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Journal articleSchwickert D, Przystawik A, Diaman D, et al., 2024,
Coupled Electron-Nuclear Dynamics Induced and Monitored with Femtosecond Soft X-ray Pulses in the Amino Acid Glycine., J Phys Chem A
The coupling of electronic and nuclear motion in polyatomic molecules is at the heart of attochemistry. The molecular properties, transient structures, and reaction mechanism of these many-body quantum objects are defined on the level of electrons and ions by molecular wave functions and their coherent superposition, respectively. In the present contribution, we monitor nonadiabatic quantum wave packet dynamics during molecular charge motion by reconstructing both the oscillatory charge density distribution and the characteristic time-dependent nuclear configuration coordinate from time-resolved Auger electron spectroscopic data recorded in previous studies on glycine molecules [Schwickert et al. Sci. Adv. 2022, 8, eabn6848]. The electronic and nuclear motion on the femtosecond time scale was induced and probed in kinematically complete soft X-ray experiments at the FLASH free-electron laser facility. The detailed analysis of amplitude, instantaneous phase, and instantaneous frequency of the propagating many-body wave packet during its lifecycle provides unprecedented insight into dynamical processes beyond the Born-Oppenheimer approximation. We are confident that the refined experimental data evaluation helps to develop new theoretical tools to describe time-dependent molecular wave functions in complicated but ubiquitous non-Born-Oppenheimer photochemical conditions.
Journal articleGarratt D, Matthews M, Marangos J, 2024,
Novel ultrafast x-ray sources based on high harmonic generation and at x-ray free electron lasers are opening up new opportunities to resolve complex ultrafast processes in condensed phase systems with exceptional temporal resolution and atomic site specificity. In this perspective, we present techniques for resolving charge localization, transfer, and separation processes in organic semiconductors and organic photovoltaic devices with time-resolved soft x-ray spectroscopy. We review recent results in ultrafast soft x-ray spectroscopy of these systems and discuss routes to overcome the technical challenges in performing time-resolved x-ray experiments on photosensitive materials with poor thermal conductivity and low pump intensity thresholds for nonlinear effects.
Journal articleMaillette de Buy Wenniger I, Thomas SE, Maffei M, et al., 2023,
Energy can be transferred between two quantum systems in two forms: unitary energy-that can be used to drive another system-and correlation energy-that reflects past correlations. We propose and implement experimental protocols to access these energy transfers in interactions between a quantum emitter and light fields. Upon spontaneous emission, we measure the unitary energy transfer from the emitter to the light field and show that it never exceeds half the total energy transfer and is reduced when introducing decoherence. We then study the interference of the emitted field and a coherent laser field at a beam splitter and show that the nature of the energy transfer quantitatively depends on the quantum purity of the emitted field.
Journal articleFrasinski LJ, 2023,
Correction for 'Cumulant mapping as the basis of multi-dimensional spectrometry' by Leszek J. Frasinski, Phys. Chem. Chem. Phys., 2022, 24, 20776-20787, https://doi.org/10.1039/D2CP02365B.
Journal articleWiesinger M, Stuhlmann F, Bohman M, et al., 2023,
Trap-integrated fluorescence detection with silicon photomultipliers for sympathetic laser cooling in a cryogenic Penning trap., Rev Sci Instrum, Vol: 94
We present a fluorescence-detection system for laser-cooled 9Be+ ions based on silicon photomultipliers (SiPMs) operated at 4 K and integrated into our cryogenic 1.9 T multi-Penning-trap system. Our approach enables fluorescence detection in a hermetically sealed cryogenic Penning-trap chamber with limited optical access, where state-of-the-art detection using a telescope and photomultipliers at room temperature would be extremely difficult. We characterize the properties of the SiPM in a cryocooler at 4 K, where we measure a dark count rate below 1 s-1 and a detection efficiency of 2.5(3)%. We further discuss the design of our cryogenic fluorescence-detection trap and analyze the performance of our detection system by fluorescence spectroscopy of 9Be+ ion clouds during several runs of our sympathetic laser-cooling experiment.
Journal articleHo C, Wright S, Sauer B, et al., 2023,
Systematic errors arising from polarization imperfections in measurements of the electron’s electric dipole moment, Physical Review Research, Vol: 5, ISSN: 2643-1564
The electron’s electric dipole moment (eEDM) can be determined by polarizing the spin of an atom or a molecule and then measuring the spin precession frequency in an applied electric field. Radiation is used to polarize the spin and then analyze the precession angle, and the measurement is often sensitive to the polarization of this radiation. We show how systematic errors can arise when both the polarization of the radiation and the magnitude of the electric field are imperfectly controlled. We derive approximate analytical expressions for these errors, confirm their accuracy numerically, and show how they can be corrected empirically. We consider spin manipulation using single-photon pulses, Raman pulses, and Stimulated Raman Adiabatic Passage (STIRAP), and show that STIRAP provides better immunity to these systematic errors. An experimental study of these errors partly supports our findings but also reveals another potential error that is not captured by this analysis.
Journal articleAhyoune S, Álvarez Melcón A, Arguedas Cuendis S, et al., 2023,
A proposal for a low-frequency axion search in the 1–2 μ eV range and below with the babyIAXO magnet, Annalen der Physik, Vol: 535, ISSN: 0003-3804
In the near future BabyIAXO will be the most powerful axion helioscope,relying on a custom-made magnet of two bores of 70 cm diameter and 10 mlong, with a total available magnetic volume of more than 7 m3. In thisdocument, it proposes and describe the implementation of low-frequencyaxion haloscope setups suitable for operation inside the BabyIAXO magnet.The RADES proposal has a potential sensitivity to the axion-photon couplingga𝜸 down to values corresponding to the KSVZ model, in the (currentlyunexplored) mass range between 1 and 2 𝛍 eV, after a total effective exposureof 440 days. This mass range is covered by the use of four differentlydimensioned 5-meter-long cavities, equipped with a tuning mechanism basedon inner turning plates. A setup like the one proposed will also allow anexploration of the same mass range for hidden photons coupled to photons.An additional complementary apparatus is proposed using LC circuits andexploring the low energy range (≈ 10−4 − 10−1 𝛍 eV). The setup includes acryostat and cooling system to cool down the BabyIAXO bore down to about 5K, as well as an appropriate low-noise signal amplification anddetection chain.
Journal articleRudolph T, Virmani SS, 2023,
The two-qubit singlet/triplet measurement is universal for quantum computing given only maximally-mixed initial states, Nature Communications, Vol: 14, ISSN: 2041-1723
In order to delineate which minimalistic physical primitives can enable the full power of universal quantum computing, it has been fruitful to consider various measurement based architectures which reduce or eliminate the use of coherent unitary evolution, and also involve operations that are physically natural. In this context previous works had shown that the triplet-singlet measurement of two qubit angular momentum (or equivalently two qubit exchange symmetry) yields the power of quantum computation given access to a few additional different single qubit states or gates. However, Freedman, Hastings and Shokrian-Zini1 recently proposed a remarkable conjecture, called the ‘STP=BQP’ conjecture, which states that the two-qubit singlet/triplet measurement is quantum computationally universal given only an initial ensemble of maximally mixed single qubits. In this work we prove this conjecture. This provides a method for quantum computing that is fully rotationally symmetric (i.e. reference frame independent), using primitives that are physically very-accessible, naturally resilient to certain forms of error, and provably the simplest possible.
Journal articleSmorra C, Abbass F, Schweitzer D, et al., 2023,
Currently, the world's only source of low-energy antiprotons is the AD/ELENA facility located at CERN. To date, all precision measurements on single antiprotons have been conducted at this facility and provide stringent tests of fundamental interactions and their symmetries. However, magnetic field fluctuations from the facility operation limit the precision of upcoming measurements. To overcome this limitation, we have designed the transportable antiproton trap system BASE-STEP to relocate antiprotons to laboratories with a calm magnetic environment. We anticipate that the transportable antiproton trap will facilitate enhanced tests of charge, parity, and time-reversal invariance with antiprotons and provide new experimental possibilities of using transported antiprotons and other accelerator-produced exotic ions. We present here the technical design of the transportable trap system. This includes the transportable superconducting magnet, the cryogenic inlay consisting of the trap stack and detection systems, and the differential pumping section to suppress the residual gas flow into the cryogenic trap chamber.
Journal articleYu S, Zhong Z-P, Fang Y, et al., 2023,
Journal articleAlexander O, Barnard J, Larsen E, et al., 2023,
Observation of recollision-based high-harmonic generation in liquid isopropanol and the role of electron scattering, Physical Review Research, ISSN: 2643-1564
Journal articleSmith AWR, Paige AJ, Kim MS, 2023,
We present a new optimization strategy for small-to-intermediate scale variational quantum algorithms (VQAs) on noisy near-term quantum processors which uses a Gaussian process surrogate model equipped with a classically-evaluated quantum kernel. VQAs are typically optimized using gradient-based approaches however these are difficult to implement on current noisy devices, requiring large numbers of objective function evaluations. Our approach shifts this computational burden onto the classical optimizer component of these hybrid algorithms, greatly reducing the number of quantum circuit evaluations required from the quantum processor. We focus on the variational quantum eigensolver (VQE) algorithm and demonstrate numerically that these surrogate models are particularly well suited to the algorithm's objective function. Next, we apply these models to both noiseless and noisy VQE simulations and show that they exhibit better performance than widely-used classical kernels in terms of final accuracy and convergence speed. Compared to the typically-used stochastic gradient-descent approach to VQAs, our quantum kernel-based approach is found to consistently achieve significantly higher accuracy while requiring less than an order of magnitude fewer quantum circuit executions. We analyze the performance of the quantum kernel-based models in terms of the kernels' induced feature spaces and explicitly construct their feature maps. Finally, we describe a scheme for approximating the best-performing quantum kernel using a classically-efficient tensor network representation of its input state and so provide a pathway for scaling this strategy to larger systems.
Journal articleLatacz BM, Arndt BP, Devlin JA, et al., 2023,
We present the design and characterization of a cryogenic window based on an ultra-thin aluminized biaxially oriented polyethylene terephthalate foil at T < 10 K, which can withstand a pressure difference larger than 1 bar at a leak rate <1×10-9 mbar l/s. Its thickness of ∼1.7 μm makes it transparent to various types of particles over a broad energy range. To optimize the transfer of 100 keV antiprotons through the window, we tested the degrading properties of different aluminum coated polymer foils of thicknesses between 900 and 2160 nm, concluding that 1760 nm foil decelerates antiprotons to an average energy of 5 keV. We have also explicitly studied the permeation as a function of coating thickness and temperature and have performed extensive thermal and mechanical endurance and stress tests. Our final design integrated into the experiment has an effective open surface consisting of seven holes with a diameter of 1 mm and will transmit up to 2.5% of the injected 100 keV antiproton beam delivered by the Antiproton Decelerator and Extra Low ENergy Antiproton ring facility of CERN.
Journal articleYu S, Zhong Z-P, Fang Y, et al., 2023,
Gaussian boson sampling (GBS) has the potential to solve complex graph problems, such as clique finding, which is relevant to drug discovery tasks. However, realizing the full benefits of quantum enhancements requires large-scale quantum hardware with universal programmability. Here we have developed a time-bin-encoded GBS photonic quantum processor that is universal, programmable and software-scalable. Our processor features freely adjustable squeezing parameters and can implement arbitrary unitary operations with a programmable interferometer. Leveraging our processor, we successfully executed clique finding on a 32-node graph, achieving approximately twice the success probability compared to classical sampling. As proof of concept, we implemented a versatile quantum drug discovery platform using this GBS processor, enabling molecular docking and RNA-folding prediction tasks. Our work achieves GBS circuitry with its universal and programmable architecture, advancing GBS toward use in real-world applications.
Journal articleEngel RY, Alexander O, Atak K, et al., 2023,
Electron population dynamics in resonant non-linear x-ray absorption in nickel at a free-electron laser., Struct Dyn, Vol: 10, ISSN: 2329-7778
Free-electron lasers provide bright, ultrashort, and monochromatic x-ray pulses, enabling novel spectroscopic measurements not only with femtosecond temporal resolution: The high fluence of their x-ray pulses can also easily enter the regime of the non-linear x-ray-matter interaction. Entering this regime necessitates a rigorous analysis and reliable prediction of the relevant non-linear processes for future experiment designs. Here, we show non-linear changes in the L3-edge absorption of metallic nickel thin films, measured with fluences up to 60 J/cm2. We present a simple but predictive rate model that quantitatively describes spectral changes based on the evolution of electronic populations within the pulse duration. Despite its simplicity, the model reaches good agreement with experimental results over more than three orders of magnitude in fluence, while providing a straightforward understanding of the interplay of physical processes driving the non-linear changes. Our findings provide important insights for the design and evaluation of future high-fluence free-electron laser experiments and contribute to the understanding of non-linear electron dynamics in x-ray absorption processes in solids at the femtosecond timescale.
Journal articleHajivassiliou G, Kassapis M, Tisch JWG, 2023,
Rapid retrieval of femtosecond and attosecond pulses from streaking traces using convolutional neural networks, New Journal of Physics, Vol: 25, ISSN: 1367-2630
Attosecond streaking is a powerful and versatile technique that allows the full-field characterisation of femtosecond to attosecond optical pulses. It has been instrumental in the verification of attosecond pulse generation and probing of ultrafast dynamics in matter. Recently, machine learning (ML) has been applied to retrieve the fields from streaking data (White and Chang 2019 Opt. Express27 4799; Zhu et al 2020 Sci. Rep.10 5782; Brunner et al 2022 Opt. Express30 15669–84). This offers a number of advantages compared with traditional iterative algorithms, including faster processing and better resilience to noise. Here, we implement a ML approach based on convolutional neural networks and limit the search to physically realistic pulses that can be specified with a small number of parameters. This leads to substantial reductions in both training and retrieval times, enabling near kHz retrieval rates. We examine how the retrieval performance is affected by noise, and for the first time in this context, study the effect of missing data. We show that satisfactory retrievals are still possible with signal to noise ratios as low as 10, and with up to $40\%$ of data missing.
Journal articleHutchison CDM, Baxter JM, Fitzpatrick A, et al., 2023,
Journal articleMukherjee B, Frye MD, Le Sueur CR, et al., 2023,
We study collisions of ultracold CaF molecules in strong static electric fields. These fields allow the creationof long-range barriers in the interaction potential, effectively preventing the molecules from reaching theshort-range region where inelastic and other loss processes are likely to occur. We carry out coupled-channelcalculations of rate coefficients for elastic scattering and loss. We develop an efficient procedure for includingenergetically well-separated rotor functions in the basis set via a Van Vleck transformation. We show thatshielding is particularly efficient for CaF and allows the rate of two-body loss processes to be reduced by a factorof 107 or more at a field of 23 kV/cm. The loss rates remain low over a substantial range of fields. Electron andnuclear spins cause strong additional loss in some small ranges of field, but have little effect elsewhere. Theseresults pave the way for evaporative cooling of CaF towards quantum degeneracy
Journal articleVogwell J, Rego L, Smirnova O, et al., 2023,
We introduce an ultrafast all-optical approach for efficient chiral recognition which relies on the interference between two low-order nonlinear processes which are ubiquitous in nonlinear optics: sum-frequency generationand third-harmonic generation. In contrast to traditional sum-frequency generation, our approach encodes the medium’s handedness in the intensity of theemitted harmonic signal, rather than in its phase, and it enables full controlover the enantiosensitive response. We show how, by sculpting the sub-opticalcycle oscillations of the driving laser field, we can force one molecular enantiomer to emit bright light while its mirror twin remains dark, thus reachingthe ultimate efficiency limit of chiral sensitivity via low-order nonlinear lightmatter interactions. Our work paves the way for ultrafast and highly efficientimaging and control of the chiral electronic clouds of chiral molecules usinglasers with moderate intensities, in all states of matter: from gases to liquidsto solids, with molecular specificity and on ultrafast timescales.
Journal articleDriver T, Pipkorn R, Averbukh V, et al., 2023,
Identification of cofragmented combinatorial peptide isomers by two-dimensional partial covariance mass spectrometry, Journal of the American Society for Mass Spectrometry, Vol: 34, Pages: 1230-1234, ISSN: 1044-0305
Combinatorial post-translational modifications (PTMs), such as those forming the so-called “histone code”, have been linked to cell differentiation, embryonic development, cellular reprogramming, aging, cancers, neurodegenerative disorders, etc. Nevertheless, a reliable mass spectral analysis of the combinatorial isomers represents a considerable challenge. The difficulty stems from the incompleteness of information that could be generated by the standard MS to differentiate cofragmented isomeric sequences in their naturally occurring mixtures based on the fragment mass-to-charge ratio and relative abundance information only. Here we show that fragment–fragment correlations revealed by two-dimensional partial covariance mass spectrometry (2D-PC-MS) allow one to solve the combinatorial PTM puzzles that cannot be tackled by the standard MS as a matter of principle. We introduce 2D-PC-MS marker ion correlation approach and demonstrate experimentally that it can provide the missing information enabling identification of cofragmentated combinatorially modified isomers. Our in silico study shows that the marker ion correlations can be used to unambiguously identify 5 times more cofragmented combinatorially acetylated tryptic peptides and 3 times more combinatorially modified Glu-C peptides of human histones than is possible using standard MS methods.
Journal articleRego L, Smirnova O, Ayuso Molinero D, 2023,
Tilting light's polarization plane to spatially separate the ultrafast nonlinear response of chiral molecules, Nanophotonics, Vol: 12, Pages: 2873-2879, ISSN: 2192-8606
Distinguishing between the left- and right-handed versions of a chiral molecule (enantiomers) is vital, but also inherently difficult. Traditional optical methods using elliptically/circularly polarized light rely on linear effects which arise beyond the electric-dipole approximation, posing major limitations for ultrafast spectroscopy. Here we show how to turn an ultrashort elliptical pulse into an efficient chiro-optical tool: by tilting its polarization plane towards its propagation direction. This forward tilt can be achieved by focusing the beam tightly, creating structured light which exhibits a nontrivial polarization pattern in space. Using state-of-the-art computational modelling, we show that our structured field realizes a near-field interferometer for efficient chiral recognition that separates the nonlinear optical response of left- and right-handed molecules in space. Our work provides a simple, yet highly efficient, way of spatially structuring the polarization of light to image molecular chirality, with extreme enantio-efficiency and on ultrafast time scales.
Journal articleAlexander R, Gvirtz-Chen S, Koukoulekidis N, et al., 2023,
Magic states are fundamental building blocks on the road to fault-tolerant quantum computing. Calderbank-Shor-Steane (CSS) codes play a crucial role in the construction of magic distillation protocols. Previous work has cast quantum computing with magic states for odd dimension d within a phase-space setting in which universal quantum computing is described by the statistical mechanics of quasiprobability distributions. Here we extend this framework to the important d=2 qubit case and show that we can exploit common structures in CSS circuits to obtain distillation bounds capable of outperforming previous monotone bounds in regimes of practical interest. Moreover, in the case of CSS-code projections, we arrive at a novel cutoff result on the code length n of the CSS code in terms of parameters characterizing a desired distillation, which implies that for fixed target error rate and acceptance probability, one needs to consider only CSS codes below a threshold number of qubits. These entropic constraints are not due simply to the data-processing inequality but rely explicitly on the stochastic representation of such protocols.
Journal articleLatacz BM, Arndt BP, Bauer BB, et al., 2023,
Journal articleLing Y, Qvarfort S, Mintert F, 2023,
The photon blockade effect is commonly exploited in the development of single-photon sources. While the photon blockade effect could be used to prepare high-fidelity single-photon states in idealized regimes, practical implementations in optomechanical systems suffer from an interplay of competing processes. Here we derive a control scheme that exploits destructive interference of Fock state amplitudes of more than one photon. The resulting preparation time for photon-blockaded quantum states is limited only by the optomechanical interaction strength and can thus be orders of magnitude shorter than in existing schemes that achieve photon blockade in the steady state.
Journal articleBird RC, Tarbutt MR, Hutson JM, 2023,
Tunable Feshbach resonances in collisions of ultracold molecules in ²∑ states with alkali-metal atoms, Physical Review Research, Vol: 5, ISSN: 2643-1564
We consider the magnetically tunable Feshbach resonances that may exist in ultracold mixtures of moleculesin 2 states and alkali-metal atoms. We focus on Rb+CaF as a prototype system. There are likely to be Feshbachresonances analogous to those between pairs of alkali-metal atoms. We investigate the patterns of near-thresholdstates and the resonances that they cause, using coupled-channel calculations of the bound states and low-energyscattering on model interaction potentials. We explore the dependence of the properties on as-yet-unknownpotential parameters. There is a high probability that resonances will exist at magnetic fields below 1000 G,and that these will be broad enough to control collisions and form triatomic molecules by magnetoassociation.We consider the effects of CaF rotation and anisotropy of the interaction potential, and conclude that they mayproduce additional resonances but should not affect the existence of rotation-free resonances.
Journal articleChen W, Lu Y, Zhang S, et al., 2023,
A network of bosons evolving among different modes while passing through beam splitters and phase shifters has been applied to demonstrate quantum computational advantage. While such networks have mostly been implemented in optical systems using photons, alternative realizations addressing major limitations in photonic systems such as photon loss have been explored recently. Quantized excitations of vibrational modes (phonons) of trapped ions are a promising candidate to realize such bosonic networks. Here, we demonstrate a minimal-loss programmable phononic network in which any phononic state can be deterministically prepared and detected. We realize networks with up to four collective vibrational modes, which can be extended to reveal quantum advantage. We benchmark the performance of the network for an exemplary tomography algorithm using arbitrary multi-mode states with fixed total phonon number. We obtain high reconstruction fidelities for both single- and two-phonon states. Our experiment demonstrates a clear pathway to scale up a phononic network for quantum information processing beyond the limitations of classical and photonic systems.
Journal articleTarlton JE, Thompson RC, Lucas DM, 2023,
Journal articleBergmann K, Eberly JH, Halfmann T, et al., 2023,
Journal articleRuberti M, Averbukh V, 2023,
Journal articleGuo N-J, Li S, Liu W, et al., 2023,
Hexagonal boron nitride (hBN) is a remarkable two-dimensional (2D) material that hosts solid-state spins and has great potential to be used in quantum information applications, including quantum networks. However, in this application, both the optical and spin properties are crucial for single spins but have not yet been discovered simultaneously for hBN spins. Here, we realize an efficient method for arraying and isolating the single defects of hBN and use this method to discover a new spin defect with a high probability of 85%. This single defect exhibits outstanding optical properties and an optically controllable spin, as indicated by the observed significant Rabi oscillation and Hahn echo experiments at room temperature. First principles calculations indicate that complexes of carbon and oxygen dopants may be the origin of the single spin defects. This provides a possibility for further addressing spins that can be optically controlled.
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