolved fashion. XUV pulse initiates molecular polarization and near-infrared pulse perturbs its evolution. Transient absorption spectra show positive optical-density (OD) change in the case of nsσg and ndπg autoionizing states of oxygen and negative OD change for ndσg states. Multiconfiguration time-dependent Hartree-Fock (MCTDHF) calculations are used to simulate the transient absorption and the resulting spectra and temporal evolution agree with experimental observations. We model the effect of near-infrared perturbation on molecular polarization and find that the laser-induced phase-shift model agrees with the experimental and MCTDHF results, while the laser-induced attenuation model does not. We relate the electronic-state-symmetry-dependent sign of the OD change to the Fano parameters of the static absorption line shapes.

Agreement between theoretical calculations of atomic structure and spectroscopic measurements is used to constrain possible contribution of exotic spin-dependent interactions between electrons to the energy differences between states in helium-4. In particular, constraints on dipole-dipole interactions associated with the exchange of pseudoscalar bosons (such as axions or axion-like particles) with masses 10-2"m"104eV are improved by a factor of ∼100. The first atomic-scale constraints on several exotic velocity-dependent dipole-dipole interactions are established as well.

Vapor cells with antirelaxation coating are widely used in modern atomic physics experiments due to the coating's ability to maintain the atoms' spin polarization during wall collisions. We characterize the performance of vapor cells with different coating materials by measuring longitudinal spin relaxation and vapor density at temperatures up to 95 °C. We infer that the spin-projection-noise-limited sensitivity for atomic magnetometers with such cells improves with temperature, which demonstrates the potential of antirelaxation coated cells in applications of future high-sensitivity magnetometers.

We demonstrate continuous measurement and coherent control of the collective spin of an atomic ensemble undergoing Larmor precession in a high-finesse optical cavity. The coupling of the precessing spin to the cavity field yields phenomena similar to those observed in cavity optomechanics, including cavity amplification, damping, and optical spring shifts. These effects arise from autonomous optical feedback onto the atomic spin dynamics, conditioned by the cavity spectrum. We use this feedback to stabilize the spin in either its high- or low-energy state, where, in equilibrium with measurement backaction heating, it achieves a steady-state temperature, indicated by an asymmetry between the Stokes and the anti-Stokes scattering rates. For sufficiently large Larmor frequency, such feedback stabilizes the spin ensemble in a nearly pure quantum state, in spite of continuous measurement by the cavity field.

We crystallize up to 15 ^{40}Ca^{+} ions in a ring with a microfabricated silicon surface Paul trap. Delocalization of the Doppler laser-cooled ions shows that the translational symmetry of the ion ring is preserved at millikelvin temperatures. By characterizing the collective motion of the ion crystals, we identify homogeneous electric fields as the dominant symmetry-breaking mechanism at this energy scale. With increasing ion numbers, such detrimental effects are reduced. We predict that, with only a ten-ion ring, uncompensated homogeneous fields will not break the translational symmetry of the rotational ground state. This experiment opens a door towards studying quantum many-body physics with translational symmetry at the single-particle level.

We propose a new method to search for hypothetical scalar particles that have feeble interactions with standard-model particles. In the presence of massive bodies, these interactions produce a nonzero Yukawa-type scalar-field magnitude. Using radio-frequency spectroscopy data of atomic dysprosium, as well as atomic clock spectroscopy data, we constrain the Yukawa-type interactions of a scalar field with the photon, electron, and nucleons for a range of scalar-particle masses corresponding to length scales >10  cm. In the limit as the scalar-particle mass m_{ϕ}→0, our derived limits on the Yukawa-type interaction parameters are Λ_{γ}≳8×10^{19}  GeV, Λ_{e}≳1.3×10^{19}  GeV, and Λ_{N}≳6×10^{20}  GeV. Our measurements also constrain combinations of interaction parameters, which cannot otherwise be probed with traditional anomalous-force measurements. We suggest further measurements to improve on the current level of sensitivity.

Ultracold atoms, produced by laser cooling and trapping, have led to recent advances in quantum information, quantum chemistry, and quantum sensors. A lack of ultraviolet narrow-band lasers precludes laser cooling of prevalent atoms such as hydrogen, carbon, oxygen, and nitrogen. Broadband pulsed lasers can produce high power in the ultraviolet, and we demonstrate that the entire spectrum of an optical frequency comb can cool atoms when used to drive a narrow two-photon transition. This multiphoton optical force is also used to make a magneto-optical trap. These techniques may provide a route to ultracold samples of nature's most abundant building blocks for studies of pure-state chemistry and precision measurement.

We investigate the photodouble ionization of H_{2} molecules with 400 eV photons. We find that the emitted electrons do not show any sign of two-center interference fringes in their angular emission distributions if considered separately. In contrast, the quasiparticle consisting of both electrons (i.e., the "dielectron") does. The work highlights the fact that nonlocal effects are embedded everywhere in nature where many-particle processes are involved.

Streaking of photoelectrons has long been used for the temporal characterization of attosecond extreme ultraviolet pulses. When the time-resolved photoelectrons originate from a coherent superposition of electronic states, they carry additional phase information, which can be retrieved by the streaking technique. In this contribution we extend the streaking formalism to include coupled electron and nuclear dynamics in molecules as well as initial coherences. We demonstrate how streaked photoelectrons offer a novel tool for monitoring nonadiabatic dynamics as it occurs in the vicinity of conical intersections and avoided crossings. Streaking can provide high time resolution direct signatures of electronic coherences, which affect many primary photochemical and biological events.

Light shifts are an important source of noise and systematics in optically pumped magnetometers. We demonstrate that the long spin-coherence time in paraffin-coated cells leads to spatial averaging of the vector light shift over the entire cell volume. This renders the averaged vector light shift independent, under certain approximations, of the light-intensity distribution within the sensor cell. Importantly, the demonstrated averaging mechanism can be extended to other spatially varying phenomena in anti-relaxation-coated cells with long coherence times.

The R&D activity performed during the last years proved the potential of ZnSe scintillating bolometers to the search for neutrino-less double beta decay, motivating the realization of the first large-mass experiment based on this technology: CUPID-0. The isotopic enrichment in [Formula: see text]Se, the Zn[Formula: see text]Se crystals growth, as well as the light detectors production have been accomplished, and the experiment is now in construction at Laboratori Nazionali del Gran Sasso (Italy). In this paper we present the results obtained testing the first three Zn[Formula: see text]Se crystals operated as scintillating bolometers, and we prove that their performance in terms of energy resolution, background rejection capability and intrinsic radio-purity complies with the requirements of CUPID-0.

A dichroic atomic vapor laser lock (DAVLL) system exploiting buffer-gas-filled millimeter-scale vapor cells is presented. This system offers similar stability as achievable with conventional DAVLL system using bulk vapor cells, but has several important advantages. In addition to its compactness, it may provide continuous stabilization in a multi-gigahertz range around the optical transition. This range may be controlled either by changing the temperature of the vapor or by application of a buffer gas under an appropriate pressure. In particular, we experimentally demonstrate the ability of the system to lock the laser frequency between two hyperfine components of the (85)Rb ground state or as far as 16 GHz away from the closest optical transition.

Dissipative forces are ubiquitous and thus constitute an essential part of realistic physical theories. However, quantization of dissipation has remained an open challenge for nearly a century. We construct a quantum counterpart of classical friction, a velocity-dependent force acting against the direction of motion. In particular, a translationary invariant Lindblad equation is derived satisfying the appropriate dynamical relations for the coordinate and momentum (i.e., the Ehrenfest equations). Numerical simulations establish that the model approximately equilibrates. These findings significantly advance a long search for a universally valid Lindblad model of quantum friction and open opportunities for exploring novel dissipation phenomena.

We use a radio-frequency 85Rb alkali-vapor cell magnetometer based on a paraffin-coated cell with long spin-coherence time and a small, low-inductance driving coil to create highly resolved conductivity maps of different objects. We resolve sub-mm features in conductive objects, we characterize the frequency response of our technique, and by operating at frequencies up to 250 kHz we are able to discriminate between differently conductive materials based on the induced response. The method is suited to cover a wide range of driving frequencies and can potentially be used for detecting non-metallic objects with low DC conductivity.

We present a novel technique of efficient optical pumping of open, high-angular-momentum systems. The method combines two well-established approaches of population manipulation (conventional optical pumping and coherent population transfer), offering the ability to achieve higher population of a sublevel with the highest or lowest quantum number m (the "end state") than obtainable with either of the techniques. To accomplish this task, we propose to use coherent-population-transfer technique (e.g., adiabatic fast passage) to arrange the system in such a way that spontaneously emitted photon (conventional optical pumping) carries away more entropy than in conventional schemes. This enables reduction of a number of spontaneous decays Nsd required to pump the system with the total angular momentum J from Nsd = J decays in the conventional scheme to Nsd ≤ log2(2J) decays in the proposed scheme. Since each spontaneous-emission event is potentially burdened with a loss of population (population is transferred to a dark state), this enables increasing population accumulated in the "end state", which is important for many applications.

Zero- to ultralow-field nuclear magnetic resonance (ZULF NMR) provides a new regime for the measurement of nuclear spin-spin interactions free from the effects of large magnetic fields, such as truncation of terms that do not commute with the Zeeman Hamiltonian. One such interaction, the magnetic dipole-dipole coupling, is a valuable source of spatial information in NMR, though many terms are unobservable in high-field NMR, and the coupling averages to zero under isotropic molecular tumbling. Under partial alignment, this information is retained in the form of so-called residual dipolar couplings. We report zero- to ultralow-field NMR measurements of residual dipolar couplings in acetonitrile-2-C13 aligned in stretched polyvinyl acetate gels. This permits the investigation of dipolar couplings as a perturbation on the indirect spin-spin J coupling in the absence of an applied magnetic field. As a consequence of working at zero magnetic field, we observe terms of the dipole-dipole coupling Hamiltonian that are invisible in conventional high-field NMR. This technique expands the capabilities of zero- to ultralow-field NMR and has potential applications in precision measurement of subtle physical interactions, chemical analysis, and characterization of local mesoscale structure in materials.